From Miller and others (1998) 
: "Mount Mageik is a broad cone-shaped volcano that rests on a basement of Jurassic sedimentary rocks at the northeast end of a 12-km-long basement ridge shared by neighboring Mount Martin. The summit area, which is largely ice-covered, consists of a central high peak (elevation 2165 m) and three smaller topographic highs, each a separate vent-cone. A small (<1 km in diameter) phreatic crater on the northeast side of the central peak contains a crater lake and supports vigorous fumarolic activity accompanied by sulfur deposition. The slopes of the volcano are moderately dissected by glacial ice, except the young lava flows of the east side. Two small debris avalanches, including the Mageik landslide - one of which occurred during the 1912 Katmai eruption 
originated from areas high and low on the south flank. The 1912 avalanches, containing boulders as big as 3 to 5 m, traveled 6 km down the broad valley of Martin Creek, south and east of Mount Mageik."