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Research about Mount St. Helens

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

At least 145 records · Page 8Linked to original sources
USGS1986

Sedimentology and clast orientations of the 18 May 1980 southwest- flank lahars, Mount St. Helens, Washington

Three lahars that resulted from the flow transformation of an inflated pyroclastic surge caused by ejected lithic debris and hydrothermal water during the cataclysmic Mount St . Helens eruption of 18 May 1980 deposited about 1 x 10 6 m 3 of massive, poorly sorted, poorly graded volcaniclastic sediment on the SW flank (SWF). Downflow changes in mean grain size and sorting occur only in the coarse fraction of the deposits larger than a critical diameter of about 4mm, and occur only in the basal portion of the deposits; both mean grain size and sorting coefficient increase slightly with distance. The deposits show weak inverse grading with respect to mean grain size and exhibit a weak trend of upwardly poorer sorting, but lahar clast fabric may be more complex and variable than previously suggested.

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USGS1986

An assessment of ground-nest depredation in a catastrophically disturbed region, Mount St. Helens, Washington

The explosive eruption of the Mount St. Helens volcano on 18 May 1980 severely affected a large ar- ray of plant and animal populations (Edwards and Schwartz 1981, MacMahon 1982, Wissmar et al. 1982) over a vast area (>600 kM2) (Fig. 1). Volcanic eruptions are relatively common agents of large-scale biotic disturbance, yet few studies have addressed either short- or long-term effects on avian populations (see Hayward et al. 1982 for entry on pre-1980 literature). We present data gathered during 1980- 1984 on relative abundances of birds in disturbed areas near Mount St. Helens. These data indicate that a ground-nesting species was numerically dominant in the early posteruption avifauna. We also test the null hypothesis that predation rates on ground nests were unaltered by the eruption. We assumed that the breeding abundance of ground-nesting species is affected significantly by nesting success in previous years (Duebbert and Lokemoen 1980) and speculated whether dramatic changes in ground-nest predation rate might have occurred as a result of the eruption.

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USGS1985

Proximal bedded deposits related to pyroclastic flows of May 18, 1980, Mount St. Helens, Washington

Thin-bedded, dacitic, pumiceous pyroclastic-flow deposits partly cover the steep northern flank of Mount St. Helens volcano, Washington. They are termed proximal bedded pyroclastic-flow (PBPF) deposits and were formed during the eruption of May 18, 1980. These unconsolidated deposits, as much as 20 m thick, are characterized by well-defined, chiefly plane-parallel bedding sets separated by erosion surfaces. Most beds dip generally parallel to the slope of the underlying volcano flank, which averages 15° to the north but locally is as much as 30°. Individual beds range in thickness from 2 mm to >1 m. Cross-bedding, in which bedding sets dip gently to the north or locally to the south, is abundant. Cross-bedding is generally associated with large longitudinal dunes, apparently antidunes. Some cross-bedding sets, however, constitute small longitudinal anti-dunes (chute-and-pool structures) containing stoss-side beds that migrated south and dip steeply south toward the crater source.

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USGS1985

Suitability of nonwelded pyroclastic-flow deposits for studies of magnetic secular variation: A test based on deposits emplaced at Mount St. Helens, Washington, in 1980

Paleomagnetic directions obtained from nonwelded pyroclastic-flow deposits that were emplaced at Mount St. Helens, Washington, in 1980 have a precision and accuracy similar to data obtainable from lava flows. It is concluded that nonwelded pyroclastic-flow deposits, like lava flows, are suitable for studies of magnetic secular variation. Although clast rotations apparently caused an “inclination error” in the paleomagnetic directions, the error is a few degrees at most.

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USGS1985

Sedimentation in a blast-zone lake at Mount St. Helens, Washington—Implications for varve formation

Sediment collected in traps in a newly formed lake in the blast-impact area at Mount St. Helens recorded a sediment yield that is about two orders of magnitude greater than for comparable basins with vegetation and similar precipitation. Most sediment was mobilized by storms and runoff at the onset of the wet season. The sedimentation response to strongly seasonal precipitation, in the absence of vegetation, produced turbidites and graded annual couplets. The style of sedimentation suggests an alternate mechanism for the formation of long sequences of graded clastic varves.

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USGS1985

The effects of catastrophic ecosystem disturbance: the residual mammals at Mount St. Helens

Individuals that survive the direct effects of community- or ecosystem-level disturbances, i.e., "residuals", can have major roles in determining the rate and pathway of subsequent secondary succession. The explosive eruption of the Mount St. Helens volcano on 19 May 1980 resulted in severe damage to a cast array of animal and plant populations (Edwards and Schwartz, 1981; MacMahon, 1982; Hayward et al., 1982). We apply the term "catastrophic" to this event because of its intensity and the large area (>600 km 2 ) over which successional processes were initiated. We present here the results of surveys for mammals, particularly small mammals (excluding bats), conducted in the Mount St. Helens region during the 40 months following the eruption. Our purpose was to elucidate any patterns in species representation that might exist along a gradient of disturbance "intensity", and thus document which species could potentially influence early plant successional patterns there. We infer whether individuals captured were more likely to have been residuals (or their descendants), or immigrants from areas less affected by the eruption, from consideration of the time span between the eruption and the capture date, the trapping location, and life history data. We also make inferences concerning the animal-environment relationships that led to our survey results, and thereby address the question of the likelihood of other types of disturbance, either natural or anthropogenic, producing similar results. Data concerning survival of Thomomys talpoides , the northern pocket gopher, have been presented elsewhere (Andersen, 1982). Initial results from our studies of the relationships among residual small mammals and plant population dynamics are detailed in MacMahon and Warner (1984), Allen et al. (1984) and Andersen and MacMahon (in press).

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USGS1984

Between Mount St. Helens and the world: How the U.S. Geological Survey provided news-media information on the 1980 volcanic eruptions

The eruptions of Mount St. Helens volcano, Wash., constituted one of the major national and international news stories of 1980 and involved the U.S. Geological Survey in more news coverage than any other event in its history. Much of the information about the volcano came from monitoring and research by geologists, geophysicists, hydrologists, and other scientists of the U.S. Geological Survey. This scientific information was distributed to the public, through news media, by U.S. Geological Survey personnel. Key members of this group were Mount St. Helens hazards assessment scientists, monitoring scientists, and research scientists; public affairs officers; and the Information Scientist for Mount St. Helens. The Information Scientist, a geologist or geophysicist, assumed the major role of on-site (Vancouver, Wash.) news spokesman about a week after the main eruption of May 18. The Geological Survey released information through news conferences, interviews, news pools of reporters and cameramen on trips to the volcano, special television and radio appearances, news releases, and informal contacts with reporters. Members of the U.S. Forest Service, Federal Emergency Management Agency, State of Washington, and other government agencies cooperated extensively with the Geological Survey. By providing assistance to news representatives, the Geological Survey and these other agencies helped effect rapid dissemination of the background information and daily events of a highly complex story while limiting disruption to the scientific working team and minimizing dangers to reporters and scientists.

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USGS1983

Terpenoid marker compounds derived from biogenic precursors in volcanic ash from Mount St. Helens, Washington

A volcanic-ash sample obtained after the 1980 eruption of Mount St. Helens, Washington, was analyzed for cyclic terpenoid organic compounds and polycyclic aromatic hydrocarbons using capillary gas chromatography-mass spectrometry-computer techniques. Various tricyclic diterpenoid acids and hydrocarbons were identified including dehydroabietic acid, dehydroabietin, dehydroabietane, simonellite, and retene. Preliminary evidence indicates that these compounds were derived from forest soils or atmospheric aerosols or both in the vicinity of coniferous forests. A diagenetic scheme involving three possible pathways for the conversion of abietic acid to retene is presented.

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USGS1983

Predicting eruptions at Mount St. Helens, June 1980 through December 1982

Thirteen eruptions of Mount St. Helens between June 1980 and December 1982 were predicted tens of minutes to, more generally, a few hours in advance. The last seven of these eruptions, starting with that of mid-April 1981, were predicted between 3 days and 3 weeks in advance. Precursory seismicity, deformation of the crater floor and the lava dome, and, to a lesser extent, gas emissions provided telltale evidence of forthcoming eruptions. The newly developed capability for prediction reduced risk to life and property and influenced land-use decisions.

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USGS1983

Seismic precursors to the Mount St. Helens eruptions in 1981 and 1982

Six categories of seismic events are recognized on the seismograms from stations in the vicinity of Mount St. Helens. Two types of high-frequency earthquakes occur near the volcano and under the volcano at depths of more than 4 kilometers. Medium- and low-frequency earthquakes occur at shallow depths (less than 3 kilometers) within the volcano and increase in number and size before eruptions. Temporal changes in the energy release of the low-frequency earthquakes have been used in predicting all the eruptions since October 1980. During and after eruptions, two types of low-frequency emergent surface events occur, including rockfalls and steam or gas bursts from the lava dome.

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USGS1983

Deformation monitoring at Mount St. Helens in 1981 and 1982

For several weeks before each eruption of Mount St. Helens in 1981 and 1982, viscous magma rising in the feeder conduit inflated the lava dome and shoved the crater floor laterally against the immobile crater walls, producing ground cracks and thrust faults. The rates of deformation accelerated before eruptions, and thus it was possible to predict eruptions 3 to 19 days in advance. Lack of deformation outside the crater showed that intrusion of magma during 1981 and 1982 was not voluminous.

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