What's in the news?

From looking at the changes in subglacial drainage of outlet glaciers before, this news article from August 2010 shows the efforts of French engineers to remove the subglacial lake which had formed from meltwater as a result of increased warming in recent years. The water, which lies under the Tete-Rousse glacier, threatened the safety of people in the underlying Saint Gervais valley with flooding from a sudden outburst event.

Indeed, the danger of this kind of event has been witnessed before. In 1892, 175 people were killed in the St Gervais valley by flooding from a subglacial lake. This occurred on the same glacier, and saw the collapse of the ice wall which had previously held in the subglacial lake. The origins of this original outburst can be seen in the paper by (Vincent et al. 2010). Today, several thousand tourists visit and stay within the valley each year, perhaps justifying the intervention seen here.

Figure 1. Large cavity from 19th century outburst

Therefore, to apply this pre-emptive measure, the engineers aimed to pump the water away by drilling through the ice and thus accessing the 2.3m³ ft subglacial lake. The process of draining took several months and aimed to reduce subglacial pressure by removing one third of the water present.

Figure 2. Drainage hole drilled into the glacier

The level of stress seen under the glacier was proposed to be as a result of both increased temperature causing greater amounts of meltwater, and by a brief anomalous cold period freezing the natural drainage routes for this meltwater.