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The forces of weathering and erosion both destroy and build our Earth's beautiful landscapes.

Powerful forces of nature are always at work. Rain pounds rocks. Waves batter beaches. Winds whip sand. Water floods the land. Gravity yanks rocks downward.

Gravity, wind, rushing water, acid, and ice are all forces of weathering and erosion. Weathering happens when rocks are broken into smaller pieces. These pieces are called sediment. Erosion happens when sediment moves from one place to another.

Some forces cause both weathering and erosion. Take wind, for example. It blasts rocks apart. Then it blows the sediment around. Over time, weathering and erosion can do a lot. Indeed, the force of weathering is stronger than rock. It rips rocks apart. It turns mighty mountains into sediment.

Breaking up a mountain makes lots and lots of sediment. It all has to go somewhere. The force of erosion carries it to new places. That builds up whole new landscapes.

In fact, some of our greatest landscapes were built by the powers of weathering and erosion. Let's take a look at a few of these majestic sights. To see them, we'll travel around the United States.

Bryce Canyon in Utah is a weathering wonder. Weathering and erosion have whittled away the rocks there for millions of years.

Today huge hoodoos rise from the canyon floor. Hoodoos are rock pillars with shapes on their tops. They tower nearly 610 meters (2,000 feet) above the ground.

The hoodoos' story began millions of years ago. That is when ancient rivers washed sediment off nearby mountains into a lake. Over time, the sediment turned into rock.

Next, ocean water flooded the area. Mud and skeletons from ancient sea creatures drifted to the seafloor. These too turned to rock.

Then the ocean dried up. A mountain of rock rose out of the receding water. The ocean had protected the rock. Now the forces of weathering lashed out at it.

A rushing river flooded the area. The water sliced its way through the rocks. It loosened softer rocks. It then washed them away.

The harder rocks remained. The river now churned around those rocks. It carved the rocks into hoodoos.

Rainwater splashed onto the hoodoos. It seeped into cracks. The water turned to ice in cold weather. The ice split apart the hoodoos. Bits of rock then fell to the ground far below.

Wind also chipped in. It blasted the hoodoos, blowing crumbling rocks away. Sediment rained down from the hoodoos.

All this took time. The forces of weathering and erosion work slowly, but they never stop. They still batter Bryce Canyon today. They will continue long after they have destroyed all the hoodoos they once carved.

Ice can topple structures even larger than hoodoos. In fact, it can tumble the mightiest mountains. Let's see how.

More snow falls on some mountains than melts each year. The snow piles up to form a glacier. That is a sheet of ice. Some glaciers are 1.6 kilometers (1 mile) or more thick.

These gigantic glaciers don't stand still. They slide slowly across the land. As a glacier crawls along, it weathers and erodes the land below.

Glaciers plow up everything in their paths. They bulldoze trees. They drag rocks. They carve valleys. They change the landscape.

A gliding glacier picks up sand, pebbles, and boulders. This is called plucking. The plucked rubble sticks to the bottom of the glacier. As the glacier moves, the rubble grinds against the ground. It cuts long grooves into solid rock.

Some of the longest glacial grooves are on Kelleys Island, Ohio. They are 123 meters (400 feet) long and 11 meters (35 feet) wide.

Making grooves isn't all that a glacier can do. It can carve up a mountain as it scrapes along. A glacier grinds away the tops of mountains. It hacks bowl-shaped holes out of mountainsides. The holes are called cirques. A glacier also cuts wide, U-shaped valleys between mountains.

A pair of glaciers can do even more damage. When glaciers meet at the top of a mountain, they can grind it into a horn.

All the time a glacier is grinding down a mountain, it is also plucking rocks. It carries the rocks far away. When the glacier melts, it litters the ground with plucked rocks and sand. This mixture of sediment is called till.

Till sometimes falls from the front of a glacier. This forms a ridge of material that the glacier had pushed along. The ridge is called a moraine. Moraines can be huge. Long Island in New York is made of two jumbo moraines.

So glaciers don't just destroy mountains. They also build whole new landscapes.

Weathering is also at work underground. You can see that at Carlsbad Caverns National Park in New Mexico. The park is home to at least 100 different caves. And those are just the ones we know about!

Exploring at Carlsbad Caverns, cavers have found amazing rock carvings. Long, stone talons dangle from the ceiling. Thin, rock straws grow from the walls. Huge hoodoos sprout from the floor.

Dripping acid water made each of those features. How did it happen?

Water mixed with chemicals in the ground, rocks, and air. That made different acids. One of the acids is carbonic acid. You already know about this acid. It gives soda pop its fizz.

Rivers then carried the water and acid underground. The acid ate away the rock. This is called chemical weathering. Over time, drip by drip, the acid-laced water cut giant rooms. It bored long tunnels. It chiseled grand galleries.

You don't have to explore a cave, hike on a glacier, or climb a hoodoo to see weathering and erosion. You can see them everywhere.

A neighborhood stream cuts the land. Waves in a local pond wash away rock. Even blowing wind in your backyard changes the land. Those are just a few close-to-home examples.

Next time you go outside, take a look at the wonderful ways that weathering and erosion are both destroying and building landscapes.

Article by Lesley J. MacDonald. Top-of-page photo by Yva Momatiuk & John Eastcott, Minden Pictures. "Earth Movers" appears on pages 18-23 of our October 2006 issue.