4F. Bottom Morphology and Boundary Currents of Southern Lake Champlain

Bottom Morphology and Boundary Currents of Southern Lake Champlain. Hollistir Hodson. May 1995.

In May 1992 Lake Champlain Maritime Museum and Middlebury College imaged a six square kilometer section of southern Lake Champlain with a high resolution, dual frequency side-scan sonar system. These side-scan sonar profiles were used to identify the sediment bedforms and submerged cultural artifacts present south of Larabee’s Point to Chipman Point. Several bottom morphologies including sediment waves, lineations, sediment furrows, and linear groups of pockmarks were recorded and mapped.

Most of the sediment waves are found in conjunction with the cultural artifacts beneath Lake Champlain’s ·surface that disturb the bottom current, creating sediment waves. These waves are classified into two distinct groups by their size, orientation, and asymmetry. The height of the waves ranged from several centimeters to 0.5 meters, and the wavelength varied from 1 to 12 meters. The two groups had orientations of 65° and 175°. Around the inside bends of the lake surrounding Buoys 37 and 38, fields of sediment furrows have developed . They are approximately 15 to 50 cm deep, 2 meters wide, up to 600 meters long, and have an average spacing of 10 to 20 meters. Furrows are evidence of either a strong, stable bottom current in those regions or an strong, episodic current that erodes the bottom sediment The pockmarks are .located along a linear trend on the eastern slope of the lake, north of Mt. Independence. This northeast trend could be related to a subsurface fault that facilitates the upwelling of biogenic gas or groundwater into the lake.

From the orientations of the sediment bedforms, the direction of the bottom currents in the study area were documented. The bottom current in this southern section of Lake Champlain behaves much like a river, flowing to the north, following the local bathymetry and topography. However, both sediment waves and furrows suggest possible bi-directional currents, as well as episodic events that are characterized by an increase in current speed. The cause of these stronger, bi-directional currents is unknown, but we are speculating that it is either related to the seiche, or the dynamics of the water where it flows around a bend in the lake, or a combination of the two processes.