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Makushin reported activity

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EVENT SPECIFIC INFORMATION

Event Name : Makushin CFE I

Start: 8790 Years BP C-14 (raw)

Tephrafall: BibCard
Pyroclastic flow, surge, or nuee ardente: BibCard BibCard
Caldera/crater: BibCard BibCard BibCard BibCard BibCard
Eruption Type:Explosive
Eruption Product: andesite BibCard
MaxVEI: 5 BibCard
Othermafic

Description: From Beget and others (2000): "The oldest deposits of Makushin Volcano that post-date the last ice age record a series of very large eruptions, culminating in the development of a summit caldera (fig. 4 [in original text]). These eruptions began about 8,400 to 8,800 years ago, when a large debris avalanche occurred on the north flank of the volcano and traveled at least 10 kilometers to the coast. On the basis of bathymetry, this avalanche deposit may extend an additional 3 to 5 kilometers off-shore. The upper part of the avalanche deposit is gradational into very coarse grained surge deposits that record a lateral blast apparently coincident with the debris avalanche."

From Bean (1999): "Two early Holocene "caldera forming" eruptive events, dated at 8050 yr B.P. and ca. 8790 yr B.P. respectively, generated the vast bulk of pyroclastic debris which fill valleys proximal to the volcano. Total erupted volume for early Holocene unconsolidated deposits approaches 10 km 3. The eruptions produced very mobile pyroclastic flows that traveled as far as Dutch Harbor (25 km away) where they buried an ancient Native American culture in more than 30 cm of hot ash and rock fragments."

"A black sintered scoria deposit forms a resistant cap approximately two to four meters thick on lava flows and flat surfaces up to 1000-1500 m elevation on the east and northeast flanks of Makushin Volcano (Fig. 4.23 [in original text]). This unit can be traced to the Lava Ramp where it is not sintered and appears as a scoria fall or flow deposit, and to fans in Makushin Valley where it forms a very resistant sintered unit containing fossil fumaroles. Two radiocarbon samples taken from under this unit have been dated at 8730 and 8710 14 C yr B.P. This black sintered deposit is also present in the summit caldera (Fig 4.23 [in original text]) where it is well exposed at several locations along the eastern caldera rim. The scoria unit here unconformably overlies approximately fifty meters of dipping pink to tan coarse to fine surge deposits and breccias that were most likely deposited during the early phase of the same eruption. The dipping surges are stratigraphically correlated with base surges in Makushin Valley."

"The unit mapped as pyroclastic lag deposits are remnants of pyroclastic valley filling flow deposits. Generally only the highly resistant lower flow unit, a scoria agglutinate to sintered ignimbrite flow unit is still intact, the less resistant overlying members having weathered away."



The Global database on large magnitude explosive volcanic eruptions (LaMEVE; 2017) reports a magnitude of 6, bulk eruptive volume of 7.5 cubic km and a dense rock equivalent eruptive volume of 3.0 cubic km for the eruption.

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Page modified: March 30, 2017 14:36
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