Description

From Hildreth and others (2007) ^[1] : "Blue Mountain consists of 13 dacite domes in a cluster ~6 km long, similar in extent and configuration to what the Kaguyak dome cluster, 200 km to the northeast, had been before its mid-Holocene caldera-forming eruption ^[1] . Three of the Blue Mountain domes form a separate group, ~1 km north of the main cluster, although they are chemically and mineralogically similar to the rest. The two large central domes (Domes 1776, 1700) abut each other and together form the main ridge of the Blue Mountain edifice. From each dome issued stubby 200-m-thick flow lobes that form three southerly trending ridges. Eight satellite domes are contiguous with the central ridge, four at its northwest end and four at its southeast end. The smallest domes have as little as 100m of relief, and the four largest stand >300 m above the surrounding apron of glacial and colluvial deposits."
"A single 40Ar/39Ar age was determined for Blue Mountain, on a groundmass concentrate of dacite sample U-19 from the south-trending ridge of summit Dome 1776. Its weighted-mean plateau age is 632+/-7 ka, 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 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."