Living Lab Curriculum
Aa: Hawaiian word used to describe a lava flow whose surface is broken into rough angular fragments.
Active volcano: A volcano that is erupting. Also, a volcano that is not presently erupting but that has erupted within historical time and is considered likely to do so in the future.
Andesite: Volcanic rock (or lava) characteristically medium dark in color and containing 54 to 62 percent silica and moderate amounts of iron and magnesium.
Ash: Fine particles of pulverized rock blown from an explosion vent. Measuring less than 1/10 inch in diameter, ash may be either solid or molten when first erupted. By far the most common variety is vitric ash, glassy particles formed by gas bubbles bursting through liquid magma.
Ashfall (Airfall): Volcanic ash that has fallen through the air from an eruption cloud. A deposit so formed is usually well sorted and layered.
Ash flow: A turbulent mixture of gas and rock fragments, most of which are ash-sized particles, ejected violently from a crater or fissure. The mass of pyroclastics is normally of very high temperature and moves rapidly down the slopes, or even along a level surface.
Avalanche: A large mass of material or mixtures of material falling or sliding rapidly under the force of gravity. Avalanches often are classified by their content, such as snow, ice, soil, or rock avalanches. A mixture of these materials is a debris avalanche.
Basalt: Volcanic rock (or lava) that characteristically is dark in color, contains 45 to 54 percent silica, and generally is rich in iron and magnesium.
Block: Angular chunk of solid rock ejected during an eruption.
Bomb: Fragment of molten or semi-molten rock, 2 1/2 inches to many feet in diameter, which is blown out during an eruption. Because of their plastic condition, bombs are often modified in shape during their flight or upon impact.
Caldera: The Spanish word for cauldron, a basin-shaped volcanic depression; by definition, at least a mile in diameter. Such large depressions are typically formed by the subsidence of volcanoes. Crater Lake occupies the best-known caldera in the Cascades.
Cinder cone: A volcanic cone built entirely of loose fragmented material (pyroclastics.)
Composite volcano: A steep volcanic cone built by both lava flows and pyroclastic eruptions.
Continental crust: Solid, outer layers of the earth, including the rocks of the continents.
Continental drift: The theory that horizontal movement of the earth's surface causes slow, relative movements of the continents toward or away from one another.
Crater: A steep-sided, usually circular depression formed by either explosion or collapse at a volcanic vent.
Dacite: Volcanic rock (or lava) that characteristically is light in color and contains 62 to 69 percent silica and moderate amounts of sodium and potassium.
Debris avalanche: A rapid and unusually sudden sliding or flowage of unsorted masses of rock and other material. As applied to the major avalanche involved in the eruption of Mount St. Helens, a rapid mass movement that included fragmented cold and hot volcanic rock, water, snow, glacier ice, trees, and some hot pyroclastic material. Most of the May 18 deposits in the upper valley of the North Fork Toutle River and in the vicinity of Spirit Lake are from the debris avalanche.
Detachment plane: The surface along which a landslide disconnects from its original position.
Dome: A steep-sided mass of viscous (doughy) lava extruded from a volcanic vent, often circular in plane view and spiny, rounded, or flat on top. Its surface is often rough and blocky as a result of fragmentation of the cooler, outer crust during growth of the dome.
Dormant volcano: Literally, "sleeping." The term is used to describe a volcano which is presently inactive but which may erupt again. Most of the major Cascade volcanoes are believed to be dormant rather than extinct.
Ejecta: Material that is thrown out by a volcano, including pyroclastic material (tephra) and, from some volcanoes, lava bombs.
Eruption: The process by which solid, liquid, and gaseous materials are ejected into the earth's atmosphere and onto the earth's surface by volcanic activity. Eruptions range from the quiet overflow of liquid rock to the tremendously violent expulsion of pyroclastics.
Eruption cloud: The column of gases, ash, and larger rock fragments rising from a crater or other vent. If it is of sufficient volume and velocity, this gaseous column may reach many miles into the stratosphere, where high winds will carry it long distances.
Eruptive vent: The opening through which volcanic material is emitted.
Extinct volcano: A volcano that is not presently erupting and is not likely to do so for a very long time in the future.
Fault: A crack or fracture in the earth's surface. Movement along the fault can cause earthquakes or, in the process of mountain-building, can release underlying magma and permit it to rise to the surface.
Fissures: Elongated fractures or cracks on the slopes of a volcano. Fissure eruptions typically produce liquid flows, but pyroclastics may also be ejected.
Flank eruption: An eruption from the side of a valcano (in contrast to a summit eruption.)
Fracture: A general term for any break in a rock including cracks, joints, and faults.
Fumarole: A vent or opening through which issue steam, hydrogen sulfide, or other gases. The craters of many dormant volcanoes contain active fumaroles.
Geothermal energy: Energy derived from the internal heat of the earth.
Geothermal power: Power generated by using the heat energy of the earth.
Graben: An elongate crustal block that is relatively depressed (downdropped) between two fault systems.
Harmonic tremor: A continuous release of seismic energy typically associated with the underground movement of magma. It contrasts distinctly with the sudden release and rapid decrease of seismic energy associated with the more common type of earthquake caused by slippage along a fault.
Heat transfer: Movement of heat from one place to another.
Horizontal blast: An explosive eruption in which the resultant cloud of hot ash and other material moves laterally rather than upward.
Hot-spot volcanoes: volcanoes related to a persistent heat source in the mantle.
Hydrothermal reservoir: An underground zone of porous rock containing hot water.
Lahar: A torrential flow of water-saturated volcanic debris down the slope of a volcano in response to gravity. A type of mudflow. Also known as a "glowing avalanche."
Lapilli: Literally, "little stones;" round to angular rock fragments measuring 1/10 inch to 2 1/2 inches in diameter, which may be ejected in either a solid or molten state.
Lava: Magma which has reached the surface through a volcanic eruption. The term is most commonly applied to streams of liquid rock that flow from a crater or fissure. It also refers to cooled and solidified rock.
Lava Flow: An outpouring of lava onto the land surface from a vent or fissure. Also, a solidified tongue like or sheet like body formed by outpouring lava.
Lava tube: A tunnel formed when the surface of a lava flow cools and solidfies, while the still-molten interior flows through and drains away.
Magma: Molten rock beneath the surface of the earth.
Magma chamber: The subterranean cavity containing the gas-rich liquid magma which feeds a volcano.
Mantle: The zone of the earth below the crust and above the core.
Magnitude: A numerical expression of the amount of energy released by an earthquake, determined by measuring earthquake waves on standardized recording instruments (seismographs.) The number scale for magnitudes is logarithmic rather than arithmetic; therefore, deflections on a seismograph for a magnitude 5 earthquake, for example, are 10 times greater than those for a magnitude 4 earthquake, 100 times greater than for a magnitude 3 earthquake, and so on.
Mudflow: A flowage of water-saturated earth material possessing a high degree of fluidity during movement. A less-saturated flowing mass is often called a debris flow. A mudflow originating on the flank of a volcano is properly called a lahar.
Nuee ardente: A French term applied to a highly heated mass of gas-charge ash which is expelled with explosive force, and hurricane speed, down the mountainside.
Obsidian: A black or dark-colored volcanic glass, usually composed of rhyolite.
Oceanic crust: The earth's crust where it underlies oceans.
Phreatic eruption (explosion): An explosive volcanic eruption caused when water and heated volcanic rocks interact to produce a violent expulsion of steam and pulverized rocks. Magma is not involved.
Pillow lava: Interconnected, sack-like bodies of lava formed underwater.
Plate techtonics: The theory that the earth's crust is broken into about 10 fragments (plates,) which move in relation to one another, shifting continents, forming new ocean crust, and stimulating volcanic eruptions.
Plug: Solidified lava that fills the conduit of a volcano. It is usually more resistant to erosion than the material making up the surrounding cone, and may remain standing as a solitary pinnacle when the rest of the original structure has eroded away.
Plug dome: The steep-sided, rounded mound formed when viscous lava wells up into a crater and is too stiff to flow away. It piles up as a dome-shaped mass, often completely filling the vent from which it emerged.
Pluton: A large igneous intrusion formed at great depth in the crust.
Pumice: Light-colored, frothy volcanic rock, usually of dacite or rhyolite composition, formed by the expansion of gas in erupting lava. Commonly seen as lumps or fragments of pea-size and larger, but can also occur abundantly as ash-sized particles.
Pyroclastic: Pertaining to fragmented (clastic) rock material formed by a volcanic explosion or ejection from a volcanic vent.
Pyroclastic flow: Lateral flowage of a turbulent mixture of hot gases and unsorted pyroclastic material (volcanic fragments, crystals, ash, pumice, and glass shards) that can move at high speed (50 to 100 miles an hour.) The term also can refer to the deposit so formed.
Rhyolite: Volcanic rock (or lava) that charactericstically is light in color, contains 69 percent silica or more, and is rich in potassium and sodium.
Ridge, Oceanic: A major submarine mountain range.
Rift system: The oceanic ridges formed where techtonic plates are separating and a new crust is being created; also, their on-land counterparts like the East African Rift.
Ring of Fire: The regions of mountain-building earthquakes and volcanoes which surround the Pacific Ocean.
Rhyolite: A fine-grained volcanic rock, which although different in texture, has the same composition as granite.
Seafloor spreading: The mechanism by which new seafloor crust is created at oceanic ridges and slowly spreads away as plates are separating.
Seismograph: An instrument that records seismic waves; that is, vibrations of the earth.
Shearing: The motion of surfaces sliding past one another.
Shield volcano: A gently sloping volcano in the shape of a flattened dome, built almost exclusively of lava flows.
Silica: A chemical combination of silicon and oxygen.
Somma: A circular or cresent-shaped ridge that is steep on its inner side and represents the rim on an ancient volcanic crater or caldera.
Stratovolcano: A volcano composed of both lava flows and pyroclastic material.
Spines: Horn-like projections formed upon a lava dome.
Strike-slip fault: A nearly vertical fault with side-slipping displacement.
Subduction zone: The zone of convergence of two techtonic plates, one of which usually overrides the other.
Tephra: Materials of all types and sizes that are erupted from a crater or volcanic vent and deposited from the air.
Tsunami: A great sea wave produced by a submarine earthquake, volcanic eruption, or large landslide.
Tuff: Rock formed of pyroclastic material.
Vent: The opening at the earth's surface through which volcanic materials issue forth.
Viscosity: A measure of resistance to flow in a liquid (water has low viscosity while honey has a higher viscosity.)
Volcanic complex: A persistent volcanic vent area that has built a complex combination of volcanic landforms.
Vulcan: Roman god of fire and the forge, after whom volcanoes are named.
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Mount St. Helens