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Gas Rocks, the reported activity



Event Name : Gas Rocks North Point Dome

Start: 25700 (± 1400 Years) Years BP Ar/Ar

Lava flow: BibCard
Lava dome: BibCard
Eruption Type:Explosive
Eruption Product: dacite BibCard

Description: From Hildreth and others (2006): "Separated by a linear trough from the much higher adjacent dome, North Point Dome appears to be an independent extrusion rather than a thick coulee issuing from its neighbor, an inference supported by its slightly more evolved composition (table 1 [in original text])."

"In common with a lava flow associated with North Point Dome (fig. 11 [in original text]), these flows have been truncated and thinned by the ice that flowed northwestward down the lake basin."

"Little or no glassy or pumiceous carapace remains on any of the domes, which were all completely submerged and scoured by glacial ice."

Hildreth and others (2006) estimate a volume of 0.5 million m cubed for North Point Dome.

"We [Hildreth and others, 2006] determined two 40Ar/39Ar ages on groundmass concentrates from samples of The Gas Rocks dacite (fig. 9; table 2 [in original text]). Sample U-1, from the small North Point Dome (fig. 3B [in original text]), yielded a weighted-mean plateau age of 25.7+/-1.4 ka, and sample U-2, from Dome 600, 23.3+/-1.2 ka. At their extremes, the two error envelopes just overlap, although nothing on the ground is known to contradict a younger age for the larger dome. Because of their petrographic and compositional similarity, it cannot be excluded that the three domes are essentially contemporaneous, plausibly fed by a common dike, the northwesterly strike of which would be similar to the present-day plate-convergence direction (which might in turn influence the direction of maximum horizontal compression)."

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