Buzzards Bay - Geology

Geology

Buzzards Bay was created during the latter portion of the Pleistocene epoch through the interplay of glacial and oceanic processes. Beginning fifty thousand to seventy thousand years ago, the edges of the continental ice sheet covering much of North America began to fluctuate, leaving moraines to mark the former extent of the receded ice. One such moraine forms Cape Cod, which is most of the eastern shoreline of Buzzards Bay.

In addition to the moraines, the melting ice sheet produced extensive outwash plains composed of mixed sediments and ice that bordered the bay to the northwest and west. Melting ice blocks in the outwash deposits formed distinctive circular features called kettle lakes. Numerous examples of kettle lakes can be found to the northwest of the Cape Cod Canal. Finally, waters released from the melting ice sheet raised sea level by sixty to one-hundred-twenty meters (198–396 feet) and drowned preexisting outwash channels. Toward the end of the last ice age, fifteen thousand years ago until about six thousand years ago, Buzzards Bay was still dry land. (See Progression of sea-level change in Atlantic Canada.) During the past six thousand years, sea level has risen an average of one foot per century, and until about four thousand years ago, the landward boundary of Buzzards Bay extended only to about the current thirty-foot bathymetic contour, forming a coastline two-thirds of the way up the current bay, between West Falmouth and Mattapoisett.

The bay's current configuration, a well-mixed central bay and fringing shallow drowned-river valleys, with their shallow depth, tidal action, and surface waves, promotes mixing of the estuarine waters to create a productive aquatic ecosystem. Like many estuaries, however, increasing development and land-use changes by the surrounding communities are accompanied by nutrient runoff leading to eutrophication (an increase in nutrient levels leading to oxygen depletion) in the smaller embayments. Decreases in eelgrass, scallops, and herring have also been noted, but direct cause-and-effect relationships are not clear. Coordinated management efforts in Buzzards Bay have helped to decrease shellfish closures, conserve habitat for sea birds, and preserve open space.