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Upheaval
Dome at Canyonlands
Setting the Scene
Canyonlands is a place of relative geologic
order. Layers of sedimentary deposits
systematically record chapters in the
park's past. With some exceptions, these
layers have not been altered, tilted or
folded significantly in the millions of
years since they were laid down by ancient
seas rivers or winds.
Upheaval
Dome is quite a different story. In an
area approximately three miles (5km) across,
rock layers are dramatically deformed.
In the center, the rocks are pushed up
into a circular structure called a dome,
or an anticline. Surrounding this dome
is a downwarp in the rock layers called
a syncline. What caused these folds at
Upheaval Dome? Geologists do not know
for sure, but there are two main theories
which are hotly debated.
Salt
Dome Theory
A thick layer of salt, formed by the evaporation
of ancient landlocked seas, underlies
much of southeastern Utah and Canyonlands
National Park. When under pressure from
thousands of feet of overlying rock, the
salt can flow plastically, like ice moving
at the bottom of a glacier. In addition,
salt is less dense than sandstone. As
a result, over millions of years salt
can flow up through rock layers as a "salt
bubble", rising to the surface and
creating salt domes that deform the surrounding
rock.
When
geologists first suggested that Upheaval
Dome was the result of a salt dome, they
believed the landform resulted from erosion
of the rock layers above the dome itself.
Recent research suggests that a salt bubble
as well as the overlying rock have been
entirely removed by erosion and the present
surface of Upheaval Dome is the pinched
off stem below the missing bubble. If
true, Upheaval Dome would earn the distinction
of being the most deeply eroded salt structure
on earth.
Impact
Crater Theory
When meteorites collide with the earth,
they leave impact craters like the well-known
one in Arizona. Some geologists estimate
that roughly 60 million years ago, a meteorite
with a diameter of approximately one-third
of a mile hit at what is now the Upheaval
Dome. The impact created a large explosion,
sending dust and debris high into the
atmosphere. The impact initially created
an unstable crater that partially collapsed.
As the area around Upheaval Dome reached
an equilibrium, the rocks underground
heaved upward to fill the void left by
the impact. Erosion since the impact has
washed away any meteorite debris, and
now provides a glimpse into the interior
of the impact crater, exposing rock layers
once buried thousands of feet underground.
Upheaval
Dome Today
Whatever the origin of Upheaval Dome,
it is the result of erosion of a structural
dome. Rock layers now at the surface within
the dome were once buried at least a mile
undergound and are not visible anywhere
else in the nearby area. While some call
this feature a crater, it is not a crater
in the traditional sense of the word,
but simply another example of the erosion
which created Canyonlands National
Park.
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