September 24, 2012
New England is full of glacial erratics: rocks which were transported and dropped by glaciers and which have a different lithology from the rocks upon which they have been deposited. Often, erratic rocks have an angular shape because they were broken off of bedrock by glaciers and have not yet had time to be weathered and rounded by water, wind, and other erosional forces. Glacial erratics can range in size from very small pebbles to very large boulders, but usually it is the boulders which are noticed since these stand out in the landscape and are not easily transported away.
I remember becoming interested in geology as a child when I began noticing large boulders in the middle of fields and the forest around my native New Hampshire. I asked my science teacher about these boulders, and he told me they were called glacial erratics and taught me a little about ice ages. Most of the erratic boulders seen throughout New England today were deposited during the last ice age, which reached a maximum around ~22,000 years ago and which ended ~10,000 years ago.
My favorite glacial erratic, which is shown in this week’s geology picture, sits on a small island in front of my parents’ lakeside cabin on Franklin Pierce Lake in New Hampshire. My parents purchased the cabin about 5 1/2 years ago, and although I had long moved away from home when they bought the cabin, I quickly fell in love with it (and its erratic island!) and try to visit regularly. Every year, my husband and I spend at least a couple of weeks at the cabin. Back in May, the cabin served as a geologist lair when my fellow geoblogger Dana Hunter visited for a few days. If you are brave, you can swim or kayak to the little island from my parents’ cabin and jump off the erratic.
Does anyone else have a favorite glacial erratic to share?