• volcanic ash
    Volcanic ash can ascend hundreds of kilometers into the atmosphere—and stay there for years.
    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.

    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.  
  • Term Part of Speech Definition Encyclopedic Entry
    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.

    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    avalanche Noun

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

    Encyclopedic Entry: avalanche
    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.

    coast Noun

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

    Encyclopedic Entry: coast
    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.

    crop Noun

    agricultural produce.

    Encyclopedic Entry: crop
    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

    a 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.

    dust Noun

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

    Encyclopedic Entry: dust
    ecosystem Noun

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

    Encyclopedic Entry: ecosystem
    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.

    lightning Noun

    sudden electrical discharge from clouds.

    Encyclopedic Entry: lightning
    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.

    magma Noun

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

    Encyclopedic Entry: magma
    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.

    pyroclastic flow Noun

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

    Encyclopedic Entry: pyroclastic flow
    raze Verb

    to destroy completely, especially by tearing down.

    reflect Verb

    to rebound or return light from a surface.

    region Noun

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

    Encyclopedic Entry: region
    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

    highest 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.

    temperature Noun

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

    Encyclopedic Entry: temperature
    tephra Noun

    solid material ejected from a volcano during an eruption.

    thunder Verb

    to make a loud, deep noise.

    toxic Adjective


    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.

    volcanic ash Noun

    fragments of lava less than 2 millimeters across.

    Encyclopedic Entry: volcanic ash
    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.

    volcano Noun

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

    Encyclopedic Entry: volcano
    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.