Volcanoes Pt. I Flashcards
what are the three main rock types?
-igneous
-sedimentary
-metamorphic
what is the source of igneous rocks and how are they formed?
-melting of rocks in crust and upper mantle
-crystallization of molten rock (magma/lava)
what is the source of sedimentary rocks and how are they formed?
-weathering and erosion of surface rocks
-transportation, depositions, sedimentation, precipitation
what is the source of metamorphic rocks and how are they formed?
-rocks under under pressure and temp in crust and upper mantle
-recrystallization/deformation of rocks in new state
what is magma?
molten rock underground
what is lava?
molten rock at the surface
what are the conditions that control igneous rock composition?
-where solidification happens
-temperature
-melting conditions
-physical setting
what are the two ways that igneous rocks are classified?
- where they solidified (above/below ground)
- silicia content
what is the name and characteristics of igneous rocks that solidify underground?
-plutonic/intrusive
-coarse grained crystals that are visible to the eye
what is the name and characteristics of igneous rocks that solidify above ground?
-volcanic/extrusive
-fine-grained or no crystals (glassy)
what crystal size in igneous rocks indicate?
the time that the rocks had to cool (bigger crystals - slower cooling time -> likely underground/plutonic/intrusive)
what is the volcanic pipe?
where magma passes to reach surface
what is a dike? what is sill? what is laccolith? what is batholith? what is xenolith? what is stock?
volcanic pipe of older volcanoes
-flat intrusion of igneous rock (same layer)
-dome-like intrusion (connected to dike)
-large intrusive igenous rocks (cooled deep in crust)
-rock embedded in magma while the magma was cooling
-a remnant of the vent of a volcano
what is pyroclastic rock?
deposits and rocks formed by eruption of volcano (extrusive)
what is tephra?
material ejected during eruption like ash/pumice
igneous rocks can be mafic, felsic, or intermediate. what are the main characteristic of this classification?
-mafic: high in magnesium and iron
-felsic: high in silica and feldspar
intermediate: intermediate
mafic rocks silica content?
45-50% (less 45% is ultramafic)
what are the characteristics of mafic igneous rocks?
-low viscosity (runny)
-melts around 1200C
-dark colour (high Fe/Mg)
- has ferromagneisian minerals like pyroxene
- has Ca-rich feldspar (plagioclase)
what is the extrusive mafic rock?
basalt
what is intrusive mafic rock?
gabbro (has no quartz)
what are the characteristics of intermediate igneous rocks?
-50-70% silicia
-intermediate viscosity
-melts around moderate temp
-purple/green/grey colour
- has ferromagneisian minerals like amphibole
- has Ca-rich feldspar (plagioclase)
what is the extrusive intermediate rock?
andesite (dacite)
what is the intrusive intermediate rock?
diorite (granodiorite), more plagioclase visible than gabbro
what are the characteristics of felsic igneous rocks?
->70% silicia
-high viscosity
-melts around low temp (800 C)
-pale/pinkish/tan/white colour
- has fewer ferromagneisian minerals
- has K-rich feldspar (orthoclase/sanidine), Na-rich, quartz
what is the extrusive felsic rock?
rhyolite
what is the intrusive felsic rock?
granite (pink crystals = orthoclase)
To melt rock, you need to do what three things? (magma= partial melt)
-decrease overlying pressure
-raise temp
-add water
magma composition depends on type of rock & conditions because of what?
rocks are made of different minerals that melt under different conditions
what is magma differentiaition?
change from one melt composition to another
partial melting and fractional crystallization often cause magma to do what? what change occurs?
-change composition (generally going from mafic to felsic)
the type of volcano that forms is often determine by what characteristic?
type of magma
why is the first melt often basaltic?
melt happens in deep crust where rocks are ultramfaic
the longer that it takes for melt to reach surface, the more melt evolves. in what way?
evolve from mafic to intermediate to felsic
what is volcano?
-central vent/fissure where molten rock, gas, rock fragments are ejected during eruption; conduit for magma
main types of volcanoes
-fissure
-shield
-lava dome
-cinder
-composite/stratovolcano
-caldera`
what are the four typical volcanic settings?
-hot spots
-divergent boundaries
-young spreading zones
-subduction/collisions zones
(literally anywhere magma is made and path exists to surface)
subduction zones - magma type
intermediate (moderate crust thickness)
hot spot under ocean crust - magma type
basalt (more direct from mantle)
mid ocean ridges - magma type
basalt (more direct from mantle); not iceland
continental rifts - magma type
varied cause crust is thinned at rifts
hot spot under continental crust - magma type
rhyolite (high silica cause thick crust)
where do most eruptions happen?
mid-ocean ridges (70%)
