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A volcanic eruption

A volcanic eruption

Volcanic ash is rock that has been pulverized into dust or sand by volcanic activity. In very large eruptions, ash is accompanied by rocks having the weight and density of hailstones. Volcanic ash is hot near the volcano, but it is cool when it falls at greater distances. Ashfall blocks sunlight, reducing visibility and sometimes causing darkness. Ashfall can be accompanied by lightning. Fresh volcanic ash is gritty, abrasive, sometimes corrosive, and always unpleasant. Although ash is not highly toxic, it can trouble infants, the elderly and those with respiratory ailments. Small ash particles can abrade the front of the eye under windy and ashy conditions. Ash abrades and jams machinery. It contaminates and clogs ventilation, water supplies and drains.

Ash also causes electrical short circuits, in transmission lines (especially when wet), in computers, and in microelectronic devices. Power often goes out during and after ashfall. Long-term exposure to wet ash can corrode metal. Ash accumulates like heavy snowfall, but does not melt. The weight of ash can cause roofs to collapse. A one-inch layer of ash weighs 5-10 pounds per square foot when dry, but 10-15 pounds per square foot when wet. Wet ash is slippery. Ash resuspended by wind, and human activity can disrupt lives for months after an eruption.