MAPPING SURFICIAL GEOLOGY AND INTERPRETING THE GLACIAL HISTORY OF THE NORTHERN HUNTINGTON RIVER VALLEY, WESTERN GREEN MOUNTAINS, VERMONT

Most surficial materials on Vermont landscapes originate from processes which occurred during the retreat of the Laurentide Ice Sheet. Glacially deposited sediment and ice flow indicators are records we use to reconstruct the geologic past. Understanding surficial geology is important, as it provides an understanding of materials for economic and state-planning purposes. We aim to update a portion of the Vermont surficial geologic map produced in the 1970s. We use field observations to interpret the glacial history within a northwestern subset of the Mount Ellen quadrangle. This area is west of the Green Mountains and includes the northernmost portion of the Huntington River Valley.

We recorded ~2,500 field observations using the Fulcrum mobile app. We used these observations of surficial materials and landforms in conjunction with LiDAR hillshade imagery, aerial imagery, and topographic maps to construct a surficial geologic map of the study area using GIS software. The surficial material in this region is primarily glacial till, Holocene alluvium, and lacustrine deposits. Other landforms that we recorded include alluvial fans, deltas, abandoned fluvial terraces, and eskers. We drew cross sections across the river valley using logs from private water wells. These cross-sections outline the geometry of the buried bedrock surface and the stratigraphy of the surficial materials filling the valley.

Glacial striations recorded along the Green Mountain ridgeline indicate ice flow from northwest to southeast. During ice sheet retreat, meltwater was directed south and deposited an esker along the valley bottom. Glacial till and erratics were deposited beneath the ice sheet. Once the ice retreated north of the drainage divide, a small lake formed in the upper Huntington River valley. Glacial till covers this mountainous region except where it’s covered by younger sediments in the valley bottom. Evidence of glacial lakes is supported by interbedded layers of diamict and sandy layers which fine upwards to silt-clay. We interpreted these as subaqueous debris flows and turbidity flows deposited in an ice-proximal setting. Following ice sheet retreat, Holocene alluvial terraces and modern alluvial channels formed and alluvium was deposited. Additional Holocene landscape changes include alluvial fans and landslides.