North Cascades National Park Complex Glacier Mass Balance Monitoring Annual Report, Water Year 2009
Glaciers cover approximately 109 km2 in North Cascades National Park Service Complex (NOCA), and are a high-priority Vital Sign in the North Coast and Cascades Network monitoring plan because they are sensitive, dramatic indicators of climate change and drivers of aquatic and terrestrial ecosystems. Since 1993, seasonal volume changes at four NOCA glaciers have been monitored by tracking seasonal surface mass balance at four-to-five sites/glacier.
Water year 2009 had a slightly below average winter accumulation, and Noisy and Sandalee glaciers had a winter mass balance of about 3 ±0.2 m water equivalent (w.e.). Higher elevation Silver and North Klawatti glaciers had lower winter balances of 2.5 ±0.2 m w.e. and 2 ±0.26 m w.e., respectively. Summer melting on all four glaciers ranked among the top three melt seasons since 1993, with North Klawatti Glacier’s summer mass balance exceeding –4 ±0.47 m w.e. The combination of an average winter mass balance and a very negative summer mass balances drove net mass balance negative for the seventh consecutive year on all four glaciers. North Klawatti Glacier had the lowest net mass balance at –2.2 ±0.36 m w.e, while east-side Sandalee Glacier had the least negative net mass balance at –1.3 ±0.44 m w.e.
Negative mass balances for all four glaciers in water year 2009 strengthened the negative cumulative balance trend since 1993 for all four glaciers. Noisy, North Klawatti, and Sandalee glaciers have cumulative net mass balances of about –15 m w.e., whereas higher-elevation Silver Glacier had a cumulative balance of –9 m w.e. Since 1993 the average annual melt rate for all four glaciers has increased by about 10% (1 m w.e.).
High rates of summer melt and average snowpack led to significant glacial contribution to streamflow at NOCA. In four major watersheds glaciers contributed 472 M m3 (120 B gallons) of water to park lakes and streams. In Thunder Creek, glaciers provided about 44% of total summer runoff, whereas in the more arid, less glaciated Ross Lake basin glaciers contributed about 10%.
Ten-year remapping of Sandalee and Silver glaciers was completed in 2009 and led to significant adjustment to the base maps used for integration of point (stake) measurement to the entire glacier. Both glaciers had net vertical surface decline exceeding 15 m. Back-adjustment of data from 2000 — 2009 with the new hypsometry data led to a significant decreases in cumulative balance of –3.30 m on Silver Glacier and –5.83 m on Sandalee Glacier.