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Types and Processes Gallery - Volcanic Landslides

Volcanic Landslides
Volcanoes appear to be permanent fixtures on the landscape, but in fact are inherently unstable structures composed of both strong (thick lava flows) and weak (fragmental and hydrothermally altered) materials. Large-scale collapse of volcanic edifices, first witnessed and documented at the start of the 1980 Mount St. Helens eruption, is now known to be a common volcanic process. Large volcanic landslides can occur with volumes exceeding a cubic kilometer at continental volcanoes and several orders of magnitude larger at oceanic shield volcanoes. These collapses can produce extremely mobile debris avalanches that can travel at high velocities in some cases for tens of kilometers beyond the base of a volcano. This process, once thought to be extremely rare, has been documented at hundreds of volcanoes worldwide. Repeated episodes of growth and collapse have occurred at many volcanoes, and large-volume volcanic landslides have been found to be the most common catastrophic destructive process at volcanoes.

Taranaki
Grass-covered conical hills dot the plains around Mount Taranaki on New Zealand's North Island. Small hills such as these, often located in lowland areas well beyond the flanks of a volcano, were once thought to be scoria cones or small secondary vents produced by explosions when a lava flow passed over a body of water. They are now recognized to be hummocks of massive debris avalanches produced by volcanic landslides or flank collapse. Debris avalanche deposits originating from repetitive collapse surround the volcano to distances of about 40 km.

Photo by Don Swanson, 1984 (U.S. Geological Survey).


Raung
An outcrop in a quarry showing the internal structure of a debris avalanche hummock, with bedded layers of tephra on the right and a segment of a lava flow on the left. Both the massive lava and the unconsolidated tephra layers were transported relatively intact for about 30 km within a debris avalanche from Raung volcano in eastern Java. The preservation of original stratigraphy from within the volcano is a common feature of debris avalanche deposits.

Photo by Lee Siebert, 1995 (Smithsonian Institution).


Iriga
Collapses at the summit or flanks of volcanoes during major volcanic landslides can create large horseshoe-shaped craters that open in the direction of the landslide, like this 2.1 x 3.5 km crater at Iriga in the Philippines. It was produced by a massive landslide during the Holocene. The resulting debris avalanche traveled more than 10 km to the SE and flowed into Lake Buhi at the upper right. This view is from the south, with the summit to the left.

Photo by Chris Newhall (U.S. Geological Survey).


Unzendake
This 18th century watercolor map of Unzen volcano on the Shimabara Peninsula shows the extent of the catastrophic landslide from Mayuyama (lower center) in 1792 that swept into the Ariake Sea at the bottom of the map. The irregular orange-colored area along the coast delineates the extent of runup of the tsunami that was created when the avalanche entered the sea. The tsunami swept a 77-km length of the peninsula and caused nearly 15,000 fatalities here and along the coastlines.

Map from Shimabara City Honko temple (published in Miyachi et al., 1987).


Hakusan
This outcrop along the Oshirakawa river east of Hakusan volcano in Japan shows textures that are common at debris avalanche deposits. Large fractured clasts are carried in a finer matrix that shows variations in color. This results from the transport of small discrete segments of the volcano for long distances without being completely broken up and mixed together. This debris avalanche was produced by a volcanic landslide from the summit and E flank of Hakusan about 4,200 years ago.

Photo by S. Shimuzu (courtesy of Toshio Higashino, Haku-san Nature Conservation Center).


Bezymianny
The small hummocks (hills) in this photo formed during a 1956 eruption of Bezymianny, an eruption that resembled the 1980 eruption of Mount St. Helens. The hummocky terrain is reminiscent of the debris avalanche deposit filling the Toutle River at St. Helens, and likewise was produced by a massive volcanic landslide when Bezymianny collapsed on 30 March 1956. The hummocks consist of material from the edifice that traveled out to 18 km E.

Photo by Dan Miller (U.S. Geological Survey).


Augustine
These small hills in the foreground of Alaska's Augustine volcano show a morphology common to debris avalanche deposits. The hummocks consist of relatively intact segments of the volcanic edifice that were transported long distances without disaggregating. This debris avalanche traveled roughly 11 km from the summit about 450 years ago.

Photo by Lee Siebert, 1987 (Smithsonian Institution).


Augustine
This wave-cut section exposes the interior of the Burr Point debris-avalanche deposit from the 1883 eruption of Augustine volcano. The different colors resulting from the transport of discrete segments of the volcano that are not thoroughly mixed are a characteristic appearance of debris avalanche deposits. The scale bar is 2 m high.

Photo by Lee Siebert, 1986 (Smithsonian Institution).


St. Helens
The hill in the background is one of many hummocks forming the surface of the massive debris avalanche deposit produced by collapse of the summit of Mount St. Helens on 18 May 1980. The different colored rocks represent portions of the volcano that were transported relatively intact over great distances. The avalanche traveled 25 km, filling the upper North Fork Toutle River to a maximum depth of nearly 200 m. The lighter-colored rocks in the foreground are pyroclastic flow deposits.

Photo by Lee Siebert, 1982 (Smithsonian Institution).


St. Helens
The steep headwall of the scarp created by collapse of St. Helens on 18 May 1980 towers 550 m above the crater floor. The white areas on the crater rim are glaciers that were truncated by the collapse. Steam rises at the right from the new crater in this August 1980 view. Mount Hood is visible in the distance to the south across the Columbia River.

Photo by Lee Siebert, 1980 (Smithsonian Institution).


St. Helens
The 2 x 3.5 km horseshoe-shaped crater at Mount St. Helens is typical of scarps formed by massive landslides. On 18 May 1980 the upper 400 m of the summit was removed, leaving the crater open to the N. This event was the world's largest landslide during historical time. The missing portion of the volcano transitioned into the debris avalanche deposits filling the North Fork Toutle River below the volcano.

Photo by Terry Leighley, 1981 (U.S. Geological Survey).


Shasta
The foreground hills are part of the Shasta Valley debris avalanche deposit produced by one of the largest known Quaternary volcanic landslides. Roughly 46 km3 of an ancestral Mount Shasta collapsed about 350,000 year ago, producing a massive debris avalanche that swept some 50 km to the north, filling the broad Shasta Valley with hummocky debris.

Photo by Dave Wieprecht, 1995 (U.S. Geological Survey).


Shasta
The hilly topography in the foreground is part of the massive debris avalanche deposit produced by collapse of Mount Shasta (center horizon). The roughly 46 km3, rapidly-moving debris avalanche swept some 50 km N. The hummocky area represents relatively intact segments of the volcano that were carried within a more fluidized, mixed bulk of the avalanche. Individual hummocks range up to a few hundred meters in height and roughly 1 km in length.

Photo by Harry Glicken, 1982 (U.S. Geological Survey).


Colima
Collapse of México's Colima volcanic complex during the late Pleistocene produced a major debris avalanche and debris flow that traveled 120 km to the Pacific Ocean. The quarried hummock in the foreground and the two brown hills in the middle distance are composed of material transported more than 100 km from Colima volcano (seen in the far distance above the left-hand hummock) and incorporated from valley floors during transport.

Photo by Lee Siebert, 1997 (Smithsonian Institution).


Colima
Textures associated with volcanic landslides are preserved in this quarry wall more than 100 km from the source of this major avalanche from México's Colima volcano. Large fractured blocks appear at the top of the exposure, and a color mottling is produced by adjacent segments of the volcano or valley floor material incorporated during transport. A 2-m-high ruler provides scale.

Photo by Lee Siebert, 1997 (Smithsonian Institution).


Acatenango
The hummocky surface in the foreground in front of the Fuego and Acatenango volcanoes in Guatemala is a massive debris-avalanche deposit in Escuintla that was produced by partial collapse of the volcanic complex sometime during the late Pleistocene to early Holocene. This is the largest known debris avalanche in Guatemala; it has an estimated volume of about 15 km3 and traveled about 50 km. For the last 30 km, the avalanche traveled over flat slopes of less than 1 degree, illustrating the extremely high mobility of volcanic debris avalanches.

Photo by Jim Vallance, 1989 (Michigan Technological University).


Fuego
The hummocky surface in the foreground in front of the Fuego and Acatenango volcanoes in Guatemala is a massive debris-avalanche deposit in Escuintla that was produced by partial collapse of the volcanic complex sometime during the late Pleistocene to early Holocene. This is the largest known debris avalanche in Guatemala; it has an estimated volume of about 15 km3 and traveled about 50 km. For the last 30 km, the avalanche traveled over flat slopes of less than 1 degree, illustrating the extremely high mobility of volcanic debris avalanches.

Photo by Jim Vallance, 1989 (Michigan Technological University).


Fuego
This roadcut provides a spectacular section through a debris avalanche deposit hummock of the Fuego-Acatenango complex in Guatemala. The pronounced color mottling is a common texture of debris-avalanche deposits and distinguishes them from deposits produced by other volcanic processes such as mudflows or pyroclastic flows. This texture results from the transport of coherent chunks of the volcano over long distances with only partial disaggregation. Individual lava flow blocks and pyroclastic units can be traced across small offsetting faults.

Photo by Lee Siebert, 1988 (Smithsonian Institution).


Pacaya
MacKenney cone, the historically active vent of Pacaya volcano in Guatemala, was constructed within a horseshoe-shaped crater produced by collapse of the summit of an ancestral volcano about 1,100 years ago. The SW crater rim forms the steep-sided scarp at the right. The blocky hill in the foreground is a hummock from the debris avalanche produced by the collapse. The avalanche extended for 25 km.

Photo by Lee Siebert, 1988 (Smithsonian Institution).


Mombacho
Las Isletas, a group of islands that were created by a large Holocene debris avalanche from Mombacho that swept into Lake Nicaragua. The avalanche traveled at least 12 km. The hummocky debris created an arcuate peninsula that extends into the lake as well as hundreds of small islands. This morphology is common where debris avalanches enter shallow bodies of water.

Photo by Jaime Incer, 1972.