U.S. Geological Survey Open-File Report 01370
Areal Distribution, Thickness, Mass, Volume, and Grain Size of Tephra-Fall Deposits from the 1992 Eruptions of Crater Peak Vent, Mt. Spurr Volcano, Alaska
Robert G. McGimsey, Christina A. Neal, and Colleen M. Riley
|Oblique aerial view from the southeast of Mount Spurr volcano and Crater Peak flank vent, which is the site of all late Holocene and historical eruptive activity at this volcanic center. Photograph by Austin Post, September 4, 1996.|
The Crater Peak flank vent of Mount Spurr volcano erupted June 27, August 18, and September 1617, 1992. The three eruptions were similar in intensity (vulcanian to subplinian eruption columns reaching up to 14 km Above Sea Level) and duration (3.5 to 4.0 hours) and produced tephra-fall deposits (12, 14, 15x106 m3 Dense Rock Equivalent [DRE]) discernible up to 1,000 km downwind. The June 27 ash cloud traveled north over the rugged, ice- and snow-covered Alaska Range. The August 18 ash cloud was carried southeastward over Anchorage, across Prince William Sound, and down the southeastern shoreline of the Gulf of Alaska. The September 1617 ash plume was directed eastward over the Talkeetna and Wrangell mountains and into the Yukon Territory of Canada. Over 50 mass-per-unit-area (MPUA) samples were collected for each of the latter two fall deposits at distances ranging from about 2 km to 370 km downwind from the volcano. Only 10 (mostly proximal) samples were collected for the June fall deposit due to inaccessible terrain and funding constraints. MPUA data were plotted and contoured (isomass lines) to graphically display the distribution of each fall deposit. For the August and September eruptions, fallout was concentrated along a narrow (30 to 50 km wide) belt. The fallout was most concentrated (100,000 to greater than 250,000 g/m2) within about 80 km of the volcano. Secondary maxima occur at 200 km (2,620 g/m2) and 300 km (4,659 g/m2), respectively, down axis for the August and September deposits. The maxima contain bimodal grain size distributions (with peaks at 88.4 and 22.1 microns) indicating aggregation within the ash cloud. Combined tephra-volume for the 1992 Mount Spurr eruptions (41x106 m3 DRE) is comparable to that (tephra-fall only) of the 198990 eruptions of nearby Redoubt volcano (3149x106 m3 DRE).
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Figure 8. Map showing areal distribution of the June 27, 1992, tephra-fall deposit (307 KB)
Figure 11. Map showing areal and mass distributions of the August 18, 1992, tephra-fall deposit (562 KB)
Figure 16. Map showing areal and mass distributions of the September 1617, 1992, tephra-fall deposit. (673 KB)
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