Abstract
AbstractHerein, we present results obtained from time-lapse imagery acquired by a digital single-lens reflex camera during 2014–18 used to monitor the Planpincieux Glacier on the Italian side of the Grandes Jorasses (Mont Blanc massif). We processed the images using image cross-correlation to measure the surface kinematics of the most active lobe of the glacier that presents a high velocity and frequent ice detachments. During the monitoring, we observed two or three periods of sharp acceleration per year that culminated with large break-offs followed by analogous decelerations. Overall, we registered more than 350 failures with a volume >100 m3, of which, 14 events had volumes larger than 10 000 m3. The study identified a monotonic positive relationship between the velocity and failure volume that may be used to estimate the volume of the collapses before an event. We identified the thresholds of velocity and acceleration that characterise the activation of the speed-up periods. The study allowed the characterisation of three different instability processes that lead to the break-off of ice chunks from the glacier terminus: (i) disaggregation, (ii) slab fracture and (iii) water tunnelling failure which can be differentiated based on the rheology, the volume involved and the trigger process.
Highlights
Climate change is having a profound impact on the cryosphere, in particular on alpine glaciers (Vaughan and others, 2013)
From the combined analysis of the evolution of the glacier morphology and kinematics, we identified different surface kinematic domains that are likely linked to the subglacial bedrock (Fig. 6d)
We estimated surface kinematics and ice break-off volumes and we found a monotonic relationship between the velocity peaks and the volume of the collapses
Summary
Climate change is having a profound impact on the cryosphere, in particular on alpine glaciers (Vaughan and others, 2013). In this environment, ice loss and warmer temperatures can amplify slopes and glacier instabilities according to site-specific environmental features, for example, morphology, hydrology, thermal conditions, prior slope histories (Deline and others, 2012, 2014). The identification and characterisation of instabilities that can affect glacier termini are often important for the quantitative risk assessment of alpine valleys. The correct identification of the geometry of a fracture and its propagation are important parameters for the assessment of the possible evolution of a glacier and the evaluation of the dimension of the volume that could break off from it (Pralong and Funk, 2006)
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