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April 10 notes
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Geology 12
Intrusive Igneous Review
Chpt. 4 p.76 – 101
NOTES:
- difference between intrusive igneous and extrusive igneous rocks
intrusive:
plutons
dikes
sills
batholiths
diapers
(activities under the crust of the earth until weathering exposes them)
terms to know:
country rock
geothermal gradient
factors effecting melting (temp., pressure, duration, H2O
magma
basalt
partial melting
- granite is the predominant rock of continents
- basalt is the predominant rock under the oceans
- different types of magmas can mix inside the mantle
- there is a sequence in which minerals crystallize = Bowen’s Reaction Series =
shows the processes that modify magma in forming different types of igneous rock
material
- (what students have to know = various minerals crystallize according
to different temp = Bowen’s Reaction Series
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April 10 notes
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Geology 12
Volcanism and Extrusive Igneous Rocks
Chpt. 4 p.76 – 101
NOTES:
extrusive igneous rock =
- magma
- magma
igneous rock that is a result of volcanic types of activity
surface rock as a result of volcanic activity
basalt (inside the earth)
lava (when magma reaches outside the earth)
- pyroclasts = rock fragments when volcano erupts
- tephra = pyroclastic debris
Volcano distribution:
p. 92 world-wide
p. 81 western North america
Effects on Humans of Volcanic Activity:
e.g. of volcanic activity = growth of Hawaii (plumes, chain of islands, show animation
video)
e.g. of near surface volcanic activity = geothermal heating (e.g. Iceland, New Zealand)
e.g. dust in the air and effect on climate due to eruptions; 1815 Indonesia (Tambora) 40
cubic kms. of material thrown into atmosphere
effected climate all over the world
(tsunami in Indonesia, volcanic activity in Indonesia: WHY?)
Volcanic Catastrophes: (page 79)
Mt. St. Helen’s 1980
Mt. Vesuvius 79 AD
Krakatoa (Indonesian island) 1883 (34, 000 people died)
p. 82 fig 4.6 fatalities due to volcanic eruptions
- question: why are there more fatal eruptions recorded from the 14th to the 20th
centuries
volcanoes can kill by:
- volcanic eruption blast
- poisonous gases
- lava
- pyroclastic gases
- degree of violent eruptions ~ 1) amount of gas in lava 2) viscosity (how thick lava is e.g.
molasses) which determines how easy gas can escape from lava
the more viscous + the more gas  the more severe the eruption
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- what influences viscosity = 1) amount of silica, 2) the temp of the lava, 3) amount of gas
less viscous = flows easier
felsic rocks = rich in silica – more viscous
mafic rocks = less silica – such lavas flow easier
Extrusive Rocks:
- named according to their texture and composition
- generally fine grained: cool and crystallize quickly
Composition
rhyolite = silicate rock, light in color, cream-tan-pink in color
basalt = low amount of SiO2, usually dark grey to black
Textures
texture = size, shape, arrangement of crystals that comprise the rock
- in most cases extrusive rocks are fine grained
- obsidian not comprised of minerals = glass, due to instantaneous cooling
- porphyritic texture = does not have a uniform fine grained texure (in text describe porphyrtic
rocks compared to raison bread) p. 85 fig. 4.9 a - slow cooling first gies crystals a chance to
grow, then quick cooling in an eruption
- trapped gases: in sudden erption, gases escape quickly making eruption very violent (e.g.
bottle of soda shaken, then when top taken off, gases explode out
- vesicles = cavaties in the rock that store the gases (vesicular rok looks like swiss cheese)
- pumice: gases cannot escape, foam type of lava, when solidifies, lots of air bubbles in rock,
rock can float
Volcano terms to know:
- vent = opening through which eruption occurs
- crater = basin depression over a vent at the summit of the volcano
- flank eruption = lave comes out from the side of the volcano
- caldera = bowl like depression at least 1 km in size, created when volcano top blown off
volcanic domes: steep sided done that solidifies over a vent, acts like a plug
Types of Volcanoes:
1) Shield: broad, gently slopping sides, low viscosity lave, does not have major violent
eruptions. e.g. Hawaii volcano types
pahoehoe – ropy, billowy type of surface
aa – jagged, broken up surface
April 10 notes
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2) Cinder Cone: builds up from pyroclastic debris, slopes about 30 degrees, most material
lands near the volcano and this is how the sides build up, life span short, smaller in size
compared to Shield volcanoes
3) Composite Volcano: (p.91 fig 4.21) - intermediate type of slopes, pyroclastic layers build
up volcano, live a long time, build up high, intermittent eruptions over thousands of years, tend
to be aligned with plate boundaries (p. 92 fig 4.22) very devastating eruptions
- Mount Fuji, Mt. St. Helens, Mount Vesuvius, Mt. Etna, Krakatoa
- can erupt for lengthy periods of time
Lava Flows:
- mafic lava: flows like wate, very low in silicate material, does not build domes but spreads
over large areas – produce plateau basalts (fig. 4.27 p. 96) can build up to several thousand
meters thick
- columnar structures (jointing) when rock cools, tension cracks the rock into a hexagonal
shape (p.97 fig 4.28
Submarine eruptions:
- most of earth’s volcanoes are under the ocean, eruptions occur but we are not aware of them
on the surface, sometimes tidal waves form as a result
- pillow basalt: as lava extrudes from surface, lava cools in shapes of pillows
assignments:
1) Define the following:
a) basalt, b) bomb, c) caldera, d) columnar structure, e) crater, f) extrusive rock, g) lava,
h) magma, i) obsidian, j) pillow lava, k) porphyritic rock, l) pyroclastic flow, m) vent, n) viscosity
2) What are the three different types of volcanoes, how do they form, what type of lava does
each exhibit?
3) What role do gases have in the type of lava and eruption with various types of volcanoes?
4) Answer the following questions in your binder. Page 100: answer #1, #6, #7, #9
- multiple choice questions: #12, #13, #14, #19, #21,
- Expanding Your Knowledge: #1, #3, (to be handed in)