A stream runs down a mountain for thousands of years. Little by little it cuts a deep, narrow valley into the rock below it. What interaction between Earth's spheres does this show?

Ocean waves pound the base of a rocky cliff at every high tide. After many years, chunks of the cliff break loose and fall into the water. What is happening between Earth's spheres?

Rainwater seeps into a crack in a boulder. On a cold night the water freezes and pushes the crack wider. Each winter the crack grows, and at last the boulder splits in two. What does this show?

Where a muddy river empties into the ocean, the sand and mud it carried settle out. Over many years, a wide, flat area of new land builds up at the river's mouth. Why do the sand and mud settle out there?

A thick glacier slides slowly down a mountain valley, dragging rock and grit along its bottom. The valley it leaves behind is wide and U-shaped. Which sphere is doing the shaping, and which is being shaped?

Underground water slowly dissolves the rock it flows through. After thousands of years, an open cave sits where solid rock used to be. What best explains the cave?

After a long rain, water soaks down through the soil and fills the tiny spaces between rocks far below the surface. What is happening between Earth's spheres?

A long ridge of high land runs down the middle of a state. Rain falling on the east side runs into rivers flowing toward the Atlantic Ocean, and rain on the west side runs into rivers flowing the other way. What does this show?

Waves reach a beach at an angle and carry sand along the shore a little at a time. Over one summer, sand disappears from one end of the beach and piles up at the other end. What is the water doing?

A river floods and spreads across nearby fields. When the water drains away, a fresh layer of fine mud is left behind, and farmers find that crops grow better there the next year. What did the water do?

A class claims that the creek behind their school is wearing away its own banks. What observation would best support that claim?

Students tilt a tray of damp sand, pour water onto the high end, and watch a channel form while sand piles up at the low end. What real Earth-system interaction does their model show?

Days of heavy rain soak a steep hillside. The wet soil and rock suddenly slide downhill and bury the road below. Which spheres interacted here?

In some places, hot rock deep underground warms groundwater until it rises to the surface as a steaming spring. Which sphere is affecting which?

A neighborhood sits on rock that groundwater has slowly hollowed out. One morning the ground drops away and leaves a wide hole. What best explains the collapse?

Every spring, melting snow makes a stream run fast and brown as it flows into a quiet lake. Over many years, thin layers of mud build up on the lake bottom. Where did most of this mud come from?

Most of the fresh water that people pump from wells is held in spaces inside sand and rock underground. What does this show about the hydrosphere and the geosphere?

Moving water can wear land away in one place and build new land in another place.

A fast-moving flood in the hydrosphere can move boulders as well as sand in the geosphere.

Waves change a rocky shoreline faster during a strong storm than on a calm day.