An avalanche
It is a snow avalanche or simply an avalanche. (Also known as a snowslide or snowslip.)
The source of a river is usually a spring. Rain sinks into soil or rock layers, then flows downhill until a point where it emerges, which is called a spring. The water then flows downhill on the surface as a river. Some rivers, however, source from the melting ice and snow at the tops of very tall mountains.
Mudflow
Grills
Runoff is the water flowing downhill across the surface of the Earth.
Water which flows after heavy rain, sleet, or as snow is melting is referred to as runoff. Runoff occurs as soil becomes too saturated to absorb more water. It is often a contributing factor in water erosion.
water
river
When water flows downward what will it posses
runoff
The direction that a river flows is called the flow or the drainages. Water generally flows downhill or from a higher elevation to a lower one.
Water flows downhill, and the topography of that region just happens to be downhill to the east.