A secondary source of sand may be as a fluvial addition from south-trending paleo-Noatak and Kobuk rivers cross the exposed subcontinent of Beringia, and reworked into Pleistocene dunes during lower sea levels. The dark medium sand reflects updrift bluff erosion of a tephraeous maar eruption about 17,000 years ago. Sand supply is maintained by onshore transport during a five-month open water period from June to November. Although in the long-term, as established by geological 14C ages, over the last 4000 years, sand transport is onshore and progradational, in the short term, storms and transient current reversals lead to offshore transport and erosion of Espenberg beaches. Locally, beaches have witnessed significant width and depth reductions in the last five years; current reversals are also possibly more common.