Sedimentary Pockmarks in Missisquoi Bay


TitleSedimentary Pockmarks in Missisquoi Bay
Publication TypeConference Paper and Presentation
Year of Publication2018
AuthorsManley, P, Manley, T, Orland, E
Conference NameLake Champlain Research Conference
Date Published2018/01
PublisherLake Champlain Basin Program
Conference LocationBurlington, VT
Abstract

Previous bathymetric surveys of Lake Champlain based on lead-line and single-beam echo sounder measurements were only capable of defining bottom structure on scales of 10-100s of meters. The use of CHIRP seismic profiling and more recently multibeam sonar technology over has provided a wealth of central lake information related to large subaqueous landslides (Gosh, 2001; Rosales-Underbrink, 2015; Silverhart, 2016), furrows (Leucke, 1995; Manley et al., 1999), large sediment drifts and waves (Hayo, 2002; Weeks, 2012; Manley et al., 2011) as well as pockmarks (North, 1997; Gutierrez, 2001; Manley et al., 2004). As part of the VT EPSCoR RACC program, Missisquoi Bay was mapped by multibeam from the 2013-2015 using a uniform 33% coverage pattern in depths greater than 12 ft. Results showed the bay to be a shallow bowl-shaped structure with the presence of a few shoals as well as numerous pockmarks concentrated around the outer perimeter of the Missisquoi River delta with decreasing numbers as distance away from the delta increased. An initial estimate of the total number of pockmarks in the multibeam data set was put at 1800 however; a more rigorous analysis on ~20% of the data set suggests a range between 7000-9000. Considering that the multibeam data only covered 1/3 of the bay, this initial range could be expanded to 21,000 – 27,000 individual pockmarks. Our initial observation at these features shows them to be better defined and deeper near the north-south central axis of the Missisquoi River delta. A vast majority of these features show no specific orientation however there are some that show preferential linear alignment suggesting fault control. Preliminary statistics show that these range in size from 2-4 m in diameter with depths varying between very shallow (0.25 m) up to at least 1 m. Whether or not these features are created from biogenic release of methane, fish nesting, groundwater or dewatering of sediment is still in question.

URLhttp://www.lcbp.org/water-environment/data-monitoring/lake-champlain-research-conference/
Status: 
Published
Attributable Grant: 
BREE
Grant Year: 
Year2
Acknowledged VT EPSCoR: 
Ack-Yes