USGS/Cascades Volcano Observatory, Vancouver, Washington
REPORT:
Effects of the 1980 eruption of Mount St. Helens on the limnological
characteristics of selected lakes in western Washington
--
S.S. Embrey and N.P. Dion, 1988,
Effects of the 1980 Eruption of Mount St. Helens on the Limnological
Characteristics of Selected Lakes in Western Washington:
U.S. Geological Survey Water-Resources Investigations Report 87-4263, 60p.
Abstract
The 1980 eruption of Mount St. Helens, Washington, afforded an opportunity to
study its physical, chemical, and biological effects on lakes near the volcano
and to describe two newly created lakes. From June 1980 to August 1982, water
samples were collected from four lakes in the blast zone and two outside the
blast zone, as well as from the two newly created lakes. Concentrations of
chemical constituents were inversely related to the distance of a lake from the
volcano. Dissolved solids and total organic carbon, measured in June 1980, had
increased from 2 to 30 times the concentrations observed in the 1970's in
Spirit, St. Helens, and Venus Lakes. Major-ion composition and the water types
of the study lakes except Walupt Lake were altered from preeruption
calcium-bicarbonate types to calcium-sulfate, calcium-sulfate-chloride, or mixed
type.
St. Helens Lake had the shallowest Secci-disc depth transparency of all the
study lakes (6 inches) and showed the least improvement by 1982. Water
transparency in Venus Lake had improved to a depth of 24 feet by 1982.
Although Spirit Lake had been heated to more than 32 degrees Celsius during the
eruption, the water surface had cooled to near preeruption levels (13 degrees
Celsius) by October 1980. Spirit Lake was anoxic through fall 1980, but by May
1981 dissolved-oxygen concentrations had become 5.2 and 3.2 milligrams per liter
near the surface and the bottom, respectively.
Phytoplankton communities in existing lakes in the blast zone in 1980 were
primarily green and bluegreen algae; diatoms were relatively sparse in the
blast-zone lakes until summer 1982. Smaller numbers of zooplankton in Spirit,
St. Helens, and Venus Lakes, compared with Walupt and Fawn Lakes, may indicate
some posteruption mortality. Rotifers, which dominated the zooplankton
community of Deadmans Lake, were absent from lakes in the blast zone in 1980,
but by 1981 were observed in all the lakes.
The recovery of physical, chemical, and biological characteristics of the lakes
will depend on stabilization of the volcano and lake watersheds, dilution and
water-exchange rates, and biological processes within each lake. Excluding
Spirit Lake from consideration, it was estimated from the study that St. Helens
Lake would be the slowest of the study lakes to recover, and Venus Lake would be
the fastest.
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11/10/98, Lyn Topinka