Volcanoes Flashcards
Name the igneous body types
Intrusive
Extrusive
3 Main things to form extrusive igneous rocks
- Lava
- Pyroclasts (airborne volcanic rock fragments)
- Volatiles (gas escape during eruption)
Main factors affecting eruption style (also controls the viscosity of magma)
- Composition of magma
- Temperature of magma
- Dissolved gasses in magma
Define Viscosity
material’s resistance to flow
what are convergent boundaries
magma produced by hydration melting
enriched in silica
magma of intermediate to felsic composition
what are divergent boundaries
magma produced by decompression melting
silica-poor asthenosphere rock
magma of mafic composition
Intraplate hotspots
discrete heat plumes that locally melt high-temp asthenosphere rock to produce magma of mafic composition
What is pyroclastic material
fragments of rock, dust, ash from lava explosions
What are the special textures of extrusive rocks
Porphyritic Texture: dark colour, aphanitic texture, containing large crystals (phenocrysts)
2 stage cooling:
- magma cooling slowly at depth creating large crystals
- magma rise quickly to surface, remaining liquid is cooled quickly create smaller crystals
The texture that is created when lava flow cools quickly on surface
Glassy Texture
The texture with many holes (volatile bubbles)
Vesicular Texture
What is pyroclastic flow
hot cloud pyroclastic material + gas forced flow downhill
when material settles, glassy fragments of pyroclastic particles welded together to produce rock called tuff
what causes a small explosion
Depending on the composition
- Mafic composition
- low silica, high temp (low viscosity) + low gas
LEAST EXPLOSIVE
what causes a large explosion
felsic(+ intermediate composition)
-high silica, low temp (high viscosity) + high gas content
MOST EXPLOSIVE
How does profile of volcano relate to viscosity of lava?
low viscosity produce long thin flow lava
high viscosity lava produce short thick flows
