# Quaternary stratigraphy and geomorphology of the Cold Bay region of the Alaska Peninsula; a basis for paleoenvironmental reconstruction

Quaternary stratigraphy and geomorphology of the Cold Bay region of the Alaska Peninsula; a basis for paleoenvironmental reconstruction
Dochat, T. M.
1997
Cold Bay, at the western end of the Alaska Peninsula, opens southward to the Pacific Ocean. Glacially deposited debris from alpine glaciers and a continental-shelf ice cap forms much of the lowland region at the head of the bay. Major alpine advances appear to have occurred asynchronously with ice-cap advances. A late-Wisconsin ice-cap (Cold Bay II) moraine partly overlies the youngest possibly pre-late Wisconsin alpine moraine. Outwash channels are cut from the Cold Bay II moraine into flat-lying sediments on the ice-proximal side of the alpine moraine. Thus landforms indicate that alpine ice retreated by the time the ice cap was at or near its maximum position during late Wisconsin time. However, absolute timing of this asynchrony is not known. Exposure of the Bering Sea floor due to lowered eustatic sea level along with the growth of an ice cap on the Pacific continental shelf would limit the amount of moisture reaching north-facing valleys. Therefore, it is hypothesized that north-flowing alpine glaciers were starved. Deglaciation was underway by $\rm 11,530\pm 200\ \sp{14}C$ yr BP. Moraines in western, northern, and eastern valleys of Frosty Peak record at least two latest-Wisconsin alpine advances that occurred before $\rm 9,090\pm 140\ \sp{14}C$ yr BP. Perhaps alpine glaciers advanced in response to increased accumulation resulting from rising sea level and ice cap collapse. A numerical model suggests that alpine glaciers could have merged on the continental shelf, forming a dome with a northerly flow component. The model lacks the resolution to distinguish the behavior of alpine glaciers during the last glacial maximum. Terminal moraines in the northern valleys of Frosty Peak preserve a record of at least four Holocene alpine advances after $\rm 1,190\pm 120\ \sp{14}C$ yr BP. Holocene sediments are dominated by wind-blown sand and volcanic ash. At least three widely distributed tephra units occur in the Cold Bay area. In a bluff exposure along Cold Bay, the lowermost of these tephra units directly overlies Cold Bay till. The differences in the preserved records of glaciation of the three volcanic peaks immediately surrounding Cold Bay could be due to differences in the volcanic history of each volcano.