Ship Rock - Glacial Erratic
Ship Rock in Peabody, MA is the second largest glacial erratic in Essex County. Glacial erratics are boulders plucked out by a glacier from mountains or hills. When the glacier melts, the boulders drop in place. They can be distinguished by a large rock or boulder resting on a softer surface of an entirely new material. This particular glacial erratic weighs 2,200 tons and is made of hornblende granite. It was carried two-thirds of a mile from a valley to the northwest by a glacier (Lockwood).
Ship Rock is located on top of a moraine. A moraine is a cluster of rocks and assorted sediment that was deposited by a glacier, usually as ridges toward the snout of the glacier. There are two major types of moraines, Terminal Moraines and Recessional Moraines (Lockwood) . A Terminal Moraine is made of till, pebbles, cobbles, and boulders that were deposited at the front of the glacier when ice pushed materials forward and melted. Once the moraine has been formed, the front of the ice will melt and reach a state of equilibrium due to the forward movement and the melting. A Recessional Moraine is when another similar moraine will form near the Terminal Moraine, indicating that the glacier continued its path. Since the new moraine does not signify the farthest advance of the ice, it is called a Recessional Moraine. The image to the right shows the head of a person next to the large erratic that sits on top of this moraine.
Ship Rock is located on a top of Recessional Moraine. This can be determined because there are more moraines in this same area that are closer to the ocean, so it suggests that glacier continued moving after depositing Ship Rock. The image to the left shows a person (center) in relation to the massive erratic (above person).
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