Alaska Volcano Observatory

Bogoslof Hill, located at the center of St. Paul Island, is a low-profile shield with a double summit composed of two cone-shaped vents. The gently sloping lower flanks (<8deg) of the volcano steepen abruptly to 30deg at the summit cones, which are formed almost entirely of welded spatter with minor amounts of scoria. The northwestern cone (on the left) is a truncated rim of spatter and layered agglutinate surrounding a shallow crater. A lava lake, now solidified, ponded in the crater and partially drained through a breach in the northeastern side of the rim. In the saddle between the cone-shaped vents is a ~30-m-wide crater surrounded by a low spatter rampart. The summit region of Bogoslof Hill is elongate east to west and is traversed by numerous subparallel east-west and northeast-southwest striking fissures. The most aerially extensive of all recent lava flows erupted on St. Paul Island extends radially from the Bogoslof Hill vent region and covers approximately 16 km2.