Glacier status and contribution to streamflow in the Olympic Mountains, Washington, USA

Abstract

The Olympic Peninsula, Washington, USA, currently holds 184 alpine glaciers larger than 0.01 km2 and their combined area is 30.2±0.95 km2. Only four glaciers are >1 km2 and 120 of the others are <0.1 km2. This represents a loss of 82 glaciers and a 34% decrease in combined area since 1980, with the most pronounced losses occurring on south-facing aspects and in the more arid northeastern part of the range. Annual rate of loss in glacier area for seven of the largest glaciers accelerated from 0.26 km2 a-1 (1900-80) to 0.54 km2 a-1 (1980-2009). Thinning rates on four of the largest glaciers averaged nearly 1 ma-1 from 1987 to 2010, resulting in estimated volume losses of 17-24%. Combined glacial snow, firn and ice melt in the Hoh watershed is in the range 63-79±7×106 m3, or 9-15% of total May-September streamflow. In the critical August-September period, the glacial fraction of total basin runoff increases to 18-30%, with one-third of the water directly from glacial ice (i.e. not snow and firn). Glaciers in the Elwha basin produce 12-15±1.3×106 m3 (2.5-4.0%), while those in the Dungeness basin contribute 2.5-3.1±0.28× 106 m3 (3.0-3.8%).