Thursday, 22 June 2017

105th Anniversary of Largest Volcanic Eruption of 20th Century

The Novarupta-Katmai Eruption

I'm 5 years late with this but it is still worth reading about! HERE is my starting point. There is a bit more HERE. The USGS report (278 pages) is HERE and is very good! And a set of 66 photos, taken this year, can be found HERE. The captions of the photos helps make sense of them.

The Novarupta or Katmai eruption of 1912 was huge - ejecting almost 30 cubic kilometers of ash and debris into the atmosphere or along the ground as pyroclastic flows. That represents ~13 cubic kilometers of magma (once you correct for all the air in ash) erupted over the course of ~60 hours. That is a rate of nearly 220 million cubic meters per hour, which is roughly 520 million tonnes per hour.

The Valley of Ten Thousand Smokes - with a name like that it is irresistible!

Simplified geologic map of Valley of Ten Thousand Smokes (VTTS) and volcanoes of the Katmai cluster. Contour interval 500 feet (152 m). From hachured vent depression around Novarupta lava dome (N, black), Episode I ignimbrite (tan) extends northwest 20 km along VTTS, as well as across Katmai Pass (KP) for 10 km down Mageik Creek on Pacific slope. Knife Creek Glaciers (blue pattern) are numbered 1-5; other glaciers are omitted for clarity. Alagogshak volcano (A), long extinct, is indicated only by its eroded crater. Mount Mageik consists of four overlapping centers (in shades of blue); only the youngest and easternmost center (for which individual lava flows are indicated) is Holocene. Mount Martin, entirely Holocene, consists of small fragmental summit cone and several overlapping coulees. Trident group consists of three Pleistocene cones, East Trident (Te), Trident I (TI), and West Trident (Tw), as well as historical Southwest Trident (Tsw) lavas and fragmental cone of 1953–1974; several peripheral Pleistocene lava domes, comagmatic with Trident, include Mount Cerberus (MC) and Falling Mountain (FM). Mount Katmai consists of two overlapping centers, Northeast Katmai (Ke) and Southwest Katmai (Kw), both truncated by 1912 collapse of hachured Katmai caldera, which is now partly filled by lake. Five youngest eruptive units of Mount Katmai are numbered (1–5) and discussed in chapter 12: 1, leveed dacite lava flows; 2, south-rim rhyodacite lavas; 3, zoned scoria fall atop unit 2; 4, dacite agglutinate sheet on caldera rim and correlative scoria-flow deposit at Knife Creek; and 5, Horseshoe Island dacite dome. Remnants of 22.5-ka plinian rhyodacite pumice-fall deposits (and ignimbrite) in Windy and Mageik Creeks (sites indicated by red X) are related to most evolved lava of unit 2. Products of Mount Griggs are subdivided by age into older (o, middle Pleistocene), middle (m, late Pleistocene), and younger (y, postglacial) exposures. Holocene debris-avalanche deposits are in bright yellow; those emplaced in 1912 are labelled: KC, Katmai Canyon landslide; KRdf, Katmai River pumiceous debris flow; ML, Mageik Landslide; NM, Noisy Mountain landslide. Uncolored basement rocks are Jurassic Naknek Formation or Tertiary porphyritic intrusions. Miscellaneous features: BM, Baked Mountain; BR, Broken Mountain; FL, site of Fissure Lake; GF, Griggs Fork of Knife Creek; JF, Juhle Fork of Knife Creek; T, Turtle; WR, Whiskey Ridge; hut, Baked Mountain Hut, research shelter; Island Camp and Camp IV were way stations between Katmai Bay and VTTS.

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