Alamagan is the emergent summit of a large stratovolcano in the central Mariana Islands with a roughly 350-m-deep summit crater east of the center of the island. The exposed cone is largely Holocene in age. A 1.6 x 1 km graben cuts the SW flank. An extensive basaltic-andesite lava flow has extended the northern coast of the island, and a lava platform also occurs on the south flank. Pyroclastic-flow deposits erupted about 1000 years ago have been dated, but reports of historical eruptions were considered invalid. From the Smithsonian Global Volcanism Program.

Location:
Latitude: 17.6° N
Longitude: 145.83° E
Elevation: 744 (m) 2,441 (f)
Volcano type: Stratovolcano
Composition: Andesite - Basalt
Most recent eruption: 870 CE