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Types and Processes Gallery - Shield Volcanoes

Shield Volcanoes
Shield volcanoes contrast with stratovolcanoes both in origin and morphology. Their name derives from their low-angle profile, which resembles the personal shields carried by warriors. They are formed primarily by the successive accumulation of fluid lava flows, which descend from summit or flank fissure systems. Although shield volcanoes are not as visually dramatic as stratovolcanoes, they are often much larger features. Oceanic shield volcanoes such as those in the Hawaiian Islands can rise as much as 8000 m above the surrounding sea floor and 12,000 m above their actual bases, which have sagged due to the immense mass of the volcano. Their volumes can exceed that of stratovolcanoes by several orders of magnitude. Most shield volcanoes are formed of fluid basaltic lava flows. Shield volcanoes can vary widely in size, and much smaller Icelandic-type shield volcanoes are common in many volcanic regions. These volcanoes can form during single long-term effusive eruptions. A less common type of shield volcano is a pyroclastic shield, whose broad low-angle slopes are formed by accumulation of fragmental material from powerful explosive eruptions.

Auckland Volcanic Field
Rangitoto is the youngest feature of New Zealand's Auckland Volcanic Field and forms a 5.5-km-wide island. The volcano, seen here from the NW, erupted about 600 years ago and is capped by a scoria cone containing a deep crater. The 140 km2 Auckland Volcanic Field contains more than 50 maars, tuff rings, and scoria cones. Of the 19 eruptions known to have occurred during the past 20,000 years, only Rangitoto has erupted during the Holocene.

Photo by Jim Cole (University of Canterbury).


Wrangell
Alaska's Mount Wrangell is one of the most voluminous shield volcanoes in the world and is more than three times the volume of Rainier. It has a diameter of 30 km at 2,000 m elevation and a volume of about 900 km3. Eruption of unusually-low viscosity andesitic lavas at high eruption rates produced long lava flows that contributed to its low-angle morphology. The small snow-covered peak on the left is Mount Zanetti, a flank vent with about the same volume as St. Helens. Wrangell is seen here from Glennallen, 80 km to the west.

Photo by Chris Nye (Alaska Division of Geological and Geophysical Surveys).


Belknap
Little Belknap (upper left) is an example of a small shield volcano in a continental margin setting. Little Belknap was constructed on the E flank of Belknap volcano and erupted lava flows over the McKenzie Pass area of the central Oregon Cascades about 2,900 years ago. Collapsed lava tubes that fed the flows diverge radially away from the summit. The summit of Mount Washington appears above the horizon to the right.

Photo by Lee Siebert, 1995 (Smithsonian Institution).


Newberry
Newberry shield volcano covers an area of about 1,600 km2 about 60 km E of the crest of the Cascade Range in central Oregon. The low-angle shield volcano covers an area of 60 km in a N-S direction and 30 km E-W. More than 400 scoria cones dot the flanks of the volcano, including Lava Butte at the left center of this photo, one of many cones formed around 6,100 years ago along the NW rift zone.

Photo by Lee Siebert, 1995 (Smithsonian Institution).


Medicine Lake
The broad 50-km-wide Medicine Lake volcano in the southern Cascade Range, seen here from the NE, is an example of a shield volcano in a continental margin setting. Its chemistry is more diverse than Hawaiian shield volcanoes and it has produced both basaltic lava flows, rhyolitic tephra, and obsidian flows during the Holocene. Eruptions have occurred during the past 6,000 years from vents within a 7 x 11 km summit caldera and from other vents on its flanks.

Photo by Lee Siebert, 1998 (Smithsonian Institution).


Mauna Loa
The steep walls of Lua Poholo pit crater, immediately NE of Mokuʻāweoweo caldera, expose a small portion of the accumulation of thin, overlapping lava flows that form Mauna Loa. This view from the NE shows the caldera rim to the upper right. Lava flows from recent eruptions fill crater floor, including the most recent 1984 eruption.

Photo by Paul Kimberly, 1994 (Smithsonian Institution).


Mauna Loa
Hawaii's two largest shield volcanoes are Mauna Loa (in the background to the S) and Mauna Kea. Mauna Loa has the classic low-angle profile of a shield volcano constructed by repetitive eruptions of thin, overlapping lava flows. Mauna Kea’s profile has been modified by late-stage explosive eruptions that constructed a series of cones at the summit.

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


Mauna Loa
Mauna Kea (left) and Mauna Loa (right), both over 4,000 m above sea level, are also the world's largest active volcanoes, rising nearly 9 km above the sea floor around the island of Hawai’i. This aerial view from the NW shows the contrasting morphologies with the smooth profile of Mauna Loa, and Mauna Kea that was modified by the late-stage products of explosive eruptions.

Photo by Lee Siebert, 1987 (Smithsonian Institution).


Mauna Loa
Mauna Kea is seen here from the S at the broad Humu'ulu Saddle between Mauna Kea and Mauna Loa. The lava flow in the foreground was emplaced during an 1843 eruption that originated on the NE rift zone of Mauna Loa. The flow traveled directly N to the Mauna Kea saddle, where it was deflected to the W. The irregular profile of the summit region of Mauna Kea is due to scoria cones and pyroclastic ejecta that are not present at Mauna Loa.

Photo by Paul Kimberly, 1994 (Smithsonian Institution).


Mauna Kea
Hawaii's two largest shield volcanoes are Mauna Loa (in the background to the S) and Mauna Kea. Mauna Loa has the classic low-angle profile of a shield volcano constructed by repetitive eruptions of thin, overlapping lava flows. Mauna Kea’s profile has been modified by late-stage explosive eruptions that constructed a series of cones at the summit.

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


Mauna Kea
Mauna Kea (left) and Mauna Loa (right), both over 4,000 m above sea level, are also the world's largest active volcanoes, rising nearly 9 km above the sea floor around the island of Hawai’i. This aerial view from the NW shows the contrasting morphologies with the smooth profile of Mauna Loa, and Mauna Kea that was modified by the late-stage products of explosive eruptions.

Photo by Lee Siebert, 1987 (Smithsonian Institution).


Mauna Kea
Mauna Kea is seen here from the S at the broad Humu'ulu Saddle between Mauna Kea and Mauna Loa. The lava flow in the foreground was emplaced during an 1843 eruption that originated on the NE rift zone of Mauna Loa. The flow traveled directly N to the Mauna Kea saddle, where it was deflected to the W. The irregular profile of the summit region of Mauna Kea is due to scoria cones and pyroclastic ejecta that are not present at Mauna Loa.

Photo by Paul Kimberly, 1994 (Smithsonian Institution).


Hualalai
Hualalai shield volcano is seen here from the SE at the summit of Mauna Loa. Its latest eruption took place in 1800-01, when lava flows from vents on the NW rift zone reached the sea.

Photo by Lee Siebert, 1987 (Smithsonian Institution).


San Quintín Volcanic Field
Isla San Martín, 6 km off the west coast of Baja California, is the westernmost volcano of the San Quintín volcanic field and the only one that is located offshore. The 2-km-wide island is a shield volcano capped by scoria cones that reach 230 m above sea level. Wave erosion has truncated part of the volcano, forming the sea cliffs seen at the left on the S side of the island.

Photo by Jim Luhr, 1990 (Smithsonian Institution).


Fernandina
Fernandina volcano in the Galápagos exhibits steep upper flanks formed by eruptions of lava flows from circumferential fissures around a summit caldera rim, contrasting with the broad, low-angle lower flanks. Scientists from the Smithsonian Institution, U.S. Geological Survey, and the Charles Darwin Research Station conduct measurements on a pahoehoe lava flow near the SE coast. Young, unvegetated lava flows cover the flanks.

Photo by Chuck Wood, 1978 (Smithsonian Institution).


Wolf
Wolf, the highest volcano of the Galápagos Islands, is located near the equator at the N end of the archipelago's largest island, Isabela. The summit caldera is 5.5 x 7 km and 600 m deep, with recent lava flows covering the broad caldera floor. Prominent unvegetated lava flows are visible on the flanks to the sea. Wolf's 1797 eruption was the first documented in the Galápagos Islands.

Photo by Lee Siebert, 1978 (Smithsonian Institution).


Darwin
Volcán Darwin, named after the Charles Darwin, seen above a narrow channel opposite Point Espinosa on the NE tip of Fernandina Island. Darwin volcano has 5-km-wide summit caldera that is largely filled by lava flows. The most recent summit activity produced several small lava flows from vents on the eastern caldera floor, and NE and SE caldera rims. Two breached tuff cones on the SW-flank coast, Tagus and Beagle, were a prominent part of Darwin's geological studies in the Galápagos Islands.

Photo by Lee Siebert, 1978 (Smithsonian Institution).


Alcedo
Alcedo is one of the lowest and smallest of six shield volcanoes on Isabela Island. Seen here from the coast of Fernandina Island to its west, Alcedo has a 7-8 km wide summit caldera. Most of the flanks and summit caldera are vegetated, but young lava flows are prominent on the N flank near the saddle with Darwin volcano. Alcedo is the only Galápagos volcano known to have erupted rhyolite as well as basalt.

Photo by Lee Siebert, 1978 (Smithsonian Institution).


Prestahnukur
The classic Icelandic volcano Skjaldbreiður is one of many small shield volcanoes that were constructed along rift zones where the Mid-Atlantic Ridge rises above sea level. Skjaldbreiður, seen here from the W along Route 52, formed about 9,500 years ago during a single long-duration eruption at the southern end of the Prestahnúkur volcanic system in central Iceland. It produced 17 km3 of basaltic lava flows and is capped by a small 300-m-wide summit crater.

Photo by Richie Williams, 1981 (U.S. Geological Survey).


Fremrinamar
Fremrinámar, NNE of Askja and SE of Mývatn lake, is a volcanic system that is constructed over the Ketildyngja shield volcano (center). Associated fissure systems, including the Sveinar fissure, extend 130 km to the N coast of Iceland. Mývatn lake formed as a result of the eruption of the 70-km-long older Laxarhraun lava flow from Ketildyngja shield volcano about 3,800 years ago. The latest eruption from Fremrinámar produced the Búrfellshraun lava flow about 2,500-3,000 years ago.

Photo by Richie Williams, 1981 (U.S. Geological Survey).