ANALYSIS OF FOUR BROTHERS SLUMP, LAKE CHAMPLAIN, VERMONT

High-resolution CHIRP (Compressed High Intensity Radar Pulse) seismic reflection profiles reveal the presence of a deep-water lacustrine slump located in the Main Lake of Lake Champlain, Vermont. Named the Four Brothers Slump, this slump is composed of a heavily disturbed sediment body that was transported down slope in a mass-wasting event. The Four Brothers Slump has an areal distribution of ~1 km² and the volume of sediment transported is ~11x10⁶ m³. Further information on the Four Brothers Slump was obtained through the use of side-scan sonar and the analysis of four 7 m sediment cores. Side-scan sonar data show the slump initiated on a structural rise to the southeast of the slumped area. Analysis of the seismic profiles and identification of the foraminifer microfossil, E. excavatum f. clavata, show that the slump occurred above marine Champlain Sea sediments. The water saturated Lake Champlain sediments over impenetrable clays may have led to increased pore pressure that exceeded the hydrostatic pressure and led to the slumping, when triggered. Utilizing core and seismic data, it is estimated that the slump occurred ~300 yr BP, which corresponds to a period of high seismic activity in the Vermont - New York Area and suggests that this slump may have been triggered by an earthquake. Recent slumping in the Quebec region of Canada (which had human fatalities) and near Mount Independence, VT, (which had extensive property damage) occurred along the Champlain Sea – Lake Champlain sediment interface and was related to high precipitation events. Analyzing the Four Brothers Slump within Lake Champlain will help in the identification of “at risk” locations for slumping in the region and along the lake’s shorelines to ultimately mitigate further human and property disasters.