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Revista do Instituto Geológico, São Paulo, 21 (112), 33-55, 2000.

SURVEY OF CRYOGENIC PROCESSES, PERIGLACIAL FORMS AND CONDITIONS IN

Dario TROMBOTTO

RESUMO

Este inventário fornece informações sobre o estado da arte e os avanços recentes da Geocriologia nos países da América do Sul onde ocorre permafrost ou congelamento sazonal dos solos e onde este campo de pesquisa tem interesse científico. O objetivo é aumentar o conhecimento das atuais áreas geocriogênicas sob impacto de influências antrópicas e/ou de modificações climáticas. Uma breve análise climática ajuda a compreender as principais regiões criogênicas sul-americanas, ainda pouco conhecidas e sem a correspondente cartografação geomorfológica. O levantamento também salienta o fato de haver poucos dados disponíveis sobre a degradação do permafrost andino de altitude. Esta degradação, causada pelos processos de aquecimento global, deveria ser monitorada, entre outras, por razões hidrológicas. Os principais processos criogênicos - como criometeorização, nivação, solifluxão, crioturbação e seleção - são descritos em diferentes litologias, lugares, etc .. São fornecidos alguns dados quantitativos sobre movimentos de solifluxão e aplicação de métodos sedimentológicos na detecção de fenômenos criogênicos. São resumidos os últimos dados sobre permafrost andino, obtidos com o auxílio de métodos geofísicos e/ou sondagens acompanhadas de medidas da temperatura do solo. As forrnas criogênicas mais comuns nos são apresentadas: microforrnas, , felsenmeer, estruturas de crioturbação, thufurs em moors e lobos de solifluxão. Mesoforrnas características dos rock dos Andes Centrais e elementos importantes de ambiente periglacial como vertentes criogênicas de sedimentação, superfícies de crioplanação ou vales assimétricos são também descritos.

Palavras-chave: Geocriologia - permafrost - periglacial - Andes - regiões criogênicas - Geomorfologia

ABSTRACT

This geocryological inventory contributes to the state of the art and to recent advan.ces of Geocryology in the countries of South America with perrnafrost occurrence or seasonally frozen ground, where this field of research is of scientific interest. The aim is to increase the knowledge about the are as of the present cryosphere being modified by man and/or suffering changes due to climatic factors. A brief climatic analysis helps to understand the main South American cryogenic regions still poorly known and lacking the corresponding geomorphological cartography. The survey also emphasizes the fact that very few data are available on altitudinal Andean perrnafrost degradation caused by global warming processes, which should be monitored for hydrological and other reasons. The main cryogenic processes observed such as cryometeorization, , , and sorting are described in different lithologies, places, etc. Some quantifications are given, such as data on solifluction movements and sedimentological methods applied to detect cryogenic phenomena. The latest data of Andean perrnafrost are summarized. They have recently been obtained with the help of different methodologies, including geophysics and/or, through borehole with ground temperature measurements. The most common Andean cryogenic forms are presented: microforms, patterned ground, felsenmeer, cryoturbation structures, thufurs in moors and solifluction lobes. Characteristic mesoforrns of the Central Andes, rock glaciers, or important elements of a periglacial environment such as sedimentary cryogenic slopes, surfaces or asymmetrical valleys are also described.

Keywords: Geocryology - perrnafrost - periglacial - Andes - cryogenic regions -

33 Revista do Instituto Geológico, São Paulo, 21 (112),33-55,2000.

1 lNTRODUCTION permafrost as welI as the most important areas with seasonal freezing or periglacial phenomena. Some Geocryology is the science that studies areas require more specificinformation (e.g.the coldest the environment and the ecology of cold regions, site in South America in , ice covers). From the > 13 million km2 that their natural, geological and physico-chemical processes in relation with cycles of freezing and correspond to the permanently frozen ground in thawing as welI as the relation between alI those the , the largest part is that phenomena and human life. of the Antarctica, whereas there is very few data The original concept periglacial about permafrost occurrence on the South American continent. (introduced by Walery von Lozinski on the Some estimations held that mountain Eleventh lnternational Congress of Geology in Stockholm in 1910), originalIy applied to describe permafrost would cover approximately 30,000 the climatic and geomorphologic processes in areas km2 (GORBUNOV 1978), but recently it is close to Pleistocene ice, was complemented by assumed that it covers even :;70,000 km2 the Russian term Geocriologija (NAUK (HAEBERLI et. ai. 1993). They divided AKADEMIJA 1960) for its wider concept permafrost into maritime permafrost in the referring to low temperatures, with permanently Southern and Tropical Andes and continental or even short term, seasonal or daily frozen ground. permafrost in the Central Andes. When the ground, like , rock and ln Argentina the term of approximately organic material, remains at or below O°C for at continuous permafrost (as introduced by least two consecutive years, it is calIed permafrost GARLEFF & STINGL 1986) is applied to the type (VAN EVERDINGEN 1998). of permafrost which is very much restricted by High latitudes together with a low MAAT topography and is limited to the MAAT isotherms (mean annual air temperature) are conditioning of _2°C and - 4 °C (at the Central Andes, 33°S factors for the occurrence of Antarctic permafrost and approximately 4500 m ASL) with and for permafrost of islands. ln our precipitations between 500 - 900 mm/y and limited to the isotherms of -1°C and - 2°C with a case the altitude provides the basis for us to classify permafrost as mountain permafrost of the Andean precipitation of 300 mm/y in the case of the type. However the variety of dry permafrost with Argentine Puna region (Table 1). temperatures below zero but without ice is also a The lower limit of Andean permafrost is frequent phenomenon, and should not be neglected restricted by a type of discontinuous permafrost when considering cryotic characteristics of the (Table 1, Fig. 2) which may be observed in some Central Andes and the region of the South parts through rock glaciers (BARSCH 1977). At American Dry Diagonal or the Desert Andes. present the lower permafrost limit at the Cordón It is the aim of this work to present the deI Plata (Central Andes, Mendoza) is:; found at an state of the art and recent advances of Geocryology elevation of 3700 - 3800 m. ln the Southern or in the countries of South America with permafrost Wet Andes, the so-called Patagonian Andes, the occurrence or seasonally frozen ground and where occurrence of permafrost was registered this field of research is of scientific interest. at 51 ° 30' S in Santa Cruz (ROIG 1986) at an The future role of Geocryology has to be elevation of 980 -1100 m in the years 1977 and emphasized because it may provide important 1978. ln the Lake Region between 35° and 45° insight to the paleoclimatic reconstruction in 30'S, in the province of Chubut however, climate changes and in South America. permafrost near Lake Vintter (approximately 44 OS)had been registered at an elevation of 2060 2 PERMAFROST m in recent years (C. Bianchi, pers. comm., 1998). The term island permafrost (Table 1) was introduced for the phenomenon of isolated patches One of the first attempts to map cryogenic at 4000 m ASL in the Central Andes of Mendoza regions in South America was made by (TROMBOTTO 1991) and relict permafrost for BARANOV in 1964. frozen ground at 3400 m but with a thick detrital The map of MAAT of South America by cover in rock glaciers. HOFFMANN (1975) (Fig. 1, adapted by Towards the , in the region of the Trombotto) and the lines for +5, O and -5°C may (6275 m ASL, ), a typical help to determine locations with possible

34 Revista do Instituto Geológico, São Paulo, 21 (1/2),33-55,2000,

60" 52' 44"

Northern Hemisphere

Biazil Southern Hemisphere

! llalialéi./ , iJ _/__ i ....!. ."h._ i I~~L. I;' \1 J ~~~/ i I ~a(\~COc#{\

Argentina 1- Venezuelall AIKfes (páramo)

3--Ecuadorian Andes (Chimboraz-o) 4~ PenJ'.'ian Andes 1.12- Colombian Andes 1 i S- Cordillosras de Carabaya - Apo]o!>amba \'PenJ • Boliviil)

'- ~jerra de la iHI 7·6- Cordmera80lNian AndesOccid!l'ntal-(Con:lilleraAJtiplanoRea~ (Nevado de Sajama. entana I CeJ(o Caquella) () 8- CordilJera de Upez - Alliplana - Puna de Atacama (laguna Cobrada. Salar de Pujsa) (Bolivia - ) 9- Puna - CordH~ra Oriental (Argenfil1"a) 10- NOl1hem Desert Andes (Soulh American A1id Diagonal) (Argentina - Chile) 11-Aconqw-ja (Argentina) \ \, í l12- Fama1ina (Argentina) \, 'I i la.. Southam Desert Andes (Argenlina - Chile) \\ I (1slasMaMnas} PracordllJera}(Argentina~Chile) ~ Falkland Isjands 11+-~ntriilChile) ~ndes {Cordil,le.ra Principal, Cordílera Fronta.', OI :~ I .15- vVel Andes -lake RegKm (CerTo ) (AfgMlii'l ~8'

FIGURE 1 - finportant Cryogenic Regions and MAAT map of South America (adapted by Trombotto) Black: MAAT O- (-5) °C (inc1uding ice covers); dash line: MAAT> 5°C tropical environment but with dry conditions, be preserved as in the ca~e of inactive ice (Table I) HEINE (1994) reported the limit of continuous found at the salt lakes in the and Puna of permafrost to be at 5250 - 5300 m ASL. Island Atacama (Bolivia and Chile) at 4300m and permafrost, also mentioned by the author, is found approximately 22° S (HURLBERT & CHANG 1984) below 5000 m. In other parts of the Andes of who assigned this type of ice to the Little . Ecuador, with soil temperatures around O°C but Thermic particularities and regional dry under humid conditions, there is no permafrost, conditions seem to reinforce the effects of but a glacial environment. periglacial processes and the persistence of ground At the same time, subterranean ice may ice in the Central Andes. Between 1991 and 1993

35 Revista do Instituto Geológico, São Paulo, 21 (1/2),33-55,2000.

AltiplanoSaltLow lakesresistivitiesin the UfvAnaesPuna l-'ermaTrOSl TropicalmChimborazoActlvelevel1Chimborazo,(35°Centralcrvoplanationand-1"Glatthaenge",NWRockASLActiveglaciers1DesertAndes--2°CActive-2/-4cryoplanation900asRockcryosediments""cryobasinLowDetriticsurfacesisothermsArgentina<55°rock'131°(aboveglaciers300AndesindicatorsAndesrock30'mm/y,resistivitiesairglaciersqlaciersglaciersAndes-°Cmm/y(6275rockslopes35°S)seaisotherm~;:,ournernairsurfacesandofsummitglaciersSiin500RockDiaaona/icethein temperature- ,qlacierscryosediments""cryobasin(?) Constantatof (1977\ ContinuousType InsularDrvContinuous"DiscontinuousDegradedmountain"ApproximatelySporadicor island (17°>limi!:m),Ecuador<175500030'Ecuador,mm/y5250-ReJict"Warm"31°m ASL-S)ice530(inf. de-1.6°C,senseAtacamIsolatedofaBarschandpatches > 20000 Q r South American Dry

lAtlLb 1 - Andean J.-'ermatrostlypes lU :South Amenca influenced by the warming process in the 1980's, cryogenic processes however influenced at much lower elevations. Signs of activity in the rock glaciers of Mendoza for example establish lower limits of permafrost; and thus the designation island permafrost (TROMBOTTO 1991). Additional investigations are required for the distribution ofAndean permafrost. It is necessary to map it, to study its topography, its ice content and its behaviour regarding global climatic change as well as its importance to domestic water supply.

3 INVENTORY OF CRYOGENIC PROCESSES OBSERVED IN SOUTH AMERICA

The main cryogenic processes observed in the South American Andes are cryoweathering (Fig. 3), nival processes, solifluction, cryoturbation, sorting, frost cracking and permafrost creeping with different lithologies. Some sites are being monitored. The studies of FIGURE 2 - Andean permafrost and at the processes in the periglacial environment in the Cordón dei Plata, Central Andes, Mendoza, laboratory and in the field were principally guided 4600 m ASL (November 1999). The observer indicates by the following phenomena. the limit between permafrost table and • Sorting: sorted materiais due to cryogenesis the O°C isotherm at the Cordón dei Plata (Andes create a cryogenic law, represented by pebbles and of Mendoza, Argentina) was found at 3865 m cobbles above and below. CORTE (TROMBOTTO et aI. 1997), most probably (1962 a, 1962 b) confirmed this law in experiments

36 Revista do Instituto Geológico, São Paulo, 21 (1/2), 33-55, 2000 .

• In comparison to other sedimentary media there is no data abour fluvial phenomena. Under the impact of winds in Mendoza taffonis of cryogenic - petrologic origin could be observed on pyroc1astic rocks at 34°S. is still discussed as an aeolian , but a cryogenic component in its origin cannot be ruled out. As TROLL (1944) assumed, freezing is an essential phenomenon in order to explain the production of in the loess. It may well be that the Patagonian loess matelial (TROMBOTTO 1996) FIGURE 3 - Cryoweathering at Cerro Hateher, Sierra as well as the Andean silt or cold loess was de Sangra, Southem Andes, 915 mASL, 48° 29' S and influenced by cryogenesis. TROMBOTTO & 72° 14' W. Length ofthe hammer: 31.8 em (Deeember REGAIRAZ (2000) have recently described a 1999). case of cold loess for Mendoza.

in the 1960's. Repeated cyc1es of freezing and thawing may cause a sedimentary sorting of material, creating a cryogenic 1aw this way that determines in which kind of 1andscapes a pelig1acia1 environment coarse sediments (> 2 mm) is found above or below fine sediment. CORTE (1962a) reproduced in the laboratory the segregation of- ice and the sorting of a granulometrical1y heterogeneous mixture, saturated with or without silt particles < 0.02 mm. The presence of silt has an important granulometrical significance to generate . With water flow and the growth of ice the transport of material in its open system is to be exp1ained. On the other hand it is assumed that the upward movement of b10cks leaves a space quick1y filled by fine matelial that stops the b10cks from settling during the thawing processo

• Proceeding in a similar way AHUMADA (1987), in her doctoral thesis, proved the same (sorting) for heavy mineraIs in the active layer.

• I mportant phenomena related with silica FIGURE 4 - Torre (3102 m ASL), Egger and Standhardt, Chalt, Adeja gJacier, Southern Andes, Santa deposition in periglacial environments were part Cruz, Argentina, ea. 49° 15'S and ea. 73°05'W of TROMBOTTO's (1988) research for his (December 1998). doctoral thesis .

• Among the cryogenic processes of the Andean • As to important cryogenic chemical phenomena cyc1es of freezing and thawing, the mechanisms VOGT CORTE (1996) had observed for a long & of different South Amelican 1ithologies and their time the possible origin of Ca C03• expelimental correlation are yet unknown (Fig. 4). The cyc1es have to be reproduced in order to • Desiccation cracks and thermal contractions simulate the observed natural conditions as in the were very much discussed among geologists in Central Andes for example, with a low content South America. The dehydration process of the of humidity and high amplitudes and temperature Pleistocene active layer and therrnal contraction oscillations between + 30°C and -20°C within may often use the same cracks (TROMBOTTO 24 hrs. 1996).

:i7 Revista do Instituto Geológico, São Paulo, 21 (I/2), 33-55, 2000.

Trollbrot is one example of an Andean cryogenesis, discontinuity or a ring with an empty space where the fragments remain together and resemble between the rOck and the sediment is found. As sliced bread. WASHBURN (1979) pointed out needle-ice occurred even in Brazil. 4 SEASONAL FROZEN GROUND On the other hand the needle ice leaves different microstructures. They are usually cmmbly and therefare they are called lumpy The area affected by seasonal freezing surfaces. Their appearance resembles plowed in South America, and Argentina in particular, is lands (WASHBURN 1979). SAPPER (1915, see much larger than that covered by permafrost. WEISE 1983) introduced the term The important processes are solifluction and the effects of needle ice. The action of the Rasenabschalung; a related term referred not directly to forms but to processes, but applied to wind or the impact of solar radiation combined areas. with cryogenesis have been studied by PÉREZ (1984, 1992). In the Central Andes of Mendoza, 5 FLUVIAL AND AEOLlAN PROCESSES IN A PERIGLACIAL ENVIRONMENT CORTE (1983) incorporated environments with seasonal freezing with small-size patterned ground and weathering pits (OpferkesseZ) into an area he In a cryogenic environment rivers and called parageocryogenical. streamlets remain frozen during some time of the On the Patagonian mesetas and in the year. When they are not frozen they play an active Argentine Precardillera keppavond (HUML UM & role in the denudation of the valleys, a1though this CHRlSTIANSEN 1998) may be found. This is the fact is generally ignored. technical term used on the Faeroe Islands to define Streamlets help to increase in active small-scale pattemed ground. areas with permafrost and contribute to the ANGELlNI (1990) and BUK (1992) formation of subterranean ice. Streams and made maps delimiting regions with a maximum subterranean ice extmded by freezing of some seasonal freezing index and mean annual freezing parts of the ground also create the characteristic frequencies in Patagonia. Segregation ice ar ice in various layers called icing ar Aufeis. It is pipkrake has a strong impact in these areas and formed by the successive flow of water that freezes influences works of civil engineering in road and is then covered by a following flow that constmction (Patagonia). Although no permafrost freezes and so on. This phenomenon may be has been detected in the Andes of Mérida and frequently observed in the Andes. Sierra de Perija (Venezuela), the periglaciallevel of The influence of the wind is also decisive these processes may reach a zone of over 1000 m for the shaping of either continental or coastal above 3600 m ASL. Sorted pattemed ground is cryogenic forms. A great variety of aeolian forms characteristic of the Páramo. At the Páramo de are found in cryogenic environments. Piedras Blancas (Venezuela) the limit of needle Clasts and blocks with one ar more ice for example, lies at an elevation of 3600 m surfaces shaped by the wind are designated (SCHUBERT 1979). In the region of the Tropical ventifacts of cold environments. Depending on how Andes, the phenomena of seasonal freezing are many sides are eroded by the wind they are called concentrated on an area called Tierra ReZada 1: Einkanter, 2: Zweikanter and 3: Dreikanter which lies above the timberline, with a MAAT of (terms of German origin). The eroded surfaces are 7° C (subpáramo) to a MAAT of - 1,5 °C at the used to determine the wind direction (GONZÁLEZ snowfalllevel (Pico Bolívar, 5008 m ASL) in the BONORlNO & TERUGGI 1952). These ventifacts so-called superpáramo (LAUER 1979). are part of the desert pavement so typical for the Two superficial miniature forms that may Andean aeolian periglacial environments. Rock be observed in these areas affected by the growth cavities caused by aeolian erosion and with some of needle ice and its pressure are gaps and participation of chemical weathering in their genesis miniature stripes. The gaps, or gaps around stones are called taffoni (see FRENCH 1988). (WASHBURN 1979), are little mounds produced These taffoni ar honeycomb forms are by needle ice and characterized by rocks that were stones with concavities produced by aeolian lifted by upheaval and are left in position. Posterior erosion (FRENCH 1988), usually in granitic to and frequently after this phenomenon a certain rocks. The erosion of sandstone in a periglacial

38 Revista do Instituto Geológico, São Paulo, 21 (1/2), 33-55, 2000.

en'vironment may produce mushroom shaped used this theory to explain the origin and the structures. AUER (1956) described mushrooms deposition of saridstone and loess sediments of the as relicts of sandstone for Tierra deI Fuego. In Pampean region up to the south of Brazil during the protected area ofLaguna deI Diamante (34°S, the dry episodes from IS4 onwards, considered to Cordillera Principal) some excellent examples of be the coldest episode of the last cycle (?). It still is erosion, particularly in tuff or pumice, may be difficult to trace back the provenance of the silt, observed. and the techniques for the exact identification of Another sediment of aeolian origin or of its genesis are somewhat limited. periglacial genesis is the covering debris (Deckschutt) in the so-called dells or periglacial 6 CHARACTERISTIC CRYOGENIC valleys, with a very important aeolian component. LANDSCAPES OF SOUTHERN SOUTH The covering debris represents a diagnosis of the ÀMERICA geoforms of cryogenic origino Cold loess is mentioned by HAMELIN & COOK (1967) 6.1 Mesas or sugar-Ioaves (HURLBERT & referring to the loess deposited in the surroundings CHANG 1988) of glaciers. Generally the loess consists mainly of

50 - 60 % silt « than 0.06 mm), 5 - 30% clay, and 5 Mesas are fIat mounds referring to - 10% sand. These values may vary by about 10%. Chilean - Bolivian perrnafrost areas (about 1 km 2) The most outstanding loess deposits of in relation with shallow saline high mountain the Southern Hemisphere are those of the lakes, as Laguna Colorada and Salar de Pujsa Pampean Plains. In comparison to other loess they (over 4000 m ASL) in the Desert Andes, which possess an important textural component of fine hide in their interior strata of pure ice, veinlets or sand and volcanic glass. These deposits consist frozen sediments. of 50% silt, 50% sand and reveal a high content They are found in areas with an active of volcanic ashes and pIagioclases. Predominant layer rich in clay and silt with calcite (eventual heavy mineraIs are hornblende, hypersthene, and thenardite), which enhances the strong reflection augite. These loess were assigned to an arid in isolation. The ice content varies between climate, but not as indicators of cold climates 10-87 %, with a thickness between 1 mm and 1 m. (TERUGGI 1957). The maximum thickness of the permafrost in this However, a loess profile located at Las area is assumed to be 25 m (GORBUNOV 1993) Carreras Valley, on the foot of the Cordón deI and the perrnafrost table lies between 20 and 70 cm. Plata, an eastern range of the Central Andes, in While HURLBERT & CHANG (1984, 1988) the province of Mendoza, Argentina, was dated believe them to be relicts forrn the Little Ice Age, with therrnoluminescence. It was assigned to the GORBUNOV (1993) thinks they are relicts from Middle Pleistocene and would express a cryomere the Late Pleistocene to Upper Holocene. -; of almost 200 ka that may be correlated with the conesponding glacial episode in the N orthern 6.2. Patterned ground Hemisphere. This fact identifies this profile as a key element for the Quaternary stratigraphy in Patterned ground is characterized by a South America. combination of processes with the intervention On the other hand it cannot be ruled out of frost heaving caused by needle ice, sorting, soil that for the silt-Ioess material from Patagonia creep, dehydration and thermal contraction (Camwy Formation, TROMBOTTO 1996) during caused by the action of freezing and thawing. the cryomeres or cold episodes, cryogenesis was According to WASHBURWs (1970) involved. As early as 1936 GROEBER pointed important classification, the most important forrns out an important cryogenic relation between cold of patterned ground in South America have been Andean environments and mechanical grouped into: nets, stripes, polygons and circles weathering. This author however, was looking for (Table 2). They may be distinguished by their an explanation of the old "Bonaerense" and the respective geometries. They are designated sorted Pampean Plains as well as for the sands called or unsorted according to their textural differences "Médano Invasor" (Invading Dunes). and the definition of shape. Recently this last theory was presented Nets (Fig. 5) or inegular shapes (Fig. 6) again by IRIONDO & KROHLING (1995). They without permafrost but closely linked to the

39 Revista do Instituto Geológico, São Paulo, 21 (1/2),33-55,2000.

problems of night frost according to TROLL (1944) appear in the Tropical Andes. As PÉREZ (1984) proved, the genesis of patterned ground in the mountains of Venezuela is influenced by solar radiation above all other factors.

FIGURE 6 - Sorted nets in transforrnation into stripe in sense of Büdel (1981), at the Lagunita deI Plata, Cordillera Frontal, Mendaza, Argentina, 4000 m ASL, ea. 33° S and ea. 69°W. Length af the measure: I m (Mareh 1996).

FIGURE 5 - Sorted nets and extrusion struetures, at the Andes (CORTE 1953). They are 10 to 30 cm wide, Lagunita deI Plata, Cordillera Frontal, Mendoza, and sometimes limited by other stripes with coarser Argentina, 4000 m ASL, ea. 33° S and ea. 69° W. material of similar size (sorted stripes). GRAF (1971) Diameter af the eamera lid: 5.4 em (Mareh 1996). mentioned giant stripes that occurred at elevations between 4800 and 4950 m in . Stripes combined The nets are usually of small size, in the with thermal contraction fissures are usually found range of a few centimeters, but under certain in the Central Andes of Mendoza with large and favourable conditions and with a more complex angular shaped clasts where the [me material is not genesis as in the Central Andes, they reach the hed out be melting water. At the Lagunita dei Plata, ranges of meters (Fig. 6). These shapes may also Argentina, the stripes are predominantly of be the result of cryoturbation. Desiccation fissures greywacke. They reveal, in thermal contraction also favour the formation of nets and there are fissures, a characteristic collapse fabric as the clasts cases of stripes combined with thermal contraction fall into the fissures with their main axes vertical1y cracks. oriented (TROMBOTTO 1991). For some time we have records of schist Stone polygons (Fig. 8) occur closely stripes in Peru (TROLL 1944) and in theArgentine related with dehydration of the soil during winter

Pattern AtAndesAraentinaLaguna"CordónArQentina,(340PáramoCentralperúPeruvian'}CordilleraPerúBolivia3800S),(110ofandAndesde0:ofmdeiPeru,AndesS)(Fia.PrincipalnearVenezuela.0:Aguascocha",3ArgentinaLocationsPlata",r 1.6of7)"CerroandMendoza,- 4.44000oftheMendoza,ReferencesTowardsdemCordilleram,(Fia.IaTROLLAHUMADATROMBOTTOGRAFSCHUBERTCORTE(1992)(1971),Argentina,Laguna"Mendoza,10)theat(1971)(1971),RealAHUMADA(1944)(1944),(1953)(1987,(1992)(1979),HASTENRATH(1991CORTE1992)(1987)PEREZ) (1953), po/ygonsstripeseire/esStrioesGiantSortedStrioes(0 =sehistdiameter)3.3000:(abovesouthinorocessesBolivia,510m-andm(Fias.sea25at4600alonaside340cm'(Fia.levei)5NetsSandand(015-206)8)5300the Andeanmcm)GiantStripesStoneNetsASlandchain.at At3.800330theS)mQU.ebrada0 and20 cmabovewithdel(01cryoturbatíonMatienzom) (3600 m,

TABLE 2 - South Ameriean Examples of Pattemed Ground

40 Revista do Instituto Geológico, São Paulo, 21 (1/2), 33-55, 2000.

FIGURE 8 - Sorted stone Polygons, Laguna dei Diamante, Central Andes, Mendoza, Argentina, 3220 m AS L, ea. 34° 10' S. Length of the' measure: 50 em. (Mareh 1995).

FIGURE 7 - Sorted stripes, Quebrada de Ias Bodegas ar Matienzo, Cardille)"a Principal, Mendoza, Argentina ca. 32° 40' S, 3700 fi ASL (March 1984). or with dehyclration of layers saturated with melting water provided by patches ar seasonal ice. FIGURE 9 - Unsorted polygons, Pampa de los Thermal contraction polygons (Fig. 9) are also Avestruees, Central Andes, Mendoza, 3600 m ASL, ea. frequently seen in the Central Andes. 34° 10' S. Length ofthe jaek-knife: 9 em (Mareh 1995). The type of sorted stone circles (Fig. 10) with a depression in the centre are also called Amundsenrings (TROMBOTTO 1991). Extrusion structures (, Frostbeule, ostiol) ar volcanoes (Figs. 6 and 11) are conical farms of fine sediments expelled by cryoturbation and cryostatic pressure in the substratum. They are frequently involved in the genesis of patterned ground. They may build micronets within circ1es ar stone polygons or else contribute directly to the cre'!tion of stonenets. During the thawing process these extrusion structures are flattened and they FIGURE 10 - Sorted eircles, at the Lagunita dei Plata, constitute isolated spots of fine material that Cordillera Frontal, Mendoza, Argentina, about resemble "cakes of sand or clay", which gave 4000 m ASL, ea. 33° S and ea. 69° W. Length of the arigin to the German name Erdkuchen apart from measure: 2 m (Mareh 1996). the term Frostbeule. They are frequently part of the sorted forms on the surface and they do not with fine material. The term nubbins was first used need permafrost. They are found very frequently to describe those forms in Northeast of Greenland. throughout the Andean Cordillera. For WASHBURN nubbins are associated The term nubbin (from middle low with the growth of needle ice inc1uding also German: knot on a tree, applied by WASHBURN Feinerdknospen, although Erdknospen in the 1979) reaches back to a medieval Germanic word Central Andes are defined as a result of extrusion for a round protuberance some times prolonged with intervention of cryoturbation (TROMBOTTO

41 RevistadoInstitutoGeológico,SãoPaulo,21 (1/2),33-55,2000.

FIGURE II - Nubbins at the Lagunita deI Plata, FIGURE 12- Solifluction sheet, Cerro Hermosovalley, Cordillera Frontal, Mendoza, Argentina, about San LorenzoNorte glacier,SouthemAndes,SantaCruz, 4000 m ASL, ca. 33° S and ca. 69° W. Argentina, 1095 m ASL, 47° 34' S and n° 13' W (December 1999). 1988). The mechanism of these structures is called subduction. It is explained by DYKE & ZOLTAl (1980) who calculate its movement to be less than 1 mm per year.

6.3 Solifluction fonns

The sIm" creep downhill of saturated soi!, caused by freezing and thawing in cryogenic regions is defined as solifluction. With permafrost it is called . Some characteristic Andean fonns are: FIGURE 13 - Solifluctioh lobes, detrital slopes and snow hollow at the Lagunita deI Plata, Cordillera Fron• • Solifluction sheets in the Central and Southem tal, Mendoza, Argentina, 4000 - 4500 m ASL, ca. 33° Andes (Fig. 12). They are observed on surfaces S. (December 1983). with little inclination. They create fonns interwoven or related with reliefs characterized by coarse with the fonnation of debris slopes. The rate of sediments. They may be observed on slopes of> 2°. movement of solifluction lobes in greywacke at A type of solifjuction layer with a reduced the Lagunita deI Plata ranged between 3 and 6 cm inclination angle contributes to the genesis of per year (1983 -1996). The maximum speed was pattemed ground or enhances solifluction contact. registered at an elevation of 4300 m (TROMBOTTO et aI. 1984, TROMBOTTO • Solifluction lobes (Fig. 13). They appear as 1991 ). protuberances ar tongues and may be identified on flanks of the slopes. Solifluction lobes may • Solifluction terraces frequent throughout the have terraced surfaces, rocky fronts and may have Andes. Solifluction terraces are relatively small• terraced surfaces, rocky fronts and may be sized, stepped solifluction fonns. They may appear combined with fissures provoked by the discharge combined with solifluction lobes and they do not of melting water at their frontal basis. ln this last require permafrost. ln the entire Andean region case the clasts are usually in vertical position. these forms are most abundant. They reveal a They are the classica1 product of vertical sorting with large quantities of fine macrosolifluction or slope solifluction as TROLL sediments. They appear in a _wide range of (1944) called it. The lobes may show a remarkable petrographical classes and with different vertical sorting on their most superficial parts. At inclination angles on the slopes. The most frequent the Cordón deI Plata, the lobes display angles slopes with terracettes in the area of the Lagunita between 28° and 29° mostly, with blocks between deI Plata, Cordón deI Plata vary between 12° and 30 and 40 cm on their surface and they are related 25°. A particular type was identified in the Central

42 Revista do Instituto Geológico, São Paulo, 21 (1/2), 33-55, 2000.

AMes (TROMBOTTO 1991) because of its plateaus (mesetas), and pattemed ground at the magnificence and because it is a geofarm that Meseta de Ia Muerte. appears in combination with snow patches. These giant forms, to be observed at the Lagunita deI • Rock streams (Fig. 15) were first described at Plata, display solifluction processes in great steps the early century by a Swedish expedition to the in combination with the influence of snow patches, Southern Andes and the Falkland lslands which persist for a long time in their frontal parts. (HOGBOM 1914).

• Garlands (Fig. 14), terracettes and steps are solifluction forms whose frontal parts are contained or marked by or stones.

FIGURE 15 - Roek streams, Cerro Hermoso valley, San LorenzoNorteglaeier,SouthemAndes,SantaCruz, Argentina, 1365 m ASL, 47° 34' S and 72° 13' W (Deeember '1999).

FIGURE 14 - Garlands, Laguna deI Diamante, Block tongues that move downhill by the 3300 m ASL, ea. 34° 10' S. Diameter of the eamera Iid: effect of solifluction characterize the periglacial 5.4 em (Mareh 1995). Andean leveI at different latitudes and elevations. Rock streams or stoneruns are a particular type Garlands do not require pennafrost. It is a fonn of of block tongues. creep stopped or restricted by vegetation with a The term kurum used in the Transbaikal generally terraced surface. They were described (ROMANOVSKIY et ai. 1989) applies to rock extensively until approximately 5000 m where nets, streams ar stoneruns whenever well-defined stripes and small stone polygons appear, as in the flows and detrital slopes or Schutthange may be Argentine Puna for example (lGARZÁBAL 1983). identified. These cover large extensions of the CORTE (1953) found garlands in Argentine, while slope surfaces. These are regional forms and they trying to explain cryopedological phenomena at the depend on altitude and the humidity regime in Pampa de los Avestruces at an elevation of 3500 m the active layer, in other words on cycles of (Mendoza). ln Peru GRAF (1971), found them at freezing and thawing. They move several mm per 4850 m at the ValleViscas (11° 35' S). In Chacaltaya, year. According to ROMANVOSKlY et aI. Cordillera Real in Bolivia, HASTENRATH (1971) (1989), they may be classified into: a) those registered them at 4500 m. created by basement rocks and b) those created ln the Southem Andes, GARLEFF (1977) reported by sedimentary sephitic rocks. solifluction farms combined with ar stopped by Wanderblocks ar ploughing blocks are vegetation in the region of the cold woods of blocks that had been uplifted by the ice which Araucaria and the subantarctic Magellan woods, slowly moves downhill due to solifluction. above the timberline, ar in the area of transition Sediments cover the side that is pushed. to periglacial soil (at Tronadar at 1500 m and at They are found in theAndean Cordillera the Fitz Roy at 1000 m approximately). even in areas with seasonal freezing. These authars also documented garlands in the Patagonian Sierras and the Patagonides, 6.4 Felsenmeer (block field, campo de bloques) Argentina, at about 1000 m in the Sierra de Tecka and in San Bemardo for example. At the same A superficiallayer of angular shattered time they mentioned lobes of blocks even with rocks farmed in either modem ar Pleistocene sorting for these elevations at the Patagonian periglacial environments (VAN EVERDINGEN

43 Revista do Instituto Geológico, São Paulo, 21 (1/2),33-55,2000.

1998). Felsenmeer are usually found on top of Andean cryoplanation suifaces (Fig. 16).

FIGURE 17 - Snow patches, cryoplanation surfaces, Laguna dei Diamante, Mendoza, Argentina, ca 3500 mASL, ca. 34° 10' S (February 19.95). FIGURE 16 - Felsenmeer at the Lagunita dei Plata, Mendoza, Argentina, ca. 4000 m ASL, ca. 33° S and ca. 69° W. The 10wer limit of perennia1 snow patches in the Andes of Mendoza (33°S) 1ies at 4300 m on the south-facing slopes. In the Southem BIGARELLA et a!. (1969) found out that Andes (38°S) however, these snow patches may certain fe1senmeer forms on the P1ateau of Itatiaia, be found in Argentina be10w e1evations of 2200 Brazi1 wou1d correspond to a semiarid and co1d m (GARLEFF 1977). The pressure and weight of episode of the P1eistocene. Other authors described the snow causes krummholz in Araucaria trees and these as a resu1t of "cryoturbations" together with Nothofagus that grow close to the tree1ine. the shaping of pediments (see BIGARELLA et a!. 1969). These relict forms ofItatiaia however rather 6.6 Cryop1anation surfaces seem to be re1ated with "bou1der streams" in the sense of MODENESI (1992) and CLAPPERTON The term cryoplanation, or EAKIN (1916) (1993) and the indirectly invo1ved perig1acia1 altiplanation, is used to exp1ain the combination of process wou1d correspond to the solifluction of phenomena, which create a cryogenic environrnent subjacent sedimentary 1eve1s. This former fact is of p1anation, cryop1anation ar a p1ain surface on very important and wou1d have to be analyzed with the summits of high mountain areas; cal1ed summit more detail, as it might represent the most northem surface in this 1ast case, or a in valleys and pa1eoclimatic limit of perig1acia1 phenomena on slopes, called cryoplanation terraces (Fig. 17). outside the Andes. They may reach a width of 250 m and a 1ength of 1 km, with a Quatemary cover of a thickness of up to 6.5 Nivation hollows 3 m (CZUDEK 1989). Among the most important processes are: Whether snow patches really react as a) the activity of snow patches or niva1 erosive agents in cryogenic environments and at phenomena, the snow-covered ground in mountain areas, b) cryoweathering, and without the participation of other factors, is c) solifluction, reinforcing the remova1 of the questioned by HALL (1998). Another possibi1ity cryosediment (DEMEK 1969). to consider in re1ation with Andean nivation hollows is that they can indicate climate Accurding to Suchodrovskiy's theory fluctuations as well as climatic changes. (1967,1979, see CZUDEK 1989) there wou1d be Seasonal or perennial snow patches are no general change caused by cryogenesis on the characteristic of the Andean 1andscapes (Figs. 13 slope, but rather an overprint processo This makes and 17). Snow patches seem to be strong1y us think of a pre-existing p1anation which for influenced by the E1 Nino / Southem Oscillation geo10gica1 reasons increases the erosion action, or ENSO phenomena and by snowfalls, in the whi1e the summit surface wou1d represent a final Cordillera as well as by the observed processes of state in a cycle of erosive states (CZUDEK 1989). a warming up climate. It cannot be ruled out that a surface of a cryogenic environment has a polygenetic origino

44 Revista do Instituto Geológico, São Paulo, 21 (1/2), 33-55, 2000.

Summit cryoplanation surfaces are closely related German Glatthang, pl. Glatthaenge). These are to Andean continuous permafrost. In the Andes of usualIy cut by the scars of snow avalanches and San Juan, Argentina (30° S) cryoplanation surfaces snow - debris avalanches and mudflows, which were taken as indicators of continuous permafrost, are characteristic of semi-arid periglacial with temperatures < - 4°C, at elevations over 5000 m environments in the Central Andes. GARLEFF by SCHOLL (1992). In the Southem Andes they (1977) described Glatthaenge for theAndes of San appear as low as 1590 m (approximately 46° S) in Juan, ValIe de Agua Negra, above 4500 m and to the area of Cerro Ap Iwan (GARLEFF 1977). the south. They have been reported in different Cryoplanation surfaces between slopes may favour parts of Mendoza, as for example in the area of the accumulation of cryoregolithe as a cryobasin the Laguna deI Diamante (>3300 m), where (Fig. 16), as in the cases of Mendoza, at almost STINGL & GARLEFF (1983) mapped these 4000 m (TROMBOTTO et aI. 1984). slopes. They studied the cryodynamics in the region of Cuyo and part of the Northwest region 6.7 Tor (felsburg) (HAMELIN & COOK, 1967) (NOA) in Argentina in search of the generating factor for this kind of slopes in this semiarid These are areas of incomplete mountain regions. The same authors emphasize cryoweathering closely linked with the structures the importance of the petrology of the Nevados of of the rocks and in particular with their degree of Famatina (29° S), with schists and quartzites, that fissility . According to the classification by help to form these slopes on the periglaciallevel above 4000 m. FRENCH (1988) the following tors may be ln Chile on the border with Perú, ABELE (1982) distinguished: 1) slope tors: located on the valIey sides and surrounded by slopes with a detrital analysed these phenomena and distinguished a cover, with inclination angles between 20° and 30°, type of gently inclined slope associated with the depending on the type of rock and 2) apical tors. cycles of freezing and thawing of another slope in The term Chalt (in aoniken, a Patagonian native the area of neblina (a misty altitudinallevel), where language) is used to describe a group of tors (Fig. the effect of the growth and hydration of the salt is observed. 4) with a shape of saw-tooth surface (R. Casamiquela, pers. comm., 1993), an example of this is the Cerro Fitz Roy. • Talus or talus cones (Fig. 18). GeneralIy great accumulations of angular shaped rocks and 6.8. Cryogenic slopes cryoregolithe of different sizes may be observed on the sides and feet of the mountains in cryogenic environments. These are created by the dynamics Due to the Andean periglacial of freezing, weathering and the contribution of morphodynamics the folIowing are the prevailing nivodetritic avalanches and are denominated talus. geoforrns on slopes: They belong to the phase that FRANCOU (1982) • Detrital slopes (Schutthaenge) of periglacial origin calIed d' eboulisation, that is the disintegration (Fig. 13) are of enorrnous hydrological importance caused by primary chutes or primary rockfalIs. for theAndean (TROMBOTTO 1991). These Many different types and combinations of this are slopes built by rocks and blocks of considerable phenomenon have been classified so far, according thickness and with an important percentage of to the changes in their genesis and according to embedded fine material or cryoregolithe, displaying their respective shapes: rockfall talus (for the falI creep or even other attached geoforrns. These slopes and accumulation of cryofragments), alluvial may contain interstitial ice or "cement ice", that talus, avalanche talus, etc. (RAPP 1959, WHITE cements rocks together and is of important 1981). hydrological value in the summer season. The FRANCOU (1984) points out that in granitic detrital slopes in the Lagunita deI Plata, Huamparcocha, Peru (12° S), above 4900 m, the Mendoza, display inclination angles of origin of the talus, apart from the exposition, is predominantly 29° to 34°, while those of the influenced by the petrographic characteristics of greywacke vary between 24° and 31°. andesites and ryolithes. These rocks, which in that region are also affected by intrusive igneous • Richter denudation slopes are wide and gentle material, are altered by tectonics and slopes (Fig. 17) with a relatively thin layer of hydortherrnalism (epidotisation), and seem to be cryofragmented rocks. Also glatthang (from

45 Revista do Instituto Geológico, São Paulo, 21 (1/2), 33-55, 2000.

FIGURE 18- Protalus and talus roek glaeier at Strelkov FIGURE J9 - Grezes litées. Portillo Argentino, Eastem glaeier valley, CerroEl Plata (6310 mASL), Cordillera slope, Mendoza, Argentina, about 3800 m ASL. Frontal, Mendoza, Argentina (Mareh 1996). Diameter of the eamera Jid: 5.4 em (Mare~ 1997). easily attacked by cryoweathering. Similar Andes. For decades their enormous hydrological conditions, with intrusives, tectonics and value for the Central Andes has been pointed out metamorphism were also determined as important (CORTE 1976, BUK 1983). factors for the genesis of periglacial forms at the Through the open system of the active Lagunita deI Plata, Mendoza (TROMBOTTO layer a water storage is produced, which maintains 1991). the geocryological balance. The solid precipitation (snow) that penetrates the active layer and the • Protalus ramparts. Protalus ramparts are freezing of the latter creates the system of water particular sedimentary forms associated with snow storage in high mountains areas. In the summer patches in postfrontal depressions, attached to the season the active layer is thawing and the discharge lateral mountain slopes on which rocks slide down of the rivers increases. Thawing, summer and accumulate at their fronts. In the Central Andes snowfalls and the lowering of the permafrost table they are very well represented and are often to greater depths, caused by the warming process interpreted as embryonic states of a type of rock of the last decades, establish a direct relation glacier. between the behaviour of temperatures on rock A transversal cut into periglacial slopes glacier surfaces and the discharge of the Andean and valleys may frequently reveal grezes litées (Fig. rivers. Frozen areas, with permafrost or debris• 19) as in theAndes ofMendoza. Their genesis needs covered ice in the Central Andes, as well as in to be studied more thoroughly. They consist of other SouthAmerican cryogenic regions constitute altering sedimentary layers, granulometrically therefore more important water suppJies than different from one another. The main axes of their glacier regions. clasts are orientated slope downwards. In the tropical Andes rock glaciers appear TROMBOTTO (1991) presented supranival and from 20° S onwards, associated with the ennival (from the upper part or from the interior of periglacial levei located at 4500 m and above a snow patch) as possible genesis of some structures (FRANCOU 1984). Francou and his colleagues on the periglacial slopes of the Andes of Mendoza. have been studying the Cerro Caquella Debris slopes and relict grezes litées are in Bolivia as indicator of climate variability abundant in the Cuyo region of Argentina, below (1999). In Argentina the first reference of rock and c10se to the present periglaciallevel, but would glaciers would be the publication by CATALANO still have to be mapped in detail. (1926), who called them litoglaciares and describes them for the Puna region. 6.9 Rock glaciers The glaciers of the Central Andes often culminate in detrital or morainic tongues that Rock glaciers are cryogenic lobular or actually represent debris-covered glaciers. Following the c1assification by BARSCH (1969) tongue-shaped mesoforms expressing the plastic these forms were designated in general debris rock deformation and creeping of mountain permafrost (see BARSCH 1969, 1977; CORTE 1976). They glaciers (Figs. 20 and 21) in order to distinguish them from the ones of exc1usively cryogenic origin are certainly the most important geoforms of the

46 Revista do Instituto Geológico, São Paulo, 21 (1/2), 33-55, 2000. or the so-called talus rock glaciers (Fig. 18). San Juan, Central Andes, Argentina. They surpass CORTE (1987) later presented a very complex 30°C (TROMBOTTO 1991, SCHROTT 1994). taxonomy incIuding other geoforms. At the same time a correlation between global radiation and daily soil temperature variations was observed to depths of 1 m (HAPPOLDT & SCHROTT 1989). Adetailed study by SCHROTT (1994) sustains that the appearance of permafrost is mainly related to the. energetic balance determined by high solar radiation (20,6 and 22,3 MJ m2 d·I). A shadowed spot with extremely low radiation would explain atypical permafrost (e.g. at low elevations, SCHROTT 1999). In the northern Chilean Andes, and within the region of the South American Arid Diagonal between 24° and 27°S, Swiss colleagues FIGURE 20 - Nose of the debris rock glacier Morenas Coloradas, Cordón deI Plata, Mendoza, Argentina, (KAMMER et aI. 1999) mapped rock glaciers with ca. 3560 m ASL, 32° 58' S and 69° 21' W (November great precision resulting in diagnostic parameters 1999). for their activity and defined their disappearance as active geoforms at a precipitation regime of :S;175 mm. Rock glaciers in the Central Andes, Argentina, show signs of activity even at MAAT of O°C at elevations of 3700-3800 m and mean annual precipitations around 500 - 600 mm. The rock glacier El Salto for example has permafrost at an elevation of 3600 m (BARSCH & KING 1989) and at Morenas Coloradas, a rock glacier of glacigenic origin, the permafrost limit reaches down to even 3400 m. These last

FIGURE 21 - Debris rock glacier Morenas Coloradas, conditions seem to be related to the dry cIimate Cordón deI Plata, Mendoza, Argentina, 32° 58' S and and the global energetic balance of periglacial 69° 21' W (November 1999). environments in the Central Andes, factors which increase the efficiency and the radius of influence The embryonic forms of talus and of cryogenic phenomena to lower elevations. cryogenic slopes (Fig. 18) fed with material from Dryness, the global energy balal}ce and nivodetritic avalanches and indications of regional atypical phenomena coincide with what movement were termed protalus or embryonic LLIBOUTRY (1986) observed for the major rock rock glaciers (TROMBOTTO 1991) glaciers in Chile, towards 33° S with signs of activity In the Central Andes and down to 3200 m down to 3500 m and temperatures of 1 to 2° C. the rock glaciers may have ice and be inactive, Among the few existing measurements but below 3000 m they are considered fossil and of rock glacier movement in·South America, there dose to this elevation they were only active during are the ones made by MARANGUNIC (1976) the Würm (BARSCH & HAPPOLDT 1985). who calculated the rate on the margins of the rock It has to be mentioned again that the air glacier El Pedregoso, in Chile, at 3700 m at temperature is usually in certain disharmony with approximately 32° S, to be llcm / year. This rock the soil temperature profile, resulting from a very glacier has a surface of 0,3 km2 and a summer particular thermal balance according to the discharge of 4-9 l/sec. radiation, orientation, constitution of the rocks, and The case of the Dos Lenguas rock glacier origin of the ice being among the most important in San Juan, Argentina, at 30° S is similar. It has a factors. similar surface and a discharge of 5-8 l/sec. High surface temperatures, between air (SCHROTT 1994). Schrott thinks that the upper and soil, as well as their evolution with depth, were basin of Agua Negra, where the Dos Lenguas is registered in the periglaciallevel of Mendoza and located, with 2 km2 of rock glaciers in total, may

47 Revista do Instituto Geológico, São Paulo, 21 (1/2),33-55,2000. oause a discharge of up to 50 l/seco On the other hand the Morenas Coloradas basin with perrnafrost and rock glaciers generates the discharge of the Vallecitos river with 505 1/sec., which is of vital importance to water supply of Mendoza. This study of periglacial hydrology is of strategic importance for the near future.

6.10 Asymmetrical valleys

Another typical characteristic of FIGURE 22 - Mallín, Turbera deI Yaucha, Central An• periglacial environments are the asymmetrical des, Mendoza, Argentina 3155 m ASL, ca. 34° 10' S valleys. In the Southem Hemisphere north-facing (December 1996). periglacial slopes are warmer and less steep with a major frequency of freezing and thawing cycles An environment of the - ar and more solifluction than the south-facing slopes. The south-facing slopes are colder, steeper and peatland type ~ is produced by the have rougher surfaces. existence of an aquatic environment, for example Periglacial saucer-shaped valleys, dells, close to mountain springs, streamlets or riverbeds many of which are asymmetrical, are characteristic ariginated by the thawing of the altitudinal geoforms of an Andean periglacial environment. cryogenic leveI soil, when the water has difficulties They may also be identified by their covering with to percolate or to drain as it encounters imperrneable solifluction sediments (see SEMMEL 1985). sedimentary beds (e.g. glacial sediments, volcanic GARLEFF et ai. (1989) made a detailed ashes etc.). inventory of fossil dells for the geomorphological Geomorphologically speaking, two main map: LaJunta-AguaNueva, where they interpreted types of anmoors or mallines are found: one in morphodynamic and paleoclimatic changes in the the valleys and one on mountain slopes. They area bordering the Andes (350 S). occur at the leveI thatAMBROSETTI et ai. (1986) called altoandean levei, or Andean tundra (see 7 PERIGLACIAL PRESENCE ON THE TROMBOTTO 1991). PEATLANDS These environments favour the growth of diverse vegetation, saturated with water and accumulated vertically, as the layers are not Many of the Andean peatlands of southem completely degraded, thus creating peatlands or South America represent the environment of a moa r very important organic in this way. The cold or anmoor, depending on their content of organic temperatures have an essential role in slowing material. In the Central Andes the peatlands down processes of the organic usually have a genesis similar to that of a material. Seasonal cryogenesis acts as a generator minerotrophic feno of thufurlike seasonal freezing forms, in the The inhabitants of such peatland environments of the Central Andes as well as in environments (Fig. 22) in certain Andean the environments of the Argentine-Chilean South subtropical regions and Patagonian call their (e.g. continental peatlands with the genus Carex mallín or vega (anmoors). These mallines and Caltha, ROlG et ai. 1985). Thufurs (Fig. 23), (plural) are also designated as humid or swampy which often appear in association with the prairies (BOELCKE 1957). They frequently periglacial phenomena, have been widely ignored border the basalt plateaus of Patagonia. These by researchers. mallines or moors are of great importance in In the area of Última Esperanza in the Geocryology as far as their present seasonal Magellan region in the south of Chile and in TieITa freezing is concemed and because many of these deI Fuego and the Andean woods in Argentina, environments are remnant ecosystems that were the moors however, are closely linked with high created as the Pleistocene ice retreated. They are precipitations and with characteristics cOITesponding also old areas associated with paleopermafrost e.g. to moors. ROlVAINEN (1954) with a paleoperiglacial environment.

48 Revista do Instituto Geológico, São Paulo, 21 (112),33-55,2000.

FIGURE 23 - Thúfur, San Lorenzo Este glacier, Río FIGURE 24 - Thermokarst, Morenas Coloradas rock Lácteo valley, Southem Andes, Santa Cruz, Argentina, glacier, Cordón dei Plata, Mendoza, Argentina, ca. 1000 mASL, ca. 47° 37' S and 72° 12' W. Length of 4100 m ASL (November 1999). the spade: 6S cm, (December 1999). appear dry or with lakes which freeze or thaw made an important classification of moors in Tierra according to meteorologica1 annual variations. deI Fuego. The characteristic moor with Another phenomenon revealing magellanicum (white moor) of Tierra deI Fuego permafrost degradation is the occurrence of is just one example. mudflows, which represent sudden movements of In the context of the works on the soil, a form of natural disasters. "Botanical Transect of Southern Patagonia" (BOELKE et a!. 1985) Roig added an ecological 9 PAST CRYOGENIC ENVIRONMENT component to the environmental concept of the AND PALEOPERMAFROST peatlands in southern South America by incorporating them into the so-called tundra Outstanding fóssil cryogenic structures ecosystem. ROIG (1984) reported permafrost at in southern South America during the Last an elevation of 900 m and at a depth 30 - 40 cm Glacial (LG) and according to various authors may and poorly developed polygonal soil structures on be observed on the accompanying map (Fig. 25). the tundra called xeric Andean tundra. The influence of the periglacial environment during the Pleistocene seems to have reached even 8 FORMS OF DEGRADATION IN into Brazil, participating in the evolution of slopes CRYOGENIC ENVIRONMENTS and leaving behind relict talus, signs of solifluction and freezing. No signs of permafrost CORTE (1980, 1997) ana1ysed are observed, as at the p1ateau of ltiatiaia fnOS), thermokarsts (Fig. 24) or cavities caused by a region with mountains over 2700 m subsidence or thawing. Here the ice began to (MODENESI 1992, MODENESI-GAUTTIERI disappear and the isotherm of 0° C raised, or facies & TOLEDO 1996, MODENESI-GAUTTIERI & of thermokarst, in debris rock glaciers in NUNES 1998). Mendoza. A degradation phase was suggested by KEIDEL (1922) described debris slopes and FRANCOU et ai. (1999) for the tropical rock summit peniplains in the Puna region (Argentina) glacier Caquella in Bolivia based on low and made first assumptions about c01d episodes apparent resistivity in the geoe1ectric soundings. in the past. CZAJKA (1955), later stated that the This topic is a1most unexplored in South rock glaciers reached down to approximately America. According to TROMBOTTO et ai. 2600 m in the Nevados deI Aconquija (NW Ar• (1997, 1999; compare BARSCH & KING 1989) gentina) at approximately 27° S and 66° W. The not only has the active layer deepened in the last same author (1957) also reported fossil rock 20 years, but also the isotherm of 0° C ascended glaciers in the Sierra de Ia Ventana (Province of altitudinally up to 3860 m at 33° S in the last Buenos Aires), at 38° S and 62°W and made one decade. A thermokarst area of the rock glacier of the first paleoclimatic deductions about Morenas Coloradas, Mendoza (at 4000 - 41 00 m) cryogenic forms and phenomena in Patagonia. does not reveal any visible permafrost occurrence He considered a sequence of climatic denudation but does reveal the original forms that today cycles, with tundra - 10ess phase during the

49 Revista do Instituto Geológico, São Paulo, 21 (1/2), 33-55, 2000.

Pleniglacial for example, when enormous Andes - Lake Region - North Patagonia (Argen• networks of Patagonian ice wedges were created. tina) and to 1000 m in the Northwest Argentina. GARLEFF & STINGL (1986) believe that the The authors consider a difference of the MAAT approximately continuous permafrost leveI between the present and the LG of 15°C in the descended down to 2500 m in the Southem Central first case, and until 9 °C and together with less

ARGENTINA

T Ice VVedge casts ~ Fossil Rock Giaclers Ú Head * Cryoturbation Forms  Relicts Rellcts Fossif Patterned Ground Cryoplanation Surfaces Felsenmeer and Stoneruns EB Oriented Lakes

~Km

FIGURE 25 - Finiglacial in Patagonia with registered cryogenic structures and forms assigned to the Last Glaciation Maximum (20 ka) according to different authors. Paleocryogenic sites on the map: (1) Malvinas, Falkland Islands; (3) Pampa dei Castillo, Holdich; (6) Río Santa Cruz; (7) Tres Lagos, Río Chalía; (10) Sierra de Ia Ventana; (11) Lago Cardiel; (12) Chimen Aike, Río Gallegos; (13) Río Deseado; (27) Las Heras (North); (28) Cerro Kensel; (30) Río Santa Cruz and Río Deseado; (31) Lago Cami; (32) Meseta El Pedrero, Region of the Meseta de Ias Lagunas Sin Fondo; (33) Romberg; (35) Puerto San Julián; (36) Telken.

50 Revista do Instituto Geológico, São Paulo, 21 (1/2), 33-55, 2000. than 50% of today's precipitation in the second Tucumán. Doctor thesis (unpublished), case. These conditions must have considerably 208 pp .. affected and stopped the cryogenic activity in the - 1992. Periglacial Climatic Conditions and South American Arid DiagonaI. Vertical Form Associations in Quebrada The Patagonian epigenetic BenjaIlÚn Matienzo, Mendoza, Argentina. casts were mentioned by AUER (1956, 1970), Permafrost and Periglacial Processes 3 (3) CZAJKA (1955, 1957) and CORTE (1967, : 221 - 224. 1997). Syngenetic ice wedge casts were recently AMBROSETTI, J.; DEL VITO, L. ; ROIG, F. mentioned by TROMBOTTO (1996). Based on 1986. La vegetación deI Paso de Uspallata, the epigenetic and syngenetic ice wedge casts the Provincia de Mendoza, Argentina. extent of permafrost during the Pleistocene Age Geobotanisches Institut ETH, Stiftung up to the rivers Río Negro and Río Colorado could Rübel, 91: 141-180. be estimated. The difference of the MAAT between present temperatures and those during the LG is ANDERSSON, J. 1906. Solifluction a co.mponent about 140 C for South Patagonia (TROMBOTTO of subaerial denudation. Journal of 1994). Geology, 14: 91-112. The Falkland Islands express the ANGELINI, U. 1990. Diseno estructural de characteristics of the past periglacial maritime caminos sometidos a Ia acción deI climate. On the Falkland Islands ANDERSSON congelamiento. Regionalización deI (1906) was one of the first scientists to mention Método. Dirección de Ingeniería Vial, solifluction, introducing the term intemationally. Ministerio de EconoIlÚa, Chubut, 56 pp. Fossil periglacial geomorphology of the maritime AUER, V. 1956. The Pleistocene of type was analysed by CLARK (1972). The islands Fuego-Patagonia. Part I: The Ice and offer a great variety of cryogenic fossil forms: Interglacial Ages. Annales Academiae cryoplanation surfaces, tors, nivation hollows, ice Scientiarum Fennicae 3(45): 226. wedge casts, felsenmeer and the famous stoneruns - 1970. The Pleistoéene of Fuego-Patagonia. or blockstroeme. Part V: Quatemary Problems of Southem Recently various authors (CORTE 1991; South America. Annales Academiae TROMBOTTO 1994, 1998; TROMBOTTO & Scientiarum Fennicae 3(100): 194. AHUMADA 1995) classified paleogeocryology under climato-stratigraphical cri teria. BARANOV, I.YA. 1964. PrincipIes of CLAPPERTON (1993) and TROMBOTTO Geocryology. National Research Council of (1996) give abundant bibliographical references , Technical Translation 1121: 85 pp. on this topic for South America, particularIy since BARSCH, D. 1969. Studien und Messungen an 1980 for Argentina. Blockg1etschem in Macun, Unterepgadin. Zeitschriftfür Geomorphologie (SuppI.) 8: 10 ACKNOWLEDGEMENTS 11-30. I would like to thank Sabine Herfert for - 1977. A1piner Permafrost - ein Beitrag zur the translation of the manuscript, Dr. Jerry Brown Verbreitung, zum Charakter und zu for his comments and the improvement of the Oko1ogie am Beispie1 der Schweizer English, and Daniel Duenas for his collaboration A1pen. ln: H. POSER (Hrsg.) Formen, with the maps. Formengesellschaften und Untergrenzen in den heutigen perig1azia1en Hohenstufen 11 REFERENCES der Hochgebirge Europas und Afrikas zwischen Arktis und Áquator. Gottingen, p.118-141. ABELE, G. 1982. Geomorphologische und hygrische Hohenzonierung des -; HAPPOLDT, H. 1985. Blockgletscherung Andenwestabfalls im peruanisch• und holozane Hohenstufeng1iederung in chilenischen Grenzgebiet. Erdkunde 82 den mendozinischen Anden, Argentinien. (4): 266-278. Zentralblattes für Geologie und Palêiontologie. 1(11/12): 1625-1632. AHUMADA, A.-L. 1987. Procesos Criogénicos y Mineralógicos. Universidad Nacional de -; KING, L. 1989. Origin and geoelectrical

51 Revista do Instituto Geológico, São Paulo, 21 (1/2),33-55,2000.

resistivity of rockglaciers in semi-arid de crioturbación pleistocénicas fósiles en subtropical mountains (Andes de Mendoza, Ia provincia de Santa Cruz. Terceras Argentina). Zeitschrift für Jornadas Geológicas Argentinas, p. 9 - 19. Geomorphologie. N.E 33 (2): 151-163. - 1976. Rock Glaciers. BIGARELLA, 1.; MOUSINHO, M. ; XAVIER 26: 175-197. DA SILVA, 1. 1969. Processes and -1980. Glaciers and glaciolithic systems ofthe Environments of the Brazilian Quaternary. Central Andes. World Glacier Inventory, In: T.L. Péwé (Edit.)The Periglacial Proceedings of the Riederalp Workshop, Environment, McGill-Queen's University IAHS-AISH Publ. 126: 11-24. Press, Montreal, p. 417 - 487. 1983. Los conceptos: geocriogénico • BOELCKE, 0.1957. Comunidades herbáceas deI parageocriogénico y glacial - paraglacial norte de Ia Patagonia y sus relaciones con en los Andes Centrales de Argentina, latitud Ia ganadería. Revista de lnvestigaciones 30°. Acta Geocriogénica 1: 48-6). Agrícolas 11 (1): 5-98. -1987. Rock glacier taxonomy.ln: 1. Giardino, -; MOORE, D. M. ; ROIG, EA. (Edit.). 1985. 1. Shroder Jr. & J. Vitek (Edits.): Rock Transecta Botánica de Ia Patagonia Austral. Glaciers. Allen and Unwin, Winchester, p. Instituto Salesiano de Artes Gráficas, 27-39. Buenos Aires, 733 pp. - 1991. Chronostratigraphic Correlations of BUK, E. 1983. Glaciares de Escombros y su Cryogenic and Glacigenic Episodes in Significación Hidrológica. Acta Central Andes and Patagonia. Permafrost Geocriogénica 1: 22-38 and Periglacial Processes 2 (1): 67 - 70. - 1992. Índice y frecuencia de congelamiento - 1997. Geocriología. El Frío en Ia Tierra. en Patagonia y región cordillerana Ediciones Culturales de Mendoza, Fundar pedemontana. Workshop Nacional Editorial Gráfica, 398 pp. "Geocriología y Paleoclima CZAJKA, W. 1955. Rezente und pleistozane Nordpatagónico", Puerto Madryn, 8 pp. Verbreitung und Typen des periglazialen CATALANO, L. 1926. Contribución aI Denudationszyklus in Argentinien. Acta conocimiento de los fenómenos geofísicos Geographica 14, 10: 121 - 140. atmosféricos. Buenos Aires: Dirección 1957. Die Reichweite der pleistozanen General de Minas, Geología e Hidrología" Vereisung Patagoniens. Geologische m __ 78 pp. (Publicación 24). CZUDEK, T. 1989. Kryoplanationsterrassen im CLAPPERTON, C. 1993. Quaternary Geology rezenten Dauerfrostboden. Acta and Geomorphology of South America. Scientiarum Naturalium Academiae Elsevier, Amsterdam, 779 pp. Scientiarum Bohemoslovacae Brno, Nova CLARK, R. 1972. Periglacial Landforms and Series 23(8): 41 pp. Landscapes in the Falkland Islands. DEMEK, J. 1969. Cryogene Processes and the Biuletyn Peryglacjalny 21: 33 - 50. Development of Cryoplanation Terraces. CORTE, A. 1953. Contribución a Ia Morfología Biuletyn Peryglacjalny 18: 115-125. Periglacial de Ia Alta Cordillera con DYKE, A. ; ZOLTAI, S. C. 1980. Radiocarbon• Especial Mención deI Aspecto Dated Mudboils, central Canadian Arctic. Criopedológico. Anales deI Departamento Scientific and Technical Notes in Current de Investigaciones Científicas, 1(2): 54pp. Research, Part B, Geological Survey of - 1962 a. The frost behaviour of soils I: Vertical Canada, Paper 80-lB: 271 - 275. sorting. Highway Research Board, Bulletin EAKIN, H. 1916.The Yukon-KoyurukregionAlaska. 317: 9-34 U.S.Geological Survey Bulletin, 631 p. 1962 b. The frost behaviour of soils 11: FRANCQU, B. 1982. Chutes de pierres et Horizontal sorting. Highway Research éboulisation dans les parois de l'étage Board, Bulletin 331: 46-66. périglaciaire. Revue de Géographie Alpine 1967. Informe preliminar deI progreso 70 (3): 279-300. efectuado en el estudio de Ias estructuras - 1984. Données préliminaires pour l'étude des

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Ia estructura deI paisaje de los Andes dades Vegetales de Ia Transecta Botánica Tropica1es. In: M.L. Salgado-Labouriau de Ia Pafagonia Austral. Primera Parte. La (Edit.) E1 Medio Ambiente Páramo, Cen• Vegetación deI Area Continental. In: O. tro de Estudios Avanzados, Editorial Arte, Boe1cke.; D.M. Moore; F.A. Roig (Edits.) Caracas, p. 29-43. Transecta Botánica de Ia Patagonia Aus• tral. Instituto Sa1esiano de Artes Gráficas, LLIBOUTRY, L. 1986. Rock glaciers in the . Data of G1aciological Studies, Buenos Aires, p. 350-519. Moscow, p. 139-144 (Publication 58). ROIVAlNEN, H.; 1954. Studien über die Moore Feuerlands. Annales Botanici Societatis MARANGUNIC, C. 1976. EI G1aciar de Roca EI Pedregoso, Río Colorado, V Región. In: Zoologicae Botanicae "Vanamo" 28 (2), CONGRESO GEOLÓGICO CHILENO, 205 pp. 1, Santiago, Actas: D71-D80. ROMANOSVSKIY, N.; TJURIN, A.; SERGEEV, MODENESI, M. 1992. Depósitos de Vertente e D.; AFONSKAIA, L.;BOIJ~OV, S.; VOLKOVA, v.; VOLCHENKOV, S.; Evolução Quaternária do Planalto do Itatiaia. Revista do Instituto Geológico 13 ZAIJTZEV, v.; KLIMOV, 1.; LISITZINA, O.; SOLOVEV, V. ; JAVELOV, A. 1989. (1): 31 - 46. Kurums de Go1zi en e1cinturón montafíés. MODENESI-GAUTTIERI, M.C. ; MOTTA DE (Traducido deI ruso). Academia de TOLEDO, M.C. 1996. Weathering and the Ciencias, Sección Siberiana, Novosibirsk: formation of hillslope deposits in the tro• 152 pp. pical high1ands of Itatiaia - southeastern Brazil. Catena 27: 81 - 103. SCHOLL, K.H. 1992. Geomorphologische Kartierung im Einzugsgebiet des oberen NUNES, M.C. 1998. Processos Geo• Agua Negra, cuyanische Hochkordillere, criogênicos Quaternários nas Cimeiras da Argentinien. Trabajo Final, 81 pp., Mantiqueira, com considerações climáti• Universitat Heide1berg (unpublished). cas. Revista do Instituto Geológico 19 (1/ SCHROTT, L. 1994. Die Solarstrahlung aIs 2): 19 - 30. steuernder Faktor im Geosystem der NAUK AKADEMIJA. 1960. Fundamental subtropischen semiariden Hochanden concepts and terms in geocryology. (Agua Negra, San Juan, Argentinien). Permafrost studies, Corps of Engineers, Heidelberger Geographischen Arbeiten, U.S.Army, Translation 28. (94): 199 pp. PÉREZ, F. 1984. Striated soil in anAndean paramo 1999. Typische und atypische of Venezuela: its origin and orientation. Permafrostvorkommen - Klimatische Arctic and Alpine Research 16 (3): 277• 289. Bedingungen, geomorphológische Indikatoren und Prospektionmethoden. In 1992. 6. Miniature Sorted Stripes in the B.M.Méise1er; R. Molenda (Hrsg.), Páramo de Piedras Blancas (Venezuelan Lebensraum Blockha1de, p. 13 -26. Andes). In: J. Dixon & A. Abrahams SCHUBERT, C. 1979. La zona deI Páramo: (Edits.) Periglacia1 Geomorpho1ogy, John Morfo1ogía glacial y perig1acial de los An• Wiley and Sons, p. 125-157. des de Venezue1a. In: EI Medio Ambiente RAPP, A. 1959. Ava1anche Bou1der Tongues in Páramo, M.L. Salgado - Labouriau (Edit.), Lappland. Geografiska Annaler 41: 34 • Centro de Estudios Avanzados, Editorial 48. Arte, Caracas, p. 11-23. ROIG, F. A. 1984. La Tundra Argentino-Chilena SEMMEL, A. 1985. Perig1azialmorpho1ogie. entre los paralelos 51° y 56° de Ertrage der Forschung. Darmstadt, latitud sur. Acta Geocriogénica 2: 174-196. Wissenschaft1iche B uchgesellschaft - 1986. Tundra y tundrización en el SW de San• Darmstadt, 116 pp. ta Cruz, Argentina. Acta Geocriogénica 4: STlNGL, H. ; GARLEFF, K. 1983. 129-140. Beobachtungen zur Hang- und -; ANCHORENA, l; DOLLENZ, O.; FAGGI, Wandentwick1ung in der Periglazia1stufe A.M. ; MÉNDEZ, E. 1985. Las Comuni- der subtropisch-semiariden Hochanden Revista do Instituto Geológico, São Paulo, 21 (1/2),33-55,2000.

Argentiniens. In: Poser U. Schunke (Hrsg), Central Andes, Argentina. Permafrost and Mesoformen des Reliefs im heutigen Periglaáal Processes 8: 123 -129. Periglazialraum, Abhandlungen der ----; ----- ; ---- 1999. Rock glaciers in the Akademie der Wissenschaften in Southern Central Andes (app.33° S.L.). Gottingen, Dritte Folge, 35: 119-213. Mendoza, Argentina: a review. TERUGGI, M. 1957. The Nature and Origin of Bamberger Geographische Schriften Argentine Loess. Journal of Sedimentary 19:145-173. Petrology 27 (3): 322-332. - ; -; CORVALÁN, J. ; HERNÁNDEZ, J. TROLL, C. 1944. StrukturbOden, Solifluktion und 1998. Present state of measurements of Frostklimate der Erde. Geologische cryogenic processes in the Lagunita deI Rundschau 34: 545-694. Plata, Mendoza, Argentina. Yellowknife, TROMBOTTO, D. 1988. Geocryogenic INTERNATIONAL CONFERENCE ON Geomorphology, East Flank of the Andes PERMAFROST, 7, Program, Abstracts and Mendoza, at 33° S. INTERNATIONAL IPA Reports, p. 200-201. . CONFERENCE ON PERMAFROST, 5, -; - ; REGAIRAZ, M.C. 2000. Preliminary Trondheim, Proceedings 1: 263-267. studies of a loess from Middle Pleistocene -- 1991. Untersuchungen zum periglazialen in the piedemont ofMendoza-Argentina at Formenschatz und zu periglazialen 33°S. In: IUGS, INTERNATIONAL Sedimenten in der Lagunita deI Plata, GEOLOGICAL CONGRESS, 31, Rio de Mendoza, Argentinien. Heidelberger Janeiro, Abstracts Volume [CD - ROM). Geographische Arbeiten (90): 171 pp. VAN EVERDINGEN, R. O. (Edit.). 1998. Multi• - 1994. El Permafrost Patagónico Pasado. Re• Language Glossary of Permafrost and vista deI Museo de Historia Natural de San Related Ground-Ice terms. University Rafael12 (4): 229-249. Printing Services of The University of Calgary. 1996. The Old Cryogenic Structures of N orthern Patagonia: The Cryomere VOGT, T. ; CORTE, A. 1996. Secondary Penfordd. Zeitschriftfür Geomorphologie precipitates in Pleistocene and present N.F. 40 (3): 385-399 cryogenic environments (Mendoza Precordillera, Argentina, Transbaikalia, 1998. Palaeo- Permafrost in Patagonia. and Seymour Island, Antarctica). Bamberger Geographische Schriften, 15: 133 - 148. Sedimentology 43: 53-64. - ; LENZANO, L. ; BRUCE, R. 1984. Estudios WASHBURN, A.L. 1970. An Approach to a Genetic Classification of Patterned periglaciales (geocriogénicos) en Ia Ground. Acta Geographica Lodzienha 24: Lagunita deI Plata. Acta Geocriogénica 2: 437 - 446. 232 - 245. AHUMADA A.L. 1995. Análisis de - 1979. Geocryology. E. Amold, London, 406 estructuras sedimentarias en los "Rodados pp. Patagónicos" causadas por Ia presencia deI WEISE, O. 1983. Das Periglazial. Gebrüder permafrost en el criómero Penfordd, Puerto Borntraeger, Berlin - -Stuttgart, 199 pp. Madryn, Nordpatagonia. Revista Chilena WHITE, S. 1981. Alpine mass movement forms de Historia Natural 68: 79 - 91. (noncatastrophic): classification, BUK., E. ; HERNÁNDEZ, J. 1997. description, and significance. Arctic and Monitoring of Mountain Permafrost in the Alpine Research 13 (2): 127-137.

Author's address: Dario Trombotto - Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA - CONICET), Bajada deI Cerro s/n, CC 330, 5500 Mendoza, Argentina. E-mail: [email protected]

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