Ryan Penny is best known for running Camp Catskill, a hiking and camping gear shop in Tannersville. He is also a member of an extensive network of geology spies that we maintain throughout the Catskills. We have to get columns out every week and we need help to do that. Our team of spies is always on the lookout for things we can write about. Recently Ryan contacted us about an interesting phenomenon he had discovered while hiking above Rte. 214, at the west end of Plateau Mountain. It was an enormous boulder that had apparently tumbled to near the bottom of that slope. Look at our first photo and you will see this very big rock. Sandstone, like this weighs about 150 lbs. per cubic foot and we guesstimate that this one is about six feet by six feet by ten feet or 360 cubic feet. Multiply by 150 and that is a 54,000 lbs. boulder! Those numbers catch your attention, don’t they? Ryan thought there might be a story here. He thought that this had been a recent rockfall, perhaps a very recent one.
Ryan met one of us, Robert, and led the way to the boulder. It was immediately obvious that he was right about that slide. There were a number of freshly broken trees with some of them lying underneath the boulder. But there was a lot more to the story. Ryan pointed uphill and there were a few more boulders. These too, had recently slid. But it all got worse, much worse as we gazed farther uphill. We suddenly saw the source of all these landslides. See our second photo.
We looked and saw a steep corridor of broken trees leading all the way to the top of the ridge. Up there was a very sizable ledge of Catskill bluestone. That appeared to be the source of these boulders. The story was getting more and more interesting. Now we understood that this was not just a simple onetime slide but that this was an ongoing process. This was in the middle of March and, along with April, that is a time that might be called the landslide season. You see, that’s when the nighttime temperatures commonly drop below freezing. During the following days, temperatures are likely to climb back above freezing. That means that water can freeze at night and melt during the day. We geologists call these freeze-thaw cycles.
We looked back up to that ledge again and realized that up there water was soaking into rock fractures nearly every day. During the nights it was frequently freezing. Water expands as it turns into ice and so those cracks were commonly expanding. When fractures expand just a little too much then the rock loosens up and every once in a whole a 54,000 lb. boulder will come bouncing and pounding down the hill slope. Along the way it will knock down all sorts of trees before finally coming to a rest. We were looking at a hill that apparently had been seeing this process underway for days or even weeks.
We have not given precise directions on getting to this site. Normally we want you to go out and see the geology that we describe. But this time is different; we think that there are real hazards here. New rockfalls can occur at any moment, including when you are there. Please don’t go. There are other hazards. We will cover those next week.
Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist.” Read their blogs at “thecatskillgeologist.com.”
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