Bogoslof Island description and information

From Miller and others (1998): "Bogoslof Island is the largest of a cluster of small, low lying islands that comprise the emergent summit of a large submarine stratovolcano that rises more than 1500 m above the Bering Sea floor (Byers, 1959, plate 39). The volcano appears to be a back-arc feature as it occurs well behind the volcanic front of the main Aleutian arc. The island has undergone dramatic changes in size and shape during historical time, an evolution that has been unusually well observed and recorded for such an isolated volcano.

"The island is presently shaped like an irregular isosceles triangle about 2.0 km long and 0.75 km wide covering an area of 0.75 square kilometers. Castle Rock, a steep, twin-spired pinnacle along the southwest side of the island is the eroded remnant of a dome extruded in 1796. Vent agglomerate produced during the explosive phase of that eruption lies in fault contact with the dome material and is best exposed in the southeast part of the sea cliff below Castle Rock.

"A blanket of basaltic agglomerate and ash is plastered against the steep north and east flanks of Castle Rock and extends north and east as a broad terrace. This material is interpreted by Byers (1959) to have been deposited primarily during the 1926 eruption but may also be from earlier Bogoslof eruptions. The tephra layer, along with a basaltic dome extruded in early 1927, comprises most of the area of the island, which is steadily being reduced by marine erosion. The 1927 dome is a rounded knob more than 40 m high and 305 m in diameter on the northwest coast, and fronts an arcuate salt water lagoon to the east. Cobble-boulder beaches fringe the island's north and southeast shores and a sand beach extends along the eastern margin.

"About 610 m northwest of Bogoslof lies Fire Island, a tiny flat-topped stack resembling a lighthouse. The island is the remnant of a dome extruded in 1883. Domes produced during other episodes of Bogoslof volcanism have been completely destroyed through subsequent explosive eruption and marine erosion."