Glaciers of Grandes Jorasses: an open-air laboratory for glacier monitoring systems development

 

Glaciological phenomena can have a strong impact on human activities in terms of hazards and freshwater supply. Therefore, a scientific observation is fundamental to investigate their current state and recent evolution. To this aim, experimenting innovative scientific survey methodologies and equipment is of primary importance. Strong efforts in this field have been spent in the glacial complex of the Grandes Jorasses massif (Mont Blanc area), where several ice break-offs glacial outburst triggered from the Planpincieux Glacier snout and the Whymper Serac and threatened the underling Planpincieux valley in the past. From 2009, the glacial complex has become an open filed laboratory where a wide set of close-range remote sensing survey systems have been developed and applied to investigate the glacial state and dynamics.

Two continuous monoscopic time-lapse cameras observe the Planpincieux Glacier since 2013. Digital image correlation is applied to the photographs to measure the surface kinematics at different level of detail. During the monitoring, image analysis techniques allowed at classifying the instability processes of the terminus and at estimating the volume of the break-off events. Such investigation revealed the presence of possible break-off precursors and a monotonic relationship between glacier velocity and break-off volume, which might help for risk evaluation.

A robotised total station (RTS) is active since 2009 to monitor the Whymper Serac velocity (Grandes Jorasses Glacier). The operative distance between the total station and targets is approximately 5000 m. A network of several prisms is installed onto the serac, but the extreme conditions related to the high-mountain environment force to replace periodically the stakes that are lost. Besides the RTS, a monoscopic camera acquires hourly images of the serac for surface velocity measurements.

In addition to the permanent monitoring systems, surveys with four different terrestrial interferometric radars have been conducted in the Planpincieux Glacier between 2013 and 2019. Helicopter-borne LiDAR and terrestrial laser scanner provided the DEM of the Planpincieux Glacier in 2014 and 2015 respectively. A sequence of six DEMs has been also produced by aerial and UAV structure from motion in the time span 2017-2019. Finally, a helicopter ground penetrating radar campaign was conducted in 2013 to evaluate the thickness of the Planpincieux Glacier and Whymper Serac.

For what concerns the mountain glaciers, the survey activity conducted in the Grandes Jorasses massif since 2009 is probably one the most intensive and variegated in European Alps. This makes such an environment an open-air laboratory for experimenting close-range remote sensing monitoring systems that it is ready for new research activities and monitoring solutions development.