ESS 106 Midterm 2
Which magma can interact with external water? - correct answer ✔✔all
-mafic more likely though
What's another name for intermediate to felsic eruptions? - correct answer ✔✔silicic eruptions
Where do eruptions involving external water typically occur? - correct answer ✔✔where we have
external water
-does not necessarily mean ocean though because seafloor in some deep places may suppress
explosivity
What is phreatomagmatic volcanism? - correct answer ✔✔magma encounters and explosively mixes
with water, for instance, where there is:
--ice (so much that it hides volcanic features)
--ground water (underground but has to interact and not drive away)
--shallow standing water (shallow ocean parts, lakes, etc)
-highly explosive >> water leads to rapid fragmentation of magma
What is fragmentation driven by in phreatomagmatic volcanism? - correct answer ✔✔interaction of
magma with external water
Describe mafic phreatomagmatic volcanism - correct answer ✔✔-when lava enters body of water
=littoral explosion (ex: in HI, lava reaches water around island and explodes violently)
-Surtseyan eruptions, maar eruptions, subglacial eruptions
Describe Surtseyan (mafic phreatomagmatic) eruptions - correct answer ✔✔through a body of water
,-ie: underwater explosion that created island of Surtsey
-create of tuff cones (conical fragments)
Describe Maar (mafic phreatomagmatic) eruptions - correct answer ✔✔through groundwater
-hole punched through ground
Describe subglacial (mafic phreatomagmatic) eruptions - correct answer ✔✔through glacier (ice)
-violent due to melting ice
Can there be silicic phreatomagmatic volcanism? - correct answer ✔✔yes
-ex: NZ eruption (Oruoanui)
--widespread ash deposits, very fine-grained
What controls how explosive phreatomagmatic eruptions are? - correct answer ✔✔explosivity depends
on efficiency of fragmentation, which depends on:
-magma composition and viscosity
-water to magma ratio (too much water will suppress, not enough won't be explosive; volume and rate
of magma erupting into the system)
How do deposits show external water was involved? - correct answer ✔✔-bedded deposits = pulsating
eruptions (as water interacted with magma to erupt then new water refills and another eruption occurs)
-field methods: record basic characteristics (grain size and shape, bedding type and thickness, evidence
for liquid water @ time of deposition)
-tuff cones
-basal deposits can show direction of eruption
Describe the Yellowstone hotspot track - correct answer ✔✔-rising plume with lithosphere moving
above it
-Yellowstone caldera is most recent
-calderas spanning from OR to present reaching 17 Ma
, -very violent explosions, outpouring of basalts
--more felsic for caldera-forming events but basalts around edges (two styles at events)
-about every 500,000 years a big caldera-forming event occurs (most recent was over 600,000 years
ago)
How old are the most recent Yellowstone calderas? - correct answer ✔✔~640,000 years ago; ~1.3 Ma;
~2.1 Ma (biggest)
-all very big but differed in size
Describe the Volcanic Explosivity Index (VEI) - correct answer ✔✔scale of explosivity (0-8 scale)
-0 = non-explosive pyroclastic (think: fire fountain, 10s of meters of plume height, ex: Hawaiian/Kilauea.
occurs daily around world)
-1 = gentle (100-1000m plume height, Strombolian, daily)
-5 = paroxysmal (>25 km, Plinian, 100s of years, ex: St. Helens)
-6 = colossal (>25km, Plin/Ultra Plinian, 100s of years, ex: Krakatau)
-7 = super-colossal (>25km, ultra-plinian, 1000s of years, ex: Tambora)
-8 = mega-colossal (>25km, ultra-plinian, 10k years, ex: Yellowstone 2 Ma)
What constitutes a super eruption? - correct answer ✔✔VEI of 8
-short term, explosive events thatt eject magma with mass of 10(^15) kg -- 11 trillion tons of magma
-produce pyroclastic deposits with volumes of 1000 km(^3)
-volume of material erupted erupted 2.1 Ma from Yellowstone was nearly 6,000x greater than the
volume released in the 1980 St. Helens eruption
What are the conditions needed to have a supereruption? - correct answer ✔✔-need a very large
volume of magma with strong explosive potential
-need an enormous amount of eruptible magma that accumulates in shallow chambers (which is only a
minor component of even larger magma reservoirs)
-continental crust (what has to be happening within it):
--low-density crust is the KEY to growth of large volume, silicic magma reservoirs
--inhibits buoyant ascent of magma
Which magma can interact with external water? - correct answer ✔✔all
-mafic more likely though
What's another name for intermediate to felsic eruptions? - correct answer ✔✔silicic eruptions
Where do eruptions involving external water typically occur? - correct answer ✔✔where we have
external water
-does not necessarily mean ocean though because seafloor in some deep places may suppress
explosivity
What is phreatomagmatic volcanism? - correct answer ✔✔magma encounters and explosively mixes
with water, for instance, where there is:
--ice (so much that it hides volcanic features)
--ground water (underground but has to interact and not drive away)
--shallow standing water (shallow ocean parts, lakes, etc)
-highly explosive >> water leads to rapid fragmentation of magma
What is fragmentation driven by in phreatomagmatic volcanism? - correct answer ✔✔interaction of
magma with external water
Describe mafic phreatomagmatic volcanism - correct answer ✔✔-when lava enters body of water
=littoral explosion (ex: in HI, lava reaches water around island and explodes violently)
-Surtseyan eruptions, maar eruptions, subglacial eruptions
Describe Surtseyan (mafic phreatomagmatic) eruptions - correct answer ✔✔through a body of water
,-ie: underwater explosion that created island of Surtsey
-create of tuff cones (conical fragments)
Describe Maar (mafic phreatomagmatic) eruptions - correct answer ✔✔through groundwater
-hole punched through ground
Describe subglacial (mafic phreatomagmatic) eruptions - correct answer ✔✔through glacier (ice)
-violent due to melting ice
Can there be silicic phreatomagmatic volcanism? - correct answer ✔✔yes
-ex: NZ eruption (Oruoanui)
--widespread ash deposits, very fine-grained
What controls how explosive phreatomagmatic eruptions are? - correct answer ✔✔explosivity depends
on efficiency of fragmentation, which depends on:
-magma composition and viscosity
-water to magma ratio (too much water will suppress, not enough won't be explosive; volume and rate
of magma erupting into the system)
How do deposits show external water was involved? - correct answer ✔✔-bedded deposits = pulsating
eruptions (as water interacted with magma to erupt then new water refills and another eruption occurs)
-field methods: record basic characteristics (grain size and shape, bedding type and thickness, evidence
for liquid water @ time of deposition)
-tuff cones
-basal deposits can show direction of eruption
Describe the Yellowstone hotspot track - correct answer ✔✔-rising plume with lithosphere moving
above it
-Yellowstone caldera is most recent
-calderas spanning from OR to present reaching 17 Ma
, -very violent explosions, outpouring of basalts
--more felsic for caldera-forming events but basalts around edges (two styles at events)
-about every 500,000 years a big caldera-forming event occurs (most recent was over 600,000 years
ago)
How old are the most recent Yellowstone calderas? - correct answer ✔✔~640,000 years ago; ~1.3 Ma;
~2.1 Ma (biggest)
-all very big but differed in size
Describe the Volcanic Explosivity Index (VEI) - correct answer ✔✔scale of explosivity (0-8 scale)
-0 = non-explosive pyroclastic (think: fire fountain, 10s of meters of plume height, ex: Hawaiian/Kilauea.
occurs daily around world)
-1 = gentle (100-1000m plume height, Strombolian, daily)
-5 = paroxysmal (>25 km, Plinian, 100s of years, ex: St. Helens)
-6 = colossal (>25km, Plin/Ultra Plinian, 100s of years, ex: Krakatau)
-7 = super-colossal (>25km, ultra-plinian, 1000s of years, ex: Tambora)
-8 = mega-colossal (>25km, ultra-plinian, 10k years, ex: Yellowstone 2 Ma)
What constitutes a super eruption? - correct answer ✔✔VEI of 8
-short term, explosive events thatt eject magma with mass of 10(^15) kg -- 11 trillion tons of magma
-produce pyroclastic deposits with volumes of 1000 km(^3)
-volume of material erupted erupted 2.1 Ma from Yellowstone was nearly 6,000x greater than the
volume released in the 1980 St. Helens eruption
What are the conditions needed to have a supereruption? - correct answer ✔✔-need a very large
volume of magma with strong explosive potential
-need an enormous amount of eruptible magma that accumulates in shallow chambers (which is only a
minor component of even larger magma reservoirs)
-continental crust (what has to be happening within it):
--low-density crust is the KEY to growth of large volume, silicic magma reservoirs
--inhibits buoyant ascent of magma
