Anatahan, Mariana Islands, Central Pacific Ocean

The two coalescing volcanoes forming the elongated, 9-km-long island of Anatahan in the central Mariana Islands are apparent in this aerial view from the south. The low point in the center of the island results in part from overlapping 2.3 x 5 km wide calderas, the largest in the Mariana Islands. The larger western caldera is 2.3 x 3 km wide and extends eastward from the 788-m-high summit of the western volcano (left). The volcano's first historical eruption in 2003 took place from a small crater within the 2-km-wide eastern caldera.
Photo by U.S. Geological Survey, 1994.

Background. The elongated, 9-km-long island of Anatahan in the central Mariania Islands consists of two coalescing volcanoes with a 2.3 x 5 km, E-W-trending summit depression formed by overlapping summit calderas. The larger western caldera is 2.3 x 3 km wide and extends eastward from the summit of the western volcano, the island's 788 m high point. Ponded lava flows overlain by pyroclastic deposits fill the caldera floor, whose SW side is cut by a fresh-looking smaller crater. The summit of the lower eastern cone is cut by a 2-km-wide caldera with a steep-walled inner crater whose floor is only 68 m above sea level. The sparseness of vegetation on the most recent lava flows on Anatahan indicate their probable Holocene age.