Boulder facts for kids

A boulder is a very large piece of rock. Imagine a rock so big you can't easily pick it up! Geologists, who are scientists who study rocks and the Earth, say a rock is a boulder if it measures at least 25.6 centimeters (about 10 inches) across. There's no upper size limit, so some boulders can be as huge as a small house!

How Boulders Are Made

Boulders are formed over a very long time by natural processes. These processes break down bigger rocks or move large pieces of rock around.

Breaking Down Rocks: Weathering and Erosion

• Weathering is when rocks are broken down into smaller pieces. This can happen in many ways:
  • Water: Rain, rivers, and waves can wear away rocks. Water can also get into cracks, freeze, and expand, making the cracks bigger until the rock breaks.
  • Wind: Strong winds carrying sand can slowly grind away at rock surfaces.
  • Temperature Changes: Rocks can expand when hot and shrink when cold. This constant change can cause them to crack and break apart.
  • Plants: Tree roots can grow into cracks in rocks, slowly pushing them apart.
• Erosion is when these broken rock pieces are moved from one place to another.

Moving Rocks: Glaciers and Landslides

• Glaciers: These are giant, slow-moving rivers of ice. As glaciers move, they can pick up huge rocks and carry them for many miles. When the glacier melts, these rocks are left behind. These are called glacial erratics because they are often found in places where that type of rock doesn't naturally exist.
• Landslides: Sometimes, large sections of rock break off a cliff or mountain and tumble down a slope. This can create many large boulders at the bottom.

Where You Can Find Boulders

Boulders can be found in many different places around the world.

• Riverbeds and Beaches: You often see smooth, rounded boulders in rivers and along coastlines. The constant movement of water tumbles them, making them round.
• Mountains and Valleys: Boulders are common in mountainous areas, especially at the base of cliffs where rocks have fallen.
• Fields and Forests: In areas that were once covered by glaciers, you might find large, lone boulders in fields or forests, left behind by the melting ice.
• Deserts: Some deserts have amazing rock formations, including large boulders shaped by wind and sand.

Types of Boulders

Different types of boulders are known for their unique shapes or how they were formed.

• Balanced Rocks: These are boulders that rest on a smaller base in a way that looks like they could fall over at any moment, but they are actually very stable. They are often formed by erosion wearing away the softer rock underneath.
• Glacial Erratics: As mentioned, these are boulders that were carried by glaciers and dropped far from their original location. They can be very different from the local rocks.
• Split Boulders: Sometimes, a large boulder can split into two or more pieces, often due to frost wedging (water freezing and expanding in cracks).

Boulders in Our Lives

Boulders are more than just big rocks; they can be important in different ways.

• Landmarks: Many large or unusual boulders become famous landmarks, helping people find their way or marking special places.
• Landscaping: People often use boulders in gardens and parks to create beautiful natural features.
• Climbing: Some boulders are popular spots for rock climbing, especially a type of climbing called "bouldering" which is done without ropes on smaller rocks.
• History: Some boulders have historical significance, perhaps used by ancient people or marking important events.

Images for kids

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  This balancing boulder, "Balanced Rock", stands in Garden of the Gods park in Colorado Springs, Colorado, United States.

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  Boulder in British Columbia, Canada

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  Kämmenkivi stone on the Pisa hill in Kuopio, Finland

See also

In Spanish: Bloque (roca) para niños