FAQs About Volcanic Eruptions
Can an eruption at one volcano trigger an eruption at another nearby volcano (for example, within about 10 km)?
There are a few historic examples of simultaneous eruptions from volcanoes or vents located within about 10 km of each other, but it's very difficult to determine whether one might have caused the other. To the extent that these erupting volcanoes or vents have common or overlapping magma reservoirs and hydrothermal systems, magma rising to erupt from one volcano may effect the other volcano's "plumbing" system and cause some form of unrest, including eruptions. For example, the huge explosive eruption of Novarupta vent in Alaska triggered the summit of nearby Mt. Katmai volcano to collapse, thereby forming a new caldera (but no eruption!).
For a few of the historic examples of simultaneous eruptions from nearby volcanoes, scientists actually consider the individual volcanoes or vents to be part of a larger volcano complex consisting of overlapping stratovolcanoes, cinder cones, fissures, vents, and even calderas. In such cases, the erupting vents (or volcano) are actually part of the same volcano complex. For example, Tavurvur and Vulcan cones that erupted at nearly the same time in September 1994 are vents located within Rabaul Caldera in Papua New Guinea. In such cases, one eruption does not really "trigger" a nearby vent to erupt; instead, moving magma "leaks" to the surface at multiple sites.
In contrast to these examples of simultaneous eruptions at volcanoes with overlapping or related magma and hydrothermal systems, two of Earth's most active volcanoes that are located close to each other -- Mauna Loa and Kilauea in Hawaii -- have separate shallow magma reservoirs that don't seem to affect each other. Even though Kilauea Volcano is located on the southeastern flank of Mauna Loa (the summit calderas are only 33 km apart) and magma rising into both volcanoes originates from the same mantle hot spot, the chemistry of their magma is nevertheless distinct from each other. Furthermore analysis of the timing of historic eruptions strongly suggests that an eruption at one volcano does not cause or trigger an eruption at the other volcano.
A few examples of simultaneous eruptions from nearby volcanoes or vents
No. Since there are on average between 50 and 60 volcanoes that erupt each year somewhere on Earth (about 1 every week), some of Earth's volcanoes may actually erupt within a few days or hours of each other. Upon closer inspection, however, the eruptions are almost always preceded by very different build-up periods in terms of time (days to weeks to months to years) and type of activity (earthquakes, ground deformation, gas emissions, and small eruptions). The "trigger" of this precursory activity is the key to understanding what causes an eventual eruption at any one volcano, not the timing of significant eruptions hundreds to thousands of km apart.
According to the theory of plate tectonics, the location and frequency of volcanism on Earth is due primarily to the way in which our planet's surface is divided into large sections or plates and how they move relative to each other, and the formation of deep "thermal plumes" that rise from the core-mantle boundary about 3,200 km below the surface. These mechanisms and the fact that even nearby volcanoes erupt magma with different and often unique chemical composition (evidence that each volcano has a separate unique shallow magma reservoir) strongly suggests there is unlikely to be any cause and effect relationship between volcanic eruptions separated hundreds to thousands of km apart.
What volcanoes in the conterminous United States have erupted
since the Nation was founded?
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Mount St. Helens, Washington
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1980-1986:
Large explosive eruption on May 18, 1980, followed by 21 smaller eruptive episodes. The last 17 episodes built a lava dome in the volcano's crater. See USGS fact sheet of activity between 1986 and 2000.
1800-1857:
Large explosive eruption in 1800 was followed by extrusions of lava that formed a lava flow on the volcano's northwest flank (Floating Island lava flow) and a lava dome on the north flank (Goat Rocks lava dome).
Late 1700's:
Layers of volcanic rocks record a variety of activity related to the growth of a lava dome at the volcano's summit, including pyroclastic flows, lahars, and tephra fall.
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Lassen Peak, California
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1914-1917:
A series of small explosions that began on May 30, 1914, was followed 12 months later by extrusion of lava from the summit and a destructive pyroclastic flow and lahars on May 21, 1915. Minor activity continued through middle of 1917. See USGS fact sheet about the eruption.
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Mount Rainier, Washington
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1894 & early 1800's:
Several eyewitness accounts describe minor releases of steam and ash-laden steam during November and December 1894. The most recent eruption that formed a thin and discontinuous tephra layer, however, occurred during the first half of the 19th century.
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Mount Hood, Oregon
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1856-1865 & late 1700's:
According to eyewitnesses, small explosive eruptions occurred from the summit area between 1856 and 1865. In the latter half of the 18th century, however, a lava dome was erupted, which was accompanied by pyroclastic flows, lahars, and tephra fall.
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Mount Shasta, California
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1786:
An eruption cloud was observed above the volcano from a ship passing by north coast California, and the activity included pyroclastic flows.
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Glacier Peak, Washington
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17th - 18th centuries:
Between about 200 and 300 years ago, small eruptions deposited pumice and ash east of the volcano, and may have been observed by Native Americans.
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Mount Baker, Washington
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1840-1870:
Historical literature refers to several episodes of small tephra-producing events in the mid 1800's, and increased fumarolic activity began in Sherman Crater near the summit in 1975 and remains elevated today.
