Delineating Glacial Features from 2-Dimensional Seismic Data (CHIRP) and development of a data processing workflow: Harrington Lake, Piscataquis County, Maine, U.S.A.
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Authors
Micander, Rachel
Issue Date
2025
Type
Thesis
Language
en_US
Keywords
Eskers , GIS , Glaciers , Harrington Lake , Laurentide ice sheet , Maine
Alternative Title
Abstract
Glacial features, including eskers, are preserved across Maine. Abundant lakes mask the glacial landscape throughout the state, obscuring spatial continuity of glacial features. Using 2-D CHIRP combined with lidar data, glacial features can be mapped below present-day lake surfaces to help improve the understanding of glacial and post-glacial landscape change.Harrington Lake is a 5.5 km-long lake located in central Maine, situated in a NW-SE trending valley and shallowing and draining to the northwest. The lake was dammed in 1930 with a 4.9 m-high dam. At present, the maximum lake depth is 42 m, suggesting the presence of a lake or a series of small ponds prior to damming. CHIRP reflection data were collected in a grid pattern covering much of the lake. Six NW-SE lines and 22 NE-SW lines were interpreted in combination with lidar data from the adjacent landscape. Points along each CHIRP line were selected to mark 1) depth to lake bottom, 2) thicknesses of Holocene sedimentary units, 3) thickness of Pleistocene glacio-lacustrine sediments, 4) thickness of the basal unit, and 5) depth to the top of the basal unit. Annotated CHIRP images were georeferenced using ArcGIS Pro and the Natural Neighbor technique was used to generate raster contour maps of the basin bathymetry and the various sediment thicknesses. In addition, drill core was recovered from the northern part of the lake following seismic imaging and used in conjunction with the thickness maps to interpret glacial geomorphology and post-glacial evolution of Harrington Lake.
A prominent esker oriented NW-SE is clearly expressed in the lidar data and extends into the northeastern part of the lake. Another small esker with a similar orientation occurs west of the prominent esker, and a third esker enters the lake along its eastern shoreline. Lake depth is shallowest over the eskers and deepest to the west and south of the eskers. Two Holocene lacustrine sedimentary units were measured and mapped along with a third sedimentary unit that is glacio-lacustrine. Total thickness of the three sedimentary units was mapped at 23 meters in the deepest parts of the lake. Post-glacial sedimentary units onlap the eskers and are absent in some areas, suggesting fluvial modification within the basin following glacial retreat. Based on initial core descriptions, the Holocene deposits consist of a post-glacial organic-rich mud unit which overlies a laminated glacial-lacustrine unit (likely varves) that is interbedded with coarser sediments in some areas. The basal unit is interpreted as glacial till, gravels associated with eskers, and/or bedrock. Basal unit thickness varies but is thinnest near the esker and along the western shore of the lake. The observations indicate that Harrington Lake now occupies a long valley that once contained a series of smaller ponds or marshes connected by a stream, as indicated by sedimentary unit thickness. The analyses of the lake bathymetry and sediment thicknesses reveal the position and geomorphology of an esker beneath Harrington Lake and provides a methodology for better understanding glacial geomorphology and deposits obscured by other lakes in Maine and elsewhere.