Fuego

Scientists use a COSPEC (Correlation Spectraphotometer) instrument to measure the sulfur dioxide (SO2) content of a volcanic plume from Fuego volcano in Guatemala. Measurements of the concentrations of SO2 and other gases in volcanic plumes are useful tools for eruption monitoring. This photo was taken from Finca Capetillo NE of Fuego during its October 1974 eruption.

Hood

Scientists from the U.S. Geological Survey take gas samples at Devils Kitchen near the Crater Rock lava dome on the upper SW flank of Mount Hood. The Crater Rock area is the largest fumarole field in the Oregon Cascades, producing vigorous gas emission and extensive hydrothermal alteration of rock masses over broad areas.

Kilauea

A Hawaiian Volcano Observatory team uses a drilling rig to extract drill core from the cooling lava lake in Kilauea Iki crater. At the time of this 1968 project, nearly a decade after a lava lake filled Kilauea Iki during the 1959 eruption, the crust had solidified to a depth of about 30 m. The drill core reached down to 60 m without reaching the bottom of the still partially molten lava lake. This project, the first to use a drill rig to sample a lava lake, allowed study of vertical variations in chemistry, mineralogy, and temperature within a cooling lava lake.

Kilauea

Among the many monitoring techniques used by Hawaiian Volcano Observatory staff at Kilauea volcano is precision leveling. Millimeter-scale variations in the elevation of two fixed points can be detected with an optical-level instrument by measuring the precise difference in elevation on leveling rods placed above them. Slight inflation of a volcanic edifice commonly occurs prior to eruptions. Measurements such as these in 1968, with the Puu O'o cinder cone in the background, are one of several techniques used to help forecast eruptive events.

Kliuchevskoi

A volcanologist from the Institute of Volcanology in Petropavlovsk, shielded from the intense heat in a reflective suit, extracts a glowing sample of lava from a flank vent of Kliuchevskoi volcano in 1983. Geochemical analysis of lava samples is used to characterize the eruption and understand the magmatic history of the volcano. Eruptions of flank and summit lava flows are common at this basaltic stratovolcano.

Mauna Loa

Hawaiian Volcano Observatory scientists conduct an electronic-distance measurement (EDM) survey on the rim of Kilauea caldera in 1987, with snow-capped Mauna Loa in the background. The procedure uses a laser beam, which is reflected back to the EDM instrument from a distant cluster of reflectors. A precise determination of the horizontal distance between the two points is made by a small computer in the EDM instrument. These measurements allow scientists to detect inflation of the volcano as magma rises to the surface prior to an eruption.

Pinatubo

The seismogram for June 15, 1991, shows the heavy seismicity accompanying the catastrophic eruption of Mount Pinatubo in the Philippines. This seismic record shows earthquakes over a two-hour period beginning at 0508 hrs. The arrow points to the earthquake accompanying a major explosion at 0555 hrs, which was preceded by many large long-period earthquakes. At about 0640 hrs, continuous overlapping long-period earthquakes or tremor began, and much of the following record was saturated so that individual earthquakes could not be distinguished.

Redoubt

An Alaska Volcano Observatory geologist uses a laser-surveying instrument to measure distances to targets installed on the flanks of Redoubt Volcano. Minute changes in distances to the targets can reflect ground deformation that may indicate magma movement. Steam rises above a lava dome in the crater of Redoubt in this photo taken on May 5, 1990, near the end of an eruption that had begun the previous December.

Redoubt

An Alaska Volcano Observatory geologist sets up GPS (Global Positioning System) instrumentation on the north flank of Redoubt Volcano. The GPS receiver calculates an extremely accurate location through satellite-based triangulation. This helps pinpoint locations for electronic distance measurements that detect deformation of the volcano related to eruptive activity. The Drift River valley extending away from the volcano to the NE was covered with pyroclastic-flow and mudflow deposits from the 1989-90 eruption.

Ruapehu

New Zealand Geological Survey volcanologist Brad Scott conducts theodolite measurements at the Crater Lake vent in 1988 at the summit of Ruapehu volcano. Measurements of the lake height, temperature and chemistry are made routinely, and along with seismic instrumentation, are used to help forecast future activity of the volcano. Intermittent steam explosions from beneath the lake have produced lahars, which have damaged ski facilities on the upper flanks and structures in river valleys below the volcano.

South Sister

Electronic Distance Measurements by the U.S. Geological Survey at South Sister volcano, with Middle Sister to the left, are conducted routinely to monitor these Cascades volcanoes for potential eruptive activity. By measuring the distance between two fixed points, these instruments can detect minor swelling of the volcanic edifice that often occurs prior to eruptions.

Spurr

Seismometers such as this one installed near Mount Spurr volcano (on skyline in background) provide the Alaska Volcano Observatory with a continuous, radio-telemetered record of volcanic earthquakes. These data are used to monitor the state of activity at the volcano and are essential for issuing timely warnings of eruptions. Ash from its 1992 eruption darkens the slopes of Crater Peak, in the center below the sharp-peaked summit of Mount Spurr, in this 1993 photo from the south.

St. Helens

U.S. Geological Survey scientists make precision leveling measurements in the crater of Mount St. Helens in February 1982 with the steaming lava dome in the background. Repeated measurement of deformation in the crater was one of several methods used by scientists to successfully predict future eruptions of Mount St. Helens.