Logo link to homepage

Types and Processes Gallery - Pyroclastic Fall

Pyroclastic Fall
Pyroclastic-fall deposits are produced by the gravitational fall and accumulation of fragmental material ejected by explosive eruptions. Tephra is a generic term referring to fragmental material of all size classes. Explosive eruptions are one of Earth's most dramatic geological processes and have been the subject of the brush and pen for thousands of years. Eruptions can involve new magma (referred to as juvenile material) or the ejection of pre-existing rock and debris from around the vent. They can range from minor, relatively passive gas-and-ash emissions reaching only a hundred meters or so above the vent to powerful magmatic explosions that can eject large volumes of material and produce eruption columns that reach tens of kilometers above the volcano. Smaller eruptions eject material that accumulates near the vent, but large explosions inject ash and gases into Earth's stratosphere, where it can circle the planet and have major impact on global climate. Pyroclastic-fall deposits vary widely in particle size, but typically have a narrow range of particle sizes at a given location and become finer-grained away from the vent. They provide valuable time layers useful in unraveling the eruptive history of a volcano and a volcanic region.

Whakaari/White Island (New Zealand)
This 4-m-wide, water-filled impact crater was formed when the block in background, with volcanologist Ian Nairn providing scale, was ejected during an eruption from White Island in New Zealand in late March 1977. The block, composed of pre-existing crater wall rock, bounced to form the impact crater, and then slid to its present location, 250 m from the source vent.

Photo by Bruce Houghton, 1977 (Wairakei Research Center).

A Vulcanian explosion from the Ngauruhoe cone of Tongariro volcano in New Zealand on 19 February ejects an ash plume and ballistic ejecta. Blocks up to 20 m across reached hundreds of meters above the vent before impacting the flanks.

Photo by Ian Nairn, 1975 (New Zealand Geological Survey).

Tephra layers from the 1994 eruption of Rabaul volcano are exposed in this pit dug at the eastern end of Rabaul town in Papua New Guinea. Individual layers are ashfall deposits from discrete explosive eruptions that occurred over three weeks. The light-colored layer near the bottom was produced by an eruption from Vulcan cone at the western end of the caldera. Most other layers originated from periodic explosions at the Tavurvur cone, closer to this site. The numbers on the scale mark 10-cm increments.

Photo by Andy Lockhart, 1994 (U.S. Geological Survey).

An ash plume rises above Indonesia's Makian volcano in this photo taken on 31 July 1988 from the neighboring Moti Island. The six-day eruption began on 29 July and produced ash plumes that reached 8-10 km altitude. Pyroclastic flows on the 30th reached the coast of the island where 15,000 residents had been evacuated. A lava dome was extruded in the summit crater at the end of the eruption.

Photo by Willem Rohi, 1988 (Volcanological Survey of Indonesia).

The unconsolidated pyroclastic flow and ash deposits emplaced during the June 1991 eruption of Pinatubo were remobilized by rain water as lahars for years after activity ceased. This photo shows erosion patterns in the deposits along the Maraunot River valley NW of Pinatubo on 27 November 1991.

Photo by Chris Newhall, 1991 (U.S. Geological Survey).

An ash plume rises above Sakurajima on 9 September 1985, where frequent explosive activity has occurred since October 1955. Eruption plumes typically rise 1-3 km above the vent, with occasional larger explosions. Ashfall commonly occurs over the island and periodically in Kagoshima City, 8 km to the west. Larger explosions eject ballistic blocks that have damaged structures on the island.

Photo by Tom Pierson, 1985 (U.S. Geological Survey).

This outcrop at Oshima volcano, in the Izu Islands south of Tokyo, shows more than 100 individual tephra layers. They were produced by eruptions of Oshima at fairly regular intervals over a period of about 10,000 years. The lower layers follow the older preexisting topography. A prominent unconformity in the center of the outcrop is an erosional surface that truncated the earlier eruption deposits. The upper layers mantled this uneven surface.

Photo by Richard Fiske, 1961 (Smithsonian Institution).

A Plinian eruption column rises above Komagatake volcano in northern Japan on 17 June, the beginning of a major eruption in 1929 that was one of the largest in historical times. The ash plume rose to a maximum height of 13 km and produced thick, pumice-rich fall deposits around the volcano. The eruption also produced pyroclastic flows that traveled down the flanks. This photo is from the shores of Onuma lake to the south.

Photo courtesy of the Komaga-take Disaster Prevention Council, 1929.

Volcanologists from the Institute of Volcanic Geology and Geochemistry in Petropavlovsk and the New Mexico Institute of Mining and Technology excavate a section through layered tephra deposits from Ilyinsky volcano in southern Kamchatka. Detailed study of the products of individual eruptions are used to determine the timing, frequency, and magnitude of those eruptions. The sequence of tephra layers shown here was deposited by explosive eruptions from Ilyinsky during the last 5,000 years.

Photo by Phil Kyle, New Mexico Institute of Mining and Technology, 1996 (courtesy of Vera Ponomareva, IUGG, Petropavlovsk).

A scientist from the Institute of Volcanology studies tephra produced during the 1975-76 eruption of Kamchatka's Tolbachik volcano. The circular pits were formed by the impact of dense volcanic blocks and bombs. The blocks, one of which can be seen in the closest pit, originated from the scoria cone in the background.

Photo by Oleg Volynets, 1975 (Institute of Volcanology, Petropavlovsk).

A volcanologist from the Institute of Volcanology in Petropavlovsk stands in front the 1975-76 Tolbachik eruption. Incandescent blocks can be seen in this nighttime photograph. This was Kamchatka's largest basaltic eruption during the past 10,000 years.

Photo by Oleg Volynets, 1975 (Institute of Volcanology, Petropavlovsk).

Following a period of explosive eruptions and lava-dome growth beginning in October 1955, a major explosive eruption took place on 30 March 1956 at Bezymianny volcano in Kamchatka. The Plinian eruption, seen here from 100 km W, produced a 40-km-high ash column, pyroclastic flow to a distance of 18 km, lateral blast, and a debris avalanche when the summit of the volcano collapsed.

Photo by I. Erova, 1956 (courtesy of G.S. Gorshkov, published in Green and Short, 1971).

An ash plume erupting from the summit crater of Kamchatka's Kliuchevskoy volcano on 9 February 1987, traveling to the west. Ashfall from earlier eruptions darkens the southern flank of the volcano and several lahar deposits are visible. Explosive eruptions from the summit crater during 1986-1990 were accompanied by lava flows from both summit and flank vents.

Photo by Alexander Belousov, 1987 (Institute of Volcanology, Petropavlovsk).

Both Cleveland (left) and Carlisle (right) volcanoes in the Aleutian islands are snow-covered, but the flanks of Cleveland in this 24 June 1987 photo, seen from the ESE, are darkened by ashfall deposits from an explosive eruption that began on 19 June.

Photo by Harold Wilson, 1987 (Peninsula Airways), courtesy of John Reeder (Alaska Div. Geology Geophysical Surveys).

This weak, pulsating ash plume at Veniaminof, Alaska, on 7 October 1983 is being directed to the east by local winds. Dark ash deposits are visible on the cone and glacier, and a lava flow was traveling down the flank.

Photo by Betsy Yount, 1983 (Alaska Volcano Observatory, U.S. Geological Survey).

An ash plume from the pyroclastic flow descending the N flank of Redoubt volcano on 21 April 1990. The ash plumes produced during the 1989-1990 eruption damaged five commercial jet liners, with an incident on 15 December 1989 causing a Boeing 747-400 aircraft to temporarily lose power of all four engines.

Photo by Joyce Warren, 1990 (courtesy of U.S. Geological Survey).

The second of three large explosive eruptions from Crater Peak, a satellite cone of Mount Spurr, 3.2 km south of the peak, occurred on 18 August 1992. This aerial view from the west shows the base of the vertical eruption plume that reached an altitude of about 13.5 km. This eruption lasted about 4.5 hours and resulted in ashfall in Anchorage, 125 km E, that resulted in closure of the international airport for 20 hours.

Photo by Game McGimsey, 1992 (Alaska Volcano Observatory, U.S. Geological Survey).

A scientist from the Alaska Volcano Observatory studies tephra from the 1992 eruptions of the Crater Peak vent of Mount Spurr volcano. Three brief explosive eruptions blanketed narrow swaths of the surrounding area with ash. Detailed investigations of deposits are necessary to understand eruption characteristics and magnitude. In this view, about 15 cm of coarse ash and lapilli is exposed in the pit and blocks from the 16-17 September 1992 eruption are scattered across the surface.

Photo by Game McGimsey, 1992 (Alaska Volcano Observatory, U.S. Geological Survey).

St. Helens
An explosive eruption from Mount St. Helens on 22 July 1980, seen here from the north, produced a Plinian eruption column that rose 16 km above the volcano. At the base of the column ash can be seen rising above a pyroclastic flow traveling down the N flank towards Spirit Lake. This was the third of three explosive pulses on July 22 and lasted more than two hours.

Photo by Jim Vallance, 1980 (U.S. Geological Survey).

Mono-Inyo Craters
The Mono-Inyo craters produced explosive eruptions and effusive lava flows. The pumice layers above the bottom of the pen originated from the South Deadman vent of Inyo Craters about 600 years ago. Interbedded finer layers record brief pauses during the course of the eruption.

Photo by Larry Mastin, 1986 (U.S. Geological Survey).

[Not a Volcano] Inyo Craters (MERGED)
The Mono-Inyo craters produced explosive eruptions and effusive lava flows. The pumice layers above the bottom of the pen originated from the South Deadman vent of Inyo Craters about 600 years ago. Interbedded finer layers record brief pauses during the course of the eruption.

Photo by Larry Mastin, 1986 (U.S. Geological Survey).

This nighttime time-exposure of México's Parícutin volcano in 1948 shows a Strombolian eruption ejecting incandescent blocks that then rolled down the slopes of the cone. Parícutin is known as the volcano that erupted in a cornfield in 1943. It grew to a height of more than 150 m within the first week of its appearance and remained active until 1952.

Photo by Carl Fries, 1948 (U.S. Geological Survey).

A Strombolian eruption at Pacaya volcano in Guatemala, November 1988. This time exposure shows the incandescent parabolic arcs of individual volcanic bombs explosively ejected from the vent. Larger bombs remain incandescent after they hit the surface of the cone and roll down its flanks. The orange line at the lower right is a lava flow extruding from a fissure on the upper NW flank of the MacKenney cone.

Photo by Lee Siebert, 1988 (Smithsonian Institution).

Cerro Negro
An eruption from Nicaragua's Cerro Negro volcano in 1968 produces an ash plume above the vent. Incandescent ejecta is visible at the base of the column. Gas and steam rise from fumaroles on the righthand side of the scoria cone. Ash and bombs fall from the eruption column at the left.

Photo by William Melson, 1968 (Smithsonian Institution).

Cerro Negro
A long-exposure nighttime view of a Strombolian explosion at Cerro Negro volcano in Nicaragua in November 1968. The trajectory of individual incandescent volcanic bombs can be seen radiating from the vent. Hot, incandescent bombs are visible on the outer flanks of the scoria cone.

Photo by Robert Citron, 1968 (Smithsonian Institution).

An erosional unconformity cutting diagonally across the center of the photo due to a glacial advance about 20,000-18,000 years ago separates two sequences of late-Pleistocene tephra layers from Ecuador's Chimborazo volcano. A less prominent unconformity below the light-colored tephra layer at the top of the sequence marks a 16,000-14,000 year old glacial advance. This ~12-m-thick exposure lies on the SW flank.

Photo by Lee Siebert, 2006 (Smithsonian Institution).

Caldera collapse in 1968 at the basaltic shield volcano, Fernandina, was preceded by lava effusion on the SE flank and a major explosive eruption on 11 June. The ash plume, seen here from Academy Bay on Santa Cruz Island within minutes of the explosion, is backlit by the late afternoon sun and was spreading at an estimated lateral speed of 80 km per hour. At the time of this photograph the ash plume was 175 km across with an altitude of 20-25 km.

Photo by J. Harte, 1968 (published in Simkin and Howard, 1970).

A Vulcanian ash plume, viewed from the SE, rises above Sabancaya volcano in northern Perú on 15 April 1991. Strong explosions were observed at intervals of 20-30 minutes during a visit to the volcano on 13-19 April. The explosions lasted about a minute and produced 3-4 km high ash plumes.

Photo by Pierre Vetsch, 1991.

Four days into an eruption of Lonquimay volcano that began on 25 December 1988 an ash plume rises above a vent on the NE flank. Winds distribute the ash to the SE. Heavy ashfall lasted over a year, causing severe economic disruption. This east-looking view shows the ice-filled summit crater of Lonquimay at the bottom right.

Photo by Jeffrey Post, 1988 (Smithsonian Institution).

Deception Island
An eruption darkens the sky above Antarctica's Deception Island in December 1967. Falling ash can be seen trailing from the margins of the eruption cloud. Winds distributed the ash plume to the NE and deposited 30 cm of ash over a 2 km swath across Port Foster caldera bay onto the Chilean Antarctic research station, where this photo was taken.

Photo by Bernardo Blass, 1967 (published in González-Ferrán, 1995).