River Erosion and Transportation
Ever wondered how rivers carve through solid rock or why some rivers flow crystal clear while others look like chocolate milk? Rivers are nature's bulldozers, constantly eroding (wearing away) their beds and banks whilst transporting massive amounts of sediment downstream.
Erosion happens in four distinct ways. Hydraulic action occurs when water smashes against riverbanks with such force that air gets trapped in rock cracks, eventually splitting the rock apart - imagine water as a powerful hammer. Abrasion works like sandpaper, with pebbles picked up by flowing water grinding against the riverbed and banks. Attrition happens when rocks carried by the river bash into each other, gradually becoming smaller and more rounded. Finally, solution dissolves certain rock types like limestone directly into the water.
Once rivers pick up this sediment, they transport it downstream through four different methods. Heavy pebbles get rolled along the riverbed through traction, whilst smaller stones bounce along via saltation - both processes are most common near the river's source where the current is strongest. Lighter particles float within the water through suspension (this is what makes rivers look muddy), whilst solution carries dissolved minerals invisibly downstream.
Quick Tip: Remember the river's journey from source to mouth - heavy stuff moves along the bottom upstream, light stuff floats in the water downstream!