REMARKS: The lake occupies the site of a glacial lake that existed here over 10,000 years ago, when a continental glacier covered much of northwestern Pennsylvania. The glacial ice, whose eastern edge was at Harrisville and Slippery Rock, dammed the westward-flowing Slippery Rock and Muddy Creeks, forming lakes in their valleys; in the latter, Lake Arthur was formed.
REFERENCES: Lytle, W. S. (1959), Field Trip C, Stop 1, Glacial Lake, in Guidebook, 24th Annual Field Conference of Pennsylvania Geologists, Pennsylvania Geological Survey, p. 67-69.
__________ (1970), Moraine State Park, Pennsylvania Geological Survey, 4th ser., Park Guide 4.
REMARKS: This 3-mile-long esker is probably the best remaining example of this type of glacial deposit in western Pennsylvania. The esker was formed during the close of the Wisconsonian glaciation, and is also known as the Miller Esker and West Liberty "Hogback."
Eskers are ridge-shaped sand and gravel deposits formed during the melting of a glacier. The ridge form marks the trace of a glacial meltwater stream that is confined within the ice mass. Esker ridges are always associated with the stagnation phase of the glacial episodes.
There are two major ways that the esker ridge can form: 1) in an ice tunnel along the base of or within the stagnated ice mass, and 2) as a meltwater channel deposit or crevasse filling on the surface of the ice.
The surface expressions of the resulting types of eskers are quite similar. A ridge will be formed, it will be somewhat sinuous, and it will be composed primarily of gravel. The distinctive difference in the surface expression is that the crevasse-filling type will have a tendency to form angular bends and the long segments (i.e., the unbended segments) will be nearly parallel. The ridge formed in an ice tunnel will have more of a sinuous-meander pattern characterized by sweeping meander bends and a few straight-line segments.
The internal composition will also differ. The tunnel esker will often have a till blanket draped over the top of the deposit. The till will be indicative of transportation within the ice, showing long-distant movement of material. A pseudoanticline draping of the sediment within the deposit is common. Ice-contact faulting may be present but is usually not extensively developed.
The crevasse filling will have fluvial-type deposition to the surface. There may be some areas that have flow till incorporated into the deposit because supraglacial material flowed into the crevasse from the ice surface. Ice-contact faulting of the sediment is common because the sides of the deposit were held in place by the ice mass, and, when the ice melted away, faulting developed as the sides of the sedimentary mass were let down.
The West Liberty Esker is believed to be a crevasse filling for the following reasons:
1) The existence of straight-line segments of the ridge connected by a sharp bend.
2) Glaciofluvial gravels are present across the whole ridge.
3) Numerous normal, ice-contact faults occur along the edge of the ridge.
4) No till blanket has been observed on the ridge.