Winter's transparent landscape offers a great opportunity for boulder appreciation. And New Hampshire has a lot of big ones, deposited by glacier action over 10,000 years ago. As the ice sheet advanced south, at it's glacial pace, it fractured and plucked many large boulders rights off mountain tops. When the glacier eventually receded, it left behind billions of these "glacial boulders."
By definition, a boulder is a rock at least 10 inches thick, and you can find many of them in the stonewalls that dot the state. But it's the giants scattered on the landscape that really grab our attention. One behemoth sits in Madison, New Hampshire (at Madison Boulder State Natural Area), and is one of the largest known glacial erratics in North America, weighing an estimated 6,000 tons. An erratic differs in composition from bedrock where it landed.
Until the early 1800s, it was assumed that giant, ancient floods moved these rocks. But the mapping of glacial boulders from Mt. Ascutney in Vermont helped geologists confirm that glaciers, not floods, move boulders. Amateur geologists joined the search for Ascutney boulders, finding them in a fan-shaped pattern that begins at the mountain and radiates across southwest New Hampshire and into Massachusetts.
