Holocene Slope Dynamics in the Area of Corvara in Badia (Dolomites, Italy): Chronology and Paleoclimatic Significance of Some Landslides

Gcogr. Fis. Dinanr. Qual. 2cf (lOOJ), 127-13'.>, (, fig!!, .. 2 tabb.

ALESSANDRO CORSINI (;1,) , MAURO MARCHETTI (;,,) & MAURO SOLDATI e')

HOLOCENE SLOPE DYNAMICS IN THE AREA OF CORVARA IN BADIA (DOLOMITES, ITALY): CHRONOLOGY AND PALEOCLIMATIC SIGNIFICANCE OF SOME LANDSLIDES

AB STRACT: C ORSINI A., MAR CII ETT I M. & SOLD ATI M ., Holocene identified and the chronology of deposits maki ng up actual land slide ac slope dyn amics in tbc area o] Coruara in Badia (Dolomit es, Italy): cbronol cumu lations to be reconst ructed. Finally, it was also prove d that the ogy and paleoclimatic significance of some landslides. (ITISSN 039 1 plain of Corvara in Badia was affected by lacustrine deposition duri ng 9838,2001). the Pr eboreal-Atlanti c and again, but to a lesser exte nt , during the Subboreal-Sub atlantic. The evidence of a significant temporal corre The area of Corvara in Badia, located in the Dolomites (NE Italy), is lation between the develop ment of mass movements on the Col Alto characterised by mountain groups over 3000 m high (Sella and Puez Pra longia slop e and the evolution of the Col Maladat land slide was G ardenaccia) which are connected to valleys located at about 1500 m in therefore proved. altitude by means of steep slopes . Beside; the lithological, neotectonic Even if the land slides investigated are clearly influ enced by geologi and climatic characteristics of the area , the high relief energy has fa cal factors, a cause-effect relationship seems to exist between the phases voure d intense gravitational slope modelling throughout the H olocene. of slope dynamics outlined by the research and the climatic and environ The study, which aimed at the reconstruction of the geomo rpholog ment al changes which have characterised the H olocene. Th e age of trig ical evolution of the slopes surrounding the village of Corvara in Badia, ger of the landslides investigated corresponds to the ear lv Holocene, a has implied the geomorphological, stratigraphic and chrono logical anal period tha t many Aut hors consider to be cha racte rised by a rapid in ysis of landslide processes, in particular of those affecting the Col Alto crease of temperature (followed by permafrost melting) and of prec ipita Pralong ia slope, situated uphill of the village. The research has also in tion. In the study area, this climate change caused in-dep th infiltration vcstigatcd lacustrine deposits found in the surroundings of Corvara in and percolation of water, also favoure d by the geological nature of the Badia and down stream of the village, which are due to events of valley bed rock. A subse quent ph ase of slope instabilit y, witnes sed by the dat damming linked to a land slide detached form the Puez-Ga rdenaccia ing of several land slide events, corresponds to the clima tic deterioration gro up (Col Malada t landslide). In particular, the analysis has made use of the Sub boreal - early Suba tlantic pe riods , which has probably caused of stratigraphic data obtained from boreholes, and of chronological data a large amount of meteor ic water to be available on slopes . derived from radiocarbon dating of wood and peat remnants collected from the cores and from excavations carr ied out close to the surface. K EY W ORDS: Landslides, Dam lakes, Climate change, Italian D o The study has pin pointed that the triggering of the large com plex lomi tes. landslides affecting the Col Alto-Pralongia slope (Col Alto land slide, Ar lara landslide and Co rvara land slide) occ ur red in the early H olocene and that sub sequent phases of intense slope movements took place on the RI ASSUNTO : CORS INI A., M ARCHETTI M . & SO LDATI M., Dinamica same slop e during the Subboreal-Subatlantic. The 1JC data gathered oloccnica dei uersanti ncll'arca di Coruara in Badia (Dolomiti , ltalia): cro from land slides affect ing the Col Alto -Pra longia slope have also permit nologia e s ign~/ica l o palcoclimatico di alcuni [cno mcni [ranosi. (IT ISSN ted the various areas progressively involved in the movements to be 039 1-9838 ,2001). L'area di Corvara in Badia, ub icata nelle Dolomiti, e caratterizzata da grup pi montuosi di oltre 300 0 m di quota (Sella e Puez-C ardenac cia) che si racco rda no con ripidi pendii a vallate paste a circa 1500 m. L'ele ("') Dipartim ento di Scienze della Terra - Uniuersita degli Studi di vata energia del rilievo, oltre aIle caratteristiche lirologiche, neotettoni Modena e Reggio Emilia - Largo 5. Eufemia 19, 41100 Modena - Italy. che e clirnatiche dell'area, hanno favorito un intenso modellamento gra Tbis research was funded by: CNR 1997 «A pplication ofnew pbvsical vitativo dei versanti nel corso dell'Olocene. dating techniques to the Holocene paleoenvironmental reconstruction in La ricerca, finalizzata alIa ricost ruzione dell'evolu zione geomorfolo tbe Dolomites (contract no. 97.00229.CT05, co-ordinator: M. Panizza)»; gica dei versanti circostanti Corva ra in Badia , ha comportato l'analisi COFlN ] 997 «Response of geomorpbological processes 10 cnuironmcntal geomorfologica, stra tigrafica e cronologica dei lenom eni franosi, in par· cbangcs» (national co-ordinator: A. Bianconi, local co-ordinator: M. Paniz ticolare di quelli che interessa no il versante Col Alto- Pra longia, situate a za) and COFlN ]999 «Mass movements as indicators of climate changes monte dell'ab itato. Sono srati studiati inoltre i depositi lacustri rinvenuti / rom tbc Latcglacial to date» (national am! local co-ordinator: M. Panizza}. in corris pondenza ed a valle di Corvara in Badia, dov uti a episodi di Tban les arc due to Prof Mario Panisza /01' bis critical supervision sba rramento de rerrninati da una frana che si distacco dalle pendici del (i th e man uscript and to Dr. Dino Dibona for bis useful information on Gruppo Pu ez-G ard enaccia (la frana di Col Maladat). In parti colare, I'a fo rest ecology. nalisi si e avvalsa dei dati stratigrafici ricavati da son daggi meccanici e

127 dei dati cro no log ici derivanti dalla datazione radiomet rica di rest i di le 1997; Solda ti, 1999), in agreement with the mo st recent gno e to rb e rinvenuti all'inter no sia dei son daggi sia in scavi in pross i results atta ined at a European level (see Ma tthew s & alii, mira della superficic. Lo stud io ha cvidcnziaro chc l'inncsco Jellc prin cipali fran c. Ji stile 1997). Nevertheless, in order to co rrectly define th e pale co rnplcsso , chc si sviluppano sui rilievo Co l Alto- Pra longia (Irana J i Co l oclimatic significance of the landslides th us dated , the Alto, Irana J i Arlara c [rana Ji Co rvara l avvenn e all' inizio J ell' Ol ocene e po ssible influ en ce of ot her geological causes, in particular che sucess ive fasi d i int cnsa dinamica gravi rativa interessaron o il versan neotectoni c and lithological ones , was also taken into te durant e il Subbo realc-Suba tlantico. Inoltre, i dati I·C relativi aile frane account. del Co l Alto-P ralon gia hann o per ll1 esso di indi vidu ate Ie aree progressi vamente co involte nei dissesti e ricostruire la cronologia dei depos iti de gli acc umuli di Frana att uali. Si e potuto constatare , infine, che la piana di Co rvara in Badi a fu interessata da condizioni di tipo lacustre nel co rso GEOGRAPHIC SETTING del P reboreale-Atlamic o e nuovarnente, in minor misu ra, nel corso del Subboreale-Subatlamico. Sussiste pertant o una signilicativa co rrelazione ternp or ale tr a l'evolu zione dei fen om en i franosi del Co l Alto-Pralongia e The area of Co rvara in Badia is located in the cent ral qu ella della fran a Ji Co l Malad a« part of the Dolomites (Italian Eastern Alps), in the Auto n Pur esse ndo cvidc nre l'influenza dei fattori gco logico-strutturali sul omo us Province of Bolzano (Sout h T yrol), and corre lo sviluppo dei Icno meni hanosi. sem bra COl11 unque esse rvi un rapporto sponds to the southernmost sector of th e Alta Badia dis di causa-cffetto tra Ie fasi di d inamica gravitative delin eate dalla ricerca e trict. The mountain ridges culminate in the dolomite peaks Ie variazioni climariche cd am bie ma li che hanno carat te rizzato l'O loce ne. L'ep oca di inn esco delle frane studiate co incide infatti con l'inizio of Puez-G arden accia (3025 01 a.s.l.) and Sella (315 1 01) in dell'Ol oc en e, un period o che da var i Auto ri e considerato cara rte rizzato the western sector and in the marl y pyroclastic peaks of da rapido inn alzarn ento della temp er atura (con consegue nte scioglimen Piz la Villa (2078 01), Col Alto (1980 01) and Pralon gia to del permafros t) e da aurne nto delle pr ecipitazioni. Ne ll'area studiata, (2571 01) in the easte rn sector (fig. 1). Acc ess to the area is cia caus a fenomeni di infiltrazione e percolazion e profonda de ll'acq ua , [avoriti dalla natura geo logica del substrate. Un suc cessive per iod o di in possible through the G ardena Pa ss (212 1 01), th e Campo stabilira dei vers anti , test imoniato dalla datazion e d i nu merosi eventi fra longo P ass (1679 01) to the southwest and the narrow nosi, avvenne in co rrispo nde nza col deterior arn enr o climar ico J el perio gorge of the Gadera stream to the north, between the vil Ji Subboreale e Sub atlant ico inferior e, che ha prob abi lmcn te reso dispo lages of Corvara in Badia and La Villa. The valley floors, nibile su i versant i una grande qu antita di acque meteoriche. on which the main water courses flow (Pissadu stream, Ru T ER,\!INI Cl l li\ VE: F rane,Laghi Ji sb arram ent o, Variazioni climati torto stream and, from their confluence, Gadera stream), che, Dolomiti. range in altitude between over 200001 near the passes and about 1500 01 near the northern boundary of the study ar-

INTRODUCTION

This paper is part of a series of investigation s recent ly carried out in the It alian Dolomites in orde r to recon struct the temporal recu rrence of landslides from the Lateglacial to date and defin e the relationships between CRODAdi these mas s wasting processes and the climatic changes al SANTACROCE (2907m) ready kn own in literature. In parti cular, th ese investiga tions were car ried out between 1996 and 1999 within the framework of national (Cofin 97 and 99, CNR 05, Vigoni ) and European (Environment and Clim ate - N ewtech ) re search projects and were concentrated in the study area surrounding the village of Corvara in Badia. The research made use of detailed geomorphological surveys and stratigraphic anal yses of the Quaternary de GRANOECIR posits; th e latter was carri ed out on cor es from boreholes FORCliLLf S mad e in collaboration with the Autonom ou s P rovince of '" Colfoseo Gar dena Pass o '. .. (1980 m) BRAlOA ,,,diSOR'" EGA Bolzano and on surfaces obse rvable th ank s to excavation '--J(2121m) r-'"\ CRl!PdcS LLA . ~~A activities for building purposes. An essent ial cont ribution . ~"..,._~..,.,...~\ Corvara in Badia '\.~ ifiLpll ! (1540 m) to research was also provided by a series of radiometric , I ~1>~ ~ PRALONGIA' dating carried out on organic finds found in supe rficial (2138m) '" I 0", ./ materials such as landslid e accumulations and lacustrine .r! ",\\. ,-,_ r deposits. / .~~J n~~\~:) CREldeMONT ,/; The interpretation of the chronological data collect ed .a. ...~.f'. and the stu dy of th e geo mo rphological evolution of the area also took adva ntage of th e kn owled ge acquired in ad Campolongo Pass f~ AL'"TOPIANOdiCHERZ J((J679 m) \ (2108 m) jacent areas with similar ph ysiographic and geo logical cha racteristics (e.g, Co rtina d'Arnpezzo) , in which rela tion ships between landslide recurren ce and climatic changes hav e been hypothesised (Panizza & alii, 1996, FIG. 1 - Location of th e Corvara in Badi a area.

128 ea. Th e slop es are usually subvertical in the upper part of ESE-verging late compressive phases (Castaldini & Paniz the ridge (in correspondenc e with the dolomite peaks ) and za, 1991; Castellarin, 1996). This is testified by the N eo mod erately incli ned in the mid-lower part. gene extension fault affecting th e Sella Group with a N -S directi on along th e Val di Mesdi and th e N eogene subver tical dislocation with a NNW-SSE direction recognisabl e GENERAL G EOLOGICAL AND along the lineament passing through the G ardenaccia pla GEOMORPHOLOGICAL FEATURES teau, th e Fraina Marada gna stream , Braida Fraida and Pa sso Incisa (fig. 2). On th e basis of several congruous ge The area of Corvara in Badia is geologically illustrated omorphological elements (among which also the deep by Sheet no. 11 «Mt. Marmolada» of the Italian G eolo gi seated gravitational deformations affecting the Col Alto cal Map at a 1:100,000 scale (Servizio G eologico d 'Italia, Pralongia slope should be mentioned and will be dealt 1970) and Shee t no. 028 «La Ma rmolad a» of the It alian with in the following chapters), the Passo Incisa fault is G eological Ma p at a 1:50,000 scale (Servizio Geologico conside red active, with a transcurrent dextral movem ent d 'Italia, 1977) . In this area well known formations cro p during the Plio-Quatern ary (P anizza & alii, 1978; Carton out , which have been exha ustively described in literature & alii, 1980; Zanfer rari & alii, 1982 ; Slejko & alii, 1989; (Leona rdi, 1967; Brondi & alii, 1977 ; De Zanche & alii, Castaldini & Panizza, 1991). 1993; Bosellini, 1996): they make up the sedimentary se On th e whole, the geomorphology of th e Corvara in qu ence of th e Dolomites in the Upper Permian-Norian Badia area is strictly related to the slopes' geological struc int erval (Servizio G eologico d'Italia , 1977 ). The mountain tu re and reflect s the different clim atic conditions of th e gro ups of P uez-G ardenaccia and Sella are con stituted by Quaternary (Cors ini & alii, 1997). From the morpho massif or stratified doloston es fro m the Upper -Middle structu ral viewpo int, the selective eros ion processes Tri assic (Dolomia Cassiana, Diirrensrein Forma tion and which led to the exh umation of previou sly buried geo log Dolomia P rin cip ale) and, subo rdina tely, by marls and pe ical structu res, have played a major role starting from th e lites fro m th e Upper Triassic (Raibl Fo rmation) (fig. 2). Miocene-Pli ocene, wh en the main valleys of th e area start The Pralongia rid ge and th e upper part of the slopes lo ed to develop (according to Nangeroni, 1938), with the cated beneath the Sella and Gardenaccia dolomite cliffs modelling of the Passo Gardena and Pralongia. At pres are mad e up of lithological complexes, prevalently with a ent th e slopes are practically vertical at th e margin of th e ductile mechanical behaviour and made up of alternating area's dolomite reliefs, highly inclined in correspondence seque nces of Upper-Middle Triassic calcarenites, marls with the Lower-Middle Triassic out cro ps of limeston es and pelites (S. Cass iano Fo rma tion) and Middle Triassic and pyrocl astic arenites and mildly inclined and undulat pyroclastic arenites and siltites (La Valle Fo rmation) . The ed in correspondence with the north-western slope of the crest of the Pi z La Villa-Col Alto rid ge is made up of Mid Col Alto-Pralongia relief, wh ere the Late Triassic sedi dle Triassic arenites and pyroclastic conglomerates and la mentary rocks crop out. vas (Fernazza Formation; Pillow Lavas) which are affect As regards the landforms and deposits linked to the ed by a dense network of joints with a substantially brittle Wurm Pleniglacial and Lateglacial periods, worthy of mechanical beh aviour. In th e north-western sector of the note are the Pleniglaci al moraines near Pralongia and Pas Pi z La Villa -Col Alto ridge, and in the lower portion of so G ardena, as well as the cirques, suspende d valleys, gla th e northern and eastern slopes of th e Puez-Garden accia cial deposits and moraine ridges which witness the pres ridge, rock types displaying different kinds of mechanical ence and progressive disappearance of valley glaciers behaviour crop out; they are mainl y Upper Permian which had developed during th e Lateglacial and Holo Lower Triassic limestones, sandstones and marls (Bellero cene. In Pralongia shale clasts are found (trapped inside phon Formation; Werfen Formation: Richthofen Con Pleniglacial deposits or inside landslide bodies); these glome rate ; Contrin Formation; Livin.illongo Formation). confirm the Austrian provenanc e of the Last Glacial Max F rom the stru ctu ral standpoint, ill . 11C Corvara in Ba imum glaciers, which stretched south as far as the 2300 ill dia area paleot ectonic eleme nt s linkc.: to the Upper a.s.l. altitu de, as alrea dy hypothesised by P enck & Permi an-Triassic ex tensiona l phases are lou n c] (<< Badioto Bruckner (1909), B. Cas tiglioni (1936 ), Sacco (1939) and G arden ese rid ge» and Passo Gardena line, fig. 2; Boselli G.B. Castiglioni (1964). ni, 1965 , 1968, 1996) together with displ acement struc On the other hand, the talus and alluvial fans border tures such as folds, faults and overthrusts resulting from ing th e base of th e Sella and Puez-Garden accia Dolomite th e Tertiary Alpine compressive phases (Leonardi, 1967 ; slopes (fig. 2) are th e result of periglacial and gravitatio n Doglioni & Bosellini, 1987; Doglioni, 1990 ; Bosellini, processes. 1996). Among the latter, west-verging features related to Particularly relevant are also th e landforms and dep os the Ca tt ian-Aquitanian Mesoalpine compressive ph ase are its due to slope movements. Landslides of various types found (Doglion i, 1987; Doglioni & Bosellini, 1987) and and dim ension s affect practically every sector of this area also south-ve rging features linked to the Serrava llian (fig. 2); some of these, in particular th ose which involve Tortonian N eoalpine compressive ph ase (Castellarin & argillaceous materials, are at present active. The situ ation s alii, 1992 ) (fig. 2) . Furthermore, some of th e structures favouring landslide processes are extremely varied, mainly whi ch developed during these tectonic stages were also dep ending on the different rock types involved and the reactivated during the Plio-Quaternary, in relation with stratigraphic and tectonic relations between the outcrop-

129 r--,------f------5165 ~1 ~2 ~ 3 ~4 [ill s

~~~-5160-

/ 6 / 7 ~ 8 // 9 /

ffilli]: ~ ~~ ~ ~ ~~ ~~ ~ ~ 10

.... o ~o :>o.. C ..l.O..(O 11 [iliill... 0 "·0 '" . 0 2km I I 12 5155 I UTM32T (European datum 1950) 13 I 715 720 725

FIG. 2 - Geological sche matic map of the Co rvara in Badia area. Legend: 1 - dolomites and marls (Middle and Upper Tri assic); 2 - alte rnances of calca renit es, marls and claystones (Middle and Upper Tri assic); 3 - alternances of sandstones and siltstones (Middle Tri assic) ; 4 - volcano clastic arenites and conglome rates (Middle Tri assic); 5 - limeston es, sandstones and marls (Upper Permian - Lower T riassic); 6 - paleot ectoni c line (Upper Permian-Lower Tr iassic); 7 - meso-n eoalpin e fault (Tertiary); 8 - meso-neoalpine ove rthr ust (Tert iary); 9 - neo tectonic fault (P lio-Q uate rnary) ; 10 - scree slopes, scree fans (La teglacia l-Holocene): 11 - alluvial or lacustrine deposits (Lateglacial-Holocene); 12 - landslides (Lateglacial-Holoce ne) : 13 - land slides investigated in detail in this paper.

130 ping formations. The development of numerous slope the Col Maladat, about 1 km north of Corvara in Badia , movements in correspondence with the margins of the thus caus ing the sedimentation of considerable layers of Sella and Puez-Gardenaccia groups appears to be linked alluvial and lacustrine deposits, which are now terraced in to the overlapping of jointed competent rocks , such as correspondence with the flat area on whic h th e village it do lostones, on materials showing a substantially ductile self is located. behaviour, such as the S. Cassiano and La Valle forma tions. In this case, various types of movement combine and tak e place on different stretches of the same slop e, af GEOMORPHOLOGICAL EFFECTS AND fecting materials with different mechanical characteristics, CHRONOLOGY OF SOME LANDSLIDES thus giving origin to vast landslides with a complex and composite movement style. Other complex landslides are In this chapter the typology, extent and chronology of started owing to situations of structural weakness, or for the landslide processes and their associated deposits sur the presence of pelitic rock types which give rise to rota rounding Corvara in Badia are described. In particular, tional slides accompanied by earth flows. In particular, in the landslides affecting Col Alto - Pralongia and the lacus order to reconstruct the Holocene gravitational slope dy trine deposits near Corvara in Badia (fig. 3) are analysed . namics, great importance is assumed by: i) rotational For this purpose stratigraphic data were used acq uired by slides / earth flows , which involve alternating sequences means of six continuous-coring boreho les (made in col of Upper-Middle Triassic pyroclastic arenites, siltites, cal laboration with the Bolzano Autonomous Province: carenites, marls and pelites along the north-western slope B17B4 and S57S6 in fig. 3) and three opencast building of the Co l Alto -Pralongia ridge; ii) rotational slides affect excavations (Sections A7C in fig. 3). Moreover, the pres ing Upper Permian-Lower Triassic limestones, sandstones ence of wood and peat remnants found at various levels and marls cropping out alon g the eastern slop e of the within the landslide and lacustrine deposits, has allowed Puez-Gardenaccia Group. In the past, one of thes e mass an important series of chronologica l data to be obtained movements barred for a long time the Gadera stream near by means of radiometric dating (tabs. 1 and 2) .

SASSONGHER ... (2665 m) \ fSS3 I ~ 8 \ ~ 2 R;~1 9 \ § 3 0 10 \ 8881 4 o II \ 5 0 12 COL PRADAT / ... (2036 m) \ ~ 6 ).A 13 A' B \ I.f B''\( / 7 '\~ \

FI G. 3 - Geomor phological ske tch of the landslides and lacustrine alluvial dep osits studied . Legen d : 1 - Co l AIm landslide; 2 - Arlura CREP de SELLA ... (1786 m) landslid e; 3 - Co rvara landslid e; ~ - Co l Malad ar landslides; 5 - land slide scarp; 6 - direction of slo pe movem ent; 7 - strike-slip fau lt; 8 lacustrine dep osit; 9 - alluvial dep osit ; 10 - cont inuo us-coring bor eh ole; 11 - tr ee remna nt sam 500 m pled; 12 - ex posed section ana I lysed; 13 - tr ace of cross secti on s sho wn in figs. 5 and 6.

131 Complex landslides on the Col Alto-Pralongia slope was obtained from a tree branch with a 10 cm diameter (sample B-93976; tab. 1) brought to light (at 2.5 m from Th e upper Col Alto-P ralongia slope is affected by nu the ground level) in the int erm edi ate portion of the accu merous complex mass wasting processes which, on the mulation zone thanks to excavations carri ed out for build whol e, may be considered as part of the same «landslide ing purposes. Th ese tree remnants have been ascrib ed to unit», as defined by Pasuto & alii (1997). Th e main gravi a Norway spruce (Picea abies Karst en ) which probably tation al movements are those from Col Alto, Arlara and grew on well developed for est soil (Dibona, person al Corvara (fig. 3). Th eir geomorphological, dynamic and communication ). Th e destruction of th e tree was prob chronological characteristics have been reconstructed ably caused by con siderable rock slides in the source area, thanks to a detailed field survey (Corsini & alii, 1998), followed by earth slides which buried even older accumu supported by the analysis of cores retri eved from four lation deposits of the landslide itself. boreholes on the Co rvara land slide (Bl -7- B4 in fig. 2), and Th e Arlara landslide is a complex slope movement, de radiom etric dating of tree trunk remnants found in the finable as a rotational rock slide-e arth flow (according to cores or in correspo ndence with river ero sional cuts or Cruden & Varn es, 1996), whi ch has affected the excavations. The numerous I·C data obtained on the land arenaceous-pelitic rock types of the La Valle Formation slides occurring alon g the Col Alto-Pralongia ridge (tab. between Col Alto and Braida Fraida (fig. 3). The land 1) have allowed the reconstruction of the slope's geomor slide, which stretches on the whole for about 1 km', is phological evolution during the Holocene. The ages quot bounded at the crown by a main scarp, in some places ed later in this text are the calendarial ages (cal. yr BP ), higher than 20 m. The source area is mainly characterised obtained by calibratin g the conventional I·C ages by by the presence of a clayey material cover which has been mean s of the Radiocarbon calibration program set up by involved in translational slides and earth flows , which at Sw ivel' & Reimer (1993) on the basis of data by Swi vel' & present are genera lly dormant. Th e main landslide accu alii (1998). In any case, for compa rison tab s. 1 and 2 show mulation zone is made up of a silty-clayey cover (some also the conventi onal radiometric dates (yr BP ). dozens of metres thick) surrounding a vast rock slab (on Th e Col Alto landslide is a rotationa l-translational which the village of Arlara rises), which is likely to have slide which has affected the pyroclastic sandstones (Fer been dismembered by deep -seated gravitational move nazza Formation ) makin g up the western slope of the Col ment s. By considerin g the geomorphological features of Alto ridge (fig. 3). Th e landslide accumulation , on which the slope, part of the materials originall y accumulated by the oldest part of the Corvara in Badia village is located , the landslide was probably remo ved by the Rutorto stretches over an area of abo ut 0.2 km, with a thickness stream, flowing on the valley floor , whe reas part of it of several dozens of metres, and is mad e up of metric could still be buried under the accumulation lob e of the boulders mixed with a silt-clay matri x. On the basis of ge Corvara landslide. Th e latter hypothesis is confirmed by omo rp hological evidence, the accumulation may be con the 10,000 year age obtained from wood remnants which sidered dormant , even if recently it has been affected by were found at great depth in the core s of bo rehole Bl (fig. more or less supe rficial reactivations, in concomitance 3), drilled at the foot of the accumulation zon e of the Cor with particularly int ense precipitation, as in 1966. Th e vara landslide (samples B-112032 and B-112033 , fig. 4 type of bedrock involved in the movement and the typi and tab. 1). The burial of this organic material was prob cally concave morphology of the source area, point to a ably linked to the development of the Arlara landslide, pr evious development following large-scale mass wasting which in this area was later covered by the deposits of the processes. Th e 2708-2 183 cal. yr BP age of this landslide Corvara landslide (see fig. 5). Furthermore, activity in the

T ABLE 1 - Dating of landslide events which have affected the Col Alto-Pra longia slope

Site Depth Sample Age I ~ C Calendar age 20 Landslide Material Landslide type {fig. 3} (rn) (lab. cod e) (yr BP) (Cal. yr BP)

Corvara B1 25.7 woo d B-112032 8820 ± 50 10,152 - 9632 Rotational slide - earth flow Corvara B1 26.4 wood B-112033 8560 ± 90 9709 - 9334 Rotation al slide - earth flow Corvara B3 22.7 wood B-112031 7920 ± 70 9009 - 8543 Rotation al slide - earth flow Corvara B2 7.5 wood B-112029 4260 ± 70 5025 - 4575 Earth flow Co rvara B2 20.0 wood B-112030 4260 ± 70 5025 - 4575 Earth flow Cor vara c 6.0 woo d B-105976 3830 ± 60 4417 - 3999 Earth flow Corvara b 4.5 wood B-105977 2860 ± 60 3207 - 2792 Earth flow Corvara a 5.0 wood B-93975 2490 ± 60 2750 - 2352 Eart h flow Corvara B4 37.4 wood B-112034 2260 ± 50 2351 -2129 Rotational slide - earth flow Arlara d 3.5 wood B-105975 6870 ± 50 7789 - 7592 Rotation al slide - earth flow Col Alto e 2.5 wood B-93976 2350 ± 60 2708 - 2183 Rotation al slide - earth flow

132 accumulation zone of the Arlara landslide during the crests made up of rock masses which are either displaced Preb oreal-Boreal is also confirmed by the 7789-7592 cal. or in their primary setting. Th e landslide head generally yr BP age obtained from sample «d» (B-I05975, tab. 1), a corresponds to sub-plain or reverse-slop e surfaces, fol tree trunk with over 50 cm in diameter, which was ex lowed by well develop ed secondary scarps resulting from posed (at a dep th of 3.5 m from the surface) in the ero rotational slides which have affected the bedrock up to a sion scar p found along the right flank of the Chiesa depth of about 50 m. Th e source area is covered by clayey stream. Owing to the geomo rphological characteristics of deposits some 40-50 m thick (B4 borehole in fig. 4). the landslide, it seems that the tree was buried by earth Th ese clayey covers are subj ect to translational slides and slides linked to the onset of vast rotational slides affecting flows which at present take place along multiple slip sur the bed rock in the source area. faces up to 30 m deep, as proved by inclinometric meas Th e Coruara landslide is a complex slope movement urements carri ed out in instrumented bo reholes. Th e (fig. 3), definable as a rotat iona l rock slide-earth flow, tra ck zone (some 300 m wide) is mad e up of a 40 m thi ck which took place between Braida Fraida and Pralongia clayey cover showing a fair density increase from abo ut 18 and affected both the La Valle and S. Cassiano formations m in dep th (B3 borehole in fig. 4). This cover is at present (Cors ini & alii, 1998). Thi s landslide, which stre tches over subject to a continuous translational movement on multi an area of about 2.5 km, is subdivided into three distinct ple slip surfaces up to 20 m deep. Moreover, the track sectors of depletion, track and accumulation. Th e source zone is still fed by flows from the source area. The accu area , which is bounded at the crown by an over 25 m high mulation lobe spreads into the Rutorto valley at the alti scarp, is composed of three main sectors, separated by tude of 1720 m circa (at the 36 th km of th e no. 244 state

B4 (1905 m) 0 B3 (1755 m) 0.0 - 0./: (l) B2 (1640 m) 0 0 Bl (1565 m) 0.0 - 0./ : (I) 0 10 (2) Cal. yr BP 5025-4575 10 10 0./ - 31.0: (3) 20 0./ - 42.7: (3)

,"- " - (2) Cal. yr BP (2) Cal. yr BP 5025-4575 20 9009-8543

(2) Cal. yr BP 30 10,152-9632 30 '-.. (2) Cal. yr BP 9709-9334 30 30 (2) Cal. yrBP 2351-2129 40 31.0 - 41.7: (4) 40 40 40 50 (m) 4/.7 -55 .0: (5) 41.7 - 55.0: (5) 50 50 (m) 50 (m) T ~ ~ . J 3 ~5 (m) , .1 1m f=:§:l2 4

FIG. 4 - Stra tigraphy and chronological data from boreholes drilled in the Corvara land slide. Legend: 1 - soil; 2 - wood or coal remnants; 3 - poorly compacted landslide dep osit ; 4 - highly compacted landslide deposit; 5 - weathered and fractured bedrock (La Valle Formation) .

133 road) and stretches over a distance of 1.5 km , as far as the and slides/ earth flows . Therefore, the dates of about south out skirts of the village of Corvara (about 1540 m). 2500-3000 years ago obtained from samples «a» and «b» This landslide portion , made up of silty-clayey material, (B-93975, B-105977 , fig. 3 and tab . 1) witness a reactiva gravel and large boulders attains a maximum thic kness of tion of the accumulation zon e du e to th e wid ening of the about 45 rn, as confirmed by boreholes B1 and B2 (fig. 4). source area. In particular, samples «a» and «b» are from In th e case of B2, a con siderable increa se of material com tree trunks with diam eters of ab out 50 ern, cropping out paction is recorded fro m 30m downward. Both the flank s of th e landslide bod y in corresponden ce with the Rut orto of the accum ulation lob e are cha racterised by often active scarp. As for th e tree species, specific analyses on a por seconda ry scarps, link ed to slide processes triggered by tion of trunk from which sample «a » was obtained (in a the undermining caused by the Chiesa and Rutorto sub-horizont al position and perpendicular to the scarp) streams, besides the gene ral down stream displacement of point to a Norway spruce (Picea abies Karsten ) growing the accumulation lob e. on a poorly develop ed preforestal soil (D ibo na, person al The most anci ent ages (about 10,000 years BP) of the communication), whi ch could easily correspond to the Corvara landslide were detected from wood remnants landslide body itself. found at great depth in the cores of two of the boreholes O n the basis of the data collected , it is possible to re drill ed on the land slide body (B1 and B3; fig. 3). As pr evi constru ct the chronology of Holocene landslide events on ously stated, it is probable that the data obtained from the the Col Alto-Pralongia slope and define, at the same time, samples collected in B1 are link ed to the ons et of the Ar the age and area of provenance of the various overlapping lar a landslide. On th e othe r hand, the date of 9009-9334 landslide bodies which make up th e Corvara landslide cal. yr BP provided by the sample collected in B3 (B (fig. 5) (Co rsini, 2000). 112031; fig. 4 and tab . 1), in th e present landslide's track In particular, th e most anci ent displacements of th e zone, witnesses an earl y activity phase of the Corvara Arlara and Corvara landslides, which took place between landslide which, by affecting the Fr eines area, took pla ce 10,000 and 8000 years ago, mo ved from th e Cianaciai by means of vast bedrock rot ation al slides and subse quent and Freines areas in corrispondence to a fault, qu oted as earth slides . neotectonic by Pani zza & alii, 1978 (fig. 3 ). Th e influ Moreover , the dat es of about 4500-5000 years ago, ob ence of this tectonic element on the onset of slop e move tained in th e Corvara landslide's zone of accumulation by ments is du e to the jointed state of the rock masses which mean s of two samples collected in B2 (B-112029, B favoured water infiltration up to a considerable depth 112030; fig. 4 and tab. 1) and tree trunk «c» (B-105976; and th e consequent triggering of rotational slid es in th e fig. 3 and tab . 1), which was retri eved from a scarp of the bedrock . Rutorto stream , could be relat ed to slides/earth flows On the contrary, th e subsequent landslide events re which rea ctivated the landslide bod y accumulated in th e sponsible for the form ation of th e present Corvara land pr evious activity phase. Th e date of 3251-2 129 cal. yr BP slide body, which go back to about 4000 years ago, provided by th e sample collected in B4 (B-112034, fig. 4 should be relat ed to the progressive dismantling of the ar and tab. 1) in the source area, at a depth of 37m, witness ea of Fr eines and the first involvement of the Bicocc a area es a second ph ase of significant retrogression of the Cor owing to scarp ret rogression. Th e age of about 2800 vara landslide's crown caus ed by both rot ation al slides years, obtained from a sample found at the bottom of

A (m) 1:«1 1 ~ 5 2100 t------I 2 ~ 6 --- 2000 F IG. 5 - Inter preted chronological cros s section of the Co rvar a [] [] [] 3 ~[] [] (Bl - B4) 7 landslid e. Legend: 1 - events ca. 10.000 cal. yr BP (provenance tOo Oo ooo~ 4 (a, b, c) 8 1900 o 0 0 0 Cianaciai: Arlara landslid e; see fig. 3); 2 - events ca. 9000 cal. yr 1800 BP (prove nence Freines; see fig. 3); 3 - events ca. 50 00-4000 cal. yr BP (p rovenance Freines and 1700 Bicocca; see fig. 3); 4 - events ca. 3000 -2000 cal. yr BP (prove - nance Bicocca; see fig. 3); 5 - La 1600 Valle Forma tion; 6 - S. Cass iano Fo rmat ion; 7 - , i i boreho les (see 1000m 100 fig. 3); 8 - tree tr un ks collected 1500 in th e Ru torto river sca rp (see NW S E fig. 3L

134 borehole B4, in the source area of the Corvara landslide, torrent OrIgm and fluvioglacial deposits (fig. 6). Moreo shows that the Bicocca area was affected by the landslide ver, in the excavation fronts analysed (Section A to Sec only in relatively recent phases. Furthermore, the dates of tion C, in fig. 3), gravel and sand deposits related to allu about 2500-3000 years obtained from samples «a» and vial deposition, thin bedded lacustrine silt-clay deposits, «b» in the zone of accumulation of the Corvara landslide, palustrine peat deposits and coarse-grained breccias mo pinpoint that the activity in the source area had significant bilised by debris flow have been recognised; they make up repercussions also on the accumulation zone, causing the top four metres of the deposits exposed in Section C such soil disarrangement that the survival of the forest (fig. 6). cover was inevitably doomed. Finally, it should be noticed Radiocarbon dating of some of the most significant that some 2500 years ago considerable slope displace samples of organic material (tab. 2) and the correlation ments affected also the Col Alto landslide. between the different types of sediments from boreholes and sections has allowed the Holocene environmental ev Col Maladat landslides and associated lacustrine deposits olution of the Corvara in Badia plain to be reconstructed. Two main phases seem to have occurred in the past, dur In the plain of Corvara in Badia two main orders of al ing which lacustrine and alluvial sedimentation linked to luvial terraces are found; they are located at a higher alti landslide damming prevailed. These phases were inter tude with respect to the Rutorto and Pissadu watercours valled by a period of erosion, which led to the cutting of es. A detailed study of this area, supported by the strati the barrage and the formation of first order terraces in the graphic data obtained from two continuous-coring bore plain of Corvara in Badia. holes carried out on the terraces (S5 and S6 in fig. 3) and In particular, the most ancient damming phase (be by the analysis of excavation fronts some hundred metres tween about 10,500 and 7200 yr BP, see fig. 6) caused the north of Corvara in Badia (Section A to Section C, in fig. formation of a lake which occupied all the Corvara in Ba 3), has revealed that the origin of the deposits making up dia plain, with the deposition of fine materials between the these terraces is ascribable to both alluvial and lacustrine altitudes of 1500 and 1522 m. The particle-size and mor sedimentation. The analysis of the geomorphological phological characteristics of the Col Maladat landslide, re characteristics of the slopes located downstream of Corva sponsible for the damming, as well as the results obtained ra in Badia has allowed the origin of the valley barrage to by Pirocchi (1991) and Casagli & Ermini (1999) on other be ascribed to rotational slides affecting the eastern slope landslide damming lakes in the Alps and Apennines, show of Puez-Gardenaccia, near Col Maladat (fig. 3). This val ley barrage was responsible for the onset of lacustrine en that the depletion of the most ancient lake is to be as vironment conditions in the plain of Corvara in Badia. cribed to the progressive erosion of the barrage sill. On The slide gave origin to a zone of accumulation made up the other hand, the most recent damming phase (between of various-sized limestone and dolostone boulders and about 4000 and 3200 yr BP, fig. 6) is related to a smaller marls, which barred the valley floor, now cut through by impoundment which led to the deposition of fine material the Gadera stream. between the altitudes of 1499 and 1503 m in the areas In particular, from the continuous-coring boreholes close to the barrage (this phase was identified only in Sec carried out upstream of the barrage in the plain of Corva tions A and B). In these areas, the cutting of the second ra in Badia (S5 and S6, in fig. 3), conspicuous layers of la phase lacustrine deposits by the Gadera stream began custrine clay interbedded with organogenous horizons some 3000 yr BP. In the upstream areas, which in this sec have been identified (especially in S6). Lacustrine sedi ond phase were not affected by lacustrine conditions (e.g., mentation is followed by alluvial deposition (especially in in correspondence with borehole S5), a phase of alluvial S5) and, to greater depths, by gravel deposits of probable deposition started, lasting in some places until the mid-20th

T ABLE 2 - Dating of the lacustrine deposits of Corvara in Badia

Site Depth Sample Age I·C Calendar age 20 Material Geomorphological event type (fig. 3) (rn) (lab. code) (yr BP) (Cal. yr BP)

S5 20.20 peat B-112026 9080 ± 70 10,401 - 10,154 Deposition in dam lake (start of 1st phase) (first failure of Col Maladat landslide) S6 20.24 peat B-112028 8810 ± 70 10,173 - 9557 Deposition in dam lake (l st phase) S6 5.47 peat B-112027 6460 ± 90 7563 - 7213 Deposition in dam lake (l st phase) Sez. C 4.40 wood B-112025 7740 ± 80 8696 - 8386 Deposition in dam lake (Ist phase) Sez. B 4.20 peat B-112023 3550 ± 70 4075 - 3640 Deposition in dam lake (start of Znd phase) (Col Maladat landslide reactivation as debris flow) Sez. B 1.44 wood B-112022 3210 ± 60 3626 - 3272 Deposition in dam lake (end of 2nd phase) Sez. A 0.48 soil HD-19408 1249 ± 22 1263 - 1090 Recent soil

135 2100 B (m) 2050 7 2000 2000 Ell 1950 1950 a 1900 Wt?~~~ 1900 8 4 1850 1850 1800 1800 b 9 1750 2 1750 1700 1700 1650 1650 1600 3 ~~.~ 1600 6 1550 1550 1500 1500 1450 1450 1400 1400 (m) (m) R.Gadera

I 1500 500

2 3 4

10.9: (5) 8.9 - UPPER LEVEL lacustrine depos itional phase 10 from 10,400 to 7213 Cal. yr BP ___ (max . elevation in 55: ca.1522 m) 11 10.9 - 11.3: (2) --- 12 4.40 - 20.30: (3) ------+ 13 11.3 - 15.2: (5) 9.4 - 9.5: (2) --.....:..-_ --- 10 14 10.4 - 10.5: (2) --- 11 15 JJ.2 • 1l .3: (2) --- 15.2 - 16.7: (4) --- 12 --- ...... /2.3 - /2.4: (2) --- 16 16.7 - 16.8: (2) 17 13 Sez. B (1504 m) 14 /4 ./ - 14.2: (2) 18 UPPERLEVEL o 0.0 - 0.3: (1) lacustrinedep ositional phase 15 from 4075 to 3270 Calyr BP }~k. 19 (max. elev. in Sez. B: ca. /503 m) 0.3-1.3: (6) Sez. C (1503 m) 16 ~QJJ.l 20 /6.4 - 16.5: (2) ___ :..!.. 1_ __ 0 0:.0.-0.3: !LL. 17 (2) Cal. yr BP 21 (1502 m) Sez.A 3626- 3272 0.3 - 4.3: (6) 18 0.0 - 0.1: (1) 2 22 o 2.0 - 2.3: (6) 0.1 ,' 0.5: (6) 19 23 (2) Cal. yr BP 20 2 24 - (2) Cal. yr BP 1263 -1090 20.6 - 29.0: (5) 21 :"'0,173- 9557 25 <, 22 26 <, 23 -, 27 \ 24 4 28 20.3 - 29.0: (5) \ (m) 25 \ 26 BASELEVELerosional phase 6 \ . 7200 - 4075 Cal. yr BP ~ . elev in Sez. B:ca . 1500m) (m) I 27 _ -L

I 28 I 6 I (m) I BASE LEVEL - r-- (m) lacustrine depositional phase --_ ~-NE .I .j4-sw- 500 m -NE+l from 10,400 to 7213 Cal. yr BP ' ...SW-500 (min. elev. in 56: ca. 1500 m s.l.m.) - ......

FIC, 6 . Stratigraphy. chronology and correlation of terraced deposits at Corvara in Badia and cross section of the Col Maladat landslide. Legend: 1 . soil; 2 . peat and coal remn ants ; 3 . lacustri ne clay and silt; 4 - lacustrine silt with alluvial inflows; 5 - alluvial and fluvioglacial gravel and sand; 6 debris flow angular bloc ks and gravel; 7 . Col Maladat landslide; 8 . valley damming elevation 10,400·7213 cal. yr BP; 9) valley damming elevatio n 4075 ·3270 cal. yr BP.

136 century (as shown by 1955 aerial photographs). The for eastern sector of the Puez Gardenaccia and the Col Alto mation of the second order terraces found in the Corvara Pralongia ridge which was previously discussed (Panizza plain is in fact a consequence of the hydraulic works im & alii, 1978; Corsini, 2000) . plemented after the 1966 intense precipitation. With the beginning of the Holocene, some 10,000 14C The 14C data relative to the lacustrine deposits of the yr BP (Mangerud, 1982), a considerable increase in tem Corvara in Badia plain show that the onset of the Col perature caused the progressive disappearance of perma Maladat rotational slide, about which no direct data exist, frost on the lower slopes, which are generally character presumably took place some 10,000 years ago (data ob ised by arenaceous-marly bedrock with a dominant pelitic tained from B-112026 and B-112028 samples, collected component, and the onset of forest vegetation, which at from S5 and S6 boreholes respectively, in correspondence the end of the Preboreal, attained altitudes near to 2000 with the appearance of fine lacustrine-type sediments; mi. Indeed, it was just during the Preboreal and Boreal tab. 2). This event barred the valley with a sill exceeding that the complex slope deformations previously described the altitude of 1520 m (which is the maximum altitude at were triggered, i.e. the rotational-translational slides and which lacustrine deposits were found in S5 and S6; fig. 6). earth flows of the Col Alto-Pralongia slope, and the Col A subsequent reactivation, which took place about 3800 Maladat rotational slide which gave origin to a long last years ago (B-112023 sample, collected at Section B; tab . ing valley barrage. 2), caused the formation of a barrage with a sill exceeding Later, during the Atlantic period, which was charac 1503 m a.s.l., which is the maximum altitude at which la terised by «optimal» climatic conditions, the already ex custrine deposits were found in Sections A and B (fig. 6). isting landslides underwent a phase of relative dormancy. From the analysis of the landslide's morphological fea In this period, the morphogenesis of the area was prob tures, it results that this reactivation took place by means ably conditioned by prevailing frost-shattering processes of debris slides and flows. The debris flow blocks that (which increased the thickness of debris and alluvial fans) were found in Section C (in which deposits ascribable to and by the action of surface water. In the area of Corvara this second lacustrine phase were not found, fig. 6) could in Badia, where a lacustrine impoundment was present, in fact belong to the landslide deposits responsible for the sedimentation processes were rather intense. The data second damming phase. concerning this area (fig. 6) show that in about 2500 years over 20 m of clay, gravel and peat were deposited, corre sponding to a sedimentation rate of nearly 1 ern/yr. The RELATIONSHIPS BETWEEN abundant input of sediments into the lacustrine impound GEOMORPHOLOGICAL EVOLUTION AND ment may also be justified by considering the erosional action of the Rutorto stream on the Arlara and Corvara PALEOCLIMATE landslide bodies. The climatic worsening which took place in the Sub The area of Corvara in Badia was affected by typically boreal period and during the first Subatlantic phase coin glacial environmental conditions until 18,000-20,000 yr cided with the reactivation, widening and retrogression of BP, when the pleniglacial cover, which attained elevations most complex landslides occurring along the Col Alto near to 2300 m, started to undergo a rapid decline. Later, Pralongia slope. The increase of precipitation during this during the Lateglacial period, the area was affected by period probably had consequences also on the erosional valley-type glaciers but, at the same time, there was a power of the watercourses. Between 6500 and 3500 years quick transition towards periglacial environmental condi ago, following the erosion of the barrage of the Col Mala tions, as shown by data resulting from studies on the tem dar landslide, the Rio Gadera cut through the materials poral recurrence of landslides in the adjacent Cortina deposited near Corvara in Badia for a thickness of about d' Ampezzo area (Panizza, 1973; Panizza & alii, 1996; Pa 20 m. This took place during the previous lacustrine nizza & alii, 1997; Pasuto & alii, 1997; Soldati, 1999) and phase, thus causing the formation of the marked terracing from the paleoclimatic reconstructions by Orombelli & still visible on the site. The gravitational activity due to Ravazzi (1996) . The latter have been taken as a reference landsliding processes continued with the further increase for the present discussion on the relationship between ge of precipitation, which occurred about 2500 yr BP, and omorphological evolution and paleoclimate. The change with a strong repercussion on the landslides of Col Mala of the environmental conditions which accompanied the dat (which once again dammed the Gadera valley), Corva beginning of the Lateglacial led to a morphogenesis ra and Col Alto. . linked mainly to frost-shattering processes and slope During the Sub atlantic, the environmental conditions movements which gave origin to both talus and debris were on the whole very similar to the present ones and fans and massive rock falls from the dolomite cliffs. The deep-seated landslides remained probably dormant. geomorphological characteristics of some complex land slides of the Alta Val Badia - which are not described in this article - seem to suggest that during the Lateglacial some slopes were subject to deep-seated gravitational 1 According to Burga (1988), during this period in the Swiss Alps deformations linked to the neotectonic fault affecting the the tree line rose from 1300 m to nearly 2000 m a.s.l.

137 FINAL REMARKS chanical characteristics are generally highly influenced by climat e conditions. At the same time, though, these rock The geomorphological and str atigraphic study of the types are responsible for a limit ed persistence of the accu landslide dep osits obse rvable on the Col Alto -Pralongia mulation forms on slop es; slide and flow-type landslides slope and of th e lacu strine sediments found near th e Cor are in fact quickly obliter ated and their persistenc e in time vara in Badi a plain, together with radiome tric datin g on is directly prop orti onal to the mat erial volumes involved. organic remnants enclosed in these dep osits, have allowe d It can therefore be inferred that, in orde r to evaluate medi a detailed reconstruction , also from the chron ological um and long-cycle climatic changes, small-sized slides and viewpoint, of the geomo rphological evolution of some flows are generally not utilisable, whereas la~dslid es in slope's portions surrounding th e village of Corvara in Ba volving large volumes of material , such as those investigat dia, identifying the phases of intense gravitational activity. ed in the stu dy area, are extremely useful. The data collected demon strate the existence of a cer Furthermore, ~ l i de and flow landslides allow apprecia tain chronological correspondence between onset of ble climate changes to be identified whe n th ey occur after movement and phase s of development of the Arlara and a sufficien tly lon g period of dormanc y, th at is afte r th e co Co rvara land slides, on th e Col Alto -P ralongia slope , and lonisation of the landslide bod y by arbo reo us vegetation. of th e Col Maladat landslides, which are held respon sible H owever, whe n one of these events takes place, the mass for th e form ation of a large dam lake in correspondenc e wasting process continues mostly indipendenrly of climate with th e Co rvara in Badia plain . condition s, until the whole slop e has come to a new equi Furthe rmore, there is likely to be a correlation be librium (relaxation time according to Allen, 1974, and tween th e da ted landslides and the climatic vicissitu des Brunsden, 1980). which have affected th e Alps since the beginning of th e On th e basis of the data available, it is th erefore possi last deg laciation. The triggering of slope movements ble to hypothesise a close relationship between deglacia chronologically corresponds to the considerable increase tion and onset of the vast slope movements present in the of temperature of the Early H olocene, which caused th e stu dy area (Arlara, Corvara and Col Malad at landslides), withdrawal of glacial tongues and the melting of penna in agreement with th e data from other European areas. At frost. O n the othe r hand, further stages of landslides' in the same time, th e support of other data would be neces tense activity correspond to the humid periods of the sec sary for maintaining the assumption of a massive resump on d half of the H olocene. tion of erosional slope activity during the humid ph ases of The data achieved in this research, altho ugh they are the Subboreal period. not sufficient for definin g a direc t and reciprocal relation ship between a slope's weathering processes and climatic changes, ha ve nevertheless confirme d some hypotheses al ready eme rging fro m previou s investigations carri ed out in adjacent areas (see Soldati, 1999; Corsini & alii, 2000). Alth ou gh a certain un certainty remains about the BIBLIOGRAPHY causes which triggered the landslides investigated (the ini tial movement might be link ed also to neotectonic caus ALLENJ.R.L. ( 974) - Reaction, relaxation and lag in natu ral sedimentary es), it seems logical to hypothesise th at du ring the deglaci systems: General principles, exam ples and lessons. Earth Science ation period the progressive disappearence of pe rmafrost Reviews, 10,263-342. allowe d water infiltration through the rocks' joint s and BOSELLI NI A. (1965) - Lineament : Strutturali delle Alpi Meridionali du other discontinuities. Therefore, th e increase in tempera rante il Permo-Trias. Mem. Mus. Stud. Nat. Yen. Trid., 15(3), 1-72. ture may be considered, in any case, a determining cause BOSELLI NI A. (1968) - Paleogeologia pre-anisica delle Dolomiti centro -set for the ancient displacements that affected the Arlara, tentrionali. Atti Ace. Naz. Lieei, anna 365 (d . sc. fis., mat. e nat.), ser. 8-9, (sez , 2a), 1-32. Corvara and Col Maladat landslides. Th e landslide events stu died and, in particular, their BOSELLI NI A. (1996)- Geologia delle Dolomiti. Athesia, Bolzano, 192 pp . phases of activation alterna ting with periods of dorm ancy, BRONDI A., MITTEMPERGI-IER M., PANIZZAM., ROSSI D.. SOMM AVIL LAE. & VUILLERMI N F. (1977) - Note esplicatiue della Carta Geologica seem to be significant geomo rphological indicators of cli d'ltalia alia scala 1:50.000, FO028 «La Marmolada». Servizio Geo lo mati c changes, altho ugh it is not possible to identify a di gico d'Ita lia, 30 pp. rect cause-effect relationship between landslides and cli BRUN SD EN D. (1980) - A pplicable models of long term landform evolu mat e changes . In particular, there are some limit s for their tion . Zeit. Geo morp h. N.F., 36. 16-26. use as indicators; indeed, the landslides investigated devel BURGA CA. (1988) - Sioiss vegetation history during tbc last 18,000 years. op ed in correspondenc e with tectonic features (considered New Phytol., 110, 581-602. as neotectonic by Panizza & alii, 1978) which might have CARTON A., CASTALDINI D. & PANIZZA M. (1980) - Schema neot ettonico caused or simply favoured the onset of displacements . riassuntiuo dell'area I ra Trento e Cortina d'A mp ezzo (Fogli P.P. Bol Moreover, the lithological charact eristics and geological zano (I O), M. Marmolada (l I) , Cortina d'A mp ezzo (I2), Trent o (2 1) e Feltrc (22)). In: Cont ributi alla realizzazione della Carta Ncotcttoni structure of the stu dy area are , on one hand, a limiting fac ca d'ltalia, Progetto Finalizzato Ge od inamiea , Pubb l. 356. 621-64 1. tor for the use of these land slides as indi cators and, on the CASAG LI N. & ERMI NI L. (1999) - Geomorph ic analysis o] landslide dams othe r hand, a determining one . Slide and flow landslides, in tbe North ern Ap ennines. Tr ans. .T ap. Geomorp h. Union, 20(3) . whi ch are produced on pelitic rocks with poor geome- 219-249.

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