Nat. Dis. Ch. 6
Hawaiian
Low Visco + Low Vola (H)
Icelandic
Low Visco + Low Vola (I)
Scoria Cones
Low/M Viscosity + M/H Volatiles + Small Volume
The presence of water ________ the melting point of rock.
Lowers
Stratovolcanoes
M/H Visco + M/H Vola + Large Volume
Strombolian
Mod Visco + Mod Vola
__________ eruptions are the most violent types of explosive eruptions.
Plinian
Most to least explosive volcanoes
Plinian, Vulcanian, Strombolian, Hawaiian, Icelandic,
Magma is ductile and flows along the surface
Spreading Center
Most volcanic activity is in the ocean
Spreading Center
Releases the most magma per year
Spreading Center
__________ are steep-sided, symmetrical volcanic peaks built of alternating layers of pyroclastic debris capped by high-viscosity andesitic to rhyolitic lava flows that solidify to form protective caps.
Stratovolcanoes
Creates cone-shaped volcanoes
Subduction Zone
Responsible for the most violent eruptions
Subduction Zone
Most explosive to least explosive
Subduction Zone, Spreading Center, Transform Boundary
Magma at great depth does not contain gas bubbles because the high pressure at depth keeps gas dissolved in solution.
True
The basaltic magmas that erupt on the ocean floor have a low SiO2 content, high temperature, and allow gas to escape easily, all resulting in non-explosive eruptions.
True
The lowest temperatures and highest SiO2 contents occur in rhyolitic magma, material so viscous that it commonly does not flow.
True
The highest temperatures and highest SiO2 contents are in basaltic magma, giving it the lowest viscosity and easiest fluid flow.
false
Most rifting occurs at spreading centers __________.
located below sea level
Lava Flow
molten rock moving downslope
Lahars
muddy water-laden rush of material downslope
Pyroclastic Flow
rapid rush of gases and materials downslope
The viscosity of magma is lowered by __________.
- Increasing temp - Dec crystal content - Dec SiO2 content
Rock may melt by _______________.
- Lowering pressure - Raising temp - Increase water content
The typical trend in a rising plume of subduction-zone magma is to increase the ____
-Percentage of SiO2 -Visco -Explosive magam by holding gases more tightly
Flood Basalts
L Visco + L Vola + L Volume
Shield Volcanoes
L Visco + L Vola + Large Volume
Over _________ of Earth's magma extruded through volcanism takes place at the oceanic spreading centers.
70%
Which of the following can help make rocks melt beneath Earth's surface?
Adding volatiles, increasing temperatures, and decreasing pressure
A caldera collapse occurs ________________.
After the magma chamber is mostly empty
__________ melting occurs when a rock melts due to a lowering of pressure.
Decompression
At oceanic spreading centers, magmas are rhyolitic in composition.
False
Most volcanism is associated with hot spots.
False
The higher the viscosity of magma, the more fluid is its behavior.
False
Lava Domes
H Visco + L Vola + S Volume
In magma, __________ is the most abundant dissolved gas.
H2O
Plinian
High Visco + High Vola (P)
Vulcanian
High Visco + High Vola (V)
The most peaceful eruptions are __________ eruptions.
Icelandic
The primary reason magma forms at subduction zones is that the subducting plate carries a cover of sediments, water, and hydrated minerals down with it, which lowers the temperature required for the adjacent overlying mantle lithospheric rock to melt.
True
The variations in the composition of magmas govern whether eruptions are peaceful or explosive.
True
The three 'Vs' of volcanology are __________________.
Visco, Vola, Volume
_________ eruptions are common first phases in the eruptions of volcanoes as they "clear their throats" before emitting larger eruptions.
Vulcanian Type
A shield volcano has a great ___________.
Width compared to its height
Pyroclastic debris is __________.
chucks of magma and rocks blown into the air by gas in a volcanic eruption
