Abstract
Abstract. Tête Rousse is a small polythermal glacier located in the Mont Blanc area (French Alps) at an altitude of 3100 to 3300 m. In 1892, an outburst flood from this glacier released about 200 000 m3 of water mixed with ice, causing much damage. A new accumulation of melt water in the glacier was not excluded. The uncertainty related to such glacier conditions initiated an extensive geophysical study for evaluating the hazard. Using three-dimensional surface nuclear magnetic resonance imaging (3-D-SNMR), we showed that the temperate part of the Tête Rousse glacier contains two separate water-filled caverns (central and upper caverns). In 2009, the central cavern contained about 55 000 m3 of water. Since 2010, the cavern is drained every year. We monitored the changes caused by this pumping in the water distribution within the glacier body. Twice a year, we carried out magnetic resonance imaging of the entire glacier and estimated the volume of water accumulated in the central cavern. Our results show changes in cavern geometry and recharge rate: in two years, the central cavern lost about 73% of its initial volume, but 65% was lost in one year after the first pumping. We also observed that, after being drained, the cavern was recharged at an average rate of 20 to 25 m3 d−1 during the winter months and 120 to 180 m3 d−1 in summer. These observations illustrate how ice, water and air may refill englacial volume being emptied by artificial draining. Comparison of the 3-D-SNMR results with those obtained by drilling and pumping showed a very good correspondence, confirming the high reliability of 3-D-SNMR imaging.
Highlights
Water circulation in a glacier is an important factor that determines ice dynamics, runoff characteristics, and water quality
Using three-dimensional surface nuclear magnetic resonance imaging (3-D-surface nuclear magnetic resonance method (SNMR)), we showed that the temperate part of the Tête Rousse glacier contains two separate water-filled caverns
Our results show changes in cavern geometry and recharge rate: in two years, the central cavern lost about 73 % of its initial volume, but 65 % was lost in one year after the first pumping
Summary
Water circulation in a glacier is an important factor that determines ice dynamics, runoff characteristics, and water quality. The recent, growing, concern over the response of glaciers to future-climate scenarios necessitates understanding of the hydrological processes in ice. A significant proportion of glaciers have a polythermal regime, where ice masses are composed of temperate ice (at the pressure-melting point) and cold ice (Irvine-Fynn et al, 2011). The coexistence of temperate and cold ice increases the potential for water storage within the glacier’s drainage system. Observations at Austre Brøggerbreen in 1998 and 2000 showed that a water volume of approximately 8000 m3 was retained in a single englacial channel (Irvine-Fynn et al, 2011). At Hansbreen, the annual water volumes in englacial conduits were estimated to be about 1.3 × 106 m3 (Benn et al, 2009). The total volume of accumulated water will depend upon channel density and dimensions, glacier size, and the rate at which summer-season outflow
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