Volcanoes Flashcards
1
Q
volcano
A
location where molten rock or pyroclastic material erupt through a vent. Often, but not always, a conical mountain
2
Q
crater
A
depression overlying a volcanic vent
3
Q
extrusive igneous rocks
A
- Form from fast cooling of molten rock (lava) at the earth’s surface OR
- Fragmentation and fast cooling of molten rock as it explovely erupts forming “pyroclasts”
- Fast cooling = small crystal size; fine-grained (microscopic)
4
Q
explosive vs. effusive
A
- explosive (BOOM):
- High viscosity magmas (like peanut butter)
- felsic – high silica content (strong chains of silica tetrahedra)
- Magmas that are gas-rich (full of volatiles)
- Ex. Mt. St. Helens - effusive (fizz… non-explosive):
- Low viscosity magmas (like honey)
- Low silica content
- Gas poor
- Dissolved gases – bubbles escape “vesicles” - lava fountains may form
- Ex. Kilauea
5
Q
Pahoehoe vs. A’a
A
- Pahoehoe = smooth, ropey lava type
- A’a = sharp, clinky lava type
6
Q
pillow lava
A
- Errupts underwater
- “skin” cools immediately, inflates with lava like a balloon until too cool -> “pops” and another baloon formed
7
Q
pyroclasts (5 types)
A
- “fire piecies” ejected out of a volcano during eruption
- Types:
- Ash: <2mm
- Lapilli: 2-64mm
- Bombs: >64m
- Pumice: floats on water, felsic
- Scoria: sinks, mafic
8
Q
pyroclastic deposits
A
- Pyroclastic flows (these kill)
- Pyroclastic fall
- Spatter (scoria)
- bombs
9
Q
gases and volcanoes
A
- Gases associated with volcanoes: H2O, CO2, N2, SO2, CL2, H2
- Effects of these gases: global warming, acid rain -> global cooling, destruction of ozone
10
Q
types of volcanoes
A
- shield volcanoes
- cinder cones
- composite volcanoes/Stratovolcanoes
11
Q
shield volcano
A
- Gentle slopes
- Basaltic
- Can be very big
- Associated with hot spots (anomalously warm regions of mantle)
- Generate hot, mafic (low silica, low viscosity) magmas
- Ex. Muana Loa
12
Q
cinder cones
A
- 100s of meters high
- Layers of pyroclastic ejecta (scoria, bombs)
- Mostly mafic
- Some lava
- Angle of repose = 30-40 degrees
- May occur on their own or on the flanks of one of the larger types of volcanoes
- Ex. Paricutin, Mexico – turned from a gassy crack in the earth to a full-blown volcano in 9 years
13
Q
composite volcanoes (Stratovolcanoes)
A
- Kilometers across, several kilometers high
- Quite steep – classic volcano shape
- Interbedded lava flows, pyroclastic flows, lahars, shot through with sills and dykes
- Full range of chemical compositions (mafic, intermediate, felsic) and volcanic products including lahars
- Ex. Mt. St. Helens, Mt. Baker, Mt. Garibaldi
- Form pyroclastic flow: hot pyroclastic material flowing downslope under gravity
- Creates hot gas (500 degrees celcius) that moves at supersonic speed (500km an hour)
14
Q
Mt. St. Helens
A
- Magma built up into volcano, earthquake happened, summit slid away and created a landslide, depressurization of magma -> giant explosion
- Explosivity: 8x all explosives in WW2
- Part of Cascadia subduction zone which is part of Paficic Ring of Fire (along with Mt Baker)
- Now there is a new dome growing in the crater
15
Q
Order of events generating felsic lava into a composite cone
A
- Migration of water into mantle above subduction zone
- Melting in the mantle above subduction zone
- Magma rising through mantle
- Underplating
- Partial melting of continental crust
- Generation of intermediate and felsic magmas
- Migration of magma towards the surface
- Eruption of viscous magma forming composite volcano
