About 50-60 volcanoes erupt every year. About half are effusive (lava flows) and half are explosive.
Where When VEI * CasualtiesComments
Yellowstone 2.1M, 1.3M, 0.6M
yrs ago
8  2.1 mya Huckleberry Ridge Tuff, Big Bend Ridge, Snake River, and Red Mountains caldera segments.
2,450 cu. km. (km3) of ash
Yellowstone 1.3M
yrs ago
7  Mesa Falls Tuff, Henrys Fork Caldera
280 km3
Long Valley, CA 760,000
yrs. ago
7 590 km3
Mammoth Lakes
Yellowstone 640,000
yrs ago
8  Lava Creek Tuff, Yellowstone Caldera
1,000 km3
Toba, Sumatra, Indonesia 73,000 years ago 8   2,800 km3 of ash.
Mount Mazama, Oregon 4650 B.C. Plinian   Formed Crater Lake
Taupo, New Zeland 186     Pyroclastic flows travelled 100 km. More than 80 km3 of ash.
Krakatoa, Indonesia c. 535 (1) 6   
Tambora, Indonesia 1815 7 38-92,000 Global climatic effects for several years. 50-150 km3 of ash.
Krakatoa, Indonesia 1883 6 37,000 Blast heard 5,000 km away. More killed by Tsunami. 10 km3
Mount Pelee, Martinique 1902 ? Pelean 28,000 Pyroclastic Flow
Nevado Ruiz, Columbia 1985 ? 23,000Mudflow
Unzen, Japan 1720 ? 14,500
Kelut, Java 1586 ? 10,000
Kelut, Java 1919 ? 5,000
Santa Maria, Guatemala 1919 ? 4,000Ash falls, Disease, Starvation
El Chichon, Mexico 1982 ? 1,800Ash falls
Laki, Iceland 1783 ? 9,350
Pinatubo, Philippines 1991 6 Plinian 8004.8-10 km3
Katmai (at Novarupta), Alaska 1912 6 ? 10 km3
Mt. St. Helens, OR 1980 5 Plinian570.4-1 km3
Cerro Hudson, Southern Chile 1991 5?
Fuji, Japan 1707-08 5?
Vesuvius, Italy 79 AD 5 Plinian16,000The famous Pompeii eruption.
Mono-Inyo (Long Valley), Calif. last 5,000 yrs. 1-4   About 20 small to moderate eruptions have occurred between Mammoth Lakes (Inyo) and Mono Lake in the last 5,000 years. The latest started about 600 years ago.
Examples of Recent Smaller Volcanoes
Shishaldin, Alaska 1999 4? 
Rabaul, Papua New Guinea 1994 4?
Augustine, Alaska 1986 4?
Galunggung, Java, Indonesia 1982 4?
Tungurahua, Ecuador 2001 3?
Vesuvius 1631  4,000
Tungurahua, Ecuador 2001  ?
Mono Lake (Long Valley), CA 1750 ?
Lassen Peak, CA 1915 3?
Mount Baker, WA 1870 ??
Mount Hood, OR 1865 ??
Mount Rainier, WA 1820 ? ??
Mount Shasta, CA 1786 ? ??
Mayon, Philippines 1968 ? Pelean?
(1) The 6th century Krakatoa eruption is still speculative, but it seems to be the best explanation for severe climate changes in 535-36.

* Volcanic Explosivity Index (VEI) at USGS (U.S. Geological Survey) Volcanoes page
VEI Type Plume Height Volume Classification Frequency Example
8 Megacolossal > 25 km >1000 km3 Ultra-Plinian >10,000 yr Yellowstone 2 Ma
7 Supercolossal > 25 km >100 km3 Ultra-Plinian >1000 yr Tambora 1815
6 Colassal > 25 km >10 km3 Plin/Ultra-Plinian >100 yr Krakatoa 1883
5 Paroxysmal > 25 km >1 km3 Plinian >100 yr St Helens 1981
4 Cataclysmic 10-25 km >0.1 km3 Vulc/Plinian >10 yr Galunggung 1982
3 Severe 3-15 km >10.6 m3 Vulcanian yearly Ruiz 1985
2 Explosive 1-5 km >105 m3 Strom/Vulcanian weekly Galeras 1992
1 Gentle 100-1000 m >104 m3 Haw/Strombolian daily Sromboli
0 non-explosive <100m >1,000 m3 Hawaiian daily Kilauea
Source: Eruption Scale at U. North Dakota
See Also: VEI at the Smithsonian

U.S. Volcanoes since 1980
Hawaiian Volcano Observatory (HVO)
Kilauea, Hawaii 1983-present  
Mauna Loa, Hawaii 1984 2002-2004, inflation and deep seismicity
Cascades Volcano Observatory
Mt. St. Helens, Washington 1980-1986, 2004-2005 1989-2003, occasional earthquake bursts, minor phreatic explosions, small mudflows
Mt. Hood, Oregon   Occasional earthquake swarms
Three Sisters, Oregon   Uplift began 1997; earthquake swarm March 2004
Medicine Lake, CA   1988-1989 earthquake swarm
Long Valley Observatory (LVO>
Long Valley, California   CA - In May of 1980, a strong earthquake swarm that included four magnitude 6 earthquakes struck the southern margin of Long Valley Caldera associated with a 25-cm, dome-shaped uplift of the caldera floor. CO2 emission from ground since 1989. Caldera unrest continues to this day, although earthquake activity within and adjacent to the caldera has remained low since mid-1999.
Yellowstone Volcano Observatory (YVO)
Yellowstone National Park   Recurrent earthquake swarms and ground deformation (uplift & subsidence), changes in hydrothermal features. In April 2004 there was an increase in earthquake activity, called a swarm, at Yellowstone National Park that drew interest from scientists and the public. There have been many swarms recorded over the past 40 years at Yellowstone.
Alaska Volcano Observatory
Redoubt, Alaska 1989-1990  
Spurr, Alaska 1992 2004-2005 earthquake swarms and melt pit at summit. Overall rate of seismicity is diminishing.
Augustine, Alaska 1986  
Iliamna, Alaska   1996 earthquake swarm and elevated gas emission
Veniaminof, Alaska 1983-1984, 1993-1995, 2004-2005  
Pavlof, Alaska 1980, 1981, 1983, 1986-1988, 1996-1997  
Shishaldin, Alaska 1986-1987, 1995-1996, 1999 2004-2005 earthquakes and tremor, thermal anomalies
Westdahl, Alaska 1991-1992  
Dutton, Alaska   1984 earthquake swarm; 1988 earthquake swarm and intrusion
Shrub Mud Volcano, Alaska   1996-1999 carbon dioxide/mud eruption
Becharof Lake, Alaska   1998 earthquake swarm
Chiginigak, Alaska   1997-1998 fumarolic activity
Akutan, Alaska 1980, 1987, 1988, 1992 Intense earthquake swarm and intrusion with ground cracks in 1996.
Makushin, Alaska 1980  
Bogoslof, Alaska 1992
Okmok, Alaska 1981, 1983, 1986-1988, 1997
Cleveland, Alaska 1986, 1987, 1994, 2001
Amukta, Alaska 1987, 1996?
Seguam, Alaska 1992, 1993
Korovin, Alaska 1987, 1998
Kanaga, Alaska 1993-1995
Gareloi, Alaska 1980, 1982
Kiska, Alaska 1987?
Pagan, Mariana Islands 1981-1996
Anatahan, Mariana Islands 2003-2005
Source: An Assessment of Volcanic Threat and Monitoring Capabilities in the United States: Framework for a National Volcano Early Warning System (NVEWS)

Active Volcanoes Worldwide

Potential future re-activation of volcanoes in the United States
See Volcanoes Hazards Updates, Smithsonian's Global Volcanism Program's (GVP).

At the USGS's An Assessment of Volcanic Threat and Monitoring Capabilities in the United States: Framework for a National Volcano Early Warning System (NVEWS), (April, 2005), they categorize volcanoes by threat score. "Volcanic threat is the combination of hazards (the dangerous or destructive natural phenomena produced by a volcano) and exposure (the people and property at risk from the volcanic phenomena)."

The NVEWS threat assessment is not a formal risk assessment of U.S. volcanoes. The latter requires that probabilities of particular hazards occurring at individual volcanoes within a set time period be calculated and that the vulnerability of people and property to the hazards be estimated as expected losses in dollars. Such an analysis for so many volcanoes is beyond the scope of this work.

Their goal is to establish monitoring levels consistent with the threat. Currently only 3 of the 18 very high threat areas are well-monitored in real-time: Mount St. Helens, Washington; Kilauea, HI; and Long Valley caldera, CA. All 18 have at least a minimal level of ground based monitoring.
Threat Num. Volcanoes
Very High
18 Alaska: Akutan (AI), Augustine (CI), Makushin (AI), Redoubt (CI), Spurr (CI)
[Regions: Alaska Peninsula (AP), Aleutian islands (AI) Cook Inlet SW of Anchorage (CI)]
California: Lassen, Long Valley Caldera, Shasta
Hawaii: Kilauea, Mauna Loa
Oregon: Crater Lake, Hood, Newberry, South Sister
Washington: Baker, Glacier Peak, Rainier, St. Helens
37 Alaska: Aniakchak (AP), Atka (AI), Churchill (Wrangell), Dutton (AP), Gareloi (AI), Great Sitkin (AI), Griggs (AP), Hayes (CI), Iliamna (CI), Kaguyak (AP), Kanaga (AI), Katmai (AP), Mageik, Martin, Novarupta, Okmok, Pavlof, Pavlof Sister, Seguam, Semisopochnoi, Shishaldin, Trident, Ugashik-Peulik, Veniaminof, Westdahl, Wrangell
California: Clear Lake, Inyo Craters, Medicine Lake, Mono Craters
Hawaii: Hualalai
Mariana Islands: Agrigan, Alamagan, Anatahan, Pagan,
Washington: Adams
Wyoming: Yellowstone
48 Alaska: Adagdak, Amak, Amukta, Black Peak, Bogoslof, Chiginigak, Cleveland, Dana, Denison, Douglas, Edgecumbe, Emmons Lake, Fisher, Frosty, Kasatochi, Kialagvik, Kiska, Kukak, Kupreanof, Little Sitkin, Moffett, Recheschnoi, Roundtop, Sanford, Snowy Mountain, Steller, Tanaga, Ukinrek Maars, Vsevidof, Yantarni, Yunaska,
Arizona: Sunset Crater
California: Coso Volc. Field, Mono Lake Volc Field, Red Cones, Ubehebe Craters
Colorado: Dotsero
Hawaii: Haleakala, Mauna Kea
Mariana Islands: Asuncion, Farallon de Pajaros, Guguan, Sarigan
Nevada: Steamboat Springs (20 km south of Reno)
New Mexico: Valles Caldera
Oregon: Bachelor, North Sister Field
Utah: Black Rock Desert
34 Alaska: Bobrof, Buldir, Buzzard Creek, Carlisle, Chagulak, Davidof, Duncan Canal. Fourpeaked, Herbert, Ingakslugwat Hills, Isanotski, Kagamil, Koniuji, Nunivak Island, Segula, Sergief, Stepovak, St.Michael, Table Top-Wide Bay, Takawangha, Uliaga, Unnamed
Idaho: Craters of the Moon, Hell's Half Acre, Shoshone Lava Field, Wapi Lava Field
Mariana Islands: Esmeralda Bank, Maug Islands, Ruby
Oregon: Belknap, Blue Lake Crater
Utah: Markagunt Plateau
Washington: Indian Heaven, West Crater
Very Low
32 Alaska: Behm Canal-Rudyerd Bay, Gordon, Imuruk Lake, Kookooligit Mountains, St. Paul Island, Tlevak Strait-Suemez Island
Arizona: Uinkaret Field
California: Amboy, Big Cave, Brushy Butte, Eagle Lake Field, Golden Trout Creek, Lavic Lake, Tumble Buttes, Twin Buttes
Mariana Islands: Ahyi, Supply Reef
New Mexico: Carrizozo, Zuni-Bandera
Oregon: Cinnamon Butte, Davis Lake, Devils Garden, Diamond Craters, Four Craters Lava Field, Jackies Butte, Jefferson, Jordan Craters, Lava Mountain, Sand Mountain Field, Washington
Utah: Bald Knoll, Santa Clara

Map of Volcanoes of Canada and the western USA. at the Smithsonian.

A hotspot under yellowstone had created three supervolcanos;

  • 2.1 million years ago created a widespread volcanic deposit known as the Huckleberry Ridge Tuff. This titanic event, one of the five largest individual volcanic eruptions known anywhere on the Earth, formed a caldera more than 60 miles (100 km) across. 5.1 cubic miles mi3 of magma.
  • A similar, smaller but still huge eruption occurred 1.3 million years ago. This eruption formed the Henrys Fork Caldera.
  • 640,000 years ago created the 35-mile-wide, 50-mile-long (55 by 80 km) Yellowstone Caldera.
There are 30 such hotspots, where magma is close to the surface, across the world, but yellowstone is the only one under land.
This hotspot was created 16 million years ago. During that time the north american plate has moved 400 miles over it and left a trail of eruptions from western Idaho to Yellowstone.
Since the last large eruption 640,000 years ago there have been 30 smaller lava flows, the latest 70,000 years ago.
See Yellowstone Volcano Observatory (YVO) a partnership among the U.S. , Geological Survey (USGS), Yellowstone National Park, and University of Utah
Volcanic History of Yellowstone,
Steam Explosions, Earthquakes, and Volcanic Eruptions - What's in Yellowstone's Future?
In 2005 the BBC and the Discovery Channel produced docudrama and documentary, "Supervolcano", about Yellowstone.
See: Weekly Volcanic Activity Report at the Smithsonian Active and Potentially Active Volcanoes in California

Ejecta: Material that is thrown out by a volcano, including pyroclastic material (tephra) and lava bombs.

Lava: Magma which has reached the surface through a volcanic eruption. The term is most commonly applied to streams of liquid rock that flow from a crater or fissure. It also refers to cooled and solidified rock.

Magma: Molten rock beneath the surface of the earth.

Pyroclastic: Pertaining to fragmented (clastic) rock material formed by a volcanic explosion or ejection from a volcanic vent.

Pyroclastic Flow (nuées ardentes): Lateral flowage of a turbulent mixture of hot gases and unsorted pyroclastic material (volcanic fragments, crystals, ash, pumice, and glass shards) that can move at high speed (100 to 500 miles an hour.) The term also can refer to the deposit so formed. Types.

Tuff: Rock formed of pyroclastic material.

Type of eruption:

Named after the Italian volcano, Stromboli, eject small to medium sized lava fragments to form incandescent arcs which can be traced in photographs. Cinder cones often use this eruptive style.
Named for the Italian volcano, Vulcano, produce short blast-like eruptions of gas and ash. These and all such eruptions occur due to the gas content of the magma being expelled.
Named after the guy who reported Vesuvius to the Romans (Pliny the Younger), are the most violent there are. The most famous plinian eruption for Americans is probably the eruption of Mt. St. Helens. Plinian eruptions are long duration explosions which send ash and debris billowing kilometers into the atmosphere. Fine ash can be dispersed over very large areas. They typically last hours and can expel truly massive quantities of debris. Fast-moving deadly pyroclastic flows are also commonly associated with plinian eruptions.
Similar to plinian, but are not so enormous. They release large amounts of ash and gas while the cloud typically forms a sort of cauliflower shape. Vesuvian eruptions are named after the Italian Mt. Vesuvius, which destroyed the cities of Pompeii and Herculaneum.
Pelean [Peléean, Nuée Ardente (glowing cloud)]
Pelean eruptions occur when the vent is held at an angle so that the eruption shoots out laterally, not up. Named for Mont Pelee in the West Indies. Peleean eruption involve viscous magma and share characteristics with Vulcanian eruptions. The key characteristic of Peleean eruptions is the eruption of glowing avalanches of hot ash.
Eruptions may occur along fissures or fractures that serve as linear vents, such as during the eruption of Mauna Loa Volcano in Hawaii in 1950; or they may occur at a central vent such as during the 1959 eruption in Kilauea Iki Crater of Kilauea Volcano, Hawaii. In fissure-type eruptions, molten, incandescent lava spurts from a fissure on the volcano's rift zone and feeds lava streams that flow downslope. In central-vent eruptions, a fountain of fiery lava spurts to a height of several hundred feet or more. Such lava may collect in old pit craters to form lava lakes, or form cones, or feed radiating flows.
Phreatic (or steam-blast)
eruptions are driven by explosive expanding steam resulting from cold ground or surface water coming into contact with hot rock or magma. The distinguishing feature of phreatic explosions is that they only blast out fragments of preexisting solid rock from the volcanic conduit; no new magma is erupted. Phreatic activity is generally weak, but can be quite violent in some cases, such as the 1965 eruption of Taal Volcano, Philippines, and the 1975-76 activity at La Soufri¸re, Guadeloupe (Lesser Antilles).

Sources: Types of Volcanic Erujptions, Basics of Volcanology, Kinds Of Volcanic Eruptions

See: Volcanic and Geologic Terms

See: Index to Volcanoes at the USGS Cascades Volcano Observatory (CVO), Vancouver, Washington
The Smithsonian Institution Global Volcanism Program : Volcanoes of the World (Region Map, Weekly World Volcanic Activity Report & Activity Map)
Volcano Live
Top Ten Earthquakes and Volcanic Eruptions
Volcanoes at MTU
Volcano Live by John Seach, Australia

last updated 4 Oct 2005