SOMES SOUND: POCKMARKS IN A FJORD-LIKE EMBAYMENT SURROUNDED BY ACADIA NATIONAL PARK

Somes Sound is a 10 km-long, 1-3 km-wide embayment on Mt Desert Island, Maine and surrounded by Acadia National Park. It has been called the only fjord on the East Coast of the US, and although it possesses some attributes of a fjord, it is small compared to typical fjords and is better termed a fjard. This talk reviews the earlier research in the Sound and presents new multibeam bathymetry, side scan sonar and seismic reflection profiles that cover the seabed. The Sound is surrounded by 200 m high mountains but averages only about 25 m deep. The outer, exposed area has a gravel bottom, but the inner Sound is floored by mud with bedrock/gravel confined to margins and small, isolated outcrops. A series of moraines block the entrance to the inner embayment, with a 45 m deep basin between them. The moraines are asymmetric in cross section with an apparently wave-reworked seaward side. Natural gas obscures much of the subbottom of the inner Sound, where more than 30 pockmarks are found. Most of these occur just landward of the moraines and a cluster exists just off the historic Hall Granite Quarry. The pockmarks range to more than 100 m in diameter and 25 m in depth. Cores from within and around the pockmarks contain enigmatic, dense mud concretions and gas-turbation structures. The gas is best understood as originating from organic matter in an earlier lake deposit, although the mechanism(s) for its release are unknown.