Geology of Umnak and Bogoslof Islands, Aleutian Islands, Alaska

Linking Magma Storage and Ascent to Eruption Volume and Composition at an Arc Caldera

“…Okmok also has six precaldera flank cones and 34 identified extracaldera vents, suggesting the presence of extensive magma transport to the volcano's flanks (Byers, 1959;Nakamura et al, 1977). The 16 extracaldera vents shown in Figure 3 are marked by basalt deposits (Byers, 1959), and all but three of these flank vents overlie the zone of negative anisotropy at 3 km depth. Thus, it is possible that primitive melts erupted at these vents migrated along dikes fed from the same mafic magma source as Cone A.…”

“…The causes of anisotropy are nuanced, however, and there exist trade-offs between melt aspect ratio, orientation, and melt segregation for a given level of anisotropy and V S reduction (Hammond & Kendall, 2016;Holtzman & Kendall, 2010;Lee et al, 2017). Despite these trade-offs, a horizontal, (Byers, 1959;Nakamura et al, 1977). Black circles show 2003-2009 seismicity within +/−500 m of the depth section (Ohlendorf et al, 2014).…”

“…In this study, we examine the volcanic system at Okmok caldera, Alaska. Okmok is a primarily mafic-intermediate arc shield volcano with a history of caldera-forming eruptions in the Pleistocene and Holocene (Beget et al, 2005;Byers, 1959;Larsen et al, 2007;Miller et al, 1998). It continues to erupt frequently in its postcollapse state and is one of the most active volcanoes in the Aleutian arc (Figure 1), having erupted at least 11 times in the last century (Beget et al, 2005).…”

“…Black triangles indicate Okmok's additional postcaldera cones as well as Mt Tulik and Idak. Black diamonds show minor vents(Byers, 1959;Nakamura et al, 1977). Black circles show 2003-2009 seismicity within +/−500 m of the depth section(Ohlendorf et al, 2014).…”

2021 Volcanic activity in Alaska and the Commonwealth of the Northern Mariana Islands—Summary of events and response of the Alaska Volcano Observatory

“…1). Mount Okmok is built on a base of Tertiary volcanic rocks and consists of three rock series: (1) older flows and pyroclastic beds of a pre-caldera shield complex, (2) pyroclastic deposits of two major caldera-forming eruptions, and (3) a post-caldera field of small, young cones and lava flows (Byers, 1959;Larsen and others, 2007). Mount Okmok has had 14 historical eruptions, which produced ash plumes that reached altitudes as high as ~49,000 ft (~15,000 m) ASL.…”