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55 Cards in this Set
- Front
- Back
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Cinder cone forms
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Relatively short-lived eruptions of pyroclastic material build up a small volcano.
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An igneous rock that cools in the crust will have a
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coarse-grained interlocking texture
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One difference between magma and lava
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magma has not erupted
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Most active volcanoes above sea level are found at
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Convergent margins
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Primary volcanic hazard to communities built along rivers near MT. Rainier
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Lahars
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Mafic flow are dangerous because
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They can flow downslope at high speed
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CO2 is major hazard because
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it causes asphyxiation
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basic requirements for lahar
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water and tephra
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2 most primary gases in magmas and lavas
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water vapour and carbon dioxide
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Cascade arc sits adjacent to a plate boundary where
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the Juan de Fuca plate is subducting beneath the American plate
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Most hazardous volcano in the Cascades
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Mt. Rainier
-active hot springs -ongoing earthquakes -ice cap -great height and mass |
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InSAR measures
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ground deformation of a volcanic area over time
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VEI based on
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duration of eruption
height of cloud volume of material |
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Pahoehoe lava flows
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Form basaltic rock
Flow in streams and valleys Smooth and ropy Can be outran by people |
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Shield volcanoes formed at
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Hot spots
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MOST important factor in determining volcano explosivity
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Silica content in magma
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Example of plutonic rock
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granite
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Why are the areas at the boundary of the Pacific Ocean called the "ring of fire"
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There are a lot of subduction zones around it, hence volcanic activity
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magma composition that will produce most explosive volcanoes
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rhyolite
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most common volcanic rock on earth
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basalt
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Which volcanic hazard can occur without eruption
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sector collapse/landslide
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Why are stratovolcanoes most common type of volcano around the Pacific Rim
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They are typical of continent-Ocean subduction zones
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Two volcanic gas products
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Carbon dioxide, and water vapour
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Maar
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Cinder cone on the flank of larger volcanoes
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Cinder cone characteristics
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Hill formed from accumulation of pyroclastic material around volcanic vent
Mafic magma types |
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Shield volcano characteristics
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Largest
Non-explosive Magma erupts through openings or vents down the sides Basalt rock type Low silica content |
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Composite volcano characteristics
(Stratovolcanoe) |
Composed of interlayered lava flow, lava flow rubble, and pyroclastic deposits
Intermediate silica content Combination of lava flows and explosive activity |
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Ring of fire
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o Approximately two-thirds of all active volcanoes on land located here
o Lie above subduction zones bordering pacific, Nazca, Cocos, Philippine, and Juan de Fuca plates |
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Subduction zones
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o Oceanic crust, which is dense than continental crust, is carried into earth’s mantle
o Rising heat dries out the subducting curst o The water expelled rises and changes the chemical composition of the overlying mantle o Presence of water lowers the melting temp of overlying mantle rocks and causes them to melt, forming magma that rises through the curst to erupt on the surface o Stratovolcanoes occur at subduction zones, thus most common type found around pacific Rim |
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Mid ocean ridges
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Plates move away from one another instead of colliding
divergent boundaries |
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Magma formed by
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Melting pre-existing rock in Earth's interior
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A'a
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Lava flow with a rubbley flow top consisting of broken fragment of lava
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Volcanic glass
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Obsidian-no crystals
Pumice-contains many bubbles (vesicles) |
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Mafic characteristics
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High temperatures
Low silica content Low viscosity Low gas content Non explosive |
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Felsic Characteristics
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Lower temp
High viscosity Erupt explosively |
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Andesite magma
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Intermediate silica
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Dacite magma
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Intermediate silica
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rhyolite magma
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high silica
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basalt magma
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low silica
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Crater
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Inside volcano, steep walled, bowl shaped depression surrounding the volcanic vent from which new material erupts
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Volcanic dome
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Pile of viscous lava that forms over a vent
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Main hazard with mafic flows
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infrastrucutre damage
people can outrun those bitches |
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Pyroclastic flows
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turbulent mixtures of hot gas and pyroclastic fragments that are emplaced laterally from a volcanic vent. Consist of ash, lapilli, crystals and other frock fragments called lithic fragments
300-400 km/hr temp 500-700 C range |
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Facets of eruption prediction
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Collect existing geologic data
Develop a monitoring scheme Create geologic and volcanic hazards maps |
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Measuring ground deformation
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Taping distance between horizontal displacement
-tiltmeteres -gps -InSar |
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Tiltmeter
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sensitive instrument that record changes in tilt of a surface
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Most useful technique for predicting volcanic activity
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Seismic monitoring
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Volcanic arcs form
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convergent margins
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Upper mantle
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Ultramafic
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Oceanic crust
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Mafic
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Continental crust
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Ranges from mafic to felsic
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Garibaldi-Cascade arc
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formed from subduction of Juan de Fuca plate beneath North American plate
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Primary volcanic hazards
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o Lava flows, ash fall, volcanic bombs, Pyroclastic flows, Pyroclastic surges, lateral blasts, poisonous gasses
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Secondary effects
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o Lahars, debris avalanches, other landslides, groundwater and surface water contamination, floods, fires, and tsunami, can also cool earth’s atmosphere for a year or so
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Kilauea
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Shield volcano produces lava flows
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