GLACIER CHANGE IN THE OLYMPIC MOUNTAINS, WA OVER THE PAST AND FUTURE 100 YEARS

Glaciers of the Olympic Mountains, Washington, have been studied, scientifically, since the International Geophysical Year in 1957. Most of the effort has focused on Blue Glacier, the largest glacier, with much less attention to the other glaciers in the region. Here we critically examine and update the inventory of glaciers, document their area and volume changes, and link their change to sea surface temperatures of the North Pacific Ocean.

Results show that since their initial inventory in 1981 the total glacier-covered area has decreased -36 ± 0.02 % by 2015, and mean glacier area decreased from 0.18 km² to 0.08 km². Like other studies elsewhere, smaller glaciers retreated more than larger glaciers and showed the most variability. To estimate changes prior to 1981 we use Blue Glacier as the index. It has a relatively long time series of area estimates, derived from historic photographs and glacial moraines, and the variation in area is highly correlated with the total area change of the other glaciers. Estimated total glacier-covered area in 1900 was 55.3 km², more than twice the area in 2015.

A simple model of Blue Glacier mass balance, based on monthly air temperature and precipitation, showed good correspondence with variations in glacier area. Interrogation of the model showed that monthly mass accumulation is equally sensitive to precipitation and temperature, suggesting the importance of temperature control on the precipitation phase. Ablation is highly correlated with temperature alone. Taken together, air temperature is the dominant influence on glacier mass balance in the Olympic Mountains with precipitation playing a secondary role. Changes in the temporal trends of glacier mass balance and area are highly correlated with regime shifts in the North Pacific showing the importance of sea surface temperature on maritime glaciers. Finally, the future of these glaciers is grim. Using a coupled global circulation model to drive a regional glaciation model shows that the glaciers of the Olympic Mountains should largely disappear by 2100.