• This GeoStory provides a brief introduction to volcanoes, including where and how they form, and some common types. The GeoStory also describes volcanic hazards and monitoring methods, as well as the role volcanoes have played in creating important natural resources and interactions between volcanoes and climate. Finally, the story presents archaeological evidence for early human encounters with volcanoes. Each storypoint uses a specific geographic location and example. New terms are defined in the text. Each storypoint begins with a probing question. Teachers should consider beginning each storypoint by having students discuss the question and state what they already know about the topic. Students should then return to these questions at the end of the lesson to discuss what they have learned.

    1. How did the volcanoes of the Cascade Mountains, in Washington and Oregon, form?

      The Juan de Fuca tectonic plate is sinking beneath the North American tectonic plate.

    2. How do calderas form?

      After a volcanic eruption, the empty cavity at the top of a volcano collapses, creating a bowl-shaped depression called a caldera.

    3. How did the Hawaiian Islands form?

      They began as underwater volcanoes (seamounts) that kept erupting until they rose above the sea surface.

    4. What volcanic deposits are cinder cones made of?

      Cinder cones are primarily made up of cinders that fall from the sky during volcanic eruptions.

    5. What is the most dangerous volcanic hazard for people living near a volcano?

      Pyroclastic flows, because they are deadly and people cannot outrun them.

    6. Can scientists predict volcanic eruptions?

      By monitoring changes to earthquake activity and changes in ground surface, scientists can tell when an eruption is more likely to occur, but they cannot predict specific eruptions.

    7. How do volcanoes affect the soil?

      Volcanic ash creates well-drained soils that are rich in nutrients and have good water-holding capacity to support crops.

    8. If the Antarctic Ice Sheet melted quickly, how might volcanoes there be affected?

      More volcanoes could emerge and start erupting because the ice would no longer be pushing down on the crust, releasing magma that rises to the surface.

  • The 1980 eruption of Mount St. Helens, in Washington State, caused nearly $1 billion worth of damage. Losses to the forestry industry and the cost of clean-up amounted to about 85% of the total cost.

    Gold that is present in magma rises to Earth's surface during volcanic eruptions. The famous gold deposits in California were created by volcanic activity in the Sierra Nevada Mountains.

    The Hawaiian Islands are formed by a hot spot of magma beneath the Pacific Plate. As the plate moves, the hot spot makes new volcanoes in the chain.

    Early pioneers made note of Crater Lake's exceptionally blue color. Crater Lake is very deep, and its water is very clear. This allows sunlight to penetrate to great depth, resulting in the intense blue color.

    There are about 1,500 potentially active volcanoes in the world today, not including the ones underwater. Most of these active volcanoes are part of the Pacific Ring of Fire.

  • Term Part of Speech Definition Encyclopedic Entry
    active volcano Noun

    volcano that has had a recorded eruption since the last glacial period, about 10,000 years ago.

    asteroid Noun

    irregularly shaped planetary body, ranging from 6 meters (20 feet) to 933 kilometers (580 miles) in diameter, orbiting the sun between Mars and Jupiter.

    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    caldera Noun

    large depression resulting from the collapse of the center of a volcano.

    Encyclopedic Entry: Types of Calderas
    cinder Noun

    tiny bits of coarse lava.

    cinder cone Noun

    hill created by tiny bits of lava blown out of a volcano and fallen down around the volcanic vent. Also called a scoria cone.

    comet Noun

    celestial object made up of ice, gas, and dust that orbits the sun and leaves a tail of debris.

    composite volcano Noun

    steep volcano made of hardened lava, rock, and ash. Also known as a stratovolcano.

    cyanobacteria Noun

    type of aquatic bacteria that can photosynthesize light to create energy. Also called blue-green algae (even though it is not algae) and (in freshwater habitats) pond scum.

    earthquake Noun

    the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity.

    feedback loop Noun

    cycle of causes and effects where the effects either directly reinforce (in a positive feedback loop) or oppose (in a negative feedback loop) the original condition.

    Global Positioning System (GPS) Noun

    system of satellites and receiving devices used to determine the location of something on Earth.

    lava Noun

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

    lithosphere Noun

    outer, solid portion of the Earth. Also called the geosphere.

    Encyclopedic Entry: lithosphere
    magma Noun

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

    Encyclopedic Entry: Magma's Role in the Rock Cycle
    pumice Noun

    type of igneous rock with many pores.

    pyroclastic flow Noun

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

    Encyclopedic Entry: The Hazards of Pyroclastic Flows
    seamount Noun

    underwater mountain.

    shield volcano Noun

    large, gently sloping volcano made from fluid lava.

    stratosphere Noun

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

    stratovolcano Noun

    steep volcano made of hardened lava, rock, and ash. Also known as a composite volcano.

    supervolcano Noun

    volcano capable of ejecting more than 1,000 cubic kilometers (240 cubic miles) of material.

    tectonic plate Noun

    massive slab of solid rock made up of Earth's lithosphere (crust and upper mantle). Also called lithospheric plate.

    tephra Noun

    solid material ejected from a volcano during an eruption.

    viscosity Noun

    measure of the resistance of a fluid to a force or disturbance.

    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: Plate Tectonics and Volcanic Activity