Glacier d'Ossoue, Vignemale - Accumulation measurement - May 24, 2020
Glaciers are climatic super-indicators since their existence is the result of the antagonistic action of the two main atmospheric parameters. Solid precipitation (winter) makes glaciers fatter and positive temperatures (summer) make them thinner. The glacial variations therefore reflect the climatic trend very concretely.
Measuring the annual mass balance of a glacier consists of two separate field campaigns. One at the end of winter to quantify snow accumulation and the other at the end of summer to deduct melting. The balance is therefore winter accumulation minus summer ablation (melting).
On 24 May 2020 at the Ossoue glacier (Vignemale), the 19th year of accumulation measurements revealed an average thickness of 5.40 metres of neve (a snow mass which, under the effect of settling and an alternation of thaws and refreezes, tends to harden and which is at the origin of a glacier), i.e. 2.92 metres of water equivalent (measurement of the quantity of water present in a snow cover). This value is slightly higher than the average (2.81m) over the last 19 years. Indeed, the snow cover in altitude (>2500m) for this spring is rather good in the Pyrenees. But between 2002 and 2019, the Ossoue glacier lost 30 metres in thickness, its surface area went from 58 to 32 hectares and its front regressed by 125 metres in length!
Figure 1: Evolution of the Ossoue glacier; Source: Pierre René, glaciologist & mountain guide
The Moraine association, created in 2001, is the Observatoire des Glaciers des Pyrénées Françaises. It was created to make up for the lack of observations of glaciers in the French Pyrenees. For 19 years, it has therefore endeavoured to carry out an annual monitoring of glacier evolution (Length, Surface, Volume) and to disseminate the knowledge acquired to the greatest number of people.
From the OPCC and thanks to the ADAPYR project, it will be possible to advance the observation and definition of follow-up indicators works of the major part of 19 Pyrenean glaciers. These glaciers are today in a sensible situation and in a clear process of retreat.