Glacier Pools Preserve is located in the watershed of the West Branch Susquehanna River in Eastern Lycoming County. At Muncy the river bends around the northernmost ridge of the broken-down ancient mountains that form parallel valleys throughout central Pennsylvania. To the north of the river is a completely different geologic province: an ancient sea floor sitting at 2000 foot elevation where mountains ought to be, preserved by top layers of erosion-resistant rock, and called the Allegheny Plateau. It ends abruptly with an escarpment called the Allegheny Front, extending for hundreds of miles, and easily visible by looking north from any of the meadows of Glacier Pools Preserve. (See the photo above.)
Glacier Pools Preserve also marks the farthest south the most recent glaciers came, the Wisconsin ice sheet (click to see link.) It sat here long enough to allow rocks embedded in the ice to drop to the ground when it melted (“erratics”)
Glacial erratic
In a few places (where the glacier was thicker when it stopped advancing?) huge blocks of ice half under the soil surface melted in place, leaving depressions which fill with water in the spring and after rain but dry completely in between. These “vernal pools” don’t support fish, and so are the preferred safe breeding grounds for many amphibians (see page on Vernal Pools.)
- vernal pool in the spring
In other areas, the glacier left gravel at its edges, and over the centuries the gravel built up into ridges stretching hundreds of feet over the land. These are very obvious as you walk through the woods. They are called “eskers.” 