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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.

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 a strombolian eruption from White Island in New Zealand in late March 1977. The block, composed of pre-existing wall rock of the crater, bounced, forming 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 Ngauruhoe volcano in New Zealand on February 19, 1975, ejects a dark, ash-laden cloud. Large, meter-scale ejected blocks trailing streamers of ash can be seen in the eruption column. Blocks up to 20 m across were projected hundreds of meters above the vent.

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

Tephra layers from the 1994 eruption are exposed in this pit dug at the eastern end of the city of Rabaul in Papua New Guinea. Individual layers are pyroclastic-fall deposits from discrete explosive eruptions during a period of a little less than three weeks. The light-colored layer near the bottom was produced by pumice ejection from Vulcan cone at the western end of the caldera. Most other layers originated from periodic explosions at Tavurvur volcano, closer to this site. The numbers on the scale mark 10-cm increments.

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

A vigorous eruption column rises above Indonesia's Makian volcano in this July 31, 1988, view from neighboring Moti Island. The six-day eruption began on July 29, producing eruption columns that reached 8-10 km altitude. Pyroclastic flows on the 30th reached the coast of the island, whose 15,000 residents had been evacuated. A flat-topped lava dome was extruded in the summit crater at the conclusion of the eruption.

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

Erosional dissection of an ash deposit at Pinatubo volcano in the Philippines created this intricate pattern. The thin, fine-grained ash deposit at the surface was produced by secondary explosions in still-hot pyroclastic-flow deposits from the devastating eruptions of June 15, 1991. This photo was taken on November 27, 1991, along the Maruanot River valley NW of Pinatubo.

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

An ash-rich eruption column rises above Sakura-jima on September 9, 1985. Almost continuous explosive activity has occurred at Sakura-jima, located at the southern end of the Japanese island of Kyushu, since October 1955. Eruption plumes typically rise 1-3 km above the vent, although occasional larger explosions occur. Ashfall commonly occurs over Sakura-jima island and periodically in Kagoshima City, 8 km to the west. Larger explosions eject ballastic blocks that have damaged structures on the island.

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

This classic outcrop at Oshima volcano, in the Izu Islands, south of Tokyo, shows more than 100 individual layers of pyroclastic-fall deposits. They were produced by eruptions of Oshima volcano at fairly regular intervals over a period of about 10,000 years. The dips of the tephra layers do not result from folding or faulting. The lower layers drape the sides of an old valley. A prominent unconformity in the center of the outcrop is an erosional surface that truncated deposits of the earlier eruptions. The upper layers mantled this uneven surface.

Photo by Richard Fiske, 1961 (Smithsonian Institution).

A plinian eruption column rises above Komaga-take volcano in northern Japan on June 17, the opening day of a major eruption in 1929. The column rose to a maximum height of 13 km and produced thick, pumice-rich pyroclastic-fall deposits around the volcano. Pyroclastic flows from the 1929 eruption, one of the largest in historical time from Komaga-take, also swept down the flanks of the volcano. This photo is from the shores of Onuma lake, south of Komaga-take.

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 pyroclastic-fall 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 5000 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 scoria and ash from pyroclastic-fall deposits produced during the 1975-76 eruption of Kamchatka's Tolbachik volcano. The circular pits were formed by the impact of dense volcanic bombs into the soft pyroclastic-fall deposits. The blocks, one of which can be seen in the closest pit, originated from the cinder cone in the background.

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

A volcanologist from the Institute of Volcanology in Petropavlovsk exults at the sight of one of nature's impressive spectacles--a vigorously erupting lava fountain. The eruption of Tolbachik volcano during 1975-76 was Kamchatka's largest basaltic eruption during the past 10,000 years, and provided scientists with a wealth of data.

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 March 30, 1956 from Bezymianny volcano in Kamchatka. The plinian eruption, seen here from 100 km to the west, produced a 45-km-high ash column that followed a lateral blast and a debris avalanche created when the summit of the volcano collapsed. A lava dome subsequently grew in the newly formed horseshoe-shaped crater. The lava dome has been intermittently active for more than four decades.

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

An ash plume ejected from the summit crater of Kamchatka's Kliuchevskoi volcano on February 9, 1987 is blown to the west. Ashfall from earlier eruptions darkens the southern flank of the volcano. 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).

An aerial view of two symmetrical Aleutian volcanoes shows the effect of volcanic ashfall. Both Cleveland (left) and Carlisle (right) volcanoes are snow-covered, but the flanks of Cleveland volcano in this June 24, 1987, view from the ESE are darkened by deposits of ash from an explosive eruption that began on June 19.

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

Explosive eruptions eject fragmental material that drops from the eruption column, producing pyroclastic-fall deposits. The surface of the glacier in this 1983 photo of Alaska's Veniaminof volcano is darkened by ash. The grain size of the pyroclastic-fall fragments (collectively referred to as "tephra") generally decreases away from the vent as larger and denser fragments fall first. The distribution of pyroclastic-fall deposits is influenced by wind direction. Eruptions much stronger than this one can distribute tephra hundreds of km or more from the volcano.

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

A dramatic, mushroom-shaped eruption column, lit by the rising sun, rises above Alaska's Redoubt volcano on April 21, 1990. Clouds of this shape, which are produced when the upper part of an eruption column attains neutral buoyancy and is spread out above the troposphere-stratosphere boundary, are common during powerful explosive eruptions. This column at Redoubt, however, did not originate from an eruption at the summit crater, but is an ash column that is rising buoyantly above a pyroclastic flow sweeping down the volcano's north flank.

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

The second of 3 large explosive eruptions from Crater Peak, a 2309-m-high flank peak of Mount Spurr volcano, west of Anchorage, Alaska, took place on August 18, 1992. This aerial view from the west shows the base of the vertical eruption column, which reached a height of about 13.5 km. This eruption lasted about 4 1/2 hours and produced ashfall in Anchorage, 125 km to the east, that forced its international airport to close 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. Detailed investigation of the deposits produced by an eruption are necessary to understand its character and magnitude. Three brief explosive eruptions blanketed narrow swaths of the surrounding countryside with ash. In this view, about 15 cm of coarse sand to gravel-sized tephra is exposed in the pit. The surface is dotted with a late shower of cobble-sized bombs from the September 16-17, 1992 eruption.

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

St. Helens
A powerful explosive eruption from Mount St. Helens on July 22, 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 north 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 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 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 spectacular nighttime time-exposure of México's Parícutin volcano in 1948 shows strombolian ejection of incandescent blocks and their trails as they roll down the slopes of the cone. Parícutin is renowned as the volcano that was born 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).

Strombolian eruptions at Pacaya volcano in Guatemala produce a colorful nighttime display. This November 1988 time exposure traces 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 flank. The orange line at the lower right is a lava flow that issued from a fissure on the upper NW flank of MacKenney cone.

Photo by Lee Siebert, 1988 (Smithsonian Institution).

Negro, Cerro
Vigorous strombolian eruptions from Nicaragua's Cerro Negro volcano in 1968 produce an ash-rich column above the vent. Strong incandescent lava fountaining can be seen at the base of the column. Steam rises from fumaroles on the righthand side of the cinder cone. Ash and cinders fall from the eruption column at the left.

Photo by William Melson, 1968 (Smithsonian Institution).

Negro, Cerro
A time exposure captures a nighttime view of a strombolian explosion in November 1968 from Cerro Negro volcano in Nicaragua. The trajectory of individual incandescent volcanic bombs can be seen radiating from the vent. Still-hot bombs continue to glow after landing on the outer flanks of the cinder cone. The 1968 eruption was one of many from Cerro Negro, Central America's youngest volcano.

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 of Chimborazo, Ecuador's highest volcano.

Photo by Lee Siebert, 2006 (Smithsonian Institution).

Caldera collapse at Fernandina volcano in 1968 was preceded by lava effusion on the SE flank and a major explosive eruption on June 11 from a vent inside the caldera. The volcanic cloud of June 11, 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 /hour. At the time of this photograph the diameter of the cloud was 175 km and its altitude reached 20-25 km.

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

An ash-rich vulcanian eruption plume, viewed from the SE, rises above Sabancaya volcano in northern Perú on April 15, 1991. Strong vulcanian explosions were observed at intervals of 20-30 minutes during an April 13-19 visit to the volcano. The explosions lasted about a minute and produced 3-4 km high ash clouds. Explosive activity at Sabancaya began in May 1990 and was continuing in 1995.

Photo by Pierre Vetsch, 1991.

Four days after the start of an eruption from Lonquimay volcano on December 25, 1988, a vigorous ash column rises above a vent on the NE flank. Winds distribute the ash column to the SE. Heavy ashfall from the eruption, which lasted over a year, caused severe economic disruption. This east-looking view shows the ice-filled summit crater of Lonquimay at the lower left. The dark area extending to the left from the eruptive vent, which formed along a fissure system trending NE from the summit, is a lava flow that originated on December 27.

Photo by Jeffrey Post, 1988 (Smithsonian Institution).

Deception Island
Ashfall 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 ashcloud to the NE and deposited 30 cm of ash 2 km 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).