Direct Rate Measurements of Eruption Plumes at Augustine Volcano: A Problem of Scaling and Uncontrolled Variables

Abstract

The March–April 1986 eruption of Augustine Volcano, Alaska, provided an opportunity to directly measure the flux of gas, aerosol, and ash particles during explosive eruption. Most previous direct measurements of volcanic emission rates are on plumes from fuming volcanoes or on very small eruption clouds. Direct measurements during explosive activity are needed to understand the scale relationships between passive degassing or small eruption plumes and highly explosive events. Conditions on April 3, 1986 were ideal: high winds, clear visibility, moderate activity. Three measurements were made: 1) an airborne correlation spectrometer (Cospec) provided mass flux rates of SO2; 2) treated filter samples chemically characterized the plume and 3) a quartz crystal microcascade impactor provided particle size distribution. Atmospheric conditions on April 3 caused the development of a lee wave plume, which allowed us to constrain a model of plume dispersion leading to a forecast map of concentrations of SO2 at greater distances from the vent. On April 3, 1986, the emission rate of SO2 at Augustine was 24,000 t/d, one of the largest direct volcanic rate measurements yet recorded with a Cospec. The results, coupled with analytical results from samples simultaneously collected on filters, allow us to estimate HCl emissions at 10,000 t/d and ash eruption rate at 1.5×106 t/d. Based on other data, this ash eruption rate is about 1/50 of the maximum rate during the March–April activity. Filter samples show that the gas:aerosol proportions for sulfur and chlorine are about 10:1 and 4:1, respectively. By contrast, measurements of Augustine's plume, together with ground‐based gas sampling in July 1986 when the volcano was in a posteruptive fuming state, are 380 t/d SO2 and approximately 8000 t/d HCl with no ash emission. The observations of large Cl releases at Augustine support the Cl abundance conclusions of Johnston (1980) based on study of melt inclusions in the 1976 lavas. The results reinforce the need for more measurements during eruptions and for better understanding of scaling of volcanic emissions of various eruptive components.

Volcanic Formation of Halogenated Organic Compounds

“…This confirms the estimate made by Cadle. However, the assumption of a proportionality between SO 2 and halogen emissions also constitutes a big simplification as shown by sulfur/halogen ratios reported in the literature [29], and the S/Cl ratio shows a dependence on the volcanic activity [60,63]. Using this approach, Symonds et al [5] also calculated halocarbon emissions.…”

“…The tectonic setting determines the halogen contents as andesitic magmas from convergent plate volcanoes generally have higher Cl and Br contents than basalts from divergent-plate or hot-spot volcanoes Volcanic Formation of Halogenated Organic Compounds [29]. The relative halogen content of single volcanoes is also not constant, but changes with different stages of volcanic activity [60,63].…”

A review of volcanic ash aggregation

“…Particle aggregates were observed falling from lee waves formed in the volcanic cloud from the 3 April 1988 eruption of Mount Augustine, USA (Rose et al, 1988;W. Rose, personal communication, 2010).…”

Magmatic processes revealed by textural and compositional trends in Merapi dome lavas

“…The phenocryst-free area of each image represents the area of liquid available for late stage crystallization, and is called the reference area (A R ). Crystal number density (N A ), or number of microlites per mm 2 , is obtained by dividing the number of crystals in an image not including those intersecting two of the four image edges (Rose, 1988) by the reference area. Crystallinity, expressed as a fraction (f) of the groundmass, was measured by point-counting microlites from printed versions of the images.…”

“…Approaches to the study of degassing at active volcanoes include direct gas sampling or flux measurements (Le Guern et al, 1982;Stoiber et al, 1983;Rose et al, 1988;Zapata et al, 1997) and interpretation of long-period seismicity thought to be associated with unsteady fluid movement (Chouet, 1996;Cruz and Chouet, 1997). In addition, volatile and isotopic studies of glasses and melt inclusions in the dome rocks themselves have yielded information about the magnitude of pre-and syn-eruptive degassing and the sealed (closed) vs. leaky (open) system nature of this process (Taylor et al, 1983;Newman et al, 1988;Anderson and Fink, 1989;Fink et al, 1992).…”