Postglacial eruptive history, geochemistry, and recent seismicity of Aniakchak volcano, Alaska Peninsula

Abstract

This page left intentionally blank. flows or surges probably would be limited to within the caldera, but ash fall could affect extensive regions downwind. Another voluminous eruption, such as Aniakchak II, is considered unlikely in the near future. Although the InSAR study indicates subsidence, the possibility that evolved magma may be accumulating beneath the central part of the caldera is worthy of consideration when interpreting future monitoring data. Pleistocene composite volcano that consists of basaltic andesite to dacite lava flows and fragmental rocks. Early in postglacial (Holocene) time, a voluminous eruption (Aniakchak I; Miller and Smith, 1987) left geochemically distinctive andesite pyroclastic-flow deposits (ignimbrite) in valleys and on the flanks of the edifice. This event was followed by dacite eruptions, at least one of which produced a widespread pumice fall deposit ca. 7,000 yr B.P. (VanderHoek, 2009). Unless otherwise noted, ages reported here are given in radiocarbon years before present (yr B.P., "present" being 1950 C.E.). This chronicle begins with a brief overview of Pleistocene ancestral Aniakchak and an account of the state of knowledge of postglacial, precaldera volcanism.

Late Pleistocene and Holocene tephrostratigraphy of interior Alaska and Yukon: Key beds and chronologies over the past 30,000 years

“…Aniakchak volcano has been very active throughout the Holocene, with two caldera forming events and dozens of smaller explosive eruptions identified from proximal stratigraphic and geochemical evidence Bacon et al, 2014). Although these tephra have yet to be reported within the study area of this report, there is potential for long-distance transport and deposition.…”

“…The zones outlined on Fig. 7 show the geochemical range of major element data produced from whole rock samples of Aniakchak CFE I and II (Bacon et al, 2014). Although these data are not directly comparable to EPMA glass data due to the incorporation of minerals, it does show that the relations between Tephra D and Aniakchak CFE II glass data (UA 1602) mirror that between the whole rock CFE I and II data for multiple elements.…”

“…Aniakchak is one of the most active volcanic sites observed in the eastern Aleutian-Arc with more than forty estimated explosive eruptions during the Holocene, including two caldera-forming events (Riehle et al, 1999;Neal et al, 2001;Bacon et al, 2014). The majority of the resulting deposits lie north and northeast of the vent, following prevailing winds .…”

“…mineralogy), would lend support to the argument for multiple events. For example, recent work examining cryptotephra in marine sediments in the Chukchi Sea claims to recreate this stratigraphy, which combined with evidence of a 400 cal yr BP eruption at Aniakchak, suggests all three may represent separate events (Browne et al, 2003;Bacon et al, 2014;Ponomareva et al, 2014). In addition to these three tephra, there are multiple samples that show a strong similarity to either the dominant rhyolite glass population of the Ankaichak CFE II (e.g.…”

Geomorphic consequences of volcanic eruptions in Alaska: A review

“…All calderas of late Holocene age in Alaska have experienced significant postcaldera volcanism, ranging from mild, effusive, lava-producing events, to more explosive eruptions involving silicic magmas (Bacon et al, 2014). As a result of this activity, a diverse assemblage of cones, flows, and vents characterizes the floors of most Alaska calderas.…”