Ground-penetrating radar and surface nuclear magnetic resonance monitoring of an englacial water-filled cavity in the polythermal glacier of Tête Rousse

Abstract

In polythermal glaciers, specific climatic, topographic, and exposure conditions may lead to the formation of englacial lakes that can produce catastrophic effects downstream in the event of abrupt natural drainage. We have determined how a combination of ground-penetrating radar (GPR) and surface nuclear magnetic resonance (SNMR) surveys helped to locate and visualize the evolution of a water-filled cavity within the Tête Rousse glacier (French Alps). We have used GPR results to delineate the roof of the cavity and monitor the cavity deformation caused by artificial drainage. Because the glacier bed and cavity have complex 3D geometries, we needed dense acquisition lines and 3D GPR views to qualitatively identify out-of-plane reflections. This 3D approach made it possible to establish a precise map of the glacier bed topography, the accuracy of which was verified against borehole observations. Then, repetitive GPR measurements were used to obtain a quantitative estimate of the vertical deflection of the cavity's roof and changes in crevasse geometry observed in response to the decrease in the water pressure when 47; 800 m 3 of water was drained by pumping. We have used 3D SNMR imaging to locate water accumulation zones within the glacier and to estimate the volume of accumulated water. The SNMR monitoring revealed that in two years, the cavity lost approximately 73% of its initial volume, with 65% lost after the first drainage. Knowledge of the water contained in the ice provided a better understanding of GPR images and thus a more reliable interpretation of GPR data. However, SNMR imaging had a much lower resolution in comparison with GPR, and consequently GPR allowed a more accurate study of the evolution of cavity geometry caused by consecutive drainage and refilling. This study demonstrated the value of combining GPR data with SNMR data for the study of polythermal glaciers.

Random Noise Suppression of Magnetic Resonance Sounding Data with Intensive Sampling Sparse Reconstruction and Kernel Regression Estimation

“…So far, the MRS method and instrument have been further researched and developed in many countries such as France, the United States, Germany, China and other countries [6][7][8]. The MRS method has been applied to hydrological investigation, observation of permafrost thaw, monitoring the cavity in glacier, water-induced disaster 2 of 32 detection, and infiltrating water surveys [9][10][11][12][13]. However, when the MRS instrument is exploited for groundwater exploration, the received signal is particularly weak and easily degraded in ambient electromagnetic interference [14].…”

“…Then, to achieve this approach, the Remote Sens. 2019, 11,1829 3 of 32 ISSR is specifically studied in depth and three sparse reconstructions are proposed and analyzed. We furtherly introduce kernel regression estimation into dealing with the MRS signal processed by the ISSR method.…”

“…Following this, we adopt the sampling frequency f s H = 8 f prop , 16 f prop , 32 f prop , Remote Sens. 2019,11, 1829…”

Investigating a firn aquifer near Helheim Glacier (South‐Eastern Greenland) with magnetic resonance soundings and ground‐penetrating radar

“…() and Garambois et al . () report their experience from the French Alps. An englacial cavern in the Tête Rousse glacier has been detected and accurately located with GPR.…”

“…However, due to difficult measuring conditions, this survey had uncertain results. Vincent et al (2012) and Garambois et al (2016) report their experience from the French Alps. An englacial cavern in the Tête Rousse glacier has been detected and accurately located with GPR.…”