The current disequilibrium of North Cascade glaciers

Abstract

Three lines of evidence indicate that North Cascade (Washington, USA) glaciers are currently in a state of disequilibrium. First, annual balance measured on nine glaciers yields a mean cumulative balance for the 1984–2004 period of −8·58 m water equivalent (w.e.), a net loss of ice thickness exceeding 9·5 m. This is a significant loss for glaciers that average 30–50 m in thickness, representing 18–32% of their entire volume.

Second, longitudinal profiles completed in 1984 and 2002 on 12 North Cascade glaciers confirm this volume change indicating a loss of −5·7 to −6·3 m in thickness (5·0–5·6 m w.e.) between 1984 and 2002, agreeing well with the measured cumulative balance of −5·52 m w.e. for the same period. The change in thickness on several glaciers has been equally substantial in the accumulation zone and the ablation zone, indicating that there is no point to which the glacier can retreat to achieve equilibrium. Substantial thinning along the entire length of a glacier is the key indicator that a glacier is in disequilibrium.

Third, North Cascade glacier retreat is rapid and ubiquitous. All 47 glaciers monitored are currently undergoing significant retreat or, in the case of four, have disappeared. Two of the glaciers where mass balance observations were begun, Spider Glacier and Lewis Glacier, have disappeared. The retreat since 1984 of eight Mount Baker glaciers that were all advancing in 1975 has averaged 297 m. These observations indicate broad regional continuity in glacial response to climate. Copyright © 2006 John Wiley & Sons, Ltd.