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The highest of the Marianas arc volcanoes, Agrigan (also spelled Agrihan) contains a 500-m-deep, flat-floored caldera. 

Quick Facts

Location: Commonwealth of the Northern Mariana Islands

Latitude: 18.77° N​​​​​​​

Longitude: 145.67° E​​​​​​​

Elevation: 965 (m) 3,166 (f)​​​​​​​

Volcano type: Stratovolcano​​​​​​​

Composition: Basalt - Andesite​​​​​​​

Most recent eruption: 1917 CE

Threat Potential: High*

*based on the National Volcano Early Warning System


Agrigan Island
Agrigan Island image taken from NASA Space Shuttle.

The highest of the Marianas arc volcanoes, Agrigan (also spelled Agrihan) contains a 500-m-deep, flat-floored caldera. The elliptical island is 8 km long; its 965-m-high summit is the top of a massive 4000-m-high submarine volcano, the second largest in the Marianas Islands. Deep radial valley dissect the flanks of the thickly vegetated stratovolcano. The elongated caldera is 1 x 2 km wide and is breached to the NW, from where a prominent lava flow extends to the coast and forms a lava delta. The caldera floor is surfaced by fresh-looking lava flows and also contains two cones that may have formed during the volcano's only historical eruption in 1917. This eruption deposited large blocks and 3 m of ash and lapilli on a village on the SE coast, prompting its evacuation. From the Smithsonian Global Volcanism Program.


Volcanic hazards in the Pacific U.S. Territories

The Commonwealth of the Northern Mariana Islands, Guam, and American Samoa lie along the western side of the famed Pacific Ring of Fire. Here, the processes of active island and submarine volcanoes produce activity both underwater and in the atmosphere that poses potential hazards to the daily lives of residents and travelers. Since 2000, CNMI volcanoes have erupted six times, and one submarine vo
Gabrielle Tepp, Brian Shiro, William W. Chadwick

2018 update to the U.S. Geological Survey national volcanic threat assessment

When erupting, all volcanoes pose a degree of risk to people and infrastructure, however, the risks are not equivalent from one volcano to another because of differences in eruptive style and geographic location. Assessing the relative threats posed by U.S. volcanoes identifies which volcanoes warrant the greatest risk-mitigation efforts by the U.S. Geological Survey and its partners. This update

John W. Ewert, Angela K. Diefenbach, David W. Ramsey

Volcanic investigations in the Commonwealth of the Northern Mariana Islands, April to May 1994

A team of U.S. Geological Survey geologists, a seismologist, and technicians gathered new geologic, seismic, and deformation data in the Commonwealth of the Northern Mariana Islands (CNMI). Nine volcanic islands on the active East Mariana Ridge north of Saipan were examined between April 20 and May 3, 1994. In addition, a new radio-telemetry seismic station was installed on the island of Agrihan (

M. K. Sako, F. A. Trusdell, R. Y. Koyanagi, George Kojima, R. B. Moore