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Research about Mount St. Helens

Source-linked reports with geographic coverage including Mount St. Helens.

157 records · Page 9Linked to original sources
USGS1983

Gas emissions and the eruptions of Mount St. Helens through 1982

The monitoring of gas emissions from Mount St. Helens includes daily airborne measurements of sulfur dioxide in the volcanic plume and monthly sampling of gases from crater fumaroles. The composition of the fumarolic gases has changed slightly since 1980: the water content increased from 90 to 98 percent, and the carbon dioxide concentrations decreased from about 10 to 1 percent. The emission rates of sulfur dioxide and carbon dioxide were at their peak during July and August 1980, decreased rapidly in late 1980, and have remained low and decreased slightly through 1981 and 1982. These patterns suggest steady outgassing of a single batch of magma (with a volume of not less than 0.3 cubic kilometer) to which no significant new magma has been added since mid-1980. The gas data were useful in predicting eruptions in August 1980 and June 1981.

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USGS1983

Petrologic monitoring of 1981 and 1982 eruptive products from Mount St. Helens

New material from the dacite lava dome of Mount St. Helens, collected soon after the start of each successive extrusion, is subjected to rapid chemical and petrologic analysis. The crystallinity of the dacite lava produced in 1981 and 1982 is 38 to 42 percent, about 10 percent higher than for products of the explosive 1980 eruptions. This increase in crystallinity accompanies a decrease in the ratio of hornblende to hornblende plus orthopyroxene, which suggests that the volatile-rich, crystal-poor material explosively erupted in 1980 came from the top of a zoned magma chamber and that a lower, volatile-poor and crystal-rich region is now being tapped. The major-element chemistry of the dacite lava has remained essentially constant (62 to 63 percent silica) since August 1980, ending a trend of decreasing silica seen in the products of the explosive eruptions of May through August 1980.

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USGS1983

Deep earthquakes beneath Mount St. Helens: Evidence for magmatic gas transport?

Small-magnitude earthquakes began beneath Mount St. Helens 40 days before the eruption of 20 March 1982. Unlike earlier preeruption seismicity for this volcano, which had been limited to shallow events (less than 3 kilometers), many of these earthquakes were deep (between 5 and 11 kilometers). The location of these preeruptive events at such depth indicates that a larger volume of the volcanic system was affected prior to the 20 March eruption than prior to any of the earlier dome-building eruptions. The depth-time relation between the deep earthquakes and the explosive onset of the eruption is compatible with the upward migration of magmatic gas released from a separate deep reservoir.

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USGS1983

Eruption-triggered avalanche, flood, and lahar at Mount St. Helens - Effects of winter snowpack

An explosive eruption of Mount St. Helens on 19 March 1982 had substantial impact beyond the vent because hot eruption products interacted with a thick snowpack. A blast of hot pumice, dome rocks, and gas dislodged crater-wall snow that avalanched through the crater and down the north flank. Snow in the crater swiftly melted to form a transient lake, from which a destructive flood and lahar swept down the north flank and the North Fork Toutle River.

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USGS1982

Impact of Mount St. Helens eruption on hydrology and water quality

The 1980 eruptions of Mount St. Helens in southeast Washington resulted in a pronounced effect on the surface and ground water resources of the state. In response to the volcanic activity, the U.S. Geological Survey intensified statewide surface and ground water sampling programs to determine the nature and magnitude of the volcanic-induced variations. Streams to the east of Mount St. Helens received the major ash fallout. Chemical effects were best noted in smaller streams sampled 60 to 70 miles northeast of Mount St. Helens. The chemical variations observed were pronounced but short lived. Sulfate and chloride increases in anionic composition were prevalent immediately following the eruption however, the original bicarbonate predominance was again attained within several days. Suspended iron and aluminum concentrations were similarly elevated during the period of greatest ash deposition (highest turbidity) however, the dissolved concentrations remained relatively constant. Depressions of pH were minor and short lived. Streams draining to the south, tributaries to the Columbia river, showed little observable changes in water chemistry. Streams draining to the west (Toutle river and its tributaries) were compositionally affected by the various volcanic activities. Chloride and sulfate anion percentage exceeded the bicarbonate percentage up to one month following the eruption period. Streams and lakes sampled in the immediate vicinity of Mount St. Helens, in addition to trace metals, contained organic compounds derived from decomposing wood buried in the debris deposits. This organic material may constitute a significant source of organic compounds to surface and ground water for some time to come.

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USGS1981

Effects of volcanism on the glaciers of Mount St. Helens

The cataclysmic eruption of Mount St. Helens May 18, 1980, removed 2.9 km 2 (about 0.13 km 3 ) of glacier snow and ice including a large part of Shoestring, Forsyth, Wishbone, Ape, Nelson, and all of Loowit and Leschi Glaciers. Minor eruptions and bulging of the volcano from March 27 to May 17 shattered glaciers which were on the deforming rock and deposited ash on other glaciers. Thick ash layers persisted after the May 18 eruption through the summer on most of the remaining snow and ice, and protected winter snow from melting on Swift and Dryer Glaciers. Melting and recrystalization of snow and ice surviving on Mount St. Helens could cause and lubricate mudflows and generate outburst floods. Study of glaciers that remain on this active volcano may assist in recognizing potential hazards on other volcanoes and lead to new contributions to knowledge of the transient response of glaciers to changes in mass balance or geometry.

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USGS1976

Potential hazards from future eruptions of Mount St. Helens volcano, Washington

Mount St. Helens has been more active and more explosive during the last 4,500 years than any other volcano in the conterminous United States. Eruptions of that period repeatedly formed large volumes of pumice, hot pyroclastic flows, domes, and, during the last 2,500 years, lava flows. Some of this activity also resulted in mudflows that moved tens of kilometres along the floors of valleys that head at the volcano. This report describes the nature of these phenomena and their threat to people and property; the accompanying maps show areas likely to be affected by future eruptions of Mount St. Helens. Explosive eruptions which produce large volumes of pumice affect large areas because winds carry the lightweight material hundreds of kilometres from the volcano. Because of prevailing winds, the 180° sector east of the volcano will be affected most often and most severely by future eruptions. However, the pumice from any one eruption probably will fall in only a small part of that sector. Pyroclastic flows and mudflows also can affect areas far from the volcano, but their effects are limited because they follow valleys. Mudflows and possibly pyroclastic flows moving rapidly down Swift and Pine Creeks could displace water in Swift Reservoir, which could cause disastrous floods farther downvalley.

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USGS1975

Widespread late glacial and postglacial tephra deposits from Mount St. Helens Volcano, Washington

Pumice layers composing four different groups of tephra beds (termed "sets"), whose stratigraphy, age, and trend away from Mount St. Helens are fairly well known, are potentially valuable stratigraphic markers in the northwestern United States and adjacent parts of Canada. All four tephra sets are less than about 18,000 yr old. The oldest set described (set S) is between about 18,000 and 12,000 yr old; the most extensive pumice layers of the set, however, probably are no more than about 13,000 yr old. Relatively voluminous layers in the next younger tephra unit (set J) probably range from slightly less than 12,000 to slightly more than 8,000 yr old; in the overlying set Y, the most extensive layers range from about 4,000 to 3,400 yr old. The largest tephra layers in the youngest tephra set described, set W, are apparently all about 450 yr old. All the extensive tephra deposits were carried chiefly east of Mount St. Helens, and the bulk of them form an arc which extends from north-northeast of the volcano clockwise around to the southeast.

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USGS1973

Earthquakes near Mount St. Helens, Washington

Seismic monitoring around Mount St. Helens, Washington, for 28 days during the summer of 1970 showed that the frequency of local earthquakes was from 3 to 13 per day and very similar to the activity previously observed near Mount Rainier, Washington. The epicenters of the well-recorded earthquakes form a roughly linear pattern trending northeast from the summit area. This is the only obvious trend in the epicenter distribution. Recent geological investigations have not revealed faults or other major geological discontinuities along this trend. This pattern of epicenters seems to be approximately aligned with the remnants of five ancestral St. Helens plug domes that trend southwest from the summit region.

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