Lava Domes

Lava domes are formed when viscous magma slowly extrudes from a vent and piles up around it. Silicon promotes rigidity in magmas because it has a +4 charge and forms multiple bonds with other elements. Domes are consequently often produced by magmas of more silica-rich dacitic-to-rhyolitic compositions. Domes are steep-sided structures typically a few tens of meters to a few hundred meters high and can form at the summit of a volcano, on its flanks, or as independent volcanic centers. Domes can form during single eruptive episodes or by periodic lava extrusion, such as occurred during the 1980-1986 eruption of Mount St. Helens. Compound lava domes, such as currently forming at Santiaguito at the base of Santa María volcano in Guatemala, are common. Some volcanoes, such as Augustine in Alaska, consist entirely of a complex of overlapping summit lava domes surrounded by fragmental material produced during growth and collapse of the domes. Dome formation is often preceded or accompanied by explosive eruptions, and dome collapse can produce pyroclastic flows and debris avalanches.

Photo by Tom Casadevall, 1986 (U.S. Geological Survey).

Merapi
A blocky lava dome produced during eruptions from 1972 to 1985, lies within the summit crater of Merapi volcano in central Java. A small spine appears on the right in this July 4, 1986 photo, which was taken during a period of inactivity prior to destruction of the dome on October 10, 1986. Merapi's historical eruptions have been characterized by repeated growth and collapse of the summit lava dome, periodically producing pyroclastic flows that have affected populated areas on the volcano's western and southern flanks.Incandescent rockfalls accompanying slow growth of the summit lava dome descend from beneath a cloudcap covering the summit of Merapi volcano in this 1993 nighttime view. Periodic collapse of Merapi's lava dome has produced pyroclastic flows down the western and southern flanks that have devastated populated areas and agricultural lands.

Photo courtesy Shimbara Earthquake and Volcano Observatory, 1991.

Unzen
This closeup view on May 20, 1991, shows the first lava extrusion of the 1990-95 eruption of Unzen volcano in Japan. The dome was extruded in the Jigoku-ato crater, which was formed by an explosion on the first day of the eruption, November 17, 1990. By May 23 the dome reached a height of 44 m and had a diameter of 110 m. It then began spilling over the east crater rim (upper right). Periodic collapse of the oversteepend front of the dome produced pyroclastic flows that traveled progressively farther down the Mizunashi valley.The 1990-95 eruption of Unzen volcano, on the southern Japanese island of Kyushu, produced a lava dome at the summit of Fugen-dake. The rising sun colors the dome, seen here from the NE on February 2, 1995, near the end of the eruption. By this time the dome had grown to a height of 1500 m, about 200 m above the pre-eruption surface. Periodic collapse of the growing lava dome had produced pyroclastic flows that devastated areas on the SE and NE flanks. Thousands of persons living below the dome faced long-term evacuation.

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

Bezymianny

The Novy lava dome at Kamchatka's Bezymianny volcano has been growing since 1956 within a large horseshoe-shaped crater. The 1.8 x 2.5 km crater formed during the catastrophic 1956 eruption when the summit of the volcano collapsed, producing a debris avalanche and lateral blast that swept to the east. This 1980's view from the SW shows the outer flanks of the pre-1956 volcano in the foreground. The lava dome has subsequently grown to the height of the crater rim.

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

Bogosolf
An aerial view shows the 1992 lava dome of Bogoslof Island, the summit of a largely submarine stratovolcano located in the Bering Sea 50 km behind the main Aleutian arc. The 1992 lava dome grew to a height of 100 m in July at the northern tip of Bogoslof Island. The island is about 1.5 x 0.6 km wide, and due to its frequent eruptive activity and energetic wave action, has changed shape dramatically since first mapped in the late 1700's.

Lava dome remnants from three historical eruptions can be seen in this NW-looking aerial view of Bogoslof Island in the Aleutians. The pinnacle on the left is Castle Rock, also referred to as Old Bogoslof, a remnant of a 1796 lava dome. The circular, flat-topped area to its right is a remnant of a 1927 lava dome. The most recent eruption of Bososlof, in 1992, produced the light-colored conical lava dome forming the tip of the island at upper right. Frequent eruptions and vigorous wave erosion have greatly modified the island in historical time.

Photo by Game McGimsey, 1991 (Alaska Volcano Observatory, U.S. Geological Survey).

Redoubt-Alaska

This oblique view from the north shows the final lava dome of the 1989-90 eruption of Alaska's Redoubt Volcano as it appeared approximately one year after the end of the eruption. The dome measures approximately 350-400 m across and represents an estimated 10 million cubic meters of material. Snow is accumulating on the cooling lava blocks although some hydrothermal activity continues to produce intermittent steam plumes. Periodic lava dome growth during the eruption was punctuated by strong explosions that destroyed earlier lava domes.

Photo by Bob Symonds, 1983 (U.S. Geological Survey).

St. Helens
Incandescence is visible in fractures in a growing lava dome in the crater of Mount St. Helens on October 18, 1980. Several earlier lava domes formed after May 18, 1980 had been removed by explosive eruptions. This photo shows the beginning stages of the lava dome that grew incrementally until the end of the eruption in October 1986.

Lava domes are formed by the extrusion of viscous, silica-rich lava that accumulates above the volcanic vent. This steaming lava dome partially fills the crater of Mount St. Helens in April 1983. Dome extrusion often follows explosive eruptions, which decrease the gas content of the remaining magma. Dome growth, however, is commonly accompanied by explosive activity and pyroclastic flows. Lava domes can form within the summit craters of volcanoes or on their flanks. They may build solitary, domical masses, or a complex of overlapping domes.

Photo by Dan Dzurisin, 1982 (U.S. Geological Survey).

Lassen Volc Center

Chaos Crags in the foreground and Lassen Peak in the background are large lava dome complexes in the southern Cascade Range. Chaos Crags consists of a group of five overlapping dacitic lava domes that were erupted a little over 1000 years ago. Lassen Peak was formed about 25,000 years ago, but last erupted during 1914-17.

Photo by Lee Siebert, 1997 (Smithsonian Institution).

Ceboruco

A small lava dome capped by blocky spines was extruded in the principal vent of the 1870-75 eruption of Ceboruco volcano in western México. Fumaroles (not visible in this photo) with temperatures measured at about 100 degrees Centigrade are located around the base of the dome. The plug dome was extruded late in the eruption in a crater formed by explosions that decapitated the main vent of the 1870 eruption and significantly lowered the crater floor.

Photo by Paul Damon, 1974 (University of Arizona).

El Chicon

A forested lava dome, seen here from the east in 1974, filled the crater of México's El Chichón volcano and formed the volcano's high point prior to a major eruption in 1982. The low ridge cutting across the middle of the photo is the rim of the pre-1982 crater. Powerful explosive eruptions in March and April 1982 removed the lava dome and replaced it with a 1-km-wide crater.

Copyrighted photo by Dick Stoiber, 1969 (Dartmouth College).

Santa Maria
Incandescent areas are visible at the top of the growing Santiaguito lava dome in Guatemala. Rockfalls from the dome produce a glowing trail down its northern flanks. The Santiaguito dome began growing in 1922 in a large crater formed on the SW flank of Santa María volcano during a powerful explosive eruption in 1902. Dome growth has been continuous since 1922 and has produced a composite, elongated dome more than 3 km long. This photo of El Brujo, the westernmost vent, was taken on November 12, 1967.

A small blocky lava dome fills the crater of Caliente vent on the Santiaguito lava dome of Guatemala's Santa María volcano on July 18, 1969. This was near the beginning of a period of renewed activity at the Caliente vent, on the eastern side of Santiaguito. Growth of the composite Santiaguito lava dome has been occurring since 1922.

Photo by Lee Siebert, 1978 (Smithsonian Institution).

Pululagua

Cerro Sincholagua (left) and Loma la Marca (right) are the southernmost of a group of lava domes pre-dating the formation of Pululagua's caldera. Seen here from the equator to their south, they are part of a chain of lava domes that were constructed on a roughly N-S line east of the caldera. Cerro Sincholagua forms the highest peak of 3356-m Pululagua volcano.

Photo by Mark Davies, 1997 (Montserrat Volcano Observatory).

Soufriere Hills

Scientists from the Montserrat Volcano Observatory make monitoring measurements in February 1997 as small rockfalls descend the flanks of the summit lava dome. Castle Peak lava dome, constructed during the previous eruption of Soufrière Hills during the 17th century, had collapsed three days prior to the date of this photograph, which was taken from the Tar River Estate house, 2 km NE of the dome. Periodic collapse of the growing lava dome produced pyroclastic flows that in some cases reached to the sea.

Photo by Richard Fiske, 1983 (Smithsonian Institution).

Soufriere St. Vincent

A blocky lava dome, 130 m high and more than 840 m wide filled much of the crater floor of Soufrière St. Vincent volcano during the 1979 eruption. Dome growth began in May, after a series of powerful explosive eruptions April 13-15, and continued until October. Steam continues to rise from the dome in this 1983 photo from the SW crater rim.