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Roger Weller, geology instructor
Craters of the Moon, Idaho
by Joshua Novinger
Craters of the Moon National Park in Idaho
Craters of the Moon National Park is located on the Snake River Plains in Idaho. The park acquired its name from the visual appearance of the volcanos and craters in the area, which are all dark in coloration, similar to what we expect on the moon. The whole park is the result of basaltic volcanic activity, occurring between about 15,000 years ago and 2,100 years ago, over the course of 8 major eruptive periods throughout that time span, with each of those periods lasting 1000 years or less, and were interrupted by periods quiet in comparison, which lasted between 500 and 3000 years. The park itself contains numerous examples of almost every different kind of basaltic volcanism. The Craters of the Moon park contains 60 lava flows and about 25 cones, with cinder cones and spatter cones being well-represented within the roughly 600 square miles of the park.
A Brief Geological History
8 million years ago, the Yellowstone Hot Spot was underneath the Craters of the Moon. At this time, the area was subject to violent rhyolitic eruptions. The next major set of events occur between 6 million years ago and 15,000 years ago, when basaltic eruptions began to produce lava flows of a thickness around 4000 feet. Between 15,000 and 2000 years ago, the landscape we know today was largely formed over the course of 8 major eruptive periods, and the lava field grows to cover the roughly 618 square miles that comprise the park today.
The first eruptions were extremely violent, and produced a lava
type called rhyolite. During that time, massive calderas began to spring up,
with some growing to 30 miles in diameter. As time went on, the basalt lava
flows began covering the rhyolitic flows as they boiled onto the surface, giving
the park the massive flows it is known for today.
One of the major features of the park is referred to as The Great
Rift, a system of crustal fractures due to a series of basaltic fissure
eruptions, running 52 miles, from northwest to southeast, along the eastern
portion of the Snake River Plain. Along the rift, there are many cinder cones,
lava cones, fissures (eruptive and non-eruptive), and shield volcanoes. The
Great Rift and other basaltic rift systems are thought to have a typical
eruptive pattern of spewing up curtains of fluid lava high into the air. As the
lava cools, it becomes silica-rich, and the lava curtain break apart into
separate vents. This is where the Rift acquires its numerous types of volcanoes
found all along its expansive run, such as spatter and cinder cones. Later
stages of the eruptions end up pushing lava streams out through the sides or
bases of the cinder cones. Finally, a solid crust begins to form over the lava
streams and tubes as the lava cools along the surface.
Another major feature of the park is the Big Cinder Butte, a
cinder cone standing more than 700 feet higher than the surrounding area.
Notably, there are 19
other cinder cones in the area that are at least 100 feet high as well.
The Kings Bowl is a phreatic explosion pit along the Great Rift, and is 280 feet long, 100 feet wide, and 100 feet deep, which was caused by lava meeting groundwater, which caused a steam explosion approximately 2,200 years ago. It is one of the significant structures within the park, and one of the most visually dominant along the rift.
The Bear Trap lava tube is a cave system stretching over 15 miles, between the Craters of the Moon and the Wapi lava fields. It is famed for its length, as well as the lava cave features it contains within that have been preserved well over the years, with lava stalactites and curbs showing the high stands of lava flows on the tube walls.
Scientists presently believe that the volcanoes of
Craters of the Moon are not extinct, but dormant, and that they are likely to
resume eruptions sometime over the next 900 years, with the next 100 years being
the most likely to produce volcanic activity within the park. It was speculated
and feared by scientist that, due to an earthquake that occurred in the early
1980s and shook Mt. Borah (the tallest mountain in Idaho), raising it by 1 foot,
would cause volcanic activity within the Craters of the Moon to resume.
Due to the nature of the lava field and the lava beds on
the Snake River Plains, it makes life difficult to thrive here. Idaho is
notorious for having high winds and a dry climate, being high desert, and the
large, black, heat-absorbing lavas tend to absorb the rainwater that falls here
rather quickly (the average yearly precipitation of which is about 15-20 inches
per year). That, combined with the high heat in the summer, both in the air and
the soil, mean that plant and animal life is somewhat scarce here. Water is
generally found only within deep holes at the bottom of craters that have blown
out, so most animals get the moisture they require while attempting to survive
here by the foods they consume.
For plant life, the soil tends to absorb moisture very
rapidly, making it difficult for plant life to survive, or even take root. Even
so, the park is home to a number of very resilient species of plant and animal
life, with plants adapting by becoming resilient to low hydration conditions and
high ability to obtain moisture, or finding moisture supplies, such as on the
northern slopes of some cinder cones, where snow and ice can survive well past
the winter, as the sun has difficulty reaching those particular points, thereby
allowing plant life to take advantage of the moisture they provide.
As with plant life, animals have also found their way to
survive, with insects, reptiles, birds, mammals, and amphibians all being
represented here. Most of these animals are nocturnal, for reasons of thwarting
predators and mitigating the summer heat.
Despite its somewhat harsh appearance, the Craters of the Moon park in Idaho is an excellent educational resource for geological subject matter, is home to many different types of flora and fauna, and can also be quite beautiful.
NPS contributors (1991). Craters of the Moon: National Park Handbook (139). Washington D.C.: National Park Service Division of Publications. ISBN 978-0-912627-44-1.
Kiver, Eugene P.; Harris, David V. (1999). Geology of U.S. Parklands (5th ed.). New York: John Wiley & Sons. ISBN 978-0-471-33218-3.
Clinton, William Jefferson (November 9, 2000). Boundary Enlargement of the Craters of the Moon National Monument (PDF). Washington, D.C.: Office of the President of the United States. Proclamation 7373.
National Parks Service. U.S. Department of the Interior, n.d. Web. 25 Apr. 2017.
Craters of the Moon National Monument. N.p., n.d. Web. 25 Apr. 2017.