To view maps of volcanoes visit the USGS online store at Maps>Hazards or Education Products>Earthquakes, Volcanoes, and Landslides.

There are about 1500 potentially active volcanoes worldwide, aside from the continuous belt of volcanoes on the ocean floor. About 500 of these have erupted in historical time. Many of these are located along the Pacific Rim in what is known as the "Ring of Fire." In the U.S., volcanoes in the Cascade Range and Alaska (Aleutian volcanic chain) are part of the Ring, while Hawaiian volcanoes form over a "hot spot" near the center of the Ring.

1. Niihau
2. Kauai
3. Oahu
4. Molokai
5. Lanai
6. Maui
7. Kahoolawe
8. Hawaii (Big Island)

Volcanoes are mountains, but they are very different from other mountains; they are not formed by folding and crumpling or by uplift and erosion. Instead, volcanoes are built by the accumulation of their own eruptive products -- lava, bombs (crusted over lava blobs), ashflows, and tephra (airborne ash and dust). A volcano is most commonly a conical hill or mountain built around a vent that connects with reservoirs of molten rock below the surface of the Earth. The term volcano also refers to the opening or vent through which the molten rock and associated gases are expelled. -- From: Tilling, 1985, Volcanoes: USGS General Interest Publication.

1975: For example, on November 29, 1975, a large magnitude-7.2 earthquake struck the Big Island of Hawaii at 4:48 a.m. 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 a.m. the same morning, and was accompanied, or closely followed, by a tsunamis, 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."

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.

More Historic Examples

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.

The type of equipment and techniques we use to study volcanoes depends on the particular volcano topic we are investigating and on the experiment we are conducting. When specialized instruments are not available for a special study or for monitoring a specific type of activity, we design and build our own; for example the acoustic flow monitor (AFM) for detecting lahars and for studying flowing mixtures of water and rock debris under controlled conditions.

For studying and monitoring restless and erupting volcanoes, several onsite and remote methods are used to gather data that also help us answer four critical questions during a volcano emergency.

For reconstructing a volcano's eruptive history so that we can identify the type of activity most likely to occur in the future as well as the areas around a volcano that are likely to be effected by future eruptions, we use many geologic mapping and dating strategies. These include:

1. Identifying rock outcrops, formations, and features on the ground and identifying their exact location on detailed aerial photographs and topographic maps or in computerized geographic information systems (GIS).
2. Collecting dozens to hundreds of volcanic rock and ash samples from sites located on or near the volcano and also tens of kilometers downwind or downstream, and then using laboratory techniques for determining their chemistry and mineral compositions.
3. Determining the ages of as many rock deposits formed by past activity of the volcano by using several common methods:
    
   • Carbon-14 dating when a volcanic deposit either incorporated or came to rest on top of vegetation or organic-rich soil and sufficient carbon-bearing material can be found. It's based on the fact that living trees and other organic matter contain small amounts of carbon's radioactive isotope (atomic weight of 14). When a tree is killed by a volcanic deposit, its radioactive carbon begins to decrease by radioactive decay at a known rate. By measuring the 14C/12C ratio in the wood sample, its age can be calculated. This technique can adequately date deposits that are as old as about 50,000 years, and each date may have an error range of between a few tens to several hundred years. The most common technique for dating recent volcanic deposits, only a few scientific laboratories in the United States can perform the carbon analysis.
      
   • Tree-ring dating when a volcanic deposit caused an unusual growth pattern of annual rings among trees growing at the time the deposits were emplaced. This technique can sometimes date deposits to an actual calendar year or to within a few years when used to on deposits of the past few hundred years.
      
   • Paleomagnetism in some volcanic areas where scientists have determined the yearly changes in the position of the Earth's magnetic pole over the past several hundreds or thousands of years and when the Earth's magnetic direction is preserved in volcanic rocks (usually lava flows and individual large rocks in pyroclastic flows); this technique usually yields ages with a range of between a few tens and several hundred years.
      
4. Representing the types and ages of volcanic rock deposits and/or identifying volcanic hazard areas around the volcano on a paper map or computerized geographic information system.

There are many paths to becoming a volcanologist. Most share a college or graduate school education in a scientific or technical field, but the range of specialties is very large. Training in geology, geophysics, geochemistry, biology, biochemistry, mathematics, statistics, engineering, atmospheric science, remote sensing, and related fields can be applied to the study of volcanoes and the interactions between volcanoes and the environment. The key ingredients are a strong fascination and boundless curiosity about volcanoes and how they work. From there, the possibilities are almost endless. Learn more about volcano training and schools.

Go to the Natural Hazards Gateway, which includes:

• Earthquakes
• Floods
• Geomagnetism (solar flares, etc.)
• Hurricanes
• Landslides
• Seismic Zone Mapping
• Sinkholes
• Tsunamis
• Volcanoes
• Wildfires

Restless volcanoes can be very dangerous places, but it's possible to work safely around them if you're properly prepared. First and foremost, scientists protect themselves by working as a team to create a "safety net" in which all the important bases are covered. Like a professional driving team, a volcano-response team includes key staff who know the monitoring equipment extremely well, experts in several scientific disciplines who can interpret data coming back from the field, a spokesperson to communicate warnings and other information to public officials and the media, and a scientist-in-charge, or "driver," who assumes overall responsibility for team performance. As part of an experienced scientific team capable of quickly assessing the past behavior of a restless volcano, installing instruments to take its pulse, and analyzing all available information to understand what the volcano is doing, a modern volcanologist is prepared to work safely even in the hazardous environment of a restless volcano.

The USGS poster Geologic Hazards of Volcanoes depicts many of the hazards associated with a volcanic eruption

To view maps of volcanoes visit the USGS online store at http://store.usgs.gov/ and look under the heading Maps>Hazards.

Climb A Volcano -
"Family Fun - Picnic at the Top"

• Sunset Crater
  Sunset Crater Volcano is closed to climbing and hiking. However, other cinder cones in the area may be climbed.

• Black Point, Mono Lake
  The hike to the top of Black Point is not an easy one; consider this an exploration, an adventure! There are no trails or signs to show you where to go. You will be walking through the cinders and ash of the volcano and sometimes progress will be difficult. If you persevere, your discovery of the fissures will seem even more spectacular because their remoteness.
• Lassen Peak
  A "well-graded" climb of 2,000 feet in 2 and 1/2 miles. Hike at a moderate pace, and take short, frequent rests. Enjoy the ever-changing view! Mount Shasta, 14,161-foot elevation looms seventy-five miles to the northwest.
• Schonchin Butte, Lava Beds National Monument
  Cinder cones are easily eroded so please stay on the established trails and don't take shortcuts. Frothy lava, cooled in the air, created the large cinder cones throughout the monument. Schonchin Butte's .75 mile trail leads you to a panoramic view from the historic fire lookout. The lookout is staffed from June to September. Children of all ages can earn a Junior Fire Lookout badge.

• Capulin Mountain
  Have you ever wanted to walk into a volcano? Well, Capulin Volcano is one of the few places in the world where you can do that. A 2-mile road spirals to the summit, ending at a parking area, where two self-guiding trails begin.

• Mount Bachelor
  Near Bend, Oregon
  Ride the Sunrise Lift to mid-mountain, walk over to the Summit Lift, and ride it to the top
• Brown Mountain
  Between Medford and Klamath Falls
  A scramble over fresh talus. View the south flanks of Mount McLoughlin.
• Crater Lake
  The 33-mile Rim Drive encirles Crater Lake, with each mile giving a different perspecitve of the lake, rim, and surrounding terrain.
• Larch Mountain
  Boring Lava shield volcano (4,056 feet), near Portland, Oregon
• Lava Butte
  Near Bend, Oregon
  In the 1930's the USFS designated Lava Butte as a lookout point and built a spiral road to the top. A 1/4-mile trail circles the crater. This trail offers spectacular views of the Cascade Mountain Range and Deschutes Plateau. A grand vista of volcanic country.
• Mount McLoughlin
  Between Medford and Klamath Falls
  A "moderately-steep" trail.
• Newberry Caldera
  20 miles southeast of Bend, Oregon
  From its junction with Road 21 within Newberry Crater, the Paulina Peak road is 4.1 miles long. On a clear day, you can see into Washington and California, and view almost the entire High Cascade Range in Oregon.
• Pelican Butte
  Between Medford and Klamath Falls
  A "reasonably well-maintained" gravel road leads to the top. It offers a 180-degree panorama of Cascade Peaks from just south of Crater Lake past Mount McLoughlin and onto the volcanoes in the Mountain Lakes Wilderness.
• Pilot Butte
  At the east city limits of Bend, Oregon
  A spiral road to the top. Pilot Butte is a cinder cone at the east city limits at Bend. Visible from its easily accessible top are the snow peaks of the Cascade Range (listed from the north): Mount Hood, Mount Jefferson, Three-Fingered Jack, Mount Washington, North Sister, Middle Sister, South Sister, Broken Top, and Mount Bachelor Ski Resort Area.
• Powell Butte
  Boring Lava cone, near Portland, Oregon
• Rocky Butte
  Boring Lava cone, near Portland, Oregon
• Mount Tabor
  Boring lava cone, near Portland, Oregon
  Miles of trails and roadways wind through tall trees and well-maintained landscape, and most lead to the top, a trip rewarded by breathtaking views of downtown Portland and the West Hills from one side, Mount Hood and the outer Eastside from the other.
• Mount Thielsen
  Southern Oregon Cascades
  The trail is a steep climb, particularly above timberline beyond which there are no markers. The last 200 feet is a difficult hand-over-hand climb. The view of the east and west sides of the Cascades, from the Sisters to Mount Shasta, is incredible.



Washington State

• Battle Ground Lake
  North of Vancouver, Washington, approximately 45 minutes from Portland, Oregon
  10 miles of hiking trails, 10 miles of bike trails, and 5 miles of horse trails. The lake's origin is volcanic, and is believed to have been formed as a "Maar" volcano. This type of volcano is the result of hot lava or magma pushing up near the surface of the earth and then coming into contact with underground water. This is thought to have resulted in a large steam explosion, leaving a crater that later formed a lake.
• Beacon Rock
  35 miles east of Vancouver, Washington
  An easy one-mile trail to the top. Fantastic view of the Columbia River.
• Mount St. Helens
  50 miles from Portland, Oregon and Vancouver, Washington
  Most climbers complete the round trip in 7 to 12 hours. A climbing permit is required. At 8,365 feet, the rim of Mount St. Helens provides outstanding views of the crater, lava dome, blast area, and surrounding volcanic peaks.

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.

All these links have volcano information:

• Volcano Hazards Program
• Cascades Volcano Observatory
• Alaska Volcano Observatory
• Hawaiian Volcano Observatory
• Long Valley Volcano Observatory

• Volcanoes
• Eruptions of Hawaiian Volcanoes: Past, Present, and Future
• Eruptions of Mount St. Helens: Past, Present, and Future
• Monitoring Active Volcanoes
• Volcanic and Seismic Hazards on the Island of Hawaii
• Volcanoes of the United States

Although Mount Rainier (Washington) has not produced a significant eruption in the past 500 years, it is potentially the most dangerous volcano in the Cascade Range because of its great height, frequent earthquakes, active hydrothermal system, and extensive glacier mantle. Mount Rainier has 26 glaciers containing more than five times as much snow and ice as all the other Cascade volcanoes combined. If only a small part of this ice were melted by volcanic activity, it would yield enough water to trigger enormous lahars. Mount Rainier's potential for generating destructive mudflows is enhanced by its great height above surrounding valleys. -- From: Scott, et.al., 1990, Sedimentology, Behavior, and Hazards of Debris Flows at Mount Rainier, Washington: USGS Open-File Report 90-385, and Brantley, 1994, Volcanoes of the United States: USGS General Interest Publication.

Five billion years ago the Earth was formed by a massive conglomeration of space materials. The heat energy released by this event melted the entire planet, and it is still cooling off today. Denser materials like iron (Fe) sank into the core of the Earth, while lighter silicates (Si), other oxygen (O) compounds, and water rose near the surface.

The earth is divided into four main layers: the inner core, outer core, mantle, and crust. The core is composed mostly of iron (Fe) and is so hot that the outer core is molten, with about 10% sulfur (S). The inner core is under such extreme pressure that it remains solid. Most of the Earth's mass is in the mantle, which is composed of iron (Fe), magnesium (Mg), aluminum (Al), silicon (Si), and oxygen (O) silicate compounds. At over 1000 degrees C, the mantle is solid but can deform slowly in a plastic manner. The crust is much thinner than any of the other layers, and is composed of the least dense calcium (Ca) and sodium (Na) aluminum-silicate minerals. Being relatively cold, the crust is rocky and brittle, so it can fracture in earthquakes. (Univ. of Nevada)

This is a brief summary of our knowledge of the earth's interior. For further information, see: University of Nevada

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.

Volcanoes are not randomly distributed over the Earth's surface. Most are concentrated on the edges of continents, along island chains, or beneath the sea forming long mountain ranges. More than half of the world's active volcanoes above sea level encircle the Pacific Ocean to form the circum-Pacific "Ring of Fire". -- From: Brantley, 1994, Volcanoes of the United States: USGS General Interest Publication.

The word "volcano" comes from the little island of Vulcano in the Mediterranean Sea off Sicily. Centuries ago, the people living in this area believed that Vulcano was the chimney of the forge of Vulcan -- the blacksmith of the Roman gods. They thought that the hot lava fragments and clouds of dust erupting form Vulcano came from Vulcan's forge as he beat out thunderbolts for Jupiter, king of the gods, and weapons for Mars, the god of war. In Polynesia the people attributed eruptive activity to the beautiful but wrathful Pele, Goddess of Volcanoes, whenever she was angry or spiteful. Today we know that volcanic eruptions are not super-natural but can be studied and interpreted by scientists. -- From: Tilling, 1985, Volcanoes: USGS General Interest Publication.