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Glacial Erratics

Glacial Erratic

Have you ever been hiking in the forest and come upon a house size boulder? Where do these things come from? How did they get there?

Last week I learned that these boulders are called Glacial Erratics. The one in the picture above is located near Table Rock in the Gunks, outside of New Paltz, New York. There are a lot bigger ones scattered through the woods there.

These huge boulders were transported, possibly hundreds of miles, by 3,000 foot thick glaciers that covered most of North America just 13,000 years ago. The boulders are called erratics because they’re made out of different rock than the local Shawangunk conglomerate that you find on the cliffs here.

So if you see big boulders in the woods around you that seem out oddly out of place, they’re not there because aliens dropped them from outerspace. Think glaciers.


  1. We have similar feature in my state on a very popular hike on "Old Rag Mountain". Its fairly legendary in Virginia and a right of passage for Scouts. With no views until the top in addition to great rock scrambles, seeing these giant boulders along the nearly 100% uphill trail helps pass the time and detracts from focusing on the endless switchbacks. Cool stuff which helps remind us all that a lot has happened to the coastal states on a very large scale.

  2. These are very common in the UK – In fact there's one in the town centre in Crook which is known as the "witches' stone". Apparently, you're supposed to walk around it three times before doing your shopping.. or something….

    Anyway, its a piece of silurian rock where everything else in the area is carboniferous.

  3. They are pretty surreal to see out in the middle of a stand of trees. They were pretty cool to see when I was thru-hiking the AT especially when there was a tree growing out of a crack. The stone fences in MA, CT and other states were also pretty cool.

  4. Out here they are a dime a dozen but I never tire of them! Washington State is littered with them, in the "U" shaped valleys (glacier carved). Even better are the "kettles", deep holes left by the glaciers, One of the islands up here has a great example of it and yep, there are erratic's in some of them.

  5. Hi, I live in high falls and am a climber. I was wondering if the boulder in the photo was on ther monhonk preserve and if so could you tell me where it is located. I am familiar with table rock and have climbed there. I don't think i've ever seen that boulder. How tall is it? Thanks, Jeff

  6. It's on the trail leading from spring farm to table rock, on the right hand side probably 100-200 yards before you get to table rock. It's not the biggest one around – probably only about 12 or 15 feet tall. There's a giant one on that same trail on the left hand side, again before you get to table rock (but I didn't get a photo of that one).

  7. National Geographic magazine (March 2012) shows different erratics. We have them in Dinwiddie County, VA both hidden in the woods and lying in farmers’ fields. There is one on a hiking trail that is about 10 feet tall or better, and about twice as wide since it is split perfectly in half. The trail actually passes between the two halves.

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