The beach and dunes together make up what is known as a barrier island, geologically similar to coastal formations more common along ocean shorelines. At Alburgh Dunes, the sand has come from a layer of glacial till, the soil that was left atop the low bluffs southeast of the beach when the last glacier melted. The bluffs have eroded over thousands of years, and the soil carried off by lake currents. Sand from that soil settles out in the pocket between the rocky "Point of Tongue" to the east and "Coon Point" to the west, forming the beach. Prevailing southerly winds, in the late summer and fall when lake levels are the lowest, blow the sand back from shore, forming dunes. It's a barrier between the lakeshore and the wetland behind, and an island because the beach and dunes, however slowly, continue to migrate into and over the wetland. Deposits of exposed peat are visible on the low end of the beach or in the shallow water just offshore. This peat was formed in the wetland; as the beach and dunes have moved back the peat has been overlaid by sand. Erosion from the waves continues to uncover it.
