Source of the Glencoe Ignimbrites

Abstract

IGNIMBRITES^1,2 are a characteristic component of the typically post-orogenic basalt–andesite–rhyolite volcanic association. These pyroclastic deposits are now generally accepted² as having been produced by eruptions of nuées ardentes in which solid particles, both rock and crystal fragments, glass shards and pumice fragments are suspended by turbulent flow in gas, probably derived in part from the glass shard and pumice material itself³. Such a fluidized system⁴ forms the basal avalanche of a nuée ardente. While associated with several types of volcanic structure, most of those ignimbrite deposits with a volume greater than 10 km³, and the source of which is known, have been related either to calderas or, for the larger volume (> 1,000 km³) deposits, to volcano-tectonic depressions³. No intrusive igneous body has yet been recognized which, on clear-cut evidence, served as a feeder for extensive ignimbrite flows³.