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2008 annual meeting – Spruce Pine Mining District: Little Switzerland, North Carolina
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DAY TWO
STOP No. 1 – New Exposure of the Linville Falls Fault
By: Peter R. Margolin, petermargolin@hotmail.com and Alex Glover
Four years ago, thanks to catastrophic flooding during hurricanes Ivan and Frances,
which destroyed the Park Service's Linville Falls Visitor Center, scientists were provided
with a new exposure of the Linville Falls Thrust Fault. At the west edge of the
Grandfather Mountain window, less than a mile above Linville Falls, the Linville River
cut a new but temporary channel across an ox-bow meander at a place called River Bend,
less than a mile from the Blue Ridge Parkway. Although the channel was abandoned in
less than a day--the time that elapsed for the river's floodwaters to subside--the effects of
this event are still quite evident, and no attempt has been made to undo them. The chief
effect was removal of a vast accumulation of soil, loose rock and vegetation as the
temporary riverbed was scoured down to bedrock. The bedrock here is a sheet of
Precambrian gneiss that is highly jointed as a result of its emplacement over Cambrian
quartzite during a major episode of late Paleozoic thrust faulting. Thanks to the joint
pattern in the gneiss, the river plucked out large angular blocks of gneiss during the
several hours it flowed through its new channel. When the waters subsided, the newly
scoured bedrock surface revealed substantial exposures of fissile mylonitic rock, a much
larger exposure of the thrust fault mylonite than had ever been available before.
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