Circular depression can be found in the area near Fishers. What are these features called?
Pockmarks
Numerous circular to oblate depressions are concentrated in a roughly 8.6-km² area north of the Clumps moraine off the western tip of Fishers Island. The depressions are typically 5-6 m in diameter and extend about 0.2-0.3 m below the surrounding sea floor, but individual depressions can reach 24 m in diameter and 1.1 m in depth. At several places the depressions overlap, forming larger depressions that exceed 50 m across. We interpret these features to be pockmarks that formed during the escape of biogenic methane from underlying sediments of the Thames River glacial delta (Lewis and DiGiacomo-Cohen, 2000).