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Sediment yield following severe volcanic disturbance - A two-decade perspective from Mount St. Helens

Geology

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, , , and

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Abstract

Explosive volcanic eruptions perturb water and sediment fluxes in watersheds; consequently, posteruption sediment yields can exceed pre-eruption yields by several orders of magnitude. Annual suspended-sediment yields following the catastrophic 1980 Mount St. Helens eruption were as much as 500 times greater than typical background level, and they generally declined nonlinearly for more than a decade. Although sediment yields responded primarily to type and degree of disturbance, streamflow fluctuations significantly affected sediment-yield trends. Consecutive years (1995-1999) of above-average discharge reversed the nonlinear decline and rejuvenated yields to average values measured within a few years of the eruption. After 20 yr, the average annual suspended-sediment yield from the 1980 debris-avalanche deposit remains 100 times (104 Mg [megagrams]/km2) above typical background level (~102 Mg/km2). Within five years of the eruption, annual yields from valleys coated by lahar deposits roughly plateaued, and average yields remain about 10 times (103 Mg/km2) above background level. Yield from a basin devastated solely by a blast pyroclastic current diminished to background level within five years. These data demonstrate long-term instability of eruption-generated detritus, and show that effective mitigation measures must remain functional for decades.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Sediment yield following severe volcanic disturbance - A two-decade perspective from Mount St. Helens
Series title:
Geology
Volume
28
Issue:
9
Year Published:
2000
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geology
First page:
819
Last page:
822
Number of Pages:
4