DESCRIPTION:
Volcano Monitoring Networks

In response to renewed eruptive activity at Mount St. Helens in 1980, the Cascades Volcano Observatory (CVO) was established in Vancouver, Washington, with the support of the U.S. Geological Survey's Volcano Hazards Program. In addition to continued monitoring at Mount St. Helens, CVO scientists have initiated geodetic and geochemical monitoring at other potentially active volcanoes in the Cascade Range. Monitoring networks were also established at other volcanoes in the Pacific Coast States, including Augustine Island, Alaska, between 1981 and 1989. Periodic reoccupation of these networks is planned as part of an overall long-term monitoring program. Reoccupation serves as a check on previous data, solidifies the baseline information, and provides an assessment of the state of the volcano. Further work is planned at these and other Cascade volcanoes as funds permit. The geodetic studies supplement a program of continuous seismic monitoring at Cascade volcanoes funded by the U.S.Geological Survey in cooperation with the University of Washington. These investigations provide useful baseline data for evaluating future deformation related to subvolcanic activity.

In response to renewed eruptive activity at Mount St. Helens in 1980, the Cascades Volcano Observatory (CVO) was established in Vancouver, Washington, with the support of the U. S. Geological Survey's Volcano Hazards Program. In addition to continued monitoring at Mount St. Helens, CVO scientists have initiated geodetic and geochemical monitoring at other potentially active volcanoes in the Cascade Range ... Field work in 1980-84 included the acquisition of baseline geochemical and geodetic information at six Cascade volcanoes other than Mount St. Helens. Geochemical studies include temperature measurements and gas sampling of fumaroles at Mount Baker, Mount Hood, Mount Shasta, and Lassen Peak. Geodetic studies consist of: (1) slope distance and vertical angle measurements at Mount Baker, Mount Rainier, Mount Hood, Crater Lake, Mount Shasta, and Lassen Peak; (2) tilt surveys at Mount Baker, Mount Rainier, Mount Shasta, Lassen Peak, and Mount Hood; and (3) precision gravity surveys at Mount Shasta and Lassen Peak. Further work is planned at these and other Cascade volcanoes as funds permit. The geodetic studies supplement a program of continuous seismic monitoring at Cascade volcanoes funded by the U.S.Geological Survey in cooperation with the University of Washington. These investigations provide useful baseline data for evaluating future deformation related to subvolcanic activity.

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.

Between 1980 and 1984, the U.S.Geological Survey's David A. Johnston Cascades Volcano Observatory (CVO) established baseline geodetic networks at Mount Baker, Mount Rainier, and Mount St. Helens in Washington, Mount Hood and Crater Lake in Oregon, and Mount Shasta and Lassen Peak in California. To this list of potentially active volcanoes, CVO extended its monitoring program in 1985 to include Newberry and South Sister volcanoes in central Oregon. The Newberry and South Sister networks were re-measured in 1986 and will be measured periodically in future years. Improvements since 1984 in the recording of endpoint and flightline temperatures resulted in better overall data than obtained previously. The improvements included: calibration of all the sensors and precision thermistors, installation of a new recording system for flightline data, and recording of endpoint temperatures 6 m above ground level. The data collected in 1985 and 1986 indicate little or no apparent deformation at either volcano between surveys.

Trilateration and distance-measuring networks have been established on 12 potentially active volcanoes in the Pacific Coast States beginning in 1980. These networks, once the baseline information has been collected, can detect surface deformation that may reflect magma movement up the conduit. The rates of deformation increase as magma approaches the surface, and these measurements can therefore help determine where and when an eruption may occur. Before 1980, electronic distance meters (EDM's) had been used primarily to monitor horizontal deformation during inflation and deflation of shield volcanoes. Little horizontal deformation monitoring had been attempted on stratovolcanoes with the exception of Usu volcano, Japan, where up to 160 m of movement was observed using trilateration techniques to monitor cyrptodomes forming in the summit area in 1977-78. Several distances at Mount St. Helens and Mount Hood were measured in 1972 but were not remeasured prior to the reawakening of Mount St. Helens in 1980. Several distances were measured twice at Mount Hood in the summer of 1980, owing to an earthquake swarm, but no complete network was established and no significant changes were observed.

In mid-April 1980, measurements of distances and angles were initiated at Mount St. Helens, primarily to monitor the rate of deformation of the bulge on the north side of the volcano. Displacements of 1.4-1.6 m/day were measured on the bulge prior to May 18, but there was little or no significant change outside the bulge area. A complete EDM network was established at Mount St. Helens shortly after the catastrophic eruption on May 18, 1980.

Monitoring networks were established at other volcanoes in the Pacific Coast States, including Augustine Island, Alaska, between 1981 and 1989. Periodic reoccupation of these networks is planned as part of an overall long-term monitoring program. Reoccupation serves as a check on previous data, solidifies the baseline information, and provides an assessment of the state of the volcano. ...

Setting up a network starts with the best topographic map available, preferably one with vegetated areas marked on it. About six instrument stations are selected at the base of the mountain, approximately 60 radial degrees apart relative to the summit. Ideally each instrument station should be visible from the next station so that measurements can be made between them, but this is not critical and is commonly difficult to achieve. Next we select reflector sites at medium to high elevations on the volcano that can be seen from at least two instrument stations. Reflector sites visible from three instrument stations are optimal. If only one instrument station can be seen and the line is considered important, then we install it. We try to form triangles when establishing stations and to connect the whole network together when possible. This ideal can sometimes be accomplished on a map but is rarely met when attempted in the field. Topography, vegetation, snow and ice cover, and bedrock outcrops ultimately dictate what can be established at any volcano. ...

During installation of a network, one person occupies a potential instrument site, and one is located at each respective reflector site. If a solid rock outcrop or large boulder firmly set in the ground is present and visibility is good, the bench marks are installed. People move around the volcano until the network is completed. ...

We typically use four people to measure a network, two at the instrument end and two separate reflector people. All parties should have two-way radio communications ... Once the reflector is sighted, the slope distance and zenith angle are measured. Two lines can be measured before someone moves. Measuring the network follows the same procedure as setting it up; people move from site to site in a leap-frog manner until all the lines are completed. ...

We have established networks on the following Cascade volcanoes: Mount Baker, Mount Rainier, Mount St. Helens, Mount Hood, Newberry, South Sister, Crater Lake, Medicine Lake, Mount Shasta, and Lassen Peak. Similar networks were installed at Augustine, Alaska, in 1988 and in late 1989 to help monitor Mammoth Mountain in eastern California. Repeat measurements of each network, except for those at Medicine Lake and Mammoth Mountain, both of which were first installed in 1989, have established baseline data.

CVO Volcano Monitoring Networks -- Volcanoes and Years Monitored

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