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How Walden Pond Was Made
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Walden Pond was made by a block of ice. This all began about 15,000 years ago.
A retreating glacier left a block of ice behind. Meltwater piled sand and gravel up around the ice.
Then the ice melted, and the ground caved in. Water filled the hole. That's Walden Pond.
Thoreau measured it with a line and a stone. He found it was 102 feet deep. A modern survey found almost the same depth.
No stream flows in or out. Rain, snow, and groundwater fill it.
The pond's shape still echoes that block of ice.
Look for a pond with no stream.
In eastern Massachusetts, a pond with no stream running in or out may be a kettle, a hole left by a block of ice. Goose Pond, just east of Walden, and White Pond in Concord are kettles too.
Data: the U.S. Geological Survey, Massachusetts DCR, and Henry David Thoreau's Walden.