Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support

Petrologic Monitoring of 1981 and 1982 Eruptive Products from Mount St. Helens

Katharine V. Cashman and Joseph E. Taggart
Science
New Series, Vol. 221, No. 4618 (Sep. 30, 1983), pp. 1385-1387
Stable URL: http://www.jstor.org/stable/1691847
Page Count: 3
  • More info
  • Cite this Item
If you need an accessible version of this item please contact JSTOR User Support
Petrologic Monitoring of 1981 and 1982 Eruptive Products from Mount St. Helens
Preview not available

Abstract

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.

Page Thumbnails

  • Thumbnail: Page 
1385
    1385
  • Thumbnail: Page 
1386
    1386
  • Thumbnail: Page 
1387
    1387