Weathering, Mass Wasting, Hydrology Basics, and Soils

The gullies below show how water erodes soil. Soil erosion is a natural part of the recycling aspect of the Earth. Every time it rains, raindrops hit the soil with a force which removes soil particles off the surface, then water across the surface carries away the dislodged particles which is called sheet erosion. After flowing as a thin sheet for a short distance, the water forms tiny streams called rills. As more water enters the rills, they erode the soil further, creating trenches known as gullies (shown below). Although most dislodged soil particles do not move far during each rainfall, large quantities eventually make their way down slope to a stream. The stream transports these soil particles, which are now called sediment, and eventually deposits them.

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The Tatacoa Desert in Colombia can be a prime example of soil desiccation. Soil desiccation is when there is a piece of land which got wet from precipitation or a natural resource and then the water in the soil was evaporated so much, creating cracks in the soil.

Colombia contains a drainage basin, Magdalena which includes its major tributary, the Cauca which covers nearly one-fourth of the surface of the country. The Cauca originates in the Andean Paramo de Las Papas. The drainage pattern of the Magdalena is of a dendritic drainage pattern because the Cauce River flows in between mountains and various surfaces that are "higher". The Cauca River, which contributes a substantial part of its total flow, rises in the mountains south of Popayán and, after passing through the floor of the Cauca valley near Cali, occupies deep canyons in most of its passage through the departments of Caldas and Antioquia before emerging onto the floodplain of the lower Magdalena.

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