Summit pumice; loose accumulation of light-colored pumice, ranging in size from lapilli to blocks as much as 50 cm in diameter. Scattered throughout these tephra deposits, and locally abundant, are angular to subangular clasts of a variety of volcanic rocks, chiefly dark-colored, porphyritic and aphyric andesitic lava, and an occasional block of granitic rock and chlorite-rich amygdaloidal lava.The lithic fragments are similar in size to the pumice fragments and are interpreted to be rock ripped from the vent conduit walls during the explosive eruption(s). Also scattered throughout the tephra are clasts of yellow-orange pumice and lithics that apparently have been hydrothermally altered. Underlying this loose surface layer of pumice and lithic debris is a frozen zone of bedded tephra, consisting of pumice lapilli and blocks and exotic rock fragments disseminated in an ash matrix. White River Ash.
Mount Churchill, Alaska: source of the late Holocene White River Ash