Sunday, September 15, 2013
Unfolding the Camden Hills
Two weeks ago my friend Colin and I climbed Mount Megunticook. I was bending his ear about a particular rock, or piece of geologic history when he asked me the question: so how did the Camden Hills get here? The question haunted me. It's certainly a question I'd pondered. I just hadn't made any headway. I'd researched it too; the answers were either non-existent, or just didn't add up. Glaciers? But, ice sheets scoured the whole state. Why leave peaks here? Granite? There may be occasional injections of the light colored rock, but no more than other, lower regions of the state. Over the intervening weeks I revisited both and decided that perhaps the answer lies in the the shattered infrastructure of the region.
I've mentioned in a previous post that this region was ground zero for a major collision between plates, and the impact is still visible on a relief map. The ridges to the north and west of the Camden Hills look like ripples in a carpet pushed up by slid furniture. If Africa was a couch, and Maine an area rug, this isn't too far from the truth. When Pangea formed, Maine's rock needed to take up less space. Like the carpet, part went up, and the rest stayed down. The difference is, rock is not so good at bending. Instead, a wedge of rock cracks off along a fault, and slides up the face of the piece next to it. This crack-slide scenario occurred twice, with state geologic maps showing thrust faults not far from two ridges: one that includes Levenseller Mountain, Moody Mountain and Philbrick Mountain and another that features Hatchett Mountain and Coggans and Clarry Hills.
If collision shoves rock skyward, extension drops it down. When Africa moonwalked its way out of Pangea, it stretched Maine behind it. Certain blocks of Earth dropped down, filling would be holes with wedges of rock. To the southeast of the Camden Hills, the land quickly plunges to ocean. The state maps once again show a fault and a cross section makes it look as though the fault block descended with extending crust.
Bloom, Arthur. Geomorphology: A Systematic Analysis of Late Cenozoic Landforms. Upper Saddle River, New Jersey: Prentice Hall, 1991. Print.
"Facing Hatchet Mountain." Hope Historical Society. Hope Historical Society, n.d. Web. 15 Sept. 2013. <www.hopehist.com/Himages/HD402.html>.
Flanders . "Mount Megunticook : Climbing, Hiking & Mountaineering : SummitPost."Climbing, Hiking, Mountaineering : SummitPost. SummitPost.org, 12 Oct. 2013. Web. 15 Sept. 2006. <http://www.summitpost.org/mount-megunticook/234387>.
Osberg, Philip H., Hussey, Arthur M., II, and Boone, Gary M. (editors), 1985, Bedrock geologic map of Maine; Maine Geological Survey (Department of Conservation), scale 1:500,000