SURFICIAL FEATURES AND BEDROCK STRUCTURES REVEALED BY LIDAR IN WESTERN VERMONT

Terrain analysis using lidar data shows great utility for mapping and interpretation of surficial deposits, landforms, and a wide variety of ductile and brittle bedrock structures, many of which are important for hydrogeological and natural hazard analysis. Our initial work has been in the Champlain Valley and Green Mountains of western Vermont. Bare-earth lidar data includes a 3.2 meter digital elevation model (DEM) for parts of Chittenden County, a 1.6 meter DEM for part of Addison County and a 1.4 meter DEM for the Missisquoi watershed in Franklin County. We derived percent slope and profile curvature maps and contours at intervals from 2 to 5 meters.

Surficial features include: a) roches moutonées and crag-and-tail landforms; b) terraces and benches of glacial, ice-contact, glaicolacustrine, marine, and fluvial origins; c) topographic depressions, which were identified using a semi-automated GIS procedure that allowed identification of numerous kettle holes as small as 10 square meters; d) microtopography within peatlands due to sphagnum hummocks and/or tree tip-ups; e) landslides, gullies, and eroding stream banks; f) recent stream channel changes, including lateral migration, widening, channel avulsions, neck cutoffs, and flood chutes; g) abandoned channels on stream terraces and late-Glacial meltwater channels; h) large talus aprons. The data reveals isostatically tilted shoreline features related to the Coveville and Upper and Lower Fort Ann Stages of glacial Lake Vermont and the Champlain Sea.

Numerous bedrock features stand out on the slope maps. These include sharply defined map-scale asymmetric folds throughout the Pre-Silurian Green Mountain Belt. When structural data is integrated with these fold patterns in the Williston area, a pronounced dome and basin pattern is evident in the metamorphic rocks of the Fairfield Pond Fm. Lineaments associated with these folds represent a weathered-out axial planar disjunctive cleavage, which is particularly well-developed on the short-limb side. In the Bristol area, the dominant cleavage in the Cheshire Quartzite is penetrative, preserves bedding in the microlithons, and is strongly deflected by a second fold set. The most prevalent fracture-based lineament set strikes E-W, dips steeply, and formed ~orthogonal to the dominant foliation.