Question

Let's say you are an old giant boulder, sitting above the San Gabriel river in the San Gabriel Mountains and came crashing down into the river, during a flood. By what mechanisms would you be transported to the sea. Explain in detail how you would eventually get there.

Answer 1

The pressure of water breaks away rock particles from the river bed and banks. The force of the water hits river banks and then pushes water into cracks. Air becomes compressed, pressure increases and the riverbank may, in time collapse. Where velocity is high e.g. the outer bend of meaner, hydraulic action can remove material from the banks which may lead to undercutting and river bank collapse. Near waterfalls and rapids, the force may be strong enough to work on lines of weakness in joints and bedding planes until they are eroded.

Eroded rocks collide and break into smaller fragments. The edges of these rocks become smoother and more rounded. Attrition makes the particles of rock smaller. It does not erode the bed and bank. Pieces of river sediment become smaller and more rounded as they move downstream.

Transportation of material in a river begins when friction is overcome. Material that has been loosened by erosion may be then transported along the river.