SURFICIAL GEOLOGIC MAP AND CROSS-SECTIONS OF RICHMOND, VERMONT
Over the course of June 2018 our team used the mobile app, Fulcrum, to collect nearly 3,000 geospatial observations of the surficial geology around Richmond, Vermont. We navigated the study area using maps consisting of aerial imagery, topographic maps, and LiDAR shaded-relief maps. These base maps and our collected observations were used to interpolate geologic contacts using both QGIS and ArcGIS software. Our explanation of the geologic history of the area is based on the compilation of our data into a surficial geologic map and a collection of stratigraphic cross sections of the Winooski river valley and the Huntington River valley.
Glacial striations provide evidence for glacial movement that extended first to the southeast over mountain peaks, then parallel to valleys when glacial ice thinned. Till is the primary sediment in all high-elevation areas being deposited as ice flowed over the area. Gravel ridges we interpret as eskers were found in north-south valleys. Lacustrine sediments were found on valley sides to a maximum elevation of about 760 ft. Our map of surficial materials combined with well data found in and around Richmond allow for a sequence of events to be constructed. The first thing deposited was till as glacial ice moved over the region. Eskers were deposited by subglacial tunnels when the hydraulic gradient of water underneath the ice was oriented from north to south west of the mountains and from west to east in the Winooski River valley. A glacial lake then formed as ice retreated down the Winooski River valley and accumulated both ice-proximal and ice-distal sediments. After the glacial lake drained, rivers formed in the region that cut through lake sediment and till, the largest being the Winooski River. High-elevation stream channels and terraces are set in both till and lacustrine sediment. The broad floodplain of the modern Winooski River is a consequence of a bedrock knickpoint.