On a mountain hike, Raven finds a boulder split right down the middle. A small pine tree grows from the crack.
"Did the tree break the rock?" Rocket asks. "Trees are not that strong!"
Raven runs her finger along the crack. "Maybe not alone. What do you notice inside the crack?"
There is a little puddle, left from last night's rain.
Nova checks the temperature. "Interesting," she says. "Up here it freezes most nights. Here is a clue: water grows when it freezes."
Weathering is the breaking down of rock into smaller pieces.
Ice is a strong rock breaker. Water seeps into cracks, freezes and expands. That pushes the crack wider.
This is called frost wedging. Day after day of freezing and thawing breaks rock apart.
Plant roots can also grow into cracks and push them open.
Erosion is the moving of sand, soil or bits of rock by water or wind.
Flowing water carries pieces downstream, from tiny grains to big stones.
Wind carries fine silt far away. It moves sand shorter distances and piles it into dunes.
Gravity pulls loose pieces downhill too.
| What happened | Is it weathering (breaking)? |
|---|---|
| Ice in a crack splits a boulder. | ? |
| A river carries sand downstream. | ? |
| Tree roots push a crack wider. | ? |
| Wind blows sand into a dune. | ? |
Land changes in two steps.
First, weathering breaks big rock into smaller pieces.
Then erosion carries the pieces away with water, wind or gravity.
You met the rock breakers and rock movers! Tomorrow we visit a place they sculpted.