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mount st. helens ash - analysis

updated sun 18 jan 98


Michael McDowell on sat 17 jan 98

Don Prey in Oregon is asking about the chemical analysis for Mount Saint
Helens Volcanic Ash, presumably from the May 1980 eruption. There is some
variation in the chemical makeup of the ash depending on the source, e.g.
Iron content seems to be greater nearer the volcano. In my January 1981
article in Ceramics Monthly I presented a synopsis of analyses from very
near the volcano to several hudred miles away. Analyses were obtained from
geologists studying the eruption. Here's the scoop:
CaO 4 to 6 percent
MgO 1.75 to 3.75 percent
Na2O 4.2 to 4.6 percent
K2O 1 to 2 percent
Al2O3 16.3 to 19.7 percent
SiO2 61 to 66 percent
Fe2O3 4.5 to 7 percent
TiO2 .5 to .75 percent

Since your sample may fall anywhere within this range, Don. You will have
to make some assumptions about approximate figures to plug into your
calculations. Anything offered to you with specific figures will just have
the assumtions made for you.

Michael McDowell
Whatcom County, WA USA