Volcano Monitoring Overview

The continuing eruptions of Mount St. Helens provide an unusual opportunity for scientists to study volcanic activity and to devise and test methods for predicting eruptions. Many successful predictions have been issued for eruptions since June 1980. Eruption prediction and information about volcanic activity at Mount St. Helens provide the basis for hazard warnings of eruptive activity to the public and to local governments.

Volcano monitoring involves a variety of measurements and observations designed to detect changes at the surface of a volcano that reflect increasing pressure and stresses caused by the movement of magma, or molten rock, within or beneath it. An eruption occurs when magma rises from its source or from a storage reservoir and finally reaches the Earth's surface. As it rises, the magma fractures overlying rocks, which causes earthquakes, and parts of the volcano deform as magma approaching the surface makes room for itself.

Monitoring at Mount St. Helens chiefly involves the measurement of surface deformation, the investigation of earthquakes generated beneath the volcano, and the study of changes in gas emission rates accompanying the underground movement of magma. Additional geophysical and geochemical information is gathered through sampling of newly erupted lava and tephra, studies of thermal patterns on the dome, surveys of local electrical and magnetic fields, measurements of changes in the Earth's gravity field, examination of photographs, and measurements of temperature at fumaroles.

Many of the methods used to monitor Mount St. Helens were developed at the U.S. Geological Survey's Hawaiian Volcano Observatory where the activity of Kilauea and Mauna Loa shield volcanoes is monitored. Although the techniques are similar, their application and interpretation have been modified and adapted to Mount St. Helens and other stratovolcanoes of the Cascade Range.

-- Excerpt from: Brantley and Topinka, 1984,
Volcanic Studies at the U. S. Geological Survey's David A. Johnston Cascades Volcano Observatory, Vancouver, Washington: Earthquake Information Bulletin, v.16, n.2, March-April 1984



Taking A Volcano's Pulse

Seismicity -- Earthquakes commonly provide the earliest warning of volcanic unrest, and earthquake swarms immediately precede most volcanic eruptions.

Ground Movements -- Geodetic networks are set up to measure the changing shape of the volcano surface caused by the pressure of magma moving underground. Techniques commonly used include electronic distance measurement using a laser light source (EDM); measurement of tilt, both electronically and by repeated leveling of triangular arrays; and standard leveling surveys to obtain elevation changes. Additionally, very simple and inexpensive techniques, such as measuring crack openings using a steep tape, or noting changes in water level around a crater lake, have proven useful in certain situations. Upward and outward movement of the ground above a magma storage area commonly occurs before eruption. Localized ground displacement on steep volcanoes may indicate slope instabliity precursory to mass failure.

Geophysical Properties -- Changes in electrical conductivity, magnetic field strength, and the force of gravity also trace magma movement. These measurements may respond to magma movement even when no earthquakes or measurable ground deformation occurs.

Gas Geochemistry -- Changes in fumarole gas composition, or in the emission rate of SO2 and other gases, may be related to variation in magma supply rate, change in magma type, or modifications in the pathways of gas escape induced by magma movement.

Hydrologic Regime -- Changes in ground water temperature or level, rates of streamflow and transport of stream sediment, lake levels, and snow and ice accumulation are recorded to evaluate (1) the role of ground water in generating eruptions, (2) the potential hazards when hot, energetic volcanic products interact with snow, ice, and surface streams, and (3) the long-term hazard of infilling of river channels leading to increased flood potential.

-- Excerpt from: Wright and Pierson, 1992,
Living with Volcanoes, The U. S. Geological Survey's Volcano Hazards Program: U. S. Geological Survey Circular 1073



Scientists' Challenge and Opportunity

The eruptive activity of Mount St. Helens has provided a good test for scientists who faced the challenge of obtaining, relaying, and explaining in easily understandable terms the information needed by the Federal, State, and local officials charged with land management and public safety. It should be reemphasized, however, that a quick response at Mount St. Helens was possible only because decades of systematic research before 1980 had contributed to a good understanding of the volcano's eruptive behavior and potential hazards. Additionally, the Mount St. Helens activity also has provided scientists a unique opportunity to learn much about the dynamics of an active composite volcano. The results of studies completed and in progress have improved the understanding of eruptive mechanisms and should refine a forecasting capability, not only for Mount St. Helens, but also for similar volcanoes in the United States and elsewhere.

Mount St. Helens has provided, and will continue to provide, an unprecedented opportunity for scientific research on volcanism. Relatively easy accessibility and a dense network of monitoring instruments have made Mount St. Helens a natural laboratory at which scientists can study processes typical of volcanoes elsewhere along the circum-Pacific "Ring of Fire." As Mount St. Helens is monitored continuously before, during, and after each eruptive episode, and its eruptive products are regularly sampled for chemical and other laboratory analyses, the information being compiled and interpreted yields a better understanding of Mount St. Helens in particular, and other composite volcanoes in general. Moreover, the monitoring techniques now being used at Mount St. Helens and other Cascade volcanoes are the same as, or variations of, those used to monitor the active Hawaiian volcanoes. Thus, in the rather young science of volcanology, a rare opportunity to compare the effectiveness of these techniques on two contrasting kinds of volcanoes--the Hawaiian shield volcanoes, which typically erupt nonexplosively, and the Cascade composite volcanoes, which typically erupt explosively. Scientists have learned that data from all types of monitoring are helpful regardless of the type of volcano. From such comparative studies, they will be able to determine which techniques are the most effective and reliable for monitoring each type of volcano. With such tools and broadened knowledge, scientists may be entering a new epoch in volcanology, in which significant advances in understanding volcanic phenomena will be achieved, accompanied by a sharpened ability to forecast and mitigate volcanic hazards.

-- Excerpt from: Robert I. Tilling, Lyn Topinka, and Donald A. Swanson, 1990,
Eruptions of Mount St. Helens: Past, Present, and Future: USGS Special Interest Publication