Acadia National Park – Glaciers

We spent today driving around Acadia National Park, on the Maine coast. Acadia has remarkable geology (to go along with interesting biology and great scenery), and interpreting it has almost been made too easy. An online book, The Geology of Mount Desert Island, by Richard Gilman, Carleton Chapman, Thomas Lowell, and Harold Borns, Jr., goes over the geology of Acadia in minute detail, including geologic and surficial maps with particularly interesting points marked on the maps. My interpretations will draw heavily from this source.

The topography of Acadia is dominated by glacial features, either directly or indirectly. The entire park was glaciated near the end of the Pleistocene, and evidence for this is everywhere. Most of the valleys in the park are U-shaped valleys, typical of glacial erosion:

The second of these two valleys has two small, rounded hills in the middle, called the Bubbles. From the side the Bubbles are asymmetrical, with the steeper side to the south (they’re the two low hills in the center of the picture):

Other hills in the park show the same pattern, with a steep southern side:

These are all glacially-sculpted granite hills. On the upstream side, the glacier slid over the hill, smoothing off the surface. As it reached the crest it plucked large rocks from the downstream side, leaving a steep lee cliff.

The eroding glaciers left the granites in the park polished in many places:

There are lots of striations and chatter marks (crescent-shaped grooves caused by boulders embedding in the bottom of the glacier abrading the bedrock):

As the ice receded, those boulders were left behind as glacial erratics. This one is on top of one of the Bubbles:

This one is at the top of Cadillac Mountain, the highest point in Acadia at over 1500 feet, demonstrating that the glaciers were at least that thick:

Gilman et al. discuss numerous other glacial features, including outwash deltas and end moraines. Unfortunately we’ve yet to see any that photograph well from ground level, but we’re going back into the park tomorrow.

Acadia also has fascinating igneous rocks (OK, I know I’m a paleontologist and I’m supposed to show nothing but disdain for igneous rocks, but these are cool!); I’ll show photos of those in an upcoming post.

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