The Katmai volcanic cluster on the Alaska Peninsula was first brought to national and international attention by the great eruption of June 1912. Although many wilderness travellers and one geological party had previously crossed remote Katmai Pass on foot, the National Geographic Society expeditions of 1915-19 first mapped and reconnoitered the volcanic terrain surrounding the pass in the course of investigating the effects of the 1912 eruption. The explosive ejection of rhyolitic, dacitic, and andesitic magma at Novarupta over an interval of about 60 hr on June 6-8, 1912, was the world's most voluminous 20th century eruption. At least 17 km³ of fall deposits and 11±3 km³ of ash-flow tuff (ignimbrite) were produced, representing a magma volume of about 13 km³. This volume is larger than that erupted by Krakatau (Indonesia) in 1883 and is known to have been exceeded by only four eruptions in the last 1,000 years. Syneruptive caldera collapse at Mount Katmai, 10 km east of the eruption site, and displacements elsewhere in the magmatic plumbing system generated 14 earthquakes in the magnitude range Ms 6 to 7 (extraordinarily energetic for volcanic seismicity) and as many as 100 greater than Ms 5.

Within 15 km of the 1912 vent at Novarupta, five andesite-dacite stratovolcanoes have erupted during the Holocene and remain fumarolically active today: Mount Katmai, Trident Volcano, Mount Mageik, Mount Martin, and Mount Griggs. The first four are virtually contiguous along a N.65°E. trend that defines the Quaternary volcanic front, whereas rear-arc Mount Griggs is centered 12 km behind the front. The frontal trend additionally includes Snowy Mountain, likewise active in the Holocene, which consists of a pair of andesite-dacite cones 10-15 km northeast of Mount Katmai; and the extinct Alagogshak Volcano, an andesite-dacite Pleistocene edifice centered 3 km southwest of Mount Martin. We have recently mapped and studied all of the volcanoes named, some of which are compound multi-vent edifices, as portrayed on the geologic map.