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Earth Rocks!

Check out five extraordinary rock formations

Take a trip around the planet and you’ll come across incredible landscapes, from towering stone arches to massive canyons. These amazing rock formations exist because Earth is constantly changing. The shifting of tectonic plates, giant slabs of rock that form Earth’s surface, can make mountains. Wind and water can sculpt stones into unusual shapes.

All types of rock formations have something in common. They formed over very long periods of time. “Rocks are fascinating because they tell the story of Earth’s history,” says Michele Koppes, an earth scientist at the University of British Columbia.

Here’s what five unusual rock formations around the world reveal about our planet’s past.

The largest rock columns at the Giant’s Causeway are 39 feet tall!

Volcanic Columns

Legend says this group of dark rock columns in Northern Ireland, known as Giant’s Causeway, was made by a giant named Finn McCool. But scientists know the real creator: volcanoes. The columns are made of an igneous rock called basalt.

Between 60 million and 55 million years ago, multiple eruptions covered the area with more than 600 meters (1,970 feet) of lava. When lava cools, it contracts. If it cools very slowly, the rock can crack, forming six-sided columns. “Mud in a puddle drying out on a hot day will form very similar patterns,” says park ranger Cliff Henry. “It all has to do with physics.”

Over time, erosion by ice and seawater exposed the columns. The landscape often surprises visitors. “Some people don’t believe it’s natural; they think it’s human-made,” says Henry.

Stone arches like this one are formed by erosion.

Amazing Arches

This arch soars 14 meters (46 feet) above ground. It’s one of more than 2,000 rock arches at Arches National Park in Utah. The arches are made of sandstone, a type of sedimentary rock.

Between 220 million and 165 million years ago, the area was covered with giant sand dunes. Over time, the sand grains were pressed together. Minerals glued the grains into stone. The arches formed when water dissolved the minerals inside the softer sandstone. That caused the rock to crumble, carving the harder sandstone into bridge-like shapes.

Erosion is ongoing, says park ranger Lee Ferguson. New arches form—and collapse—all the time. Since the 1980s, the park has lost about 50 arches. “The rocks are constantly changing,” Ferguson says.

Rain transforms the salt flat into a giant mirror.

Miles of Salt

This huge expanse of white is the world’s largest salt flat. The deposit of salt in Bolivia, known as the Uyuni Salt Flat, spans 10,582 square kilometers (4,086 square miles)! That’s twice as large as the state of Delaware.

More than 15,000 years ago, the area was a lake. The lake was formed by rainwater and snowmelt coming off the nearby Andes Mountains. The flowing water carried salt and other minerals from the mountains. Over time, the lake dried up. The minerals sank to the lake bed, forming a salt flat up to 10 meters (33 feet) thick.

When it rains, a thin layer of water pools at the surface. The water reflects the sunlight, turning the salt flat into a giant mirror. 

The folded rocks are made of tiny pieces of shells. 

Folded Rocks

Crunch! These rocks on the Greek island of Crete look like they’ve been smashed together. But more than 45 million years ago, they lay flat at the bottom of the sea. The rocks are made of layers of limestone and silica, types of sedimentary rock made of shells from tiny marine animals.

As tectonic plates pressed against each other, the rock layers were slowly squeezed. Over millions of years, those tectonic forces created the folds and pushed the rocks out of the sea, says Charalampos Fassoulas, a geologist at the University of Crete.

You can find folded rocks in many places around the world. Keep an eye out for them when you’re hiking!

The Great Blue Hole is about 1,000 feet across and 400 feet deep.

Underwater Caves

Looking at this photo, you might wonder: Did someone poke a hole in the middle of the seafloor? This round hole off the coast of Belize is known as the Great Blue Hole. It’s a sinkhole leading to a deep underwater cave!

The cave started forming about 150,000 years ago, when the area was above water. Rain seeped through soil into the underground limestone. The water dissolved the limestone, creating a cave about 122 meters (400 feet) deep, says John Pohlman at the U.S. Geological Survey.

In the thousands of years since, the sea level has risen. The cave eventually filled with water. Its roof collapsed, forming a sinkhole. That’s the large circular opening you can see today!

Continue the Learning Journey
Rocks and Minerals

Learn about the different kinds of rocks and minerals in our world

As you watch the video, write down the rocks and minerals you recognize. Can you find some of them around your home or neighborhood? With a trusted adult, go on a rock and mineral scavenger hunt! Take photos of or draw the rocks and minerals you find. Then make an eye-catching collage that shows off your findings!

Imagine you’ve just taken a trip to one of the rock formations in the story! Create a postcard of your trip. A postcard usually includes a photo of a place and a message on the other side. Using a half-sheet of paper, draw the rock formation on one side. On the other side, draw a vertical line that divides the paper in half. On the left-hand side, write a paragraph about your visit, describing what you saw and how you felt. On the right-hand side, address your postcard to a family member. Then give it to them and read it together! 

Make a Salt Flat

Follow these steps to see how salt flats form in nature. 

The Uyuni Salt Flat in Bolivia formed when a lake rich in minerals dried up, leaving a thick layer of salt. Check out the slideshow above to see that process in action, and make your very own salt flat!

Write a Legend

Here’s how to plan and write your own legend.

The Giant’s Causeway in Northern Ireland was formed by volcanic eruptions, but legends say that a giant named Finn McCool created the odd-looking rocks to build a bridge across the water. A legend is a story, often passed down through time, that is widely believed but cannot be proved. It usually explains how or why something in nature happened. Use the slideshow above to write your own legend of how another one of the rock formations in the story came to be.

This article was written by Alessandra Potenza for SuperScience magazine.

Image Credits: Peter Unger/Lonely Planet Images/Getty Images (arches); Stephen Emerson/Alamy Stock Photo (Causeway); Jim McMahon (maps); iStockPhoto/Getty Images (salt flats); NJphoto/Alamy Stock Photo (folded rocks); Norbert Wu/Minden Pictures (blue hole)