ORIGIN OF DE GEER MORAINES IN THE SEACOAST REGION OF NEW HAMPSHIRE
Date of Award
Program or Major
Master of Science
Joseph M Licciardi
Joel E Johnson
During the last glacial period, the Laurentide ice sheet (LIS) dramatically modified landscapes in New England and produced a variety of erosional and depositional glacial landforms. Previously unrecognized clusters of regularly spaced low-relief ridges have recently been discovered in the Seacoast region of New Hampshire from light and detection ranging (LiDAR) data acquired in 2010-2011. Based on their morphometry and distribution, these features are interpreted as De Geer moraines that formed during the deglaciation of the LIS. De Geer moraines are widely recognized as products of ice margin retreat in glaciomarine settings, but specific modes of moraine genesis are debated. In this project, geospatial mapping and morphometric analyses, detailed stratigraphic and sedimentological investigations, and ground penetrating radar (GPR) subsurface profiling were conducted to provide a first-order characterization of De Geer moraines in New Hampshire. Sedimentological investigations focused on two morphometrically distinct moraines in the towns of Durham and Lee, New Hampshire. Trenches were excavated perpendicular to each ridge crest to examine a cross-section of the deposits. Individual sediment facies were described and classified, and samples were collected for pebble fabric and grain size analyses. The ice-proximal portion of the ridge exposed in Lee is composed predominantly of massive subglacial deformation till with sheared cobbles of the metasedimentary Eliot Formation, and likely formed by a combination of proglacial pushing and subglacial shearing. The ice-distal portion of the moraine examined in Durham is dominated by angular clasts of the Exeter diorite and a sandy/gravely debris flow deposit that likely formed at an oversteepened segment of the ridge at the ice margin. Morphometric analyses indicate that moraines in the Seacoast region are on average 1.2 m tall, 885 m long, 30 m wide, and spaced 98 m apart. The results of this study indicate De Geer moraine formation in New Hampshire was likely driven by annual oscillations of the LIS margin in a tidewater setting. In this interpretation, the average spacing between moraines in the Seacoast would represent annual ice margin retreat at a rate of 98 m/year, which is in line with a previously published average ice recession rate of 118 m/year across the state of New Hampshire.
Sinclair, Samantha Noelle, "ORIGIN OF DE GEER MORAINES IN THE SEACOAST REGION OF NEW HAMPSHIRE" (2015). Master's Theses and Capstones. 1062.