The Northern Marianas island of Alamagan is located 146 nautical miles (270 km) north from Saipan and is 11.12 km² (4.295 sq mi) in area. The island's volcano (Bandeera Peak) has a large caldera at the summit. The volcano last erupted around 870 AD, with an error bar of 100 years. It involved pyroclastic flows, and had a VEI of 4. Any claims of historical eruptions are inaccurate, though uncertain eruptions have occurred as late as 1887.
The west side of the island is cut by deep gorges covered with high savanna grass. The southeast side is a steep slope of bare lava. There are deep valleys with caves. Coconut palms grow on the gradual slopes. Warm fresh water springs are located on the northern part of the west coast.
Alamagan is the home of the endangered Nightingale Reed-warbler, Acrocephalus luscinia which presently can be found only here, Saipan and possibly Aguijan .
Historically the island has been sporadically populated; as of late 2005 there were seven inhabitants on Alamagan, all or most living in Alamagan Village. The 2000 census reported an official population of six persons. The island is part of the Northern Islands Municipality.
In September 2009, Typhoon Choi-wan passed directly over Alamagan, destroying many of the island's trees and forcing the evacuation of the island's residents to Saipan.