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 2 millimeters (.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 2 feet) deep, while areas closer to the volcanoes were buried under 150-213 centimeters (5-7 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 7 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, 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.  
Human and Environmental Impacts of Volcanic Ash
Volcanic ash can ascend hundreds of kilometers into the atmosphere—and stay there for years.
Andisol
Andisol is a type of soil formed from volcanic ash. Andisols are generally very fertile, support extensive agricultural development, and exist mostly around the Ring of Fire.
Pompeii Preserved
One of the most famous explosive volcanic eruptions occurred in 79 CE, when Mount Vesuvius buried the Roman (now Italian) cities of Pompeii under 18 meters (60 feet) of ash. The ash buried the cities so completely that it preserved entire buildings, paintings, and artifacts. It also created very detailed molds around the bodies of people who were killed.
 
Starting in the 18th century, archaeologists began excavating Pompeii. They discovered the hollow impressions left by bodies in the hardened ash and developed a way to inject them with plaster to create casts of the bodies. Today the excavated city and its gruesome models of dead and dying people and animals are popular tourist attractions.
Flying High
Scientists recently discovered that the eruption of Alaska’s Mount Churchill roughly 1,200 years ago produced an ash fall that reached from Canada to Germany some 7000 kilometers (4350 miles) away. The discovery was especially surprising given that the volcano ejected a relatively small amount of ash of 50 cubic kilometers (12 cubic miles). As the ash spread, however, it transformed into microscopic shards called cryptotephra that had a unique compositional signature.
 
Scientists were able to identify these distinct shards in Nova Scotia, Greenland, and across Northern Europe, suggesting that the cryptotephra was so light that it travelled easily along the high-altitude winds of the Northern Hemisphere. 

Smoke Signal
When Mount St. Helens, in the U.S. state of Washington, erupted in 1980, a column of ash from the volcano rose 19 kilometers (12 miles) into the air.

abrasive
Adjective

harsh or rough.

absorb
Verb

to soak up.

airborne
Adjective

transported by air currents.

aircraft
Noun

vehicle able to travel and operate above the ground.

air traffic controller
Noun

person who monitors the position, speed, and direction of different aircraft to ensure safe and efficient air travel.

Noun

layers of gases surrounding a planet or other celestial body.

Noun

large mass of snow and other material suddenly and quickly tumbling down a mountain.

aviation
Noun

the art and science of creating and operating aircraft.

bind
Verb

to connect or stick together.

cancel
Verb

to stop a planned event.

cement
Noun

hard material used as a building material or a binding agent for stronger building materials such as concrete.

characterize
Verb

to describe the characteristics of something.

cite
Verb

to give as an example.

coarse
Adjective

rough or composed of large, jagged particles.

Noun

edge of land along the sea or other large body of water.

collapse
Verb

to fall apart completely.

communication
Noun

sharing of information and ideas.

computer
Noun

device designed to access data, perform prescribed tasks at high speed, and display the results.

coordinate
Verb

to work together or organize for a specific goal.

costly
Adjective

expensive or having a lot of value.

Noun

agricultural produce.

damage
Noun

harm that reduces usefulness or value.

debate
Verb

to argue or disagree in a formal setting.

debris
Noun

remains of something broken or destroyed; waste, or garbage.

deform
Verb

to put out of shape or distort.

deposit
Verb

to place or deliver an item in a different area than it originated.

disease
Noun

harmful condition of a body part or organ.

dispatch
Verb

to systematically send off.

disrupt
Verb

to interrupt.

disseminate
Verb

to scatter or spread widely.

dissolve
Verb

to break up or disintegrate.

drastic
Adjective

severe or extreme.

Noun

tiny, dry particles of material solid enough for wind to carry.

Noun

community and interactions of living and nonliving things in an area.

efficient
Adjective

performing a task with skill and minimal waste.

eject
Verb

to get rid of or throw out.

electricity
Noun

set of physical phenomena associated with the presence and flow of electric charge.

emergency
Noun

sudden, unplanned event that requires immediate action.

energy
Noun

capacity to do work.

engine
Noun

machine that converts energy into power or motion.

enormous
Adjective

very large.

equipment
Noun

tools and materials to perform a task or function.

erode
Verb

to wear away.

expand
Verb

to grow or get larger.

explosive
Noun

material that can quickly and violently expand due to a chemical change.

famine
Noun

an extreme shortage of food in one area during a long period of time.

fragment
Noun

piece or part.

government
Noun

system or order of a nation, state, or other political unit.

grid
Noun

horizontal and vertical lines used to locate objects in relation to one another on a map.

havoc
Noun

violent destruction.

illness
Noun

disease or sickness.

industry
Noun

activity that produces goods and services.

inflammation
Noun

pain, tenderness, and disturbed function of an area of the body.

infrastructure
Noun

structures and facilities necessary for the functioning of a society, such as roads.

inhale
Verb

to breathe in.

inhibit
Verb

to slow or prevent.

landfill
Noun

site where garbage is layered with dirt and other absorbing material to prevent contamination of the surrounding land or water.

lava
Noun

molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.

Noun

sudden electrical discharge from clouds.

liquid
Noun

state of matter with no fixed shape and molecules that remain loosely bound with each other.

lung
Noun

organ in an animal that is necessary for breathing.

machinery
Noun

mechanical appliances or tools used in manufacturing.

Noun

molten, or partially melted, rock beneath the Earth's surface.

magma chamber
Noun

underground reservoir that holds molten rock.

massive
Adjective

very large or heavy.

menacing
Adjective

threatening or perceived as harmful.

mineral
Noun

inorganic material that has a characteristic chemical composition and specific crystal structure.

molten
Adjective

solid material turned to liquid by heat.

mountain
Noun

landmass that forms as tectonic plates interact with each other.

park
Noun

area of land set aside for recreational use.

Patagonia
Noun

large plateau in southern South America, stretching from the Andes Mountains to the Atlantic Ocean.

phenomenon
Noun

an unusual act or occurrence.

plume
Noun

single, upward flow of a fluid, such as water or smoke.

powder
Noun

solid substance reduced to fine, loose particles.

power
Noun

ability to do work.

precaution
Noun

action taken to avoid a negative outcome or event.

procedure
Noun

method or steps followed to achieve a goal.

propel
Verb

to push forward.

public
Noun

people of a community.

Noun

current of volcanic ash, lava, and gas that flows from a volcano.

raze
Verb

to destroy completely, especially by tearing down.

reflect
Verb

to rebound or return light from a surface.

Noun

any area on Earth with one or more common characteristics. Regions are the basic units of geography.

rock
Noun

natural substance composed of solid mineral matter.

sand
Noun

small, loose grains of disintegrated rocks.

sewage treatment
Noun

process of removing harmful pollutants and contaminants from water discarded by homes and businesses, so the water is safe for most uses.

sheer
Adjective

utter and unmixed with anything else.

sludge
Noun

liquid waste, such as that from the coal mining and cleaning process, also called slurry.

solar radiation
Noun

light and heat from the sun.

solidify
Verb

to make solid.

stall
Verb

to cause to slow or come to a stop.

stratosphere
Noun

level of Earth's atmosphere, extending from 10 kilometers (6 miles) to 50 kilometers (31 miles) above the surface of the Earth.

suffocate
Verb

to be unable to breathe.

Noun

degree of hotness or coldness measured by a thermometer with a numerical scale.

tephra
Noun

solid material ejected from a volcano during an eruption.

thunder
Verb

to make a loud, deep noise.

toxic
Adjective

poisonous.

traffic
Noun

movement of many things, often vehicles, in a specific area.

tropical storm
Noun

weather pattern of swirling winds over a center of low pressure above warm ocean waters. Tropical storms are less powerful than cyclones and hurricanes.

turbine
Noun

machine that captures the energy of a moving fluid, such as air or water.

unique
Adjective

one of a kind.

violent
Noun

strong, destructive force.

visibility
Noun

the ability to see or be seen with the unaided eye. Also called visual range.

Noun

fragments of lava less than 2 millimeters across.

volcanic eruption
Noun

activity that includes a discharge of gas, ash, or lava from a volcano.

volcanic glass
Noun

hard, brittle substance produced by lava cooling very quickly.

volcanic lightning
Noun

bolts of electricity produced in a volcanic plume. Also called a dirty thunderstorm.

volcanic winter
Noun

drop in global temperatures due to volcanic debris in the atmosphere blocking the sun.

Noun

an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.

weather pattern
Noun

repeating or predictable changes in the Earth's atmosphere, such as winds, precipitation, and temperatures.

wind
Noun

movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.

wood
Noun

hard material that makes up the trunk and branches of trees and shrubs.

wreak
Verb

to inflict or bring about something painful.