T.C. Pierson R.L. Dinehart J. E. Costa J. J. Major 2000 <p><span>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 (10</span>⁴<span>&nbsp;Mg [megagrams]/km</span>²<span>) above typical background level (∼10</span>²<span>&nbsp;Mg/km</span>²<span>). Within five years of the eruption, annual yields from valleys coated by lahar deposits roughly plateaued, and average yields remain about 10 times (10</span>³<span>&nbsp;Mg/km</span>²<span>) 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.</span></p> application/pdf 10.1130/0091-7613(2000)28%3C819:SYFSVD%3E2.0.CO;2 en Geological Society of America Sediment yield following severe volcanic disturbance - A two-decade perspective from Mount St. Helens article