Waterfalls and valleys Crossword

What type of rock sits on top of soft rock
How does a plunge pool form
Which way does a river retreat
Where are v-shaped valleys formed
The action of trapping air into rocks, which break the rocks.
When acidic water dissolves sediment
When rock particles bang about and break into smaller pieces
When sediments wear down the bedrock and the banks
When light material is carried along in the water
When large boulders and rocks are rolled along the river bed.