Basalt of Gertrude Creek
Start: 501950 yBP ± 14000 Years [1]
Event Type: Explosive
- Cone [3]
Description: From Hildreth and others (2004): "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 (Fig. 1 [in original text]), near the trace of the Bruin Bay Fault (Riehle and others 1993). 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 frost-disrupted apron of blocks and slabs of dark-gray, massive to finely vesicular, basaltic lava. The subalkaline high-alumina basalt (49.8% SiO2, 6.8% MgO) contains abundant small phenocrysts of olivine, cpx, and plagioclase, and inclusions (in olivine) of Cr-spinel. A slab of holocrystalline lava near the north rim gave a 40 Ar/39Ar plateau age of 500+/-14 ka (Hildreth and others 2003b)."
References Cited
[1] Blue Mountain and The Gas Rocks: rear-arc dome clusters on the Alaska Peninsula, 2007
Hildreth, Wes, Fierstein, Judy, and Calvert, A.T., 2007, Blue Mountain and The Gas Rocks; rear-arc dome clusters on the Alaska Peninsula: in Haeussler, P.J., and Galloway, J.P., eds., Studies by the U.S. Geological Survey in Alaska, U.S. Geological Survey Professional Paper 1739-A, 27 p., available at http://pubs.usgs.gov/pp/pp1739/a/ .[2] Rear-arc vs. arc-front volcanoes in the Katmai reach of the Alaska Peninsula: a critical apprasial of across-arc compositional variation, 2004
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.[3] Age and tectonic significance of volcanic rocks on St. Matthew Island, Bering Sea, Alaska, 1975
Patton, W. W. Jr., Lanphere, M. A., Miller, T. P., and Scott, R. A., 1975, Age and tectonic significance of volcanic rocks on St. Matthew Island, Bering Sea, Alaska: U.S. Geological Survey Open-File Report 75-0150, 18 p.Complete Eruption References
Blue Mountain and The Gas Rocks: rear-arc dome clusters on the Alaska Peninsula, 2007
Hildreth, Wes, Fierstein, Judy, and Calvert, A.T., 2007, Blue Mountain and The Gas Rocks; rear-arc dome clusters on the Alaska Peninsula: in Haeussler, P.J., and Galloway, J.P., eds., Studies by the U.S. Geological Survey in Alaska, U.S. Geological Survey Professional Paper 1739-A, 27 p., available at http://pubs.usgs.gov/pp/pp1739/a/ .
Rear-arc vs. arc-front volcanoes in the Katmai reach of the Alaska Peninsula: a critical apprasial of across-arc compositional variation, 2004
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.
Quaternary geologic map of the Mount Katmai quadrangle and adjacent parts of the Naknek and Afognak quadrangles, Alaska, 1993
Riehle, J. R., and Detterman, R. L., 1993, Quaternary geologic map of the Mount Katmai quadrangle and adjacent parts of the Naknek and Afognak quadrangles, Alaska: U.S. Geological Survey Miscellaneous Investigations Series Map I 2032, unpaged, 1 sheet, scale 1:250,000.
