A volcanomagnetic observation on Mount St. Helens, Washington

Details A volcanomagnetic observation on Mount St. Helens, Washington A volcanomagnetic observation on Mount St. Helens, Washington

Mar 1984

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984georl..11..225d&link_type=abstract

Geophysical Research Letters (ISSN 0094-8276), vol. 11, March 1984, p. 225-228.

Physics

3

Geomagnetism, Magnetic Measurement, Volcanology, Electric Fields, Magnetometers, Washington

Scientific paper

Total magnetic fields were recorded at five sites on Mt. St. Helens between October 23 and November 11, 1981, an interval which included an extrusive dome-building eruption of the volcano. Two of the magnetometers located in the volcano's crater measured reversible magnetic changes, which correspond to fluctuations in tilt measured nearby. However, the relationship is highly nonlinear. Electric fields were measured on the east flank of the volcano near its summit to search for electrokinetic effects. They show no correlation with the magnetic changes and, in the long term, are uncorrelated with eruptive activity. The interpretation of the magnetic changes favored is that they result from stress-induced changes in the magnetization of the volcano. Magnetic field values returned to preanomaly values. This reversibility rules out pressure-induced magnetization as the dominant mechanism, and places an upper limit of about 300 bars on the stress changes. The limited spatial extent of the magnetic anomaly field places the source of stress at shallow depth beneath the crater floor, consistent with models based on strain data.

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