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Volcanic blast, not giant bear claws, formed Wyoming's Devils Tower
By Scientific American, adapted by Newsela staff on 03.19.15
A view of Devils Tower. Photo: Wikimedia Commons
Native Americans believe that giant bears made long scratch marks in Devils Tower as they
attempted to climb to the top.
But the vertical lines along the sides of the almost 390-meter-tall (nearly 1,300 feet) rock
formation in Wyoming are not claw marks. They are actually the edges of columns of igneous —
volcanic — rock. The column formed as the molten rock cooled and contracted, cracking apart.
Czech Scientists Check It Out
But how did the columns of Devils Tower form — below the ground or as part of a violent
volcanic eruption?
Scientists have suggested many theories over the years. The most popular today hold that
Devils Tower was born 49 million years ago as a rising half dome of magma, molten rock. The
magma was squeezed to the surface either between underground layers of rock or deep inside
a volcano.
Prokop Závada, a geologist at The Czech Academy of Sciences, and three other researchers
became interested in the mystery of Devils Tower. They found a clue in another butte in the
Czech Republic, called Boren. A butte is an isolated hill with steep sides and a flat top. Boren is
similar to Devils Tower, although it is more rounded and covered with trees.
Maar-Diatreme? It's A Blast!
The researchers concluded that Boren was created by a sudden type of volcano called a maardiatreme. This kind of volcano blasts a crater on the Earth's surface when molten rock
underground meets groundwater. After the blast, the researchers think, a flat dome of lava filled
the crater, acting like a plug. Wind and rain eroded away at the edges of that dome until only the
innermost portion remained. We call that isolated core Devils Tower. Because Devils Tower is
so similar to Boren, the Czech team decided to see it was formed in the same way.
The researchers looked at two main characteristics of Devils Tower. They studied the shape of
its distinctive columns and the position of magnetic minerals within them.
The National Park Service let the researchers collect one new rock sample from Devils Tower in
order to analyze its magnetic properties. The researchers discovered that near the base of
Devils Tower, tiny needle-shaped minerals within the rock are oriented close to vertical. That is
the direction the lava flowed before it hardened. Closer to the top, the minerals turn horizontal.
Plaster And Computer Models
Based on that information, the researchers made digital and physical models.
For the physical model, they mixed some magnetic particles in with soft plaster. They squeezed
the material upward through an upside-down cone full of earth and rock until it formed a mound
on the surface. This resembled the eruption of lava following a maar-diatreme volcano.
When the plaster hardened, the researchers cut the cone open to examine the inside. They
measured which way the magnetic particles pointed just as they had done at Devils Tower. They
also made a computer simulation of cooling volcanic rock. The simulation let the researchers
compare columns created as Devils Tower cooled under different conditions.
The columns of Devils Tower matched the expected pattern exactly. In the plaster models, the
direction of the magnetic particles also matched the direction of the minerals from Devils Tower.
They were closer to vertical around the base and horizontal near the top. In a paper, Závada
and his team concluded that Devils Tower was caused by an underground volcano like Boren in
the Czech Republic.
This Bears Further Study
Western Washington University’s Bernard Housen was not involved in the study. He said the
work was “interesting and certainly very plausible” or believable. However, he was not convinced
it ruled out other possible explanations. The problem is that there isn’t much data from Devils
Tower itself, since the government has allowed so few samples to be taken. “So, it is likely that
the origin of Devils Tower will remain uncertain," he said. This is in part because the government
wants to make sure that the butte is preserved, Housen said.
It might be possible to study the similar, if less spectacular, buttes near Devils Tower, however.
They were likely formed in the same way — with or without the help of giant bears.
Quiz
1
2
3
Which answer option contains two central ideas of the article?
(A)
Devils Tower is a rock formation with very unusual columns on its
sides.The columns look like they were made by the claws of bears.
(B)
Devils Tower is a rock formation with very unusual columns on its sides.
Scientists are trying to discover what caused the tower to form.
(C)
Devils Tower is an unusual rock formation that is similar to a rock formation
in the Czech Republic. Scientists in that country have studied what caused
both formations.
(D)
Devils Tower is an unusual rock formation. Researchers have made plaster
and computer models that prove without a doubt how the rock formation
was made.
Which of the following options is an objective summary of the article?
(A)
Devils Tower is a fascinating rock formation that has been of interest to
scientists for many years.
(B)
Devils Tower has been studied by various scientists, many of whom think
the tower was formed by a volcano.
(C)
Scientists think that the amazing rock formation called Devils Tower was
caused by a volcanic eruption.
(D)
Scientists have discovered that the most helpful way to study Devils Tower
is by making models of the tower.
Which sentence BEST compares the photograph in the article with the text in the
introduction of the article?
4
(A)
The photograph shows what the columns of the tower look like, while the
text provides information about how the columns were formed.
(B)
The photograph shows why the columns on the tower look like a bear's
claw marks, while the text explains why it was difficult for a bear to make it
to the top.
(C)
The photograph shows what the tower looks like, while the text in the
introduction only describes the types of rock in the tower.
(D)
The photograph shows the height of the tower, while the text provides
information about the width of the tower.
The first paragraph in the section "Maar-Diatreme? It's A Blast" corresponds with
the diagrams labeled A and B. Which information is provided in the text that is
NOT shown in the diagrams?
(A)
that a volcano explosion blasted a crater in the Earth's surface
(B)
that wind and rain eroded away the edges of the lava dome
(C)
that lava from the volcano explosion plugged up the crater
(D)
that there are rocks below the Earth's surface