FAQs About Volcanic Eruptions
Q: Can an eruption at one volcano trigger an eruption at another nearby volcano (for example, within about 10 km)?
A: 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.
For more information here are a few examples of simultaneous eruptions from nearby volcanoes or vents.
Q: Is there evidence for a cause and effect relationship between eruptions that occur at about the same time from volcanoes located hundreds to thousands of km apart?
A: 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.
Q: Is there a relationship between large earthquakes (>M 6) that occur along major fault zones and nearby volcanic eruptions?
A: Sometimes, yes. A few historic large regional earthquakes (>M 6) are considered by scientists to be related to a subsequent eruption or to some type of unrest at a nearby volcano. The exact triggering mechanism for these historic examples is not well understood, but the volcanic activity probably occurs in response to a change in the local pressure surrounding the magma reservoir system as a consequence of (1) severe ground shaking caused by the earthquake; or (2) a change in the "strain" or pressure in the Earth's crust in the region surrounding where the earthquake occurred.
Historic Examples
Kilauea Volcano, Hawaii
1975:
A large earthquake (7.2 on the Richter Scale) struck the Big Island of Hawaii at 4:48 a.m. on November 29, 1975. It was centered about 28 kilometers southeast of Kilauea Volcano's summit caldera at a depth of 5 kilometers; the earthquake occurred within the volcano's south flank. The earthquake was preceded by numerous foreshocks, the largest of which was a 5.7 magnitude jolt at 3:36 the same morning, and was accompanied, or closely followed, by a tsunamis (seismic sea wave), massive ground movements, hundreds of aftershocks, and a short-lived eruption in Kilauea's summit caldera.The eruption began at 5:32 a.m. from a 500-meter long fissure on the caldera floor and ended by 10:00 p.m. According to scientists at the USGS Hawaiian Volcano Observatory, the eruptive activity "was apparently triggered by the 7.2 magnitude earthquake. The small volume and brief duration of the eruption suggest that the shallow magma might not have reached the surface under its own buoyant energy without a triggering mechanism apparently provided by the violent ground shaking."
Source:
Tilling, Robert I., Koyanagi, Robert Y., Lipman, Peter W., Lockwood, John P., Moore, James G., and Swanson, Donald A., 1976, Earthquake and related catastrophic events, Island of Hawaii, November 29, 1975: A preliminary report: U.S. Geological Survey Circular 740, 33 p.
1868:
The largest historic earthquake (estimated between 7.5 and 8.1) on the Big Island occurred beneath the south flank of Mauna Loa Volcano on April 2, 1868. The earthquake was followed by a small eruption from Kilauea's southwest rift zone and from a fissure on the caldera wall that flooded the adjacent Kilauea Iki crater with lava. Also, within Kilauea's caldera, part of the floor subsided about 90 meters. This activity occurred nearly simultaneously with an eruption from the southwest rift zone of Mauna Loa volcano.Source:
Macdonald, Gordon A., Abbott, Agatin T., and Peterson, Frank L., 1983 (2nd edition), Volcanoes in the Sea -- The geology of Hawaii: Honolulu, University of Hawaii Press, 517 p.
Mount Pinatubo, Philippines
Mount Pinatubo's huge explosive eruption on June 15, 1991, occurred within 11 months of a magnitude 7.8 earthquake that occurred about 100 kilometers northeast of the volcano. Many scientists have since asked, "Was the eruption triggered by, or otherwise related to the earthquake that had occurred on July 16, 1990?" A recent study by scientists of the Philippine Institute of Volcanology and Seismology and the U.S. Geological Survey Study suggests that there was indeed a relationship between the two events.
The study suggests that the "failure stress along faults of the Pinatubo area" after the big earthquake "were probably not a cause of Pinatubo's awakening. However, compressive stress on the magma reservoir and its roots was about 1 bar, possibly enough to squeeze a small volume of basalt into the overlying dacitic reservoir. Alternately, strong ground shaking associated with the Luzon earthquake might have done the same or triggered movement along previously stressed faults that in turn allowed magma ascent."
Source:
Bautista, B.C., Bautista, L.P., Stein, R.S., Barcelona, E.S., Punongbayan, R.S., Laguerta, E.P., Rasdas, A.R., Ambubuyog, G., and Amin, E.Q., Relationship of Regional and Local Structures to Mount Pinatubo Activity in: Newhall, C.G., Punongbayan, R.S. (eds.) Fire and mud: Eruptions and lahars of Mt. Pinatubo, Philippines, Philippine Institute of Volcanology and Seismology, Quezon City and University of Washington Press, Seattle p. 351- 370.
Restless Calderas
A recent study of the historic activity at calderas from around the world showed that "caldera unrest occurred at least 79 times in close temporal association with regional earthquakes or, in a few instances, with swarms of regional earthquakes. By close temporal association we mean within a time span that is short in relation to the usual recurrence intervals of both the regional earthquakes and the unrest, usually within a few months or less."
"Fifty regional earthquakes (most M 6 and above) were followed within hours to months of unrest at nearby calderas... Twenty seven of these episodes culminated in eruptions, and three others are continuing without eruptions as yet (Rabaul, Wrangell, and Yellowstone)." Rabaul caldera in Papua New Guinea erupted in 1994.
The authors also found that "at least 27 regional earthquakes occurred within 100 kilometers of a restless caldera during or shortly after caldera unrest" and concluded "that magma bodies beneath young calderas often react to changes in regional tectonic strain, and that unrest at calderas is sometimes a general, long-range precursor to regional earthquakes."
Source:
Newhall, Christopher, G., and Dzurisin, Daniel, 1988, Historic Unrest at Large Calderas of the World: U.S. Geological Survey Bulletin 1855, vol 1, p. 19-20.
Karymsky Volcano, Russia
For a recent example, see the May 1996 report on Karymsky Volcano on the Kamchatka Peninsula in Russia from the Smithsonian Institution's Bulletin of the Global Volcanism.
