Gaseous constituents in the plume from eruptions of mount st. Helens

Measurements in the stratosphere of gaseous constituents in the plume of Mount St. Helens were obtained during five flights of the NASA U-2 aircraft between 19 May and 17 June 1980. Mixing ratios from gas chromatographic measurements on samples acquired about 24 hours after the initial eruption show considerable enhancement over nonvolcanic concentrations for sulfur dioxide (more than 1000 times), methyl chloride (about 10 times), and carbon disulfide (more than 3 times). The mixing ratio of carbonyl sulfide was comparable to nonvolcanic mixing ratios although 3 days later it was enhanced two to three times. Ion chromatography measurements on water-soluble constituents are also reported. Very large concentrations of chloride, nitrate, and sulfate ions were measured, implying large mixing ratios for the water-soluble gaseous constituents from which the anions are derived. Measurements of radon-222 present in the plume are also reported.     

Impact on agriculture of the mount st. Helens eruptions

Ash from Mount St. Helens has fallen over a diverse agricultural area, with deposits of up to 30 kilograms per square meter. Crop losses in eastern Washington are estimated at about $100 million in 1980-about 7 percent of the normal crop value in the affected area and less than was expected initially. Production of wheat, potatoes, and apples will be normal or above normal because the favorable conditions for growth of these crops since the ashfall helped offset the losses. Alfalfa hay was severely lodged under the weight of the ash, but ash-contaminated hay is apparently nontoxic when eaten by livestock. The ash as an abrasive is lethal to certain insects, such as bees and grasshoppers, but populations are recovering. The ash has increased crop production costs by necessitating machinery repairs and increased tillage. On soil, the ash reduces water infiltration, increases surface albedo, and may continue to affect water runoff, erosion, evaporation, and soil temperature even when tilled into the soil. Ash on plant leaves reduced photosynthesis by up to 90 percent. Most plants have tended to shed the ash. With the possible exception of sulfur, the elements in the ash are either unavailable or present in very low concentrations; and no significant contribution to the nutrient status of soils is expected.     

Carbonyl sulfide and carbon disulfide from the eruptions of mount st. Helens

Ash from the massive 18 May 1980 eruption of Mount St. Helens readily gave off large amounts of carbonyl sulfide and carbon disulfide gases at room temperature. These findings suggest that the sulfur that enhances the Junge sulfate layer in the stratosphere after volcanic eruptions could be carried directly to the upper atmosphere as carbonyl sulfide and carbon disulfide adsorbed on ash particles from major volcanic eruptions.     

Airborne studies of the emissions from the volcanic eruptions of mount st. Helens

The concentrations of particles less than 10 micrometers in diameter in the ash emissions from Mount St. Helens have been more than 1000 times greater than those in the ambient air. Mass loadings of particles less than 2 micrometers in diameter were generally several hundred micrograms per cubic meter. In the ash clouds, produced by the large eruption on 18 May 1980, the concentrations of several trace gases generally were low. In other emissions, significant, but variable, concentrations of sulfur gases were measured. The 18 May eruption produced nuées ardentes, lightning flashes, and volcanic hail.     

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.     

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.     

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.     

Size distributions and mineralogy of ash particles in the stratosphere from eruptions of mount st. Helens

Samples from the stratosphere obtained by U-2 aircraft after the first three major eruptions of Mount St. Helens contained large globules of liquid acid and ash. Because of their large size, these globules had disappeared from the lower stratosphere by late June 1980, leaving behind only smaller acid droplets. Particle-size distributions and mineralogy of the stratospheric ash grains demonstrate in-homogeneity in the eruption clouds.     

Absorption of visible radiation by aerosols in the volcanic plume of mount st. Helens

Samples of particles from Mount St. Helens were collected in both the stratosphere and troposphere for measurement of the light absorption coefficient. Results indicate that the stratospheric dust had a small but finite absorption coefficient ranging up to 2 x 10(-7) per meter at a wavelength of 0.55 micrometer, which is estimated to yield an albedo for single scatter of 0.98 or greater. Tropospheric results showed similar high values of an albedo for single scatter.     

Monitoring the 1980-1982 eruptions of mount st. Helens: compositions and abundances of glass

The Mount St. Helens eruptive sequence of 1980 through 1982 reflects the tapping of successively less water-rich, more highly crystallized, and more viscous, highly phyric dacitic magmas. These changes reflect both syn- and preeruption processes. The decreasing water content points to a continued decline in the volume and intensity of explosive pyroclastic activity. This decreasing water content appears to be composed of a long-term trend established during a long period of repose (about 130 years) imposed on short-term trends established during short periods (about 7 to 100 days) of repose between eruptions in the present eruptive cycle. The last two eruptive cycles of this volcano, the T (A.D. 1800) and W cycles (about A. D. 1500), exhibited similar trends. These changes are inferred from a combination of petrographic, bulk chemical, and electron- and ion-microprobe analyses of matrix and melt-inclusion glasses.     

Trajectories of the mount st. Helens eruption plume

The plume of the major eruption of Mount St. Helens on 18 May 1980 penetrated 10 to 11 kilometers into the stratosphere, attaining heights of 22 to 23 kilometers. Wind shears rapidly converted the plume from an expanding vertical cone to a thin, slightly inclined lamina. The lamina was extruded zonally in the stratosphere as the lower part moved eastward at jet stream velocities, while the upper part slowly moved westward in the region of nonsteady transition from the westerlies to the summer stratospheric easterlies. Trajectories computed to position the NASA U-2 aircraft for sampling in the plume are described. Plume volume after 8 hours of strong volcanic emission is estimated at 2 x 10(6) cubic kilometers. Only about 1 percent of this volume is attributed to the volcano; the rest was entrained from the environment.     

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.     

Tsunamis generated by eruptions from mount st. Augustine volcano, alaska

During an eruption of the Alaskan volcano Mount St. Augustine in the spring of 1986, there was concern about the possibility that a tsunami might be generated by the collapse of a portion of the volcano into the shallow water of Cook Inlet. A similar edifice collapse of the volcano and ensuing sea wave occurred during an eruption in 1883. Other sea waves resulting in great loss of life and property have been generated by the eruption of coastal volcanos around the world. Although Mount St. Augustine remained intact during this eruptive cycle, a possible recurrence of the 1883 events spurred a numerical simulation of the 1883 sea wave. This simulation, which yielded a forecast of potential wave heights and travel times, was based on a method that could be applied generally to other coastal volcanos.     

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.     

Biological responses of lakes in the mount st. Helens blast zone

Loadings of dissolved organics and suspended particulates from destroyed forests and volcanic debris produced by the 18 May 1980 eruption of Mount St. Helens altered the trophic structure of many blast zone lakes to the extent that anoxic conditions and chemoorganotrophic and chemolithotrophic microorganisms prevailed. High bacterial counts and high adenosine triphosphate concentrations were directly related to enhanced concentrations of dissolved organic carbon, and plankton chlorophyll a was inversely related to light extinction. The recovery of these lakes to the preeruption state appears dependent upon the oxidation of organics and the stabilization of watersheds.     

Chemical changes of lakes within the mount st. Helens blast zone

Differences in the dissolved chemistry of lakes devastated by the 18 May 1980 eruption of Mount St. Helens are attributable to location relative to the lateral blast trajectory of the eruption and to the emplacement of mineral deposits. Elemental enrichment ratios of pre- and posteruption measurements for Spirit Lake and comparisons of the chemical concentrations and elemental ratios for lakes inside and outside the blast zone reflect the influences of the dissolution of magmatic and lithic deposits. The pH changes were minor because of buffering by carbonic acid and reactions involving mineral alteration, dissolved organics, and biological processes.     

Eruption prediction aided by electronic tiltmeter data at mount st. Helens

Telemetry from electronic tiltmeters in the crater at Mount St. Helens contributed to accurate predictions of all six effusive eruptions from June 1981 to August 1982. Tilting of the crater floor began several weeks before each eruption, accelerated sharply for several days, and then abruptly changed direction a few minutes to days before extrusion began. Each episode of uplift was caused by the intrusion of magma into the lava dome from a shallow source, causing the dome to inflate and eventually rupture. Release of magma pressure and increased surface loading by magma added to the dome combined to cause subsidence just prior to extrusion.     

Changes in stratospheric water vapor associated with the mount st. Helens eruption

A frost point hygrometer designed for aircraft operation was included in the complement of instruments assembled for the NASA U-2 flights through the plume of Mount St. Helens. Measurements made on the 22 May flight showed the water vapor to be closely associated with the aerosol plume. The water vapor mixing ratio by mass in the plume was as high as 40 x 10(-6). This compares with values of 2 x 10(-6) to 3 x 10(-6) outside of the plume.     

Measurements of the stratospheric plume from the mount st. Helens eruption: radioactivity and chemical composition

Gas measurements made in the stratospheric plume from the eruption of Mount St. Helens on 18 May 1980 were not consistent with a reported large injection of radon-222 into the atmosphere. No enrichment in the volatile element polonium was found in filter samples, and the ratio of polonium-210 to lead-210 was not different from background values. Data obtained with an experimental impactor, flown shortly after the eruption, showed an increase of 10(3) in the stratospheric number concentration of submicrometer sulfate particles compared to concentrations before the eruption.