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48 Cards in this Set

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1. A conduit, opening in the magma chamber, that is a linear tear
2. May erupt a curtain of lava
3. Evolve into discrete vents
Flood basalt
1. Huge sheets of particularly hot, low-viscosity lava erupted and spread out in vast sheets
2. Successive eruptions can build up a broad plateau
1. Solid products of eruption (lava and/or pyroclastic debris) accumulate around a conduit to form a mound or cone
2. Circular depression shaped like a bowl up to 500 m across and 200 m deep
3. Develops either during eruption as material accumulates around the summit vent or just after eruption as the summit collapses into the drained conduit
1. Gigantic volcanic depression
2. Can be kilometers across, larger than a crater, steep sidewalls and flat floors
3. Forms from massive explosive (felsic) eruptions when center of the volcano collapses into the large, drained magma chamber below
4. Ex:
• Crater Lake, Oregon
• Yellowstone National Park
Lava flows
Sheets or mounds of lava that flow onto the ground surface or sea floor in molten form and then solidify
Pyroclastic flow
1. Intermediate and felsic lava more viscous and more gas-rich so more explosive
2. Ash ejected from explosive eruptions
3. Gravity pulls part of rising column of ash down the side of the volcano in fast-moving avalanche, nuée ardente (glowing avalanche)
Volcanic gases
1. Water, carbon dioxide, sulfur dioxide, hydrogen dioxide
2. More silica contain more gas
3. Low-viscosity magma, gas bubbles rise faster than magma can move
4. High-viscosity magmas, gas has trouble escaping because bubble can't push through sticky lava
1. Lava flows
2. Low-viscosity basaltic lavas
3. Shield volcanoes
1. Pyroclastic debris
2. Gas expands in the rising magma but cannot escape
3. Sometimes caldera
4. Cinder cones
Mid-Ocean Ridges
Melting occurs beneath
1. Products cover 70% of our planet's surface
2. Develop along fissures parallel to the ridge axis
3. Erupt basalt, forms pillow mounds because it cool so quickly underwater
4. Erupts black smokers, water that heats up as it circulates through the crust near the magma chamber and bursts out of hydrothermal vents
Convergent Boundaries
Yields a volcanic arc
1. (Subduction zones) volcanoes forms when volatile compounds such as water and carbon dioxide are released from the subducting plate and rise into the overlying hot mantle
2. Causes melting and produces
3. Rises through the lithosphere and erupts
4. Grow on oceanic crust, volcanic island arcs (Marianas of western Pacific)
5. Grow on continental crust, continental volcanic arcs (Cascade volcanic chain of Washington and Oregon)
6. Effusive, pyroclastic, explosive eruptions
7. Composite volcanoes (Mt. Fuji and Mt. St. Helens)
Continental Rifts
Melting occurs beneath
1. Wide array because of magma from partial melting of the mantle and partial melting of the crust
2. Basaltic fissure eruption, curtains of lava or linear chains of cinder cones
3. Explosive rhyolitic volcanoes, stratovolcanoes
Ocean Hot-Spot Volcanoes
1. Basaltic magma erupts at the surface of the sea floor
2. Irregular mound of pillow lava
3. Grows to become island
4. Basalt lava flows as thin sheet over great distance
5. Dome-shaped shield volcano
6. Large submarine slumps--portions can't resist the pull of gravity and slip seaward
Continental Hot-Spot Volcanoes
Yellowstone National Park
1. String of calderas--oldest 16 m.y.
2. Both basaltic lava and rhyolitic pyroclastic debris
3. Because basaltic magma rising form the asthenosphere (upper layer of earth's mantle below the lithosphere) heats up and partially melts the continental crust
4. Rhyolitic eruptions produce thick tuffs that now crop out as yellow and red rocks in the canyon
Flood-Basalt Eruptions
1. Flood basalts form when a mantle plume first rises beneath a region that is undergoing rifting
2. As the plume reaches the base of the lithosphere, it has a bulbous head containing a huge amount of partially molten rock
3. Stretching and thinning of the overlying lithosphere results in further decompression of the plume head, causes even more to melt
4. Melt rises along fissure that form in the rift, and erupts
Iceland--a Hot Spot on a Ridge
1. Mid-Ocean ridge volcanism has built a mound of basalt that protrudes above the sea
2. At divergent plate boundary, being stretched apart
3. Narrow rift where youngest volcanic rocks
4. Fissure eruptions, curtain of lava or linear chins of cinder cones
erupting, recently erupted or likely to erupt
hasn't erupted in hundreds to thousands of years
not capable of erupting (no longer any magma)
1. low SiO2
2. 1200°C
3. low viscosity
4. smooth, flowing (effusive)
5. shield: broad, gentle
6. basalt, pahoehoe, a'a, scoria, pillow basalt
7. oceanic divergence: MORs, hot spots, fissures
8. Iceland, Hawaii
1. Intermediate-SiO2, T, viscosity
2. Smooth or explosive, lava flows & pyroclastic flows
3. Composite: relatively steep
4. andesite, tuff, breccia, tephra (ash bombs)
5. Convergence; ocean-ocean, ocean-continent
6. Pinatubo, Vesuvius, Mt. St. Helens, Andes
1. High SiO2
2. ~800°C
3. High viscosity
4. Explosive
5. Cinder cones: steep, ash, silica plugs
6. Rhyolite, obsidian, pumice, pyroclastics
7. Yellowstone
resistance to flow; mainly controlled by silica content, temperature, and amount of dissolved gases
High viscosity lava
highly resistant to flow; lava is "sticky" and erupts violently
Low viscosity lava
flows easily and erupts relatively gently
Composition/silica content
the general categories of lava and rock compositions are related to their amounts of silica (SiO2);
more silica-rich the lava is, the higher its viscosity
Melting temperature (Tm)
higher the lava's melting temperature, the lower its viscosity
the higher the amount of dissolved gases, the lower a lava's viscosity
Borad with gentle slopes; basaltic; Hawaii
1. Effusive
2. Ocean Hot-Spot/rifts (East African)
3. Mafic
Shield--ropey lava
1. Warm, pasty surfaces wrinkles into smooth, glassy, rope-like ridges
Shield--forms when basalt loses gas thickens, breaks into fragments
1. Surface layer of the lava freezes then breaks up due to continued movement of the lava underneath
2. Becomes jumble of sharp, angular fragments, creating a rubbly flow
Columnar basalt
Forms when lava flows cool and shrinks
1. Final stages of cooling lava flows contract and fracture into roughly hexagonal columns
Pillow basalt
Forms when basalt erupts into water
1. Because of rapid cooling, forms a glass-encrusted blob, or pillow, on freezing
2. Rind of pillow momentarily stops flow's advance, but pressure of lava squeezing into the pillow breaks the rind, a new blob of lava squirts out, and freezes itself into a pillow
Steeper slope; andesitic; Fuji, St. Helens, Vesuvius
1. Convergent plate boundaries O-O, O-C (Fuji, Andes)
2. Alternating layers of lava, tephra, debris
3. Large and cone-shaped
4. Explosions or landslides may destroy the classic shape
Eruption of Mt. St. Helens 1980
Lateral blast, pyroclastic flows, lahars (destructive mudflow), ash cloud
1. Earthquake
2. 80 m crater opened, emitting gas and pyroclastic debris
3. North side bulged, filling with magma
4. Earthquake triggered 3 cubic km to slide away
5. Sudden landslide increase pressure of magma, sudden expansion of gases blasted through side of volcano
6. Vertical column
7. 60 mph
unconsolidated deposits of pyroclastic grains, regardless of size
1. blocks, bombs, tuff
Geological premis of Dante's peak
an eruption like Mt. St. Helens in the Cascades
1. O-O convergence
2. Intermediate silica
Accurate effects
1. enormous power unleashed during eruption
2. stratovolcanoes in Cascade Range erupt explosively and produce pyroclastic flows, couds of volcanic ash, and debris flows (lahars)
Inaccurate effects
Lava flows usually thick and slow moving, unlike fluid flows in the movie
1. Clastic (fine-grained/well-sorted)
2. Clay, fossils
3. Pond, swamp, lake
Quartz sandstone
1. Clastic (well-rounded/well-sorted)
2. Quartz, sand
3. Beach
1. Clastic (angular grains/poorly-sorted)
2. K-spar, quartz, Fe-oxide
3. Alluvial fan, arid region, i.e. desert
1. Clastic (angular grains/poorly-sorted)
2. Rock fragments, quartz, clay matrix
3. Deep sea fan--trubidites
1. Clastic (mod. well-rounded grains, poorly-sorted)
2. Quartz pebbles, Fe-oxide (yellow)
3. Stream, river
1. Clastic (angular grains/poorly-sorted)
2. Rock fragments (limestones), Fe-oxide (red matrix)
3. Landslide, talus cone, alluvial fan (base of a cliff)
1. Chemical
2. Calcite
3. Deep marine, tropical
Oolitic limestone
1. Chemical
2. Calcite ooids
3. Warm tropical beach (water has to be warm for calcites to come out of the solution)
1. Biochemical/bioclastic
2. Calcite, shells
3. Beach