From Feeley and Winer (1999): "Samples prefixed SWP- were collected from lava flows that are well exposed in coastal cliffs at Southwest Point. Here at least two lava flows are present. The lower flow (SWPB1) is ~2.4 m thick and has poorly developed columnar jointing. This flow is covered by a thin layer (~0.5 m) of sediments, suggesting a significant hiatus prior to eruption of the overlying units. Sampels SWPT1, -2, and -3 are from thin (<1m) poorly vesiculated lava horizions separated by autoclastic breccia zones. Although these units are petrographically distinct in hand specimen and thin section, geochemically they are very similar, suggesting that they represent either eruption of three compositionally similar flows or different lobes of a single compound flow."
Evidence for fractionation of Quaternary basalts on St. Paul Island, Alaska, with implications for the development of shallow magma chambers beneath Bering Sea volcanoes