Mount Katmai

This article is about Katmai, the volcano. For other meanings see Katmai (disambiguation).

Mount Katmai
Mount Katmai and its crater lake in September 1980.
Elevation	6,716 ft (2,047 m)
Location
Location	Katmai National Park and Preserve, Alaska, USA
Range	Aleutian Range
Coordinates	58°16′43.0″N 154°57′24.9″W / 58.27861°N 154.956917°W / 58.27861; -154.956917
Topo map	USGS Mount Katmai B-3
Geology
Type	Stratovolcano
Volcanic arc/belt	Aleutian Arc
Last eruption	1912[1]
Climbing
Easiest route	basic snow/ice climb

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 6.3 miles (10 km) 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 6,716 feet (2,047 m). In 1975 the surface of the crater lake was at an elevation of about 4,220 feet (1,286 m), and the estimated elevation of the caldera floor is about 3,400 ft (1,040 m). The mountain is located in Kodiak Island Borough, very close to its border with Lake and Peninsula Borough.

Geology

Mount Katmai is one of five vents encircling the Novarupta volcano, source of the VEI 6 eruption and associated voluminous pyroclastic flows in 1912. The volcano has caused ten known fatalities due to gas exposure. Katmai consists chiefly of lava flows, pyroclastic rocks, and non-welded to agglutinated air fall. The Quaternary volcanic rocks at Katmai and adjacent cones are less than 5,000 ft (1,500 m) thick. Much of the volcano is mantled by snow and ice and several valley glaciers radiate out from the flanks and three glaciers.

Katmai volcano is built on the sedimentary rocks of the Naknek Formation of Late Jurassic age, which are exposed just west of the caldera rim at an elevation of about 5,000 feet (1,520 m), as well as north and southeast of the crater. Sedimentary rocks have been reported at an elevation of over 6,000 feet (1,830 m) in the west wall of the caldera and near the bottom of the eastern wall near 3,400 ft (1,040 m).

Map showing volcanoes of Alaska Peninsula.

Volcanic activity

Little is known about the historical activity of Katmai volcano before the great 1912 eruption. Early U.S. Coast and Geodetic Survey maps suggest a pre-caldera summit elevation of about 7,500 ft (2,300 m), and local villagers reported in 1898 that one of the volcanoes in the general area "smoked" occasionally.

On June 6-9th, 1912, the most spectacular Alaskan eruption in recorded history and one of the two largest eruptions in the world in the twentieth century (the other being Mount Pinatubo in 1991) resulted in the formation of a large summit caldera at Katmai volcano. The over 60-hour-long eruption actually took place at a vent about 6 mi (10 km) to the west of Mount Katmai (at theNovarupta Volcano) from which an estimated 30–35 km³ of ash flows and tephra were ejected rather than at Mount Katmai itself.The withdrawal of magma beneath Katmai resulted in the collapse of the summit area, forming the caldera. Following the subsidence, a small dacitic lava dome known as Horseshoe Island was emplaced on the floor of the caldera; this is the only juvenile material erupted from Katmai caldera during the historical eruption. It was visible at the time of the expedition in 1916, but has since been submerged by the crater lake. Still, the eruption from Katmai had a VEI of 3, and possibly involved phreatic eruptions.^[2]

In 1919, geologists noted a lake covering a large part of the caldera floor, but by 1923 the lake was gone and numerous fumaroles, mud pots, and a large mud geyser had replaced it. The lake has since refilled to a depth of over 800 ft (240 m). Small glaciers have also formed on a bench within the caldera beside the lake.

See also

• List of volcanoes in the United States of America

Sources

1. ^ There are no credible reports of eruptions at Katmai since 1912
2. ^ http://www.volcano.si.edu/world/volcano.cfm?vnum=1102-17-&volpage=synsub

• "Katmai". Global Volcanism Program, Smithsonian Institution. http://www.volcano.si.edu/world/volcano.cfm?vnum=1102-17-. Retrieved 2009-01-01. 
• Alaska Volcano Observatory: Katmai
• Wood, Charles A.; Jürgen Kienle, eds. (1990). Volcanoes of North America. Cambridge University Press. pp. 354 pp. ISBN 0-521-43811-X. 

Further reading

• Hildreth, W., J. Fierstein, and J.E. Robinson. (2003). Geologic map of the Katmai Volcanic Cluster, Katmai National Park, Alaska [Geologic Investigations Series Map I-2778]. Reston, VA: U.S. Department of the Interior, U.S. Geological Survey.