Monitoring:  | Gas | Ground Deformation | Hydrologic | Remote Sensing | Seismicity |

Illustration by B. Myers
| hydrology | ground deformation | seismicity | gas | remote sensing |

Monitoring Strategy

Volcano monitoring methods are designed to detect and measure changes in the state of a volcano caused by magma movement beneath the volcano. Rising magma typically will (1) trigger swarms of earthquakes and other types of seismic events; (2) cause swelling or subsidence of a volcano's summit or flanks; and (3) lead to the release of volcanic gases from the ground and vents. By monitoring these phenomena, scientists are sometimes able to anticipate an eruption days to weeks ahead of time and to detect remotely the occurrence of certain volcanic events like explosive eruptions and lahars (see lahar detection system).

We work as close as possible to the active vent(s) of a volcano so that we can observe and measure changes that often occur when magma rises toward the surface. When a volcano shows signs of unrest or is erupting, we often make several visits a week to conduct various surveys and to install and maintain instruments that enable us to track its activity 24 hours a day. If an eruption causes significant changes to nearby watersheds, for example by killing vegetation and depositing fresh volcanic debris over broad areas, we work extensively in river valleys to keep track of erosion and sedimentation downstream from the volcano. We also collaborate with scientists specializing in satellite remote-sensing techniques to provide real-time warning of hazardous events (for example, eruption clouds).

Working directly on the rugged slopes of a volcano to measure and observe changes in its activity and to install and maintain a network of volcano-monitoring instruments are crucial for determining when a volcano might erupt. When a volcano begins to show new or unusual signs of activity, our monitoring data help us answer four critical questions for reducing the risk from volcanoes:

• Does the current unrest involve the movement of magma?
• If yes, when is an eruption most likely to occur, if at all?
• During an eruption, what real-time warnings are needed to prevent loss of life and property damage?
• When is the eruption really over?

The monitoring data we collect also helps address a variety of other important questions, including:

• What is the nature of a volcano's magma-reservoir system?
• What is the cause of specific volcano-seismic events?
• How do volcanic ash clouds disperse downwind of an erupting volcano?
• How susceptible to massive slope failures (landslides) are volcanoes?

Monitoring at U.S. Volcano Observatories

• The Alaska Volcano Observatory (AVO) is a cooperative effort of the USGS Volcano Hazards Program, University of Alaska Fairbanks Geophysical Institute (UAFGI), and State of Alaska Division of Geological and Geophysical Surveys (ADGGS). AVO monitors about half of the 42 historically active volcanoes of Alaska, which not only threaten local populations but also aircraft and travelers using major air routes across the North Pacific. AVO also disseminates warnings and information on dangerous eruptions and ash clouds from Kamchatkan volcanoes in the Russian Far East.
• The Hawaiian Volcano Observatory (HVO) conducts an intensive program of seismic, gas, ground-deformation, and observational monitoring of the frequently active volcanoes of the Island of Hawaii.
• The Cascades Volcano Observatory (CVO) in Vancouver, Washington, monitors and assesses hazards from the volcanoes of the Cascade Range of Washington, Oregon, and California. Seismic monitoring is shared with the USGS center in Menlo Park, California, (for northern California) and the Geophysics Program of the University of Washington in Seattle (for Washington and Oregon). CVO also is home to the Volcano Disaster Assistance Program.
• The Long Valley Observatory (LVO) in Menlo Park, California, conducts seismic, deformation, hydrologic, and geochemical monitoring and research to interpret the recent unrest and assess the hazard from this large and potentially dangerous caldera system.
• The Yellowstone Volcano Observatory is the most recent U.S. volcano observatory. The goal of the observatory is to improve the existing collaborative study and monitoring of active geologic processes and hazards of the Yellowstone Plateau volcanic field and its caldera. The Observatory is supported by the U.S. Geological Survey, University of Utah, and the Yellowstone National Park. The park was the world's first National Park. It contains the largest and most diverse collection of natural thermal features in the world.

When is the volcano going to erupt?

Imagine working at a volcano observatory and one of the volcanoes you've been monitoring is showing very obvious signs of activity. Is the volcano going to erupt? Can you tell when? What kind of warning should you issue? When is the volcano going to erupt? presents case histories of recent eruptions to show the kind of warnings issued by the U.S. Geological Survey and the data upon which the warnings were based.