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22-554: Mount Katmai is one of five vents encircling the Novarupta volcano, source of the VEI 6 eruption and associated voluminous pyroclastic flows in 1912. 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

44-515: A VEI of 3, and possibly involved phreatic eruptions . Following the eruption, thousands of fumaroles vented steam from the ash, creating the Valley of Ten Thousand Smokes . In 1919, geologists noted a lake covering a large part of the caldera floor. 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 formed on

66-606: A VEI of 8. There have been at least 10 eruptions of VEI-7 in the last 11,700 years. There are also 58 Plinian eruptions, and 13 caldera-forming eruptions, of large, but unknown magnitudes. By 2010, the Global Volcanism Program of the Smithsonian Institution had cataloged the assignment of a VEI for 7,742 volcanic eruptions that occurred during the Holocene (the last 11,700 years) which account for about 75% of

88-543: A bench within the caldera beside the lake. Pumice still floats on Naknek Lake nearby. Novarupta Novarupta is a volcano that was formed in 1912, located on the Alaska Peninsula on a slope of Trident Volcano in Katmai National Park and Preserve , about 290 miles (470 km) southwest of Anchorage . Formed during the largest volcanic eruption of the 20th century, Novarupta released 30 times

110-603: A cloud of suffocating gas and ash that blackened the sky. The inhabitants of the town of Kodiak , with ash falling on them, were led to the United States Revenue Cutter Service revenue cutter USRC  Manning where they sheltered and were cared for by the crew, remaining in the harbor because Captain Perry determined "an attempt to leave here would be unwise" because the eruption made navigation dangerous. The withdrawal of magma beneath Katmai resulted in

132-399: A magnitude of 8. A value of 0 is given for non-explosive eruptions, defined as less than 10,000 m (350,000 cu ft) of tephra ejected; and 8 representing a supervolcanic eruption that can eject 1.0 × 10  m (240 cubic miles) of tephra and have a cloud column height of over 20 km (66,000 ft). The scale is logarithmic, with each interval on the scale representing

154-461: A tenfold increase in observed ejecta criteria, with the exception of between VEI-0, VEI-1 and VEI-2. With indices running from 0 to 8, the VEI associated with an eruption is dependent on how much volcanic material is thrown out, to what height, and how long the eruption lasts. The scale is logarithmic from VEI-2 and up; an increase of 1 index indicates an eruption that is 10 times as powerful. As such, there

176-448: Is a discontinuity in the definition of the VEI between indices 1 and 2. The lower border of the volume of ejecta jumps by a factor of one hundred, from 10,000 to 1,000,000 m (350,000 to 35,310,000 cu ft), while the factor is ten between all higher indices. In the following table, the frequency of each VEI indicates the approximate frequency of new eruptions of that VEI or higher. About 40 eruptions of VEI-8 magnitude within

198-495: Is a scale used to measure the size of explosive volcanic eruptions. It was devised by Christopher G. Newhall of the United States Geological Survey and Stephen Self in 1982. Volume of products, eruption cloud height, and qualitative observations (using terms ranging from "gentle" to "mega-colossal") are used to determine the explosivity value. The scale is open-ended with the largest eruptions in history given

220-417: Is known about the historical activity of Katmai volcano before the great 1912 eruption. Early United States 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. Between June 6 and 9, 1912, the most spectacular Alaskan eruption in recorded history and

242-607: Is located on the Alaska Peninsula, across from Kodiak Island, with headquarters in nearby King Salmon , about 290 mi (470 km) southwest of Anchorage. The area was originally designated a National Monument in 1918 to protect the area around the 1912 eruption of Novarupta and the 40-square-mile (104 km ), 100-to-700-foot (30 to 210 m) deep, pyroclastic flow of the Valley of Ten Thousand Smokes. Volcanic explosivity index The volcanic explosivity index ( VEI )

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264-496: The 1883 eruption of Krakatoa (4.8 cu mi or 20 km of tephra). The Novarupta eruption occurred about 6.59 mi (10.61 km) from the peak of Mount Katmai Volcano and 4,000 ft (1,200 m) below the post-eruption Mount Katmai summit. During the eruption a large quantity of magma erupted from beneath the Mount Katmai area, resulting in the formation of a 1.2-mile (2 km) wide, funnel-shaped vent and

286-479: The 20th century's largest measured volcanic eruption formed a large summit caldera at Katmai volcano. The eruption happened at a vent about 6 mi (10 km) to the west of Mount Katmai (at the Novarupta Volcano ). During over 60 hours, the volcano erupted an estimated 6.7 cu mi (28 km) of ash flows and tephra representing 3.1 cu mi (13 km) of magma volume. The eruption produced

308-629: The 20th century, only the 1991 eruption of Mount Pinatubo in the Philippines and the 1902 eruption of Santa María in Guatemala were of comparable magnitude; Mount Pinatubo ejected 2.6 cubic miles (11 km ) of tephra , and Santa María just slightly less. At least two larger eruptions occurred in the Dutch East Indies (now Indonesia ) during the 19th century: the 1815 eruption of Tambora (36 cu mi or 150 km of tephra) and

330-474: The collapse of Mount Katmai's summit, creating a 2,000-foot (600 m) deep, 1.9 by 2.5 mi (3 by 4 km) caldera . The eruption ended with the extrusion of a lava dome of rhyolite that plugged the vent. The 295-foot (90 m) high and 1,180-foot (360 m) wide dome it created forms what is now referred to as Novarupta. Despite the magnitude of the eruption, no deaths directly resulted. Eyewitness accounts from people located downwind in

352-413: 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

374-507: The eruption formed the Valley of Ten Thousand Smokes , named by botanist Robert F. Griggs , who explored the volcano's aftermath for the National Geographic Society in 1916. The eruption that formed the Valley of Ten Thousand Smokes is one of the few in recorded history to have produced welded tuff , producing numerous fumaroles that persisted for 15 years. Established as a National Park & Preserve in 1980, Katmai

396-517: The flanks. 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). Little

418-525: The last 132 million years ( Mya ) have been identified, of which 30 occurred in the past 36 million years. Considering the estimated frequency is on the order of once in 50,000 years, there are likely many such eruptions in the last 132 Mya that are not yet known. Based on incomplete statistics, other authors assume that at least 60 VEI-8 eruptions have been identified. The most recent is Lake Taupō 's Oruanui eruption , more than 27,000 years ago, which means that there have not been any Holocene eruptions with

440-552: The path of a thick ash cloud described the gradual lowering of visibility to next to nothing. Ash threatened to contaminate drinking water and destroyed food resources, but the Alaska Natives were aided in their survival by traditional knowledge passed down through generations from previous eruptions. However, the Native villages experiencing the heaviest ash falls were abandoned and the inhabitants relocated. Pyroclastic flows from

462-513: The total known eruptions during the Holocene. Of these 7,742 eruptions, about 49% have a VEI of 2 or lower, and 90% have a VEI of 3 or lower. Under the VEI, ash , lava , lava bombs , and ignimbrite are all treated alike. Density and vesicularity (gas bubbling) of the volcanic products in question is not taken into account. In contrast, the DRE ( dense-rock equivalent ) is sometimes calculated to give

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484-652: The volume of magma of the 1980 eruption of Mount St. Helens . The 1912 eruption that formed Novarupta was the largest to occur during the 20th century. It began on June 6, 1912, and culminated in a series of violent eruptions. Rated a 6 on the volcanic explosivity index , the 60-hour-long eruption expelled 3.1 to 3.6 cubic miles (13 to 15 km ) of ash, thirty times as much as the 1980 eruption of Mount St. Helens. The erupted magma of rhyolite , dacite , and andesite resulted in more than 4.1 cubic miles (17 km ) of air fall tuff and approximately 2.6 cubic miles (11 km ) of pyroclastic ash-flow tuff. During

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