Volcanoes Flashcards
What is a volcano?
- Any landform (on land or beneath the ocean) that releases lava, gas, or ashes, or has done so in the past
- Most occur at divergent or convergent plate boundaries
- Anomalous volcanism can sometimes occur in the middle of a plate (intraplate volcanism)
- Anomalous volcanoes may be the result of: hot magma rising from the core-mantle boundary or asteroid impacts
Good evidence that Hawaii is situated over a:
hotspot (islands in a row b/c plate is moving making holes as it moves = islands, tells us plate motion)
Magma (and lava) can be:
felsic, intermediate, or mafic
How does magma chemistry influence the nature of volcanic eruptions?
- Fewer covalent bonds between tetrahedra = thin, runny magma (mafic, low silica)
- More covalent bonds b/w tetrahedra = thick magma (felsic, high silica)
Mafic (basaltic) lava flows easily and erupts gently
- Low silica content
- Low viscosity (good at off-gassing (releasing gas) due to low viscosity)
- Low gas
Mafic (basaltic) lava flows easily and erupts gently
- Low silica content
- Low viscosity (good at off-gassing (releasing gas) due to low viscosity)
- Low gas
Mafic lava textures
Aa - rough, fragmented lava blocked called “clinker”
Pahoehoe - smooth, shiny, and ropy surface
Felsic magma tends to erupt catastrophically
- High silica content
- More viscous (resistant to flowing)
- High gas content (trapped between silica tetrahedra/crystals)
- Expanding gases fragment magma and rock, producing pyroclastic debris or tephra
Intermediate magma eruptions are less
explosive
Types of pyroclastic debris
- Ash
- Lapilli (tiny pieces of rock)
- Volcanic bombs (rocks size of fist)
- Volcanic block (house/car size)
- Welded tuff (compacted tiny rocks into rock)
- Pumice (vesicular)
H2O, CO2, SO2 are the most
abundant gases released during an explosion
What happens to the SO2 gas released during an explosion?
Sulphuric acid = acid rain
Volcanoes can be classified into 2 groups:
- Central vent volcanoes: central vent, summit crater
2. Large-scale volcanic terrains: no central vent, network of source material, extend over a large area
Types of central vent volcanoes
- Shield Volcanoes
- Stratovolcanoes
- Rhyolite Caldera Complexes
What is a shield volcano?
low silica, low gas magma originates in mantle, low viscosity creates broad gentle slopes
What is a stratovolcano?
Alternating layers of mafic to intermediate lava flows with layers of intermediate to felsic explosively ejected pyroclastic fragments, explosive eruptions are common due to buildup of gases
What is a Rhyolite Caldera Complex volcano?
High silica, high gas magmas, massive explosions (most explosive of all types), withdrawal of magma from the magma chamber causes collapse, produces an “inverse volcano” or caldera
Large-scale volcanic terrains
- Mid-ocean ridges develop at divergent boundaries, basaltic flow creates a global network of interconnected seafloor ridges
Volcanoes are highly variable in terms of:
size
Volcano type is related to:
kind of magma
Divergent boundary: mafic
lava flows
Oceanic hot spot:
mafic lava flows, shield volcanoes
Continental hotspot:
felsic to mafic lava flows, can be any type
Oceanic-continental subduction zones:
felsic to mafic
Ocean-oceanic:
intermediate to mafic lava flow, shield or stratovolcanoes, volcanoes form an island arc
