Erosion has made huge changes in the surface of the Earth and is still doing so today. Erosion is the removal of materials from the Earth’s surface by a variety of processes. The material is eventually deposited elsewhere, often far from where it started. Most erosion is caused by the action of wind, water, or ice. Water causes the most erosion. Weathering is the breaking down of rock into smaller particles. Erosion differs from weathering in that erosion involves something moving—wind, rain, or a glacier. During the natural process of erosion, the landscape is changed over thousands or millions of years. Mountains are worn down, valleys are filled in, and rivers change their courses. These changes are gradual, but many of the practices of man speed up the process of erosion and cause serious problems around the world. Construction is one of the biggest culprits. Topsoil, minerals, and nutrients are lost from every construction site. About 80 percent of the erosion in Florida is due to manmade activities. Cutting the forests and plowing the land has also contributed to erosion of the land. Human activities cause topsoil to be lost, along with the minerals and nutrients it contains. This affects agriculture. Erosion causes ugly gullies in the landscape. Materials from water erosion can clog culverts and streams. Recreational areas and residential areas are damaged by erosion. Wildlife may be destroyed and its environment altered to the point that it can no longer support wildlife. Water erosion includes stream erosion, beach erosion, and erosion by flooding. Stream erosion is most common. Streams carry sediment from one place to another. The amount of sediment carried and the amount dropped depend on the speed of the water. Water speed is affected by many factors, including the steepness of the slope and the shape of the channel through which the stream flows. The faster the water moves, the more material it can carry, and the larger particles it can move. When water goes around a bend, sediment is removed from the outer part of the bend and swept downstream. Water flows more slowly on the inside of the curve, so sediment accumulates here as it is dropped by the slowing water. Valleys eroded by streams are V-shaped, as opposed to the U-shaped valleys eroded by glaciers. Heavy rains in spring can increase the velocity of a stream and cause more erosion to take place. Sandy ground erodes more easily than rocky ground. At its most extreme, stream erosion has created wonders like the Grand Canyon. This vast canyon was eroded by the Colorado River, although some scientists now believe other rivers helped cut the canyon. The canyon, which is 227 mi (446 km) long, averages 4,000 ft (1,219 m) deep. Its deepest point is 6,000 ft (1,829 m) and the widest point spans 15 mi (24 km) This erosion took place over a period of millions of years. Beach erosion occurs along ocean shores and can be caused by natural phenomena or by humans. Natural phenomena that can cause beach erosion include currents, storms, earthquakes, winds, waves, and tides.