chapter 5 volcanoes
Terms
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- aa flow, p 144
- a type of lava flow that has a jagged, block surface
- batholith, p 167
- a large mass of igeous rock that formed when magma was emplaced at depth, crystallized, and was subsequently exposed by erosion.
- block lava
- omit
- caldera, p 147
- A large, basin-shaped depression, more or less circular in form, usually caused by collapse or ejection of the summit area of a volcano. Typically steep-sided, found at the summit of a shield volcano . Calderas are 1 km in diameter or more. See the diagram on p. 689.
- cinder cone, p 151
- a rather small volcano built primarily of ejected lava fragments that consist mostly of pea-sized to walnut-sized lapilli. See the diagram on p. 690.
- columnar joints, p. 166
- A pattern of cracks that forms during cooling of molten rock to generat columns.
- composite cone, p 153
- A volcano composed of both lava flows and pyroclastic material. See the diagram on p. 690.
- concordant, p 163
- A term used to describe intrusive igeous masses that form parallel to the bedding of the surrounding rock.
- conduit, p 147
- a pipelike opening through which magma moves toward Earth's surface. It terminates at a surface opening called a vent.
- crater (volcanic), p 147
- a depression, either at the summit of a volcano or at a meteorite impact site. Volcanic craters are less than 1 km in diameter.
- dike, p 163
- a tabular-shaped intrusive igenous feature cutting through the surrounding rock
- discordant, p 163
- a term used to describe plutons cutting across existing rock structures, such as bedding planes
- eruption column, p 142
- buoyant plumes of hot ash-laden gases that can rise up to thousands of meters into the atmosphere
- fissure, p 159
- a crack in a rock that has opened up (some cracks don't open up) so that there is a distinct separation between sides that were once joined
- fissure eruption, p. 160
- an eruption in which lava is extrudedf from narrow fractures or cracks in the crust
- flood basalt, p 160
- Flows of basaltic lava issuing from cracks or fissures. Flood basalts usually cover wide areas(some the size of states) to great thickness (hundreds of meters)
- fumarole, p 147
- a vent in a volcanic area from which fumes and gasses escape
- intraplate volcanism, p 174
- igenous activity occurring within a tectonic plate far way from plate boundaries (not near the edge of the plate)
- laccolith, p 166
- a massive igneous body intruded between preexisiting strata. see diagrm on p 695
- lahar, p 157
- a debris flow on the slopes of a volcano. Lahars form when layers of unstable ash and debris become saturated with water (and vapor) and flow downslope, usually along stream channels
- lava dome, p 161
- a bulbous mass found at the main vent of many old-age volcanoses. Lava domes are produced when thick lava is slowly squeezed from the vent. They sometimes act as plugs, deflecting subsequent eruptions of gas.
- lava tube, p 144
- a tunnel in hardened lava acting as a horizontal conduit for flva flowing from a volcanic vent. Lava tubes allow fluid lavas to advance great distances underground before they surface.
- massive pluton, p 163
- a pluton that is not tabular in shape, but rather blocky or irregular in shape. Massive plutons are quite large.
- nuee ardente, p 156
- Hot, hot, volcanic debris buoyed up by incandescent gasses moving downslope in a glowing avalanche called a pyroclastic flow. Temperatures can be 1500 degrees F. Speeds can be 150 miles per hour.
- pahoehoe flow, p 144
- a lava flow with a smooth surface or a surface that looks like ropes piled up.
- parasitic cone, p 157
- a volcanic cone that forms on the flank of a larger volcano
- pillow lava (pillow basalts), p 145
- Basaltic lava solidifying underwater. The surface of pillow lavas look like a mass of piled up pillows.
- pipe, p 147
- a vertical conduit or pipe letting magma escape as lava
- pluton, p 162
- an igneous structure formed as magma is emplaced and crystalizes as it cools slowly beneath the surface of the earth.
- pumice, p 147
- light-colored, glassy, vesicular rock with a granitic composition
- pyroclastic flow, p 156
- a highly heated mixture, largely of ash and pumice fragments. A pyroclastic flow travels down the flanks of a volcano and along the surface of the ground at the base of the volcano.
- pyroclastic material, p 146
- the volcanic rock ejected during an eruption. Pyroclastics include ash, bombs, and blocks.
- scoria, p 147
- vesicular ejecta of basaltic composition; also called "cinder"
- scoria cone, p 151
- same as a "cinder cone"
- shield volcano, p148
- a broad gently sloping volcano built from fluid basaltic lavas.
- sill, p 164
- a tabular igenous body intruded parallel to the horizontal layering of pre-existing rock
- stock, p 167
- A mini-batholith . . . a pluton similar to a batholith but not as large
- stratovolcano, p 153
- see "composite cone"
- tabular pluton, p 166
- an igenous pluton much longer and wider than it is tall
- vent, p 147
- a surface opening of a volcanic conduit or pipe
- viscosity, p 141
- a measure of a fluid's resistance to flow. Hot maple syrup is less viscous than cold maple syrup.
- volcanic neck, p 162
- an isolated, steep-sided, erosional remanant consisting of lava that once occupied the main vent of volcano.
- volcano, p 147
- a mountain formed from lava, or pyroclastics, or both.
- xenolith, p 168
- an inclusion of unmelted country rock (local rock found underground that has broken off) in an igneous pluton
- Volcanic ash
- The dust-sized, sharp-edged, glassy particles resulting from an explosive volcanic eruption.
- Volcanic Bomb
- a lump of lava ejected from a volcano that has acquired a characteristic tapering form as a result of its solidification while traveling through the air
- Pacific Ring of Fire
- The Ring of Fire is a zone of frequent earthquakes and volcanic eruptions that encircles the basin of the Pacific Ocean. It is shaped like a horseshoe and it is 40,000 km long. It is associated with a nearly continuous series of oceanic trenches, island arcs, and volcanic mountain ranges and/or plate movements. It is sometimes called the circum-Pacific belt or the circum-Pacific seismic belt.
- Mount St Helens
- an active volcano in the Cascade Range in southwestern Washington; erupted violently in 1980 after 123 years of inactivity
- Crater Lake, Oregon
- A lake of southwest Oregon in a volcanic crater of the Cascade Range. Iis the second-deepest lake in North America and the deepest in the United States.