The Geology of Mount Desert Island
A Visitor's Guide to the Geology of Acadia National Park
Summary of Glacial History
Perhaps the best way to relate the wide-ranging topics discussed here is to take another look at the area around Jordan Pond House. From this vantage point we can easily examine glacial features that illustrate most of the concepts that we have talked about. Figure 26 is a series of maps and sections illustrating the various stages in the evolution of the landscape.
Looking north from the Jordan Pond House, we see the striking effects of glacial erosion during the main onslaught of the Wisconsin ice sheet: the deeply scoured U-shaped valley now occupied by Jordan Pond and the rounded profiles of The Bubbles at the north end of the pond (Figure 20). High on the southeast shoulder of South Bubble, you may also be able to see Bubble Rock, an erratic which was left in its seemingly precarious position after traveling for miles within the ice sheet (Figure 22).
Right around Jordan Pond House is a low ridge of glacial till, The Jordan Pond moraine, which forms a natural dam containing the lake. A short walk in this area will reveal some of the boulders that melted out of the glacier as the moraine accumulated. Narrow lobes of ice extended down the Jordan Pond valley and other neighboring valleys of Mount Desert Island during deglaciation, and moraines such as the one seen here accumulated at their southern ends.
If we walk or drive down the road to a point about one-half mile southeast of the Jordan Pond House (heading toward Seal Harbor), we find ourselves on a flat surface. This is the top of a delta composed of sand and gravel that washed southward into the ocean when the ice margin stood right behind the Jordan Pond moraine. This delta is complex and in part received some of its sediment from meltwater that flowed into Jordan Valley from the east (Wgd1 and Wgd2 on the surficial geologic map - pdf format). The Jordan Pond delta began to form at a time when the relative position of sea level was 230 feet higher than today. Depression of the Earth's crust under the weight of the glacier allowed the sea to encroach to this high level and submerge much of the low-lying coastal terrain.
The lack of erosional modification or clay deposits higher than the Jordan Pond delta suggest that the sea never rose above the delta top. However, the presence of beach features at lower and lower elevations to the south reflects the drop in sea level during rebound. As the sea retreated, streams flowing from Jordan Pond began to cut into the delta and reduce it to its present size.
Most of the events shown in Figure 26 occurred in a fairly short time. The longest time span, from about 10,000 to 2,000 years ago, is not well represented here because the sea level was much lower (Figure 24) and no evidence exists for it on Mount Desert Island.
Last updated on January 11, 2008