Location map for the Valley of Ten Thousand Smokes, showing the
120-square-kilometer extent of the 1912 ash-flow sheet and the five composite
volcanoes nearby. (Mounts Griggs, Katmai, Trident, Mageik, and Martin all have
active fumaroles and have undergone Holocene eruptions.) One ash flow
penetrated Katmai Pass and ponded up to 25 meters thick in Mageik Creek on the
Pacific slope, but 99 percent of the ash-flow volume moved northwestward to form
the Valley of Ten Thousand Smokes. Its thickness is not known in the upper
Valley, but may be as great as 250 meters; it thins to
around 30 meters just above the moraine that partially blocked its path near
Three Forks and to less than 10 meters at its now-eroded snout on the Ukak
River. Mount Cerberus and Falling Mountain are Holocene dacite domes adjacent
to the 1912 vent at Novarupta. Baked Mountain and Broken Mountain consist of
Jurassic sedimentary rocks, which, like Falling Mountain, were truncated by the
eruption and subsidence in the Novarupta caldera.
The Katmai River debris flow is a
deposit of remobilized ejecta that debouched from a single narrow gorge fed
from the glaciated south slope of Mount Katmai, which was in the sector of
heaviest tephra fall.
The Valley of Ten Thousand Smokes constriction is where the ash flows left
marginal veneers and constructional hills of tuff.
Part of the Mageik Creek
ash-flow lobe is now covered by the 1953-1960 lava flows from Trident.
-- Excerpt from: Hildreth, 1983, The Compositionally Zoned Eruption of 1912 in the
Valley of Ten Thousand Smokes, Katmai National Park, Alaska:
Journal of Volcanological and Geothermal Research, v.18., p.1-56.
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