Types and Processes Gallery

Lava Dome
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.

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 by Ruska Hadian, 1993 (Volcanological Survey of Indonesia).

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.

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

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.

Photo courtesy Shimbara Earthquake and Volcano Observatory, 1991.

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 Yuri Doubik (Institute of Volcanology, Petropavlovsk).

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 Lee Siebert, 1997 (Smithsonian Institution).

Chichón, El
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.

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

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.

Photo by Charles Pineo, 1967 (Dartmouth College, courtesy of Dick Stoiber).

Santa Maria
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.

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

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 Lee Siebert, 1978 (Smithsonian Institution).

Pululagua is a relatively low, forested volcano immediately north of the equator, 27 km north of Quito. Loma Pondona (left) and the lower Rumiloma (right center) are two of a group of lava domes that partially fill a 3-km-wide summit caldera. They are seen here from the SE caldera rim. The caldera was formed during the latest dated eruption of Pululagua about 2400 years ago. Pululagua produced large explosive eruptions accompanied by pyroclastic flows during the late Pleistocene and Holocene.

Photo by Lee Siebert, 1978 (Smithsonian Institution).

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 Mark Davies, 1997 (Montserrat Volcano Observatory).

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.

Photo by Richard Fiske, 1983 (Smithsonian Institution).