Climate change impacts on NATURAL EVENTS 3.4 MASS MOVEMENTS |
3.4.0 Mass movements all types |
3.4.1 Shallow landslides |
3.4.2 Deep landslides |
3.4.3 Rock fall |
3.4.0 MASS MOVEMENTS ALL TYPES
Type of knowledge |
Results and interpretation |
Observation and analysis methods |
References |
Reconstructions |
Europe: At present, there are not enough data to link landslide activity with past climate conditions. It seems clear that activity in Holocene times is not exclusively due to the retreat of glaciers and that landslides have been taking place since that time. Some shallow landslides can be directly related to rainfall events, whereas most of deep-seated landslides can not. It is not probable that large landslides can always be associated to changes in climatic regime and, earthquakes, mountain upfliting, and stress relief may be found as alternative triggering factors. The role of deforestation in the increasing historical landslide activity is not well known. Datings made in Switzerland and UK show that the large post-glacial landslides were not produced just after the glacial retreat, but with a delay of up to several thousand years (Schoeneich 1991). These movements could not have been simply produced by basal undermining of the slope by glaciers. It is necessary to find other factors which could explain this delay, such as the presence of deep permafrost and its thaw or simply the time needed for the development of a failure. |
Bibliographic synthesis |
Corominas & al 1994 - R: EPOCH |
Europe: With regard to the last two centuries, another important result is the demonstration of the significance of human factors and their frequent implication in the triggering or activation of earth movements. The part played by earthquakes is demonstrated in the Dolomites but, taking account of the seismic distribution in the regions studied, it appears to be a subordinate role by comparison with anthropic and above all climatic causes. |
This synthesis is based on many studies done in the framework of the programme EPOCH. The researchers engaged in the programme used the same methodologies for the collection, storage and analysis of data. |
Flageollet 1994 - R: EPOCH | |
| Swiss Alps: Around 13 000 BP, the local glaciers are still in the bottom of some prealpine valleys located above 1200m and prevent any mass movement triggering. From the beginning of the Würm glaciation until the end of the tardiglaciaire, the prealpine regions in flysch area are not the place of many mass movements because of the climatic parameters inducing very low limit of permafrost (around 1500m). The next period with many landslides in the Flysch area in the PreAlps is the one between the recent Atlantic (6000 BP) and the end of the Subboreal (2700 BP). For example, the first movement of the Falli-Hölli in the Fribourg Pre Alps (Gurnigel Flysch) has been dated around 5000 BP. Between 5000 BP and 2300 BP, five major reactivation periods have been observed in this slope. Three periods occurred during “warm” period with glacier retreat. Furthermore, during the Subboreal, the reactivation are corresponding to “wet” period, reconstructed from Gerzensee drilling. The period between the recent Atlantic and the Subboreal end seems to constitute a period favourable to deep mass movements (more than 10m deep) in the Alps. The Falli-Hölli example is not isolated case and other mass movements from the Singine area (Hohberg slide) have been recently dated between 1715 BP and 3190 BP (Subboreal). The La Lavanche mass movement (Ormont valley) shows also a reactivation during this period (1870 BP). In Austria and Germany, some rocky slides have been dated with C14 method around the Subbreal end. These isolated data tend to confirm the correlation, as for the Preboreal, between milder climate and deep landslides frequency during the recent Atlantic and the Subboreal. After the precipitation increase recorded in Singine during the 1978-1988 period and the rise of minimum temperature during winter and spring, many instabilities area near the Falli-Hölli site in the Lac Noir valley get reactivated. |
Geology, geomorphology, archives, dendrochronology, C14 dating, cadastral maps, maps and various measurement techniques allowed to reconstruct partially the past and recent history of unstable slopes during the Quaternary. Recent surface movements of landslides were recorded with geodesic point control by theodolithes or by GPS antennas. The landslide plans were detected by inclinometric measures in drillings or by geophysic prospecting. |
Lateltin & al. 1997 - R: PNR31 | |
Italian Dolomites: The first cluster includes landslides of various types which occurred in the early Post-glacial when, after the retreat of the Würmian glaciers, slopes became prone to mass movements. On the one hand, these movements consist of rock slides of considerable size (e.g. Zuel and Col Drusciè landslides) detached from the steep dolomitic rock walls no longer sustained by ice masses, as a consequence of glaciopressure implications (cf. Panizza. 1973); on the other hand, they consist of complex movements (Corvara), rotational slides (Col Maladat) and earth flows (Lacedel, Cortina, La Riva) which affected the pelitic formations outcropping in the middle and lower part of the slopes, as a consequence of higher availability of groundwater; the latter is likely to be connected to increased precipitation and permafrost melting (cf. Soldati, 1999). In a European perspective, the period during which these landslides took place coïncides with the oldest period of frequent post-glacial slope movements identified in Europe by various authors (e.g. Starkel, 1966; González Díez et al., 1996; Berrisford and Matthews, 1997; Lateltin et al., 1997; Margielewski, 1998). The second cluster of landslides, which coïncides with the Subboreal period, includes, in both study areas, mostly earth flows involving pelitic rocks. The dated movements are likely to be reactivations of older landslides rather than first time failures, since the same slopes appear to have been mobilised more than once in the past. The period of occurrence corresponds with an increase of precipitation reported in literature. However, the hypothesis of a direct influence of this climate change on landslides, partially confirmed by other European case smilles (e.g. González Díez et al., 1996; Berrisford and Matthews, 1997; Lateltin et al., 1997), still needs further verification especially through the comparison with other alpine sites. However, the Cortina d'Ampezzo and Alta Badia areas have been affected by landslides also during other periods of the Holocene: the recurrent activity bas been favoured by non-climatic factors such as seismic events and litho-structural characteristics of the rock types involved which are either affected by dense networks of joints (dolomites) or markedly ductile (pelitic rocks). Also extreme meteorological events, not specifically related to climate changes, may have triggered mass movements. |
As regards the area of Cortina d'Ampezzo, more than thirty landslides of different type, size age and degree of activity have been identified (Panizza, 1990; Panizza et al., 1996; Pasuto et al., 1997), several of which have been dated by means of radiocarbon method. In Alta Badia a series of radiocarbon dates of landslides and related lacustrine deposits have been collected (Corsini et al., 1999). Many of the dates available refer to movements of the Corvara landslide, a complex phenomenon (slide-flow) located just south of Corvara in Badia. Palaeoclimate curves are from Orombelli and Ravazzi (1996) and Goudie (1992); chrono-zones boundaries are after Orombelli and Ravazzi (1996). |
Corsini & al 2000 - A | |
| Swiss Alps: The heterogeneous repartition of mass movements in the Fribourg Canton during the Late Glacial and the Holocene has been highlighted and periods with high frequency periods have been clearly identified. The following periods show high mass movements frequencies: 11000-10250, 6250-4800, 3600-2100 and 1700-300 cal BP. Despite the fact that correlation is harder to assess for whole Switzerland than only for Fribourg Canton, 4 main periods with high frequency have been identified for Switzerland: 11600-10200, 7000-4800, 3800-2100 and 1900-150 cal BP. At the European level, correlation can be provided between data from different countries, as for the East-West axis linking Western Europe, Central Europe and Eastern Europe. However, strong differences limit the mass movement occurrence analogy for the North-South axis. When comparing these results with the climatic data, the mass movement high frequency periods seems to occur when wetter and colder climatic conditions take place. Water remains the determining parameter for mass movement processes, wetter climatic conditions are far more important than colder climatic conditions. Indeed, enhanced mass movement periods are well correlated with permafrost melting that occurred after the glacial recurrence of the Daun and Recent Dryas. However, cold and wet climatic periods have also occurred with few or none mass movement occurrence. The vegetation cover seems to also play a great rule in stabilizing the slopes despite climatic conditions favourable to mass movements. On one hand, vegetation cover has consequences on hydrologic balance and on the other hand on the superficial layer stabilisation, thus vegetation cover is an important factor affecting slope stability in alpine and pre alpine area. Furthermore, it seems obvious that rock falls and rock collapsing react in different ways to environmental conditions fluctuations, for example to the climatic oscillations, than landslides, debris flows and mud flows. The time distribution of mass movements during the Late Glacial and the Holocene change greatly, depending on the mass movement type considered. |
A mass movement chronology has been built by using dendrochronology and radiocarbon methods. 69 samples, collected in 6 slope instability area in the Fribourg Pre Alps have been used in this chronology. The samples collected in the shallow layers (first 5 metres) are easier to collect than the deep layer sample; thus the shallow layer samples represent the main part of the data set. Samples collected in various Swiss sites have also been considered in a way to increase the spatial scale of the slope instability comparison and to improve the events calibration. Then, the Swiss results have been compared with data from various European sites from North Spain (Cantabric mountains and Pyrénées) to the Carpathians, including South and North Italy, Western and Bavarian Alps, Eastern Rhine and United Kingdom. Comparisons have been conducted between the slopes instabilities chronologic series for the Fribourg Canton and the multiple data describing the time evolution of passive factors such as climatic conditions (temperature and humidity), local, regional and global. |
Dapples 2002 -T | |
Northern Apennines (Emilia Romagna slope): From the available climatic and radiocarbon data, it seems reasonable to gather the dated landslide events in three main groups. The first group refers to landslides that occurred near the transition between the Late Pleistocene and the Holocene, probably as a consequence of the rapid climatic changes that preceded (placed approximately in the Alleröd stage 13,350–12,650 cal y BP) a warm climate oscillation occurred between Dryas II and Dryas III (12,650– 11,600 cal y BP) and followed the Dryas III. Successively, the presented database shows a lack of events for 1,500 years (6,500–4,900 cal y BP). This is the warmest phase of the entire Holocene known as the Atlantic period where also the climatic optimum was reached about 5,750 years before present. Landslide activity took place again at the passage between Atlantic and Sub Boreal periods. In particular it is possible to separate two main periods of activity: the first one (4,900–3,900 cal y BP) during the “Piora oscillation” and the second one from 3,195 to 2,000 cal y BP. Italian peninsula: Eastern Italian Alps (Dolomites): These data are in partial disagreement with other investigations carried out in Central and Northern Europe (González Díez et al., 1996) that show an increase in landslide activity in wetter and maybe warmer periods. As underlined also by Dikau and Schrott (1999) the unconformity of landslide activity across Europe might possibly be explained by both local climatic and geomorphologic factors. |
Tree stumps were found buried by the landslide debris. This
occurrence can produce accurate radiometric dating of the landslide
event, if the stump is still in place.
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Bertolini & al 2004 - A | |
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Observations |
Europe: In Normandy (France), the juxtaposition of annual rainfall diagrams and the annual number of cases recorded shows a close relationship between years of heavy rainfall and the number of movements. The best adjustment is provided by a mobile average calculated over three years. The pluviometric structures and their combinations are decisive: heavy or very heavy rainfall in the preceding month or years. A factorial analysis of multiple correspondence shows that if the pluviometric conditions preceding earth movements are varied, disturbance can occur even after relatively dry months, if they were preceded by abundant annual rainfall. In Bachelard valley (France), the mean threshold intensity for the occurrence of overland flows as determined from rainfall simulations is about 42 - 47 mm/h over at least 5 minutes. If the regolith is very wet the threshold rainfall intensity is much lower: 3 mm/h. In dry regolith mean sorptivity values measured were 0.14 cm/min. In Rheinhessen (Southern Germany), the geomorphological, geological and climatic context are still akin to the regions above but there is no longer a destabilizing marine action and the land use and its development have doubtless been a very strong factor. Nevertheless we still observe the same essential rate of rainfall in landslide occurrence and activity. In Spanish Eastern Pyrenees, heavy rain is responsible for triggering landslides, as are wet periods, and a threshold of 140 mm in 2 days may be accepted as an essential condition for triggering mudslides, though not sufficient in itself. Several rainfall events have exceeded this threshold without causing reactivation, for example in Clos d'Esquer. The results of tree examination cannot all be accepted as a sign of landslide activity, and when rainfall data are not available landslide activity deduced exclusively from dendrochronology must be based on a representative number of trees affected (at least three). In Sicily, movement phases are found to be linked with the highest cumulative rainfall values over 50 days. Shallow slides are more likely to occur after short heavy showers which do not infiltrate easily. This aspect is part of a proposed double-threshold model for forecasting future landslides when rainfall reaches a given intensity/time configuration. |
This synthesis is based on many studies done in the framework of the programme EPOCH. The researchers engaged in the programme used the same methodologies for the collection, storage and analysis of data.
Raw pluviometric data was converted into effective rainfall by calculating the evapotranspiration by different models, sometimes Thornthwaite, sometimes Turc, and we used various methods of relating rain to movements, including graphic correlations, factorial analysis and multiple correspondance, or mathematical formulae defining alert threshold values from the ratio between rainfall intensity and duration. Finally a significant part of the research was devoted to a short period, the last five to ten years, in order to confirm the processes involved, particularly in debris flow, to measure movements, both on the surface and in depth, to analyse their seasonal rhythm and to establish hydrological prediction models. |
Flageollet 1994 - R: EPOCH |
Switzerland: In certain cases, prolonged precipitation periods can be directly correlated to the acceleration of movement vectors.The La Serra landslide was strongly reactivated at the end of 1992, following October and November precipitation (200% of the multiannual average in the La Valsainte station). Many instabilities area get reactivated since 1990, near the Falli-Hölli site in the Lac Noir valley after the precipitation excess and the rise of the minimum temperature during winter and spring in the 1978-1988 period. |
Lateltin & al. 1997 - R: PNR31 | ||
Swiss Alps: The significant modification (exceeding 15% above the interannual norm) and durable of the annual precipitation pattern would have strong consequences on the biggest landslides activity. More or less general large landslides acceleration has characterized the last 20 years in the studied area of Western and Southern Switzerland. This acceleration is linked to a precipitation increase that mainly affects the underground water runoff, but also the surface running water. More constant precipitation pattern over the German-speaking and Eastern part of Switzerland lead to a constant large landslides activity during the last century. Historical landslides are almost always due to the partial or total reactivation of prehistoric landslides (almost always related to the glacial retreat). This reactivation is whether the consequence of prolonged precipitation period or the result of very heavy short-term rains if these ones influence the river system level by undercutting. |
Study of 13 unstable sites: search and synthesis of existing data, cartography, geodesic points of the triangulation network, GPS measurements, photogrammetry, nonstop movement measures for one site, inclinometric measures in drillings. Inventory and analysis of ISM pluviometric data for all the sites and comparison with the mass movement activity. |
Noverraz & al. 1998 - R: PNR31 | |
Swiss Alps: Climatic parameters such as temperature and sunshine play a relatively minor part in reactivating movements, at least outside the permafrost areas. Precipitation has more influence, although the situation is not clear. There is no simple correlative relationship between precipitation volume data and mass movements. The rain which fell in the last 20 years tended to be concentrated on the cold season, the time when it is more effective in destabilizing landslides. The 15-30% increase in the last 20 years precipitations in Western Switzerland has resulted in intensification and reactivation of land movements of all kinds (usually in connection with large landslides). In the Eastern Switzerland, the events due to instability are in form of slope-type mudflows rather than large mountainside landslides caused by more constant precipitation. |
Bader & Kunz 2000e - R: PNR31 | ||
Europe: Establishing link between climate & landslides is very difficult: • because of the relatively few records of landslides events (date, incomplete databases); • because of the variety of landside types, shallow or more deep-seated, affecting earth, debris or rock materials, etc, and therefore controlled by a variety of factors. In relation to hydroclimatic events, landslides can be triggered (not exhaustive): - by intense rainfalls (especially shallow soil slips and debris flows), - by a sequence of long duration rainfalls and hence a modification of the regional groundwater tables, - by undercutting related to a rise in the discharge of streams; • because landslide activity related to climate can be: - episodic (one-step landslide, e.g. failure -> runout -> definitive stop), - not only episodic (the same dates/periods of activity are in common each year, for instance for slow-moving persistently active mudslides or rockslides). There is actually no general clearance or evidence of a relation between coldest periods and less landslide activity or warmest periods and higher landslide activity, even if it is fairly obvious that a period of increased rainfall will increase landslide activity. Matthews et al. (1997) demonstrated (all over Europe) an increase in landslide activity during the Little Ice Age (characterized by increased rainfall combined to a lowering of temperatures). |
Malet 2006 - C1 | ||
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Modeling |
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Hypothesis |
Alps:
Considering winter peak flows, they should interact with changes in sediment fluxes and, locally, with the hydraulic geometry of rivers, increasing waterborne risks. The increased elevation of permafrost due to increased temperatures will decrease the cohesiveness of soils, and trigger mass movements. |
Haeberli et al. 1990 in Bravard 2006 - P | |
Spain - Santander: If there is a warming of 2 to 3° by the end of the 21 st century we will be closer to "Atlantic" climatic conditions and we should therefore expect a reduction in earth movements, but we should not lose sight of the fact that the "Atlantic" was also a period of intense deforestation, and account must be taken of the land use, particularly the forestation rate. |
Flageollet 1994 - R: EPOCH | ||
Alps:
Glacier shrinkage and permafrost degradation induce complex problems of slope stability in bedrock as well as in non-consolidated sediments (moraines, scree). Such problems may become more acute in the future and develop beyond existing historical experience if atmospheric warming indeed continues or even accelerates. |
Haeberli & al. 1997 - A | ||
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Swiss Alps: It is not possible to propose a general estimation of the quantitative consequences of the precipitation increase or decrease on the mass movement. It is important to note that for the scenarios for the next 50 years, it is expected that the annual precipitation would decrease and the winter precipitation would increase. This increase may have a negative impact on the small mass movements and at low altitude, where the precipitations are mainly under liquid form. Some violent reactivation have been consecutive to late snow melting (Saas Fee-Halde, Chesières-Les Tailles); a snow cover decrease may not lead to a mass movement increase in the future for the first six months of the year. There is no reason to expect a systematic acceleration of the large slopes movements at middle term, in relation with the climatic changes observed at the Swiss scale. The great number of cases studied or analysed confirm that each movement react with its own context, geologic, hydrogeologic, hydrographic, topographic and climatic. As each movement has its own variability and it is not possible to find long term trends valid for all the slopes and the entire country. |
Noverraz & al. 1998 - R: PNR31 | ||
Swiss Alps: |
Bader & Kunz 2000e - R: PNR31 | ||
World / Alps: |
Dehn & al 2000 - A | ||
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Swiss Alps: The main threatening for alpine and pre alpine slopes instabilities are coming from a possible temperature and precipitation increase. A precipitation increase would automatically lead to a mass movement occurrence probability and activities increase. The climate warming would have no direct consequences on slope instability for the low and medium altitude, but could lead to strong perturbations in the slope stability in high mountain area, where there is today permafrost occurrence. |
Dapples 2002 -T | ||
Alps: As permafrost temperatures in the Alps show a clear upward trend, warming permafrost could lead to an increase of permafrost-related slope instabilities. In view of the melting process that might trigger a landslide, maximum radiation values seem to be the most important radiation values as they indicate maximum energy input. |
Noetzli & al. 2003 - P | ||
Alps: The atmospheric temperature increase, which would not constitute an extreme of temperature (according to the IPCC definition), would melt permafrost up to a significant degree, which would reduce the mountain slope cohesion and would increase the potential of rockfalls and mudslides. |
Beniston & Stephenson 2004 - A | ||
Northern Apennines: Most of the cases of landslide dams occurrence over the Northern Apennines in historic time occurred from the end of the 16th century to present (Casagli and Ermini, 1999). The sudden increase of historic chronicles in the second half of the 16th century can probably be related to the beginning of a period characterized by a colder and wetter climate known as the “Little Ice Age”. Another important triggering factor that can explain the increase in landslide activity during the “Little Ice Age”, is probably the extensive deforestation that took place since the 15th century. The spatial distribution of the main landslides in the Emilia Romagna Region seems to strengthen the hypothesis that climate changes, that occurred between the Pleistocene and the Holocene, with particular reference to the sharp oscillations that characterised the beginning and the end of Dryas III, could be the triggering factor of those landslides. |
Bertolini & al 2004 - A | ||
World:
On steep slopes, freshly exposed or thawing non-consolidated sediments can become unstable, resulting in debris flows and landslides of varying magnitudes. Once one event has occurred in a particular valley, the remaining slopes may become destabilised even further. In places of pronounced glacier retreat, changes in stress distribution and surface conditions of rock walls in deeply cut glacier troughs could induce large mass instabilities. The general tendency is towards a shifting of hazard zones with considerable changes in the processes involved and a widespread decrease in the stability of high-mountain slopes. |
Kääb & al. 2005 - A | ||
Alps:
Extreme rainfalls and increased average winter temperatures, increased alternations of freezing and warming in weak rocks, will increase landslides and rock fall hazards. However, recent catastrophic events in the Mattertal (Valais region) in 1987, 1993, and 2000, and above-average concentration of events have been proved to be caused by insufficient and short archival data (Stoffel et al, 2005). These changes in slope processes will increase sediment inputs into rivers, will induce deposition and will raise the level of floods, interacting with land occupation issues along valley floors. This trend could affect northern regions of the basin, as predicted by Beniston et al. (1995). |
Stoffel & al, 2005 ; Beniston & al. 1995 in Bravard 2006 - P |
Type of knowledge |
Results and interpretation |
Observation and analysis methods |
References |
Reconstructions |
French Alps: For the French Alps, the period favourable to mass movement was the time of climatic change, during intermediate stages between cold periods and temperate periods, when the morphodynamic activity was more intense. |
[See detailed results in the final report of the programme EPOCH: "Temporal occurrence and forecasting of landslides in the European Community", 1991–1993] |
Flageollet 1994 - R: EPOCH |
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Observations |
Swiss Alps: The general precipitation increase observed for two decades (since 1977) in the Wesstern part of the country and for the Ticino canton led to mass movements increase. Most of them were linked large mass movements and to the reactivation of these large movements. More or less general large landslides acceleration has characterized the last 20 years in the studied area of Western and Southern Switzerland. |
Study of 13 unstable sites: search and synthesis of existing data, cartography, geodesic points of the triangulation network, GPS measurements, photogrammetry, nonstop movement measures for one site, inclinometric measures in drillings. Inventory and analysis of ISM pluviometric data for all the sites and comparison with the mass movement activity. |
Noverraz & al. 1998 - R: PNR31 |
| Swiss Alps: The precipitation increase observed during the last 20 years (15 to 30%) led to landslides enhancing and reactivation in the Western part of the Swiss Alps (generally linked to very large landslides). In the Eastern part, these instabilities events are more often mud flows and are linked to long term precipitation pattern. |
Bader & Kunz 2000e - R: PNR31 | ||
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Modeling |
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Hypothesis |
Flysch area in Switzerland: The expected climate change scenarios should not lead to an increase of the size of the sensible area to landslides in the Flysch area. But, in some potentially instable regions, located in the altitude between 1000 and 1500m, some old sleeping landslides may get reactivated. In these regions, a general speed increase of the slow landslides (cm/year) should be expected, even for some isolated cases like the Falli-Hölli slide. |
Cartagrophy, geologic, geodesic, modelling, surface water balance, dendrochronology, climatology, GIS... |
Lateltin & al. 1997 - R: PNR31 |
| Swiss Alps: There is no reason to expect a systematic acceleration of the large slopes movements at middle term, in relation with the climatic changes observed at the Swiss scale. The great number of cases studied or analysed confirm that each movement react with its own context, geologic, hydrogeologic, hydrographic, topographic and climatic. As each movement has its own variability and it is not possible to find long term trends valid for all the slopes and the entire country. It is not possible to propose a general estimation of the quantitative consequences of the precipitation increase or decrease on the mass movement. |
Noverraz & al. 1998 - R: PNR31 | ||
| Swiss Alps: Some instable areas that are actually in movement with low speed (cm/year) may move with greater speed (dm/year) under changing climatic conditions. A minimum temperature and precipitation increase during spring and winter may lead to speed increase in the instable area (prealpine regions) and small movements reactivation (<1km²) under 1500m a.s.l. |
Bader & Kunz 2000e - R: PNR31 | ||
| Alps: Until 2030 : increase of slope instability and mass movements. |
CIRPA 2002 - R* | ||
| Alps:
Our actual climate change scenarios indicate increased rainfall combined to a rise of temperatures and increased rainfall in Winter and less in Summer. We have no idea if this "new" combination will do, and increase or not slope failures. There is actually no general clearance or evidence of a relation between coldest periods and less landslide activity or warmest periods and higher landslide activity, even if it is fairly obvious that a period of increased rainfall will increase landslide activity. |
Malet 2006 - C1 |
Type of knowledge |
Results and interpretation |
Observation and analysis methods |
References |
| Reconstructions |
Europe: Datings made in Switzerland and UK show that the large post-glacial landslides were not produced just after the glacial retreat, but with a delay of up to several thousand years (Schoeneich 1991). Schoeneich (1991) stated that in the Swiss Alps, several datings of catastrophic events are grouped between 0 and 500 years A.D. and might correspond to an increase in heavy rainfalls. Starkel (1966) argued that the time of Holocene failures had not been completely random, but had been climatically controlled. He identified three main periods of activity: one in younger Dryas when permafrost was generally vanishing (between 11,000 and 9,000 yr. B.P.), and two more humid and warmer, the first one during the Atlantic period (7,000-5,000 yr.B.P) and the last one during the Sub-Atlantic period (1,500-500 yr. B.P.). Using additional data, the authors of the present study can not confirm these statements for the whole of Europe. Landslides have taken place in other different periods and they are especially frequent during the last hundreds years. At present, the scarcity of dated landslides does not allow us to get an insight into the actual temporal distribution but all locations. Landslides have occur continuously since the glaciers retreated. With regard to deep-seated landslides, Johnson (1987) also concluded that there are no sufficient data available yet for a proper testing of Starkels hypothesis. The last century exhibits a very active period of landslides. |
Bibliographic analysis |
Corominas & al 1994 - R: EPOCH |
Europe: Synthesis [WP5]: Several periods of intense movements (in terms of numbers and volume moved and eroded) are correlated with an increase in rainfall.. |
This synthesis is based on many studies done in the framework of the programme EPOCH. The researchers engaged in the programme used the same methodologies for the collection, storage and analysis of data. |
Flageollet 1994 - R: EPOCH | |
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Flysch area in Switzerland: Around 13 000 BP, the local glacier are still in the bottom of Pre Alpine valleys located above 1200 m a.s.l and prevent any mass movement triggering. From the beginning of the Würm glaciation until the end of the Tardiglaciaire, the Pre Alpine regions do not experience important mass movement activity because of the climatic condition leading to very low permafrost occurrence (around 1500m a.s.l). During the first part of the Holocene (Preboreal, around 10 000 BP), many slopes instabilities are developing in the Flysch area in the Alps and PreAlps, with movements surface more than 10m deep. May catastrophic events (large movements or rock falls) occurred in the Alps during this period. The next period with many landslides in the Flysch area in the PreAlps is the one between the recent Atlantic (6000 BP) and the end of the Subboreal (2700 BP). The period between the recent Atlantic and the Subboreal end seems to constitute a period favourable to deep mass movements (more than 10m deep) in the Alps. On the basis of the available data, the period between the Middle Age and the end of the LIA is not very linked to important deep mass movement in the Flysch area activity at the regional scale. After the precipitation increase recorded in Singine during the 1978-1988 period and the rise of minimum temperature during winter and spring, many instabilities area near the Falli-Hölli site in the Lac Noir valley get reactivated. |
Cartagrophy, geologic, geodesic, modelling, surface water balance, dendrochronology, climatology, GIS... |
Lateltin & al. 1997 - R: PNR31 | |
| Swiss Alps: The mass movement’s high frequencies in the Fribourg PreAlps occur under wetter and colder climatic conditions. The water remaining the determining factor for the mass movement process, wetter climatic conditions are much more important than the colder climatic conditions. The mass movement increase periods are well correlated with the melting permafrost period following the Daun and Recent Dryas glacial recurrences. But there are also observations of wet and cold period with no or few mass movements. |
Dapples 2002 -T | ||
Dolomites (eastern Italian Alps): The first phase of marked slope instability is observed in the Preboreal and Boreal (about 11,500 – 8500 cal BP), and includes, on the one hand, large translational rock slides, which affected the dolomite slopes following the withdrawal of the Würm glaciers and the consequent decompression of slopes, and on the other hand, complex movements (rotational slides and flows) that affected the underlying pelitic formations and was probably favoured by high groundwater levels resulting from an increase of precipitation and/or permafrost melt down. A second concentration of landslide events is found during the Subboreal (about 5800 – 2000 cal BP), when slope processes, mainly rotational slides and/or flows, took place in both the study areas. These slides may be considered reactivations of older events linked to the phase of precipitation increase that has been documented in several European regions during this mid-Holocene period. On the other hand, during the Little Ice Age, the scarce number of landslides dated in the study areas does not enable an increased frequency of landsliding to be detected. The recurrence in time of landslide activity since the Late glacial was certainly also influenced by non-climatic factors but many landslide events previously described might be considered as indicators of climatic changes. Europe: The comparison with bibliographic data relating to other European mountain areas is significant. In fact, concentrations of landslides during periods similar to those of the areas studied were reported in various European regions, such as the United Kingdom, the Iberian Peninsula and Eastern Europe. Investigations carried out in the Swiss Alps (Lateltin et al., 1997) pinpointed a concentration of events in the Preboreal, between 11,200 and 10,000 cal BP, in the Subboreal, between 5900 and 3500 cal BP, and in the lower Sub-Atlantic, between 2600 and 1700 cal BP. To this, an intensification of events occurring during the past 500 years should be added. Some agreement between the temporal distribution of landslides in various European regions and in the Italian Dolomites are evident. Indeed, all the cases previously described fall more or less precisely into the two periods of greater activity thus identified. In a European perspective, the Preboreal period coincides with the oldest period of frequent postglacial slope movements in Europe that was identified by various authors. On the other hand, a second period of occurrence corresponds to an increase of precipitation reported in literature. However, the hypothesis of a direct influence of this climate change on landslides, partially confirmed by the European case studies above mentioned, still needs further verification. |
Research carried out in the past few years has led to a typological and chronological characterisation of the various landslides found in Alta Badia and Cortina d’Ampezzo areas. During these investigations, numerous tree trunks and wood remnants were found along erosion scarps or during excavations and borings together with soils, sediments rich in organic matter and peat that had been buried by landslide deposits. Moreover, samples of wood remnants and peat were found within lacustrine deposits that in turn resulted from landslide damming of rivers. Conventional radiocarbon dating of these remnants allowed the chronological reconstruction of the mass wasting processes occurring in the two study areas. An effort has been made to assess which of the numerous
radiocarbon dates collected in the study areas are related to events of
a type or magnitude that can be indicators of Holocene climatic changes.
The degree of paleoclimatic significance of each of the dated landslides
has been assessed on the basis of the following criteria: |
Soldati & al 2004 - A | |
| Observations |
Swiss Alps: More or less general large landslides acceleration has characterized the last 20 years in the studied area of Western and Southern Switzerland. This acceleration is linked to a precipitation increase that mainly affects the underground water runoff, but also the surface running water. More constant precipitation pattern over the German-speaking and Eastern part of Switzerland lead to a constant large landslides activity during the last century. |
Noverraz & al. 1998 - R: PNR31 | |
Modeling |
French Alps: [In Barcelonette basin], the scenarios of the frequency of landslide reactivation f generally follow the mean precipitation scenarios. Distinct trends in f were simulated in none of the GCMs. Apparently, decreased summer precipitation and increased evapotranspiration are cancelled out by increased winter and spring precipitation. The presentation of scenarios for landslide reactivation, based on low-quality analog-downscaled precipitation scenarios, seems senseless. However, it is done merely to show that the underestimation of precipitation is amplified in f (ECHAM4, 1960 to 1989: 17.5% precipitation to 81% f on average). This shows the importance of consistent, plausible precipitation scenarios in order to obtain consistent impact scenarios. A distinct change in the frequency of landslide reactivation was simulated with only 1 specific combination of GCM and downscaling approach (multiple regression, ECHAM4). This indicates that the consideration of not only different GCMs but also different downscaling methods is justified and recommended in order to better quantify the overall uncertainty in climate change impact studies. The influence of interdecadal variability of precipitation is considerable [in the scenario of landslide reactivation for multiple regression and ECHAM4 for all the time intervals]. This influence seems greater than the influence of increasing temperature, which would have resulted in a smoother decline. Temperature is important, but becomes decisive when precipitation changes are slight or become cancelled out between the seasons. The major anomalous situations occur in the target periods 2030 to 2059 and 2040 to 2069 have also been studied. These were not considered in the other 2 downscaling approaches. This illustrates the importance of considering the entire scenario period instead of only 2 or 3 selected target periods in order to capture the most radical impact changes. Finally, the scenarios of different f quantiles [in the anomalous situations] are further apart than the scenarios [of landslide reactivation for multiple regression and ECHAM4 for all the time intervals]. This shows that climate variability not captured by the multiple regression, or in general by the applied methods, adds a considerable amount of uncertainty to the simulated impacts. This variation is not revealed when using the other downscaling methods, but should always be considered as an important part of local climate. |
A model of
landslide reactivation as a function of climatic parameters was fed with 1 temperature and
several precipitation scenarios obtained by applying 3 different methods (direct GCM interpolation, downscaling with multiple regression and analog-downscaling) for downscaling 3 different
general circulation model (GCM) simulations of the large-scale climate (ECHAM4, HCGG and HCGS). This model quantify the relation between landslide reactivation and climate by comparing the time series of net precipitation with landslide reactivation data derived from tree ring analyses (Buma 1998). The associated temporal resolution is yearly. The model gives a threshold of 270 mm. Whenever the amount of net precipitation over 3 mo exceeds 270 mm, a landslide reactivation should occur, according to the model. The threshold only allows events and ‘nonevents’ to be discriminated; the model is too coarse for event magnitudes to be assessed, the match is not perfect and the duration of landslide reactivation is systematically overestimated by the model. The frequency of landslide reactivation (f) was also calculated. This model still carries too many uncertainties for a successful application to climate change impact assessment. However, the focus of this paper is to determine the influences of different GCMs and downscaling methods on simulated climate change impacts on landsliding. For this purpose even a theoretical model relating climate to landslide activity would have been suitable. Therefore, the landslide model is considered good enough for the scenario study. |
Buma & Dehn 2000 - A |
Hypothesis |
Swiss Alps: The main threatening for Alpine and Pre Alpine slopes stability are linked to the possible precipitation and temperature increase. Precipitation increase would lead automatically to occurrence presenting permafrost at the moment. Probability and mass movements’ activity increase. The climate warming may have no direct effects on the mass movements in the low and medium altitude area but may lead to important perturbations of high mountain slopes, |
Dapples 2002 -T | |
Swiss Alps: Following the precipitation increase, there should be debris flows and landslides increased risk. The expected modification are sometimes far above the natural fluctuations observed in the past. Thus, the Society will probably notice them. |
OcCC 2003 in Frei & Widmer 2007 - E | ||
Alps:
There is actually no general clearance or evidence of a relation between coldest periods and less landslide activity or warmest periods and higher landslide activity, even if it is fairly obvious that a period of increased rainfall will increase landslide activity. |
Malet 2006 - C1 |
Type of knowledge |
Results and interpretation |
Observation and analysis methods |
References |
Reconstructions |
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Observations |
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Modeling |
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Hypothesis |
Flysch area in Switzerland: Important reactivation of old landslides should be expected during spring. |
Lateltin & al. 1997 - R: PNR31 |
Type of knowledge |
Results and interpretation |
Observation and analysis methods |
References |
Reconstructions |
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Observations |
Swiss Alps: The general precipitation increase observed for two decades (since 1977) in the Eastern part of the country and for the Ticino canton led to mass movements increase. Most of them were linked large mass movements and to the reactivation of these large movements. More or less general large landslides acceleration has characterized the last 20 years in the studied area of Western and Southern Switzerland. This acceleration is linked to a precipitation increase that mainly affects the underground water runoff, but also the surface running water. More constant precipitation pattern over the German-speaking and Eastern part of Switzerland lead to a constant large landslides activity during the last century. |
Syntehsis of the cartographic, geodesic, precipitations... data. |
Noverraz & al. 1998 - R: PNR31 |
Modeling |
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Hypothesis |
Swiss Alps: The expected climate change scenarios should not the size of the sensible area to landslides in the Flysch area. In some potentially instable regions, located in the altitude between 1000 and 1500m, some old sleeping landslides may get reactivated. |
Cartagrophy, geologic, geodesic, modelling, surface water balance, dendrochronology, climatology, GIS... |
Lateltin & al. 1997 - R: PNR31 |
Swiss Alps: Some instable areas that are actually in movement with low speed (cm/year) may move with greater speed (dm/year) under changing climatic conditions. A minimum temperature and precipitation increase during spring and winter may lead to speed increase in the instable area (Pre Alpine regions) and small movements reactivation (<1km²) under 1500m a.s.l. |
Bader & Kunz 2000e - R: PNR31 | ||
Swiss Alps: The climate warming may have no direct effects on the mass movements in the low and medium altitude area but may lead to important perturbations of high mountain slopes, presenting permafrost at the moment. |
Dapples 2002 -T | ||
World: The general tendency is towards a shifting of hazard zones with considerable changes in the processes involved and a widespread decrease in the stability of high-mountain slopes. |
Kääb & al. 2005 - A |
Recommendations
|
Remarks |
Object |
References |
Adequate knowledge of the landslide context (type of movement, dynamics and morphological features) is needed for the search of datable elements associated to it and for a proper interpretation of the data obtained. A better understanding of the triggerring factors of old landslides is needed before establishing their eventual climatic relationship. |
The landslide dynamics (frequency and areal extent) can be deduced from dating successive landslide events. Dendrochronology is specially valuable in frequency-magnitude analysis of shallow movements such as debris flow, in which magnitude is considered as both the volume of flow deposits itself, and the areal extent of these phenomena triggered by a single rainfall event. Nevertheless, series obtained from dating old landslides should normally be very incomplete because only very few individual events can be dated. Landslide reactivation is also difficult to detect. These facts may lead to an underestimation of the activity. |
Corominas & al 1994 - R: EPOCH | |
The implementation of the new federal recommendations for the consideration of mass movements in the land planning will allow to appreciably reduce damages caused by landslides, by avoiding using the most threatened sectors to establish new building zones. The construction of protective structures and the enforcement of evacuation plans should also be studied. These passive measures must be supported by local authorities and an important work to raise public awareness has to be planned, by showing the benefits of prevention. The active measures (biological engineering, drainage, slope modification…) to avoid the triggering of these phenomena will remain but will be always more expensive. The preservation of protective forests is also a major stake to fight against erosion in the Pre-Alps. |
Lateltin & al. 1997 - R: PNR31 | ||
A targeted monitoring, periodic and well implemented for each risk situation allow the risk manager to not be overtaken by the exceptional events. |
Noverraz & al. 1998 - R: PNR31 | ||
Accurate spatial modelling and careful field surveys are therefore necessary to identify areas susceptible to permafrost degradation and ensure that engineering structures and settlements are not adversely affected. In any event, thermal changes brought about by the engineering works themselves may impact on permafrost stability, so that detailed permafrost surveys prior to engineering design are prudent within all high mountain regions. |
Mountain permafrost has a complex spatial distribution that depends largely on altitude, radiation and snow distribution in space and time. |
Permafrost and enginnering design |
Harris & al 2001 - A |
It is important to take into account the climate change and changes in the vegetation cover for the middle and long term mass movements previsions. |
Vegetation cover |
Dapples 2002 -T | |
Many damaging natural hazards can occur in the absence of an intense or rare climate event that actually triggers the hazard. The permafrost example is relevant: the degradation of permafrost, whereby a rise of atmospheric temperatures beyond a certain threshold that would not on itself constitutes a temperature extreme (according to the IPCC definition), can melt the permafrost to a sufficient degree for a significant reduction of the cohesion of mountain substrata to occur, thus enhancing the potential for rock and mud slides. |
Permafrost, mass movements and climate change |
Beniston & Stephenson 2004 - A | |
In the northern Apenines (Italy), landslides characterised by larger dimensions are, as a general rule, placed at elevations between 600 and 1,200 m, in those areas that were more affected by the climate variations that took place at the end of the last glacial phase (Val Parma stage, Pellegrini et al., 1998), where physical weathering processes were probably particularly severe. As a consequence, ancient huge earth-flows, like Morsiano (~13,500 cal y BP) and Succiso (~9,500 cal y BP) landslides, were probably triggered by the combined action of permafrost thawing and new morphogenetic factors. Except for some partial reactivations these landslides are prevalently dormant or inactive. This fact strengthens the hypothesis that they have been triggered in climatic conditions different from those at present. Because of this prevalent dormancy, since ancient times, several villages have been built on the debris displaced by the landslides while these encountered their most prolonged dormant phases. However these landslides are not completely stabilized and the low frequency of their reactivation (very often partial) makes them very difficult to be detected and to be managed with urban planning purposes. |
Bertolini & al 2004 - A | ||
System interactions in high mountains clearly show the urgent need for integrated hazard assessments to account for a variety of relevant processes and their linkages on different timescales. The general tendency is towards a shifting of hazard zones with considerable changes in the processes involved and a widespread decrease in the stability of high-mountain slopes. Special measures are needed to ensure the structural stability and durability of installations for tourism, transportation and telecommunication in permafrost areas. Similarly, detailed hazard assessments must be undertaken routinely and regularly to avoid damage to hydropower installations due to the impact of glacier-derived floods, which can cost many tens of millions of Euros. If, in fact, environmental conditions in high-mountain regions were to evolve beyond the range of Holocene and historical variability, hazard assessments may become increasingly difficult because estimates of hazard potential based on empirical data from the past (historical documents, statistics, geomorphological evidence) will not be directly applicable under new conditions. The concept of sustainable development in the highest belts of cold mountain areas becomes questionable, because large-scale climatic forcing would by far outweigh any local environmental influences. The main challenge would, in fact, be to adapt to high and accelerating rates of environmental change (Haeberli and Beniston 1998). Empirical knowledge would have to be increasingly replaced by improved process understanding, especially concerning runoff formation and slope stability. Robust numerical models would have to help with the design of hazard mitigation measures at high altitudes. |
High mountain hazards |
Kääb & al. 2005 - A |
Type of knowledge |
Results and interpretation |
Observation and analysis methods |
References |
Reconstructions |
Europe: A close relation has been found between heavy rains and triggering of shallow landslides like debris flows, mudflows, slab slides or rock falls (Rat 1984, Gallart & Clotet 1988, Zimmermann & Haeberli 1992, Corominas 1993). Nevertheless it is not always possible to establish a direct relationship from the frequency distribution of landslides, as it was seen in the Barcelonette area in the French Alps (Braam et. al. 1987a); although it is assumed that climate should have played a role in combination with factors such a bedrock, slope characteristics among others (Weiss 1988). |
Bibliographic synthesis |
Corominas & al 1994 - R: EPOCH |
|
Observations |
Switzerland: For superficial phenomena, notably debris flows or pellicular landslides, the triggering factors are the extreme meteorological conditions. Values higher than 100 mm of precipitation in 24 hours are critical and the triggering of mudslides or superficial landslides must be expected on potentially unstable slopes in flysch zones. |
Lateltin & al. 1997 - R: PNR31 |
|
Swiss Alps and pre-Alps: It does not seem possible to relate the frequency and intensity of slope-type mudflows quantitavely to different temperatures and precipitation ; no causal relationship between climate change and triggering of slope-type mudflows. The slope-type mudflows have a tendency to increase with altitude. Extreme meteorological events are the determining factor in triggering slope-type mudflows, particulary in the stormy summer season (July and August) but their future development is uncertain. The transition from event to non-event (of slope-type mudflow) for hourly precipitation corresponds generally to a treshold of 40 mm (Alps) and 70 mm (edge of the Alps) or 21 mm/h and 32 mm/h respectively. The "precipitation and hydrological histrory" of a location before an event cannot be clearly quantified yet, any more than the exact role of snow cover. There are differences in the precipitation structure leading to mudflows: torrential rains are responsible for mudflows mainly in the Pre-Alps and Northern Alps, whereas prolonged period of rain, often combined with a high 0°C isotherm, lead to mudflows in the higher region of the central and southern Alps. Mudflows are more frequent in summer and autumn, especially at high altitudes. |
Bader & Kunz 2000f - R: PNR31 | ||
Swiss Alps: The 1987 storm analysis proved that almost half of the mudslides came from probable permafrost zones or zones covered with ice before 1850. In Ritigraben (Wallis), several mudslides came from the rock glacier located in 2 500 m asl these last ten years. |
Götz & Raetzo 2006 - P* | ||
French Alps (for Hautes Alpes and Isère French Départements): For the 34 slope movement events observed in the Barcelonnette watershed over the 1975-2004 period, in 62% of the cases, the 5 days preceding a landslide are caracterised by a precipitation amount sharply superior to the “normal”. The remaining 38% are explained by very located thunderstorms, “not seen” by at least one of the three reference stations. So, the daily precipitation maximum over the 3 days preceding the 34 listed cases is 18 mm against 11.5 for the Normal (1975-2004). For a 6-day period, we obtain 23.1 mm against 17.5 on average. Beyond a week, the difference does not seem significant any more: 30.7 mm against 28.2 on average for D-15 and 36.7 against 35.2 mm for D-30. On the other hand, the pluviometric amount is always more marked for the same intervals preceding the phenomenon ( 106.6 mm / 86.9 for D-15 and 186.2 mm / 168.6 for D-30). |
For the Barcelonnette watershed, over the 1975-2004 period, 34 events have been observed. From daily precipitation data from 3 representative stations (Condamine, Allos and St Paul ) and maps of the general atmospheric situation, correlations between movements and meteorological phenomena have been performed. An analysis of the daily precipitation over the month preceding the triggering of each mass movement allowed clarifying the precipitation influence. The chosen value corresponds to the maximum found in one of the three stations. |
Maquaire & al. 2006 - E | |
| Modeling |
Italy - Eastern Dolomites: The combination of three modelling steps, namely expanded downscaling, hydrological and rheological modelling to derive displacements of a mudslide from GCM experiments, is a new and promising approach. In comparison to earlier studies (Buma and Dehn) there now exists the possibility to assess climate change impact not only concerning years with or without activity but also the amounts of displacement of the simulated mudslide. One major problem still limits the practical application of the method in this stage of development. Besides inherent problems of the two slope models including extrapolation of results of one borehole, great differences sometimes occur between observations, ANA (downscaled processes stemming from the analysed circulations), and the years 1964–1986 of SCA (modelled circulations). [...] Therefore, following the experiences of two of the authors (Buma and Dehn) it is highly recommended to use more than one GCM experiment for assessing climate change impacts. In this way, at least GCM uncertainty can be narrowed to some degree. A further improvement would be the use of more than one downscaling technique. Uncertainties of the model chain stemming from the two slope models have already been mentioned. One part of this uncertainty is due to the limited length of the measurement period used for model calibration. Further, both slope models are simple lumped approaches that are unable to adequately represent the spatial variability of geotechnical and hydrological parameters of the slope. The decrease in displacement from March to May can be attributed to two changing parameters. The average temperature in winter (DJF) increases significantly, and, more importantly, the average winter temperatures are all above 0°C from the year 2050 onwards. Furthermore, precipitation in DJF decreases more strongly than in the other seasons. A combined effect of these findings is a clearly reduced storage of precipitation as snow. Therefore, the release of melt water, which, under the present conditions contributes to high groundwater levels and hence strong displacement in early spring, is significantly reduced. This effect can be suggested as a conceptual explanation for the strong reduction of future landslide displacement in spring. The physics of this effect have not been investigated in detail, however. |
In the present study, due to computing and time resources, [the authors] were only able to use the ECHAM4/OPYC3 GCM, which was downscaled with EDS. The monitoring equipment [of the mudslide] consists of four inclinometric tubes, 11 piezometers and 11 extensometers all equipped with electric pressure transducers connected to an automatic recording system. Furthermore, a meteorological station has been collecting data since 1989. Observed climate records from the Italian Meteorological Survey consist of daily precipitation for Cortina d'Ampezzo (1922–1996), Misurina (1922–1975) and San Vito (1921–1987). Misurina is located 10 km ENE and San Vito 12 km SE of Cortina d'Ampezzo. The data of Cortina were tested on a monthly basis for homogeneity against the other two stations, which did not show any problems. Daily minimum and maximum air temperature were available from the same source for Cortina only. |
Dehn & al 2000 - A |
|
Hypothesis |
Swiss Alps: The future incidence of slope-type mudflows in the high mountains will be closely connected with the glacier retreat and changing temperatures in the permafrost zone (especially the active layer). With more water circulating more freely and penetrating fissure, more loose material will be released - especially on steep slopes and crags. Any significant future change in mudflows activity in the peri-Alpine regions will probably be very limited (the effects of climate change on the mudflows activity will be hardly perceptible because of the great variability of the events). |
Bader & Kunz 2000f - R: PNR31 |
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World / Alps: |
Dehn & al 2000 - A | ||
Swiss Alps: Only a specific kind of landslides would react to climatic influences (in the Viège valley, Swiss Valais), this is the superficial landslide type (creeping, solifluxion). Their magnitude remains limited< |