Event Name : Blue Mtn Domes
|Start: 632000 (± 7000 Years) || Years BP Ar/Ar || |
|Lava flow: ||
|Lava dome: ||
|Eruption Product: || dacite ||
From Hildreth and others (2007): "The main central dome of Blue Mountain yields an 40Ar/39 Ar age of 632+/-7 ka..."
"A single 40 Ar/39 Ar age was determined for Blue Mountain, on a groundmass concentrate of dacite sample U-19 (table 1 [in original text]) from the south-trending ridge of summit Dome 1776 (figs. 3A, 6 [in original text]). Its weighted-mean plateau age is 632+/-7 ka (fig. 9; table 2 [in original text]), categorically middle Pleistocene and about 25 times older than the lithologically and compositionally similar domes at The Gas Rocks. At Blue Mountain, the several satellitic domes surrounding dated Dome 1776 (fig. 3 [in original text]) are unlikely to differ much in age, although the noncontiguous northern group might conceivably do so. We discerned no significant differences in degree of erosion, and the chemical and petrographic similarities of nearly all the domes in both groups suggest no basis for inferring an exceptionally protracted eruptive sequence."
"Present-day volumes of the Blue Mountain domes have been estimated, recognizing that at least 20 percent of the initial lavas, and a completely unknown pyroclastic volume, have been glacially eroded away. The noncontiguous northern cluster of three small domes totals ~60 million m cubed in volume. The central mass of the main cluster, including Domes 1776 and 1700 (fig. 3A [in original text]), totals ~500 million m cubed in volume, and its satellites’ volumes are estimated as follows: easterly Dome 1572, ~180 million m cubed; the three small southerly domes, 35 to 45 million m cubed each; westerly Dome 1600, ~160 million m cubed; and crystal-poor northerly Dome 1200, ~35 million m cubed. These estimates provide a total surviving volume of 1.05 km cubed of Blue Mountain dacite."