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Types and Processes Gallery - Geothermal Activity

Geothermal Activity
Ascending hot magmatic fluids mix with near-surface groundwater to form active geothermal systems with dramatic surface features such as hot springs, solfataras, fumaroles, mudpots, geysers, and hot acid lakes. These hydrothermal features are common at stratovolcanoes and young calderas and can persist for hundreds of thousands of years. Active hydrothermal systems often precipitate colorful deposits of native sulfur and other minerals. Spectacular geysers are popular attractions in places such as Yellowstone and at Icelandic volcanoes. Reservoirs of steam or hot water in geothermal fields have been tapped for electrical power in many volcanic regions.

Vigorous steam plumes rise from vents near the summit of Ontake in central Honshu, Japan, on 9 November 1979. The first historical eruption began on 28 October and produced a 1.5-km-high eruption plume with ashfall to the NE. Intense gas-and-steam emissions with minor ash continued for several months.

Photo by T. Kobayashi, 1979 (courtesy Tokiko Tiba, National Science Museum).

Raususan [Mendeleev]
Brightly-colored deposits of elemental sulfur surround fumarolic vents on the NW side of the central cone of Mendeleev volcano, in the southern Kuril Islands. These fumaroles are located within several craters where the central cone meets the inner caldera wall. Hot springs occur on the NE flank and along the NE coast, where the Goriachi-Pliazh geothermal field is located.

Photo by Yuri Doubik (Institute of Volcanology, Petropavlovsk).

The Dvoinoi (Sugar) geyser is one of nearly 30 found in the "Valley of Geysers," a major geothermal area along a 4-km-long valley near the eastern margin of the Geysernaya caldera at Kamchatka's Uzon volcano. High heat flux near the eastern ring faults of the caldera produces active geysers, boiling hot springs, and mud pools.

Photo by Sakharnii (courtesy of Oleg Volynets, Institute of Volcanology, Petropavlovsk).

A large steam column rises from a fumarole at about 1,600 m elevation on the N flank of Chiginagak volcano on the Alaska Peninsula in May 1994. Strong steam emission is a common occurrence at this volcano and can be mistaken for eruptive activity.

Photo by Chris Nye, 1994 (Alaska Division of Geological and Geophysical Surveys).

A small mudpot vent in Pocket Basin at the north end of Yellowstone's Lower Geyser Basin produced this intriguing feature that mimics a spatter cone that issued a lava flow. Mudpots form in areas of intense, clay-rich hydrothermal alteration where the thermal system is dominated by gases.

Photo by Dan Dzurisin, 1983 (U.S. Geological Survey).

Riverside Geyser in the Upper Geyser Basin is the most regular of Yellowstone's geysers. About every six hours it ejects a 25-m-high inclined jet from a small vent hole on the east bank of the Firehole River 2 km downstream from Old Faithful.

Photo by Lee Siebert, 1968 (Smithsonian Institution).

Santa Ana
Thermal activity at the surface of a volcano is evidence of volcanic heat below. The fumarolic activity seen here produces vigorous gas-and-steam plumes along the sulfur-coated wall of the summit crater at El Salvador's Santa Ana volcano. Thermal activity is common during non-eruptive periods at many volcanoes, and may persist for many thousands of years. The interaction of high-temperature volcanic fluids and gases with groundwater in hydrothermal fields can produce geysers, hot springs, and mud pools.

Photo by Kristal Dorion, 1994 (U.S. Geological Survey).

Mud pots boil in this 1978 view of the San Jacinto thermal area at El Salvador's Telica volcanic complex. The alignment of fumaroles and mud pots suggests an underlying fault running NNE. Magmatic steam and gases have been emitted from the thermal area for many years at a fairly constant rate.

Photo by Jaime Incer, 1978.

Vigorous mud eruptions occur at Las Hornillos thermal area on the W flank of Costa Rica's Miravalles volcano. A geothermal project in the 15 x 20 km Guayabo caldera (containing Miravalles) provides a major component of the electrical power needs of Costa Rica.

Photo by William Melson, 1988 (Smithsonian Institution)