Earth Rocks!

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.

This group of dark rock columns is found in Northern Ireland. It’s known as Giant’s Causeway. Legend says it was made by a giant. He was named Finn McCool. But scientists know the real creator. It was volcanoes. The columns are made of basalt. It’s a type of igneous rock.

Many eruptions happened between 60 million and 55 million years ago. They covered the area with more than 600 meters (1,970 feet) of lava. Lava shrinks when it cools. The rock can crack if it cools very slowly. That formed 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.”

Erosion by ice and seawater revealed the columns over time. The 40,000 columns often surprise visitors. “Many people don’t believe it’s natural,” says Henry. “They think it’s human-made.” 

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.

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

The area looked different between 220 million and 165 million years ago. It was covered with giant sand dunes. The sand grains were pressed together over time. Minerals glued the grains into stone. Water dissolved the minerals inside softer sandstone. That caused the rock to crumble away. The harder sandstone was left. It formed bridge-like shapes.

Erosion is ongoing, says park ranger Lee Ferguson. New arches form all the time. They also fall down. The park has lost about 50 arches since the 1980s. “The rocks are constantly changing,” Ferguson says.

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. 

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

The area was a lake more than 15,000 years ago. It was formed by rainwater and snowmelt. They came off the nearby Andes Mountains. The flowing water carried salt and other minerals from the mountains to the lake. The lake dried up over time. The minerals sank to the lake bed. They formed a layer of salt. It’s up to 10 meters (33 feet) thick.

A thin layer of water pools at the surface when it rains. The water reflects the sunlight. That turns the salt flat into a giant mirror.

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!

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

The rock layers were slowly squeezed. That happened as tectonic plates pressed against each other. Those forces created the folds over millions of years. They pushed the rocks out of the sea, says Charalampos Fassoulas. He’s 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!

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!

Look at this photo. Did someone poke a hole in the middle of the seafloor? That’s what you might think. This round hole is found off the coast of Belize. It’s known as the Great Blue Hole. It’s a sinkhole. It leads to a deep underwater cave!

The cave started forming about 150,000 years ago. Back then, the area was above water. Rain seeped through soil. It trickled into the underground limestone. The water dissolved the limestone. That created a cave. It’s about 122 meters (400 feet) deep, says John Pohlman. He works at the U.S. Geological Survey.

The sea level has risen in the thousands of years since. It filled the cave with water. The cave’s roof fell in. That formed a sinkhole. That’s the large round opening you can see today!