|Start:||December 1912 ||Observed|
|Debris-avalanche, volcanic avalanche, or landslide: ||
|Eruption Type:||Not an eruption.|
Mount Mageik experienced a large landslide during the 1912 eruption of Novarupta and Mount Katmai. That deposit is described by Hildreth and others (2000) as follows: "The youngest of the three [debris avalanches] was emplaced in Martin Creek on 6 June 1912 during the eruption at Novarupta, presumably triggered by the seismicity accompanying caldera collapse at Mount Katmai (Hildreth, 1991). The deposit is overlain by most of the 1912 fallout but not by the earliest layers (Fierstein and Hildreth, 1992). Described in detail by Griggs (1920, 1922), who called it 'the Mageik Landslide', the 1912 avalanche deposit extends 6 km southeast of its headwall and overruns the medial part of the more subdued larger deposit [see fig. 2 in original text]. Consisting predominantly of angular blocks of fresh dacite, it broke loose from a steep face glacially carved into a stack of dacite lava flows that make up the southeast planeze of the Southwest Summit edifice, leaving behind a 120-m-high scarp with a rim at the 3,000-ft level. The deposit has millions of angular blocks larger than 1 m (mostly dacite, plus sparse basement sandstone), contains dacite slabs as long as 20 m, and supports hummocks as high as 20 m. It locally left superelevated trimlines and ponded drainages along its abrupt margins. About 800 m wide proximally, the deposit spreads out to 1.5 km medially and covers about 6 square km. Griggs (1920) estimated its area as more than 10 square km, but this included parts of the subjacent older deposit. Although thickness (5-30 m) is hard to average, the volume is probably in the range 0.05-0.1 cubic km." While impressive, this landslide does not represent a volcanic eruption.
Powers (1958) erroneously (see note by Fierstein and Hildreth, 2001, below) reported an ash eruption at Mount Mageik in 1912.
From Fierstein and Hildreth (2001): "Not a single one of the 20th century tephra eruptions of Mageik listed in Simkin and Siebert's (1994) "Volcanoes of the World" seems plausible. Configuration of the crater has not changed since it was first photographed in 1923; there are no juvenile ejecta in the crater or around its rim (except a scattering of 1912 pumice clasts from Novarupta); and the only late Holocene fall deposits on the or near the lower flanks of Mageik are the Novarupta pumice falls of 1912 and the black Trident ash of 1953."