Holocene slope instability in the Italian Dolomites: paleoclimatic significance of landslides in a European perspective

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1 FORM-OSE OSE POST-GRADUATE TRAINING SCHOOL Living with hydro-geomorphological risks: from theory to practice September Strasbourg, France Holocene slope instability in the Italian Dolomites: paleoclimatic significance of landslides in a European perspective LANDSLIDES Temporal occurrence of landslides Several papers report landslide dates obtained through different methods and showing different chronological distributions CLIMATE Climate change In literature: chronological schemes of the Holocene showing climate changes Correlation between landslides and climate change Mauro SOLDATI (soldati@unimore.it) Dipartimento di Scienze della Terra, Università degli Studi di Modena M e Reggio Emilia 1 Chronological schemes for different European regions

2 Climate changes occurred since the Late-glacial have certainly influenced landslide occurrence indirect direct direct Glaciers retreat permafrost melting precipitation increase 7 8 MAIN LANDSLIDE CAUSES in the Dolomites GEOLOGICAL CONDITIONS - stratigraphy (brittle dolomite rocks overlay plastic pelitic rocks) - tectonics (intense faulting and jointing favours seepage in depth and the formation of detachment zones and sliding surfaces) - neotectonics (few cases of earthquaketriggered landslides: e.g. Cinque Torri earthflow, 15 sept Friuli earthquake) GLACIATIONS - glacio-pressure (related to Würm pleniglacial LGM- ice cap, particularly intense at the confluences of different tongues, caused rocks to deform in correspondence of structural discontinuities favouring the formation of sliding surfaces at deglaciation) -permafrost melting (made rocks weaker and more water available at greater depths) Val Gardena Val di Fassa Gardenaccia Sella olzano Trento Val adia Corvara in adia Marmolada Settsass Reconstruction of ice cap at ca m a.s.l CLIMATIC VARIATIONS CASE STUDIES in the Dolomites - temperatures (and related changes in vegetation cover and altitude) - rainfall (changes in annual total precipitation and precipitation pattern) Holocene Hypsithermal HUMAN ACTIVITIES Late-glacial (early settlements = deforestation?) LGM

3 24 Landslides dated in ALTA ADIA Case Study 1: ALTA ADIA San Leonardo (ALTA ADIA) - earth flow event dated to ca cal yr P - reactivated in 1997 San Cassiano (ALTA ADIA) Mudflow event dated to ca cal yr P (organic soil in excavation) / C yr.p Cal. yr P Samples location (-11.1 m, wood in borehole cores) (trunk in excavation) / C yr P / C yr.p Cal. yr P Cal. yr P 16 Passo Gardena (ALTA ADIA) Rockslide event dated to ca cal yr P Passo Gardena (ALTA ADIA) Earth flow event dated to ca cal yr P (-38.5 m, wood in borehole cores) / C yr.p Cal. yr P A C D C D R surface exposure dating by cosmogenic 36 Cl AMS measurement in dolomite rock from the main scarp AGE: from about to 8500 yr P 17 with erosion rates from 20 to 10 mm/ka respectively D 18 3

4 Colfosco (ALTA ADIA) Col Maladat (ALTA ADIA) -Rockfall / rock avalance event dated to ca cal yr P Series of rotataional slide events datated from ca cal yr P by way of dam-lake deposits Col Maladat / C yr.p Cal. yr P 19 oreholes ( S6 ) 20 Excavation Sections (ex. Sez ) Colfosco Pescosta Corvara COL MALADAT (Wood 5.4 m) / C yr P Cal. yr P (tree trunk, m) / C yr P Cal. yr P Erosion scarps (Rutorto stream) Corvara (ALTA ADIA) Series of Earth flow events dated from ca to 2000 cal yr P oreholes ( 1 ) A A A (tree trunk, -6 m) / C yr.p Cal. yr P (wood, m) / C yr.p Cal. yr P 24 4

5 11 Landslides dated in CORTINA D AMPEZZO Case Study 2: CORTINA D AMPEZZO Col Druscié (CORTINA D AMPEZZO) Pierosà (CORTINA D AMPEZZO) Rock slide event dated to ca cal yr P Rock slide event dated to ca cal yr P (tree trunk, m) / C yr.p Cal. yr P (tree trunk, -4.5 m) / C yr.p Cal. yr P Lacedel (CORTINA D AMPEZZO) Earh flow events dated from ca to cal yr P Cortina-begontina (CORTINA D AMPEZZO) Series of earh flow events dated from ca to 3000 cal yr P GX GX (tree trunk, -5.0 m) (tree trunk in borehole S1, m) (tree trunk in borehole S2, m) / C yr.p / C yr.p / C yr.p Cal. yr P Cal. yr P Cal. yr P

6 Pezzié (CORTINA D AMPEZZO) Cortina-Staulin (CORTINA D AMPEZZO) Earh flow event dated to ca cal yr P Earh flow event dated to ca cal yr P GX (tree trunk, -3.5 m) (wood in borehole, m) / C yr.p / C yr.p Cal. yr P Cal. yr P 32 A total of 62 dates have been collected in Alta adia and Cortina. ALTA ADIA Are they all climatically significant??? The degree of CLIMATIC SIGNIFICANCE of each dated event has been assessed on the basis of the following aspects: Geomorphological context in which the dated landslide took place Type of dated landslide Size/magnitude of the dated landslides Material involved in the dated landslide (rock, earth, debris, ) CORTINA D AMPEZZO 33 Type of dated material (wood, peat, soil, ) Depth at which the dated material has been found orehole stratigraphy (if dated material is from cores) 34 Temporal distribution of climatically significant landslide events In the Dolomites In Europe From: Goudie, A., Environmental change. Third Edition, Oxford Univ. Press, Oxford, 329 pp Increase of precipitations Landslides?? Deglaciation & permafrost melting

7 Can a concentration in time of landslide events indicate a climatic variation?? WORK IN PROGRESS A national research project has recently been founded by the Italian Ministry of Instruction, University and Research (MIUR): Yes, but not necessarily Other uncertainty factors Non-climatic causes -Lithology -Tectonics -Morphology -Hidrogeology -Vegeatation -Land use -Human activities -etc. 37 COFIN 2002 Geomorphological evolution of slopes and climate changes: landslide analysis and paleoclimatic reconstructions in Northern Italy Scientific Coordinator: Mauro Soldati Dipartimento di Scienze della Terra, Università degli Studi di Modena e Reggio Emilia Dipartimento di Scienze dell'ambiente e del Territorio, Università degli Studi di Milano icocca Dipartimento di Scienze della Terra, Università degli Studi di Torino Dipartimento di Geologia, Paleontologia e Geofisica, Università degli Studi di Padova Dipartimento di Scienze della Terra, Università degli Studi di Parma 38 Data collecting Database and GIS Archive of dated landslides in the Alps and in the Northern Apeninnes (in construction) Published on the internet ( Dendrochronological Analysis Paleobotanical Analysis Paleoenvironmental evolution during middle Holocene: information on climate, vegetation, slope instability, snow avalanches and human activity

8 Archaeological surveys Future developments in the framework of global climate recostructions: comparison with other environmental proxies Case study S. Leonardo - Sotciastel Holocene records of the lake-level fluctuations in the Jura mountains (Magny, 1999); Dated Cortina and Corvara landslides events; Periods of enhanced landsliding in the Western Swiss Alps (Dapples et al, 2002); Phases of glacier retreat in the Central Swiss Alps (Hormes et al, 2001); Holocene variations of glaciers in the Alps (Gamper and Suter,1982); Landslide event dated at 5600 cal P The PCI at GISP2 (Mayewski at al., 1997); nearby a ronze Age fortified Village 43 The IRD events marked by Icelandic glass and hematite-stained grains (core VM , North Atlantic, ond et 44al., 1997) Chronozones (Orombelli and Ravazzi, 1996) Thanks for your attention! 45 8