Tidal Spits in Dorchester Bay

Provided and copyright by: Rob Sheridan
Summary authors & editors: Rob Sheridan

Sea water carries sand and silt in proportion to its velocity and turbulence, both of which increase when moving water comes in contact with shallow zones. However, when water velocity and turbulence decrease, at the turn of tides or in the periphery of zones of constricted flow commonly bordering deeper channels, sand and silt are deposited. The result is the formation of "spits" or "bars" of sand and silt that can be hazards to navigation or can ultimately form "land bridges" between otherwise separate islands. On the photo above, "Thompson's Bar" is the sand spit between Thompson's and Moon Islands in Dorchester Bay, Massachusetts.

Related Links:

• Dorchester Bay Map
• Geology Glossary
• About Tides