Water erosion shapes Earth's surface. Moving water is the major agent of erosion and has formed landforms over time. Runoff from rain carries soil particles and causes sheet and rill erosion. Rills grow into gullies which join to form streams and rivers. Rivers erode the land to form V-shaped valleys and deposit sediments in flood plains and deltas. Waterfalls form where a hard rock meets a softer rock downstream as the softer rock erodes faster. Flood plains are wide river valleys that are flooded during heavy rains, depositing fertile soils.