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.
