Mack Park - Roche Moutonnee
Mack Park, at first glance, is just an ordinary park in Salem, Massachusetts where kids come to play basketball, swing on the swings, or challenge their friends to a game of softball. However, upon closer inspection, Mack Park transforms into a place brimming with geological history, with extraordinary glacial features around every corner.
While most people would not think twice about the long scratches in the rock, an expert eye can determine that these scratches tell an amazing story about the glacial activity that took place in this very park thousands of years ago. The rocks in this park are special - instead of being ordinary rocks, these slabs of bedrock contain glacial grooves and glacial striations. To top it off, the entire park is built on an impressive roche moutonnee.
Glacial Grooves
Glacial grooves are erosional glacial features formed when the assorted rocks and boulders frozen and stuck under the ice advance with the glacier over solid bedrock and scratch the underlying rock. One of the largest glacial grooves in Essex County can be found here, measure at 30 feet long, 3 feet wide and 5.5 inches deep (Lockwood). Glacial grooves and striations can help determine the way the glacier was flowing. Based on the direction the groove pointed, the continental glacier was flowing to the Southeast from the Northwest when it left the glacial grooves at Mack Park. These abrasions are roughly 22,000 years old, because this was approximately when the Laurentide Ice Sheet was flowing over this area (Lockwood).
Glacial Striations
Also found at Mack Park are glacial striations. Glacial Striations are similar to glacial grooves, but on a smaller scale. While glacial grooves can be massive, glacial striations are typically smaller and thinner. In the image to the left, notice the size of the abrasions compared to the larger, wider groove in the image above. Striations are also formed when material stuck to the bottom of a glacier slides across the ground, causing abrasion and erosion in the bedrock. Just like the glacial grooves, the striations were also formed around 22,000 years ago when the Laurentide Ice Sheet advanced over this region. In addition, the striations also signify a Southeastern motion form the glacier.
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