Class Notes: Earth Materials cont'd and Volcanoes Flashcards
What 4 things does the study of rocks involve?
- Mineral composition
- Texture
- Age
- Locality
What are the 2 major rock textures?
crystalline and clastic
What texture are most igneous rocks and many metamorphic rocks?
clastic
What is a crystalline texture?
Crustals grew in place
What 2 precipitates are crystalline texture?
chemical and groundwater
What time of texture are sedimentary rocks?
clastic
What texture are some igneous rocks?
clastic (pyroclastic)
Do clastic rocks have open or closed space?
open (or pore) spare
What are the steps in the lithification of clastic rocks?
Sediment, cementation and compaction (lithification)
What is crystallization?
- growth from magma
- (freezing of magma)
What is precipitation
-growth from dissolved solids in a liquid (e.g. water)
What type of texture does both crystallization and precipitation lead to?
crystalline texture
What is metamorphic ‘recrystallization’?
solid-state reorganization of ions
What does metamorphic ‘recrystallization’ lead to?
mineral stability
What does the recrystallization of a protolith (any igneous sedimentary or pre-existing metamorphic rock) lad to?
metamorphic rocks (wide range of metamorphic rock types)
At what temp does a protolith undergo chemical alterations?
300 degrees C - 250 degrees C
What 4 things result from grind water deposits?
- veins, cracks, fracture
- concretions and nodules of ground water
3) ore bodies
4) cave deposition
What are concretions?
Little bodies where cementation has occurred.
- groundwater precipitation
- nodular – many shapes (spherical-irregular)
- many different chemical compositions
What do pores in rocks hold?
- hold water (groundwater for humans, irrigation for crops)
- hold petroleum (oil and gas fields)
- fill (partly) with natural cements
What serves as disposal well for liquid industrial waste?
pores in rocks
What element do pores in rocks sequester?
CO2
How do you determine the volume of a rock?
pores / total rock
What is permeability?
ease of flow
What are 3 things that indicate porosity?
- intergranular
- fracture
- bedding contacts
What type of flow is an aquitard?
retards flow
What type of flow is an aquiclude?
almost no flow
What type of flow is an aquifer?
easy flow
What are the three uplift processes?
1) Orogeny: orogenic uplift
2) Isostasy: isostatic uplift (sinking)
3) Epeirogeny: epeirogenic uplift (sinking)
What are rocks the products of?
nature, time, proceeds and environment
What is the make-up of each rock body controlled by?
The processes which formed the rock and by the environment in which the rock was formed.
What are the two types of igneous rocks?
extrusive and intrusive
What do igneous rocks derive from?
magma
What are the two types of extrusive igneous rocks?
lava and pyroclastic (e.g. volcanic ash)
What does the silica content of igneous rocks vary from?
45-75%
What are the 4 types of igneous rocks?
1) felsic igneous rock
2) intermediate igneous rock
3) magic igneous rock
4) ultramafic igneous rock
What does felsic rock contain?
-contains many light coloured minerals: feldspar (mainly) and quartz with minor other minerals
What are 2 examples of felsic igneous rocks?
rhyolite (volcanic) and granite (intrusive)
What is the silica content of felsic igneous rock?
65-75%
What is the Tmelt of felsic igneous rock?
650-750
What is the silica content of intermediate igneous rock?
52-65%
What is the Tmelt of intermediate igneous rock?
1000-750, 800
What does magic igneous rock contain?
more dark colour minerals
A magic igneous rock may be still mainly___.
feldspar
What is the silica content of magic igneous rock?
48-52%
What are two examples of magic igneous rock?
basalt (volcanic) and gabbros (intrusive)
What is the Tmelt of magic igneous rock?
1000-1200
What is the silica content of ultramafic igneous rocks?
45-48%
What is the Tmelt of ultramafic igneous rocks?
1600
Do ultramafic igneous rocks exist today?
no
When did ultramafic igneous rocks exist?
Archean
What is viscosity?
stiffness of a magma and controls what kind of volcano will form, what type of eruption will occur
What is low viscosity mean?
fluid, flows easily
What is high viscosity?
stiff, does not flow easily
What does viscosity vary with?
silica content and temperature
What type of silica content is rhyolite?
high
what type of silica content is basalt?
low
What does a high silica content equal?
stiff, high viscosity
What does a low silica content equal?
more fluid, low viscosity
What does a high temp equal?
more fluid, lower viscosity
What does a lower temp equal?
stiffer and higher viscosity
When does a given lava flow becomes more viscous?
As it flows away from the vent, cooling as it flow
What does a high viscosity equal with temp and silica?
high silica low temp
What does a low viscosity equal with silica and temp?
low silica high temp
What are the 6 types of volcanoes?
- fissure eruptions
- cones
- composite volcanoes (stratovolcanoes)
- shield volcanoes
- lava domes
- caldera eruptions
What are fissure eruptions (flood or plateau basalt)?
Ex?
- highly fluid basalt
- many successive overlapping flows, 0-100 m thick
- Ex. Iceland
What are cones?
- small volcanoes, any composition though most are basaltic
- may result from single (or a few) eruption(s)
Cones=___to___cones
cinder to ash
cones=___(type of noise)
spatter cones
What are composite cones?
small cones
What are the two types of cones?
lava cone and pyroclastic conde
What is the difference between a lava cone and a pyroclastic cone?
Pyroclastic cone has a wider crater than lava cone which had a small crater. Pyroclastic has wider crater because the explosion
What is the difference between a caldera and a grater?
calder is large and crater is small
What are composite volcanoes (stratovolcanoes) and what are they built of?
- built of the products of many separate eruptions, lava plus pyroclastic
- large conical volcanoes that form on continents and many volcanic islands
- may have flanking cones
- have crater or small caldera
- up to several Km high and 50 km in diameter
What types of lava do composite volcanoes have?
moderately viscous lava
What are some examples of composite volcanoes?
mt. fuji, mt. st. helen
What are shield volcanoes? Where are they only found? Many or few eruptions? Composition of flows?
- large, rounded volcanoes
- many eruptions, almost entirely fairly fluid basalt flows, all on oceanic crust
- small caldera
- up to 10 km high and 100 km in diameter
what are some examples of shield volcanoes?
Hawaii: Kilauea and Mauna Loa (biggest volcano on Earth)
What is the difference between
Shield volcanoes are hotter than composite volcanoes and there isn’t as much material that flows away as with composite volcanoes
What two types of volcanoes may have flanking cones?
composite and shield
What type of volcano may have radical fissures?
shield
What are lava domes?
small features that form in the crater/caldera of shield, composite, or caldera volcanoes
-up to 300 m high and ~1 km width
What is the shape of lava domes?
May be anywhere from spike-shaped to pancake-shaped
What are upwellings of viscous lava (any composition) commonly just after a pyroclastic eruption?
lava dome
What does a lava dome become if it is a blast dome, blast-dome sequence?
volcanic ash
What are craters?
constructional vents, typically less than 1 km across
What are caldera?
destruction, typically greater than 1 km across.
What are pit craters?
Small destructional/collapse vents
What may destruction from a caldera be by?
collapse, explosion, or any combination
What are the two types of destruction by caldera?
- rapid collapse
- explosion blows top off volcano
- could be explosive plus or minus collapse
What are caldera rapid collapse previously?
shield or stratovolcano
What is the width of caldera rapid collapse?
50 km
What does a calder explosion start with?
existing shield or stratovolcano
What happens in a rapid collapse?
Centre of volcano falls. Partly drained magma chamber. Does fall at once…cm by cm
-basalt
What is a Caldera explosion?
Magma chamber degasses violently
-rhyolite
What comes out of a caldera explosion?
pyroclastic debris
What is eruptive violence controlled by?
- gases, explosive production of steam
a) contact with water
b) internal gas content – degassing: the manner of degassing is controlled by the viscosity
What type of magmas retain gas until very high, explosive pressures are reached?
viscous
What type of volcanoes to basalts tend to form?
(hot and fluid) tend to form quiet volcanoes
What type of volcanoes to rhyloties tend to form?
(cooler and more viscous) tend to form violent, pyroclastic volcanoes
Where can pyroclastic flows take place?
on land or under shallow water
What is pyroclastic airfall?
wind blows material around globe
What is Earth’s atmosphere made up of?
N -- 80% O -- 19% H2O -- < 1% CO2 -- .25 % Others < .25%
What What is mainly a recycled meteoric water?
H2)
What do all gases interact with?
the ocean and rocks
O:___fixed in minerals; some to___.
- some
- atmosphere
N: mostly to___, some to___.
- atmosphere
- soil
What was the atmosphere like on early earth? What elements and their percentages?
On early (primitive) earth, the atmosphere more directly reflected volcanic gases then it does today; after interaction with sunlight,w water and packs, it probably contained about: N -- 30% CO2 -- 50% O -- <<1% Others -- > 20%
What was the first plant life on Earth? When?
microbes first, 3.8 Ga, green algae
When did land plants (moss and ferns) appear?
0.5 Ga to present
When did trees, flowers, and grass appear?
66 Ma to present
How do plants affect the composition of the atmosphere?
photosynthesis
What is photosynthesis formula?
CO2 + H2O + sunlight –> Food to O2 (as a waste product)
What is the summary of atmospheric development
- Volcanic Gases (4.5 Ga)
- Primitive Atmosphere (rich in Co2)
- Photosynthesis (3.8 Ga)
- Present Atmosphere (300 Ma)
