25 Modern Glacial Processes and the Glacial Sedimentary Record: In Honor of Joe Hartshorn (CC)

Monday, 23 March 2009
7:50 AM - 12:00 PM

THE MALASPINA GLACIER, ALASKA AND THE SOUTHEASTERN MARGIN OF LAURENTIDE ICE, NEW ENGLAND: AN ANALOG REVISITED

Paper number: 25-13
Program: Symposia Sessions
Time: 11:40 AM – 12:00 PM

Authors

Abstract

Malaspina Glacier, first suggested as a partial analog for the southeastern margin of the Laurentide Ice Sheet, because lobes of the Malaspina are similar in size to end moraine lobes in southern New England and estimated ablation rates, surface slopes, and meltwater discharge per unit surface area of Laurentide ice appeared to be similar to measured rates for the Malaspina. Meltwater is known to move from the surface of the Malaspina downward through moulins to the base of the ice to emerge at the ice margin from tunnels and fountains as reported by Russell (1891). Sediment transported as bedload and suspended load in subglacial and englacial tunnels is the source of fluvial and lacustrine deposits and landforms on the Malaspina Foreland. By analogy, morphosequences deposited in southeastern New England by meltwater from retreating Laurentide ice had a similar water and sediment source. In the time between the original field work around the Malaspina (late 1960s-early 1970s), publication by Gustavson and Boothroyd (1987) and the present, the Seward lobe has surged (1987-1988) to completely fill Malaspina Lake and then retreat to a 1975-equivalent position. Parts of the Seward and Agassiz lobes have retreated and/or downwasted to form new outlets for tunnels, new morphosequences, and new ice-cored moraines. These events lend additional credence to the use of the Malaspina as a meltwater analog.

Additional work by many glacial geologists in southern New England has resulted in a clearer understanding of morphosequences, a calendar timescale using both the New England Varve Chronology and Be10 dating of end moraines, and a clearer picture of Laurentide deglaciation by reinterpretation of USGS surficial maps of the 1950s and 1960s, new quadrangle-scale mapping and synthesis to larger-scale maps on a state-wide basis. Laurentide ice stood at the Late Wisconsinan glacial maximum position south of Block Island at 24-28,000 BP with a recessional position at the Charlestown-Buzzard's Bay Moraine (CBBM) at 20-21,000 BP. Ice retreat northward from the CBBM was during a time of extreme cold with known permafrost conditions. The Malaspina warm-based analog fails at this point but recent studies of Greenland polythermal outlet glaciers present an analog with meltwater to the base of the ice during summer in an area of active permafrost.