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Temperature and rockfalls monitoring activities at Aiguilles Marbrées North face (Mont Blanc Massif, France)
No full textDetecting climatic treelines in the Italian Alps: the influence of geomorphological factors and human impacts.
No full textTreelines are widely studied worldwide in relation to climate changes because they are hypothesized to be sensitive climate proxies. However, forest treeline expansion toward higher altitudes may be influenced both by a warming climate and by other factors, such as surface morphology and, in the European Alps, the decline in alpine farming. Our results from five valleys in the inner and peripheral regions of the Alps show that present-day treeline altitudes mostly depend on anthropogenic and orographicgeomorphologic factors. Climatic treelines are limited to steep and inaccessible slopes, and occur at higher altitudes and farther from mountain peaks in the inner regions than in the peripheral regions of the mountain range. Looking for sites in which to study treeline responses to climate change, we recommend investigating the inner regions of the Alps where treelines are farther from human disturbances and from geomorphologic constraints, potentially resulting in freer upward shifts under warmer temperature conditions. We also found that, in the valleys selected, human disturbance is mainly concentrated about 165 m below non-climatic treelines, suggesting a homogeneous influence on treelines, regardless of geographic position
Chemical elements and heavy metals in European larch tree rings from remote and polluted sites in the European Alps.
No full textAir pollution dispersal in the European Alps has been studied both for glacial and forest environments. In this study, chemical elements and heavy metals in the tree rings were analyzed for seven sites of European larch (Larix decidua Mill.) in the Italian European Alps. At three sites in the proximities of the Mont Blanc Tunnel (MBT) entrance the analyses were performed at the yearly scale on the periods 1950-1970 (comprising the MBT opening in 1965) and 1985-2008 (comprising the 3-yr MBT closure after the 1999 car accident) with the aim to check if trees recorded at the yearly scale variations in chemical elements and changes in heavy metals concentrations over time. At the regional scale, the analyses on heavy metals were conducted without annual resolution for most sites on the common periods 1950-1970 / 1985-1998 with the aim to detect possible ongoing trends and differences between some Alpine sites. Chemical elements concentrations at Entrèves (EN) sites varied significantly between heartwood and sapwood with generally higher concentrations in sapwood. At EN sites no clear patterns were found for heavy metals before and after the MBT opening and during its 3-yr closure. We found that the "high" site (ENH) was generally less polluted than the "close" (ENC) and the "far" (ENF) sites. At site ENC we found higher values of Cr, Ni and Cu, whereas at site ENF we found higher values for all the other elements analyzed. The analysis of heavy metals at the regional scale revealed generally no significant temporal changes in concentrations except for Cr and Cu, showing higher values in the recent period. On comparing the heavy metals concentration between the seven sites, the Palud site showed almost always the highest concentrations, except for Ni and Cu that were higher in two remote sites close to glacial environments in the Gressoney and Valtellina valleys. Dendrochemical analysis revealed that the temporal information in the tree rings is covered by too many signals and no environmental changes are recorded at the yearly scale by European larch. However tree rings may provide useful information on ongoing long-term trends and on the spatial definition of pollutant dispersal in the Alpine environment
Climate warming and recent treeline shift in the European Alps : the role of geomorphological factors in high-altitude sites
No full textGlobal warming and the stronger regional temperature trends recently recorded over the European Alps have triggered several biological and physical dynamics in high-altitude environments. We defined the present treeline altitude in three valleys of a region in the western Italian Alps and reconstructed the past treeline position for the last three centuries in a nearly undisturbed site by means of a dendrochronological approach. We found that the treeline altitude in this region is mainly controlled by human impacts and geomorphological factors. The reconstruction of the altitudinal dynamics at the study site reveals that the treeline shifted upwards of 115 m over the period 1901-2000, reaching the altitude of 2505 m in 2000 and 2515 m in 2008. The recent treeline shift and the acceleration of tree colonization rates in the alpine belt can be mainly ascribed to the climatic input. However, we point out the increasing role of geomorphological factors in controlling the future treeline position and colonization patterns in high mountains
Climatic isotope signals in tree rings masked by air pollution : A case study conducted along the Mont Blanc Tunnel access road (Western Alps, Italy)
No full textThree sites at about 1400 m a.s.l., were chosen for this study along the Mt. Blanc Motorway in Italy. Chronologies of stable isotope ratios (δ 13C, δ 18O, δ 15N), total N concentration and ring width of Larix decidua Mill. were analyzed to observe changes in growth and climatic signals in tree rings after significant changes in air pollution emissions occurred locally over time. The tunnel opened in 1968 and was closed for three years from March 1999 to March 2002. The obtained series from the three sites (Close = C, High = H and Far = F from the highway) for the analyzed periods, 1950-1970 (only sites H and F) and 1985-2008 (all sites), did not show any particular long-term change except site H that showed significant changes in δ 18O (enrichment), δ 15N (depletion) and total N (increase) δ 13C values at site C were enriched in the first year of the tunnel closure (1999), showing an opposite trend in δ 13C at site C, in comparison to the two control sites H and F, which cannot be explained by climatic factors. Since no great differences in δ 18O were recorded in 1999, this enrichment in δ 13C could be related to an enhancement in photosynthetic rate during periods of low air pollution loads. Opposite to δ 15N, total N concentration shows a generally good correlation between sites, and site F was measured as the most N enriched. In a correlation analysis performed on the two study periods between the climatic parameters and ring width, we did not find any clear relationships, whereas for the series of stable isotopes and total N, we found the strongest and most significant relationships only between δ 13C and summer (June to August) temperature (positive correlations) and precipitation (negative correlations) at sites H and F. These same relationships at site C were, instead, mostly insignificant, indicating an alteration of the climatic signal recorded in the δ 13C chronology, caused by direct exposure to the high level of air pollution at this site. Given that site C is more affected by pollution with respect to the other two sites (whereas the same climatic conditions influence tree growth at all sites), the lack of a climatic signal in the δ 13C chronology at this site can be ascribed to air pollution. Few other long-term changes were recorded by tree rings (e.g. at site H), indicating that trees probably record better the pollution events or the worsening of the environmental conditions rather than a lack of pollution for a relatively short time period in a polluted environment
Local ground movements and effects on infrastructures
No full textUsually local ground movements are monitored and studied in low- and middle-range mountain
environments, where the interaction and the hazard to human settlements are more elevated. In
high mountain range these movements are rarely investigated, because of (1) logistical difficulties,
(2) scarce interaction with infrastructures and villages and (3) the low level of knowledge on the
phenomena related with the cryosphere.
Recent increase in global temperature and the ever more presence of human tourism and
infrastructures in high mountains, has pointed out the importance of a more detailed study of these
phenomena.
The presence of permafrost in high alpine environments increases the difficulty in dealing with the
analysis of local ground movements. In fact, the current approach on analyzing slope deformations
and landslides has often been hydro-mechanical, i.e. the tensions and deformations have normally
been related to water pressure and mechanical stress-strain relationship. If this approach may be
well suited for low range mountain elevations, this might be insufficient in high elevations, where the
thermal effect could play an important role on the stability (Harris). For this reason it is important to
start the monitoring of these phenomena in high alpine sites, and include to the current monitoring
techniques the measurements of temperature. This will ultimately allow correlating the
deformations of the slope to temperature variations. Furthermore, the presence of permafrost and
its degradation could be taken into consideration in the analysis, in order to evaluate the hazard of
high mountain environments to future climate change.
These movements have rarely been noticed and categorized in the past, due to the remoteness of
the locations and the low interest. Nowadays more people are present at high elevations, thanks to
winter and summer sports, and so various infrastructures (shelters, refuge, cable cars...) have been
built. This has therefore increased the attention on this environment and also opened the path to a
regular investigation and inventory of the occurrence of these phenomena. The frequency of
occurrence is consequently hard to define because of the scarce database available.
Permafrost, infrastructures and local ground movements are sometimes linked together. Sometimes
permafrost has been found while building an infrastructure, e.g. discovering ice cores in the rock. At
the same time, local ground movements have been noticed by recording damages in the
infrastructures, probably related to permafrost degradation. It is thus important to analyze the
effects of local ground movement on infrastructures in an environment characterized by permafrost,
in order to infer common problems and find possible correlations between slope movement and
permafrost degradation
Chapter 4: Local ground movements and effects on infrastructures
No full textLocal ground movements may be defined as phenomena of instability that affect slopes or flat ground in a surface of hundreds to thousands of square meters. Local ground movements are a common feature in permafrost areas, and include:
•Horizontal downslope movements, due to the creep of permafrost bodies.
•Vertical settling movements, due to the melting of ice bodies and/or interstitial ice.
These movements may cause damages to buildings and infrastructures or more rarely represent a hazard for persons:
•Damages to buildings are mainly due to differential settling of the ground. Some mountain huts are endangered by the collapse of the rock foundations.
•Cableways are the most common and sensible infrastructures in alpine permafrost areas. Movements of pylons and of start and end stations lead to problems of cable alignement. It induces increased maintenance costs, and reduces the lifetime of the investment.
•The stability of hazard protection infrastructures can be changelled by permafrost degradation.
•Thermokarst phenomena due to the removal or compaction of the surface layer can cause substantial damage to planation works like ski tracks or roads.
In many cases, it must be emphasized that the infrastructure may induce itself the degradation of the undelying permafrost, through heat conduction by the infrastructure, or through the modification of the insulation capacity of the ground. An adapted conception of the infrastructure can, in many cases, avoid both the influence on the permafrost state and damages due to movements.
When planning an infrastructure in a high mountain environement (e.g. above 2400 m), the possible presence of permafrost should always be investigated prior to the conception. The permafrost distribution map can give a first indication. Geophysical methods permit to detect the possible occurrence of frozen ground. But only a drilling can give reliable information on the presence and thickness of ground ice. Monitoring of temperature and movements during at least one year will give more informations on potential surface movements.
If permafrost is present, an adapted design should be developped, such as:
•A thermal insulation in order to avoid heat transmission from buildings into the frozen ground.
•Adapted foundations in order to accommodate movements.
Arctic countries have a long experience in adapted design of infrastructures. Guidelines for building on mountain permafrost were edited by Swiss authorities
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