What Are the Effects on Water After a Volcano Has Erupted?

Contamination

• Volcanoes produce ash that consists of fine particles of minerals and rocks. The ash falls over everything in its path including uncovered water. If the water is part of the drinking water supply, the ash will quickly contaminate the water, according to the U.S. Geological Survey. It cites the example of Anchorage, Alaska, in 1953 following the eruption of Mount Spurr. A mere dusting of volcanic ash caused the turbidity of the city's water supply to rise dramatically. Turbidity measures water's ability to absorb light; high levels indicate murky water which leads to bacterial growth. It took six days for the water to return to normal.

Mudflows

• Mudflows consist of sediment and rocks from the volcanic eruption mixed with water. Mudflows can resemble thick water or wet concrete and can destroy anything in their path such as buildings, bridges and highways, according to Tulane University. Mudflows can continue for years after a volcanic eruption. In 1980 following the eruption of Mount St. Helens in Washington state, mudflows formed from volcanic debris, melting snow and nearby streams.

Supply

• Volcanic ash disrupts water supplies including the equipment that delivers the water. In the first few days following a volcano, the demand for water increases as people cope with the damage and clean up volcanic ash. Equipment at water treatment plants may be damaged by the ash, restricting the flow of water. Decreased supply and increased demand lead to water shortages. Communities imposed water rationing following Mount St. Helens, according to the U.S. Geological Survey.

Temperature and Water Levels

• One long-term effect of a major volcanic eruption is the lowering of temperatures around the world. This occurs as a result of the volcanic ash being sent high into the atmosphere where it blocks out sunlight. From June 1783 to February 1784 Laki volcano in Iceland erupted, sending volcanic ash containing sulfur dioxide into the atmosphere. Temperatures in the Northern Hemisphere dropped by as much as 5.4 degrees Fahrenheit, according to NASA. These lower temperatures caused many conditions including low rainfall levels that led to record low water levels for the Nile River in Egypt. Further research dating back to 622 confirms that every period of a record low water level for the Nile coincided with a volcanic eruption.