SURFICIAL GEOLOGIC MATERIALS AND INTERPRETATIONS IN THE LITTLE RIVER VALLEY, NORTHERN VERMONT

The Little River valley is located on the eastern side of the Green Mountains in northern Vermont and its surficial composition has been shaped by a complex glacial history. The underlying bedrock consists of a graphitic schist of Lower Cambrian age. We produced a geologic map and three cross-sections to show the three-dimensional distribution of surficial materials in the Little River valley around the Waterbury Reservoir.

During June, 2017, we collected nearly 1,500 observations of surficial materials and landforms with a smartphone app, Fulcrum, primarily using shaded relief light detection and ranging (LiDAR) imagery as a base map for guidance. We constructed our map using ArcGIS and QGIS. We utilized the excellent resolution of geologic landforms visible on LiDAR imagery to help interpolate geologic contacts between our field observations. We base our interpretation of the glacial history of the Little River valley from (1) the mapped distribution of surficial materials, (2) water well logs, and (3) a stratigraphic section measured in an exposed landslide.

We measured glacial striations in five locations which trended between 156˚ - 195˚, indicating that the ice sheet generally moved north – south across the area. Till was distributed ubiquitously across the higher relief areas of the valley as the glacier melted. Stratigraphic data from the well log at Little River Campground in addition to exposed landslides suggest the following sequence of events. Gravel at the base of the section was most likely deposited in a subglacial tunnel or subaqueous fan. Lacustrine silt/clay lie directly on top of the gravel, which is characteristic of a low-energy lake environment (Glacial Lake Winooski) following the retreat of the ice sheet. An abrupt change in from silt/clay to sand indicates a rapid drop in water level from Glacial Lake Winooski to Glacial Lake Mansfield. On top of this is a layer of gravel and many abandoned terraces which were most likely deposited by the Little River as it eroded through older lacustrine deposits.