volcanoes (5) Flashcards
Compare the 1980 eruption of Mt. St. Helens to a typical eruption of Hawaii’s Kilauea Volcano.
Mt. St. Helens- massive eruption with death and destruction
Kilauea- magma slowly seeps out and isn’t that dangerous
Magma
A molten rock found at depth, including any dissolved gases and crystals
Lava
Magma that reaches Earth’s surface
Effusive Eruption
A quiescent eruption that produces mainly outpourings of fluid lava
Viscosity
A measure of fluid’s resistance to flow
The more silica present in magma, the _____ its viscosity
Greater
Eruption Column
Buoyant plumes of hot, ash-laden gases that can extend thousands of meters into the atmosphere
List these magmas in order from highest to lowest silica content:
mafic (basaltic) magma
felsic (granitic/rhyolitic) magma
intermediate (andesitic) magma
Felsic
Intermediate
Mafic
What are the two primary factors that determine the manner in which magma erupts?
Viscosity
Gas content
Are volcanoes fed by highly viscous magma more or less likely to be a greater threat to life and property than volcanoes supplied with very fluid magma?
Highly viscous magma is a greater threat
Aa Flow
A type of lava flow that has a jagged, blocky surface
Pahoehoe Flow
A lava flow with a smooth to ropy surface
Lava Tube
A tunnel in hardened lava that acts as horizontal conduit for lava flowing from a volcanic vent. Lava tubes allow fluid lavas to advance great distances
Block Lava
Lava that has a surface of angular blocks associated with material having andesitic and rhyolitic compositions
Pillow Lava
Basaltic lava that solidifies in an underwater environment and develops a structure that resembles a pile of pillows
Volatiles
Gaseous components of magma dissolved in the melt. Volatiles will readily vaporize (form a gas) at surface pressures
Pyroclastic Material
The volcanic rock ejected during an eruption. Pyroclastic include ash, bombs, and blocks
Contrast pahoehoe and aa lava flows.
Pahoehoe are more rapid, lower viscosity and rope-like
List the main gases released during a volcanic eruption.
Water vapor Carbon Dioxide Carbon Monoxide Sulfer Dioxide Hydrogen Sulfide Nitrogen
How do volcanic bombs differ from blocks of pyroclastic debris?
Bombs leave the volcano as liquids
What is scoria? How is it different from pumice?
Vesicular rock with a basaltic composition
Fissure
A crack in rock along which there is a distinct separation
Conduit
A pipeline opening through which magma moves toward Earth’s surface. It terminates at a surface opening called a vent
Vent
The surface opening of a conduit or pipe
Volcanic Cone
A cone-shaped structure built by successive eruptions of lava and/or pyroclastic materials
Crater
The depression at the summit of a volcano or a depression that is produced by a meteorite impact
Caldera
A large depression typically caused by collapse or ejection of the summit area of a volcano
Parasitic Cone
A volcanic cone that forms on the flank of a larger volcano
Fumarole
A vent in a volcanic area from which fumes or gases escape
Shield Volcano
A broad, gently sloping volcano built from fluid basaltic lavas
Seamount
An isolated volcanic peak that rises at least 1000 meters above the deep-ocean floor
Describe the composition and viscosity of the lava associated with shield volcanoes.
Mafic, low viscosity (ooz out)
Are pyroclastic materials a significant component of shield volcanoes?
No, they only make up a few percent
Where do most shield volcanoes form-on the ocean floor or on the continents?
On the ocean floor
Cinder cone
A rather small volcano built primarily of ejected lava fragments that consist mostly of pea-to-walnut-size lapilli
Describe the composition of a cinder cone.
Pyroclastic, mafic, scoria is formed, sometimes a lava flow from the base
How do cinder cones compare with shield volcanoes in terms of size and the steepness of their flanks?
Cinder cones are much smaller and much steeper
Composite Volcano/Stratovolcano
A volcano composed of both lava flows and pyroclastic material
What is the name given to the region having the greatest composite volcanoes?
Ring of Fire
Describe the materials that compose composite volcanoes.
Pyroclastic material and lava flows
How do the composition and viscosity of lava flows differ between composite volcanoes and shield volcanoes?
Composite volcanoes have silica rich intermediate magma
Shield volcanoes tend to be basalt only (less variety than composite)
Pyroclastic Flow
A highly heated mixture, largely of ash and pumice fragments, that travel down the flanks of a volcano or along the surface of the ground
Nuee Ardente
Incandescent volcanic debris buoyed up by hot gases that moves downslope in an avalanche fashion
Lahar
A debris flow on the slopes of a volcano that results when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels
Tsunamis
The Japanese word for seismic sea wave
Why are pyroclastic flows capable of traveling great distances?
Gases reduce friction
List 3 volcanic hazards besides pyroclastic flows and lahars
Tsunami
Aviation risk from ash
Respiratory health
Fissure Eruption
An eruption in which lava is extruded from narrow fractures or cracks in the crust
Basalt Plateau
The broad and extensive accumulation of lava from a succession of flows emanating from fissure eruptions
Flood Basalts
Flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses of hundreds of meters
Lava Dome
A bulbous mass associated with an old-age volcano, produced when thick lava is slowly squeezed from the vent. Lava domes may act as plugs to deflect subsequent gaseous eruptions
Volcanic Neck/Plug
An isolated steep-sided, erosional remnant consisting of lava that once occupied the vent of a volcano
Describe the formation of Crater Lake.
Mt. Mazama was erupting explosively that emptied out the magma that was feeding the volcano, the volcano collapsed, rain filled it
How do the eruptions that created the Columbia Plateau differ from the eruptions that create large composite volcanoes?
The Columbia Plateau was created by fissure eruptions (flood basalts) low viscosity
What type of volcanic structure is Shiprock, New Mexico, and how did it form?
Volcanic neck
Ring of Fire
The zone of active volcanoes surrounding the Pacific Ocean
Volcanic Island Arc
A chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another
Continental Volcanic Arc
Mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent. Examples include the Andes and the Cascades
Intraplate Volcanism
Igneous activity that occurs within a tectonic plate, away from plate boundaries
Mantle Plume
A mass of hotter-than-typical mantle material that ascends toward the surface, where it may lead to igneous activity. These plumes of solid yet mobile material may originate as deep as the core-mantle boundary
Hot Spot
A concentration of heat in the mantle, capable of producing magma that, in turn, extrudes onto Earth’s surface. The intraplate volcanism that produced the Hawaiian Islands is one example.
Superplume
A large area of the mantle that is dominated by the upwelling of hot mantle rock, which originates near the mantle-core boundary
Are volcanoes in the Ring of Fire generally described as effusive or explosive?
Explosive
Ex: Mt. St. Helens
How is magma generated along convergent plate boundaries?
Subduction zones; hydrated minerals release water to surrounding mantle which lowers the temperature melting point MAFIC MAGMA
Volcanism at divergent plate boundaries is most often associated with which magma type?
Mafic (iron and magnesium)
What is thought to be the source of magma for most intraplate volcanism?
Plumes, hot spots, rising material
What three factors do volcanologists monitor in order to determine whether magma is migrating toward Earth’s surface?
Changes in Earthquake patterns
Change in size
Change in inflation of cone
Change in gases
What volcanic hazard does the warning system installed around Mount Rainier aim to identify?
Lahars
