Winnipesaukee – How did it get here?

When I was a child, I was always curious about why the landscapes I saw looked the way they did. In fact, I have a very distinct memory of cruising on my family’s boat out by Hanson Cove and asking my father why the mountains “looked like that.” He went on to explain how a giant sheet of ice once covered the area and helped to shape the mountains and the surrounding landscape. I was in awe of his answer, imagining a massive sheet of ice towering over where I was standing. This little moment of curiosity led me to pursue a degree in earth sciences, with a special interest in glaciology. The Lakes Region has an interesting geologic history that may satisfy your own curiosities about the region.

Through decades of research, dedicated geologists have discovered that this beautiful, serene region has experienced a complicated history. Ancient seas lying here for millions of years, rocks compressed by earth-forces that our minds can’t comprehend, and volcanoes with violent explosions. Then, recently, geologically speaking, ice was given the chance to carve out the landscape. The dominant feature of the area is Lake Winnipesaukee and the lowland in which it lies. The lowland was formed through the erosion of a significant area of weak rocks by streams and tide and glacial ice. During the last glacial period, there was a large continental ice sheet about a mile thick called the Laurentide Ice Sheet that covered most of Canada and the northern U.S. This ice sheet began to retreat as the last glacial period came to end approximately 12,000 years ago. Sand, clay and other loose materials were deposited irregularly throughout the region by the retreating ice sheet. As the ice melted, melt-water filled the depressions resulting from the irregular deposits and with some rain overtime, created the lakes. The ridges and hills that were too high to be submerged are now the peninsulas and islands.

Rising to the northeast above the Winnipesaukee lowland is the Ossipee Mountain Range, another prominent and interesting geologic feature. Looking at a topographical map of the region, the Ossipee Mountain Range sticks out with an almost perfect ring-like shape. This formation is a classic example of a ring dike – a circular feature that emerged from the subterranean “plumbing” of an ancient volcano. Ring dikes are not common features, thus the Ossipee ring dike is very interesting and a rare geologic formation right in our backyard. The Ossipee ring dike formed approximately 90 million years ago by the second of three major eruptions that occurred throughout the active period of the volcano related to the structure. The original volcano was thought to be about 10,000 feet tall. Another example of a ring dike is found on the southern end of the lake, the Belknap Mountains. The diameter of the outer dike extends for about 6 miles and includes Rattlesnake Island. Therefore, Rattlesnake Island out in the middle of the lake is actually a part of the Belknap Mountains.

There are many other interesting geologic features and historic geologic periods that contributed to forming the beautiful Lakes Region we know today. If you are out and about and see something interesting, I suggest asking “why does it look like that?" You never know where your curiosity may take you.

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Jacquelyn Bellefontaine is the conservation outreach manager for the Lake Winnipesaukee Association. She manages communications and outreach initiatives. Jackie can be reached at jbellefontaine@winnipesaukee.org. 

The Lake Winnipesaukee Association is a nonprofit dedicated to protecting the water quality and natural resources of the lake and its watershed. To learn more, visit winnipesaukee.org.