Junior Ranger: Red Hot Lava!

NPS

Lets check out some of the strange shaped rocks you might see in the park.

This type of lava is in a formation called columnar jointing, sometimes called columnar basalt. About 90% of lava rock on earth is made of basalt. This type of lava rock is found all over the Columbia Plateau, especially at the edges of large canyons.

Many other places around the world have this type of lava rock. In fact, two National Monuments are famous for their columnar basalt: Devil's Tower and Devil's Postpile. The Giant's Causeway in Ireland is also a great example. These types of columns have even been found on Mars!

NPS/Jim Peaco

Here is a close-up, cross section of one of the columns.

They are hexagonal and have six nearly-equal sides. The lava makes this shape because of how it cools. Spots called 'centers' start cooling first. If the lava is very smooth and if the centers are evenly spaced, then there is a good chance that hexagons will form.

The forces that pull in toward those centers create these straight-sided chunks that look like dense crystals. So, the smoother the lava is, the more even the cooling, the more likely it will create the columns.

These columns can be short - like the length of your arm - or as tall as a cliff or mountain. It all depends on how smooth the basalt lava was and how evenly it cooled. If it cooled slowly from top to bottom, it could create whole mountainsides of columns.

In this diagram, five 6-sided hexagons are fitted together to form a flat layer, illustrating how columnar basalt creates these shapes as it cools. A central point of each column is labeled and arrows show how the force moves from the outside to the center during cooling.

Fun Lake Roosevelt Lava Facts:

• Although you'd have a difficult time finding a volcano around here, scientists have actually counted over 300 lava flows in this region.
• These lava flows are over 6000 feet (1800 meters) thick.
• The lava came from long vents or cracks in the earth, some over 93 miles (150 kilometers) long.
• These lava flows are between 6 million and 17 million years old, so you're perfectly safe camping by the lake!
• The huge hot spot that created these flows eventually moved to the east and now bubbles under Yellowstone National Park.

Activity: The Ground Is Lava!!!!!!

• Find a friend or family member
• Decide what you can stand on and what you can't: What do you think can survive the heat of the lava bubbling up from below? Are rocks safe? Can you balance on a stick? Maybe only a bandanna or some extra shoes and a piece of paper? Be creative!
• Decide on a starting point and an ending point
• Try not to fall in!

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Part of a series of articles titled
Junior Ranger - Lake Roosevelt National Recreation Area.

Previous:
Junior Ranger: Rock Scavenger Hunt

Next:
Junior Ranger - Rockin' Rocks

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• Lake Roosevelt National Recreation Area

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