Mount Katmai is a large stratovolcano (composite volcano) on the Alaska Peninsula in southern Alaska, located within Katmai National Park and Preserve. It is about in diameter with a central lake-filled caldera about 3 by 2 mi (4.5 by 3 km) in area, formed during the Novarupta eruption of 1912. The caldera rim reaches a maximum elevation of . In 1975 the surface of the crater lake was at an elevation of about , and the estimated elevation of the caldera floor is about . The mountain is located in Kodiak Island Borough, very close to its border with Lake and Peninsula Borough.