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Analysis of difference between direct and geodetic mass balance measurements at South Cascade Glacier, Washington

Geografiska Annaler, Series A: Physical Geography

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Abstract

Net mass balance has been measured since 1958 at South Cascade Glacier using the 'direct method,' e.g. area averages of snow gain and firn and ice loss at stakes. Analysis of cartographic vertical photography has allowed measurement of mass balance using the 'geodetic method' in 1970, 1975, 1977, 1979-80, and 1985-97. Water equivalent change as measured by these nearly independent methods should give similar results. During 1970-97, the direct method shows a cumulative balance of about -15 m, and the geodetic method shows a cumulative balance of about -22 m. The deviation between the two methods is fairly consistent, suggesting no gross errors in either, but rather a cumulative systematic error. It is suspected that the cumulative error is in the direct method because the geodetic method is based on a non-changing reference, the bedrock control, whereas the direct method is measured with reference to only the previous year's summer surface. Possible sources of mass loss that are missing from the direct method are basal melt, internal melt, and ablation on crevasse walls. Possible systematic measurement errors include under-estimation of the density of lost material, sinking stakes, or poorly represented areas.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Analysis of difference between direct and geodetic mass balance measurements at South Cascade Glacier, Washington
Series title:
Geografiska Annaler, Series A: Physical Geography
Volume
81
Issue:
4
Year Published:
1999
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
653
Last page:
658
Number of Pages:
6