Devils Tower

Devils Tower

History of Devils Tower

Far out in the wilderness of Wyoming, a giant rock formation towers above the landscape. The Lakota and other American Indian tribes in the area consider the rock formation a sacred site. Legends describe the columns of the tower being formed by the claws of a bear, and the Lakota name for the formation is Mato Tipila, which means “Bear’s Lodge.” In 1875, Mato Tipila was incorrectly translated into Bad God’s Tower, which later became Devils Tower.

The formation has been a national monument since 1906, but people have been visiting this huge tower of rock for thousands of years. How did Devils Tower form, and why is it so much taller than the surrounding landscape?

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Devils Tower is made of igneous rock, but is surrounded by sedimentary rock. These two types of rock are formed by different processes. Exploring the different geological processes that formed Devils Tower can help explain its history.

Poll

Could the rock that created the Devils Tower come from the sedimentary rock it is surrounded by?

• yes

• no

When you first see Devils Tower rising up above the dry landscape, it’s hard to imagine that the whole region was once underwater.

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​However, two hundred million years ago, this area of Wyoming was covered by a shallow sea.

• ​Blowing wind and falling rain weathered nearby rock formations over and over, causing small pieces to break off and become sediment

• Bits of sediment ran into each other, they became smaller and smaller, and were driven downward by moving water and gravity into the sea

• Over millions of years, compaction and cementation turned the sediment into solid sedimentary rock.

• Gradually, the sea drained away, leaving dry land in its place.

Multiple Choice

This statement, "bits of sediment ran into each other, they became smaller and smaller, and were driven downward by moving water and gravity into the sea", best describes...

• weathering

• erosion

• deposition

• cementation

Multiple Choice

What was Wyoming like before Devils Tower formed?

• covered in a massive mountain range

• flat and without any land formations

• covered in snow and glaciers

• underwater and covered with a shallow inland sea

Interestingly, Devils Tower itself is not sedimentary rock. About 50 million years ago, rock underneath Earth’s outer layer in this region melted into magma.

A column of the hot magma forced its way up into the layer of sedimentary rock, then cooled and became hard igneous rock called phonolite (FO-no-lite).

This only happens when rock gets up to very high temperatures—in the hundreds of degrees Celsius.

• After the magma solidified, it cracked into columns of rock.

• Over time, the sedimentary rock that covered the igneous rock was weathered and eroded away by wind and water, leaving a tower of hard igneous rock standing like a skyscraper above the surrounding land. 

Open Ended

How did Devils Tower form?

Poll

Considering that Devils Tower is still standing and the sedimentary rock that was surrounding it is gone, what claim can you make about igneous rock when compared to sedimentary rock?

CHOOSE ONE ANSWER

• Sedimentary rock is stronger than igneous rock.

• Igneous rock is stronger than sedimentary rock.

• Both types of rock are equal in strength.

What will happen to Devils Tower over time?

Even though the igneous columns of Devils Tower are very hard, they are slowly being weathered and eroded—that is, they are being worn away as temperature changes, wind, and water remove bits of sediment from them. The tower that now stands is much smaller than the original mass of magma that pushed up from below. Millions of years from now, Devils Tower will be completely weathered and eroded away

Open Ended

What will happen to the sediment that forms from the weathering and erosion of Devils Tower?

This is Shiprock in northern New Mexico. It is similar to Devil's Tower and was formed from a intrusion of magma into the surrounding sedimentary rock. Some of the sedimentary rock was melted and became part of the magma. So, even though Shiprock is made of igneous rock, it came from the sedimentary rock that was melted from the heat in Earth's interior.