Geology

About 28,000 years ago, New Hampshire and much of the northern United States and Canada were covered by a thick glacier known as the Laurentide Ice Sheet.  The furthest advance of the ice sheet is today marked by Long Island, Nantucket, Martha’s Vineyard, Block Island, and Cape Cod.  As this ice sheet began to recede, glacial lakes formed at the edge of the retreating ice sheet.  In New Hampshire, starting about 16,000 years ago, there were several glacial lakes that changed in size and location as the glacier continued to recede until it finally left the state around 13,000 years ago. 

 

One of the glacial lakes that existed in this part of the White Mountains was known as Glacial Lake Israel and this extinct lake extended from the Bowman section of Randolph to the Riverton section of Jefferson.  Cherry Pond is a remnant of this long-ago glacial lake. Geologists date the draining of Glacial Lake Israel to 13,600 years ago based on Carbon 14 samples and varve records that correlate this date. The actual spillway is seen at the outlet of today’s Cherry Pond.

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Besides Cherry Pond, evidence of the glacier can also be seen in several large boulders found just off the Little Cherry Pond Trail. Geologists believe that these boulders are “glacial dropstones”, which are large rocks picked up by the glacier and embedded in the ice.  In this case, an iceberg carrying the rocks melted and dropped them into the sediment at the bottom of Glacial Lake Israel.  To access the boulders, look for a short, unmarked path on your right as you head out to Little Cherry Pond on the western loop of the Little Cherry Pond Trail (Note:  On the Pondicherry Wildlife Refuge Map & Guide, this loop is called the Goshawk Loop).  You can see the boulders, covered in ferns, from the main trail. 

 

Another interesting geological feature found at Pondicherry is the “ice push rampart.”  Over the last 13,600 years, when the water in Cherry Pond has frozen, gravel and other sediments, as well as small boulders, have been pushed by the ice up onto the shore of Cherry Pond, creating a low berm (or rampart).  On portions of the Shore Path and the Rampart Path, you actually walk on top of this rampart and can easily see this unusual phenomenon.  Click here to read a fascinating article by David Govatski about this subject.

 

If you would like to learn more about the Laurentide Ice Sheet and how it shaped the landscape in the White Mountain region, a good book to consult is The Geology of New Hampshire's White Mountains, by J. Dykstra Eusden et al, published in 2013 by Durand Press.  Also, on the WhiteMountainHistory.org website, there is a fascinating series of articles from the journal Windswept (published by the Mount Washington Observatory) which discuss the glacial lakes (including Lake Israel), as well as the Paleo-Indians who first settled in this area after the ice sheet retreated.  Included in this discussion is an explanation of sediment cores taken from Cherry Pond that shed light on the glaciation of this region.

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