8 research outputs found
Monitoring Climatic Change Impacts on Protection Forests in Aosta Valley (Italy) and in Drôme (France) Using Medium and High Resolution Remote Sensing and Mateloscopes Plots
Get PDFUnderstanding the recent evolution of a small Alpine glacier: from geodetic mass balance reconstruction (1991-2020) to local variability of glaciers retreat.
No full text&lt;p&gt;High Alpine environments are rapidly changing in response to climate change, and understanding the evolution of small glaciers is a crucial step to investigate future water availability for populations that inhabits these areas. With an average loss of 1.6 km&lt;sup&gt;2&lt;/sup&gt;&amp;#160;of regional glacier area every year,&amp;#160;Aosta Valley is predicted to lose most of its glaciers before the end of the century.&amp;#160;With this study, we present a comprehensive analysis of a small glacier&amp;#8217;s recent mass balance evolution (1991-2020) where no specific previous mass balance data was available. To do so, we combined historical data (topographic surveys and LiDAR DEMs of the area) with newly acquired satellite stereo imagery and aerophotogrammetric surveys to reconstruct different digital elevation models of the Thoula glacier (0.52 Km&lt;sup&gt;2&lt;/sup&gt;), located on the Italian side of the Mont-Blanc Massif. The ice volume loss that occurred over this period was assessed by accomplishing two GPR surveys to investigate the ice thickness and the underlying bedrock. The Thoula glacier shows a significantly lower loss of volume in comparison to other glaciers located in the Aosta Valley region as well as most of the WGMS (Word Glacier Monitoring Service) reference glaciers for Central Europe. Particular weather-climatic conditions of the Mont Blanc Massif area, generally characterized by a greater amount of snowfall, could explain the observed differences, however, the present study shows how understanding spatio-temporal local variability of small glaciers can significantly contribute to recognizing different regional patterns developing in response to climate change.&lt;/p&gt;</jats:p
Geophysical and geomatic recent surveys at Whymper hanging Glacier (Aosta Valley &#8211; Italy)
No full text&lt;p&gt;The Grandes Jorasses Massif culminates at 4203m at the Punta Walker summit on the border between France and Italy. The south slope of Grandes Jorasses is widely glaciated and overlies a populated and highly frequented area, the Val Ferret, presenting the main infrastructure being the road in the valley bottom and different hamlets the most important being Planpincieux village. Located at an altitude between 3900 and 4100 m, the Whymper Serac is a hanging glacier that undergoes periodic gravity-driven instabilities. On 1&lt;sup&gt;st&lt;/sup&gt; June of 1998, 150.000m&lt;sup&gt;3&lt;/sup&gt; of ice fell, and the resulting ice avalanche reached 1750m, at a mere 400m from houses of the Le Pont village and the main Road. The monitoring activity started in 1997: a &amp;#160;series of boreholes had been drilled to assess the basal thermal regime of the Serac and subsequently install a monitoring system for failure prediction time. Since then, no other thermal investigation was repeated.&lt;/p&gt;&lt;p&gt;In September 2020, three thermistor chains in three different boreholes were installed by means of hot water diesel-powered drill machine on Whymper Serac. Geophysical and topographic reconstructions at Whymper Serac are crucial for the volume estimation of possible instabilities; therefore, to assess ice thickness changes and morphological modifications, different geophysical soundings and topographical surveys were performed in 2020. The ice thicknesses were estimated employing a first airborne GPR survey on the 4&lt;sup&gt;th&lt;/sup&gt; of July 2020 using a pair of orthogonal 25 MHz antennas; a second airborne GPR survey was performed using a single 40 MHz antenna on 14/12/2020. Moreover, an in-situ measure was performed through passive seismic sounding later processed as HVSR analysis to assess ice thickness estimation.&lt;/p&gt;&lt;p&gt;The geomatic analysis was performed by aero photogrammetric UAV surveys, and additional GCPs were materialized. The first assessment of thermal regime variation on the Serac suggests that risk scenarios, as well as monitoring possibilities, are rapidly evolving. According to these findings, bigger volumes could be involved in the destabilization of the Serac, and the evolution of the Serac from cold-based to polythermal poses a big challenge in the monitoring of deformations for the possibility of time prediction of failures. Therefore, experimentation of a long-range GB-InSAR surface deformations measures has begun to implement the existing monitoring network based on a robotized total station with reflective prisms used on the Serac. The installation of more thermistor chains is planned for summer 2021, to validate the previous results. Ground-based GPR soundings and more HVSR seismic measurements have as well been planned for 2021 for the more robust reconstruction of the bedrock geometry.&lt;/p&gt;</jats:p
Analysis of the Miage Glacier Lake GLOFs (Aosta Valley - Italy).
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&lt;p&gt;Miage Glacier Lake is a glacial marginal lake that forms on the right snout of Miage Glacier, located in the Val Veny Valley (Aosta Valley &amp;#8211; Italy). The lake has been experiencing seasonal drainages at least since the 1930&amp;#8217;s and 15 events have been documented from 1930 to 1990. The lake position has been almost unvaried since the first existing maps of late 1700, but lake morphology experienced major changes after the drainage event of September 2004, after which the water level could not reach again a sufficient height to fill the 3 depressions that used to form a bigger lake until 2003 (36.000 m&lt;sup&gt;2&lt;/sup&gt;). The lake having decreased its volume and surface, it did not seem by that time that GLOF from Miage Lake could cause any risk downstream (Deline et Al. 2004), but recent observation of Sentinel 2B satellite images &amp;#160;led to the individuation of unusual lake expansion towards its north shore. Thus, an UAV survey was performed to assess the actual lake area in July 2019, and the integration of satellite images and UAV surveys demonstrated a consistent lake area expansion since 2015. Moreover an emptying occurred in late August 2019 so that another UAV survey could be performed, and water volume estimation could be performed by means of DEM differencing. An important water volume was individuated, reaching 196.000 m&lt;sup&gt;3&lt;/sup&gt; and an estimation of maximum subglacial GLOF debit has been performed. Global evolution trend of the glacier mass has been evaluated by analyzing different airborne Lidar surveys (1991-2008). A cumulated geodetic mass balance could be thus inferred and found good matching with remote sensed analysis (2003-2012) performed by means of stereo satellite imagery by Berthier et Al. in 2014. Average surface lowering of the glacier surface could be analyzed and average values of -1.12 m/yr could be observed around lake Miage. The strong elevation loss of Miage Glacier lower snout is probably the cause of the lowering of the piezometric level in intra-glacial water limiting maximum altitude that water level can reach in the lake, so that the bigger basin of 2004 cannot be filled anymore. Moreover, an analysis of recent GLOFs of Miage Lake gave an insight about the possible dynamics of lake subglacial drainage, suggesting the existence of 2 different mechanisms of emptying as some events occur with lower water debits, earlier in the season, and other events occur later in the summer season with major water debits. Similar GLOF behavior has been described at Plaine Morte Glacier Lake in the Canton of Bern-Switzerland (Fahrni 2018). Field surveys of 2018 showed very likely evidence of hydrostatic uplift of the ice dam, so multi temporal UAV surveys and GNSS field surveys are planned for 2020 to possibly highlight evidences of hydrostatic uplift of the glacier prior to GLOFs.&lt;/p&gt;
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Numerical modelling of ice avalanches from the Planpincieux glacier (Italy)
No full text&lt;p&gt;Forward simulations of ice avalanches are important to inform risk management. However, the reliability of such simulations often suffers from the dependency of model parameters on the process magnitude, hampering the simulation of unprecedented events in a given area. We suggest a reliable, straightforward and practically applicable work flow for the forward simulation of ice avalanches for the purpose of risk management with regard to the Planpincieux glacier, located on the Italian side of Mont Blanc massif.&lt;/p&gt;&lt;p&gt;Since 2013, the Planpincieux glacier, has been studied to analyse the dynamics of ice collapses in a temperate glacier. Several documented ice avalanches and glacial floods (1929, 1952, 1982, 2005, 2017), which, in some cases, threatened the village of Planpincieux and damaged the municipal road, have been linked to this glacier. Starting from the summer of 2019, a fast moving ice volume, partially separated by the rest of the glacier tongue by a large crevasse, has drastically increased the occurrence of a new collapse with possible implications for the valley floor. Considering the potential risk, a glacier constant monitoring (GbInSAR) and an avalanche early warning system (avalanche Doppler radar) were deployed, and numerical modelling of ice avalanches from this glacier was made.&lt;/p&gt;&lt;p&gt;Thereby, we couple an empirical-statistical model with a physically-based mass flow model: (I) the rules of Alean (1985) for the angle of reach are fed into the software r.randomwalk in order to estimate worst-case reference travel distances for various scenarios of starting volumes, (II) the basal friction angle used in the physically-based tool r.avaflow is optimized against those reference travel distances for each volume scenario, (III) the travel distances and travel times are checked for plausibility against well-documented events, (IV) flow pressures and flow kinetic energies are computed with r.avaflow for each volume scenario.&lt;/p&gt;&lt;p&gt;The model results are well supported by empirical data for smaller events, whereas direct reference data for the larger scenarios are not available. Interpretation of the results further has to take into account that (A) for some scenarios, the empirical relationships had to be extended beyond their known range of validity, introducing additional uncertainty, and (B) the relationships do not work for snow-covered trajectories, that, for example, would decrease the friction and lead to longer travel distances. As a result, the outcomes can be, with some care, considered as worst-case assumptions for ice avalanches in summer, but are not valid for ice avalanches during the other seasons.&lt;/p&gt;</jats:p
Ice avalanche risk management from the Planpincieux glacier (Courmayeur - Italy)
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&lt;p&gt;Instabilities occurring on temperate glaciers in the Alps have been the subject of several studies, which have highlighted preliminary conditions and possible precursory signs of break-off events.&lt;/p&gt;&lt;p&gt;Since 2013, the Planpincieux Glacier, located on the Italian side of Mont Blanc massif (Aosta Valley), has been studied to analyse the dynamics of ice collapses in a temperate glacier.&lt;/p&gt;&lt;p&gt;These analyses have been conducted for several years, enabling the assessment of surface kinematics on the lower glacier portion and the different instability processes at the glacier terminus. During the period of the study, especially in the summer seasons, increases in velocities of the whole right side of the glacier tongue have been recorded. This fast sliding movement is mainly induced by water flow at the bottom of the glacier.&lt;/p&gt;&lt;p&gt;In 2019 summer season, the increase of speed coincided with the opening of a large crevasse, which outlined a fast moving ice volume, assessed by photogrammetric techniques as 250.000 m&lt;sup&gt;3&lt;/sup&gt;.&lt;/p&gt;&lt;p&gt;According to the risk scenarios, the collapse of this ice volume from the glacial body would have reached the valley floor, potentially affecting the access road to the Val Ferret valley.&lt;/p&gt;&lt;p&gt;Considering the potential risk, a civil protection plan has been deployed by the monitoring team of the Aosta Valley Autonomous Region, Fondazione Montagna sicura and CNR-IRPI.&lt;/p&gt;&lt;p&gt;Glacier displacements, variations in the glacier morphology and environmental variables, such as air temperature, rain and snowfall, have all been taken into account to implement the monitoring plan.&lt;/p&gt;&lt;p&gt;This work outlines and summarises the steps used to develop the scientific knowledge into an integrated monitoring plan and a closure plan for the Val Ferret valley.&lt;/p&gt;
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Basal thermal regime investigations at Whymper hanging Glacier (Aosta Valley &#8211; Italy)
No full text&lt;p&gt;The Grandes Jorasses Massif culminates at 4203m at the Punta Walker summit on the border between France and Italy. The south slope of Grandes Jorasses is widely glaciated and overlies the Val Ferret, a populated and highly frequented area presenting different hamlets, the most important being Planpincieux village. Located at an altitude between 4000 and 4100 m, the Whymper Serac is a hanging glacier that undergoes periodic gravity-driven instabilities. On 1&lt;sup&gt;st&lt;/sup&gt; June of 1998, 150.000m&lt;sup&gt;3&lt;/sup&gt; of ice fell, and the resulting ice avalanche reached 1750m, at a distance of about 400m from houses of the Le Pont village and the main road. The monitoring activity started in 1997: a&amp;#160; series of boreholes had been drilled to assess the basal thermal regime of the serac and subsequently install a monitoring system for early warning signs and risk assessment&lt;/p&gt;&lt;p&gt;In September 2020, three thermistor chains in three different boreholes were installed on Whymper Serac. Temperature profiles were measured at different periods between October and November 2020. In September 2021 another three thermistor chains were installed and their temperature profile measured in October 2021. During the same survey, temperature profiles of the 2020 thermistors could be measured again on 2 out of 3 boreholes, (one being too close to the serac front was not safe to reach) confirming data acquired on the 2020 field campaign. The outcome of basal temperature measurements of 2020 and 2021 give good spatial coverage of the serac allowing comparison with data from the 1997 measurements, despite on the fact that most of the ice mass fell in 1998.&lt;/p&gt;&lt;p&gt;A warming trend in most of the temperature profiles is evident in comparison whith 1997 data; 5 out of 6 points of measure still show temperatures below 0&amp;#176; C. One point of measure shows evidence of temperate ice at the ice/bedrock interface. Whymper Serac measurements provide evidence that the glacier is still frozen to the bedrock, but one part of the serac shows the beginning of a potential transition from cold based regime to temperate based regime. If, on one hand, surface displacements of the ice mass still show low displacements (typical of a cold based glacier), on the other hand, a velocity anomaly was detected on a small portion of the serac corresponding to the temperate based sector. Further research is needed to better understand the evolution of the thermo-mechanical conditions of the Whymper Serac in the current climate change scenarios. Therefore, thermo-mechanical modeling of the Whymper Serac is underway, based on the Elmer/Ice model.&lt;/p&gt;</jats:p
A novel risk score predicting 30-day hospital re-admission of patients with acute stroke by machine learning model
No full textBackground: The 30-day hospital re-admission rate is a quality measure of hospital care to monitor the efficiency of the healthcare system. The hospital re-admission of acute stroke (AS) patients is often associated with higher mortality rates, greater levels of disability and increased healthcare costs. The aim of our study was to identify predictors of unplanned 30-day hospital re-admissions after discharge of AS patients and define an early re-admission risk score (RRS).Methods: This observational, retrospective study was performed on AS patients who were discharged between 2014 and 2019. Early re-admission predictors were identified by machine learning models. The performances of these models were assessed by receiver operating characteristic curve analysis.Results: Of 7599 patients with AS, 3699 patients met the inclusion criteria, and 304 patients (8.22%) were re-admitted within 30 days from discharge. After identifying the predictors of early re-admission by logistic regression analysis, RRS was obtained and consisted of seven variables: hemoglobin level, atrial fibrillation, brain hemorrhage, discharge home, chronic obstructive pulmonary disease, one and more than one hospitalization in the previous year. The cohort of patients was then stratified into three risk categories: low (RRS = 0-1), medium (RRS = 2-3) and high (RRS >3) with re-admission rates of 5%, 8% and 14%, respectively.Conclusions: The identification of risk factors for early re-admission after AS and the elaboration of a score to stratify at discharge time the risk of re-admission can provide a tool for clinicians to plan a personalized follow-up and contain healthcare costs
