Southwick Beach State Park - Lagoons and Sand: Geology of Eastern Lake Ontario

Lagoons and Sand: Geology of Eastern Lake Ontario

The sandy beaches at the Park are part of a 17-mile (27 km) length of sandy shore between Sandy Pond to the south and Black Pond to the north. Another comparable stretch of sandy beach on Lake Ontario is at Sandbanks Provincial Park in Prince Edward County, Ontario, Canada, which is along the northeastern shore of the lake. These are the main areas with sandy beaches on Lake Ontario.

Bradford B. van Diver has described the eastern Lake Ontario dunes as "similar in many details to the south shore of Long Island, with drowned river mouths forming lagoons behind a smooth curving line of barrier bars." The lagoons to which van Diver refers are the notable ponds of this region, including (from north to south) Black, Lakeview, North Sandy, and South Sandy. Both the rivers themselves, and their mouths, are no longer evident. Shortly after the cessation of the last ice age about 10,000 years ago, the water level of Lake Ontario was much lower than it is today; one needs to envision large rivers flowing into a lake some tens of meters lower than today's level. The river mouths were then "drowned" by the rise of the water level of Lake Ontario above this low point. Similarly, sand itself is no longer being formed in abundance; the sand present on today's beaches was probably formed long ago, and transported down from higher elevations during the post-glacial period of low water levels in the lake.