UNDERSTANDING CONTROLS ON CONNECTICUT DRUMLIN MORPHOLOGY, LOCATION, AND ORIENTATION USING LIDAR AND GIS ANALYSES

The surficial material in Connecticut was deposited primarily during the Quaternary glaciations. Much of this material occurs as till deposits of varying thickness. Some of the thicker till deposits have been elongated in the direction of ice flow to form drumlins. These features may reveal important information on the paleoglacial conditions that formed them. In this study, streamlined deposits of thick till were mapped using high resolution, LiDAR-based DEM data. LiDAR was used because of its higher spatial resolution than Landsat or topographic maps; thick till deposits are clearly differentiated from bare or thinly covered bedrock in the LiDAR data.

Detailed measurements of drumlin length, height, and width were manually digitized using GIS software for three major drumlin fields located in northwest, north-central and northeast Connecticut. These measurements were obtained by using the GIS aspect function to accentuate the drumlin axis, and a 5 ft contour map generated from the LiDAR data to determine the height and general shape. The recorded measurements were then compared with those of the published state Quaternary map to check for accuracy. Other parameters such as bedrock lithology (determined from the state geologic map) and general topography of these areas were also analyzed. The degree of anthropogenic and fluvial modification of these forms was also determined using road maps and Google Earth images.

Results of this study indicate geologic and topographic controls on drumlin locations and orientation patterns, and thus on ice flow directions. Drumlin orientations in the Hartford basin form a divergent pattern suggesting the obstruction and subsequent diversion of ice flow around the central ridge of erosion-resistant basalt. The highest concentrations of drumlins in the basin are on the upflow side of the basalt ridges, in contrast to the other major drumlin fields which are located on the downflow sides of topographic highs. A secondary topographic control is obvious in the northeastern field, where drumlins are clustered en-echelon along the tops of structure-controlled ridges. Otherwise, drumlin orientation and morphology do not appear to be influenced by geology. Comparisons of drumlin length to width ratios indicate morphology is independent of substrate lithology.