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| A series of linked potholes
in large boulders of Triassic diabase in the Susquehanna River near Three
Mile Island, Pennsylvania. |
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| Intersecting potholes at Falmouth,
off the southern end of Three Mile Island, in the Susquehanna River,
Pennsylvania. They were exposed during the summer of 1999 when the water
level was low. |
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| A cluster of potholes at the Holtwood
Gorge along the Susquehanna River, Pennsylvania, formed in a steep cliff of
Wissahickon Schist with quartz boudins. Potholes in the vicinity range
in size up to 9 metres deep and 4-6 metres in diameter. References to previous
studies can be found here. |
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| Potholes at Falmouth, off the southern
end of Three Mile Island, Pennsylvania. Holes occur in the rocks where adjacent
potholes intercept. The potholes typically widen with depth. Water marks
show the level of the Susquehanna River was lower than normal. The form of
the partial potholes is clearly unrelated to the water levels, suggesting
currents were not the cause of the potholes. |
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| Small linked potholes form grooves
in this boulder. |
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| Careful observation shows that current
action has not carved these potholes; eddies in streams are not anchored
to their positions, but move along with the current and disappear, while
new eddies are continually formed. The eddies or vortices do not drill down
into the rocks of a stream bed. It is suggested the potholes were formed due
to the effects of the release of vertical stress during the removal of overburden
by flood waters in catastrophic conditions. The river merely exposed them
by eroding away the pothole contents. |
Photos by Mark Brinkman. Used by permission.