Volcanic ash is made of tiny fragments of jagged rock, minerals, and volcanic glass. Unlike the soft ash created by burning wood, volcanic ash is hard, abrasive, and does not dissolve in water. Generally, particles of volcanic ash are two millimeters (0.08 inches) across or smaller. Coarse particles of volcanic ash look and feel like grains of sand, while very fine particles are powdery. Particles are sometimes called tephra—which actually refers to all solid material ejected by volcanoes.

Ash is a product of explosive volcanic eruptions. When gases inside a volcano's magma chamber expand, they violently push molten rock (magma) up and out of the volcano. The force of these explosions shatters and propels the liquid rock into the air. In the air, magma cools and solidifies into volcanic rock and glass fragments. Eruptions can also shatter the solid rock of the magma chamber and volcanic mountain itself. These rock fragments can mix with the solidified lava fragments in the air and create an ash cloud.

Wind can carry small volcanic ash particles great distances. Ash has been found thousands of kilometers away from an eruption site. The smaller the particle, the further the wind will carry it. The 2008 eruption of Chaitén in Chile produced an ash cloud that blew 1,000 kilometers (620 miles) across Patagonia to Argentina, reaching both the Atlantic and Pacific Coasts.

Volcanic ash deposits tend to be thicker and have larger particles closer to the eruption site. As distance from the volcano increases, the deposit tends to thin out. The 1994 double eruption of Vulcan and Tavurvur in Papua New Guinea covered the nearby city of Rabaul in a layer of ash 75 centimeters (about two feet) deep, while areas closer to the volcanoes were buried under 150-213 centimeters (five to seven feet) of ash.

In addition to shooting volcanic ash into the atmosphere, an explosive eruption can create an avalanche of ash, volcanic gases, and rock, called a pyroclastic flow. These incredibly fast avalanches of volcanic debris can be impossible for humans to outrun. Pyroclastic flows are capable of razing buildings and uprooting trees.

Volcanic Ash Impacts

Plumes of volcanic ash can spread over large areas of sky, turning daylight into complete darkness and drastically reducing visibility. These enormous and menacing clouds are often accompanied by thunder and lightning. Volcanic lightning is a unique phenomenon and scientists continue to debate the way it works. Many scientists think that the sheer energy of a volcanic explosion charges its ash particles with electricity. Positively charged particles meet up with negatively charged particles, either in the cooler atmosphere or in the volcanic debris itself. Lightning bolts then occur as a means of balancing these charge distributions.

Volcanic ash and gases can sometimes reach the stratosphere, the upper layer in Earth’s atmosphere. This volcanic debris can reflect incoming solar radiation and absorb outgoing land radiation, leading to a cooling of the Earth’s temperature. In extreme cases, these “volcanic winters” can affect weather patterns across the globe. The 1815 eruption of Mount Tambora, Indonesia, the largest eruption in recorded history, ejected an estimated 150 cubic kilometers (36 cubic miles) of debris into the air. The average global temperature cooled by as much as 3° Celsius (5.4° Fahrenheit), causing extreme weather around the world for a period of three years. As a result of Mount Tambora’s volcanic ash, North America and Europe experienced the “Year Without a Summer” in 1816. This year was characterized by widespread crop failure, deadly famine, and disease.

Airborne volcanic ash is especially dangerous to moving aircraft. The small, abrasive particles of rock and glass can melt inside an airplane engine and solidify on the turbine blades—causing the engine to stall. Air traffic controllers take special precautions when volcanic ash is present. The 2010 eruption of Eyjafjallajökull, Iceland, produced an ash cloud that forced the cancelation of roughly 100,000 flights and affected seven million passengers, costing the aviation industry an estimated $2.6 billion.

Volcanic ash can impact the infrastructure of entire communities and regions. Ash can enter and disrupt the functioning of machinery found in power supply, water supply, sewage treatment, and communication facilities. Heavy ash fall can also inhibit road and rail traffic and damage vehicles. When mixed with rainfall, volcanic ash turns into a heavy, cement-like sludge that is able to collapse roofs. In 1991, Mount Pinatubo erupted in the Philippines at the same time that a massive tropical storm wreaked havoc in the area. Heavy rains mixed with the ash fall, collapsing the roofs of houses, schools, businesses, and hospitals in three different provinces.

Ash also poses a threat to ecosystems, including people and animals. Carbon dioxide and fluorine, gases that can be toxic to humans, can collect in volcanic ash. The resulting ash fall can lead to crop failure, animal death and deformity, and human illness. Ash’s abrasive particles can scratch the surface of the skin and eyes, causing discomfort and inflammation. If inhaled, volcanic ash can cause breathing problems and damage the lungs. Inhaling large amounts of ash and volcanic gases can cause a person to suffocate. Suffocation is the most common cause of death from a volcano.

Volcanic Ash Clean Up

Volcanic ash is very difficult to clean up. Its tiny, dust-sized particles can enter into practically everything—from car engines, to office building air vents, to personal computers. It can severely erode anything that it contacts, often causing machinery to fail. When dry, ash can be blown by the wind, spreading into and polluting previously unaffected areas. Meanwhile, wet ash binds to surfaces like cement and removing it often means stripping away what is found underneath.

Cleaning up volcanic ash is a costly and time-consuming procedure. Communities must make coordinated efforts to dispose of ash while ensuring the safety of their residents. The 1980 eruption of Mount St. Helens covered the city of Yakima, Washington, U.S.A., in tons of volcanic ash. Declaring a state of emergency, Yakima received donated maintenance equipment and workers, who were then dispatched throughout the city in a grid pattern. Citizens also helped with a block-by-block cleanup effort. Yakima removed 544,000 metric tons of ash and disposed of it in landfills and local fairgrounds. The city even filled in a wasteland to create a new city park. The process took seven around-the-clock days and cost the city $5.4 million, often cited as an efficient and cost-effective example of ash cleanup.

Organizations such as the International Volcanic Health Hazard Network, the USGS Volcano Hazards Program, and the Cities and Volcanoes Commission create and disseminate information to the public about preparing for and cleaning up volcanic ash fall. Their guidelines are used throughout the world by city and town governments and by the citizens they serve.