Glaciation
The Wisconsin glaciation was the most recent glacial period. The maximum ice extent in North America occurred approximately 21,000 years ago and at that time the ice sheet covered most of Canada, the Upper Midwest, and New England, as well as parts of Idaho, Montana and Washington. The glacial advance and retreat caused significant erosion, altering the landscape, carving New Hampshire’s famous notches, and leaving many fascinating geological features such as kettle holes, eskers, drumlins, potholes, and of course the ever present glacial erratics.
An umlaufberg is a lesser known glacial feature; a stand-alone, rounded hill that is formed when glacial meltwater flowed around more resistant bedrock in a river.
How Sunset Hill Was Formed
Figure 1.
Before the Wisconsin glaciation Sunset Hill was part of the mountain just to its East, and the pre-glacial Mad River flowed north of that ridge into the Pemigewasset. You can see the course of pre-glacial Mad River as a broad sand-filled valley just to the north of Sunset Hill.
Figure 2.
As the Wisconsin ice sheet retreated, the ice margin stood for a time approximately along the course of the present-day Mad River. This blocked the pre-glacial Mad River that was just north of Sunset Hill. Glacial meltwater ran along the edge of the ice along the northern flank of the ridge and, finding a path of less resistance, eroded a course through a bedrock pass that connected Sunset Hill to the mountain east of it.
Figure 3.
After the glacier retreated, meltwater had isolated Sunset Hill from its neighbor to the East, and had carved a new course for the Mad River south of Sunset Hill.
Looking at the terrain may help visualize this process.
Other New Hampshire glacial umlaufbergs are Hark Hill in Shelburne NH where the Androscoggin River flows into Maine, and Bald Mountain in Milan, just northwest of Success Pond.
Logging Requirements:
1. Park at the posted coordinates. You are now parked on the side of Sunset Hill. Look to the Northeast. Describe the shape of the valley below. What do you think the valley floor is composed of? How did it get that way?
2. Drive around Sunset Hill to the Stage 2 coordinates. This should take 5 min or less. Imagine you were at this same spot before the Wisconsin Glacier arrived. Look to the South. What would you have seen back then? How is this different from today?
Source: VanDiver, Bradford B. Roadside Geology of Vermont and New Hampshire. Missoula : Mountain Press Publishing Company, 1987.