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Craters of the Moon National Monument |
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Two kinds of lava: Pahoehoe (on the left) and
A'a |
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Paved pathways make rough lava fields accessible. |
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One of the most extraordinary geologic sites
in North America is located within a couple of hours of
Twin Falls, Idaho. The Great Rift volcanic zone is a fifty-three
mile-long tear in the earth's crust that extends roughly from
the southern end of the Pioneer Mountains to a point that
is eighteen miles northwest of the town of American Falls
on Interstate 86, just to the west of Pocatello. The Great
Rift varies in width from just under a mile to slightly over
five miles and was the source for scores of volcanic eruptions
and huge lava flows dating back nearly 17 million years. Geologists
have found evidence of major eruptions happening on average
every two thousand years over the last 10,000 years. It is
thought that the source of magma and mantle heat that fed
these lava flows could be the same one that is currently causing
heightened activity in the Yellowstone basin which, in turn,
is of growing concern to the administrators of Craters of
the Moon National Monument.
One of the largest lava fields in the Great
Rift volcanic zone is located in Craters of the Moon National
Monument. The Craters of the Moon lava field had sixty separate
flows and is the largest basaltic lava field in North America.
This "rip in the earth's crust" has provided an
easy way for roadtrippers to get an up-close view of amazing
volcanic structures like cinder cones, shield volcanoes, lava
tubes, volcanic bombs, tree molds, and the three principal
forms of lava -- pahoehoe, block and a'a. You could fly to
Hawaii and see some of these features being formed in real
time -- but this is a lot easier.
The Craters of the Moon visitors center is
on US-Highway 93 between Arco and Carey, a few miles west
of EBR-1, the world's
first breeder nuclear reactor on the Idaho nuclear testing
range. Before my recent visit in late July, I had last visited
the park a decade earlier. The level of trail work the park
service has completed in the intervening years is nothing
short of amazing. Walking on lava fields without trails can
be extremely hazardous, because much of the material is razor
sharp and very fatiguing to hike across. Most of the trails
in the vicinity of the Loop Drive Road are either paved asphalt
or hard-packed lava and provide easy walking access to features
that otherwise would be inaccessible to most park visitors. [Continued
on Page 2]
Mark
Sedenquist
September 4, 2005
