Recent Trends in Glacial Volume
Late-season snow and cool spring and summer temperatures can help glaciers build small increases in mass balance (volume) like they did in 2011. The past water year (October 1, 2010 - September 30, 2011) was the third largest winter accumulation observed since 1993, while the summer melt was below average. Both 1997 and 1999 had higher amounts of accumulation. Combined, the heavy winter snow accumulation and slower melt halted eight consecutive years of negative mass balance readings between 2003-2010 for three of four glaciers. The overall trend in the last 19 years has been a rapid decrease in volume of glaciers, as shown by the cumulative net mass balance charts.
Results from the first two years of monitoring (1993-1994) witnessed negative net mass balances of all five glaciers. Water year 1995 marked a change evident by the positive mass balance of the east-side Silver and Sandalee glaciers. This was unexpected, since we had anticipated that glaciers on the west slope of the range would be the first to show a positive year because they receive more snowfall. In reality, the east side glaciers receive a more consistent amount of snowfall and are better at conserving it due to their relatively high elevations and the fact that most are well shaded on the north sides of mountains. The years 1996 and 1997 were positive for all of the glaciers, and may have been the first consecutive years of positive balance since 1975-1976. Therefore, the two-year positive gain in 1996-1997 was by no means a long-term trend, as was confirmed by the return of negative net annual balances in 1998, 2001 and 2003-2010.
Figures 15 and 16 are a summary of available data for all four glaciers and South Cascade Glacier for the past 19 years. The vertical axis is in meters of water equivalent (m.w.e.).
Did You Know?
In addition to Wilderness, Recreation Areas and National Park designations there are also five Research Natural Areas in the complex: Silver Lake, Pyramid Lake, Boston Glacier, Stetattle Creek and Big Beaver Valley.