Surficial deposits on northern Adak Island, Alaska include a variety of volcanic, glacial, eolian, and beach sediments. These deposits are the primary water-bearing units on the island and their distri- bution is shown on the accompanying surficial geologic map. An extensive sequence of volcanic debris-flow deposits (lahars) was identified on the eastern slope of Mount Moffett. The sedimentary characteristics of the lahar deposits indicate that they are related to volcanic eruptions of Mount Moffett and are evidence for Holocene volcanic activity at this volcano. Similar lahar deposits also are present on the southern slopes of Mount Adagdak. The surficial geologic map units described in the report are a basis for island-wide assess- ments of ground-water conditions, aquifer proper- ties, and general hydrogeologic conditions, and will be useful for determining the availability of potential construction materials.
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Surficial geologic map of northern Adak Island, Alaska