Harrys Ridge

Shortly after the May 18, 1980, eruption, geologists reestablished a surveying network on the volcano to measure changes that might signal additional eruptive activity. Glass prisms atop heavy steel towers on the volcano's upper flanks were surveyed with an electronic distance meter and theodolite from instrument towers placed at the base of the volcano. Reestablishment of the network began on May 24 with angle measurements from Butte Camp. Measurements of slope distance began from Butte Camp on May 29, South Fork Toutle on June 4, Clearcut on June 7, Muddy and Road 100 on June 18, and Harrys Ridge on June 29.

-- Excerpts from: Brantley and Topinka, (eds.), 1984, Volcanic Studies at the U.S. Geological Survey's David A. Johnston Cascades Volcano Observatory, Vancouver, Washington: Earthquake Information Bulletin, March-April 1984, v.16, no.2, and Swanson, et.al., 1981, Geodetic Monitoring After the May 18 Eruption: IN: Lipman and Mullineaux, 1981, The 1980 Eruptions of Mount St. Helens, Washington: USGS Professional Paper 1250, 844p.