The Geology of Mount Desert Island
A Visitor's Guide to the Geology of Acadia National Park
Recent Geologic Processes on Mount Desert Island
Changes to the landscape, both along the ocean shore and at higher elevations, have by no means stopped since the glacier which covered Mount Desert Island receded. Following the post glacial uplift of the Maine coast, worldwide sea-level rise caused a gradual encroachment by the ocean which continues today. The sea continually attacks the shore, eroding dikes and other weaker rocks to form chasms such as Thunder Hole, and cutting cliffs, caves, and sea stacks. Eroded rock material is carried away from these high-energy zones and deposited either as coarse beaches, or in mud flats in areas of quiet water. The coarser beach deposits (sand and gravel; Figure 27) are shown as Hb on the surficial geologic map (pdf format).
While the sea works on the shoreline, the interior areas of Mount Desert Island are continually worn down by other processes. Glacial erosion left steep, jagged cliffs along the valley sides. Although the rock in these cliffs is strong, it is so fractured that it will not stand for long in a vertical position. Water seeping into the fractures and freezing, together with gravity, causes blocks of the bedrock to break away and fall or slide down the slopes. At the bottoms of the cliffs they join other fallen blocks in a pile of rubble called talus (Ht on the geologic map). One of the largest talus piles occurs on the west side of Huguenot Head, along Route 3 south of Bar Harbor.
There is not a great deal of modern sediment accumulation on Mount Desert Island, partly because there are no major rivers to erode and re-deposit the glacial materials. However, there are significant wetland areas in which organic-rich sediments are being deposited. These areas include salt marshes along the coast (Hs on the geologic map) and freshwater wetlands (Hw). Some of the freshwater deposits are peat bogs, such as The Heath on Great Cranberry Island.
Last updated on January 11, 2008