Kanatak 33 mi (53 km) SE Egegik 47 mi (75 km) NW King Salmon 49 mi (78 km) NW South Naknek 56 mi (90 km) NW Anchorage 309 mi (498 km) NE
DESCRIPTION
This feature is part of the Saddlehorn Creek Cluster of volcanoes, as defined by Hildreth and others (2004) [1]. From Hildreth and others (2004) [1]: "Basalt of Gertrude Creek makes up a 1-km-wide remnant of an ejecta cone and lava-flow apron that form a glacially smoothed domical swell about 5 km NE of Becharof Lake, near the trace of the Bruin Bay Fault [2]. Surviving outcrop has about 60 m of gentle relief and includes a 200-m-wide degraded crater now only 5 to 8 m deep, rimmed by brick-red scoria blocks and sheets of blobby agglutinate that are broken and frost-heaved into slabs. Outside the rim is a massive to finely vesicular, basaltic lava. The subalkaline high-alumina basalt (49.8% SiO2, 6.8% MgO) contains abundant small phenocrysts of olivine, clinopyroxene, and plagioclase, and inclusions (in olivine) of Cr-spinel. A slab of holocrystalline lava near the north rim gave a 40Ar/39Ar plateau age of 500 +/- 15 ka [3]."
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Hildreth, Wes, Fierstein, Judy, Siems, D. F., Budahn, J. R., and Ruiz, Joaquin, 2004, Rear-arc vs. arc-front volcanoes in the Katmai reach of the Alaska Peninsula: a critical apprasial of across-arc compositional variation: Contributions to Mineralogy and Petrology, v. 147, n. 3, p. 243-275.
Hildreth, Wes, Lanphere, M. A., and Fierstein, Judy, 2003, Geochronology and eruptive history of the Katmai volcanic cluster, Alaska Peninsula: Earth and Planetary Science Letters, v. 214, n. 1-2, p. 93-114.
