geology midterm 1

Question 1

Why study geology?

Answer 1

Geology plays a key role in how we use natural resources, Geologists are involved in extracting fossil fuels, Geologists can also help manage renewable resources that can be replaced or regenerated, Geologists also study natural hazards created by geologic processes, geology is where other scientific disciplines intersect in the concept known as Earth System Science

Question 2

Scientific Method

Answer 2

1. Observation
2. Question
3. Background research
4. Hypothesis
5. Test Hypothesis
6. Results

Question 3

What are the differences between impact craters, calderas and salt domes

Answer 3

-impact craters are formed by meteor impact. Look for area that underwent extreme heat: melted rock, pressurized minerals
-Salt dome - created by rising salt
-Caldera - formed by volcanic eruption. look for igneous rock

Question 4

rheological layers

Answer 4

1) lithosphere: crust and upper mantle. cold, brittle, broken into plates,
2) asthenosphere: closer to core. hotter. ductile. flows but not liquid, still solid rock
3) core

Question 5

compositional layers

Answer 5

-Crust: two compositions. Continental (40 km thick, felsic, 2.7 g/cm density). Oceanic (8km thick, mafic, 3 g/cm density)
-Mantle: ultramafic, 3.3 density
-Core: mostly iron and nickel

Question 6

Convergent boundaries

Answer 6

-Plates are colliding
-Convergent boundaries occur where two plates collide and one plate subducts (slides beneath) the adjacent plate. Typically, the plate that subducts is the more dense plate.

Question 7

what kind of formations occur at each type of convergent boundary?

Answer 7

-oceanic-continental convergence=volcanic arc
-continental-contintal convergence=high mountain ranges
-oceanic-oceanic convergence=island arc

Question 8

Divergent boundaries

Answer 8

-Plates are pulling apart
-most commonly associated with spreading centers in oceanic crust and are associated with MORs.

Question 9

mineral properties

Answer 9

1) luster: metallic or nonmetallic
2) Hardness
3) crystal habit: the way the crystal grows
4) crystal cleavage: how the mineral breaks. number of cleavage planes and orientation of those planes
5) color: mafic and ultramafic=darker
felsic=lighter

Question 10

polymorphs

Answer 10

minerals with identical composition but different crystalline structures

Question 11

composition of different tetrahedral

Answer 11

independent and single chain: ultramafic
single chain and double chain: mafic
framework and sheet: felsic

Question 12

rocks

Answer 12

classified based on texture, composition, and the way they form

Question 13

igneous

Answer 13

Igneous rocks
-Rocks that crystalize from a liquid magma
-Can happen deep inside the earth (below volcanoes) and at the surface of the earth (where volcanoes form)
-Look different depending on where they cool
-Fine-grained if they cool quickly
-Coarse-grained if they cool slowly

Question 14

sedimentary rocks

Answer 14

-Bits and pieces of rocks that get weathered from the mountain, go down a river into a low area and pile up to make new rocks
-Clastic sedimentary rocks
-Chemical sedimentary rock - water carrying rocks has a small percentage of elements (ex: chlorine, sodium) that are dissolved in the water. When the water evaporates it leaves behind minerals like salt. The salt piles up

Question 15

metamorphic rocks

Answer 15

-Rocks are changing due to getting buried or heated up
-Minerals and textures morph due to changing pressures and temperatures

Question 16

thermal melting

Answer 16

increase temperature. most uncommon form. happens during magma assimilation

Question 17

decompression melting

Answer 17

decrease the pressure. happens at MORs and hot spots

Question 18

wet melting

Answer 18

add water to a rock the temperature required to melt a rock decreases. happens at subduction zones.

Question 19

intrusive rock types (coarse grained)

Answer 19

felsic: granite
mafic: gabbro
ultramafic: periodite

Question 20

extrusive rock types (fine grained)

Answer 20

felsic: rhyolite
intermediate: andesite
mafic: basalt

Question 21

relationship between tectonic setting and composition

Answer 21

-oceanic crust (MORs and hot spots) is more mafic
-subduction zones/volcanic arc are more felsic

Question 22

partial melting

Answer 22

-the transformation of some fraction of the mass of solid rock into a liquid as a result of decompression, heat input, or the addition of a flux.
-More felsic minerals melt first - leaving the remaining rock to be more mafic
-In general, a partial melt of an ultramafic rock will form a mafic magma, and a partial melt of a mafic rock will form a felsic magma.

Question 23

Fractional crystallization

Answer 23

-Fractional crystallization occurs when a magma slowly crystallizes during cooling. Because silica-poor minerals have higher crystallization temperatures, they crystallize first as the magma cools. These early formed crystals tend to sink through the magma which becomes increasingly silica rich.
- fractional crystallization causes magmas to become more felsic as they crystallize during slow cooling.
Ultramafic minerals crystalize first - the remaining magma is more felsic than the initial magma (lighter in color)

Question 24

Magma assimilation

Answer 24

-Magma assimilation occurs when rising magma raises the temperature, and triggers thermal melting, of the rock through which it is passing. These thermal melts then mix with the original magma, and this mixing can change the composition of the original magma
-magma assimilation tends to make magmas more felsic because melts of the crust tend to be felsic in composition

Question 25

Igneous texture

Answer 25

1) Coarse-grained
-Can see crystals with the naked eye
-slowly crystallize deep within the Earth and are called ‘intrusive’ or ‘plutonic.’
2) Fine-grained
-Can’t see crystals with the naked eye
-quickly cool at (or near) the surface of the Earth and are called ‘extrusive’ or ‘volcanic.’
3) Porphyritic texture: describes an igneous rock with some coarse crystals and some fine crystals. These rocks form when coarse crystals initially form through slow cooling deep within the crust, but when these early-formed crystals and the remaining magma erupt to the surface in a volcano, the remaining magma crystallizes quickly to form fine-grained crystals. Because these rocks form in volcanoes, porphyritic rocks are considered to be extrusive/volcanic.

Question 26

type of intrusive rock formation: pluton

Answer 26

a crystalized batch of magma

Question 27

type of intrusive rock formation: batholith

Answer 27

a bunch of plutons

Question 28

type of intrusive formation: dike

Answer 28

a fracture that forms usually vertically in the rock, formed by where magma flows, cutting across other layers

Question 29

type of intrusive formation: sill

Answer 29

magma flowing along a fracture in the rock which instead flows parallel to the layers, rather than across

Question 30

type of intrusive formation: chilled margin

Answer 30

Dikes and sills often display ‘chilled margins’ characterized by margins that are finer-grained than the interior of the igneous body. Chilled margins form when the margin of an igneous body cools more quickly than its interior because the margins are in direct contact with the (cold) country rock.

Question 31

type of intrusive formation: vein

Answer 31

Veins form through precipitation of minerals from a hydrothermal fluid (hot water with minerals dissolved in it) rather than crystallization of minerals from a magma. Veins can be differentiated from dikes and sills because veins typically only include one mineral.

Question 32

extrusive textures

Answer 32

-Porphyritic texture: describes both coarse and fine grained rocks
-Aphanitic texture: whole rock cooled quickly
-vitric/glassy texture: magma erupted to surface, cooled so quickly not even microcrystals could form. Looks like glass. No crystalline structure or minerals.
-Vesicles: gas bubbles in liquid lava. When magma rises to the surface, the bubbles release. Little holes left in the rock where the bubbles were.
-pahoehoe: higher viscosity. Erupted at lower temp.
-Aa: lower viscosity. Erupted at higher temp

Question 33

pyroclastic eruptions:

Answer 33

violent eruptions, causing pyroclastic flow

Question 34

-pyroclastic flow:

Answer 34

mixtures of hot ash, rock, and gas rush down the slopes of a volcano.

Question 35

-ignimbrite:

Answer 35

deposits left by pyroclastic flows. Layer from eruption event, rock and ash left behind. Makes a rock called Tuff, consisting of mostly ashfall. Tuff is in the ignimbrite

Question 36

volcanic eruption consequence: lahar

Answer 36

giant mudflows, creating a rock, which is also called lahar

Question 37

volcanic eruption consequence: bombs

Answer 37

lava splats, forming a round, solid shape

Question 38

controlling factors of volcanic eruptions

Answer 38

1) viscosity
2) gas content

Question 39

viscosity

Answer 39

-in part controlled by temperature, bigger factor is composition (mafic or felsic)
-Resistance to flow
-High viscosity flows very slowly - lower temperature
-Higher viscosity = stronger eruptions
-Low viscosity flows quickly - higher temperature
low viscosity=Weaker eruptions
-In part, viscosity is dependent on temperature.
-Viscosity is also partly dependent on the composition of the lava. In general, more mafic magmas are lower viscosity.

Question 40

gas content

Answer 40

-Higher gas = stronger eruption
-Ash - is basically micro-pumice. It forms when lavas with high gas contents move toward the surface of the Earth. As the lava moves up, the pressure on it is reduced, and the gas bubbles expand forming a violent explosion. The lava explodes outward forming droplets of lava that crystallize as glassy bits of vesicular ash.
The concentration of gas in magma/lava is controlled by:
1) tectonic environments associated with wet melting, which increases the gas content of the lava
2) by tectonic environments with viscous magma which tends to retain gas longer than low-viscosity magma.

Question 41

eruptive landform: shield volcano

Answer 41

• Shield volcanoes (feeble) - Low-viscosity lava flows tend to form shield volcanoes with low slopes, Tend to form at MORs and hot spots

Question 42

eruptive landform: stratovolcano

Answer 42

Large, steep-sloped volcanoes that form through multiple eruptions (feeble) - tend to form at volcanic arcs (due to wet melting and higher gas contents, higher velocity)

Question 43

eruptive landform: caldera

Answer 43

a crater at the top the volcano that forms after the eruption

Question 44

eruptive landform: stock

Answer 44

(distreme): eroded remnant of a volcano

Question 45

fissure eruption

Answer 45

magma gets to the surface along a fracture in the earth