Effect of summer snowfall on glaciermass balance

Abstract

It has been postulated that heavy summer snowfalls have a large impact on the mass balance of mid-latitude glaciers, because they simultaneously add mass to the glacier and reduce the amount of absorbed solar radiation. An automatic weather station (AWS) on the snout of Morteratschgletscher, Switzerland, registered a large summer snowfall event on 10-11 July 2000. Sonic rangers recorded about 20 cm of new snow on the snout and about 50 cm near the equilibrium line.We have used data fromthe AWS to study the impact on themelt process.The data show that in the ablation zone of the glacier the snow has melted and the effect on the albedo has disappeared after about 5 days. The suppression of themelt by the high albedo of the fresh snow is an important effect. For the ablation zone we find a feedback factor of about four, that is, the total effect of the snowfall event on the annual specific balance is about four times the amount of mass added during the event.We have also used a mass-balance model with 25m spatial resolution to assess the impact of the snowfall on the net balance of the entire glacier.We find the strongest effects just below the equilibrium line. Averaged over the glacier, the amount of snow deposited was 224mmw.e. The calculated effect on the total mass balance of the glacier is 354mmw.e.