Erosion is the wearing down of soil or rock by the action of wind, rain, rivers, ice and gravity. A volcanic eruption produces lava, ash and gases. This debris creates new sediments, igneous rock formations and landforms. Volcanoes cause limited erosion directly; the underside of a new lava flow scours topsoil or loosely consolidated sediments. Volcanic eruptions are the indirect causes of substantial erosion through the action of volcanic debris on the atmosphere, land and water.
Volcanic eruptions produce an atmospheric haze composed of suspended dust particles, or aerosols. These absorb solar radiation, scatter it back into space, and produce a net cooling effect on Earth. The 1815 Mount Tambora eruption produced an atmospheric haze that spread throughout the Northern Hemisphere and caused the following year, 1816, to be the "year without a summer." Snowfall and frost occurred in June, July and August. This precipitation eroded landscapes.
Volcanoes emit sulfur and carbon dioxide gases. These gases dissolve in rainwater and produce an acidic precipitation. Acid rain erodes limestone by dissolving the carbonate rock and produces crevasses and caves.
Lahars are catastrophic mudflows. Snow and ice top the large volcanoes characteristic of those in the Rocky Mountains of North America and Andes Mountains of Central and South America. The heat produced by an eruption melts the snow that, in turn, triggers massive landslides down the volcano's slope. These uproot trees, and erode soil and rock cover. Lahars can destroy entire communities. The 1985 eruption of Nevado del Ruiz in Colombia killed 23,000 people.
Substantial amounts of lava, rock debris and ash from a volcanic eruption is capable of impounding river courses and creating lakes. When water pressure breaches this volcanic barrier, the subsequent flooding erodes sediment downstream. Lava dams in the Grand Canyon breached throughout the Pleistocene era between 1.8 million and 10,000 years ago.
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