Mount Katmai is a large stratovolcano

Stratovolcano

A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

 (composite volcano) on the Alaska Peninsula

Alaska Peninsula

The Alaska Peninsula is a peninsula extending about to the southwest from the mainland of Alaska and ending in the Aleutian Islands. The peninsula separates the Pacific Ocean from Bristol Bay, an arm of the Bering Sea....

 in southern Alaska

Alaska

Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

, located within Katmai National Park and Preserve

Katmai National Park and Preserve

Katmai National Park and Preserve is a United States National Park in southern Alaska, notable for the Valley of Ten Thousand Smokes and for its brown bears. The park covers , being roughly the size of Wales. Most of this is a designated wilderness area, including of the park...

. It is about 6.3 miles (10 km) in diameter with a central lake-filled caldera

Caldera

A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

 about 3 by 2 mi (4.5 by 3 km) in area, formed during the Novarupta

Novarupta

Novarupta, meaning "new eruption", is a volcano located on the Alaska Peninsula in Katmai National Park and Preserve, about southwest of Anchorage. Formed in 1912 during the largest volcanic eruption of the 20th century, Novarupta released 30 times the volume of magma as the 1980 eruption of...

 eruption of 1912. The caldera rim reaches a maximum elevation of 6716 feet (2,047 m). In 1975 the surface of the crater lake

Crater lake

A crater lake is a lake that forms in a volcanic crater or caldera, such as a maar; less commonly and with lower association to the term a lake may form in an impact crater caused by a meteorite. Sometimes lakes which form inside calderas are called caldera lakes, but often this distinction is not...

 was at an elevation of about 4220 feet (1,286 m), and the estimated elevation of the caldera floor is about 3400 ft (1,036.3 m).