Observations on Pingos Müller, F

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Observations on Pingos Müller, F.

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TECHNICAL TRANSLATION 1073

OBSERVATIONS ON PINGOS

FROM MEDDELELSER OM GR~NLAND.VOL. 153, NO. 3, 1959. 127 P.

TRANSUTED BY

D. A. SlNCLAlR

THIS IS THE ONE HUNDRED AND EIGHTH OF THE SERIES OF TRANSLATIONS PREPARED FOR THE DIVISION OF BUlLDlNG RESEARCH

OTTAWA

1963

---.- -- NATIONAL RESEARCH COUNCIL OF CANADA

Technioal Trans lation 1073

Title: Observations on plngos (~eobachtungen8ber Pingoa)

Author : Fritz ~8ller

Reference: Meddelelser om ~rbnland,Vol. 153, No. 3, 1959. 127 PO

Translator: D.A. Sinclair, Translations Section, N.R.C. Library PREFACE

This translation of an intensive study of pingos in the Mackenzie River delta region of northern Canada, and in East Greenland, is of particular interest to the Division of Building Research in its studies of the fundamental and engineering aspects of permafrost and the natural features associated with this phenomenon. Pingos are the most striking landforms in the permafrost region and their origin has long been the subject of much speculation. Prior to the investigations reported in this work, field atudies in North America of these unusual features were limited and scattered. Observations have been made in Siberia for some years but the resulting Russian publications have not been generally avaiiable. During the summer of 1954, the author, who la now Field Director of the Jacobsen-McGi11 Arctic Research Expedition to Axel Heiberg Island conducted systematic detailed surface and subsurface inveatiga- tions of pingos In East Greenland. This waa followed in 1955 by similar investigations of several pingos near Tuktoyaktuk, N.W.T., in the Mackenzie River delta region. The Di~iaionof Building Research was privileged to be able to assiat Dr. Muller with some of his field equipment and soil testing and has since maintained close contact with him. His findings enabled him to make well-founded suppo~itionsas to their origin and history which have contributed to a better understanding of some of the geological processes associated with permafrost. Thanks are due to Mr. D.A. Slnclair, Translations Section, National Research Council, who translated this document.

Ottawa N.B. Hutcheon May 1963 Assistant Director Page

Foreword ...... 5 I . Introduction A . General survey ...... 7 B . Purpose of the work ...... 7 C . Basic concepts ...... 7 D . The technical term "pingo" ...... 9 . The pingos south of .the Werner Bjerge. East Greenland A . Topographical and geological-morphological description ...... g B . The Classical Plngo ...... 10 C . The A~nphitheatrePlngo ...... 12 D . The Rock Pingo ...... 12 E . The Mineral Lake Pingo ...... 14 111 . The pingos on Trail1 Island. East Greenland A . Introduction and geographical-geological description ...... 16 B . Equipment ...... 17 C . The Trout Lake Plngo ...... 18 D . The Crater Lake Pingo ...... 22 E . The Source Pingo ...... 25 F . The Glacier Pingo ...... 28 G . The Goose Plngo ...... 32 H . The Antecedence Pingo ...... 33 I . The pingos in the Maanedal ...... 33 N . Morphogenesis of the East Greenland pingos A . Outline of permafrost and climatic conditions in East Greenland ...... 34 B . The East Greenland pingos as an open system and a permafrost phenomenon ...... 37 C . The physics of East Greenland ping08 ...... 39 1. Mechanical forces ...... 39 2 . The temperature regime ...... 42 D . Formulation of the hypothesis for the formation of pingoa of the East Greenland type ...... 45 E . Discussion and criticism of earlier hypotheses on the formation of East Greenland type pingos ...... 46 V . The plngos in the northeast Mackenzie delta. Canada A . Introduction ...... 47 B . The Crater Summit Pingo ...... 49 C . The Sitiyok Pingo ...... 53 D . The ice cellar at Toker Point ...... 55 E . Sumnary and discussion of some properties of the pingo ice body ...... 56 1. Crystal dlmenoions and density determinations ...... 56 2 . Temperature conditions ...... 58 VI. Morphogenesls of the blackenzle pingos A . The historical cycle of the Mackenzie ping03 .the closed system ...... 59 B . Dl3cusslon and review of earlier explanations of the Ilackcnzie plngo:, ...... 62 C . Surnrr.ary ...... 63 VII . The diatributlon of pingoe in the light of the investigatlona of the East Greenland and Mackenzle plngos A . Introduction and terminology ...... B . Outline of the d1stributlon of plngos ...... 1 . Greenland ...... 2 . Canadian Arctlc ...... 3 . Alaska ...... 4 . Eurasia ...... C . Reults of the study of plngo dlatributlon ...... VIII . Concluding remarks ......

Plates ...... Note on the translation of geographic namea ...... OBSERVATIONS ON PU00S

Detailed Investl~atlonnin East Greenland and in the Canadian Arctic

Foreword

In the summers of 1950 and 1951 Dr. huge Koch, Leader of the Danish East Greenland expeditions had a number of photographs of the pingos of East Green- land taken by the aerial photographer E. Hofer. Some of these excellent docu- mentary photographs have since been reproduced and diacussed on several occasions (~atler1954, plate V; Plaarleveld and Van den Toorn 1955, p. 350; Pissart 1956, p. 127; Hofer 1957, p. 55, 116). Until the smer expedltlons of 1954, and especially 1955, there had been no opportunity for a field study of the pingo phenomenon. Prof. Dr. P. Bearth, with whose team I was associated in the summer 1954 in the Werner Bjerge, strongly supported my intention of investigating the pingos to the south of this group of mountains. It is thanks to him and to the vigorous help of niy associate Dr. R. Ganzoni that we were able to collect some extremely valuable data on these highly interesting pingos within a few days in August, 1954. A grant of the Carnegie Foundation for the academic year of 1954-55 made it possible for me to continue my investigations on pingos at the Arctic Institute of North America and at McGill University, Montreal. The Institute there afforded me an opportunity of examining a large part of the literature on this subject which is difficult of access. In the spring and early summer of 1955 I organized a small expedition to the Plackenzle delta, N.W.T., Canada, under the auspices of the Arctic Institute of North America, for the purpose of making a comparative study of the very numerous pingos there with the East Greenland formations. The U.S. Air Force provided free transportation froin Edmonton to the field and back. The Eskimo, David Nasoguluak of Tulctoyaktuk, who conducted me to the various work sites with hi3 dog team, gave me continuous, faithful assistance in the strenuous work of digging and drilling. In July, 1955, 1 returned, with hiproved equipnient and nicl;hodologic~l experience, to the East Greenland pingos. Expedition leader Dr. Lauge Koch and H. ~ctlerlliade 11; posnible for me to devote the entire summer of 1955 to the study of the plngoo In the Interior of Trail1 Island. Edmond Oiroux gave mc- oplcndld aasiatancc in the oornetimeo very strenuous field work. After this .a" expedition I returned to Canada for three months In order to conclude my study of the litcratwc in the PIontreol office of the Arctic Institute of North America. The con~plctionof the manuscript was delayed until the summer of 1957 by my participation in the Swiss Mount Everest Expedition, 1956. I must express my warmest thanks to all the above-named persons and institutions. This applies particularly to expedition leader Dr. Lauge Koch, and to Dr. K. ~6tlerand Dr. P. Bearth, all of whom contributed greatly to the success of this work both by their many-sided encouragement and by the fact that they always gave generous support to my field work within the framework of the overall programme of the East Greenland Expedition. I must also express my heartiest thanks to my honoured teacher at the ~niversit%t~Grich, Prof. Dr. H. Boesch, for his many-sided support and encouragement. During hls trips to An~ericahe missed no opportunity of making known his keen interest in my work, reserving several days in New York, and later again in Chicago, for a dlscusslon of it. I am also very grateful to Dr. A.L. Washburn, who was kind enough to look through the description of conditions in the Mackenzle delta and who also performed valuable services in preparing that expedition. In regard to the literature I must inform the reader that sources of various quality have been used. In particular, many of the Russian papers were unfortunately available to me only in the form of abstracts In "S.I.P.R.E. + Report 12, Bibliography on Snow, Ice and ernl la frost" or in the same form In "~euesJahrbuch f6r Mineralogle, etc.". These publications are

therefore marked with a "+'I and are listed separately in the bibliographical section. In transliterating the Russian names of places and persons I have followed the system of the Library of Congress, Washington, as given in S.I.P.R.E. Report 12. For typographical reasons I have written the diphthongs ts and la without a tie.

+ SIPRE = Snow, Ice and Permafrost Research Establiolm~ent,Corps of Engineer-o, U.S. Army. Pingos are hill-like formations which are found in the active state only in pernlafrost regions. They nlny rise 50 m or riior'e above the surrounding terrain. Thcir banes arc generally circular or oval in ahapc and often measure several hundred ~netrcsin circumference . Their internal structure 13 characterized by the presence of a 1i1as3lve ice lens. The present study presents detailed observation material on a number of plngos In two separate reglono of East Greenland coresb by Land and Trail1 Island), which is conpared with observat ions and rneasuremcnts on two typical plngos in the Canadian Arctic (northeastern Mmkenzle delta, N.W.T.) (~lg.1). Follor.rFn~the interpretatlon of these two groups of pingos a fclv exa:nplen of other pingos from the literature, especially in Alaska and Siberia, are discussed.

B. Purpose of the Work

The aim of these investigationn is twofold: first, by accurately des- cribing the phenomena and reportln~;tile results of cxtcnoive excavation:, and drillings, It 1s hoped that a clear structural picture of the most irl~portant types of pingos will be obtained. The Interpretation of this nlaterlal should contribute to a better understanding of an altogether unique phenomenon of the periglacla1 reglon. Second, by the very nature of the pingoo, this study cannot but contribute to our ~eneralknowledge of permafrost, and in particular to the question of ground water conditions in permafrost.

C. Basic Concepts

Even a quick perusal of the literature clearly reveals that the occur- rence of plngos is linked to the presence of special pertuafrost conditions. However, slnce perrnafrost is a special branch of periglaclal morspholo~ythat would appear to be unfamillnr even to &cologisto and geographcra, let us first; consider a few terms, facts and theories from the ccience of perinafrost. The tern1 "pernlafrost" denotes that zone of the lithosphere which reniains permanently (or for tuo years at least) frozen. In the case of material contalnlng no moisture, periliafrost can be dcfinccl only on the ba31s of tenlyeraturc and t11r.e (so-called d1.y pcrr,wfrost). li~tt~c pr'escncc of moi~tul-e, in additlon, the material must be in the colic1 state (cf. Taber 13k3, Q- lIl3G; Mullcr 1347, p. 3 and p. 219; Proa t 1952, p. 225). 13eti1ccn the active zone, which freezes and thawa annually or daily, and the pcri~.afrosttable, zonc3 of ~iiatcl-la1that remain unfrozen for long pcrlods of time can occur even within the body of permafrost. The Russlann refer to these unfrozen places in and around the permafrost zones by the name "talik" (lkiuller 191~7, p. 223). Of opecial interest 13 the kind of talik that inter- laces the pcrniafrost zone lilce a net. This type of tallk owes its existence to hi& hydrootatic pressures, mineral salts that lower the melting point, or to the ascent of self-compressing gases, etc. This promotes an exchange of water between supra- and sub-permafrost regions. As a consequence the ground water in permafrost rcgions is specified as sub-, intra-, or supra-peninfrost water (~olstikhln1932+, 1933+, 1935+, 1939+, 1947+; Cederstrom et al. 1953, P. 6 - 9). Distribution and extent of permafrost About one-fifth of the total earth's ourface is underlab by permafrost (~iuller1947, p. 4). According to Black (1954, p. 839) it may be as much as 26% The largest permafrost regions are grouped around the Arctic Ocean. Both the extent and continuity of the permafrost area decreases towards the temperature latitude. In the sub-arctic regions in general only sporadic islands of pcrmafroot are still found. In the high Arctic, on the other hand, huge quantities of permafrost have been established. For the Yakut Lowland and the Khatanga basin, Tolstlkhln (1947+) cites a permafrost thickness of 100 to 600 in, and for the Tunguska basin up to 500 m. In the coal mines of Braganza Bay on Spitsbergen the permafrost reaches a thickness of 320 m (Werenskiold 1953, p. 197), in Resolute Bay, N.W.T., Canada, 390 m rank A. Cook, personal cornmunicatlon), in Point Barrow, northern Alaska, 400 m ()laccarthy 1952, p. 591). Permafrost appears to be a relict from glacial times; it can, however, arise locally even under modern climatic conditions (14uller 1947, p. 4). The fact that the greatest thiclcnesses of permafrost occur in the formerly non-glacial zones of the Arctic points to a relationship between the extent of the Pleistocene glaciation and the present-day distribution of permafrost (~ikiforoff1928+). According to calculations by Werenskiold 1353, which were confirmed by measurements, no permafrost forms under bodies of water and ice of a certain size, even at strongly negative mean annual temperatures. Large rivers also appear to Inhibit permafrost strongly (~gluller194-1, p. 24 and Fig. 13 and 14; Hcmstock 1953, p. 42; Cederstrom et al. 1953, p. 9). D. The Tcch~licalTern1 "Pingo"

Tile word "pingo" or "plnll;orsariukt' is used by the Eskimos of the blackcnzie delta exclusively to denote the many hundreds of hills, for the most part re~ularlyconical, which rise to heights of 50 m above the gently rolling landscape In the northeastern part of the Mackenzie delta. According to V. Stefansson (letter of November, 1954) the word pingo can be traced back to the demonstrative pronoun "piklta", later "pinga" which means "up there". The syllable "aar" in "pingorsariuk" has the connotation of "starts to push out of the ground" (oral communication of Father LeMeur, Tuktoyaktuk) . Porsildls suggestion (1938, p. 46) that the term pingo be used lnterna- tionally is fully supported by the author of the present work on the basis of the simplicity and definite character of the word. Moreover, the expression is already being used by many North American authors (~uller1947, Richards 1950, Black 1950 and 1954, Washburn 1950, Sager 1951, Frost 1952, Pihlainen et al. 1956, Stager 1956).

11. The Pingos South of the Werner Bjerge, East Greenland

A. Topographical and Geological-l~lorpholoQica1 Description

Between Schuckerts Flod and the centr2.l grsteds Dal there is a direct connecting link. This connecting valley runs more or less due east and west. It lies along 71°48'N and extends from 23030fW to 240101W. It Is about 30 km long. Because of the many plngos in it the name "Pingo Dall'* has been suggest- ed for this tributary valley of jdrsteds Dal. The small lake near the summit of the wide open through pass to Schuckerts Flod Is known as "hmsfitl. On the "~orel8bl~tKort 1 : 50,000, Northern Iilinhe; Conlpany, copenhagen" this lake is shovrn as havine; an altitude of 510 rn above sea level. The mountains to the north and south of the Pingo Dal, the Werner Bjerge and Gurreholms Bjerge, rise to heights of 1300 m and 1100 m above sea level, respectively. In shape, the valley has a glacial character. In Its present highly matured state, however, direct evidence of glacial origin, e.g. in the form of lateral or frontal moraines or even glaclal striation, Is difficult to find. However, along both sides of the valley there are massive terrace system which must be interpreted as the remains of a basal moraine up to 50 m thick. In the region of ~0ns.bthe proportion of crystalline rubble is very great; in the lower part of the Pingo Dal granite and gneiss pebbles are found only here and there.

.--. * Approved by the Danish Geopaphical Nar,~esConunisslon on 29.4.1357. 'l'odny the tributary glaciers no longer reach the niain valley. The quaternary depositv of the yrcoent-day flood plnln are all of a fluviatile character. Surficlal denudation due to sollfluction in thls region is considernble, This explain3 in part vrl~ythe glaclal renlaina are not very prominent. Thc Inany extensive, now hardly active polygonal oil forrne suggest a slackening of the cryolo~lcnlproceosco. The nurileroue n~ushfrostforms and micropolygonal ooile which are encountered point to the frequent fluctuation of summer ten~peratureaabout the freezlng point. The Elesozoic and in part Palaeozoic oedimenta whiah extend from Jameeon Land into Score~byLand for the most part rise gently towards the Werner Bjerge. In the east-west section a slight dip towards the east can be dis- cerned in the eandstonea which characterize the Pingo Dal. Going down the valley from rams6 one notes first the prevalence of grey sandstones (e.g. as exposed In the "b~ineralLake P~~O")whlch are later replaced by red sandstones (e.g. in the M~lassicalpingo"). These formatlons are probably of Carbonifer- ous age. Further east, in the vicinity of the "~ock~Ingo", multi-coloured rows of sandstones with calcareous binders crop out. Gypsum is observed In the northern tributarj valley, which has Its mouth near the "~mphitheatre Plngo", and also In the "Rock ~lngo". As far as the hydrological conditions of the region are concerned, or at least equal Importance to the stratigraphic sequence of the sediment8 are the thick basaltic veins and sills which radiate outwards from a centre of Tertlory action in the Werner Bjerge. Several basalt veins cut laterally across the Plngo Dal. The basalt bars bring about a conipartlnentalization of the ground water in the Plngo Dol.

B. The Classical Pingo

Deocrlption

The Classical Pingo, which is situated about 17 km east of Lornab, Is described first because In its form, and to some extent also in Its toakcup ntlcl situation, it conotltutes a sort of Ideal example of a pingo. It otarldn on the north slde of the Pingo Rlver. It Is about 300 rn horizontal distance l'rorn the alluvial plain of the present river in the direction of the slope. Its base la about 20 rn hIgher t;han the river level. This pingo is recognizable fro111as far as 5 krn away by its regular truncated cone shape. It8 base parnnl- eter IG410 ni, Its top pc~rltneter220 m. Thc nraxlmum elevation above the surrounding anclent area, from rough measurements wlth atring and clinonleter, 18 32 rn, and the ~c~conc Jcvatlon 27 111. The sidc?o of the 8 - 12 rn deep crater hnvc an incllnntlon of 35" - 115O. The outer olopcr, are oomcwhat less nteey, 1InvIne a Illcnn slope of only 30 - 35O. On t.hc floor of the crater are two mound-like protubcranccs of 4 111 hcigtlt each (Fig. 11) and two miniature lakca 8 rn and )I nr long and 1.2 rn and 0.7 m deep, respectively. Thcse measurernento all relate to conditions at the end of August 1954. On the south side of the crater floor there rnust have been another miniature lake 3 m deep a short time ago which was drained through a gap In the outside wall on the river side. This 10 m deep notch in the wall appears to have acted as the drainage course of a lake that formerly filled the entire crater. An alluvial fan of corresponding size opens out from this point on the pingo to the river plain. Only just now have a few plants been able to obtain a footing on this delta. This and the ~eneralimpressl~n made by this deltaic detritus suggest that until quite recently this water course was used by a greater volwlle of water than would be accounted for by the melting of the winter snow accumulation in the crater. IIovrever, we were not able to verify the presence of spring water as later found in other pingos. In order to get a better picture of the structure of this pingo six test pits were dug along an east-west profile. In all of these we encountered a red, coarse-grained sandstone and its disintegration products of the same type as that cropping out in the surrounding terrain. In sonic cases a stratification running parallel to the outside slope could be recognized in the flanko of the pingo. On the east slope, halfway up the pingo, a layer of fluviatile gravel up to SO crn thick was found. This observation Is of special interest. In the interior of the crater boulders up to 2 m In size were strewn at random. The fragnlented and detrital fine material came from the satne sandstone. In the centre of the crater and on the walls up to a height of about 5 m the fine material had the appearance of being recently baked. In the pit dug in the east mound (Fig. 11) the material began to get increasingly wet at a depth of 60 cm. Unfortunately the digging could not be extended deeper than 1 m, so that the presence of the body of ice preswned to be a little deeper could not be verified for this pingo. -Interpretation The conditions found in the Classical Pingo can be interpreted as follows: 1. The sandstone Involved in the pingo structure, which also occurs in the vicinity, here lies directly below the Quaternary rock. The latter is at most a few metres thick. Forces acting at practically a single point have lifted the bedrock and Quarternary deposits si~nultaneously. 2. liater originating in the Interior of thc pingo appears to have participated in the brealtdowrl pro- - cess. 3. The two mounds are interpreted a3 reactivations. - 1.r-

C. Thc At~~plllt,heatrcPillgo

Description

This pingo 13 situatcd at a point where a comparatively large tributary vallcy e~nptlesinto the Pingo Dal. Thc small, voluminous river has washed away about a third of this pingo. Tllc remaining horseshoe-shaped mound has a rnaxinlurn height of 12 rn above the river plain, by whlch the pingo is surrounded, the average height being about 8 m. The outer slope has an inclination of 25", the inner about 30 - 33". The floor of the crater Is more or less flat. It Is slightly elevated above the gravel plain of the river. Both the remaining circular wall and the floor of the crater consist of eroded material. Large boulders lie at the south foot and on the crater rim. These angular sandstone boulders have edge lengths up to 30 and 50 cm. Interpretation

This amphitheatre-shaped plngo rentnant is completely inactive and probably very old. The solifluction and polygonal soil forms on the crater floor and encircling wall, the state of erosion of the coarse components and the character of the vegetation suggest that this plngo is only a little younger than the Pleistocene ancient areas along the present-day alluvial meadow. The large boulders on the periphery of this pine;o are difficult to explain. They may have been carried to this location by the pingo-forming process.

D. The Rock Pin~o

The Rock Pingo is the one farthest down the valley of those which we visited. It is 20 km from hmsb and extends across the valley like a barrier. The main rise of the Rock Pingo is about 120 m to the north of the river. The outcropping bedrock participates In the structure of this pingo not only in the form of loose debris, but a130 as nlassive and in part also continuous complexes of rock. This is a co~rrpactsandstone with a slightly calcareous binder. A periodic alterr~ationof yellow-brown, gray and red bands glves the appearance of a multi-coloured texture (Fig. 6). Striking and of special Interest are the flst-size to head-sizc lurnps and lensea of gypsum ernbcddcd in these sandstone layers. They consist of a very flnc-grained, alabaster-like gypsum. At isolated points the gypsum has been leachcd out, leaving reccsses with a hollow cellular structure. Elsewhere It has been redcposlted in slntcr fashion. In small joint planes of this well- bedded rock wc find la~~~ellifor~n,transparent msum crystals. The finsures that lie perpendicular to the stratification, and which often show sllde ncratchcs, are especially rich in beautiful gypsun1 crystals. A CI:IIII~~C-Xof this ~mterlalof at, 1c:ast !.; ~IIthick wan laid dokrn 11, t,hc

Fioclc Fingo w1.t.h oloycs up to '70O In dcpth. Ttie caster11 arlli has ever1 been sll~atlyoverturned arhd bent In two by Its own wciglht, but nevertheless it

extends a full 26 ni alniost vertically upwards. The higtlest polnt of the Rock Plngo, situated on the west side, rises 25) m above the river level. In the uppermost parts this rock cover breaks up into individual bouldero up to 20 m' in volume (FI~.6). At the very top where the sedlmentary envelope Is no longer continuous

because of the curvature, an irregular crater has formed whlch Is about 4 nl deep. In the centre of thls depression is a miniature lake. At the end of August 1954 thls lake was 1; in deep. The temperature of the water was only +0.5OC at Its rnaxifilun. h the excavation at the shore of the lake wc found pure ice underneath a layer of unfrozen sand 10 to 30 cm thlck. Unfortunately the time available to u3 was Insufficient to carry out granulometrlc and density measuremento of thls transparently clear ice. The undl>alncd lake owes its origin to the incipient melting of the Ice body. The outline of the Rock Pingo itself, like the crater and Its lake, is rrear It is oval to pear shaped. Its basal perl~neterIs 380 rn. The fisoures that run radially In relation to the centre of the pingo nnd divide the crater into several peaks, extend to the base and some cvcri 1.eacl1 out beyond the sharp bend between the pingo and the area In front of It far out into the gravel plain. The fissures running southward are very clearly narked, despite their being overlain with gravel (Pig. 8). Some of the fissures are as much as 1.5 m wide. Transverse fissurcs Iiiay also be ohscrvcd. Two of these, which arc concentric to the main pin~o,were remarltable for their fresh appearance. Both possessed extetl3lons Into i;lltx gravel plain of the present-day river. We were able to establish that thcue f lssures had opened up folb the f lrst time after the previous sprlnc flood . This observatioll shows that the Rock Pingo is still growing. The networlt oi' fissures renders the flat antlcllnal which extcnds to thc south ao far as the opposite side of the valley, especially striking. This is a kind of contlnua- tlon of the pingo. A cplel~didcross-3csction of thls antlcllnal has bccn cxposcd by the Pln~,o River (Fig. 9). T11c outcropping str.ucturc 13 nbsolut;cly idcritical with that observed In the two sedlr,icntary arms of the Rock Plngo Itself. Of particular Interest Is the obccrvat.1on that in the cross-secl,lori of thc chasm tthc l'lvcl, gravels cllr~ibtkie ULJ~OIIIC~sandstone banlco on t;hc upscl-cam oldc wltll a 3ul'fa~e discordnncc of 2 - 3". 01) the top of thc nntlcllnal they arc only 1 - 2 I;I m ".. t;hick. At the end of the west arw, ~O~IC~VCI-,!:11cy 'L~;Ivc a thI~lcr~c33of at least

5 Ill. Tllc 1:~citJonof the cham and the otructural conditiorls of the gravels in Lts vlcl;~i~hi~~tly bc Irltel-pl-ctcd as follol13: 1. The rlvcr is antecedent to the pingo formation. 2. The Rock Pingo anticlinal rose up more quickly than the river was able to cut into the terrain, as can be proved by reference to glacial terraces upstrearii. 3. On the other hand, the updonling appears to have taken place very slowly. The slowly incrcasiny; discordance betvrcen the bedrock and the gravela indicates that this process must have lasted many centuries. 4. It appears that today erosion Is holding its own against the uplift, for at the present stage only a very slight damning of the river is still evident and may be interpreted as a sign of the decay of the pingo-forming process. ' In conJunction with this pingo, which lies athwart the valley, a preclpi- tous basalt seam may be observed. It is exposed at tvro places in the valley irmnedlateljr belorv the Rock Pingo. It can also be recognized on the valley sides. On the NNW side of the Rock Plngo at the 5 m height is a water drainage course. The rill has washed away the thin gravel cover overlying the outcropping rock on this side. At the end of August, 1954, very little water was flowing out. The entire course of the rivulet is marked by white effl ores- cences. 1:iy thousands of musk ox tracks converge on this spring. The phenomenon cannot be interpreted as an indicatio~~of cornrnon salt. The geochemical analysis of the efflorescences shows 70% Ca (data kindly supplied by Professor Kranck, ICcGill University, blontreal). From conditions in the high meadow3 of the Alps it is knoi:n that under sparse pasturing conditions both cattle and game aninlals developed a great need for calcium (~rwinUehlin~cr, 1954 1. In summlng up it may be said that the forces active in the Rock Pingo are not localized, but extend along a line running across the valley. As u result the entire pingo structure receives an elongated form. Probably the basalt seam bears a causal relationship to this form and Its orientation in the terraln, the basalt barrier on the one hand acting as a ground water dain and on the other serving to diminish the per~~iafrostzone. Xrl addition to this the structural conditions of the bedrock have been wcakened by gypsum.

Descrlptlon

Tne Mlncral Lake Pingo (~1~.10) Is situated 10 km down the valley from Iomsb l~ulediatclyto tile south of the Pingo Illver. It possesses three section:, situated 011 a line running nol*th to south and partially nested one inaidc the other. The t~vonorthern sections rise from the level of thc present-day river plain; the south section stands on the ancient surface about 5 m higher. The wl~olecomplex of elevations is 200 m long and measures about 70 m across at the widest point of the base. The central group is the largest. Its maximum ' elevation is 18 m above river level. This centre section is almost circular in outline. The outer slopes are very steep. Slopes of 40' were measured at several places. In the Interior of the Irregular crater a young pine;o has formed. The top of this mound is at the same altitude as the rim of the surrounding crater. The north section is divided into separate parts by large fissures. On the surface the material has broken down into fragments, but at . some depth it consists of more or less continuous rock complexes. Verlfica- tions of this have been found at the north end, where the river has eaten away the Mineral Lake PLngo. There, in the vicinity of the pingo the horizontal sandstone layers are folded towards the pingo over a short distance and reach a steepness of 50°, and locally up to as much as 90' (Fig. 11). The gray arkose sandstone, which partly comprises the structure of the Elinera1 Lake Pingo, is finely bedded. Thirty metres south of the river and parallel to it a seam of basalt runs across the pingo elevation and is thereby exposed for a distance of about 60 m. At the peak this seam of basalt has been broken up into individual blocks by the plngo-forming process. It was therefore partially Involved in the pingo formation. South of this pingo is a large mineral lalte. From two clearly visible exits halfway up the pingo waters rich In mineral salt must have emerged. In the shallow trough about 500 m long they have evaporated and deposited their burden in the form of what is today a clearly visible, snow-white precipitate. A qualitative chemical analysis of these deposits by Professor ~cbeli(ETH, Zurich) showed that they consist of limy efflorescences containing gy-psum. As in the case of the Rock Pingo, thousands of musk ox tracks lead down to the mineral lake. The fact that there has been little erosion of the slope of the pingo by the water, as well as the fact that the mineral lalce has no overflow to the river plain about 5 m lower, indicates that thcse springs have never been very abundant. On the other hand, the large amount of mineral salt that has been deposited suggests that the mineral lalce has been fed over a very long time. It must be assumed that durlng the winter, Ice formed on top of it. On the south-west slope of the main pingo there Is a third sprlng. This was not active at the end of August 1354. Thc greater degree of erosion and the -" srnaller quantities of efflorescences Indicate that this point of water emergence is active over shorter periods. Sunnary and Interprctation The Mineral Lake Pingo is the third of the four pingos described so far which embrace the local bcdroclc and has involved it in the updoming process. Lilce the Rock Pingo, it is aosociated with a basalt seam. The relationship to a msum layer could be inferred only lndircctly, 1.e. by analysis of the efflorescences. It is assumed that there is still a prsctlcally undisturbed body of ice in thc interior of this pingo.

The Pingos on Traill Island, East Greenland

A. Introduction and Geo~raphical-Geological Description

In the valley of the Karup River In the central part of Traill Island (~lg.2) there are more than 20 pingos within a small area. Even from a pre- liminary reconnaissance flight it was evident that both growth and disintegration forms were present. Some of these pingos are situated in the alluvia of the valley floor, while others rise from the exposed rock of the valley sides. Miniature forms alternate with massive structures. Isolated pin~osas well as groups are found. In most groups it is possible to distinguish a main pingo surrounded by smaller subordinate ones. The central part of Traill Island, in which the field observation3 described below took place, is situated at 72.5ON and 23 - 24"W. Clinlatically and geographically the island belongs to the outer coastal zone. At the summLt of the pingo-bestrewn Karup River valley the island Is about 45 Ian wide. Our main camp was situated in the upper part of the valley. From there we were able to visit the pingos in the Plaanedal. The topographically prominent highland fault, as ~Gtler(1955, p. 15) and others have designated the topographical verification of the post-Devonian master fault in East Greenland, runs through Traill Island. This fracture line separates the Devonian mechanically from a succession of younger deposits. The downwarped Carboniferous, Permian, Trlasslc, Jurassic and Cretaceous deposits east of the highland are very noticeable segmented by basalt dikes and sills. The generally undisturbed and sometinies horizontal outer coastal sediments are thus segmented in relation to the ground water in. a ~r~anner slmilar to those south of the Werner Bjcrgc. The many fault systems which cross both the Karup River valley and the b'aanedal in a direction more or less parallel to the highland fracture, 1.e. from SW to NE, must have an effect on the underground hydrological conditions similar to that of the basaltic seams. The Karup River valley is a wide glacial valley. Very striking evidence mm h of Pleistocene l la cia ti on is found (1) In the region of Holms Inlet in the form of basaltic ridge3 which show n~a[=nlficicntglacial traces with stoss direction 1'1-or11ttic vrc3t, and (3) In thc n~id-vall.eysection, where ccker-like clt~bank~ncnto3on1c l:ilornctrc=, long line the Karup River. The prcsent-day valley plain, r.rhich 13 a3 much as 2 km wide in some places, 13 dominated by poot-glacial deposits. Terraces caused by isostatic, and probably alao eustatic movements run inland. Thcy consist mostly of mcdium-grained to coarse-pained sand and have been shown to consist of marine deposits up to an altitude of 45 rn above sea level. The hl@cst locatlono at which shell fragments vrerc found arc about 11 krri inland on the south side of the river. Remnants of the same yellovr, weathered sand can be found up to altitudes of 150 m above sea level, but without shells, e.g. In the water divide region between the iCarup River and the Guden River. The remnants of still higher terraces which run along the valley side must be interpreted as accumulation terraces from the main period of valley glaciation. Lrl some terraces thick ice wedges are found under a thin layer of sand. A complex of pure fossil ice of this kind has been uncovered on the second lowest terrace in the vicinity of Holms Inlet. From the standpoint of ground water and permafrost, which is of primary interest here, it is also In~portantto note that the widespread gravels of the present-day Karup River do not go very deep. In the middle region the river is eroding the Carboniferous sandstones of the rock floor in several places. It my be assumed with certainty tha,t the per~rrafrost, unless disturbed by local factors such as the transport of heat by the river, etc., goes deeper than the Quaternary depooits of this valley. The valley sides are encrusted wlth a thick layer of periglacially formed deposits consisting of solifluc- tions, striated soils and cellular stony soils, etc. The'processes underlying these fornations are to some extent still going on. The reason for this 13 that the present-day pel*nafrost table is at such a great depth that surface drylng of the active layer can begin soon after the snow melts. The maxiniuni thickness of the active layer varies between 0.5 m and approximately 3 m, depending on the ve~etationcover, the heat conductivity of the material and Its exposure. Although all the pingo:, in the Karup valley lie in the region of the Carboniferous sandstoncs, wo niust nevertheless, in our context, refer to the nearby gypsum occurrcncc of the marine Upper Permian (~atler1355, p. 111)) which are extensively exposed and visible on the Inselberg to the north of the

Karup River on a peak 550 nl above sea level.

B. Equipment

In addition to the usual hcavy entrenching tool a hand drill for Ice was used which had bccn devclopcd by 11.11. Ward (13511) for cold ice. However, oince we r:~ust expcct to find mineral i~tlpuritieoin the pingo ice lenses a few modifications were made. The teeth of the drill head were to be made of tungsten-carbide hard mctal and not simply of hardened steel. The tempcrature nlcanurements down to depths of 14 m in both ice and pernlafrost wcre carried out with copper-constantan thermocouples. With the two-ntunber potentiometcr (No. 8657 C) of the Leeds and Northrup Company used for readlng purposes an accuracy of k0.25~~could be attained. Experience from sl~nilarfield works In 1357 showed that for tasks of this kind thermis- tors (resistance thermometers connected to a Wheatstone bridge) would be better, since this apparatus is not only more accurate, but also more rugged for expedition work. For the determination of weight per unit volunle of the different kinds of ice Ward's (1952a) method and set of instruments were employed. For maintain- ing the chief characteristics of the ice the "rubbing method" developed by Selipn (19119) was found to be extremely effective in the field for these studies. The valuation was carried out by colnparison with logarithmically increasing equivalent circular areas.

C. The Trout Lalte Pingo

Description In the middle rcachea of the Icarup River (Fig. 2, No. G) Lriunediately south of the river on an old gravel plain which is about 4 m hieher than the present river level, thcre Is a lake encircled by a group of 5 large plngos. The lalce is lcnovrn as ~orelsb*because of the abundant brook trout found In It. The three pingos standing directly on the lakeshore are practically circular at their bases. Their individual base perin~etersare approximately 500 m each. From their surxnit to the periphery there are radial clefts; so far, however, none of these three pingos has experienced any disintegration. The two pingos adjacent to the Karup River are much more complex in structure. The western one has two annular walls, one nesting inside the other, which, like the case of the Amphitheatre Pingo, have been opened up by erosion on the oide nearest the river. However, since this erosion occurred at a tirne when the Karup vras still at the same level as the old terrace, an age of probably several hundred years must be attrlbuted to this plngo. On the other hand a new-loolcing n~ound in the centre of the crater of this pingo suggests a much later reactivation of the pingo building forces.

"- * Approved 23.4.1957 by the Danish Corm~litteeon Geographical Na~oes. The fifth and higher plngo of this group (Fig. 12 and 13), which rises to a height of 29 ni above the level of the Karup River, la oval shaped at the base and has a perimeter of 515 m. The major axis, which runs parallel to the river is 190 nl in length. This pingo aroused our special interest because of a massive reactivation on the eastern side. An active young form was growing through the consolidated old pingo. Although scarcely anything that could be called a crater was present in the old pingo, the young structure resulted in a true eruption with splendid crater formation. The crater walls have a slope of approximately 60°, in some cases up to 80°. The flat floor of the crater, about 45 m in diameter, appears to be the bottom of a former, short-lived lake. The lake bottom, even though lying right beside the Karup River, muat have been 16 - 18 m higher than the latter. Today the annular wall on the north side is pierced by a kind of canyon. This sharply incised ravine begins for apparently no reason at all in the centre of the crater floor. A second arm of the ravine connects with a flat dome on the south side of the crater floor. This mound Is 15 m In diameter and 2 -5 m high. It could not be determined whether plngo water emerges from time to time at the ends of these two ravines, or whether they are formed by mere gully erosion from the melting of the winter snow. The cross-section To get an idea of the Internal construction of this pingo, six excavations (sites 1 to 6) and one drilling (site 2) were carried out. The resulting observations have been summarized in a cross-sectional diagram (Fig. 13). The principal structural elements of this plngo are as follows: (1) an lmmense body of ice of still undetermined dimensions in the Interior, and (2) and overlying layer of frozen sediments 6 - 8 rn thick in the reactivated part and about 20 m thick In the old part of the pingo. On the crater floor the layer of earth over the ice is only about 80 cm thick. In all the test pits in which the body of ice was reached (numbers 1, 2 and 3) there was a definite sharp line of separation between the overlying material and the pingo ice (Fig. 14). Nowhere in this pingo was the ice found to be intermingled with layers of sand and loam. In test pits 1 and 3 the surfaces of contact between the ice and the overburden were still dry at the beginning of August, 1.e. the o0 isotherin had still not reached the Ice body; the surface of separation was wet only in excavation 2. The ground Ice

.- At site 2, 1.e. about at the centre of the crater, we drilled into the ground ice to a depth of 14 m. The entire hole extended through ice that was black in situ. In the light this ice was clear as glass and contained relatively few air bubbles. Although at the present stage of ice mechanic0 an - interpretation of the air inclusion condition in the individual glacier graln and in the texture is possible only witl-1 extreme caution, it is nevertheless polnted out that in the ice of the Trout Lake Pingo in many crystal assemblies the air bubbles in different crystals showed widely different directions, but ran parallel within one and the same crystal. This air bubble anomaly will be discussed further in connection with the Mackenzie pingos. The granulometric values of Fig. 15a show: 1. Qreat differences in the grain size (the largest crystal has an area of 71.5 cm2, the smallest, one of 0.03 cm2). 2. The larger crystals predominate in area (66.5% of the total area ie occupied by crystals with more than 12.6 cm2 equivalent area). These results will be discussed only I& connection with the results of investigations of crystal structure in other pingos. Although the diameter of the drill cores did not exceed 4 cm, it can nevertheless be stated that the nature of the ice changed little with increasing depth. With regard to the resistance to mechanical drilling it was observed that the very hard, 20 cm thick layer on the surface was followed by a softer zone. From 0.8 to 1.1 m depth a second, very hard layer was encountered. For the next 10 m the advance of the drill was very regular. The weight per unit - volume of ice was determined at depths of 1 m and 10 m. At both these depths the mean value for three measurements in each case was 0.90 g per cm3, with a measuring accuracy of k0.01. The entire 14 m drill hole did not reveal the slightest mineral impurity. With the available apparatus it was impossible to reach the bottom boundary of the ground ice. By folding back the overlying fine material into the original position the thickness of the ground ice can be estimated. In the Trout Lake Fingo it must be put at 33 to 36 m. Covering of sedimentary rock In the artificial exposures (sites 4, 5 and 6 of Fig. 13) we attempted to determine the character of the material overlying the ground ice. The original stratification is particularly clear at site 6. The surfaces of the layers run parallel to the outer slope of the pingo. They have an inclination up to 60° and in one place as much as 80'. The granulometry of a typical sample of the overlying material as determined by the Permmafrost Section* of the National Research Council, Ottawa, Canada, was as follov~s: loam 17$, silt 53$ and sand 3@, using the following classification system: clay <0.002 nun, silt 0.002 -

.-. * Now called "Northern Research Group". .,- 6.06 nu;i, sa~d0.06 - 1.2 t11n and gravel >1.2 rnm. The upper parts of the soil profile, characterizing In particular the rise towards the highest point, contain a larger pe~*centae;eof gravel. In site 5 (Fig. 13) It was not possible to get down to the original stratification along the entire test excavation because the material had been . shifted by solifluction and sliding. This made it impossible to determine exactly whether the ground ice ascends towards the highest point a little further In. In the old part of the pingo, despite the advanced stage of pingo formation, no melting of the ground ice had occurred. In the view from the direction of the Karup River It is obvious that the topsoil material was tipped up while still In the frozen state, and hence In the form of a compact slab more than 150 m long, and up to 40 rn wide and 20 m thick. To sum up, it is evident that the protective cover of thie pingo ice consists completely of alluvia of fluviatile character which are primarily loamy and silty at its base, sandy in the thick middle part and gravelly in the topmost layer. This profile is very similar to that of the first terrace of the valley slope.

.- Temperature conditions in the ~roundice On August 3, 1955, 10 thermocouples were frozen into the borehole of site 2. For technical reasons, and In order to facilitate comparisons with temperature measurements In the American Arctic, the following depths for the measuring points had to be observed: ice surface, 2% ft., 5, 73, 10, 15, 20, 25, 30 and 40 ft. It was found that disturbances to the thermal conditions by the mechanical drilling method employed here were very slight, because equllib- rium had become established after only two days with a measuring accuracy of ti0c . Two of the nine sets of readings taken in the Trout Lake Plngo are given in Fig. 16. On the basis of these measurements, as well as the theory, the temperature of -5OC measured at the 40 ft. depth is almost free of annual variatione. The front of the wave of increasing temperatures penetrating slowly to greater depths had reached a depth of 25 to 30 ft. In Ausst. This explains why in all nleasurements at the depth of 30 ft. a higher temperature was found than either above or below this level. In the top 2 to 3 ft. of this ground ice the decreasing temperatures begin to be noticeable. A comparison of the family of curve:, of Fig. 16 with that obtained from the Crater Sumit Pingo in the 1.lackenzie delta (~1~.39) shows that while the magnitude of the temperature variation is smaller, its direction is nevertheless the same. To surn up, it lilay be aaicl that the telr~peratureconclitiono in the Trout Lalcc Pingo show no anori~alics,but follow the regularities of the standard temperature course in pe1.111afrost. This fact indicates that in the Trout Lake Pingo it is scarcely likely that a distinct hydrolaccolith exists under the ground ice, as was postulated and on occasion observed by Inany Russian authors (~uslov1947, p. 152; Boch 1948'; Strugov 1955+; Tolstlkhin 1932+ according to the abstract Stoltenberg, p. 63; Petrov 1934). Interpretation The impression gained during the first reconnaissance flight, that there was a comection between the individual pingos of this group, was strengthened continuously durlng the 4 weeksf field work. The observation that the quantity of water flowlng from orel lab is 2 to 3 times greater than the surface water flowing into It led us to believe that thls lake may be fed by sub-permafrost water. It Is also noteworthy that brook trout live in this lake and that on August 5, 1955, the temperature of the ~orelsbwater was 10°C, whereas in a much shallovrer, smaller lake without any outlet about 4 k111 down the valley the temperature was only 8°C. It is an obvious deduction that not only Forelsb, but also the entire group of the pingos close by owe their origin to thls upthrust of sub-permafrost waters. In the three pingos on the lake the sub- pernmfrost water in no case broke through. It only succeeded in forming Ice lenses. In this region the permafrost appears to be of the critical thickness, Just great enough to prevent a breakthrough of sub-permafrost water, and con- sequently the latter is always searching for new places in which to rise. Similar conditions appear to be present in Tobias Dal o old with Hope Land) (see plate v).

D. The Crater Lake Pingo -Note On the 1 : 250,000 map of Trail1 Island (~ongOscars Fjord, 72 E.2) there Is a circular mark designated as "mud volcano". Our investigations in August of 1955 showed that this etas actually a typical pingo, not a mud volcano. Description Thc Crater Lake Plngo (~ig.17) 1s about 1 L~llfurther up the valley from ~orclsb. It stands in the centre of the gravel plane of the Karup River. It la charactertized by an almost circular crater lake. The north-3outh diameter - of the lake is 105 m, the cast-west diartieter 107 n~. The depth of the lake was sounded along thcse tbro profiles. For thcse ~r~casurcir~entswe devised a float- ing cork buoy rihlch could be controlled froie the shore. The results show that the unusuall:; stecp crater walls (I10 - 90') continue down Into the lake. The depth taken 10 m away from the shore on the west, north and south side3 respectively were 6.2 m, 6.2 ni and 5.3 ni. On the east side the undervtater slope is somcv~hatflatter. From 15 m from the shore out to the centre of the lake the depth of thc water increases only about 2 m. The niaxinium depth

(8.1 111) was obtained slightly to the east of the centre of the lake. The surface of the lake Is 2.2 m higher than the main arm of the Karup Rlver, ~rhichflows around the north slope of the crater side. On the northwest side there is a breach in the crater wall that is used by a sr~~allstreamlet. The rate of flow of this riverlet was measured several tin~eo. On August 20, 1955, it was little more than 3 litres per minute. At this time there wa3 no snow left In the crater which could havc produced water by rnclting. A soap test showed that the crater lake water is much softer, i.e. contains less lime, than the water of the ping03 which arc to be dlscu3scd below. At its highest point the annular wall rises 11.6 rn above thc surface of the laltc. The ridge line of the crater is 3'75 m long. The base perimeter of this pingo is 720 m. This large perimeter is due to the fact that several concentric old forills are interwoven wit11 the present-day pingo. The wide flat bulges on the south side can be interpreted as the rcrnnants of a donic of large radius in which no breakthrough occurred. Wide radlal cracks run from the new crater across the flat old bulges and thus suggest a close relationship betwecn the two stages. Evidently the old forrns were reactivated during the last upthrust. This hypothesis is supported by the results of a large excavation on the southern, inside vrall of the crater (FIE. 18). A vertical strip 6 m wide was excavated frorn the ed~eof the crater down to the surface of the lalce. At this point the crater was 10 rn high and had a slope of 70'. Under a layer of loose slide material ice was exposed. This occupied a little more than the lower half of the profile. The mass of ice was divided by a complex surface of separation Into two clearly differentiated sections. The loner half consisted of cloudy, white, non-transparent ice. Of 1107 measured crystals in a vertical section through this cloudy ice, only 8 crystals possessed an equivalent diamcter of 2.5 cni; a11 other crystals (86% of the total area) had snlallcr dia~:,eters. The mean diameter was 0.3 cm. The mean weight per unit volwiic of this ice based on three riiea3urec1ents was 0.89. The upper section of the ice was transparent and contained a niuch larcer proportion of large crystals: only 345 of the total area was occupicd by crystals with diameters sn~allerthan 2.5 cm. The largest crystals had equiva- ". lent diarncters of 2.5 crrr and more (30 out of a total of 203 crystals) and areas of' 22 cm2. The Itl.can crystal diameter of the transparent ice was 1.6 cn, the vrcldlt per unit volu~nc0.90. It contained far fcvrer alr bubbles than the ice below It. fit thc ~:urfnccof scparatioti betwccn tllu cloudy, cmall-grained and the clear, largc-~,ralncdIce the t~:ornassco of ice were just barely intermingled. The deforn:atlon which had taken place in this zonc appears to have been chiefly of the plastic type. In addition, a clear reduction of the crystals by cataclasls bras clearly evident in the zonc of contact. Many of the cracks ran through several crystals. No cracks were observed to cross the surface of separation between the two kinds of ice. By drilling horizontally, and then at angles of 30° and 45O downwards, we attempted to deternline the extent of these bodies of ice. In all three directions the drillings, which started 1.2 m above the surface of the lake, had to bc discontlnucd for technical reasons at a depth of 6 m before the end of the ice had been reached. Fivc short drlllings wcre used to determine the ~hape of the surface of separation between the ~ihiteand transparent ice. As far as we could tell from thc core samples, this surface appears to dip towards the south a very short distance in. Above the ice lay a conlplex of frozen, well stratified sand which was considerably thicker on the right-hand side of our profile (Fig. 18). In the oblique section this stratification was practically horizontal and sloped towards the outside of the crater at about 20°. The surface of separation between ice and sand was sharp and irregularly zigzag in its course, a8 though Individual pieces had broken out. A wedge of frozen sand, having an edge length of 30 cm, was found in the middle of the clear ice. In the vicinity of the surface of separation between ice and sand there were three very distorted layers of sand about 3 to 10 cm thick and 30 to 40 cm long which had been squeezed dry. These Inclusions appear to have moved again. In the boundary zone between the ice and the sand it was noticed that many of the ice cryotals had been broken. The upper 5 m of exposed rock consisted of river gravels of the kind being deposited today by the Karup River. Cross stratification and alternate depositing of coarse and fine material characterize this zone to a large extent. In the lover half of the gravelly top layer, boulders of considerable size (diameters up to 40 cm) were frequently encountered. The finer components predon~inatedIn the upper~r:ost parts. The increased number of larger stones at the surface Itself nlust have becn due to the blowing away of the fine materlal by thc wind. In the vicinity and on the slopes of this pingo the wind forri,~sand dunes. The absence of a vegetation cover must therefore not be interpreted as an indication of any special recent activity on the part of this plngo.

-%. Swrur~aryand 11lterpl.etat ion Two different bodieo of ice and tvro deposited n~aterialsof different kinds have contributed to the construction of the Crater Lalcc Pingo. Thc undcl-l;ring, non-trarispnrcnt ice can bc rcgardccl tcntativcly ac the rerrmant of thc body of ice which forrncrly occupicd thc prescnt-day crater and the crater spacc abovc it. So far about 130,000 cubic metres of this body have melted away*. This inelting-down process 13 in part, at least, of endogenic character, 1.e. the ascending sub-pernufrost water adds to the n~eltingdue to swnnler heating from outside by the transport of heat of melting from below. By the end of August, 1955, surface melting of the ice had started only at a single point, and has only begun there because the waves on the lakc had undermined the protecting layer of gravel and cause it to slide. The white, apparently younger ice extends under the line of coarse crystals, which must have been preserved primarily in the half-moon shaped bulge on the south and east side of the pingo. The relationships between the different kinds of ice at the surface of separation and between the Ice and the sand are interesting from the standpoint of the mechanics of pingo formation. It Is apparent that the ice of the Crater Lake Pingo has been subjected to considerable mechanical stress. To this It has reacted both plastically (internilnEllng at surface of separation and expulsion of forcicn bodies) and rigidly (fragmentation of crystals and formation of cracks up to 40 cm in length).

E. The Sou17ce Pinp;o

Description Thc Source Pingo is the sn~allestof three pingos forming a distinct group which is situatcd 3 km dov~nvalley froiri the Crater Lake Pingo in the rnlddle of

the gravel plane of the Karup River, (FIE. 19). The southernmost of the three, ' evidently owing to a thick top layer, has only progressed to the stage of a distortion of wide radius of the uppeniiost pernlafrost layers. Even the Karup, which has worn away approximately of this 9 m high pingo on the south sidc, has not bzcn able to expose the layer of ice. Thc next pingo to the north 13 of larger dimensions. Its base perirrieter Is 350 m. This rcclains only as a ruln. Its highest point is 11 In above the lcvcl of the Karup. The crater floor, measuring approxirnatcly 30 rn by 50 m, is only partially occupicd by a lake. The cratcr ~13111s picrced in the northwesterly direction. The Source Pingo, thc northernmost of the three, is a reactivation of part of the cratcr wall of the decayed main pingo. The shape of the Source -. * For. this calculation the ourface of thc: laltc was assurrlud to be the centre cr-oxs-scctlon. Thc 1 owcr boundary of the ice lcns niust be approximately 5 m below thc bottom of ihc prcsent-day lake. Pingo at thc base is therefore clliptical. In the longitudinal direction the crater measures 31 m. The perimeter of this omall, but very characteristic pingo is only 70 m. The base perimeter is 150 m. The highest point is g m above the level of the Karup. In the middle of August 1355 the crater contained an oval shaped lake 15 rn long and 7 m wide. The surface of this lake was 5.3 m above the Karup River. On the west side the lake was scarcely 20 cm deep. Its maximum depth of 1.2 m was found to be in the eastern third of the lake. At this point rising air bubbles and irregular bubbling betrayed the presence of a vigorous spring. A little to the west of this was another spring which could be observed through the transparent water. A third water source was situated a little above the western ohore (~ig.21). On August 9, 1955, the water emerging from this spring had a temperature of O.Q°C. The te~nperatureof the lake itself was 2OC. Two breaches which pierced the crater wall to the east and to the west, respectively, acted as overflow channels for the various springs. At the time of our field investigation only the eastern channel was operating. The little brook rushing down the steep eastern slope of the Source Pingo emptied into a side arm of the Karup River. On August 9, 1955, its rate of flow was 1.4 rn per second. A second measurement on August 27 showed the same productivity for these three springs. At the spring to the west of the lake a hole was dug. Below a layer of 15 - 20 cm quicksilt (granulometric analysis showed 23% clay, 54s silt and 23% sand), which was comparatively dry on the surface but saturated below, smooth ice was encountered. As soon as the ice surface was exposed water erupted in small fountains from many vertical pipes. Over an area of approxi- nately 2 m2 the ice rescrnbled a sieve with holes of 2 - 20 mm diameter. Xn addition, there was a crack 80 cm long and 5 - 10 cm wide from which water was also flowing. Three holes started with the drill in this region had to be discontinued at 1 m, 1.3 m and 0.8 m depths, respectively, because the ice was very strongly infiltrated with silt and sand. In all three holes an ice-free zone 30 crn thick was encountered at a depth of 50 cm. This horizontal gap was filled with an unfrozen, thickly viscous silty muck. The ice below it was very 30iled. The 3oiling, and the varied resistance encountered by the drill indicated that this body of ice was in the process of decay. Not until we were 4 m away from the shore of the lake did we encounter frozen silt with ice laminae. An unusual feature was the discovery of hollow spaces as large as a fist in this frozen ooil. No explanation of this phenomenon could be given. Towards the rim of the crater to the west and to the north the zone of completely frozen fine rnaterial dips bclovr a layer of gravels and coarse sand of increasing thickness v~hichwan moving in the direction of the lake a8 a rcoult of slldin~;and oolifluction. Excavations on the lnoide wall of the crater showed that with respect to material the Source Pine0 la asymmetrical, Inasmuch ao the entire south side is colnposed of eilt,'while the north slde conalsts of sand and grovels. This lo due to the fact that the Source Fingo is incorporated In the renialno of a larger, now inactive plngo. The gravel layers viere involved In the same way In the construction of the old pingo. The sllt layers, on the other hand, which In the old pingo ascend towards the south, because they form part of the northern ridge, were overturned In the Source Pingo and now climb in the northerly direction. In the course of thls process the well-stratlfied silts were broken up into blocks and displaced. Special characteristics of the icc and water in the Source Pingo The ice found in the Source Pingo differs in various respects from typical pingo Ice. The Individual crystals were decldedly columnar in const~ction. The colunuls were up to 10 cm long. Thclr principal axes were perpendicular to the crater floor. Elcan dlarneter calculations of the ice crystals, based on a cross-section parallel to the base spinacoids, showed a slnaller value than for plngo ice. The mean dlanleter of 619 crystalo was 1.28 cm, compared with 1.6 - 2.7 crn. On the other hand, the shape of the grain-size curve in this ice was very slmllar to that of normal pingo ice (~lg.25). The averaged density of this columnar ice from three measurements repeated three times each was 0.89. This value Is a little lcss than that for typlcal pingo ice. The qualltatlve geochcnlical analysis of a oalnple of the Source Pingo water, extracted in August 1955, showed it to be a normal lime water contalnlng some gyp sun^, but poor In chlorldea. It contalns no rare gases, no methane gas and no hydrogen oulphldcs. No traces of blturlen or natural gases were found. Water of thls quallty is suitable for drinking but a bacteriological analysis Is still nceded. o or this analysls of the water I thank Prof. ~:beli, Analytical-Che~r~ical Institute of ETII, ~urlch). The results of the analyses of certain prominent precipitates from this water stood In good at;rcenlcnt with the 1-esults of the water analysls. The former overfloer channels, lilte thooe of today, trcre distlnppishcd by an Intense reddish colour duc to the prcsencc of ferric hydroxlde. Quantitative analysls of the tiny crystal3 which ~thltenthe shore of the lake and the ed~esof the broo!c, showed the follov!ln~con~~~osltlon: CaSO, 59.6;; Si02 7.65; Al,O, etc. 6.7s; CaO -t CaCO, 2.3;;; Na In traces; CIBrI, K and Dl:: not present. (~111s analysis was ltlndly carrlcd out for mc by Prof. Kranclc, Goolol;ical Institute of 14cGlll Unlverslty, 1:gntrcal. ) S[u;ur~aryand lntcr;)llt: tnt Ion The Source I'1ni;o fully confli-mo what has hitherto been assumed, naniely that the sub-permafrost water is the decisive elenient In the constmction of the pingos of this region. The icc found in the Source Pingo is of unusual character. Its or1C;in is probably nosociated with the formation of surface ice in winter, since thcre was injection of spring watela into the uppern~ost part3 of the pingo. The InJection would take place pritnarily In the latter pal% of mid-winter, whcn on the one hand the ourface Ice cover is especially thiclc and on the other hand the accuri~ulateddynamic pressure of the hydro- statically stressed v~atcris at a niaximurn. J. Putallaz and A. Perrenoud in the spring of 1956 observcd that a thiclc laycr of surface ice had in fact fol-mcd at the Source Pin~o(oral co~nrn~~ication).

F. The Glaclcr Pingo

General Dcscrlption The great dome of the Glacier Pingo is visible from far off, halfltay up the south side of the valley, approxlmatcly 400 rn from the Karup River and about 50 n hlghcr. It llco to the southeast of the Source Pingo. It co~npriseo a cornplex base of irrcgularly round outline, with a pcrimeter of approx1n;~tely 1,000 m. Seen froin che air it vras evident that this was the ruin of an old giant pingo on which the present-day pingo is centrally superimposed. The height of the new pIn(=o by Itself is 33 m and Its basal perl~neteris 350 m. The re~ainsof the old base and the many snnll satellltc plngos In the vlclnity are d1stin~;ulshedby yellovr sands, k~hcreasthe new, superimposed main plngo 13 covered with uniformly grey niica sandstones and their disintegration products. Only isolated larger coinponcnts of this are st111 present. The renlalnder consists of a detritus brought about for thc most part by the action of rnechanical forces. Slidcs, folds and displacen~cntsof all kinds are very frequent. The transverse profllc thllou~hthis pingo shows that the young part itself con;- prlses at least 3 systcns nesting one Inside the other, bettrccn which there are scarcely any considcrable dlsintc~rationstages. The illaterial constitutin~;the Glaclcr Pingo is forcign to this landscape of frost gravel and vci3y pl,?..stlc 1on1,ly soil in Plcistocenc and post-glacial dcposlto . The sand3tonc: Involvcd in thc construction of the pingo must COIIIC directly from thc Carboniferous substructure of the rc~lon. The absence of a frost [:ravel and plasclc 3011 cover over the satidstones of thc pingo nlay be due to thc fact that thc prcscnt-day pingo, dccplte Its enor;nous size, has rcactivatcd the core zone of a still lnr~crp111go irhich 13 still partially ?re~e~-vcdin thc ycl1ovi :;and barlc. The G~aclci-Pingo lo situated on a large fault which tl avr-.r3~3tllc vnl lcy of 1.hc: i:,?lbup llivc'r. Tlle spr-lng and thc ~:llrllatul.e -- sul;11111t zlacicr

The 1no3t rer:larlcable feature of this pingo was the miniature glacier situated on the cast alope in the crater-like saddlc. The highest point of the pirl~oprojected about 8 m above it. In the middle of August 1355 it mcanurcd 27 nl by 30 r,i. Thc south tongue was thicker than the north one. In thc centre of the elacier Pras an almost circular hole 15 m in diameter. From the greyish black r~~oracrsat the bottom of this hole, which xias about 2.5 m deep, water and gas were enler~ingat several points. It was estimated that the volume of gas emerging was about half a3 great as that of the water. On Aupgst 16, 1955, the teti~pcratureof the water at the outlet waa 0.1 - 0.2OC; on August 31, 1955, it was otill 0.0 - O.l°C. The rate of flow of the main spring was measured slmultaneouoly with the3e two data. The figures were 1 - 1.1 litres per second. The total amount of water flowing from this pingo could not be determined accurately because the water melting from the glacier added itself to the spring water in the three overflow channels. It is estimated at approxirnately 2 m per second. The hydrochemlcal analysis of a sample of this spring water carried out by Prof. ~sbellshowed it to be water sLmllar to that obtained at the Source Plngo. The .gypsum content was somewhat greater, the lime content, on the other hand, smaller. Neither radloactlve material nor bituminous residues were found. The content of chlorides was smaller. This watel- must have come from shallower depths than the water described by Rosenkrantz (1940, p. 125) from a West Greenland pingo, which must be described as a sodium carbonate xater. At the same tine, a saniple of the gan eri\erging in irregular puffs was investigated by Prof. ~abell. Its colnposition differed but little from air. The carbon dioxide content was srnnll. No methane gas could be detected. Hydrogen sulphide was also aboent. There was no radioactivity. The gae was found to be of totally different con~posltionfrom that of the sample frorn an active West Greenland pingo, for which Roscnkrantz (1940, p. 653, and elsewhere ) gives approximatc ly 75s methane and a compa~atively small anount of nitrogen. Two of the overflow channels of the Glacier Pingo were rc~narkablefor their chernlcal eff lorcscences . The wider overflow to the south, which spreads out into a large gravel fan (FIE. 22), was colourcd vividly red and white from precipitates of ferric hydroxide, linic and gypsum. On the surface of the glacier therc were ncota of otiiall conglomcratcd calciun~carbonate and Eypsurn cry3ta.1~. Surface material and condltlons of contact

On the north side of the glacier In August 1955 there was an appendage to a crater formation. The little brook flowing in this direction had worn a gorge-like breach through the 1 - 2 rn high wall. Along a stretch of about 4 m the surface material had closed over it again, sothat the little brook was flowing subterraneously. This settlement of the erosion base caused the drying up of part of the spring cavity and the zone between the glacier and the crater rim. As a result we were able to carry out three excavations and two drillbgs. Figure 24 shows the results of these investigatione In a partial pr~ofile through the Glacier Pingo. On August 17, 1955, thawing had progressed only 2C$ In the fine material of the north slope (41% silt and 59 sand). The frozen material below it, which contained some rather sharp-edged components, was bounded at a depth of 80 crn in site 1 by a body of Ice. The transition from the soil to the ice was not as sharp as, for example, In the crater of the Trout Lake Pingo. Blocks and lamellae of silt and sand were suspended in the ice to a depth of 50 cm. No special deformations or even ripplings of the foreign material contained in this ice could be observed. Only the many elongated air bubbles In this zone, which were curved like worms, indicated a certain Internal motion. Two test excavations produced the Interesting result that the surface material in the vicinity of the spring to a distance of 5 m away was not frozen, but formed a viscous morass 60 cm deep, which unllke the conditions In eite 1 was sharply separated from the body of ice. The ice below it was free of mineral inclusions. This obse~~vationsuggests that the repeatedly encow- tered sharp surface of separation between ice body and overlying material is of secondary nature and can be regarded as proof of the fact that the dishte- gration of the ice body in question has already begun. Under primary conditions of contact a zone of transition is to be expected in which the two elements are Intermingled. Primary zones of contact are of special interest in relation to the pingo-forming mechanism. Unfortunately, primary contacts are very rarely discovered. The ice-sand boundary in the Crater Lake Plngo (Fig. 18) and the conditions at the entrance to the ice cave at Toker Point (Fig. 36a,b) can be cited as examples of primary contact. The body of Ice In drill hole I (Fig. 24) very hard and occasional soft layers of 5 to 8 cm thlclcness alternated regularly in the first 72 cm. At this depth the drill encountered a hollow space 5 cm across, which was about half filled with the same mixture of ailt and sand that characterized the overlying material. This inclusion was unfrozen. Fror~i 1. m to 3.2 n the ice offered very little resistance to the pcnctrntion of the drlll. It crumbled in the drill head into a snowy rilaso owing rather to the high degree of porosity due to the presence of many air bubbles than to the somev~hatsmaller size of the ice crystalo.

At a depth of 2.45 nl the drill again entered a hollovr space 2 cm across. Beneath this, partially frozen, were about 5 cm of sllt, sand and sharp-edged stones. After another 8 cm of ice the drill encountered conlpletely frozen material again, through which it could not penetrate. Apparently this drill hole I was still very much within the range of the primary zone of contact. Drill hole I1 was started at the edge of excavation 1 nearest the spring and was inclined at an angle of 72O in the direction of the centre of the Ice body. After piercing a layer 15 cln thick of very hard ice at the surface the drill for the next 10 m traversed fragile, snowy ice of the type that had characterized a section of drill hole I. Only at 60 cm depth was there a layer 5 cm thick of ice which offered considerable resistance and was completely free of air bubbles. At 82 cm the drill broke Into a hollow space 31 cm across. This appeared to communicate with the upper hollow space of drill hole I, on the one hand and possibly also with the spring system on the other. The 3 cm of fine material in the gap was unfrozen and water-soaked. At a depth of 2.6 m another hollow space was encountered. It was 6 cm across and contained no material. From 7.7 to 8 m the ice was soiled by lamellae of frozen silt and sand about 1 - 2 mm thick. At 10.5 m the drill broke without reaching the bottom of the ice body. As a rough estimate, this would lie at approximately 35 - 38 m. After the accumulated drill cores had melted completely a chemical residue consisting chiefly of CaSO, and CaCO, remained, proving that the efflorescences observed on the glaciers and in the overflow channels also occur in the ice body of the Glacier Pingo in high concentration (analysis by Prof. ~fibeli). With the aid of thermocouples it was established that the uppermost hollow spaces of the two drill holes are in col~nunicationeither with the outside or with the very large hollow space in the interior of the pingo. Thermocouples were installed in drill hole I1 at 25 ft., 10, 20 and 30 ft. depths. Their calibration was the same as in the Trout Lake Pingo. In Fig. 16 the tenlperaturc curve of August 30, 1955 is cornpared with the same data from the Trout Lake Pingo. This curve shows distinctly lower temperatures. The differences In the lower part especially are more than lac. The thcrnocouple 80 cn down was freely suspended in the uppern~osthollow space of drill hole I1 and at all times recorded slightly positive temperatures. Lcc anfl surfacc icc

The icc from the interior of thc Glacier Plngo falls well within the classification by granulometric processes of the already known exanlples of pingo Ice (~13.25 and Table 11). Thc ice of the glacier, on the othcr hand, differs clearly in several respects from pingo Ice. The mean diameter from 811 crystals of glacier Ice tras only 0.18 cln, cornparcd with 1.6 cm for the ice taken from the Interior of the Glacier Pingo. The granulonictric curve not only Is displaced In the direction of very small values, but it is also steeper than the curves of typical pingo ice. The 1velC;ht per unit volume of thls ice barely attains a value of 0.88, cocipared with 0.90 and more for plngo ice. Since no crystal patterns of truc surface ice exist as yet, it Is difficult to decide whether the glacier of the Glacier Pingo really consists of surface ice, 01. is rather made up of true firn. Preference, however, is given to the first Interpretation because It can hardly be believed that such a mass of Ice would remain Intact a full 300 to 400 m below the firn line, merely as a consequence of local climatic factors. According to an oral communication of Elr. Jean Putallaz of Geneva, thls glacier survived the swluner of 1956. The stratification in the ice of the glacier which can be seen in Fig. 23, can probably be attributed to annual accumulation. On thls basis the glacier rnust be at least 20 years old.

G. The Goose Pintyo

At the suggestion of Dr. B~tlerthe pingo described by him in the northern tributary valley of the Karup River (Batler 1355, Table VII) was again visited. Beginning at the northwest shore of the 50 m wide crater lake, the depth of the lake was sounded at intervals of 5 m and the following values were obtained: 3.4 m; 3.4 m; 3.4 m; 2.0 m; 2.2 m; 3 .O m; 4.0 m; 1.8 m; 0.7 n1. Much more important than the slight asy~nmetryof this profile is the fact that a new doral warping was indicated in the centre. At thc end ~f August 1955 this had a height of 2 m, although at its hl&cot point it was still a full 2 m below the surface of the lalce. The conditions present in the Goosc Pingo force8 us to conclude that thls mound in the centre of the lake is entirely of sub- aquatic origin. According to ~ileasurenentsby 14r. Aagc de Lemos, Copenhagen, the maximum Ice thickness on a simllar fresh-water lake near the expedition base on Ella Island Is not more than 1.6 m. If these assumptions are correct the Goosc Pingo Is of great theoretical interest. It was proved that the direct external lnf luc>nces, e .6. the annual te~:,pcraturevarlatlons, arc of minor importance. The formation of the pincoo Is presun~ablydetermined rn\lch more by the temperature variations and ground water conditiono In the interior of the permafrost.

H. The Anteced'ence P1np;o

At a distance of 2.5 krn down the valley from ~orelsbon the south side of the Karup River is a flat dome of huge dimensions situated on the valley floor. This is the Antecedence Pingo, visible from afar. hiedlately to the west of it is a similar, smaller formation (Fig. 26). The axis of the Antecedence Plngo, which runs parallel to the river, is about 700 m long. The minor axis at right angles to this is 400 m. The elevation of the dome is about 15 m. Several radial cracks are visible. It would have been difficult to determine whether this vlas an erosion phenomenon or a true plngo, had not an earlier course of the river, which antedates the uplift of the pingo, cut through the latter like a ribbon from southeast to northwest, practically traversing its highest point. The depth of this now dried out river bed is 1 - 2 m. As the pingo slowly rose it forced the tributary river corning from Svinhufvuds Range to adopt a strikingly unusual alternative course, which is shown in the 1 : 250,000 topographical map of Trail1 Island. Today the waters of this small river branch in front of the large pingo to the east and to the west. From the preoent state of these two river beds, which nust be of approximately the same age as the ylngo, we can estimate the latter to be already several centuries old. Uplifts like that of the Antecedcnce Pingo are found In many of the valleys of East Greenland. These extremely high formations, distinguished by a special symnletry to vrhich the tern1 pingo 1~normally restricted, are probably only extreme cases of a frequent process which 13 of somewhat greater importance from the standpoint of periglacial morphology than has hitherto been assumed.

I. The Pln~osln the Kaanedal

On a 5 knl stretch in the upper Maancdal we find no fewer than six characteristic pingos. With regard to the uppermost one, situated actually on the other side of the flat vratcr divide at the top of the Ihancdal, Dr. ~atler (1355, Plate VII) has demonstrated that lt stands directly over a basalt seam which crosses the valley. Thc same was also shown for a pingo 5 km down the valley. Two of the other pingos deserve opecial ~ncntion. In the reelon of the water divide a very small pingo, but a very typical one as far as lto shape 13 concerned, stands on 3 gravel fan cowing from the south. On tlugust 27, 1955, It had a basal diamctcr of 6 m and a height of 2.5 m. This small thanedal pln~ornust alrcady bc illany years old, bccaucc the droppingo and pcllets deposltcd by the snowy owls, which crown thc pingo lllcc a white cap, could scarcely have becn accun~ulated in a single year. Despite its small nize and ~eneralappearance, therefore, this cannot be a so-called "annual" pingo, of the type slcetched and described by Porsild (1938, p. 51 and p. 53-54) in the Maclcenzie delta. On the other hand, It Is uncertain whether this pingo is of similar origin to the type dcscrlbed in this prcscnt work. The lal-gcst pingo of the I~iaanedal is situated halfway between the trro pingos which have the distlnctlve basalt bars, approxi~~atelyat the point where a large fault separates the Carbonlfcrous sandstones from the Triassic which cuts across the valley. The major basal diameter of this oval pingo was 200 m. Its n~aximumelevation above the river level was 19 m. At the end of August 1955 there was a large, ditch-like crack cutting across this pingo. On the north side, halfway up the slope, water was cmcrglng and running down the ditch, which was about 8 m deep. The remarkable thug about this spring was that the water emerged directly from the frozen sand through many fine channels. It must have broken out just shortly before our visit. The temperature of the water was comparatively high (+3.5OC).

IV. Morphogenesis of the East Greenland Pinf{os

A. Outline of Perlnafrost and Climatic Conditions In East Greenland

Pingos are a pernaf rost phenomenon. Unfortunately lltt le is known about either Pleistocene or recent climatic conditions In relation to permafrost. The first few data wcre obtained in the course of the mining activities started in 1951 in the region of Vig (vie = Lllct), giving us a point of departure for the problems and regions dealt with by us. Dlesters Vig is situated in the northeast corner of Scoresby Land, East Greenland, at 72"15'N and 24"W. Both geoy;raphically and climatically, It occupies a position approximately mldvtay bctrleen Pingo Dal and the Karup Rivcr valley, our two regions of investigation, and therefore, with certain rcserva- tion, it can bc takcn as rcprcsentative. Permafrost and ,rr,rour.d water In- the !.;esters Vir; reelon The temperature conditions in the perl~lafrostlayer In the lead mines of IiIesters Vig are prcscntly being invcsti~ated. blr . 3. BonBam, Cirbnlands Geologiske ~ndcr~s#~ctlsc~,Co?enhagen, oupplc~~icntinghis published note of 1955 - to thc effect that the pcr.:i~afrost in Blylclippen had a thiclcness of approxl- mtely 100 rn (paZe lo), was l.:ind enouzh to zivc tnc thc follow in^ data: 1. Thc ir,dividual value.; for the th2cl;ncss of the pern~nrrostvary widely. At the 335 r,: lcvcl frozrn 3~1125 to 30 III dccy v!as found. HIchcr up the slope, ,h . at thc 390 111 lcvcl, ttlc pcrliiafrost is approxin~atcly-15 m thlclc. Thls 13 again 1n sandstone. XII a lift shaft a per~oafrostthickneos of approxirnately 125 m was found. Possibly the tapcrlng off of the permafrost frorn the slope towards the valley bed is due to the fact that the valley trough vns occupied by a glacier at the time the pernlafrost was forming. The view that glaciers retard the formation of pel-~nafrostis regarded today as well founded (~uller131~7, p. 4; Werenskiold 1953, p. 200; Black 1954, p. 842). The thermal action of the rivers continued to thin the permafrost after the melting of the glaciers. The rivers of this region flow all year round (Bondarn 1955, p. 10). The fact that permafrost formation In valley beds and on the lowermost parts of slopes is reduced by former glaciers and present-day rivers helps to explain why pingos are always found in valleys, never on ridges and elevated plateaus. 2. The geothermal gradient in the permafrost of Blyklippen, according to Bondam's current reports, is approximately 15 m. In the lower parts of the mine, below the permafrost the temperature Increases only by about 1°C per 50 - 75 m. These figures still lack sufficient confirmation and must be treated with caution. However, even if we take into account the considerable Influence of the SSE exposure this small geothermal gradient In the permafroat of the Blyklippen lead mine can be taken as an indication that the region of Mesters Vig lies within the zone of transition to discontinuous permafrost, for according to Black (1954, p. 843) the vertical temperature gradient in such a zone gets progressively steeper. In northern Alaska, where the permafrost lo about 300 m thick, values of 24 - 66 have been measured (Mac~arthy1952, P. 589). 3. At the end of gallery 335 a water vein active all year round was encountered in a fault. The water was subject to a pressure of approximately 1.7 kg/cm2; its temperature was about +0.5OC This observation confirms the assumption expressed by various investiga- tors in connection with pingos, that in this region of Greenland there are sub- permafrost waters, and that these associate themselves by preference with geological disturbances . In sununing up, it may be stated that the thickness of the permafrost, estimated by Poser (1932, p. 1'7) at 360 rn (SIPRE Abstract 3465 states this as a fact) for a region a little to the north of l~lestcrsVig, has been assigned too high a value. Climatlc conditions today -.. In order to characterize the cl111ratcof the East Greenland pingo regions we shall flrst present the mean monthly and annual te~npcratures, the corresponding maximum and siinimum values and the prccipltatlon condit ions at the Danish bleoters Vlg vrcathcr station (Table I). On the basis of Shostakovichfs rule of thumb a3 reported by Troll (19411, p. 645), whereby

mean alr temperature for the winter months Dec. to Feb. 111eunsnow depth In January (cm) h 0.5

conserves existing permafrost or forms more, we find that prencnt-day cllmatic conditions in Nesters Vig arc no longer favourable to permafrost In all yeara. It may be assumed, for example, that the reserves of cold in Mesters Vig permafrost suffered a setback in the wlnter of 1953-54, Table I also gives a number of mean values of temperature and prcclpita- tion data from the Norwegian Nyggbukta Weather Station. Myggbulcta la situated In the area of the northernnlost pingo that has been observed to date in East Greenland. The same table presents a few values from the southern part of the East Greenland pingo area (~apTobin at Scoresby Sund). All those data give us a few points of departure concerning the.climatic conditions for the pingos of East Greenland. Even the few figures which are available from Nesters Vig Station which vras opened only in 1952, show extremely wide variations, especially with regard to the precipitation. The same applies to Kap Tobin. These marked differences between the individual annual values have already been cited by ~ovrrdller(194'7, p. 93) as characteristic of the East Greenland climate. Even these short-term fluctuations have an effect on the permafroat. They are manifested In the body of the pcrmafrost with a lag of some years. Accordingly, the reactions of the intra- and sub-permafrost waters occur only some years later. Lon~r,-termclimatic variations Shostakovich (1927) states that the present-day climate had to be held responsible for the presence of perniafrost . Sunlgln (1929, l932+, 1935+) however attempted to prove that permafrost ls a product of an earlier, colder epoch. The prevailing opinion today is that both factors are involvcd l lack 1954, p. 846 and 847). kle shall therefore diocuss very briefly the effect8 of long- term clinlatic variations . These variations, extending over hundreds and so~netimesthousands of years, are manifested in the body of the permafrost with correspondingly greater tlmc lags. Several clinlatic changes rnay be recorded simultaneously in the same perniafroot mass. For regions with great thlclcneos of permafrost (e.~.Yakutla In northeast Siberia, where the pcrmafrost In up to 600 m thick) it 1s believed po3slble to rcconstruct the cli~natichistory of the recent past from the te~npcratureprofiles. A Russian v~orlcrecently translated Into Engllsh deals ::ith thc p~r:~:a1'1~1ltlyfroze11 so113 of Vorlcuta, Siber.ia, prcscntin(; a n;athcl,:atical-physical analysis of 1;his phenoi~~crlon(~cdozubov lglr6). This Idca, that thc frozcn ground can servc as an indication of the occular cllnlatic changes, had already been e;:pressed by Sumgin (1932+ ) . In this connection tllc clinatic fluctuation3 in East Greenland in historical tinle3 as vrorlccd out by Dr. Lau~eKoch (1945) are of grcat interest. At the present stage of the lnvcsti~atlonit 13 still not possible to correlate these long-tc~iilclicatic variations with greater or lcsser pingo activity. !.le can rrlercly say that under present-day cli~iaticconditions only 2 of thc 28 plngos lnvcstl~atedin East Greenland are clearly In the process of grov~th, v!hercas 7 of them show definite lndlcatlons of disintegration. h 6 pingos build-up and dlslntcpation arc going on simultancouoly. The rennin- ing 13 exam?les appear to be stationary.

B. The East Greenland Pingos as an Open System and a Permafrost Phenomenon

The key to an understanding of the East Greenland pingos was found when the emergence of water at the surface was observed In the Source and Glacier Pingos. These waters ascend centrically through the body of ice and are accompanied by bubbles of gas. This obscrvatlon had already bcen made earlier. Rosenlcrantz reports of a pingo "in faint eruption" which had bcen discovered during the Nugssuaq Expedition on the peninsula of the same name in West Greenland (~osenkrantz et al. 1942, p. 42). "~ud,crave1 and stones are hcre thrown up to the surface by ground water, the pressure of which is due to a consldcrable constituent of gases, chiefly I~lctan [sic], which makcs thc water foam (hence the name used by the Greenlander:, : Qapiortoq = the foalilcr )" . Thc oan:e authors describes a "mud volcano" of the Svartcnhulc Pel~insula(~osenkrantz ct al. 1342, p. 41-42, Fig. 17 and 20, and Plate 5). The dcscrlption and photograpl~sof this plngo and Its vlcinity are almost identical 1~1ththc Source Plngo on T:.aill Island; the only difference is that in the East Greenland p11lgo investlgatcd by us no indications were found of a relatlonshlp of the plngo to the presence of bituminous earth. Thc results of hydrochernical and ~;cochcliiIcalanalyses of six 3011 samples, two water sari,ple=l and one very carefully handled gas sample by various experts (prof'. ~abcli,Prof. Kranclc and Dr. ~ahn)perniit no such conclu~ions. Even the anclyses discussed bclow of certain isotopic groups of plnco waters and plnco lcc ~lvcus no reason to supposc the existence of a relationship to bil;u;71r~ou3earth: here 13 not the 3lil;hte~tlndica tlon in thc icotopic data for such a relationship" (oral coilu~unlcatlonof Dr. H. Craig, Scrippa Institute of Oceanography, Univcr3ity of ~alifornia). In thc Gnrlco lPcrl~~lIt13titut;c for EIuclcar Sl;udlco, Univcrslty of Chicago, five sall~pleoof pillgo vrcltitr vrerc subjcctcd to 1na03 opectromctric analyaio under the dil-ection of Prof. l1.C. Urcy. Xpotein and &layeda (1953, p. 2211) had pointed out that the Isotopic con~ponitlonoof different 1vatcr3 ohovr wlde scatter and dcpcnd strongly on the origin and hlotory of the viater. In ordcr to clctcrnline the connoctlon betvrccn the 111ao3of Ice and the spring water from a given pln~o,icc sar,~glcsfrol~r the Glaclcr and Crater Lake Pingos vrcre also 1nveotit;ated for their Isotopic propel-tics. The ratlos of dcuteriwn to hydrogen as obtalncd from these sar~~pleswere compared with those of an average 8ca water; this quotient was related to the ratio of isotopcs 0,, to 0,, (~ralg et al. 1956). Thc rcoults of this double quotient

D/II:; rclatlvc to avera~~ocean water 0, ,/0, ,$ relative to avcragc ocean water " 9 were interpreted by Prof. Urcy and Dr. Craig (con~~unicatedby letter) as follor.1s : 1. Pingo Ice and pingo spring water are sufficiently identical with respect to their isotopic conditions that they can be asswried to have the same orlgln. 2. The pingo waters are -not of Juvenile, 1.e. magn~atlc-volcanic origin. They consiat of mctcorlc water. 3. The posniblllty that this water consisted of old oea water circulating within the pingo could be definitely rejected in favour of locally circu- lcting metcoric water. The abovc ratio of approximately 9 proves that pingo water has not under~oneintensive evaporation*. This rules our Svietosarovts hypothesis (1934)~ whereby the pingoo would be fed by juvenlle xater, at least as far as East Greenland pingos arc concerned. Gu3sowts v1c.r~(19511, p. 2226) that pingos are survivors of Pleistocene ice masses, 13 now scarcely tenable for East Greenland plngo3, either. The fact that the plngo spring rratcr and the pingo Ice lnass dcrlving from it are of dcflnltely local ~n~;.tcol~lcorigin 1itcal1s that in the Eaot Greenland plngos we are dcal.lng with "open SYB~CI!~S"in Tabcrls scnsc (1930). The quect- tlon of whether thcsc cyclical vratcr syntcrns are closed abovc or below the permafrost is anssrcrcd by thc fact that in all the pingos we Invcstlgated the thickncsn of thc r,:atcrinl overlying thc 111ass of ICCwa3 greater than the

* Thc full ~li~nificanccof thcsc rcsulto can bc realized only within the fr31i1~- v~orlcof a larzc.r coi,?ar~tiv~otudy. A dctailcd dlscusslon is thcrcfore to bc includc-d in a 1Iubllcatlon now In pr.eparation (cz3a16 and Ihyeda, now In prcas). ~~~nxl~i~i~r~ld(:pt.tl of Sllia:i:l(:Iu t.hauinlr,. Ti113 111t>:lnstknt tti~'~at.(:rn above the perma- fr~3stdo i~otplay Lklc dcciolvc role 111 the forl~iatlonof the East Grecnland pin~os. F'ln~osarc the product of 1ntr.a- and sub-pol.niafrost waters. The core of a pinco llcs Inside the pcrriiafi-ost. This hitherto rncrely presumed condition can now be regarded as oufficlcntly wcll cstabllohed to scrvc as a --crltcrion for a truc plnw, Any ortiall pingo-like forn~swhich are fed by waters above the permafrost, and whlch thus rncrely hcave up the active layer and generally sub- side again in the same year as they are for*nled, ahould not be regarded as pingos . C. The Physlcs of East Greenland Plnros

1. Mechanical forces In the Interior of Slbcrian plngos Ruosian scientists have discovered thick water lenses which have forced their way In the manner of laccollths between the mass of ice and the frozen ground below (Tolstlkhln 1332+ , Petrov 1934, Andreev 1936). The term "hydrolaccolith" used especially by Tolstikhln (1332+) is based on thls observation. It should be avoided, because it applies the name of one part to the whole, and In any case It Is not certain that a hydrolaccolith, in the strict sense of the term, is present In every plngo. Several examples of explosive eruptions of true hydrolaccoliths are known. Tolstlkhln (lgj2+, Abstract Stoltenberg, p. 65) reports that In such an explosion a small lake could be formed In place of the hill. The eruption of a hydrolaccolith In the valley of the Byrtsa River (~iberia)in July 1938 has been described in detail by Strugov (1955+). A report like a cannon shot was heard up to 7 km away, and nlasses of ice and earth were said to have been thrown 8 to 12 rn In the air. The hydrostatic pressure of a liquid is always perpendicular to the boundaries. Neglecting the force of gravity, this pressure can be taken as equal In all directions. The conrpl-essive force exerted on the overlying material is therefore propoiltlonal to the size of the surface under attaclc. The compressive forces of water ascending through talllc pipes are transferred by the water lens fl-oln a si:~allto a large area (FIG. 2'1, and Formula 1). Thl~ Is an application of tile very effective mcchanlcal prlnclple of the hydraulic press. In the talllc pipes of East Greenland pin~osvrt? haw, In the cxtrcrne case, on the baslo of the 1000 - 2000 m diffcrencc of hclght h the ~i~lnlty, a hydrostatic pressu1.c of 100 - 200 1cr/ctrl2. This hyclrootatic prcasure in the lntcrlor of the pingo, caused by the ground b~ater, is In ccrtain InJivIdunl cn3t.z ~.elnf'or~ccdby ttlc pressure of gas expansion. Thc gas pr'c:;su:~c3 in unopericd pin~oscan bc very conside~nble. The escape of gases in conjunction with pingos, as observed In the Source and Glacier Pingos, are also mentioned in the literature: Andreev (1936+), Rosenkrantz et al. (1942), etc. In the first phase of pingo development two forces oppose the pressure of the ascending waters and gases, namely the compressive forces of the overlying soil and the binding forces in the overlying frozen ground. The latter are mainly cohesive forces. Berezantsev (1947') s tates that the CO~~S~VEforces, and hence also the maximum tensile stresses occurring under load, vary between 2.5 and 18 k.g'cm2. The 20 m thick silt (specific gravity = 2.6) of the kind covering the mass of ice In the Trout Lake Pingo, for example, produces an overburden of 5.2 ke;/cm2. In view of the shape of most pingos we can assume in first approximation a point source for the forces. After the initial bending of the permafrost cover by the ascending water and gases severe tensile stresses arlse in the upper part of the resulting dome. When the pingo forming pressures have exceeded the breaking limit of the overlying permafrost layers, which would be at approximately 20 kg/cm2 for the frozen silt of the Trout Lake Pingo (54% of grains between 0.002 and 0.06 mm, moisture content 26, temperature up to 3OC) (according to Tsytovich and Sumgin, 1937, cited by Muller 1947, p. 43), division into single blocks takes place. For further lifting of these blocks only gravity has to be overcome. In this connection we must cite a Russian paper in which an attempt was made to determine experimentally the total pressures In the hydrolaccoliths of a plngo. Petrov (1934) measured a freezing point displacement of O.Q°C due to pressure with the aid of electrically recording thermometers in a pingo-like structure, whence a total internal pressure In this pingo of 52 atm can be calculated*. This value is even higher than was to be expected from our estimates. Actually, in ground water drilllngs into pingos pressures as hi~has this had to be regarded as danger points. Shumskii (1955, translation 1957, p. 124) measured a gauge pressure of 0.5 atm in the air inclusions at the base of a sniall ice laccolith. The decrease of presoure at the time of fracture of the permafrost cover results in a melting-point rise of some tenths of a degree. This change la very slight; however, in considering the mechanical conditions in pingos it cannot be neglected because it usually takes place in supercooled water. In such a critical state even a very slight change in the melting-point can result in recrystallization.

+ A prcssure decrease of n . kg . cm-' reaults in a melting-point rise of n . 0.0075"C (~uckli1950, p. 100). When the hyd~~olaccolithis transformed into an ice laccolith a new force enters the picture, the so-called crystallization pressure of the ice. This is a very ln~portantfactor. At -0.3OC it is already equal to 40 ke;/cm2. Its effective range, however, is restricted. It is used up In the familiar expansion that takes place during the transition from water to ice. The further construction of a pingo must take place not only agalnst the gravity and cohesive forces of the overlying mineral matter, but also againat the resistance of a growing ice lens. The maximum reslstance of ice to bending is given by Tsytovich and Sumgin (1937, cited from Muller 1947, p. 37) for temperatures of the range found in the ice of the East Greenland pingos (-3' to -5'~)as 18 kg/cm2. The orientation of the ice crystals, which must be taken into account in determining the resistance to bending of most kinds of ice, Is of no importance in pingo ice, since no special orientation of crystals appears to exist. The reaction of the pingo ice mass to the various stresses is sometimes rigid, sometimes plastic, as was clearly evident from the Crater Lake Plngo. It can be presumed that the intermittent growth of many pingos is due at least in part to the cyclically alternating mannFr of reaction of the pingo ice. With overstressing, cracks and faults would form (rigid behaviour). The associated rapid decreases of pressure can only be recovered slowly. During this slow buildup of pressure, wrinkles, etc., form. Evidence of such plastic deformation is often observed clearly, especially in the zone of contact between the ice and the overlying soil. Superimposed on this unique rhythm of plastic and rigid behaviour are the fluctuations in the supply of ground water. One would expect the above cycle to be reflected in a shell-like structure of the pingo ice. It has not as yet been possible to establish the existence of such a structure. In order to clarify this question It would be neceosary to obtain larger bore cores than has hitherto been possible with the available drilling equipment. In addition to the forces thus far held responsible for pingo construction, there is also the upthrust, whlch is the vertical resultant of a geo- static field of force. Upthrust Is therefore added in a very simple manner to the forces of the ascending water and gases directed against the mass of ice and the overlying soil. Its existence is due firstly to the great difference In specific weight of ice-water-gas on the one hand and the overlying gravel, etc., on the other, and secondly to the possibility that both ice and overlying material can behave plastically. In order to determine at least the order of - magnitude of the upthrust a rough calculation was carried out for the Trout Lake Pingo. A specific weight of the silts of 2.6 and an ice volume of 75,000 m3 were assumed, whence we calculated an upthrust pressure of 5 to 6 kg/cm2. Assuming, as is theoretically quite justified, that pingo ice masses can also be formed at great depths, the rcsult of the uplift forces would have to be a diapirism comparable to that of salt and gypsum domes. Thls possibility of a dlapiric ascent of the pin00 Ice :nass had already been n~entlonedby Butler (1354, Plate V) to explain a plngo In the ~andb8lValley in Kap Franklin rneglon, East Greenland. ~fitlerspeaks of an "ascending dome of ground lce". The same author mentions a second exarnple where "the upthrust against the weight of the heavy gravels overlying the Ice lens" agaln constitutes a plngo- forming elcment (~Gtler1955, Plate vII). In his latest work Helm (now at the printers) ralses the possibility of ice diapirism on the basis of purely theoretical consldel-ations. The rrrlnlclings found In the zone of contact between the ice and the overlying material thus far in the field (Fig. 36a,b) are still insufficient to provide a clear proof of the diapiric behaviour of pingo ice masses. The question of whether present-day pingo ice masses are now in their orlglnal position or have only arrived in that poaition by diapirisrn and upward niovenients due to hydrostatic pressure requires further study of the wrinkllngs of the sands, silts, etc., in the boundary zones and further investigations of the crystal conditions in the ice masses themselves. In this connection we may cite the valuable paper on structures in salt domes by Balk (1949).

To conclude this dlscusslon of the pingo-forinlng forces we may present a diagram and a symbollc formulation of the conditions (Fig. 27). Formula (2) gives the condltlons under which further updorning (>) or at least continued existence (=) of the pingo is posslble. Thls holds as long as the artesian water does not overflow at the open end of the open system.

2. The ternperatul-e rc~lme Tic exogenic teniperature Influences on the for~nationof pingos, e.g. the effect of frost penetration, teinperature varlatlons and their rate3 will only be discussed after the r~~aterialfrom the invcot1f;ations of the Mackenzie plnzos has bcen presented. I-Icrc nc arc concerned prlniarlly with the speclal temperature conditions produccd by the sub-pcnnafrost and intra-permafrost watcrs which are charact;e~~isticfor East Greenland-type plngos. Group for~natlonand thc: scatterinfl of water outl.ets - In the crystallization process about 80 calorles of heat are liberated per gram of ncvrly for.~ncdice. In the for~~~ationof the ice nwss in the Glacler Pingo, for examplc, It is estir~~atedthat 10'' cal have bcen liberated In the vlcinity of the pertuafrost surface. This heat, transnlltted primarily to the water, results in (1) a slowing down of the pingo-forming process and (2) a . thinning of the pernlafrost In the imrnediate vicinity of the pingo. On the other hand, the exposure of the pingo to the outside cold (less insulation by snow, etc.), and the fact that the ice has a lower conductivity than frozen sand or silt (~uller1947, p. 54, Pig. 26) means that the isothermal surfaces in the pingo are shifted upwards and brought closer together. As a result a sort of cold plug develops in the centre of the pingo. Since all permafrost materials react to a lowering of temperature first of all by increasing their resistance to bending, 1.e. by becoming more rigid, this development of a store of cold in the core of the built-up pingo cuts off its further growth. The sub-permafrost waters now seek escape routes. In this stage of development the weakest parts are in the flanks of the giant pingo. This tendency to escape into the adjacent permafrost zone is favoured by the fact that frozen silts and clays thaw even at negative temperatures (sometimes as low as -2Oc) (~ersesova1951). The above considerations have been stated in order to explain the following observations: 1. Large pingos are very often surrounded by a whole group of smaller "subordinate pingosl', taking the form either of appendages or of independent structures (see Plate V). 2. At the foot or in the loner parts of largc pingos which are still intact, very frequently we find small water outlets, often two or three of them in the same pingo. These generally scattered water outlets, which initiate the disintegration of the pingo, are very often visible from far off by reason of their strongly coloured mineral salt deposits (see Fig. 10). This can be regarded as proof of the fact that the first eruptions of pingo waters are often rich in mineral salts. The increased salt content, because of its lowering of the melting-point, is a factor that may be of very great importance in these melting processes. Ln addition to the pertinent observations (~ineralLake Pingo, Rock Plngo, Source Pingo, Glacier pingo) see also the works of Tolatlkhin (1931+) and Dzcns-Litovakli (1938' and 1945').

Disintegration proccsa and aKc By extrapolation of the temperature profiles from the Trout Lake and Glacier Pingos (~ig.16) we find that the ice masses of these plngos are probably no longer underlain by a watcr-filled space. A further Indication that the ice mass, especially of the Glacier Pingo, is no longer subject to *a. hydrostatic pressures Is the fact that when drilling rras carried out ncar the centre wide gaps were found which contained no water. This breakup and loo::~7ll~n~of Llic: ~)dn[;o Ice itlass 111 Lllc! initlal phase. of cllsintc:gr.ation 13 possibly duc to ::rilll.c>l' cold, since tllc hard f~*ozc:nlayers ncar the nur~face alotl,.: with the icc cover are liftcd off like a lld, or 111ay even be shattered by a toy ice explosion. A col~rpariso~~of thc ter;iperature curves fro111the Trout Lake Pingo wlth those obtained In thc Glacier Pingo further draws attention to the fact that the break-throupJ1 of water was accornpanled by a general rise in the temperature of the Glacier Pingo ice mass. Thc difference in August 1955 was

approximately ~$OC. Assu~~ingthat thls la the result of Inclpient disintegration, it means a decrease in the reserves of cold of about 9 10'' cal* on the part of the approximately 120,000 m3 of ice In the Glacier Pingo. In order to eliminate this reserve entirely and to ~rieltthe entire body of ice a further (18 + 960) - 10" cal** rrlust be applied. Before trying to estimate the time it would take for the praters flowing In the Glacier Pingo In August 1955 to furnish this quantity of about 10'' cal, let us consider the result of an experiment in nature. On the 30th of August 1955 a slnk hole was observed on the sloplng ground below the mountain on the south side of the Karup River which is characterized by gypsum dornes and basalt sills. A stream was flowing at a rate of a few litres per second for a distance of about 120 n beneath a thick complex of frozen sands. At the place of emergence the temperature was Q°C lower than at the sink hole (dropping from +6" to +2OC). Taking thls ter~iperatu~edrop of !c0C for 120 m contact with permafrost as a rough indication of the rate of hcat transfer, It would take about 300 years to melt the ice lllass of the Glacier Fine;o. Thlo Is assuming that the Glacier Pingo spring would continuc to flow at about one lltre per second. No absolute value can be assigned to this figure. It provides at best an Idea of the order of rnagnltude of the time required for the destruction of a pingo. Gases whicl~accornpany the waters upward through the ice niass slow down the dlsintegratlon plboccss on account of the intenne cooling effect of the gas expansion (~olstikhln1931 + ). Arnong the forces ~ihichprolnote disintegration we must also nicntion inciting due to the outside surrullcr tempe~~atures.In large plngos thc protecting covcr of frozen mineral l~iaterlalIs often too thin and Is broken by radial cracks. As a consequence the upyeri~lostparts of the Ice inass are exposed to melting. If water frolrl both the melting of ice and the melting of snow collcct in thc crater In the form of a pond and Is tihen warmed,

,~-- * Speclflc heat of icc = 0.5 ~al.~-'.oc-1 ** Approzlmately 18.101° cal for the destruction of the remainln~;store of cold and around 360 . 101° cal for the nrel tint: process. this liiay not only inltiatc the dislr~tc~ratior~of t;hc plngo, but may conslder- ably accelerate It a3 well. Ultinlatcly the initially closed annular wall 18 broken through. If only water of melting Is there to be dralned off, the brooklet flowing down frorn the higher crater pond Is only a temporary one. Later the sub-permafrost waters will emerge into the pond and use the same water course as the water of melting. In advanced stages of plngo dlsintegra- tion the broolclet will flow all year round, and in winter may forzn an ice cover. Permaf root sprlngs which do not form pingos It is a nlatter of observation that large sheets of water or water at high temperature in the permafrost of East Greenland are not able to form pingos. This could be seen in two examples on the north side of the Karup River, on both sides of the mountain slope there. In the first case 8 to 10 litres of water per second were emerging from the permafrost soil at a temperature of +2.5OC. In the second case about 7 litre per second were comlng out undusturbed at +3OC. From the region of Kap Tobln and Kap Hope (southern most tip of Liverpool Land) Pedersen (1926) describes a number of springs which dld not form plngos despite their association with pcrmafrost. The warnlest of these springs, thc one at Kap Tobln, had a temperature that varied between 60.4O and 62OC; the temperature of the coldest was +2OC. Rosenkrantz (1942, p. 54), who a180 mentions the springs at Ibp Hope, writes that there Is scarce any difference between the summer and winter temperatures of these springs. Thio again confirms the view that the aub-permafrost waters are primarily indebted to the long-term changes In the store of cold of the permafrost area in question. An ice mass, and hence a true pingo, can only form when more or less static conditions prevail at least in thc initial stage of pingo formation for n comparatively long timc and which become dynamic only much later. An essential condition for the fo~mationof a pingo must be presumed to be that only co~lparatlvelysmall quantities of water rise. Sub-permafrost springs which yield e.g. 1500 litres per second, as dcscribcd by Shvetoov and Sedov (1942+ ) disturb the temperature conditions to such an extent that a pingo cannot forii~.

D. Formulation of thc 1iypoi;heols for th? Formation of Pingos of the East Greenland

* In East Grcenland pingos occur where inti-a-pernnf rost and sub-perrnaf rost waters and gases conic to the surface under hydrostatic pressure in quantities and at temperatures that are sufficiently restricted so that no rcvolutlonary dlsturbancc of the p(:rlil~fl'031; talte3 pl a(:?. Ttle i;hickncoo of Lhc permafrost, averogin~about 100 n~, varico grmeatly. At a dcpth of a few metres up to a naxlnlwn of 30 rn, 1.e. still within the perrr~afrootzone, first a true hydrolaccolith foi'ms. Prom this a body of Ice forms, partly undcr the influence of the perrnafrost cold nlaximum situated a :Little below it. The resulting crystallization pressures, etc., heave up the overlying frozen and unfrozen layers of sand, gravel or even outcropping roclc (Plate I). Since the thermal and mechanical forces involved, which are always in a state of unstable equilibrium, primarily attack the centre of a co~nparativelysmall area, the familiar volcano-like pingo form results frorli this process (plate 11). Departures from this shape occur particularly where the ascent of the intra-permafrost and sub-permafrost waters has been restricted by some linear obstruction in the form of a basalt seam, fault, or the Like (~ig.5). The ascending water and gases are of local meteoric, not Juvenile origin and do not generally bear any causal relationship to bituminous formations. The formation of "satellites" (??late V) and the appearance of lateral water outbrealcs which initially are usually rich in mineral salts (~ig.10) is due to the fact that a "cold plug" develops In a mature pingo. The disintegration of the pingo is brought about on the one hand by external heat, which begins melting the mass of Ice at the point where the masses of gravel, rock, etc. on top of it are no longer able to protect It, and on the other hand by the same waters which led to the for~nationof the mass of ice In the first place. The crater lake, which is often formed by surface ~nelting, is later also fed by the same waters rising up through the ice mass (plate 111). Drainage of the lake exposes additional paxVtsof the body of Ice to meltlng from outside. This explains why the very strllting symmetry of the East Greenland type of plngo is often destroyed during thc disintelp-atlon period. It can be taken as typical of East Greenland pingos that new generations are repeatedly born from the ruins of earlier ones (Plate Dl). The ratc of construction and destruction of the pingos must be assumed to be very slow. The 0.5 m annual upward growth csti~natedby Shlunskli (1355, translation 1957, p. 1.23) Iiny be regarded as an outside limit.

E. Discusoion and Crit;icisni of Earlier 1lypothcscs on the Formation of East Gi7eenl.and-Tjyc Plnzoz

kffingv~ell (1919, P. 154) v~ascvidcntly thinlcin~;of East GI-cenland-type plngos when he wrote In hls physiographical monograph on the Canning River .a- region In northern Alaslca: "~on~cfield evidence point3 towai-ds a large outflow

of watcr from some of the mounds .'I Thcsc he explains as ori~inatingfrorn "hydraulic pressure". In this tcrrn Lefflnp~cllincludes both the hydrostatic pressure suggc:sted by the rclicf coridltlonn in thc vicinity and the hydraulic pressure per se resulting from thc deep penetration of the frost over a water- i~npern~eablelayer. Lefflngr.rcl1 seeks to solve the question of the origin of sub-pernlafros t waters by attributing the whole pingo-for.ming process to the beghing of thc cold era In which the permafrost was created. We believe this fact can be explained much more simply by the presence of tallk, 1.e. masses of unfrozen ground may be present underneath lakes, rivers and glaciers, through which the uater can seep below the permafrost (see also Werenskiold 1953, P. 200). Especially the areas in front of rapidly receding glaciers should yield large quantities of water for the sub-permafrost zones. Leffingwellls idea of how his hydraulic pressure takes effect is today only of historic Interest. His Interpretation "... a great outflow of water which carried up material from the underlying beds. The coarser material may have been deposited at the outlet of the spring, thus building up a mound" might be refuted by Investigations of the kind that were carried out at the Trout Lake Plngo, among others. The accepted view today, that the type of pingo found In East Greenland is a product of sub-permafrost and intra-pernlafrost water, was probably first enunciated by Russian scientists (~olstikhln1932'; and others). It has also been stated by ~Etler(1954, 1955).

V. The Pingos in the Northeast plackenzie Delta, Canada

A. Introduction

For a companion study to the investigations in East Greenland the Eskimo village of Tuktoyaktuk (6g0271N, 133°0.41W) in the northeastern part of the 14ackenzie River delta (N.W.T.) was chosen as a base of explorations. Besides affording an extraordinarily large choice of pingos at many different stages of development this region offered the additional advantage that good nieans of transport and local labour for the work of excavating and drilling were available. The Crater Smit and Sitiyolc Plngos had already been recognized from aerial photographs in the National Air Photographic Library in Ottawa as particularly we 11 suited for dctallcd study. For the vrhole of the rnonth of Play I carrlped in the crater of the Crater Summit Pingo* in lLiulc** 6 km SSW of Tuktoyalctuk (calledl"hktuk" for short).

d" * Nanc of the pingo on tllc imp entitled "~pproachesto Port ~rabant",1950. *+ Local Es!tino nalnc. After the work had been completed there except for periodic measurement checks, the camp was moved to a small pingo 43 km to the northeast of Tuktuk, where I again stayed for one month. Since this pingo was too small to have a name on the map, it was given the Eskimo designation Sitiyok (= hard), because it offered considerable resistance to our digging and drilling tools. Before good travelling weather arrived and before the ice broke up, I went by dog- sled to an ice cave which an Eskimo had erected in a plngo at Toker Point; thia also afforded an opportunity of having a brief look at some of the interesting pingos to the north of Tuktuk, Including the Toker Point Pingo, which is more than 50 m high. Spring and early summer were found to be very suitable for this kind of field work. The Tuktuk region consists chiefly of deltaic deposits. The silts, sands and gravels In many places show a well developed stratification, often with cross-bedding. There is clear evidence, at the same time, of former glaciation in the form of sharp-edged, sometimes large erratic boulders, fine, unstrati- fled material of the bottom moraine type, and on Richards Island the remains of two large, highly eroded eskers. The character of the moraine material, as well as some marine Pleistocene fossils on Herschel Island and Kay Point (0'~eill1924, p. 11A, 30A, 33~) afford proof of a transgression of the sea in the Pleistocene. From the results of investigations on Wollaston Peninsula, Washburn (1950, p. 43) has advanced the hypothesis that the transition took place simultaneously with the glaciation. The combined effect of delta formation and the transgression and regres- sion of the sea has produced a gently rolling landscape with thousands of lakes and swamps nestling between low hills. Along the coast, where the sea has created new exposures, huge ice lenses up to 15 m in thickness are seen to lie beneath the surface material of this region. The delta of the present-day Mackenzie River, which lies farther to the west, differs sharply from the landscape just described. Present-day views tend towards the theory that the Tuk Peninsula is the transformed product of a succession of old deltas of the Mackenzie River (Mackay 1956). The most striking feature of these older delta areas are the pingos. Stager (1956, p. 16) has counted 1380 pingos in the area to the east of the present-day delta and north of the Eskimo Lakes. Ten percent of them are said to have a height of more than 25 m. Almost all of them occur in shallow lakes or former lake beds. According to Stager (1956, Table I) thia is true of 985 - of the blackenzie pingos. The isopleth map of pingo distribution constructed by Stager shovrs that the largest accumulation of pingos is along the south shore of the east arm of the present-day Mackenzie River. Here there are said to be as Inany as 12 pin1;os per 10 km2. Another belt of high plngo density runs along the coast from K1tti~;azuitto Toker Point. In thls area a3 many as 8 plngos per 10 km2 were counted. My own Investigations took place in the northeast part of this belt. As for as could be determined from aircraft flights and aerial photographs, there arc no pineos in the new delta. A few examples only exist on the west side of Richards Island. These have already been observed by Porsild (1933, p. 49), Stager (1356, p. 19) and Mackay (1956, P. 11). Only detailed Investigations can determine whether these pingos in the new delta arlse under different conditions from the examples described below from the old delta further to the east. Earlier studies of pln~osin the northeast Mackenzie River delta The first mention of ping03 to the east of the mouth of the Mackenzie River was made by Richardson (1828, p. 40-44). Later, he again made reference to this phenomenon (~ichardson1851, p. 2G7,249,250). Some of these landmarks, which are visible from far off, were included in Harrlson'a map (1908, p. 196- 197). The pingos of thls region are again mentioned briefly by Anderson (1913, p. 438-439). In Porsild's fundamental study (1938) on the pingos of Alaska and northwestern Canada the large forms In the vicinity of Tuktuk are mentloned In various places. On page 54 a photograph of the Crater Sumrnit Pingo is reproduced. The first direct investigation of the Inner otructure of the plngoa in the northeast Mackenzie delta was made by Pihlianen et al. (1956).

The Crater Surnnli t Pin~o

General description The Crater Sununit Pingo pi able I) is situated at the geometric centre of a former lake which had an area of somewhat over a square kilometre. Today a stream still rrieanders throum the flat lake bed. It drains the marsh land, which surrounds the pingo and is covered by ice wedge polygons, directly into the sea. The surface of the sea is only 2 - 3 m lower than the base of the pingo. During spring floods and storrns from the west the sea breaks Into the former lake bed, leaving behlnd huge piles of driftwood at the foot of the pingo and along the low hills encircling it. The plngo itself rises abruptly from the plain. Its chnracteristically fissured summit toilers high over the surrounding landscape. The chart "~pproachesto Port ~rabant"(1950) sets the height of this pingo at 136 feet b4 (42 m). The base per1rr:cter measures about 300 m. Thc large crater In the sununit contains a small lake which measured 5 by

8 m at the end of June 1955 and was about 1 171 deep. The surface of thls lake was 11 m below the west-southwest surrunit of thc crater wall. Apparently the lalce rcnlains the entire sunmler. No evidcncc could be found that the overflow channel, which follows a structural crack, has ever been used by any considerable quantities of water, as was so often observed in Greenland. The results of seven excavations and explorations, and of a 14 rn deep drill hole in the Crater Summit Pingo have been assembled into a schematic cross-section (~ig.29). The main elements are as follows: (1) a huge body of ice in the Interior, and (2) a layer approximately 16 m thick of frozen sediments which have become fragmented in the course of pingo growth. The excavations at sites 3, 4 and 5 inside the crater exposed the clear almost black (in situ) ice of the ice lens at a depth of 40 - 60 cm. The thin surface layer consisted chiefly of unstratified sand. This is apparently material that has slid down into the crater in the course of erosion of the summit parts. At site 5 a ditch 10 m long was dug along the sharply defined surface of contact between the ice and the mineral surface material (Fig. 30). At site 4, using the sane portable ice-drilling equipment as in Greenland, a hole 14 m deep was drllled into the body of ice. Down to thi~depth no mineral inclusions were found. The vrelght per unlt volume of the ice from the drill core and the crystal dlmensiono were measured for various depths. No strlklng variations could be detected. Before freezing a set of 12 thermocouples into this drill hole a sample of ice was taken and analysed at the Enrico Fermi Institute for Nuclear Studies, University of Chicago, in the same manner as the sample6 from the East Greenland pingos, for the oxygen isotopes 18 : 16 and their ratio to dcuteriwn. The very slight difference in the ratio obtained here from that of the examples from East Greenland may be interpreted as a peculiarity of the local atmospheric water of the E'ackenzie district. The total thickness of the body of ice must be considerably greater than 14 m. From the known dimensions of the pingo (Fig. 29) it can be estimated, by folding back the overlying sediments into their original positions, that the base of the ice nzust lie 10 to 14 m below the surface of the former lake.

The sediments overly in^ the ice of the Crater Summit Pingo So as to be able to construct a stratigr.aphlc profile of the overlying sediments (pig. 31) a ditch was excavated about 1 m deep and 20 m long at site 6. The higher parts of the profile were absent from the east side because of erosion. For this reason a shaft 4 m deep was excavated at site 1 on the west side into the per~nanentlyfrozen overlying nlaterial. The overlapping of - ." sections B and C is not very great, but the error in calculating the total thickness should scarcely be more than .f: m. Section Ii of thc stratigraphic profile, which is about 9 m thick, consists entirely of washed-out sands. The principal characteristics of this sand complex are (1) the beautifully f onned s tratlfIcatlon, Including cross-bedding (~1~.32) and deltiflcation, and (2) the tilting of these originally horizontal layers by 30 - 50°. The wholly undisturbed stratification of this sand complex proves that the overlylng material was elevated as a whole and in an already frozen state. Driftwood was found In the exposures of the crater walls at two points on site 6 At a profile depth of 9 m a tree trunk of around 14 cm in diameter was frozen into the sand layers there. The age of a sample of this material waa found by Dr. Oesch~erof the C,, Laboratory of the Physics Institute, University of Berne, to be 28,000 ? 2,000 years. 3 m deeper in the proflle was the wedge of driftwood shown in Fig. 32. Section A terminates above in a layer about 1 m thick of strongly deformed strata with many cryoturbation f orms . Sections B and C, 1.e. the upper 6 rn of the profile, conaist predominantly of silt and clay*. The mean value from 5 grain-size measurement8 showed 75% by weight of all grains to have a diameter of less than 0.06 rrm. The deposits of Sections B and C are much less clearly stratified than those of Section A. Section B (but not A and C) shows several features which normally indicate glaciation: (1) Sharp-edged drift of Carbonaceous character with a mean grain size of 5 - 10 cm; (2) A few large crystalline erratic boulders, one of which had a diameter of & m and a polished and clearly grooved surface; (3) No sign of stratification in the matrix, which consists of a sandy silt with a relatively high portion of clay (35% sand, 35% silt and 30$ clay). The most surprlslng observation was, however, that these evidences of former glaciation were intermingled with organic material. In particular, several lenses and nests of wood fragments were found. The bottom 10 - 15 cm of this section consisted wholly of organic material, namely the minute remnants o'f planto. Section C, 1.e. the top 4 m of the stratigraphic profile, was characterized by a hi@ content of pure ice. At regular intervale of 50 cm we determined the molsture content. It was calculated on the basla of weight from the

* Translator's note : - The Gcrman words "Silt" and "Schluf fa' are both norn~allytranslated as "silt". Obviously, the author malces a distlnctlon here, and applies "Schluff" to a coarser grade. ratio of ice, or equivalent amount of water, to dry, mineral material, and 13 expressed in percent. The mcan moisture content of Section C is approximately 10@. Figure 33 shows the typical pattern of this icc-silt separation: the segregated ice surrounds the parts of frozen fine material, which are conglom- erated in lumps. The diameter of these lunpo of silt varies from a few rnm to several cm. Because of the great practical importance in permafrost soil of the relation between the wain size of the mineral content and the proportion of ice, or value of the moisture content, the test results relating to this have been included in the legend of Fig. 31. The characteristic volume increase of Section C due to excessive frost heave proves that sufficient water was available at the time when this material froze permanently. The striking red interlayers in the uppermost parts of Section C, which were already noted by Porsild (1938, p. 54), are the result of a very high ferric hydroxide content. The unusually blue colour of the silty material below it is due to the presence of phosphorous. h he geochemical analysis of these samples was kindly undertaken by Professor Kranck, McGill University, Montreal.) Section C shows a great many organic conclusions. About 60 cm beneath the surface vre find the first layer of small driftwood fragments. The shells of snails and other molluscs are very densely distributed at a depth of around 3 m. Porsild, who briefly investigated the surface layer conditions of a large pingo near the lower eaat arm of the Nackenzie River, found basically the same sequences (~orsild1338, p. 51). He distinguished between an upper zone of clay-silt character and a layer of sand and "boulder clay" of undetermined thicheos. A similar description of overlying material In a pingo of the ~~ollastonPeninsula, Banks Island, N. W .T., has been given by \lashburn (1950, p. 43 and Plate 13, Fig. 2). He describes an upper complex of stratified flne material with relatively few pebbles, and a lower series of "silty till". Interpretation of the stratigraphic profile The profile is much more coniplex than had been expected. The approxl- mately 15 m of sedimentary cover of the Crater Plngo is composed of three sections of quite different character. Only the material of Section C, 1.e. the top 4 rn of the profile can be definitely attributed to a slow energence and f illlng process. Section B, on the other hand, appears to be the result of a glaciation vrhich may have taken place at n time when this region lay below sea level. This could explain the unusual mixture of glacial nnterial with organic deposits. The presence of driftv~oodrenmanto at 3.5 m and 12.5 m in the stratigraphic profile is proof of a sea trann~rcoslon,because the folding back of the scdimcnts that were puohed up in the course of the pingo process would put the drif't~voodat about 10 - 13 n~ below the level of the sea. It would be difficult and premature, from these few isolated observations, to attempt any statecient conccrnin~the extent of the transgression, or even the nature of the la cia ti on of thc blaclccnzic delta. Thc sand complex lrdncdiately overlying the ice may be Interpreted as an interstadlal, and probably even an interglacial deposit, in view of the fact that the age of the tree trunk found there 13 approximately 23,000 years. On the basis of this result the cryoturbation foms at the boundary between Sections A and B are to be attributed to periglacial phenomena on an ancient land ourface. Sumn~ingup the IntcrpretatIon of the stratigraphic profile, we can say that Porsildls view (1938, p. 56)) that the layers of sediments overlying the pingo ice consist of filled material in a lake, Is only partly correct. The fact that glacial deposits and old delta material, as established by the crystal habit and age determination, have participated in thc f ormation of this sedimentary shell is important in the interpretation of the Mackenzie pingos, for this attests to a structure that no doubt bears some relationship to the filling in of the lakes, but whose root origins lie far below the former lake bottom.

C. The Sitiyolc Pintgo

Description

ThLs small pingo of classical form is situated 4 km mil2 from Wctuk, about 300 m from the shore of 1-hckenzie Bay. It rises a bare 10 m above the surface of the almost circular lake surrounding it. Its base perimeter is about 210 m. The basin in which It stands, of which about one-third the areas is now occupied by a lake, is only about an eighth the size of the basin In which the Crater Surnnit Pingo is situated. The marsh land encirclin~the lake, the floor of the shallow lake and even the pingo Itself are interconnected by a oystcm of ditches which run concentrically and in a few caseo radially in relation to the pingo. This produccs a network of almost rectangular fields. The ditches are often as much as 3 m wlde and 1.5 rn deep. It took about 500 hours of worlc to carry out the excavations represented in Fie;. 34 and 35. On the south slope of the pingo n shaft 2 m by 3 m and 2 m deep was

'.- excavated, the "south cave". From this a tunnel 4 ni long was driven in the northern direction. Thc latter connected with the "central shaft", which rras sunk from the highest point of thc pingo to its centre. This central ohaft was at Icast 3 rlr wldc at the uurfacc, but tnppcred down to GO crn at 3.5 m and wldcncd alpin only at 5.5 m when the actual pingo ice moc wao reached. At

th13 depth an "ice chan~bcr"about 3 x 2 >( 2 m wa3 excavated. In order to get further lnfo~~~nationabout the dimenoions, ohope and character of the body of ice in this pingo two holcs were driven from the floor of the ice chamber, each clevintln~~,about 3' from the perpendicular. At 4 m and 4s m rc3pcctively below thc floor of the Ice chamber, frozen sand was rcachcd. Aoouming thin to bc the sedimentary baae, the total thickneoo of thio pingo ice body, about 65 rn, vrhlch would put the baae ltoelf at about 3 m below surface of the preaent-day lake. The dcpooita below the ice body were found to be identical with thooe directly above them. In the couroc of excavations In the ice chamber a peculiarly shaped oand inclu3ion wan observed (see Fig. 35 bottom). The Medusa-like pattern wao ourrounded on all oldcs by pure ice. Thia formation, conolatlng of oand laycro about 3 cm thick, gave thc Impreanion of having been punhed up from below under prcooure, 2.4 m deeper in the body of icc the drlll cores again showed ouch oand lamcllae. Thc strati~aphicprofile of the overlying oedlments of the Sitiyok Pingo shows great olmllarity with those of the Crater Sununit Pingo. Directly above the pingo ice, oharply diffcrcntinted from it, la n complex 2 m thick of frozen oand wlth a fcw rounded pebblen in the lower part. The granulometric analyola of thio material gave the following compooition: 5% clay and silt, 92$ sand, 3$ gravel. In this part of the overlying material thc Ice occupiea scarcely more than the pore volume. The moisture content was 32% and leos. The upper complex, 4 m In thlckneos, conslnts of silt (granulometry: ?0$ clay, G4$ ~iltand 16$ sand), characterized by a high moi3tue content. The frozen scdimcnts of this oectlon are no longer preoent in the form of contlnuouo laycrs, but are brolcen up into blocks and fragments vrhlch are now only partly In contact wlth one another and are therefore often surrounded by pure ice. Owing to the fact that on the othcr hand oomc ice lenoes were completely surrounded by ocdinicnto it can be concludcd that the ice of this oection lo due not to a late lnjcction of water in conjunction with the formmationof thc plngo, but orlginatcd by direct aegrcgatiotl frorn thc water-saturated silt. Also charactc.riutic of this silt zonc 13 the very high content of organic ~naterlal. Thio con31ot3 chiefly of the nhcllo of various opecieo of anallo and othcr molluoco and thc rcnmanto of plants. This organic nlaterial occu~m - not only In a thick layer at the ourfacc, but also in dccp pockets and lenses. 'i'hc invcr;tip,atlon~of thio material still being carried on by Dr. Lubinnkl, I.Zontrca1, indicate that when thcoc plant and anlrl~alrcmaino wcrc deposited the climate of thin rcglon vrno wnrrilcr than it 1s today. Tllc ice in thl3 scctlon 13 rcmarkab1.y white, owing to the numerous parallel air tubes, which are oftcn as niuch as 10 cm long. According to Shumskll (1355, translation 1957, p. 107) this discovery suggests rapid growth of the crystals. The direction of these air tubes bisects the angle between the plumb and the perpendicular to the external shell of the plngo. This unusual angle, as well as the habit and size of the air bubbles, may give us a hint as to the niodus and the rate of formation of the plngo. A diagonal cleavage, which runo across the highest point of the Sltlyok Pingo contains a large ice rqedge, the surface of which is covered with 60 cm of humus. The central shaft (~ig.34 and 35) is alrnost completely contained within this rrcdge. The maximum widZh of the wedge is 3 m. The point of the wedge penetrates at least 1.2 m into the pingo ice. The ice of the wedge is clearly distinguished on the one hand from the pingo ice, and on the other from the Ice that has segregated from the sediments of the 6outh cave. It presents a milky white appearance both from the top and from the side and consists of very s&ll crystals (cf. Table I1 and Fig. 37). "~ubbings"from the top part of ice wedge show that G4$ of the crystals there have a mean diameter of 0.25 cm and less; in the lower part of the wedge the proportion of these small crystals goeo as high as 94%. Rows of slightly soiled strips running sub-parallel to the walls of the wedge give the cross-section of the wedge a fan-like structure (Fig. 35), as already described by Black (1954, p. 844) in ice wedges in Alaska. These cracks sonetimes contain well-preserved plant remains, in particular leaves conforming to the present-day vegetation cover of the pingo. Interpretation of the cross-section through the Sitiyok Pingo The lower parts of the sediments of the Sitiyok Pingo overlying the true plngo ice show close agreement with Section A of the stratigraphic profile of the Crater Swmlt Pingo. However, the glacial deposits are completely absent from the Sitiyok Plngo. The top 4 m of the profile can be interpreted as marine deposits. The thick ice wedge running transversely across the Sltiyok Pingo has no causal connection with the pingo formation.

D. The Ice Cellar at Toker Polnt

In the vlclnity of Toker Point, about 24 kn~to the north of Tuktulc, an Eskimo hunter had excavated an ice cellar into a pingo-like hill. In the ..- approach to the celler layers of ice and sand 5 - 20 cm thick alternate regularly. Tile oand ha:, an admixture of 155 clay and silt and 5% gravel. Thme layero dip to the wcst at an angle of 43 - 50°. In thc Interior of the hill thrc2e chambers were excavated. These are situated in pure ice. The crystal size of this ice is clearly smaller than in the hithc~toinveotigated ice bodies of pingos. The mean diameter of 94 crystals war anly 1.3 cm. In the boundary zone between the sand-ice layers and the pure ice there Is a series of highly deformed and crimped layers of sand (Fig. 36a and b). This striklng pheno~nenon is evidently due to a relative movement between the body of ice and its overlying material. The 20 - 50 cm thick zone of highly fragmented white ice at the outside edge of the ice body must also be the result of such relative movements. Since we were unable to establish a definite direction of shear in this system of wrinkles, it is difficult to find a clear explanation of this phenomenon. Perhaps the primary folding during the formation of the body of ice was followed by subsequent expansions and contractions in the boundary zone. Such alternating movements in the boundary zone, traceable to annual temperature fluctuations, were actually observed in the Crater Summit Pingo. A contraction fissure of this type is shown In Fig. 30. It is at least 2 m deep and was about 3 cm wide on May 20. On July 1st it was still half open.

E. Summary and Discussion of Some Properties of the Pin~oIce Body

1. Crystal dimensions and density dcterrninations Even under the spring weather conditions of the kclcenzie delta the "rubbing method" of Sellpan (1949, p. 256) proved satisfactory for determining the crystal size. Around 5000 ice crystal areas were determined by comparison with standard circles of logarithmically decreasing diameters. Other types of permafrost ice in addition to pingo ice were Investigated, e.g. the ice of a wedge from an exposure on the sea coast. In Table 11 a few typical results from the Elackenzie delta are presented and compared with a selection of test results from East Greenland. In order to be able to compare the percentage distribution of the crystals to a number of standard sizes for various kinds of ground ice, the granulometric curves for a few types of ice of the Mackenzie delta were plotted (Fig. 37 1. The mean crystal diameter for pingo ice in thc Ebckenzle delta varies between 1.5 cm and 2.7 cm. The values obtaincd from measurements of ice crystals from East Greenland ping03 lie within these limits. The diameter of all previously measured pingo ice crystals is on the averaze a little greater than the mean value obtained by Nllma~and Drocssler (1949, p. 2-11 and 272) for the alrnost stagnating ice rim of the Stor Glacier in S~.~cdIshLapland (I .'7 cni). On the: othcr hand, the niearl diamcter of the plngo Ice crystal appears to be soniewhat smaller than that of the colnpletely stagnating icc In a cave at the ed~eof the Isfalls Glacier. Comparison with the results of mcasuremcnt at the edge of the Inland ice in West Greenland (~oydand Callleu 1954) shows that from the cryotallographlc point of vlew there is a great similarity between pingo ice and nlovily moving polar ice. In order to be able to interpret the small crystalline ice that went Into the structure of the central wedge in the Sitiyok Plngo "rubbings" wcre taken from other types of ice. The ice of a wedge that had been exposed by erosion by the sea showed by far the closest similarity (cf. Fig. 37), so that the wedge character of the thick wedge of white ice In the Sltlyok Plngo can be regarded as proved. Wedge ice differs very distinctly from pingo ice. This difference is further emphasized by a comparison of the corresponding densities a able 11). The largest crystals in the pingo ice investigated by us had areas of 79.5 cm2 and 71.5 cma ('Table 11). Seligrnan (1947, p. 260) found crystals of similar dimensions in dead alpine Ice. Ahlmann and Droesoler (1949, p. 274) mention that in the dead ice investigated by them in northern Sweden they observed actual bands of tiny Ice grains ( < 1 mil2) alongside numerous large crystals, Pingo ice shows no such accumulation of snlall crystals. It Is noteworthy that the extreme sizes arc rather rare, hence the steepness of the granulometrlc curves of pingo ice. Pingo ice also shows certain peculiarities with respect to the crystal .form. The compact, rounded, only 8liL;htly jagged forms clearly predominate (Fig. 38). The difference from active "~nterlockin~"glacier ice is very striking. Sharp-edged forms are still rarer in plngo ice than ln the dead Ice described by Ahlnann and Droessler (1949, p. 2-13) and by Seligman (1349, p. 261). Air bubbles wcre found In almost all san~plesof pingo ice. It is very frequently observed that the air bubbles wlthln an lndlvldual crystal run parallel; frorn one crystal to another, however, they show diotinctly different directions (FIG. 33). This same observation vras made by Ahlmann curd Drocn~ler (1943, p. 274) In a sa~npleof dead Ice from the Kcbnepakte Glacier. At the present stage of developnient of glaciolo~,unfortunately, all that can be stated is that the form and orientation of the air bubbles in ice cryotals are probably dctermincd (1) by the anlsotroplc character of these crystals, and (2) by the polarity of the principle crystallographic main ax13 (~ader1950, p. 443). It would be premature, hov~cver, to attempt to draw any basic conclusions concerning the generating ~ncchanisl[~of the pingo ice body from the above observation. Even the evidence collectcd by Shu~~lskii(1955, translation 1357, p. 52-55, 99-101, 107) on air bubbles on ice cannot adequately explain thi3 phenonienon . 2. Temperature conditions In the Sitiyok Pingo the follovring tcmperaturcs were measured on June 30, 1959, with the aid of thermocouples: In the frozen overlying layer: 1.6m (5 ft.) below the surface 2.0°C 3.2 m (10 ft.) below the surface 2.5OC 4.7 m (15 ft.) below the surface 5.0°C In the pingo Ice body: 6.2 m (20 ft.) below the surface 6.5OC 9.2 m (30 ft.) below the surface 7.0°C 11.0 m (35 ft.) below the surface 8.z°C By June 30, 1955, the thawing process In the highly organic material in the Sitiyok Pingo had reached a depth of only 20 - 30 cm. In the drill hole of the Crater Summit Pingo 12 thermocouples were placed at regular Intervals down to a depth of 12 m below the surface of the pingo ice body. From May 28 to July 1, 1955, two measurements were carried out weekly. Three of these series of measurements, one from the beginning, a second from the middle and a third from the end of the measuring period, are plotted in Fig. 39. In the top 6 m a considerable increase of temperature was noted in the course of the observation period. The temperature variations observed in the lower 6 rn were only slightly greater than the instrumental error. For the

potentiometer employed this was ~&OC. Accordingly, the wave front of penetra- , ting spring warmth had reached a depth of approximately 6 m (17 - 20 ft.) by the end of June. The climatological reports of the Tuktoyaktuk Weather Station indicate that the change from falllng to rising tenlperatures in the atmosphere of this region takes place at the end of February or the begi~ingof March a able 111). The snow and the sand cover in the crater delay the penetratlon of this change of temperature trend at the surface of the ice body by at least one to tyro months. On this assumption it can be estimated that a period of two to three months io required for this effect to penetrate through a 6 m layer of pingo ice. A cornparison with other empirical results on the extent to which deep temperatures lag behind surface temperatures, obtained from the permafrost of Point Barrow, Alaska (14ac~arthy1952, p. 590), and in the permanently frozen limeatone deposit in Resolute Bay, N.W.T. (cook 1955, p. 241) shows that this phase disp1acen;ent 13 snlallcr in pingo icc than in perniafrost of mixed compo~itlon. Thcorctical colculatlons based on the work of Ruckll (1950, p. 121-123) conf ism that this lag of the form

which is linear with rcspect to the depth X (where a = coefficient of temperature conduction* and T = period of the observed temperature oscillations), must be smaller in Ice than in mlneral material. Field observatlonc and theory are thus in good agreement.

VI. Morphofienesis of thc blackenzie Pin~os

A. The Hlstorlcal Cycle of the Mackcnzle Plngos - The Closed System

In discussing the origin of the East Greenland pingos, primary importance was assigned to the sub-permafrost waters which circulate in an open system and ascend under hydrostatic pressure. For an understanding of the Mackenzie pingos, their intimate relationship with the circular lakes which at one time or another surround almost every pingo, possess this baslc importance. Unfortunately there are still no studies relating the plngo height or volume statistically to a former or the present-day lake area. The correlation coefficient of these two values could be used as a standard against which to assess the value of the following theory of origin. To date no conclusive measurements of the thickness of permafrost in the Mackenzie delta are available. We are only able to compare the climatic conditions of Tuktulc with those of stations at vrhich the thickness of the permafrost zone is h~,~vrn.Ustt-Port (between 6g0 and '70"~)in the Yenisei delta region of Siberia, has a mean annual air temperature of -10.8OC (January mean = -30.6OC; August mean = +14OC) and a permafrost thiclmess of 140 m and 125 m, respectively (~yabukhin1939+). Nesters Vie, with a mean annual temperature of barely -lo°C, has about 100 m permafrost. For Tuktuk, where the mean annual temperature is -10.'7°C and the mean annual total precipitation is much less than that of FIestcrs Vig, we lnight in first approxlmatlon reckon with a pernafrost thiclmcss of certainly more than 100 m. For the new delta of the Maclccnzie River, Brown (1956, p. 23) malces the follolring e3timate:

"Permafrost. . .I3 believed to extend dovm many hundreds of feet. "

heat conductivity . --. * Temperature conduction a = ,,eat "ice = 58.4 cm2/h; a_,and - 22 cn12/h (Ruckll 1350, p. 13k, Tablc UIX, after Dcslcovl). For our iy,rpot;hcc;is of tkic ri~eclianiurr~of pinto origin in thc Macltcnzie region we a33~1ii~that ti?^ ground watcr horizon (dead rock or other water- ln~pcr~neablclayer) lics no deeper than the lower boundary of the permafrost. With reference to the pcrmafrost conditions at zone of transition from land to watel7 we follow Werensklold (1953, p. 197-200). He attempted to answer the qucstion of what the rninin~umdiameter of a fjord must be so that the permafrost will not close below the body of water, by mathematical evaluation of the superposition of two temperature fields TI and T,. These are of the following form:

(1) T, = y-. arc tan 5, where To = temperature at the surface of the land x = horizontal dlstance from the shore y = depth below the surface; (2) Tn = 9Y, wherc q is the reciprocal of the geothermal gradient. (1) gives the gradual change of temperature from the land surface to the water surface ; (2) gives the linear change of temperature with depth. Putting, for Tulctuk, To = -ll°C and q = %O m to 1/30 doc* we find that the permafrost will close beneath an elongated lake of at least 140 m wide, but certainly not below one 420 m width. The lakes in the region of Tuktuk are mostly circular in shape. The diameter for a circular shape must be greater than would follow from the calculation for the fjord form. In rough approximation It may be reckoned that the permafrost begins to close under the lakes of the Mackenzie delta as soon as their diameter is less than 300 to 400 m. The surface of separation between the frozen and unfrozen ground which Interests us here, constitutes a special case among isothermal surfaces. As long as the size of the lake remains above the critical value of 300 - 400 m, the surface of separation between the permafrost and the unfrozen ground advances from all directions towards the centre of the lake until it reaches a certain line, where It then drops and recedes (Pig. 40, stage 1). In the centre of the lake botto111there 13 a hole through which the lake has direct contact with the unfrozen subsoil (tallk). In the course of a continuous filling process such as occur3 in the lakes in the Tulctuk region from the settlement of organic material and the drifting in of sands, clays, etc., this

* \!erenskioldls valuc (1353, p. 197) for the temperature gradient in the frozen soil of Spitsbcrgcn = */a rn/O~ is ccrtainly too omall for the region of Tuktuk, erhcrc rrc havc frozen ~l;ravcls,sands, clays and peat. ilol c col1t;rac L3 COI~~;~IIUOIIL:~~(llid firlal.1 y dlsapycarr, altogc t.her. Idow we havc a body of highly saturated rnatcrial trapped, so to spcalc, bcterccn the impern~cable ur~dcl-layers(probably dead roclc) and tlw slowly advancing pennafros t (Fie;. 40, stage 2). This is tlx raw lnatcrlal for the production of the l~hckenziedelta- tjpc pingo. It is clcar that In t;hIs initial nituatlon rhrc have a closed system. In this respect the Idaclcenzie pingos differ essentially from the East Greenland type. On the other hand, it has been found that the Maclcenzle pingos once Inore lnvolvc a completely Internal pc17rnarrost phenorncnon . As the permafrost continues to advance the volwnetric expansion aosociated with the freezing process produce3 a continuously increasing hydrostatic pressure In the closed talilc space. follow in^; the path of least resistance, the reaction talces place in the centre and upwnrda. The excess water present creates for itself a narrow ascent channel (pig. 40, stage 3). The centre of attack of the forces appears to be still more restricted in area than in the Bast Greenland pingos. Probably the bcll-shaped sand structureo found in the body of ice of the Sitiyok Pingo (see Fig. 35) can be regarded as evidence of the effect of the forces In the production of the Mackenzie pingos. In the rileantime the lake above has become shallow right to the centre and the lake bottom consints of permafroat except for a slr~allactive layer. The injection of hydrolaccoliths will occur at the depth where the forces from below are able to push up the hard-frozen surface sediniento. In principle these are the same forces operating in the formation of the East Greenland pingos. The assumption that the ice bodies of the blackenzie pingos are also formed through a hydrolaccolithic intermediate stage appcars justified, particularly from the findin~sin the interior of the Sitiyok Pingo. The ice veins driven deep Into the organic and mineral pernafrost material, as well as thc large blocks of frozen sand and silt enclosed in the Ice body,can scarcely be explained in any other way. The size of the Ikckenzle pingo depends on the amount of water available in the closed off unfrozen part of the former lake bottom. The rate of pingo growth is a function of the rate at which the yel.mafrost penetrates this still unfrozen space. The growth of the pingo ceases when the talilc space beneath the former lalrc has bee11 rcduccd to zero (FIE. 110, stagc 14 ) . The Crater Summit Pingo appears to have finished growing, whereas the Sitiyok Pingo clay still be in the proccso of construction. Tributary pingos are rarer in the r.lackcnzic area than In East Greenland. Their origin appears not to stand in the sa111edirect causal relationship with the construction of the ~nalnpingo a3 was the case in East Greenland. In the 1.laclcenzle region tributary pingoo more lilccly result from the permanent frcezln~of 3cparatc Lays In lalces of co~~~plexshape. Not a sin~lc~~:31:iplc v~a3 found vlhcre several large ylngos had arlsen in a single circular lalcc. The nestinf, one insidc the othcr of oeveral pingos, as was so frequently observed In East Greenland, was not found at all in the ~~ckenciedelta. These two observations support our vlcw that the l*lackenzie pingoa develop out of a closed system and are due to a non-repetitive procese. Accordin~ly,the disintegration of the llacltenzie pingos differs from what occurs in East Greenland. It Is due exclu3lvely to the process of melting from outside and therefore leads to more rcp;ular remnants than in the East Greenland type. This fact is of importance for periglaclal morpholow, which is exploring the Pleistocene periglacial regions for remnants of former pingos. In this connection we nust mention the work of PIaarleveld and van den Toorn (1955) in ~ihichthe many kettle-like forlnations in the northern parts of the Netherlands are tentatively interpreted as disintegrated pingos. Similar relief anomalies in thc Belgian Ardennes (~issart195G), in the viclnity of Paris (~ailleux1956), near Bordeaux (Boy6 1957), in Denmark (~ailleux1957) and in Schleswlg-Xolsteln (B. ~6ller-~attle,oral cornniunication) can also be explained In terms of plngos. Apparently they are due predominently to remnants of Mackenzie-type pingos .

B. Diocussion and Review of Earlier Explanations of the Fhclcenzie Pingos

The theories held up to 1919 were summarized and discussed by Lcffingyell (1919, p. 152-155). For the most part they are now only of historical lnter- est. Richardson (1828, p. 40-41) originally thought the bhckenzie pingos were sand dunes. Later (~lchardson1851, p. 247) hc explained them as remnants of sand formations which had withstood the erosion of the sea in flood. Lcffln~;~ell(1919, p. 154) rejected all these views and explained plngos as resulting from hydraulic pressure. The importance of this hypothesis for the pingos of the East Greenland type has already been discu~sedon page 45. It has also contributed basically, however, to an understanding of the ISckenzle pingos, bccauae Lcffinp~ell~sdescription of the advance of the permafrost ovcr a v:aAier impernmeable layer forcshadowcd Porcild ' s "theory of local uphcaval". Porsild's formulation of this theory for the 14ackenzie pingos (1938, p. 55) rcfi1a1r.s valid even in the li~htof our detailed investigations. It runs a3 follot-1s: "The Kiickenzic pin~os. . . were formed by local upheaval due to expansion following the progrcs3ivc do1:nvrard freezing of a body or lens of water or -.a. -.a. semlfluld n~ud or silt enclosed bctwecn bedroclc and the frozen surface soil". It!ash'ourn (1950, p. 30) clasaif ico the f oi1ce3 undcrlylng hi3 "cryostatic hypothesis" as follows: "(1)The stress due to growth of ice crystals, and (2) the stress due to the Increasing hydrostatic pressure of the confined and still unfrozen ruddy material as dovrnward freezing from the surface ncars the perrnafros t table. " As noon as wc translate the expression "permafrost table" logically a3 "water obstruction", we sec that thi3 hypothesis, which can explain co many polygonal soil phenomena, also embraces the for~mationmechanism of the Mackenzie pin~os(cf. Washburn 1956, p. 842-843). It appears that Russian scientists, independently and even earller, have arrived at an Interpretation of this type of pingo v~hichis equivalent In principle. This 1s evldent e.g. from the work of Evladov (1937+) : e eaves (plngos) develop as the excess water In and around taliks freezes". (SIPRE summary 5439 ) .

The extensive excavations and drillings in the Crater Summit Pingo and Sitiyok Pingo, as well as the investigationo of the ice cave at Toker Point, have shown that the construction of the Mackenzie pingos is practically identical with that of the East Greenland plngos. The overlying sediment covers, the thicknesses of which are 14 m and 6 m, respectively, consist in their upper part of fine marine drift material; the lower layers are formed from Pleistocene residues and very old, probably interstadial, delta deposits (age of wood remnants in the Interior of the Crater Summit Pingo: 28,000 f 2000 years). The crystallometric inveotigations of the ice body gave results very similar to those obtained in East Greenland. The pressure which leads to the upthrust of a 14ackenzle pingo Is due to the slow contraction of the talik space in the subsoil beneath the former lake. After the lake has shrunk to a critical diameter of approximately 600 m a closed system develops made up of the water-inlpermeable subooil (bedrock or layer of clay, etc.) and the fronts of the permafrost accretion process. The reaction to this continuously Increasing hydraulic pressure takes the form of eruption of the confined water in the direction of least resistance, 1.e. upwards. When the water enters the zone of annually fluctuating temperatures, the permafrost of which shows exceptionally high resistance to bending, a true hydrolaccolith forms. From this, apparently at the same place, an ice laccolith immediately develops owing to the severe coollng. The disintegration of the Mackenzle pingos la due to exogenous proceoses, primarily melting off. The above-described mechanism of construction should explain the following observations: (1) the occupation by the Mackenzie ping08 of lake basins which are almost or completely filled; (2) the absence of grouping of the kind encountered In East Greenland; (3) the absence of reactivation of disintegrated pingos . The C,, dating of the wood remnants from the crater of the Crater Summit Pingo leaves a good deal of leeway for the age of this pingo.

VII. The Distribution of Pingos in the Light of the Investi~atione of the East Greenland and Mackenzie Pingos

A. Introduction and Termlnolo9;y

A world-wide survey of the distribution of pingos confronts almost insuperable difficulties. This chapter can therefore lay no claim to completeness. A good portion of the literature dealing with pingos is difficult or impossible to obtain. This refers particularly to the many Russian reports. Translations, abstracts and summaries can be used only with great caution. SlPRE Report 12, an otherwise excellent aid, gives the name pingo everywhere, e.g. in Summary 13461, to the 15 - 40 cm high frost hillocks in the Carpathians, called "palsen" by the author. Another difficulty arises from the fact that many of the descriptions of plngos and pingo-like formations, which are mentioned in travelogues, geological and botanical works, etc., for the most part only In passing, are not sufficiently concerned, of course, with the details. Unfortunately, instead of simple descriptions, inadequately defined terms are all too often employed. The purpose of this chapter is to compare our own observations on ping08 in East Greenland and in the Mackenzie delta with other occurrences, thereby placing them within a global framework. At the same time it is hoped to provide a basis for a fiture classification of the various frost mound fom. In Siberian Russia they use the expression bulgunniakh (plural: bult.gunniakh1) instead of plngo. This comes from the region of Yakutia, where it is applied to formations which have a definite plngo character (~osmachev 1953, p. 111-112). This name is genetically neutral, but not the often employed expression "gidrolakkolitl', English - hydrolaccolith, which is used especially by Russian scientists (~olstikhin1932+, Andreev 1936+, Boch 1948+, Grave 1956), but also by German and French authors (~toltenber~1935, ~Gtler *",. 1954 and 1955, Plalsance and Cailleux, at the printers). The term pingo is preferable. 1 ( nilnal cd ) orlp;lnritc?, nccol>dlnl: to Surngln (19!+1f ), frorll the freeziny, of oucccssivc layers of water that elncrge clther directly from the soil or fro1.1 craclcs in the ice cover of winter rivers. Troll (131~4, p. 646) states that in thc Yalcut language naledy are termed taryn. According, to Muller (191L'{, p. 223) the narne taryn can be given only to naledy which do not melt during the year of thelr origin. The corresponding German expression for naledy is "~ufeis"(~n~llsh: "top ice"). Since there appears to be a close connection between East Greenland ping06 and certain Icinds of naledy we shall cite a few literature references to typical naledy. Tolstlkhln and Obldin (1936+) explain the eastern Tmnsbaikal naledy as a product of "underground sources". The naledy rnentioncd by Sedov and Shvetsov (1940a+) in Northern Yakutia are believed to get their water from craclcs in outcropping rocks. The total output of thesc springs which feed the naledy in the region of the lower Kyra River (in the viclnity of the Yana- Indiglrka water-shed) is said to be 3000 litres per second. According to the reports these waters still run at -70°C outside temperature and produce huge naledy. The same authors (Sedov and Shvetsov, 1940b+, 1940~+ , and Shvetsov 1947a+ ) report naledy which are several kilometres long and several kilometres wide. Shvetsov and Sedov (1342+ ) suggest a classification of nalcdy based on investigations in the Tas-Khayakhtakh range (near the world's coldest point) one of the naled springs there is said to have an output of 1500 litres per second. Shvetsov (1346) photographed a naled which covered an area of approximately 26 km2 and was estimated to contain 39,000,000 n13 ice. The continuous melting of these enormous ice masses throughout the whole surruner largely deterrilines the water economy of thesc regions. In his next report Shvetsov (1947a+ ) reports naledy from the region of Verkhoyanslc and the Kolyila Mountains of much larger dimensions still. Suslov (1947, p. 151-153) uses the expression earth-naledy, by which he describes formations vrhich we would regard as pingos. A clcar description of the naledy and their ice are found in Shunskii ( 1355, translation 1357, p . 108- 103). Although there is often scarcely any difference genetically between naledy and bulgu.nniakh1 (pingos) (strong sub-permafrost springs produce naledy; weak sub- and intra-permafrost springs produce pingos ), nevertheless these morphologically very different foi-mations have to be clearly distinguished in name . It is 111uc11more dif f lcult to oepai-ate pingos terr:iinolo~icallyfrom all those types of frost ~:~ounclawhich are of oiniilar nlol-phological appearance but have quite dif f erent f orn~ationmechanis~no . Thls applies , for example, to peat .- hills of the kind described by Kats (1937+) in the Kola Pen1noul.a and the Pechora region. Thc same holds for some of the palsen of Scandanavia am berg 1915, p. 616-619; Lundqvist 1951, 1953; and others). It also appears that certain of thc dome-shaped upthrusts of the Siberian forest soil, known as "drunlcen forest" possess a true pingo character. Troll (1944, p. 647) mentima that V.N. Sulcachev was able to put the age of such a "drunken forest" mound at between 100 and 162 years by countlag the annual rings of the bent larch trunks. Despite the lack of clarity remaining in the terrninoloe;y, we shall nevertheless attempt in Section B, on the world-wide distribution of pingos, to compare the types described In the present report on East Greenland and Mackenzie types with slmllar forms In other permafrost reglons.

B. Outline of the Distribution of Pingos

1. Greenland On the east side of Greenland the pingos appeared to be confined to a strip between Scoresby Sund and Hochstetters Forland. The most favourable region for them appears to lie between 71° and 7h0N. They occur mostly in the sediments and alluvia of the zones near the coast. Thus far only a single example 13 known to exist in the vicinity of the inland ice, namely the remnants of a pingo in Aggassiz Dal, describcd by Flint (1948, p. 203-206). In West Greenland the Pingo formations appear to reach a climax in the region of Svartenhuk and Nugssuaq Peninsula and on Disko Island, 1.e. about at 70 - 7Z0N (~osenkrantz1950, p. 112). It can be presumed from earlier descriptions that these are predominantly plngos of the East Greenland type. The pingo-like formations on Disko Island described by Porsild (1925), which are associated with warm springs, also appear to be similar to the East Greenland pingos . 2. Canadian Arctic Ward (1952b, p. 16-21) reports dome-shaped upthrusts in the south-east approaches to the Barnes ice cap, Baffin Island. These he interpreted as "forms (which) arose from differential melting of dead glacier ice underlying older ablation rr,oraines" (p. 17). The description and photographs, however, permit their lnterprctation as true plngos. Fronr the personal reports of Dr. H. ~(;thlisber~er,who took part In the Baffin Island Expedition of 1953, It appears that in the region of Pangnirtung Pass upthrusts are taking place slmllar to those described by Porsild (1925) for Vest Greenland and Lefflne;r.~ell(1913, p. 158) for Alaslca. Boas (1885, p. 18) described from the region of that Pass "a 30 m high niound of ice thiclcly covercd with herb and atones, so that I was only accidentally enlightened ao to its nature". He Interpreted it as "an unusual piece of evidence of rather severe glaciation a short time ago". Possibly, however, it was a pingo. In the chapter on the ping08 of the Mackenzie delta it was mentioned that , about 1400 examples were counted in the region of the old delta alone. From an aircraft the writer was able to determine that on the continent to the south and eant of the Eokimo Lakes where the land 13 bestrewn with basal moraines, there were an additional 200 to 300 pingos, some of them quite large. At the same time it was established that Porsildls note (1938, p. 49) to the effect that "there are said to be some pingos on the coastal flats east of - Cape Bathurst" does correspond to the facts. Indeed what is probably one of the earliest photographs of a pingo (~tefansson1913, p. 574) stem from this region (in the vicinity of Cape parry). Washburn (1950, p. 41,43) mentions several occurrences similar to the Mackenzie pingos on Wollaston Peninsula, Victoria Island (70'~). Porsild (1945, p. 10-11) also reports small pingos, similar to those in the Mackenzie delta, at Macmillan Pass in the Mackenzie Mountains (just east of the Yukon-N.W.T. boundary, 63'~). The three pingo- like formations described by Fraser (1956, p. 20-23) on the slopes of Black .I Mountain (~ichardsonMountains, Mackenzie delta region) appear to be true plngos of the East Greenland type. Strangely enough, to the best of my knowledge no other pingos are known in the broad expanses of the eastern Canadian Arctic or on the many Islands of the Arctic archipelago. 3. Alaska In Alaska there are many pingos of many different kinds. In his exhaustive work on the Canning River region Leffingwell (1919, p. 150-155) devotes an excellent study to the "Pleistocene and recent gravel mounds". He reports that he counted 30 pingos from a triangulation point in the vlcinity of the Shaviovilc River within an arc of 140°. The highest pingo visited by him rose 70 m above its imnlediate surroundings. Many of these plngos were used as surveying points and are Included on the map contained In Lefflngwell's report. Some of the pingos explained by Leffingwell in terms of "hydraulic pressure" are certainly of the East Greenland type. Among earlier references to pingos In North Alaska we may cite: Mendenhall (1901, p. 207)~Schrader (1904, p. 94), Tyrrell (1904, p. 232-236), Harrison (1908, p. 196-197), Anderson (1313, p. 438-439) and Smith (1913, p. 28). Smith describes the ping03 of the Noatak-Kobuk Region as follows: .". " ... here and there rounded hills one-half mile in diameter at the base rise 100 to 300 feet above the general surface of this plain ... suggest, when viewed from a distance, giant haystacks. It - Porsild (1333, p. li7?48,58) acquaints us with a whole series of additional pingo regions in Alaska. In addition to the many occurrences in the northern coastal plains, he mentions nunlerous pingos on the north slope of Scward Peninsula and in the region of Kotzebue Sound (west Alaska, just north of the Arctic Circle). Apparently most of these exanlples are to be classified as East Greenland types. The rapid advances of recent years in the techniques of aerial photography and its Interpretation has brought new Insights into certain aspects of the pingo problem. In addition to valuable information on the distribution of ping6S it has been possible above all to make interesting contributions on the relations between pingos and permafrost, ground water and other morpho1oe;ical elements (sager 1951; Frost 1952; Hopkins, Karlstrom et al. 1955). The follow- Ing summary of the distribution of pingos in Alaska by Frost (1952, p. 236) is largely the result of aerial photographic evaluation: I1 ... they occur in an area extending from the Canadian border generally west- ward to \4ainwright; in the narrow coastal plain region between Pt. Hope and the Sevlard Peninsula; the coastal plain which forms a fringe around the maJor part of the Seward Peninsula; to a limited extent in the delta region of the lower Kuskokwim-Yukon valleys; and in the interior of the Seward Peninsula A. which is in the Kuzltrin-Noxapaga Basin. A few scattered mounds occur in isolated areas In the interior, principally in some of the major stream

valleys. " In addition, aerial photography enabled Frost (1952, p. 239) to describe the following regional features of the pingos of the north coast of Alaska: "... for the most part, the mounds in the areas east of the Colville appear to be older, larger and more irregularly shaped than the mounds west of the Colville, which appear to be young, newly formed, regular in shape, associated with recently drained lakes, and are little altered by eros1on.l1 We also find in Alaska pingo-like formations dlrectly associated with springs (~opkins,Karlstrom et al. 1955, p. 139). Two additional "mud volcanoes1' with springs were mentioned by Frost (1952, p. 237); it is not certain whether these formations, which are considerably to the south (62' and 65ON, respectively), are true pingos . Sharp (1942) describes "ground-ice mounds" of relatively small dimensions

from the tundra of the Wolf Creek region northwest of St. Elias Range (G~ON, 140" W ) . He interprets them as follows : ".. . They are forliled throu* undonling of thc tundra surface caused by the vertical and latel-a1 growth of bodies of ice in the thawed layer above perennially frozen .gr<>und." (sharp 1342, p. 421). Ccr.tainly these "&round-ice mounds" of Sharp arc! neither East G~~cenland- type or Mackenzle-type pingos. It io possible, however, that where these ground-ice mounds are sufficiently large another type of pingo may be formed by secondary ascending and in-growing of the permafrost surface into the interior of the frost mounds. The "perennial ice mounds" described by Sumgin (1940+) appear to be of slinilar origin. 4. Eurasia

We shall review the Eurasian permafrost region from east to west. Grave (1956) reports bulgunniakhi from the region of the Anadyr Plateau (latitude of the Arctlc Circle and approximately 173'E). On one of the largest of these (15 - 20 m high) the remains of a prehistoric hunting, camp were discovered. Age determination of this find by Okladnikov (in Grave 1956, translation by Hope, p. 2) showed an age of at least 200 years for this pingo. Considerably younger pingos, still in the process of growth, are said to be present in this district : "since the process of peating and drying up of the lakes on this terrace is continuing even at the present time accompanied by penetration of the permafrost into the bottom deposits." (Grave 1956, translation Hope p. 2-3). It is apparent that these Anadyr bulgunnlakhi are very similar to the Mackenzie pingos wlth respect both to their surroundings and the mechanlsrn of their formation. No data are available on the thickness of the permafrost in this area. It probably does not vary greatly from that in the lower Anadyr Valley, given by Kachurln (1938, p. 60) and Shvetsov (1947bf) as 100 rn and 60 - 150 HI, respectively. The permafrost reaches its greatest depth in northern Yakutia and in the basin of the Khatanga River, where Toln tlkhln (1947+) gives permafrost depths up to 600 m. Some of the "ground naledy" mentioned by Shvetsov (1947a+ ) from the region of the Verkhoyan and Kilyma Mountains can probably be regarded as bulgunnlnkhi of the East Greenland pingo type. On the other hand, the large bulgunnlakhl mentioned by Suslov (1947, p. 153) in the delta of the Indigirka appear to be of the Mackenzle plngo type. For central Yakutla, Eflnlov (194~+) cites permafrost thicknesses up to 200 m. Kosnlachev (1953) reports that the very classlcal bulgunnlakhi of Yakutla, of which he presents excellent photographs and which are said to be 20 - 30 m high, were already mentioned k~old legends, so that they must have an age of at least several centuries. He explains the origin of these extraordlnarlly regular bulgunniakhi by the freezing of ground waters which have risen into the uppermost soil strata (~osmachev1953, p. 112), indicating a genetic relationship wlth pingos of the East Greenland type. However, pingos of the Mackenzie type also seem to occur in thls dlstrlct. A drawlnc by Angcr (1337, Fig. 191) shows a lake in the taiga between Yakutslc and Okhotsk, in the centre of which there is a circular "surface ice ~nound", which we must include among the Ihckenzie-type plngoe. Further south, in the Transbalkal region, where the mean annual air temperature 1s only slightly below oOC (Sumgin 1932+), the permafrost 13 no longer contlnuous. According tb Tolstikhin (1947+) It nevertheless reaches a mean value of 100 m in the upper Lena basin. In addition to the one-year mounds (1 - 2 m high and 5 - 30 in diameter) the Transbalkal region also has permanent, considerably largcr ones (up to 10 m high and 80 m In diameter). These are found both on the floors of wide valleys and on mountain ridges. It is mentioned that crater-shaped depresslons often forin In the place of peaks. In the latter there Is often a morass, sornetlmes a small lake. Not infre- quently a ground-water-fed brook flows out through a gap in the crater, generally towards the south. "Jurassic argillaceous ochist and sandstone are Involved in the construction of some hydrolaccoliths of the Indoga region" (~olstikhln1932+, p. 65). The bulgunnlakhi of Transbalkal show an extraordinary resemblance to the pingos of East Greenland. The permafrost of the Tunguska basin Is up to 500 n thick in Its northern part. In the south, on the other hand, there are many gaps in it (~olstlkhln 1947+). The pingos of thls region described by Kushcv (1934+), the helghts of which vary between 1 in and 12 m, lie In the zone of transltlon from contlnuous to discontinuous permafrost (between 64' and &ON). In the region of the mouth of the Yenisl, where the thickness of permafrost is around 140 nl, Ryabukhln (1939+) found bulgunnlakhi In the vicinity of the mouth of the Malaya Kheta River reaching heights of 22 m and diameters of 50 m. In the northern part of the West Siberian Plain the permafrost reaches thicknesses of 400 m (~olstlkhln19117+) but disappears completely from the southern part of thls lowland. Andreev (1936+) made a detailed study of the hydrolaccoliths of the tundra of thls region. There is no doubt that Andreevls hydrolaccoliths are in fact classical pingos. We also know from Evladov (193;+) that many plngos of the northern and central parts of the Yamal Peninsula are cleft by radial fissures and are the process of dlsintepation. In the north Urals "hydrolaccoliths" and "peat mounds" of 10 - 40 m diameter and up to 1.5 In in height are nlentioned (~och1348+). Insldt these formations, beneath a laycr of thick peat, blue ice with air bubbles was found, while others contained water. The "peat mounds" of the Kola Peninsula and the Pechora Valley mentioned by Kats (1337+) are said to have a height of 3 - 4 m and cllan1trtcl*3of 15 rn and up. In both cascs they are bclieved to have origlnatcd by hydro3 tatic pressure. Possibly both pheno~ricnaare to be counted among the third type of pingos, mentioned on page 69, with which we have not dealt specifically and the ice bodies of which are formed by the accretion of many years and a simultaneou3 rise in the permafrost level. In sun~ningup the conditions found in Eurasia we see that the pin@;os are not confined to Yakutia, but occur from the Bering Strait to the White Sea and extend far to the south (see also Tllchonllrov 1948+). The fact that the permafrost in Siberia extends far to the south into the subarctic coniferous forest belt and in some cases even beyond, as far as the steppe region to the north of the Gobi Desert, results in certain modifications in the form and the mechanism of construction of plngos. In these southern permafrost regions the phenomenon of "constant thawing zone" is widespread roll 1944, p. 645). This is a special kind of talik in regions where the permafrost is no longer in equilibrium with the climate of today, but is in the process of dlaintegra- tion and therefore actually exists only as a relict.

C. Results of the Study of Pingo Distribution

This survey of the world-wide distribution of pingos confirms their close dependence on the presence of talik in the permafrost region. The pingos of the East Greenland type are particularly closely associated with special permafrost conditions . Tolstikhir) (1933+) already noted that intra- and sub-permafrost waters are found chiefly in zones of small permafrost thickness. laere the thickness of the pernlafrost is very great and the depth of thawing is small, the probability of pingo formation is greatly reduced. Possibly this holds the answer to the question of why so far no definite pingo phenomena have been reported on the Tainiyr Peninsula and the New Siberian Islands. Possibly this may also explain the virtually complete absence of pingos on the islands of the Canadian archipelago. This outline of pingo distribution also draws attention to the importance of the material base. Crystalline rocks appear not to be especially well suited for pingo construction. This is assuredly less a queotion of mechanical resistance during the updoming process than one of the nature and manner of ground water transport. This may explain why Ire know of no plngos In the crystalline zoncs of East Greenland. It also explains, at least in part, the absence of pingos in the northeast part of continental Canada. In summing up, it may be said that the pingos occur primarily in regions where the continuous pernlafrost la thinning out. In relation to material and general position there Is a strong association with the alluvia of flat plains and broad valley floors. The most suitable rmterial for pingo formation appears to be alluvial cands. This is particularly true of the Nackenzie type. For pirlgos of tlw o~~cnaystcr~i bcdroclc is a130 aul1-.abl.e, pilovrLdcd it conducts ground xat~l-. E3?ecially strut tured and l'inely-banded sed inicntary rocks, which havc further been n~odificdby (=colo~icaldisturbirnccs such as faulting, basal dikes, ctc., affol>d a good base for ping03 of the East Greenland type.

VIII. Conc luding; Rcrnnrks

Onc of thc rlrain concerns of this study wac to provide a sound morphometric basis for an explanatlon of the origln of pingos. Extensive excavations and drillings in pingos of two very different regions of the Arctic, nlountainous East Grcenland and the flat Idlackenzie delta in northern Canada, havc been illustrated in cross-sections. Cornparison of these profiles shows closc slrfillarity in respect to the general structure of the pingos in East Greenland and in the bkckenzie delta. The crystallometric investigations of the pingo Ice revealcd no differences for the two regions. The pingo ice shows the same characteristics found in the ice of almost stationary glacier tongues, 1.e. dead ice. Despite the many similarities and the conformity in general appearance of the two phenomena, ncvertheleos two very dlffcrent genetic mechanisms must be assumed. The East Greenland pingos are a unique, perinafrost-caused phenomenon in the nleteorlc water cycle of that region. They are the product of an open system. The Hackenzie pingos, on the other hand, owe their origin to a closed system. This is just another way of sayln~that the Kast Greenland pingos developed with the expansion or new formation of talik, 1.e. they are assocl- ated with a local degradation of the pern~afrost. The pingos of the Nackenzie delta, on the other hand, form as a result of contraction of an existing talik space, 1.e. where the permafrost is locally undergoing aggradation. As a consequence of these differences we must treat East Greenland and Plackenzie pingos as two separate typcs. Posslbly a study of all pingo-likc formations wlll reveal other Independent t~ypcs. In the East Greenland pingo region (70 - 74'~)the permafrost has an approximate thiclmecs of 100 n. The blaclcenzic pingoo occur only a little more to the south (69 - 70~14). The per11iaf1-ost thlckncss there Is probably about the sanie. Out own field ~bse~vatiorlsas wcll as the study of the literature on the dlstrlbution of plngos revealed that pingos occur within a certain range of latitudes that are subject to spcclfic cli~naticand pelmafrost conditions. This belt, broadly speaking, llcs between G5O and '75ON, in relation to the permafrost wherever it Is still Inore or less continuous, but is nevertheless beginning to thin out perceptibly. In Siberia the pingo belt dips conslder- ably to the south. Althou&h no prccise data can be given on thc life of pingos, it may be said that ~rowthand destruction of both Mackenzie and East Greenland-type pingos extend over very lone; periods of time. Hundreds and possibly thousands of years are involved. The annual increase of height of 0.5 m estimated by Shumskil (1955, translation 1957, p. 123) is probably rarely exceeded even by the fast-growing East Greenland pingos . Both of the pingo types described in this study constitute sources of drinking water. Because of the genetic mechanism of the East Greenland pingos, their springs cannot be expected to yield large quantities, but will last a long time. The melt water in the crater lakes of the Mackenzie pingos is potable even when the surrounding water is salty or brackish. In the ice bodiee of some pingos the Eskimos have excavated chambers for the preservation of meat. The assumption expressed in various quarters that pingos are an arctic variant of the mud volcanoes familiar as indicators of mineral oil, may be rejected on the basis of this study. Pingos are special forms of large-scale transformations of the top 100 m of the lithosphere in pernlafrost regions. They often involve not only alluvia but also the exposed rock. These processes, to be considered as geo- cryological, are more widespread and more active than had hitherto been assumed. In this connection, reference must be made to the numerous marsh and kettle formations in certain west and north European lowlands which may turn out to be pingo relicts (cf. p. 62). 1. Dircct Sourccs

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FI.INT, It. k',, t4.)'t8;Slu~lirs III KI;II.I;II~~(IIII~~ :III~~~~n~~~or~~l~olo~y (I9:i:). 111: Ih~~tl. I.. A,: Tltr (:II;IS~ of \f~rll~~w*lI;~I~I-II~;IIII~. ~\IIII.~~I.;*II(;vogr;~[~I~ir;~l Soc'it*I..v. Sl~~~ci:~l1'ut)li1,:1li1111 \(I. :Ill, 11. '.)I-.-.2IO.

F~ASVU,J, Ii., l'.l56: I'l~ysio~ri~~~Iri~~IIO~O~IJII ft*:1111r~s 111 IIIV!4,1<.k1%117.ic l)cll;~ ;trpil. C>II);II~~;III (;rt~gr;~l~l~csr,So S. 1). IS-.-?:!. I:nos~. I{. L.:., I'J52: Intsrl)r~~t;~ll~~n1~fjl~'rlnafrost fv;~l~~r~.s fr.0111 ;c~rltllotos. In: I'rosl a1,1inn ill soils, l'.S. lli~l~\v;~yIltsr:~rv\~ lio:trtl, Sl+ts~.ialIt~-pt)rt KO. 2, 11. 12:i- 2 /,I; ~IA~IIIK.III:,I\ lq.l15: Y.II~ I~I~IIII~IIIS#It-r Vorgii~~ct,it11 I~;~IIIII~II*IIIII~~III (if:lrirrt*n IIIIII

i\~~ll;~~~~*~~.st~\vit>I~I~IIII~~~IIII~I~II 11111,rtli~h ~,rsla* lk;l I:II~I,II~II~I*IISi SIIII.~IIIIIIII Viirl~:~n~lIinp~r,1111. 37, 1). 582 -61:). ~IAIIIII>~IN. I\. 11.. 190H : III S~wrrl~01 ;I I'ol;~r(:ontinr~~l, I'30:1-Oi. Arnold, I,ontlon. ?t.ld2 1s. IIF.Iw, ,\IINOI,IB (in 1)rurk): ll1~111111<~11111ngrn~it~rr I~~;I]I~~~SIIIIIS 11 KMSTIII:K, 11. ,I., lc,lh!l : I'(~~III:I~VIIS~;at \or~n:~n\Vrlls, \.~\,'l'., 11nll~riaIOil l.t~l., (;;iIpry, I!1:1:l, 100 11. I~I)~F.II.la;., 1957: ;\rklis~.l~t~IIivic.r;~. I~IIIIIIIIP~~Y1(L I'rry Vrrli~~. llcrn, I25 11. I~IITLINS.I).51.. '1.. \. \I. Irl 72. 111. 6, 11. :!f~i---:lGO (n~itI~IIKI~s~II?~ ?.IIS;II~IIIC~~~IS~II~~). \IAI;(;A~TII\. t;. I<.. l!Y12: (;CO~IIITIII;II i~~vrsIi~:~Iionson ll~r ;~rt.li~- sIo11e 01 .\I~rskn. .1 . r;rns,~t~Iiol~s 111 1111~;\111t*ri1.;111 (~I~O~B~I~S~I':I\ t~lli1111, VoI. :I:{, %I>. 6, 11. 5H9---59:l. \IACKAY,.I. I<., l!l!~ti: 31;11~kt~nziell~~ll;~s-~i~ l~roKrrbss r1,11orl. (:;III~II~~;I~Gcogral~t~cr, so. 7, 11. I--I?.

\II.YIIY.N II A 1.1.. \\-.(;.% \:In\ ; I\ ~~~IITIII:I~SS;$II~,~~ in I~II! sorlo~~ I{;I,Y rp~inn, .\l;~ska. in 1!100. In: Itr~.on~~;~iss;il~crsin Ill? (:;III(' \IJIII~~ ;11111 Sorlon I1;l.y regio~ls, ;\l:~ska, in l'.l!~ll. 1.3. (~I~IIIOKII~;IISII~~I*)-, Slt1~1,i,11 I'II~I~~I~;I~~IIII, 11, 187--218. 111 I.I.KU, S. \\'.. 196;: I'~br~n;~ff'ostor I'~~III;I~I~II~~~~'~IJY.I-II (;~I)IIIII~i~n~i l~)r,\IICII~K;III, 2:iO 11. SF,RSF.SO~A,Z. ;\., l'?S!: (:OII~I~~II~I)K IIIC~nt*l\in~ (11 irr in Il~t!K~OIIII~ i1I nrp~live Irn~~~rr;~Iurt~s,l~~~kI:~tly ;\k;~tI~-n~ii S;III~ SSSlt. T(IIII 79, XCI. :I. 1,. 507-508. 1:rc.r Ir;~nsl;rlion \\it11 :IIII~III~III~~II~S hy I. V. I'oiri,. I:.S. (;roIogi(~;~l Sr~rvey, FIOL~II (Iroun~lSl~~tlic-s. O'\FII.I., .I. ,I., l'.I2[1: GroIo~y01 Ilic Ar1.111. t:o:~sl 01 (;;III;II~;I, \vest 01 ~IIC1it:nt I'~II~IIs~\;I. lorl of thr (;an:~tli;~n .\rrIi~. lC~p~~(lilion1'Yl:i--~lgJ18, Vol. XI, 1';arL '1, OII;I\!;I, 11. I :\--I07 :\. I'E[IKIIS~:Y,,\,, IYl2ti: l)e v;trlnc liil(l~*rVIVI Sror~~st~ys~~nd. ~lr~l~lclrlst!r 0111 (iren. 1;111rl, lid. 68, \r. p. 25:i-257, I'ETIICI\,\'. (;., l!l:$!a: .\II ~ILII>IIIIIL ~II111~Irr111inr 1111, llr(>ssurv of gro1111(1nillrr In

pingos. 'Crl~tly \i~>n>issii110 \?.I~[~~II~II~~II~IV~\IIIO~ ll1*r7.\oly, 'Yon> :I, 11. 59 .--72 II<~.V, .I. .\, IIIICI;III~I~~~, l!t:16: l'i~~goin 1111, \I~I~:~I~II?.II-I)t-lt;~- N,\V.'r, 13~1Ilt~. tin 01 111~(;r~ol~~gi~~:~I Soi.ir!ly 111 J\IIII,~I~~;I, Val. (~7,11. I I I!) --I122. I'ISY~IIT,.\., lc.l:~ti: I,'~lriKi~\r~~~rigl:~vi:~irr (\I*$.. vivit~rs tl~va I\;III~.I*S ~';IKII~S. .\IIII;I\I*~ 111, I;&Socii-Ii* (;i*oIt>gi1111~111s 1ii~I~i1~11~.I OIIII- ;'I, 11. I1 I I!)- . ll l:ll. I'L~IL*>I.K,(;. 111111 .\. (;AII.I.EIIX (in I)ruvk/: I)ir.liorl~~i&ir~~II~SSOIS. Ira .\~:I~SIIII I~IIS~~I~IIV,l'~~ris. 1'1111s11.11,.\. I*:., 1!1.?.5: I;I~II:I~I'ISI>~OVI-r 111'11 ~~IIIII.IIII!S~I~ liillleis ((id.: SPrsill~~~), I\I*IIS \!irIini~>gt*r~,;I;I V~*grl;~lionr~~I>E .l~~r~lt>\~crll.~~l~~~~. Gvr>p,~IiskTi~tsskrilt, IltI. 2n. Il rrlc :I,11. I 7 I I 7'3 (n~i1 v~~glisc.llt-r %IIS;IIIIIIII.~~:IS~IIIICJ.

I!b$!i: '1'111, ;IIII~III, llor,~of 1111, r;isl SIIIIII*01 \I;~t~kvnx.ie~II)IIII~;I~IIS, Sorll~\vcsl 'Y~brril~~r~~,s.\;~lion;~l 1l11sc111n or (:;~~~;rtla.Il~~ll~*lin So. 101. lJioIo~iri~lScrips \I). :ill, :I:, 11. \II,I>~V~.Itttav, 1). V., lt.b'al',; 3'111. Ir~~tb~~~~r,tl~tr~~III*III Ians 111 Iltt! l~rr~~~;tr~t*ntI)lrozrn gr1t1111(lof IIII. Vork111;t tlislrir~l..'I'rt~lI!. I~~slilt~l:~\Ir~r~.lolc~v~~rl~~nii;~ ~IIIV. A. Ol~r~~t.l~c~v;~.'I'IIIII 1. 11. I:{?-166 (It~lssist.l~]nil ~~~~lisrl~rr%11~:1rnrncnf;1%~unfo, sirl~c;IIII,~I; Sll'l\l~ 'l'ra~rsl;~tit)r~ So. 17, l95'a. I~I(:II~IIIIP,II. (;., I!l:10: I'ost~l;~ri;~l111;1rillr sul~~r~cr~c~nceof .\rrlir Nor111 .\mrrirn \\ill1 sl~rr.i;~lrrfr-rcncr lo llte hl;~r.kl~nrirl)(.I1:1. I'rorrc-cli~~~sof the hrneric:c~n I~ltilost~~~l~it~;~lSot,~c-Iy,\'ol. 9'1, XI). I, 11. :!I -:I:.

I~OX, *I ., I82U: '~o~~~t~r;~~~I~iv;~l;III~I ~I-CIIO~I~~;II11o1i1.r~. In: Fr;~r~kl~n,J .: \;trr;~livr or ;I S(~r'o11t11Sxl)c-1lilion lo 1111. S1111rc.sor llte I'ol;~rSea in tho ye:rrs 1825, 1826, l U2;. ;\l~l~cnrl~xI, 1,. 1-58, - 1851: .\rctir Scnrl.l~in):I*:xl>rrl~tion, Yo). I I.on~lt~;~n,llronn, (ireen and Long. 111,tn's. l,o1rtIt1n, ',l:l 11. Ilos+..r~n~?r~z,A., I!I6O: (:cnlo~isktb I:~~It:~gl~lst~ri Vestjirc~r~l;~nd, Sornrncren 19:l3. >lctl~lplt~lscrfr:~ ,\ka~Ir~~~iet ~I)I. 111a t~kniskcViclrnsk;~l)c!r, \r. 1, p. 124-126. - 119!12 : 'l'l~e I.owcr Juressir rocks of I!;rat Grcenlnntl, part ?. hlcddelclaer on) Gronli~ntl, Iltl. 110, Sr. 2. 56 11. - 1950: 1)gntlvulk:rnrr. In: Ii~rkrl.Sl~~ill~,li.: Grrrnl:~ncls 1lo~c.n I. .C;t:l~~~ltzVorl~lg. li~~)c~~l~;~vr~,1). 112-1 I:{, I{IILE~KIIANTZ, A. untl ;trlrltsrc', 1960: I 1er1 I)anskc Sugssu:rq Kksl~rdilion19:19. >lr~tlrlelrlsrrIra 1)11nskGcniorisk Forrning, 11t1. 9, llrft 5. 11. 65:l-663. - 19'r2: .\ ~cnlo~ic'alrr.c~onn;riss:~~~cc of IIle soull~rr~rp:~rl 01 the Sv.~rlrnhuk E'minsula, \\'cst Grrcr11:1r111. >l~~l~lel~~lsr~ron1 GronI;~nd, Iitl. 135, Sr, 3* 72 1). 1luc~1.1,Il., 1950: Dcr Frost i11r Ii:~u):ri~r~tl.Springer-Verl;~~, \\'ivn, 279 1). Sager, l7. C.. I951 : Aerial analysis of pcrnr:~nenllyfrozen grounll. l'hologrammclrir Engir~e~rir~g,\'ol, 17. So. i,1). 351-571. Swocrn~ov~c~,V. H., 192;: Iler c\\~Kgelrorrne Iioden Sibiricns. Zeilsrhrill der Grscllscl~afl l~irErclk~~n~le 211 Ilrrlilr, Sr. 7-8, p. 396-427. Suu~swri,1'. A.. 1955.1'l1ersel7.i1n~1!1.57: I'rinciprs de glarioltrgie structurale. .\nn;tlrs tlu Cerrlre tI'l:t~~drsrt tie liot.umrnt;~tioni';~li.or~tolo~iclues, So. 22. 309 11. t'1)erselzt von .I. I'i~;lrcsson dl* Saint-Aubin unll .I. Ii;~uer. Scl~n~o~n.F. C., 1904 : .\ rt.i.onnaiss;~nrein Sortltern Alaska. ell:. in 1991. I1.S. (;rological S11rve.v. I'rolt~ssion:tl P:rl~cr 20, 139 p. Scli~mann.G., 1989: 'l'he ~ro\vtl~of the glacier rrystal. Journal of (;lariolo~y, Vol. I, So. 5, 1'. 2Sh-2h6. SI~~RP,13. It.. 19;2: (:ruuntl-ice mounds in 1undr;r. Gcojiral)l~icnlIleview, Vol. 32, SO.3, p. 417-423. SHVF.TSOV,1'. I'., I9'tG: The part ~~layedhy pcrrnalrost an11 s~~b.~srr~r~alroswaters in lhe I~yrlrologyof tlrc Ir~lli~irkna1111 Yitna hnsins. Izvrsliy;~Ak:rdcnlii S;III~ SSlt, S~riya(;roll~g~c.l~rsk;t?'ii~ \o. 6. 11. 137-152 (1~i1ssisr11n~it rnulisrher Zusarn~~~rt~f:tbsung\.(I'riv.~tc, nuszr~gs~veise~brrselzrcng ins Englisclrc von Dr. T. .\rr~~slrong.Sroll I'oli~r Ilrsr;trt.t~Inslitutr. C:~mbri~lp). SYITH,1'. S.. 1YI:i: ?'he So;rlak-lhic der I;SS\l . . . 111111Zc11tral-hien. I,cnin- gr;~~l-\lnsk;~u.5'111 11. (Itr~ssiscl~),(I1rivale L'berset7.urrK p. 151-153 ul~rlp. 170 -172 von i;.Hrrrter uncl .\. Iir1i~cr). Sv~c~~l\hnt)\,I. &I., 1934: Ilyrlro~~ulnji,~of ~~r*rl~eln;~llyfrozrn rrgi0n.s tbascd on invrsti~;~lir~ns in the r,-~iort of tl~cI.()\\ 11 of Y ekoltlsk I'rul~lcn~ySnvclskoi Gt-~~loxii,'~IJII~ [a, yo. t0, 1). I l9-l:l2 (1~11ssIs~11mil ~~~r~lisrltrrZ~~sa~n~nrnf.issung). TAHE~.5 . t!l30: The mer1t:rnit.s of frost hravlt~~.Journ;rl of (;rology. Vol. 38, p. 3O:l-3 1i. - 1N3: 1'r~rcnni;tlly frozrrr ~ro~tnclin ;\l;~skn: its ori~inant1 11islor.v. Ilnllelin ol iltc (;eoln):iral Sorir4.v of .\lncrir;~, Vol. 5h, 11. 1433-15iH. l'nor.~.. (:., 19fa4; Str~~klurl~orlt~~~,,Soliflr~ktior~ ur~d Frostklin~;~te tlrr Erdc. Ccolo- ~iscl~ell~~ndscl~;~~, :I;, 11. 55.5-6!li. 'r~611.1. (:. 119:8: ~)I-I.s~~ll~li\.;tl,- o1I11r IIP~~KI;I~.~;III'Z5kl11s rlvr L tc-n~bil;~li~~l.ICr~lk~~~ltJt., . . 1\11. 2. l.fy. I-;I. (I. 1--21. I SVTI)~II.II5. .\. IIIIII I. \I. SI \I*;I s, I ?:I; : l'ri111~i1111-sof JII-I,II;III~I.S 01 I:rc17.i~1 (;~IIIIIIIIS, .\~.:trl(.nry of Sc.irtn~.c*s,1 'SSIt. .\l~~.;ro~v-l.t.nin~r;~l.::i2 11. (tiussisrl~). (%ilic:rl I>;IPII \i~~llrr,S.\V., I'I'.;). . , I > nnr~.~.,.I. 11,. l!Wi : (:r~%lol~t~i,r~esor t111ri1<II~II;I~ of (;I>IIIOK~,Vnl 12, 10.:I, [I. ?:I2 --?:lG, t EII 1.1 vt;l:n, I.;., l!l55 : l)i{, I l~~nc~~rkr;~r~kt~?it.\VIIC 7,1iricl11-r %f-il~~n~. \o. 2272/;f,, 17. Sq11. l!j55, \\-.*III*,\\'. 11.. 1'.):~2 ;I: I~;~IIII~IIII(-II~;ind I~~I~~IIIII~III-S. l';~rl :I in: '1'11~ l~l.~ri~~lo~~t~;tl SI~~tlit~sof Ilir l{i~fli~~IsI;II~II l;h]w~iilio~~ 1!1:10. .1011rn;1lof (;l;~riolo~,v,Vol, 2. \I>. 12, I>. ll:,-~l2l, -- 1952 1): Tl~rp11ysil.s of ~l~*gl.~~~i:~tionuf (;CIIIVLII 1S;tffin ISI;IIIII.l';~rt 2 111: '1.111: Gla~~ioI~~~iralSt1111irsof IIIC Ihffin lsl:~n~lEx~~(~tiilio~~ I!l50. .lor~rn;~l uf C31:11~ioIo~y, VOI. 2, \o. I I, 11. 9-22, -- 1!)54: I'orlal~le ice-boring erl~lipr~~cnl.I'arl t in: 5lutlirs in ~I:rril#r~>l~ysics OII ttlr I'i,nn\' Ire Cap, Ilaffin lslantl, 1953. Jo~~rl~alof (;l;~riolo~y. Vol. 2. Yo. 16, (I. 4:la-436. \\'.\sIIII~HY, .\. I.., I!):,O: I'i~ltvrn~~fl~rountl. I(P\.IIP C;~n;~tlirnne111, (i(.uKrnl;t~ir, \'ol, 4, so, 3-'a, [I. :-:,{.I, - 1951;: Clnssifiv:~lionor r~;~ltrrnrilKrtr~~nrl ~III~I r~.vit*n of su~fi~~sitilor~gins. Iil~llctin or the Geologi1.:11Socirly of ;\rnerir;~. Val 1;:. 1). H.L:l-XG6, \\LRESS~IIII.~.\\'.. 1!)5:4: The cbxtt.nl of frozcn ~rul~ntlunder 1111. s1.n bollo~nan11 glacier tleds. Jor~rncllof (;lacinlog!, Vol. 2. \o. 13. 1). llJ:-200.

2. Indirect Sources (marked in text with +)

Iirnulzl als rl1~feralea,rrsrl. *;~l~slr;rrls.in: NEII~.SJAI(RHII(,II FUR S~I\ERAI.OI;IE.(;EIILOI;IF. I \I) I'*I.\I,\T~I.~I;II:.I9:15, 19:);. 1'340, I;. .\nnol;~ted Jlil~lio~r;~~~t~yCJII Sno\v, 11.p ill111 I1erm;l- frost. \'ol. 1-1. 1.il1r;lr.v of Concress. \\~;~sl~inyli~r~.for: '1'111. Sno\v. Ire. an11 I'errnitfrost I

..\>UREE V, V. Pi.. 1936: 1.r~J~ydrol~c~olithes des loundras tlr In SibPric! oc~riI~III, (~{IIss~sI~~I). Sll'ltlC 117G5.

SIJ~.II;I?, 31. I., !!1:{2: ~':III,~1li18 .\IBII;I~IIIII* 11t>s I<~S~IIII~~~IIS., , . ill I'SSIt , , . , (I~IIs. his(.l~).\. .I;al~rl~.\li~a. I!l:I5. I{(.f. ? (Slnllr~~l~~~r~j11. GI. IIII~I Sll'ltl.: 1727. .. - !51:!5: 011 I~IISIII~K~;III~I~~IIII of ~BI*~III;I~~II~~, (~~llshis~~tl~Sll'ltl~: :~It.lh.

- 1!I51l: 011 Ill(, lor~~~:~licw~II(~I.~IIII~:I~ i1.4- III(IIIII~~S Il~~l~~~~r~~ii~klrs.(It~~sl)iht.l~I. Sl l'lt l-:21 8. -- 1!14 1 . 11.ilags ;IIII~ia ir~gIII~~IIIII~S. (Itl~shisc.l~).S1 1'1tIC :101:1. TI k IIOWIIl~rlllgs611 1111. 'l'r;~~~.\I~;~ik;al.(Itr~ssis(~l~~. Sll'l{b: .'bO:i'.I. -- I'.):i'?: I)ir Or~~n~l\\;tsht.r'Sri~~~ht~;~~ki~lit~~~s IIIII) 111rv Ily~lrol;akk~~liIl~~~, (I~IIss~sI~II). 5..l:~l~rtb. ,!1i11, 1(.135s it14. 2 (SIIIII~~IIIII*~~]lb. li:l-li5 IIIIII Sll1I{l-; l72G. - I!l:l:{: (;roll~ltl t\:~lt*rill IIII- QII;II~~II;I~~~II~III~I~~IIIIS 01 III-~III~I~~~S~r~~~.iolls. (Itr~shis~~l~).SIl'ltl< 9:1lll;. - 1!,:15: (:~(IIIIII~-\\;I~I'~ of lt~~rii~t.\Io~~g~~li;~~~.\SSl{. (Ilril1111i1111of 1111' gro111111\v;~ll*r. (1t11ssih1,ta). S11'1t15 HH75. 'J'I,I.\TI*.IIIN. Q. I. IIT)II\. I. OIIII~IY. !!):it..: 1vi11~of Itat. 1:.1s11~r11Y,;ata;~ik;~I, (lt11s~is1.11). sll'ltb; :101;2. Table I Temperature and PI-ecipitation conditions in the East Greenland pin~oregion. The values fol* Nesters Vie and Kap Tobin are baed on the data of the Danish EIeteoroloy,ical Institute in Cha1310ttcnlund. The fi for blyggbukta Mere taken from Hovqdller (lOLir;, p. 3j,88yres PESTERS VIG (72"111'N, 23O55'W; 11 m above sea level )

2- Mean n~onthlyte~iiperntures In OC 2 2 0) c 3 P, Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dcc. I-J 1953 -20.8 -25.3 -24.5 -15.9 -3.3 3.9 4.8 7.9 0.9 -5.9 -12.6 -17.5 -9.1 1354 -22.4 -20.5 -27.0 -14.7 -3.9 0.7 3.6 4.9 -0.7 -8.4 -11.2 -16.6 -3.7 1955 -25.6 -26.8 -19.4 -12.3 -5.9 0.7 5.0 5.4 1.1 -6.9 -16.0 -18.9 -10.0 1956 -23.2 -21.1 -23.5 -13.2 -7.7 1.1 5.9 5.3 -2.3 -3.7 -14.3 -12.5 -10.0

rt blonthly precipitation totals in mrn gzw c CI cs I-' 1 1952 21.0 4.0 0.0 1953 20.9 15.1 10.8 0.2 3.8 96.0 3.4 77.1 1.3 71.1 120.6 65.3 500.6 1954 42.4 79.2 2.5 4.3 3.6 35.8 7.6 18.9 5.7 16.0 5.3 39.5 313.8 1955 6.5 1.7 2.7 10.9 0.0 0.0 57.0 32.7 121.3 8.5 6.1 53.0 305.4 -. 1956 22.9 42.8 24.3 0.0 4.0 5.5 64.5 13.7 36.6 26.7 54.0 90.3 391.3

MYCCBUKTA (73030t14, 21°30'W; 2 m above sea level) ------Average mean monthly and annual ten~peratures for the period 1922-193'7 (in C)

Average monthly and annual precipitation total3 for the period 1932-1337 (in mm)

SCORESBY SUND (KAPTOBIN) ('70°251N, 2l05U1\J; 42 m above sea level) Average mean monthly and annual temperatures for the period 1948-1956 (in OC) 1-16.01 -16.11 -17.61-12.-(1-4.2 1 1.1 1 2.9 1 3.2 1 -0.2 -6.1 -11.1 -14.2 -7.6') 1) The individual annual means varied between -6.51~and -9.2'C. Average monthly and annual precipitation total8 for the period 1950-1356 (in IMI)

26 33 2 1 23 11 40 27 3 6 32 38 36 50 ~78~) 2) The individual annual totals varied between 202 mm and 560 nun. Table I1 Granulon~etricvalues and densities with typical examples of pingo ice from East Greenland and Mackenzic delta, Canada, with corresponding figures from other kinds of ice of this permfrost region (density determination according to Ward 1952a, p. 120)

Character No. of Largest Smallest Mean hIean Origin crystals dian. of the ice examined Crystal in cm2 in cm density Trout Lake Pingo. Pingo ice 0.90 'u . . 13 6 71.5 0.03 2.3 G Crater Lake Pingo. . Plngo ice 203 25.5 0.02 1.6 0.90 urlCP Source Pingo ...... Pingo ice? 619 15 0.04 1.2 0.89 a d, Glacier Pingo ...... Pingo ice 8 7 16.5 0.03 1.6 0.93 a Glacier Pingo...... Surface ice 811 0.18 ~0.01 0.18 0.88 .I Crater Su~mit Pingo Pingo ice 507 79.5 0.12 1.5 0. 90 Sitiyok Pingo ...... Pingo ice 4 2 35.5 2.7 0.90 d 0.12 a Toker Point Pingo ice? 0.89 'u a ...... 94 7.0 0.04 3 a Toker Point...... Cataclastic ice 4 G in boundary zone 275 1.9 0.6 ccl - N 0.02 '* Sitiyok Pingo...... Ice wedge, top 644 0.2 < 0.01 0.3 0.88 Sitiyok Pingo...... Ice wedge, bottom 3795 0.1 ((0.01 0.1 0.88 Shore near Tuktuk.. Wedge ice 682 0.3 ((0.01 0.2 0.88

Zona of conllnuour parmofroat Zona 01 dascontmuoua parmofrort [ ZOM of sporadic parmafro.1

1-lap of pcr.r?af rust dir,tl'ribution in t;l~c no:'tlicrn hcr:~lspklcrc accol-ding Lo I1.F. Clacl< (135'1, 1). kY11 ). Ttlc arr-ovls point Lo Lhc 1-cr:ion:; e;licrc tl112 lnve:; Ligations r.~c:rc conduct;eir l'or the j)r.cscnt ~:ork 0 10 20 30

Pingos investigated

Fig. 2 Sketch map of the region of investlgatlon In East Greenland (bhp based on World Aeronautical Charts 40 and 55) 1 - Mineral Lake Pingo, 2 - Classical Pingo, 3 - Amphitheatre Plngo, 4 - Rock Plngo, 5 - Antecendence Pingo, 6 - Trout Lake Plngo, 7 - Crater Lake Pingo, 8 - Glacier Pingo, 9 - Source Plngo, 10 - Goose Pingo, 11 - Flaanedal Plngos The Classical Pingo In Pingo Dal, East Greenland, cf. Fig. 2, No. 2. Height above surrounding terrain: 32 rn; basal parameter 410 m. (Three people are encamped in the semi-circle)

Fig. 4 The easternmost of the two mound-like protuberances in the crater of the Classical Pingo. Dimensions are indicated by the man standing near the centre of the picture The Rock Plngo. The main axis of the oval-shaped pingo runs across the valley. The maximum elevation above the river plain Is 29 m. In the mid-ground of the photograph, directly to the left of the main pingo, is the new gorge of the river corning from the right (for scale see man in circle)

Fig. 6 In the crater of the Rock Pingo. Looking towards the precipitous, very irregular sandstone complexes of the crater wall. Thickness of this outcrop: 3.5 n~ Fig. 7 The 26 m high and at least 8 m thick east arm of the sedimentary envelope of the Rock Plngo

Fig. 8 Network of fissures on the low ridge forming the southern extension of the Rock Pingo. In the background, the new bed of the river The young main river gap through the flat Rock Pingo Anticlinal. The water flows from right to left

Fig. 10 The Mineral Lake Pingo seen from the south. Highest elevatlon above the river plain: 18 m. Ln the foreground the white area of the now dried up mineral lake Fig. 11

The upflexed sandstone layers of the Mineral Lake Pingo

Pig. 12 The Trout Lake Plngo In the Karup valley on Trail1 Island, East Greenland, seen from the north. To the left, the young, reactivated part. Highest elevation above river level: 29 m. In the foreground, the . Karup River. To the left behind the plngo, the Forelsd Gravel Sand Pinga ice Silt showing structural direction Fig. 13 cross-section through the eastern part of the Trout Lake Plngo. Numbers 1 to 6 indicate the places of excavation. At location 2 the ice body was drilled to a depth of 14 m and thermocouples were Installed

Fig. 14 The sharp division between the overlying material and the ice body in the Trout Lake Pingo, location 1 of Fig.- 13. The ice crystals are outllned by the soiled water of meltinc ...... , - .-. ," . Typical crystal pattern from the Ice body of the Trout Lake Plngo, location 2. llorizontal section 30 cm below the top of the ice ------unclear crystal boundaries. The grain size values arc as follows:

Diameter of equivalent circle in cm ...... 0.25 0.4 0.6 1.0 1.6 2.5 4.0 6.3 10 Number of crystals . . . 4 13 20 33 34 16 10 5 1 Percentage of total area occupied by the different size groups ...... 0.1 0.3 1.2 4.8 12.6 14.5 23.2 28.8 14.5 I I I I I I I I I Average grain size: 4 cni2 Pig. 15b Original contact impression abstracted from Fig. l5a. Note the parallel air bubbles within the separate crystals, but with directions changing from one crystal to another -..-.-..- -.,-.-.-.-. -.- -.-.- - -, . -.-. . . - .- .- -.. - .-.-..- -. ,,- - . ~-z--Sand and si -~+:-:+r-;:?k;?. ------'-2 -2y--_-_-1r-7--L-1=LTTII-x It - - .- .- Wave -froht of A de- -& 1~4fi~3--

-rr.-urv-rL-

Pig. 16 Pig. 17 Comparison of temperature conditions in the The Crater Lake Pingo in the valley of the ice body of the Trout Lake Pingo Karup River, Basal parameter approximately with those In the Qlacier Pingo 720 m. Diameter of crater lake 105 m. Highest elevation of the crater wall above the lake surface, 12 m. The Karup River flows from bottom left to top right. In the background the ~orelsdand the pingos there. (~erialphotograph by E. Hofer) lo lo 0 0 0' 0 0 O:.ol 0 0 .o 0 ~9,000,",9;3,4;o;o;o,0, feet

Sand

Pinqo ice transparent Pingo ice opague

Structuresin the ice

Water I0 20 30 40 50 rn Trenches

0 10 20 30 k0 50yards (excavations) Fig. 18 Fig. 19 Profile through the south crater wall Sketch map of the pingo group near the of the Crater Lake Ping3 Source Eingo (x = height in rn above the Karup River plain) Fig. 20 The Source Plngo from the southwest, Height of the plngo itself 9 m

Fig, 21

The sprlng-fed lake in the crater of the Source Plngo. In the foreground one of the springs. In the background the overflow, 1.4 litres per second Fig. 22 The Glacier Plngo. Surface ice ln the crater, active overflow and formation of delta on the south aide. Height of the plngo itself, 38 m; basal perimeter, 350 m

Pig. 23 The miniature glacier in the crater of the Glacier Plngo. In the centre the hole made by the spring water. The hapsack gives an idea of the scale Sorina I I

Surface ice

Pingo ice

,YYQ -., Y2/v-&-2w -r- Y V Frozen sand Y Y ry--w- '. \./ .i Excavation boundaries -h h ^. ,ft. 72'---

Fig. 24 Cross-sectional diagram showing the results of drilling and excavating in the Glacier Pingo Grain size curves of typical kinds of ice found In East Greenland plngos . On the abscissa, log- . arlthrrilc scale of crystal dlalneters ; on the ordinate the cun~ulatlvecrystal areas In percent of total area, plotted in arithn~etlcal scale

$/z mile

---- Former Ca~vseof river

Sketch rriap of Antecedcnce Pingo (right) shovrIng the now dry ri\~c1.course anLeccdcnt to the pingo forn111at1on Sand,~tc. 68s

Mass of Ice in process Water of but id up

Fig. 27 Hypothetical cross-section through a pingo of the Bast Greenland type Kw 1,2 = Pressure of water Kg 1,2 = Pressure of gas Kk = Vertical resultant of compressive fopce of the ice due to crystallization Ka = Uplift force of water, ice and gas K: = Compressive force due to weight of overlying soil and ice Kb = Resistance of overlying soil and ice to bending F 1,2 = Surfaces of attack of forces

Kwl + F1 (~rincipleof the hydraulic press) Kw2 + $2 = Preseht-day delta

50 100 km Pi ngos investigated

Fig. 23 Sketch map of the area adjacent to the mouth of the Mackenzie River, N .W .T., Canada (in part after Ihckay 1956, p. 2)

wsw ENE Feet m 150 - - a0 120-

IUNN YNN- N -^v I<- -

N N::N N

--3;.---,I ---,L --,- L ------,;; ------,------,---- 60 120 180 feet 30-r 10

C lay and s11t [ Saf)d a Plngo ice

Fig. 29 Schematic cross-section through the Crater Sunlnit Pingo in the northeast Elackenzie delta. This section is the result of the diggings and excavations at locations 1 to 7. In test hole 4 the ice body was drilled down to a depth of 111 ni. The dotted extension of the drill hole indicates the conjectured thickness of pine0 ice lens. The slllall crater lake is situated between locations 3 and 4 Pig. 30 The sharp line of separation between unatratified frozen sand (above) and black, transparent plngo ice (below) from the Crater Summit Pingo. Note the contraction crack In the ice 2 cm wide Gre silt clay (447.clay. 42% silt, 14Xsand). At the end of ky 1953 unfrozen down to a de th of 60 crn; red inter layers; much organic material (roots and !ranches of willows).-- Blue cLa ey silt (38% clay 4 % silt 14% sand - high ice content ?moisture content ~6~7;Ice lenses up 16 8 cm thick and 90 cm long; isolated fragments of driftwood.

Blue sandy silt (217. clay, 42% silt, 37% sand); lum of organic material rn a matrix of pure ice (moisture content !LOX); 'ig. 33 various organic material. -- Blue clayey silt (317. clay, 417. silt, 28% sand); moisture con- Cent 62%: the ice encloses lum~sof mineral material as well as numerhus shells of lacustrine snails and other molluscs.-- Grey mixture of clay silt, sand, coarser components and segre 7nted icc; in addition to round river gravel stones we also kind sharp-edged, eroded and scratched stones; a ver great deal of organic material, chiefly driftwood; a special characteristic oi this zone: no stratification. - 10-15 cm thick layer ot almost purely organic material. Brown sand, the ireatly distorted stratification of which suggests cr otur ation; ice is present only as a filling in %ores 0% the sand; no organic material. Delta stratification in pure sand.

Clean sand with very good stratification; very little ice (moisture content 19%).

Sand, partly sand gravel with very clear cross stratification driftwood trunk 14 cm in diameter, aged 28,000 2 2.000 years. -

Pure sand with distinct stratification and red inter layers.

Com lex distortion in sand with delta stratification (probably setElement before the setting in of permafrost). Small £raiments of driftwood enclosed in sand and gravel with Fig.32 cross bed ing. Fine-grained sand with good stratification; no segregation of ice.

Coarse-grained interlayer. - Well stratified fine sand. -- 48 feet pingo ice

Fig. 31 Stratigraphic profile thrbougtl the scdlmcnt cover overlying the Ice body of the Crater Su~;u~~ltP111~;o Pig. 32 North wall of the excavation at site 6, Crater Summit Plngo. We can recognize (1) a wedge with remnants of driftwood and (2) frost stratification In a band that was originally horizontal but now stands at an angle of 50° in the peak part of the plngo. (scale in Inches; depth of excavation, about 70 cm)

Fig. 33 Frozen lump6 of silt (bright) in a matrix of pure ice (dark) at a profile depth of 3 m. Abstracted from Section C of the stratigraphic profile of overlying sediments; Crsat.er SllrnrnT t. Pinun -_ ..------> -- * .--"------m ft, South cave Central Shaft

Alternating layers Sand ~~lngoice of silt and pure ice Fig. 34 Schematic cross-section through the Sitiyok Plngo with excavations and drillings, and the probable foundation of this pingo ice body

Organic material

S11t with dircctton of structurre 6 / a Frozen sand -20 Segregated ice

[I Wedge ice with impurities

-2b P~ngolee

...... Depth of thawed zoneat end of June

-28 .-.- Ekcavat ion boundary

Section through the per~tiafrost;irl the region of the excavations in the Sitiyolc Pingo. (Scale representation of oetailn, supplement to Fig. 311) Fig. 36 a and b Two cuts from the thick vault of stron ly fol ed sand belts In the zone of contac between the sediment cover (outside) and the ice body finside 3at the entrance to the ice cave at I . Toker Point. Note the zone of white, cataclast .c ice on the Inside of the folded band of sand (measuring tape graduated Fn inches; pencil, 15 cm) Granulo~netriccu18vcs of various ltlnds of Ice In the Phckenzic delta. The abacisaa gives the critical diar,~cter,the ordinate thc cua~ulat,Ivecrystal areas in percent of total area

Sketch of a contact irl~pr.csslonfrdril 1;t~icc 01' the Crater SUIILII~~ P1ny;o. lior.lzonta1 sections 30 C;IL below the sullface of ttlc plngo ice body; site 11 of Fil;. 2'). hr'gc, ~~iostlys1r;lple crysta1.s; alr bubbles insldc the inciivldual crystals parallc 1; from c~~ystalto c1-~r,tal,hov~?vcr, niar~kcd differ'onccs in ci~r~l.~ction.1.lotc: also that "o~cl.la~)~~l~.~::all' bubbler," OCCUI* h~'1-c;u~d tll<'r(!, (: . r;. bo t. toiri 1 i- f t k 0 m a 0 w tQ a c3 O aJ ad fi N C v$2 aJ mz. 01 cd Q, C UW C dh u 0 cd kr= u 0 md r-lcd r-l E dk 0 Ck crO Q, X cO PLATE I

Fully developed Mackenzie pingo Aerial photograph of the Crater Summit Pingo, situated 6 km south southwest of Tuktoyaktuk, northeast Mackenzie delta, N.M.T., Canada; position 6gi0N, 133"W. The external din~ensionsof this pingo are as follows: base perimeter, 900 nl; elevation of highest point above the surrounding marsh land, 40 m. Because of its size and prominence it is used by coastal navigators as a landmarlc. A layer 14 rn thick of originally horizontal river and marine sedinients was updonled in the frozen state to a steepness of 30 to 45O and broke up into blocks which are no longer able to cover the fully developed ice body at all points. The diameter of the ice lens can be put at at least 150 m and its thickness in the centre at 55 m. Its Ice is unsoiled and the crystals are remarkably large. The Crater Sumnlit Pingo is the product of a slow contraction of the talik (unfrozen material surrounded by permafrost) below the bed of the former lakc. After the diameter of the lake had receded below the critical value of about 600 m the advancing permafrost generated increasingly high hydrostatic pressure (see Fig. 40) in the closed system comprising the impermeable bedrock and the advancing permafrost front. The reaction took the form of an eruption of the entrapped water in the direction of least resistance, 1.e. upwards. On entering the zone of seasonally fluctuating temperatures (in the Mackenzie delta this occurs at a depth of 10 to 20 m) the resistance to warping in the overstep and the cooling of the ascending water increased to a point where a true hydrolaccolith fornled from which the ice laccolith developed in situ. Driftwood found in the upper sedi~nentsof the crater wao about 28,000 f 2,000 years old, a3 dcter~liinedby the C ,, method. This leaves a very wide margin for the age of this pingo. PLATE I PLATE 11

An East Greenland pingo in the first stage of breakdown

A pingo about 30 m in height in the ~andb6lDal, Kap Franklin region, central East Greenland; position, 730201N, 22020fW. (~crlalphotograph of the Dr. Lauge Koch expedition, taken by E. Hofer) (see also ~Gtler,1954, Plate V. ) This representative East Greenland pingo stands In the centre of the recent gravel plane of a valley floor. It owes its origin to the ascent of Intra- and sub-perniafrost waters and gases that are subject to the hydrostatic pressure of the surrounding region, which rXses about 1000 m above it. The quantities and temperatures of the ascending waters were such that no direct outbreak occurred at the surface. As in thc Elackenzie pingos, the ascent came to a halt in the toprnost 5 - 15 rn of thc permafrost (see Fig. 2'7). A true hydrolaccolith f or11led dlrectly below these rigid surface layers of permafrost. The reserves of cold in the permafrost zone, which was about 100 m thick, transformed the hydrolaccolith into a giant ice lens which lifted the permafrost layers above it. It could not definitely be determined whether any diapiric lifting of the Ice lens was also Involved. The small crater lake has resulted from ablation of the ice lens In places where it was no longer protected by frozen gravel. The regular volcano shape of this pingo reflects the very localized character of the origination mechanism. Wherever the ascent of the ground water Ln the perrnafrost is predetermined by geological structures such as basalt dikes, faults, etc., which is very often the case for East Greenland pingos, irregular, usually elongated outlines developed. PLATE I1 PLATE I11

An East Greenland pingo in an advanced stage of breakdown

The Crater Lake Pingo In the valley of the Karup River on Trail1 Island, central East Greenland; position: 72p~,23S0W. (~erialphotograph of the Dr. Lauge Koch expedition, taken by E. Hofer. ) The diameter of the crater lake varies between 100 m and 110 m; only a few metres from the shore the depth is already about 5 m and increases gradually to 8 m towards the centre; the surface of the crater lake is at least 2 m above the Karup River. At its highest point the crater wall, which is vertical In some places, rises 12 m above the surface of the lake; the lower half of the wall consists of pure ice covered with a thln layer of lancl- slide material. In most cases the breakdown of East Greenland pingos is brought about by the same forces that lead to their construction. Sub- and intra-permafrost waters and gases break through the ice lens itself and, in the course of centuries, melt it away. In August 1955 the spring of the Crater Lake Pingo was flowing at a rate of more than 3 litres per minute. From this example and from similar springs in the interiors of other pingos it could be demonstrated that the pingos producing ground water and gases are of purely local meteoric origin, lnvolvlng juvenile Influences nor bituminous deposits. The overflow of these spring waters (see right-hand side of picture) has exposed other parts of the ice lens to ablation by the heat outside. PLATE I11 PLATE N

Reactivation of an old pin~oof the East Greenland type This example of two generations of pingos in concentric arrangement, is situated in Tobias Dal in East Greenland; position: 73O45'N3 21°W. (~erialphotograph of the Dr. Lauge Koch expedition, taken by E. 1Iofer. ) A musk-ox (in the semi-circle) indicates the ~cale of the photograph. The annual wall incised by former overflow channels is a typical old form of an East Greenland pingo which was destroyed by the same ground waters and gases that built it in the first place. The young pingo produced by the reactivation process is smaller. Experience shows this to be the rule in such ca8es. PLATE N PLATE V

Formation of groups of East Greenland pingos

A view of the group of pingos in Tobias Dal. The pingo of Plate IV can be seen at the centre. (~erialphotograph of the Dr. Lauge Koch expedition, taken by E. Hofer.) Deflected by the cold plug in the adult, but not yet dis- integrating nlaln pingo (see text, pp.112-43) the ascendMg ground waters very often produce several subordinate pingos. These "satellites" are usually Irregular in outline, generally smaller and lack craters; cracks generally form, but the top permafrost layers do not brealc open, nor does the ground water emerge. It can be assumed, however, that these subordinate forms also contain a core of ice. Because they are better protectcd these Ice cores should last longer than those of the main plngo, which in the depicted group had already been almost completely dissolved. Pingo-like structures similar to these subordinate pingos are much more numerous in certain parts of the Arctic than had previously been assumed. PLATE V Note on the Translation of Geographic Names

The geographic names used in the present work presented some special problems which the translator has attempted to solve mainly with the convenience of the reader in mind. Since Dr. ~Gllerquite properly assigned descriptive names in his own language to the pingos of East Greenland investigated by him, there seemed to be no reason for not translating these designations In full - Trout Lake Pingo, Crater Lake Pingo, etc . Well-established Danish names, however, especially those found on small-scale nlaps, have been left entirely In the original o on^ Oskars Sund, Kap Franklin, etc.). Exceptionally, however, the generic parts of certain relatively obscure names have been translated where this was possible without perpetrating a linguistic crime - hence, Trail1 Island, Karup River, Guden River, but ~orelsb rout hke), Lomsb (~iverLake), Maanedal (~oonValley), etc.

D.A. Sinclair