| In addition to its primary responsibility of monitoring active Mount St. Helens, the David A. Johnson Cascades Volcano Observatory (CVO) has been charged with obtaining baseline geodetic and geochemical information at each of the other potentially active Cascade volcanoes. Dry tilt and/or trilateration networks were established during 1975-82 at Mount Baker, Mount St. Helens, Mount Hood, Mount Shasta, Lassen peak, Crater Lake, and Long Valley caldera; coverage was extended during September 1982 to include Mount Rainier. The dramatic reawakening of Mount St. Helens in March 1980 focused increased attention on the possibility of future eruptions elsewhere in the Cascade Range. Mount Baker had stirred briefly only 5 year earlier, prompting the installation of dry tilt (1975) and trilateration (1981) networks there to monitor possible ground deformation associated with increased thermal activity. A trilateration network was established on Mount Hood in 1980; tilt and trilateration networks were installed at Mount Shasta, Lassen Peak, and Crater Lake during 1981 and remeasured with null results in 1982. Dry tilt stations were likewise installed at Long Valley caldera during summer 1982, in response to increased seismicity and ground deformation there since 1978. This program of geodetic surveillance was extended to Mount Rainier during September 1982, to supplement continuous seismic monitoring there by the U.S.Geological Survey and The University of Washington. -- Dzurisin, et.al., 1983 |
