VARIABLE MORAINE SPACING ON MOUNT DESERT ISLAND MAINE, MOUNTAIN BUTTRESSING OF THE ICE FRONT AND/OR REGIONAL SLOWING OF RETREAT DUE TO CLIMATE COOLING?

From south to north on Mount Desert Island (MDI) there are about 300 distinct small scale moraine ridges (3-5 m high, 30-50 m wide) that occur where the glacier was marine based. Such moraines are lacking or very subdued on the flanks of the northeast-southwest trending mountain range on MDI wherever the elevation is above the 70 m high stand of sea level. The prominence of thrust features in exposures of such moraines elsewhere in the region indicate they are grounding line or push moraines from annual winter readvance of the ice front across the sea floor.

On the southern part of MDI the push moraines have a somewhat variable spacing of 30 – 100 m, a spacing intermediate to that of the closely and widely spaced zones to the north. In the center of the MDI at the south ends of the glacial troughs between the mountains there tends to be several much larger moraines with some closely spaced small moraines between them. In the middle of the troughs cut through the mountains the steep slopes retain almost no glacial deposits. Along the north flanks of the mountains and a few km north of them, the moraine spacing is distinctly closer at 30 - 60 m. On the northern part of MDI the push moraines have a distinctly wider 100 m or so spacing. That wide spacing on northern MDI continues north 20 km to north of Ellsworth.

As indicated by the moraine spacing on MDI, retreat of the ice front slowed when the front reached and was just north of and parallel to the northeast-southwest mountain range. That suggests that the mountain range buttressed the ice front once it moved to the north side of the mountain ranges, thereby slowing the retreat rate. The large moraines (100+ volume of material relative to the push moraine) at the south ends of the glacial troughs through the mountains suggests that there was a period of near stability or very slow retreat when the mountains first projected through the ice. Tracing the small push moraines to the northwest across an area without the MDI mountain range to Pineo Ridge though indicates that there is a belt of closely spaced push moraines across the entire region. In the Greenland Ice Sheet Project (GRIP) ice core 18O record, there are dips to more negative 18O values indicative of a colder climate, at 16.1±0.2 and 15.7±0.2 ka , times when the ice front should have been at the downeast Maine coast.