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Supplements of Geografia Fisica e Dinamica Quaternaria
Volume I - 1988

 

Proceedings of the meeting:
The Morphotectonics in Italy

OROMBELLI G. & SAURO U.

I Lavini di Marco: un gruppo di frane oloceniche nel contesto morfotettonico dell’alta Val Lagarina (Trentino) – The Lavini di Marco: a complex of Holocene Iandslides in the morphoneolectonic context of bigh Val Lagarina (Val d’Adige, Southern Alps, ltaly)

Pages 107-116

Abstract

This rcporl examines a group of seven large landslides on the western slope of MOllnt Coni Zugna, between Rovereto ~md Serravalle all’Adige (Trentino, SOUlhem Alps, Italy), of which the largest is the complex landslide known as Lavini di Marco. ‘l’he morphological features of the failllrc and accumulation zones are described, ancl the chronological ordcr of eVCnlS is tentativcly establishcd, by means of clating of buried soils ami analysis of thc dif· ferent clegree of clevclopment of thc kal’slic col’rosion microforms. The evolutioll of this large slope in the regional morphoteclOnic contcxt is also consielered. Thc landslieles examined here, which involved the large elip slope of a monoclinal relief of hogback type, may be classifiecl as rranslational slieles, some of which cvolved imo dcbris uvalanches. Thc diffcrences in altitucle range bctween 300 and 1200 ll1 anel the elistances travelled between a Cew dozen meters and about 5 km. Thc thickncsses involved are genernlly small and in any case less l’han apPl’Oximatcly 100 m; the volumes mobilizeel range between 0,5 ancl 200 million mJ , ln some landslides or parts of them slieling soon stopped, withollt l’eaching complete dismembering anel crllshing of the rocky masses, while in other cases the mobilized masses were completcIy crllshcd amI rransformecl into elcbris avalanches, capable of f10wing for consielerable horizontal distances, even along the vallcy bottom (more than 1,5 km in the case of the main dcbris dcposit). The mocles of flow of these elcbris avalanches may be interpreted by rccaIJing some internaI structurcs observed in artificial sections of the quarry faces in the Lavini di Marco: conccntration ancl «floating» of the coarser boulders on rhe surface; fine matrix, clcarIy dominant at elcpth; – flow sub·units, which maintain their ielentity to a cettain extent both Iithologically and morphologically, forming concentric imbricated stmcturcs whose thrust planes clip towarcls the interior of the accumulation zone. The superfjcial morphology of these strllcturcs is provideel either by a succession of smaII crescent-shapecl banks, or by bclts of different grain size, as showll by vegetation. From the viewpoint of typologies, spatial interrelations and relative ages, obtained from analysis of thc elcgl’ec of devclopmcnt of corrosion microforms, most of the fandsliclcs may be coeval, exccpt for the slide at 772 m, which is older than tbc main sliele. This is also confiJ’llleel by a C14 dating of one of il’S bUl’ieci soils (5630 + 80 H.P.). The largc Lavini slicle is of complex type: parts of thc nichc and of the slide sUl’face are stili aclive or at least subject te slow clescent anel clcfonllation. The accumulation zone is composed of both «1 Lavinil) anel the «Gran Ruinal> neal’ thc hOllses of Pinel’a (markcel Lavini di Marco on the topographich map). lts emplacement may be coeval with that of the Val’ini slide, to which an age of 1300 B.P., calculateel on a bllrieel soil, is arU’ibutcd (this age, if calibrated, may be considered compatible or quasicompatible with the High Meclieval ages of 369 allei 883 A.D”" founel in some historical records). ‘l’he degl’ee of development of karst microforms on the l’ocky surfaces indicate that, in this 6 km-Iong sector of rhe Idt slope of the Val d’Adige, at least two separate landsliele events occurl’ed, involving sevcral accllmularions, not always c1early separate hom each other. The mosl spcctacular of these two cvents was the more recent, which ali data and finding so far available indicate as histotical. This means that the phenomenon of large scale landslicles was repeated duriog the Bolocene, and many morphological signs indicate that the great slope is stiIJ involvecl in clcforrnationnl proccsses which rnay produce future landslicles. The problcm thercforc ariscs of carcful evaluation of morphotectonic signs, which ma}’ support the correlation between earthquakes anel landslicles. Thc literatlll’e contains many indications and evidence of active tectonics in this part of the Southctr1 Alps. Many morphologicnl aspccts of thc Coni Zugna rielge point to recenttectonic movemcnts. In parriculat, large-scale ridge splitting with the formation of longitudinal furrows anel opposed scarps may be observed for more than 3 km along the top of the ridge. Thcse fotms, caused by slope tectonics may be the consequence l10t only of gravity, but also tilting of thc enti!’e ridge, with a tendcllcy towards uplifting in the castem edge. Thc ridge is cut obliqucly by NW-SE faults causing small fault scarps and f1exul’es, expressions of reccnt or nctive tectonic deformation. In particular, in tbe lower l’art of the large dip slope on the nOl’thel’n margin of thc main lanelslicle there is a fallir scarp facing NE, and a S\YJ facing []exllre scarp in the intermecliatc l’art of the slope. ‘l’he flexure defining one part of the edge of the lanelslide nichc may have formeel eluring the lanelslide evento In this case thc Ial’ge slielc may have been triggered by a seismo-tectonic event involving diHcrenrial movcments along the fault anel the flexure. The colIcctcd clata thercfore tend to suppon the hypothesis of a seismo-tectonic trigger mechunisl11, which woulcl also plUllSibly explain thc contcmporaneity of several cootigllOUS landslieles.

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