Volcano Flashcards
Most volcanic activity is associated with ______
plate boundaries
Volcanoes are associated with which types of boundaries?
Convergent, divergent
Volcanoes not on plate boundaries are on what?
Hot spots
Spreading ridges are _____
Volcanoes
Divergent boundaries:
Crust being pulled apart, mid-ocean ridges and continental rift
Subduction zones:
Ocean crust being recycled into mantle
Hotspots:
Oddballs, volcanoes not associated with plate boundaries
What kinds of plate boundaries are in the northern triangle?
Transform, convergent
What do plate tectonics control?
Where and how rocks are melted to create magma
The type of magma produced controls…
what volcanic material erupts at the surface
Hazards associated with a volcano is directly related to -
the properties of the volcanic material that comes out of it
Divergent plate boundaries separate what?
Two lithospheric plates
What fills the space created from the lithospheric plates separating?
Asthenosphere - fluid like mantle material
What happens in the asthenospheric mantle?
The mantle melts to create magma
Why does melting occur at divergent plate boundaries?
Because pressure on the hot mantle rock is decreased
Volcanic rock is typically…
Basalt
What is basalt?
A fluid, low silica, lava
Magma has little ____ and ____ in it
H2O, gas
When basalt erupts from mid-ocean ridges what forms?
Pillow basalts on the sea floor
What occurs when there are eruptions on land?
Cinder cones, basalt lava flows
Mid-ocean ridge eruptions are usually from…
fissures
Where does magma come from that is from rift volcanoes?
Straight from the mantle
Mantle rocks are only ____ melted
partially
___% of original mantle rock melts to form basalt magma
10
Minerals with ___ silica melt at lower temps
high
When a rock partially melts, the resulting magma has a ____ silica content than the parent rock
higher
What also changes when a rock partially melts?
The amount of other elements
What controls the physical properties of magma?
Chemical composition
Viscosity
Resistance to flow
What happens to silicate ions in vicious magma?
They stick to each other to form chains
What ions want to form with silicon atoms?
Oxygen
What breaks the silicon-oxygen chain?
H2O
Viscosity of magma is dependent on…
SiO2 content
Most magmas start off as…
Basalt
How can magma properties change?
When it travels through existing crust during eruption
What happens with magma at mid-ocean ridges?
It makes new crust, has little to no interactions and results in basalt
What happens with magma during continental rifting?
larger potential for interaction/mixing, andesite/rhyolite may erupt first followed by basalt
Rifting results in ____ ____ of mantle rock
decompression melting
What does rifting produce?
Hot, low silica magma
What kind of magma comes from rifting?
Magma is fluid (low viscosity) and usually has low volatile (water and gas) content
How can volcanic material be modified?
Interaction with overlying crust
