Blue Glacier, Olympic National Park, Washington, USA

Blue Glacier is a small temperate glacier in the Olympic Mountains of northwestern Washington, 55 km from the Pacific Ocean, with an altitude range of 1275 to 2350m. Icefalls separate two accumulation zones, the snowdome (out of view in the top right of the photograph) and the cirque, from the lower valley glacier. Compared with other glaciers (South Cascade). in this region and elsewhere in the world, Blue Glacier has changed little in the past 40 years, in either thickness or areal extent.

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Blue Glacier, September 1995

Link to an illustrated guide of Blue Glacier.
The Duwamish Indians called the region Sun-a-do, but when the English navigator John Meares saw the snowcapped mountains from his ship in 1778, he thought they could be the home of the Gods and named the highest peak Mt Olympus. In more recent times, Blue Glacier (location and map of glacier) has been subjected to studies (some publications) by groups from University of Washington, California Institute of Technology, Ohio State University, US Geological Survey and the US National Park Service.

I. Terminus changes

Evidence from terminal moraines indicates that about 1815 the termini of both Blue and White Glaciers were joined in Glacier Creek. By the mid 1950's Blue Glacier had retreated more than 1400 m and it has remained near that position for the past 40 years (length history). Recent measurements however, indicate that the mass balance has been strongly negative since 1976 and the glacier is now well out of equilibrium with the present climate. If present conditions persist, retreat of Blue Glacier is inevitable (Rasmussen and Conway, J. Glaciol., 47, 159 (2001)).

II. Long-term volume and annual mass balance changes

Annual mass balance is the net gain or loss of mass of a glacier each year (time series ). Mass is gained from snowfall and lost by melting. Winter snow depths typically vary from about 3 m (on the lower glacier) up to 20 m (in the upper cirque). The average daily summer melt rate is about 2.5 cm. Measurements of glacier mass balance are difficult to obtain and are subject to uncertainty. Annual mass balance has not been measured systematically at Blue Glacier, but an estimate has been made for each since 1956. In some years, balance has been estimated from probing of residual snow depths in late September and stake measurements of cumulative ice and firn melt. For 1987 to present, we have estimated anual balance from late season observations of the equilibrium line altitude (ELA), using a regression developed over the years when both ELA and balance were measured. Now we are now investigating monitoring the seasonal progression of the snowline (and hence glacier mass balance) remotely using a camera that takes sequential photographs through the year from a fixed location.

Other sources for estimating glacier changes are published and unpublished maps and surveying data. We have maps of surface elevations based on aerial photography taken in 1939, 1952, 1957 and 1987 and we also have theodolite surveying notes of Mark Meier (1957 and 1958) and Keith Echelmeyer (1977 and 1978). During the spring and fall of 1995 we surveyed a few positions on and surrounding the glacier using geodetic quality global positioning (GPS) instruments. The positions, located with respect to the existing network of GPS stations at Neah Bay (Cheeka Peak) and Victoria, BC, are accurate to within a few centimeters. During the spring of 1996, colleagues from the University of Alaska flew four profiles along the glacier surface using a light aircraft equipped with GPS and laser profiling equipment. We have used these measurements to estimate the surface topography of 1 October, 1995.

Comparison of the mapped surface topographies indicates the mass balance of Blue Glacier has changed less than 7 meters (water equivalent) since 1939 which is minor compared with other glaciers in the world. Further comparison with the map changes shows that the field estimates of annual balance (1956-1997 mass balance) are too positive by about 0.4 m/a, indicating that considerable caution is needed when interpreting time series of mass balance, (Conway and others, 1999 ).

III. Recent climate changes in Western Washington

Our studies have shown that temperatures on Blue Glacier can be closely estimated using measurements from radiosonde balloons launched at Quillayute about 65 km WNW of the glacier. The National Weather Service have launched balloons in western Washington twice daily since 1948. Measurements indicate annual temperatures at 850 mb (~ 1450 m) have increased by 1.2oC since 1948. This rate of warming is about five times higher than the global average. Most of the warming has occurred during winter; the average winter temperature (January through March) has warmed 3.3oC (seasonal variation). We scale measurements from Forks to estimate the total precipitation on the glacier. Results indicate precipitation has decreased and, in addition winter warming has changed the rain/snow mix of precipitation. Snow accumulation (1914-1996 snowfall) on the glacier has changed considerably. Annual snowfall near the terminus has decreased by more than 500 mm since 1948 (Rasmussen and others, 2000 ).

People involved with the research

Al Rasmussen, Hans-Peter Marshall, Dave Skinner, Andrew Boudreaux, Haley Wight, Kurt Cuffey, Tony Gades, Dave Morse, Nadine Nereson, Tom Neumann, Charlie Raymond and Howard Conway (University of Washington)
Tolly Adalgeirsdottir and Keith Echelmeyer (University of Alaska).

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