Description: The Driftwood Pumice is the youngest of three large explosive eruptions from Makushin volcano ^{[2] [1]} . The bulk of the deposit fell to the north and northeast of the summit of Makushin and is found in thicknesses of over a meter in Driftwood Valley and Waterfall Valley and ~2 cm in the Dutch Harbor area ^{[2] [4]} . The eruption produced ~0.3-1.6 km^3 bulk pumice and scoria tephra fall deposits (minimum estimate from Lerner and others [2018] ^[4] ). The yellow pumiceous deposit serves as a distinct marker unit within Makushin Holocene tephra deposits ^[2] . Radiocarbon dating by Bean (1999) ^[2] and Larsen and others (2020) ^[1] result in a deposit age between 6,400 +/- 20 and 5,070 ± 160 14C yr BP (between 7,417-7,271 and 6,498-6,215 cal yBP). Bean (1999) ^[2] assigns a VEI of ~4.
Lerner and others (2018) ^[4] subdivided the Driftwood Pumice into four layers: three pumiceous layers (units PL, PM, and PU) and a capping ash layer (Mcap). The lowest pumice layer (PL) is 3-20 cm thick, reversely graded, and composed of well-sorted, brown-beige pumice, ranging in size from 1 to 6 mm in diameter with a mean diameter of ~4 mm. This layer also includes abundant smaller lithic fragments consisting almost entirely of black, dense, vitric material (23 wt% of the layer). The middle pumiceous layer (PM) is 10-15 cm thick, moderately well-sorted, ungraded, and composed of vitric lapilli and fine blocks ranging in diameter from 3 mm to more than 100 mm with a mean diameter of ~11 mm. PM has sparse, smaller lithic fragments making up 5 wt% of the layer. The upper pumiceous layer (PU) is 3-20 cm thick and a darker yellow-brown than the underlying PL and PM layers. The PU is composed of a mixture of brown-beige pumice (42 wt%), dark gray-black scoria (23 wt%), and an abundance of non-vitric lithics (32 wt%). PU lapilli are poorly sorted and vary in mean grain size (6-14 mm); scoriaceous clasts with a mean diameter of ~12 mm are larger than both the pumiceous and lithic fragments. Within 10 km of Makushin’s summit, scoriaceous bombs in the PU layer are up to 10 cm in the long dimension. The top ash layer (Mcap) is a dark brown-gray ash (3-12 cm thick) that caps the deposit and is composed of gray-brown glass shards, plagioclase crystals, mafic minerals, and lithic fragments. The contact of PU and Mcap is irregular with the overlying Mcap ash filling gaps between the uppermost PU clasts. The upper Mcap is commonly reworked and overlain by a soil.
Whole rock geochemical analyses of juvenile material from the Driftwood Pumice range from low-silica dacite to andesite ^[4] . Glass major-oxide geochemistry is found in Bean (1999) ^[2] , Lerner and others (2018) ^[4] , and Larsen and others (2020) ^[1] ; matrix glass compositions range from dacite to trachydacite.