Gco.f!r. Fis, Dl nant, Qu al., 7 (198-/), 41-48, 9fj:

FRANCO FORCELLA (*) & GIUSEPPE OROMBELLI (**)

HOLOCENE SLOPE DEFORMATIONS IN , CENTRAL , (***)

ABSTRACT : FORCELLA F . & O ROMB ELLI G ., Holocene Slope In qu esto caso tuttavia la relati va un iforrnita delle graciture Deformations in Valfurva} Central Alps} I taly (IT ISSN 0084 ­ dei piani di discontin uita verso NE, indipendente dalla local e 8948, 1984 ). or ien tazione ed espos izione del .pendio, il movimento per incre­ men ti successivi accertato lungo una di tali superfici, la di str i­ For ms and str uctures recognized on both sides of th e Val­ bu zione area le di tali strutture, che formano una fascia allun­ furva Valley (Ce ntra l Alps, Italy ) are here described. They are indi­ gata in direzion e W NW-ESE parallela all'a sse dell a VaIfurva, cative of H olocene slope deformati ons and are represented by: suggeriscono che la fenomenologia presente possa essere sta ta 1) discontin uous sequences and sheaves of uphill-facing scarps; contro llata da deformazion i tettoni che recenti inquadrabili nel 2) downhill-facing scarps; 3) ope n tension cracks, furrows and campo di stress che det ermina l'att uale evoluzione neot ettonic a trenches. Up hill-facing scarps with walls up to 10 m high delle Alpi Centrali . prevail on th e northern side of th e valley , while downhill­ facing scarps and trenches are more comm on on th e southern TERMINI CHIAVE : Neot etton ica; stabilita di versante; 010­ side . cene; I talia; Alpi Cen trali . On both sides th e above menti oned str uct ures cut mo raines and rock glaciers of Lat e-glacial age, while in other cases th ey are covered by similar deposit s. These forms are commonly related to gravitational spreading of rid ges and /o r deep seated rock INTRODUCTION creep. Nevertheless in th is case th e relatively uniform attitude of th e shear surfaces, dipping nort heastward s, independe ntly Lineaments or sheaves of lineaments were traced from th e aspec t and inclina tion of th e slop e, sugges t th at such with the photogeological analysis in a wide area of th e discontinuities are th e superficial expression of neotecton ic de­ formations, which fit into th e fram ework of th e present neo­ Central Alp s in occasion of the participation to the CNR tecton ic activity in Centra l Alps. Neotectonics Subproject (FORCELLA & alii, 1982). A few of th ese lineaments were considered active during RIASSUNTO: FORCELLA F . & O ROMBELLI G. , Dejormazioni olocenicbe dei uersanti in Valfurva} Alpi Centrali, I talia (IT ISSN th e last 70 000 years (interval Ive + V of the abov e 008 4-8948 , 1984 ). mentioned Subproject). Vengono esamina te forme e stru tture pr esenti sui fianchi Three groups of fractu res belonging to this cath e­ della Valfurva (Alpi Cen tra li, Italia) indicat ive di deformazion i gory have been recognized in the area covered by the oloce niche dei versa nti. Si tratta di : 1) sciam i discontinui di IGM topographical map « ». In particular the contropenden ze di versante, talora associate 0 solcate tr asversal­ sheaf trending WNW-ESE, located between Bormio and mente da trincee naturaIi beanti; 2) superfici di collasso imm erse a fra napogg io, 0 rotture di pendio, che det erminano scarpa te S. Maria di , was synthetically described as fol­ rivo lte verso valle; 3) ·fessur e di tra zion e e tr incee naturali low s: « Fractures parallel to the thrust surface between beanti con aperture fino a 1-2 m. th e Sedimentary Unit and th e Crystalline Unit, slightly SuI versa nte orografico destro della valle sono in prevalenza transversal to the schistosity. To the East they are em­ pre senti contro pendenze, con pareti alte fino a 10 m, suI ver­ sante opposto prevalgono invece net tamente superfi ci di collasso pha sized by slope breaks represented by subvertical rock e rotture di pendi o. walls, further to th e W est by the drainage system and Su entra mbi i versanti Ie stru tture descritte tagliano in ta­ by th e saddling of Pa sso d'Eira . The eastward continua­ lun i casi morene e rock-glaciers tard o-glaciaIi. Queste for me sono diffusamente presenti anche in aree limitrofe ove sono sta te tion of these structures is represent ed by th e Valfurva attribuite a cedimento di versante in seguito a decomp ression e. valley, whose dir ection is opp osite with respect to the River main valley . Th e alignment of the spr ings of S.Caterina Valfurva, Bagni di Bormio (thermal) and ("') Centro di studio per la Stratigrafia e la Petrografia delle Alpi Centrali - CNR, Via Mangiagalli 34, Milano. S. Mich ele in Val Viera di Livigno is parallel to these ("d') Dipartimento di Scienze della Terra} Universita di Mi­ discontinuities » (FORCE LLA & alii, 1982 , p. 254). lano, V ia Mangiagalli 34} Milano. Afterwards we analysed some large-scale air photo­ (""''''') Th e present work was carried out wit h the contribu­ graphs of th e Valfurva area ( Region flight, tion of the Consiglio Nazionale delle Ricerche. The Authors thank prof. BARTOLINI C. and prof. D RAMIS F. for the review of the 1975 -76 ) and th e parti cular frequ ency of recent deforma­ manuscript .and for constructive suggestions. tions on the slopes of this valley was verified.

41 GEOLOGICAL OUTLINE These phenomena are arranged almost continuously OF THE EXAMINED AREA on both sides of the Valfurva, even if they are more concentrated in some areas. The most significant zones The studied area belongs to the Ortles Austroalpine are here described. Nappe. The sedimentary cover outcrops on the northern margin of the area and is locally represented by the ALPE CRISTALLO steeply northward dipping strata and banks of the Cri­ stallo Dolomite. The WNW-ESE trending Zebru Line A sheaf of uphill-facing scarps, striking WNW-ESE separates the carbonate formations from the crystalline and from 1 m to 5-6 m high, is present between 2,480 basement outcropping to the South and its strike and and 2,560 m elevations, just downstream the Zebru dip are conformable with those of the Cristallo Dolo­ Line. In the easternmost part of Alpe Cristallo such mite (POZZI, 1965; 1968). scarps affect the metamorphic bedrock and the regolith Such line is interpreted on the geological map « Bor­ cover and intersect minor morphological features due mio» (1st edition, 1970) as the thrusting of the Sedi­ to the presence of small valleys and interfluves, whose mentary Unit onto the Crystalline Basement, but the trend is transversal with respect to the scarps them­ fact that it may represent a simple decollement surface selves. The same morphologic features are up thrown cannot be excluded, as frequently mentioned in the lite­ downstream and the displacement is 5-6 m without any rature. The prevailing lithotype of the crystalline base­ sign of transcurrent movements (fig. 2). ment is represented by the Bormio Phyllites, with inter­ The central sector of Alpe Cristallo is covered by a beddings of lineated muscovite-gneiss, amphibole-schist, Late-Wiirm moraine complex whose internal part looks quartzite, and saccharoidal limestone and it has been like a rock glacier with blocks up to several cubic me­ recently studied by ARGENTON & alii (1980). tres in size deriving from the overlying carbonate wall Superficial deposits of various types are very com­ of the Reit. Two uphill-facing scarps belonging to the mon, mainly of Late-glacial and Holocene age. They above mentioned sheaf also displace the moraine-rock cover large areas of the slopes and of the valley bottom. glacier complex and their maximum height is about 3 m They are Late-Wiirrn glacial deposits, often forming end (fig. 3). moraines of the main Valfurva glacier or of minor gla­ One of these two uphill-facing scarps is the conti­ ciers of the lateral valleys. Late-Wiirrn outwash deposits, nuation of one of the scarps affecting the bedrock. They locally forming terraces, are also present, as well as clearly break the continuity of the crest line of the mo­ rock glaciers, mostly located in the upper part of the raines and the concentric structures of the rock glacier lateral valleys. The Holocene deposits are represented and generate locally a few small blind valleys. The by widespread talus and flood plain deposits and by big northernmost of these structures disappears inside the moraines near the glacier fronts. Some of them were moraine-rock glacier complex, while the southernmost mapped or described by DESIO (1967) and CATASTA & one cuts it transversally and penetrates again into the SMIRAGLIA (1978). Only the deposits that either appear metamorphic bedrock where it generates scarps up to deformed or cover undisturbed the movement surfaces 3.5 m high. Generally the uphill-facing scarps produce are represented in fig. 1. asymmetric ridges with the uphill slope steeper than the downhill one (fig. 4) . This kind of asymmetry ­ opposite to the one of lateral moraines - proves the FORMS AND STRUCTURES deformational nature of such surfaces and excludes any possibility that they are right-lateral moraines of the The forms and structures recognized in the studied La te-W iirm valley glacier of Valfurva, as suggested by area are: other Authors. This is also excluded by their overlap­ a) downhill dipping shear surfaces · that generate ping onto the local moraine-rock glacier complex of slope breaks and downhill-facing scarps; b) uphill-facing Alpe Cristallo, contrary to the usual relationships bet­ scarps reIated to various types of mechanisms; c) fur­ ween tributary and main valley end moraines. rows and trenches along the slopes and open tension The uphill-facing scarps that affect the rock base­ cracks whose width ranges from a few dm to a few ment are clearly higher and more frequent than those metres; d) denudation scars in superficial deposits and /or affecting the moraine deposits. This indicates that the in the bedrock. mechanisms, which produced such shear surfaces, were

FIG. 1 - Studied area. 1) Collapse surfaces dipping downhill, marked by sharp slope breaks or band-shaped denudation scarplets. They are represented with a dashed line when presumed, the thickness of the line is proportional to the height of the scarp. 2) Denudation scars of the bedrock and/or debris with blocks of different sizes. They are mostly associated with surfaces of type 1. 3) Uphill-facing scarps, related to uphill dipping surfaces (3a), or associated with natural trenches caused by release of the slope (3b) . The triangles are uphill-facing. 4) Minor open tension cracks and other unclassified features. 5) Zebru Line, arrows indicate plunge of the fault plane. It separates the sedimentary cover of the Ortles Nappe (to the North) from the metamorphic basement of the Ortles and other Austroalpine units (to the South). 6) Military road of the Reit, cut by a surface of type 1 at 2,261 m elevation. 7) Accumulation forms of various nature: end moraines (7a), rock glaciers (7b), debris accumulations (7c). Only those covering or cut by the above mentioned forms and structures are represented here. Symbols of the key map: A) Austroalpine and Pennidic Units. B) Southern Alps . C) Main intrusive bodies of Alpine age. D) Alluvial and glacial 'deposits along the northern margin of the Po Plain.

42 /// /5:< 4

1I\\\\\ mJlTt"I71r11I11 ~ rr 2 - ..i. . -.- 5 ~@8]]@f 7 b

("'"._.-- ~/ " '-':;) 6 3 11""'" 0--- ' \ LX:» 7c 1 ( 2km -_..:-= ==' -s, \.N Ftc. 2 - Sheaf of uphill-facing scarps cutting the crystalline basement of Alpe Cri stallo at 2,500 m elevatio n. The slope is int errupted , with th e downhill side uprhrown, without any sign of transcur­ rent movements. M indi cat es th e eastern limit of the end moraine complex, the crystalline basement outcrops in the fo­ regr ound. B indicates th e bend of the milit ary road of th e Reit also shown from the opposite side in fig. 3.

already active before the deposition of the local moraine exposing crumbled walls in the basement and blocky complex and were reactivated after its deposition. There­ debris in the moraines. fore the height of the scarps in the bedrock should be To the East and to the West the Alpe Cristallo is the result of repeated increments. These scarps are re­ bordered by steep slopes under rapid erosion, empha­ lated to upslope dipping shear surfaces, as proved by sized by spoon-shaped collapse surfaces dipping down-

FIG. 3 -O ne of the uph ill-facing scarps tha t pene tra te into th e end moraine com plex of Alp e Cristallo where it ge­ nerates minor scarp s (1-3 ill high), ind io cared with bl ack arrows. B: as in fig. 2, but from the opposite viewpoint.

their intersection with the aforementioned small valleys slope. In the western sector (Val d'Uzza), along the and interfluves. military road of the Reit, built during the 1st World Immediately downstream from the sheaves of up­ War, the bend at 2,261 m elevation is intersected by a hill-facin g scarps, a wide denudation band affects both well defined collapse surface. The road pavement .is cut the crystalline basement and the moraine complex, by an ENE-WSW trending shear surface and is entirely

FIG. 4 - Cross section of the uphill­ facin g scarps at 2,500 m elevation and th eir main geometrical characteristics.

44 the western flank of the Valle del Pasquale. Th ey trend WNW-ESE and are rather regularly spaced between 2,400 and 2,700 m elevati ons . The scarps at lower ele­ vations develop on gently dipping grassy slopes and their height is 2-3 m (fig. 6). Their geometrical characteristics and the resulting top ography are similar to tho se gene­ rated by the uphill-facing scarps at Alpe Cristallo, pre­ viously described. Because of the grass cover it was not possible to ascertain whether they affect the rock base­ ment or superficial deposits. Upstream the slope is furrowed by other uphill­ facing scarps much more evident than the previous ones. Thes e scarps generate steps up to 8-10 m high and break the metamorphic basement which outcrops almost continuously above 2,450 m elevation. The outcropping basement is crumbled and supplies coarse material that FIG. 5 - Uphill-facing scarps th at intersect the southern flank of Alpe Cri stallo between the 2,000 and 2,100 ill elevations forms bands embanked by the single scarps. Further­ near Alpe Solaz di Sopra (indicated with white arrows). They more the bedrock is cut by a network of ' subvertical are locally associated with natural tr enches of moderate width. open tension cracks generally a few dm , but locally up to more than 1 m wide. The y are arranged In two main downthrown about 5 m northwestwards. The collapse groups which are almost perpendicular: the trend of the surface in this place seems to affect only superficialrle­ first one ranges from 110° to 140° and is almost parallel posits. Other uphill-facing scarps , isolated or grouped to the strike of the 'scarps, the second one ranges from into sheaves, are present at lower elevations along the 40° to 60° and cuts them almost perpendicularly. The same slope and their trend ranges from E-W to NW-SE. continuity of the rock crest of the scarp is int errupted Locally they are associated with natural trenches in the by transversal trenches with wall surfaces so compl e­ bedrock, 1-2 m wide and up to 5 m high (fig. 5). mentary that their previous fitting can be recognized. Th e dip of the uphill-facing scarps ranges from 30° Such tension cracks are locally open down to several to 48°. Also in this case the shear surfaces are post­ meters depth , in some cases they are covered on top by glacial, becaus e they intersect rock surfaces shaped by a natural roof , probably because of lateral sliding of rock the Late-Wiirm glaciers, and they do not show any sign slabs according to models which can also be observed of glacial erosion themselves. at a smaller scale (fig. 9). Th e wh ole area between Lago del Pasqu ale and Baite del Pastore shows a block topograph y and the A RE A BETWEEN CORNA ROSSA AND LAGO DEL P ASQU ALE blocks are completely disrupted by the intersection of A sheaf of uphill-facing scarps can be observed along the two abov e mentioned systems (fig. 7 ). The uphill-

FIG. 6 - Sheaves of uphill-facing scarps between the 2,400 and 2,500 m eleva tio ns on the north ern flank of Valfurva Valley up ­ stream fro m the S. Caterina Valfurva village (tha t can be seen on the valley bottom ). Th ey stri ke WNW-ESE and run up slope diago nally in a direction which is opposite to the downflow oft he main river. T his fact, as well as the clearly asvmrne trical cross sections wi th an ups lope side which is much stee per than the grad ient of the slope that they cut, excludes any poss ibility tha t they. are lateral m o~a i n e s relate d to th~ Wiir m valley glacier. .The up hill-facing scarps at grea ter elevations represent a levee for the debris bands supplied by the overlying crumbled outcropping bedrock . T he black arrow in the foregro und poi nts to a natur al trench that cuts the scarps themselves.

45 FIG. 7 - Op en tension cracks striking in various directions, which dissect the to­ pography on the western slope of Valle del Pasquale. They are indicated with black arrows.

facing scarp s of the western flank of Valle del Pa­ was coming down from Mount Sobretta and joined the squale continue southeastwards inside the stream bed main glacier of Valfurva at 2,042 m elevation. The two itself which is covered by coarse debris. The scarps are mor aines can be followed from 2,275 m elevation down smaller but still clearl y distinguishable in the river to the aforesaid confluence. On the air photograph the channel, as already observed on deposits of different right moraine app ears intersected by two discontinuity kind at Alpe Cristallo. surfaces trending NW-SE, which generate steps on the Eventually it has to be stressed that the rock sur­ crest line, and the downstream tracts appear to be down­ face of the uphill-facing scarp at 2,580 m elevation ap­ thrown. The lowe rmost discontinuity can be observed pears very smoo th though it does not coincide with the at 2,170 rn elevation and appears as a slope break foliation of the rock. That is clearl y in contrast with marked by a scarp 4-5 rn high. A small level ground the rou gh and crumbled morphology of the rock out­ is pre sent at its base. The slope break occurs in cor­ cropping alon g the sections of the slope lying between respondence with an outcrop of bedrock and could have the scarps themselves. been generated by a step of the substratum on which the moraine is lying. Another break in the crest line, RIO Dr SCLANERA much more evident and continuous, can be observed at Tw o lat eral moraine s can be observed WSW of 2,250 m elevation. In detail it consists of three scarps, S. Caterina Valfurva, along the Sclanera Stream. They close to one another, transversal to the moraine and were deposited by a glacier that during Late-glacial time trending NW-SE. The uppermost one is not more than '

FIG. 8 - A collaps e sur face dipping down ­ hill (indicated with white arrows) inter­ sect a lateral mor aine (M) and an out­ wash plain (A) on the right side of the Rio di Sclanera Valley . I t generates a scarp 4-5 m high.

46 1.5 m high and can be followed for a short distance, the intermediate one is the biggest and is about 4 m high, its dip is 30° and it shows a good continuity for several tens of meters. The lowermost one is a simple undulation of the crest. The main scarp continues along the inner side of the moraine and cuts two more recent mo raines. On the outer side the scarp continues and runs across a marginal outwash plain, where it generates a step 4-5 m high (fig. 8) . A little further on, where the bedrock is out­ cropping, a trench in the rock can be observed trending NW-SE (140°), discontinuous and slightly winding. It is 1-2 rn wide and bordered upstream by a scarp 3-4 m high. The trench does not generate any uphill-facing scarps and its origin seems to be related to a disconti­ nuity surface dipping downhill. The rock outcrops are also intersected by numerous open tension cracks trend­ ing approximately N-S (0°_10°). The whole slope shows rock surfaces shaped by the glaciers, subsequently fractured and partly dismantled because of collapses. Also the slope between th e Sc1a­ nera Stream and the Sobretta Valley is affect ed by a remarkable sheaf of uphill-facing scarps trending NW-SE, which are cut by a network of trenches and open ten­ sion 'cracks trending ESE-WNW and NW-SE, with the downhill sector downthrown.

VAL Dr CALV ARANA The northeastern flank of Cima Bianca is affected by shear surfaces, trending NW-SE, that generate scarps, slope breaks and trenches with the same trend. T hese elem ents affect the metamorphic complex of the Bormio Phyllites and locally also superficial deposits. Near Grasso di Solena at about 2,300 m elevation trenches in the rock were observed trending WNW­ E SE and NNW-SSE , 1-2 m wide and down to 5-6 m deep. On the whole th e morphology is that of a rock relief broken into blocks downthrown in a downhill direction. Other remarkable trenches can be observed from Baita dei Pastori to Mount Sobrettina (fig. 9) . The big­ gest ones trend NW-SE, they are up to 10 m wide and show a good continuity for more than 200 m. All these forms are mainly due to shear surfaces dipping down­ hill in a northeastern direction with dips of 40 -55°, as indicated by the intersection of these surfaces with re ­ liefs transversal to them. Yet uphill-facing scarps are also present, which can be related to shear surfaces dip­ ping uphill, that is in the opposite direction. These scarps are less important' and less frequent than the previous ones. Also in this sector the shear surfaces mu st be considered postglacial because they cut an out­ was h apron and a probable moraine of Late-glacial age .

CONCLUSIONS FIG. 9 - An open fracture covered on top by a natural roof on Some general observations can be made about the th e southe rn side of Valfurva, near Baita dei P astori. It is open forms and structures previously described. down to seve ral met ers depth wh ere it seems to wedge out. These are slop e deformations in a topographic con­ Compare thi s fracture with the smaller one pr esent on the la­ teral sur face of a block . Th e movement may hav e tak en place text characterized by a high energy relief. They are due by opening of an extre mity of the rock mass (black arrow) to relative movement along shear surfaces or to simple around a subve rt ical axis (background in th e figure ).

47 parting of the two sides . Th e surfaces of movement assem blage of forms and structures is not present on are never single, but arranged into sheaves that form the crest and on the northern flank of the ridge . And band s a few hundreds of meters wide and up to 3 km not even the proposal of ]ACKLY (1965), that postulates long. Th ey develop in the middle of the slope between a differential uplift of the valley bottom with respect to 2,000 and 2,700 m. the slopes due to melting of the valley glaciers , seems to Th e displacement along each discontinuity rang es be in accordance with what we hav e observed . fro m a few dm to 10 m, the cumulative displacement If we consider that: 1) some of the gliding surfaces along a single sheaf is up to 100 m. The age is recent, (Alpe Cristallo) show a stick slip type activity; 2) the mostly Holocene , as it can be inferr ed by considering area of Bormio is characterized by a seismic activity, the relationships with Late-glacial forms and deposits. even if modest (BELLONl , 1974 ; PAVONl & MAYR-RoSA, . On the whole the trend of such surfaces ranges 1978); 3) the observed structures are limited to an area from WNW-ESE to NW-SE, parallel to the Valfurva elon gat ed in a \'\7NW -ESE direction, parallel to one axis. Th erefore they are generally conformable with the of the two trends congru ent with the field of stresses contour lines, but locally the y can be arranged transver­ presently activ e in thi s part of the Alps, we can hypo­ sally or even perpendicularly to them. In particular this thesize that such ph enomena represent the superficial happ ens at the conflu ence of the Valfu rva Vall ey with response to neotectonic movements, even if controlled th e Zebru Valley, which repr esents a valley of analo­ by the gravitational component alwa ys present in areas gous rank. This indicates that there is no exact corre­ of high energy relief. Such neotectonic movements could lation between topo graphy and the strike of such sur­ have produced a step morphology in the area with the faces. Fu rthermore th eir strike does not coincide with NE sectors systematically downthrown. that of the schistosity and forms an acut e angle with the main local structure, represented by the Zebru Line. SELE CTED REFERENCES As it can be deduced from their intersection with the topography, the surfaces of mov ement are mostly ARGENTON A., DAL PI AZ G. V., M ARTIN S. & SCHIAVON E. (1980) - Osseruazioni preliminari sul uersante o ccidentale represented by planes, and only locally do they appear della dorsale G ran Zebru-Ceuedale-Corno dei T re Signori slightly spoon-shaped. They plunge mainly northeastwards (Austroalpino superiore, A lpi Centrali) . Rend. Soc. It. Min. and their dip ran ges from 35° to 5Y about. This produces Petrol., 36, 65-89. . a non specular distribution of the forms on both slopes BELLONI S. (1973) - T erremoti. Annuario Ecologico Lombardo. Gruppo Terra. Rapp. Avanzamento n. 4 (Alluvioni e Terre­ of Valfurva. In fact on the northern slope the shear mo ti). Mil ano. surfaces dipping uphill are almost exclusive and generate CATASTA G . & SMIRAG LIA C. (1978) - II versante della R eit uphill-facing scarps, while downhill dipping surfaces pr e­ (bassa Va lfurva). Quad erni P arco N az. Stelvio, 1, 32 pp ., vail on the opposite southern slope and produce scarp s 13 Iigs., 1 geomorp h . map . 1 : 25 000 . Bormio. D ESIO A. (1967) - I ghiacciai del G ruppo Or tles-Ceuedale (Alpi and trenches. Slope deformations similar to the abov e Centrali) . CNR, Com. G lac. I t. , 875 pp ., 207 tabl es. Torino. described ones have already been reported in the litera­ FORCEL LA F. (1983) - Un eccezionale esempio di tettonica gra­ ture and have been variously nam ed and interpreted as: vitativa di versante: il Sackung sviluppato tra il M . Padrio deep-seat ed large-scale rock slides , deep-seated mass rock e il M . V aradega, Alpi Centrali, I talia. Riv. Museo Sc. Nat. Berga mo , 5, 11-23. creep , deep-seat ed gravita tional slope deformation, Hang­ FORC ELLA F. (in pr ess) - Brevi note sulla tettonica gravi tativa tekt onik (slope tectonics), Sackung (<< sagging »), Glei­ di versante nelle Alpi Centrali. Rend. Soc. G eol. I t. tung (sliding), grav ita tional spr eading of ridg es, etc . FORCELLA F., G ALLAZZI D. , MONTRASIO A. & NOTARP IETRO A. (HE lM, 1932 ; SANDER, 1948; RADBRUCH-HALL, 1978; (1982) - N ote illustrative relative all'eoo luzione neotettonica dei f ~gl i 6-Passo dello Splu ga, 7-Pizzo Bernina, 8-Bormio, SORRlSO-VA LVO , in pr ess). 17-Chzaven na, 18-, 19-. In: «Contributi Realiz­ Examples of slop e deformation have already been zazione Carta Neot ettoni ca Italia », Progetto Finalizzato C eo­ recorded in the neighbouring areas (FORCELLA, 1983, in dinami ca, n . 513 , 239-288. H ElM A. (1932) - Bergsturz und M ens chenl eben. Fretz und press); these were considered as the resultof gravitational W asmuth, 218 pp ., Zurich. tectonics due to slope failure caused by pr essure release. ] ii. CKLI H . C. A. (1965 )- Pleistocene glaciation on th e Swiss Yet from certain points of view the phenomena descri­ Alps and signs of postglacial di fferential uplift. G eol. Soc. bed here seem to be different from tho se of the adjoin­ America, Special P aper , 84, 153-157. P AVONI N . & MAYER-ROSA D . (19 78) - Seismotekt onische Karte ing areas. In fact the recorded asymmetry of th eir distri­ del' Scbioeiz 1/ 750 000. Eel. Geol. H elv., 71, 293-295 . bution leads us to think that only the features of the POZZI R. (196 5) - Schema tet tonico dell'alta Va lt ellina da Livigno southern slope can be related to slope gravitational glid­ al Gruppo dell 'Grtles. Eel . Geol. H elv., 58, 21-38. ing, char acterized by main collapse surfaces, sometimes POZZI R. (1968) - La G eologia del Parco Nazionale dello St elvio. In: « II P arco Nazionale de llo Stelvio », 148 pp ., Art i Gra­ associated with minor antithetical surfaces. The latter fiche R . Ma nfrini , Rovereto. produce uphill-facing scarps arranged en echelon down­ RAD BRUCH-H ALL D .H . (1978) - Gravi tat ional creep of rock hill along the slope . On the contrary this model does masses on slop es. I n : « Rockslides and Avalanches, 1 Natural not seem to be applicable to the northern slope , where Phen omena », 607-657, Elsevier Sc. P ubl. Co., Amsterdam. SANDER B. (1948) - Einfiihrung in die G efiigekunde der geo­ there are no trac es of main gliding surfaces congruent logis chen Korper. Vol. 1, 215 pp., 66 figg., Wi en . with the num erous uphill-facing scarps, which should SERV IZIO GEOLOGICO D'lTALIA (1969-70) - Carta G eologica d'Ita­ represent the conjugate gliding planes. It is not even lia alia scala 1 : 100 000. F. 8 - « Bormio » and Explanatory possible to include the features of the northern slope N otes, 123 pp., Poligrafica & Cartevalor i, Ercolano (Napoli) . SORRI SO-VALVO M. editor (in pre ss ) - A tt i del 1° sem inario del into a collapse model of the crest area of M. Forcellino­ Gruppo « Dejormazioni Gra vitative Prof ond e », Roma, 1983. M. Confinale, with ridg e spreading, because an adequate Rend. Soc. G eol., Roma.

48