Midterm Flashcards
(150 cards)
1
Q
What does the world geology mean? Why is it important?
A
Geo = earth
Ology = the study of
Therefore geology is the study of the earth.
It is important for energy and natural resources, solving environmental problems, building cities and highways, and predicting and preventing natural disasters.
2
Q
What is the fundamental principle of the concept of uniformitarianism, and what does it mean? What is the timescale of the earth measured in?
A
The present is the key to the past. This means that the processes that we see shaping th earth today are the same as the processes that shaped the earth millions of years ago. Geological time is meausred in billions of years.
3
Q
When when did the Big Bang occur?
A
~14 billion years ago
4
Q
What theory is generally excepted as correctly explaining the formation of the solar system? Describe it.
A
The Nebular theory - 5 billion years ago. A nebular made up of hot gasses - mainly hydrogen and helium. The nebular cloud contracted under gravity and began rotating. The rotating instigating central pedal force, which caused elements to concentrate in the centre. Gravitational energy converted to thermal energy. This became the sun. The other, heavier elements began to fuse together into planets and moons, which continued to rotate around the sun.
5
Q
Explain how the earth was formed, and what layers formed.
A
Formed by rock collisions. The heavier elements (Fe, Mg) migrated inwards and became the core. The lighter elements (oxygen rich elements) migrated outwards and formed a very thin crust. The middle area between the crust and the core is called the mantle. In the process, gasses escaped and formed the atmosphere.
6
Q
Describe the names and the layers of the world.
A
- Lithosphere (“sphere of rock”)
- the crust AND the upper most mantle - split into plates that move over top of the asthenosphere - Asthenosphere (“weak sphere”)
- liquid - due to unequal heat distribution in the earth convection currents occur here, the lithosphere rides on top of them, in CONTINENTAL DRIFT - Core
- very dense and under extreme heat, intense pressure keeps the core a solid - Ni, Fe
7
Q
What causes more geological activity, convergent or divergent boundaries?
A
Convergent boundaries
8
Q
What is a divergent boundary?
A
Occurs when plates move apart due to tensional stress. This allows for upwellling of material in the mantle, forming ridges and rifts. It is the cause of SEA-FLOOR SPREADING.
9
Q
What is a convergent boundary?
A
The primary cause of geological activity. Occurs when denser, oceanic plate descends below lighter, continental plate. This is known as SUBDUCTION, and it forms a trench. The denser, oceanic plate reaches far enough into the asthenosphere that it begins to melt. Sometimes, this allows for melted magma to protrude and form a volcano, which eventually erodes into sediment. It is at convergent boundaries that earthquakes and volcanoes often form.
10
Q
What is subduction?
A
The descent of the denser oceanic lithosphere beneath the lighter, continental lithosphere.
11
Q
What does Pangaea mean? What evidence is there to support it?
A
Pan = all, Gaea = earth
- Fit of the continents
- South America and Africa fit together at a depth of 900 meters (at the continental shelf) - Fossil evidence
- Fossils match across continents (ex. Mesosaurus fossils found in East S.A. and South Africa) - Rocks and Structures
- ex. Appalachian mountains and Scandinavian mountains form a continuous chain - Paleoclimatic Similarities
- ex. finding coal in ancient tropical swamps in places that are now glaciated; finding striations from glaciers in tropical areas today
12
Q
What are the 4 spheres of the earth? How do they interact?
A
Earth is a dynamic system of interacting spheres.
- Geosphere - the earth and rock sphere
- Hydrosphere - the sphere of water
- Biosphere - the sphere of life, ranging from the hydrosphere, slightly into the atmosphere
4, Atomsphere - thin and tenuous sphere of gases, producing weather and climate
13
Q
Where are new rock types mainly produced at?
A
Converging boundaries
14
Q
Explain the rock cycle, beginning at magma.
A
Magma crystallizes to form igneous rock, igneous rock is weathered, transported, and deposited to form sediment, which is cemented to form sedimentary rock, sedimentary rock undergoes metamorphisis to form metamorphic rock. Metamorphic rock melts to form magma. Metamorphic rock can become sediment by weathering, as can sedimentary rock. Igneous rock can also undergo metamorphisis under heat and pressure to form metamorphic rock.
15
Q
What are minerals? How many are there? How many are common in the earth’s crust? How are they produced?
A
Minerals are inorganic substances formed by nature that combine together to form rocks. Their elemental composition, chemical structure, and bonding determine the properties that the mineral will have. There are 4700 known minerals, but only about 20 are predominant in the earth’s crust.
16
Q
What type of mineral is the most abundant?
A
Silicates
17
Q
What are silicates? What is their structure, and elemental composition?
A
Silicates are composed of Silicon and Oxygen, covalently bonded to each other to form tetrahedrons (SiO4)4-. Because oxygen is an anion, and therefore negatively charged, metal cations such as Fe2+ and Mg2+ can ionically bond. This ionic bonding is weaker than the overall covalent bonding, which usually results in a spot of weakness along the mineral, which becomes the cleavage point.
18
Q
What is the composition of a dark silicate?
A
Ferromagnesian - therefore with Fe and Mg within the silicate tetrahedra.
19
Q
What are the four ferromagnesian silicates? Describe their bonding, and cleavage?
A
- Olivine
- single tetrahedra, covalently bonded, with Fe2+ and Mg2+, no cleavage - Pyroxene
- single chains of tetrahedra, with metals between them, cleavage is 2 at 90 degrees - Amphibole
- double chains of tetrahedra, with metals between them, cleavage is 2 not at 90 degrees (60 and 120) - Biotite (black mica)
- sheets of tetrahedra with metals between them, cleavage is basal/platy
20
Q
What are the four non-magnesian silicates? Describe them.
A
- Muscovite (white mica)
- perfect basal cleavage, often used for muscovy window glass - Feldspar
- strongly bonded 3D network of silica tetrahedra
a. Orthoclase (K feldspar) with potassium, cleavage is 2 at 90 degrees.
b. Plagioclase (Ca/Na feldspar) with calcium in mafic rocks and sodium in felsic rocks, cleavage is 2 at 90 degrees. - Quartz
- very strong, purely covalent silica tetrahedra, has a hardness of 7, can form crystals with sufficient space in nature. (SiO2)
21
Q
Name the two types of non-silicate minerals, and describe them.
A
- Carbonates (CO3)2-
a. Calcite (CaCO3) - used in cement and limestone
b. Dolomite (MgCaCO3) - Evaporites
a. Halite (NaCl) - table salt
b. Gypsum - plaster and drywall
22
Q
Name the metallic, non-silicate type of mineral.
A
Ores of metals
- Hematite/Magnetite (Fe)
- Sphalerite (Zn)
- Pyrite/Chalcopyrite (Cu)
- Galena (Pb)
23
Q
Where are igneous rocks? Where does the name come from? Which types of minerals are in igneous rocks?
A
Igneous = fire
Igneous rock crystallizes from molten SILICATE magma, which is formed deep in the earth under high temperatures and pressures.
24
Q
What are the two options for magma at the site of a volcano? What type of rock does each location of formation form? Typically what are the textures of this rock?
A
- Intrusive - forms plutonic rock - texture tends to be PHANERITIC
- Extrusive - forms volcanic rock - texture tends to be either PYROCLASTIC, APHANITIC, OR GLASSY, due to quick cooling, or quenching by air or water.
25
Does flowing lava tend to be mafic or felsic? How about lava that violently erupts to form glassy textures or pyroclastic material?
Mafic = flowing, hot, runny
Felsic = more viscous, violently erupts
Viscosity is directly dependent on the silica content of the parent magma
26
What types of rocks are formed by felsic magma? How much silica does it contain, and what minerals form the rocks?
1. Granitic rock - phaneritic texture
2. Rhyolite - aphanitic texture
Minerals - quartz, biotite, orthoclase, Na-rich plagioclase
70% silica content, therefore very viscous
27
What type of rock does intermediate magma tend to produce? What percent of it is silica?
1. Diorite - phaneritic
2. Andesite - aphanitic
Minerals - amphibole, plagioclase
60% silica
28
What type of rock does mafic magma produce? What minerals are in the rock? What is it's silica content?
1. Gabbro - phaneritic
2. Basalt - aphanitic
Minerals - Ca-rich plagioclase, pyroxene
50% silica
29
What type of rock does ultramafic magma produce? What are the minerals in it? What percent of silica is it?
1. Peridotite
Minerals - pyroxene
40% silica content
30
Where is basalt found?
In the upper oceanic crust and on volcanic islands - the most abundant rock in the crust
31
Where is gabbro found?
In the lower oceanic crust
32
Where is peridotite found?
The main rock of the upper mantle
33
Name the four types of intrusive bodies, and their characteristics.
1. Dyke - discordant, tabular
2. Sill - concordant, tabulat
3. Laccolith - concordant, bulge
4. Batholith - discordant, bulge
34
What about Bowen's reaction series is continuous? What is discontinuous? How does it work?
Ferromagnesian silicates are discontinuous, non-ferromagnesian silicates are continues.
Bowen's reaction series states that heavier minerals have a higher melting point, and precipitate from the melt first. Lighter minerals precipitate from the melt last. This is how lighter rocks can be produced from mafic magma, as the mafic magma becomes felsic.
35
Out of olivine and pyroxene, which precipitates first?
Olivine, then pyroxene
36
Which mineral is left over after most of the magma melt has precipitated out?
Quartz - this is how granite can be formed from ORIGINALLY BASALTIC MAGMA
37
Why do volcanoes occur? What two things can lava do upon extrusion?
Gas builds up in the magma chamber, causing pressure that needs to be released. Lava can either flow down the side, or blow through the top.
38
What is extrusive, mafic magma also known as? What are its physical characteristics like?
Basaltic magma - it is hot and runny, and runs quietly downthe volcano before hardening
39
What is extrusive, felsic magma also known as? What are its physical characteristics?
Rhyolitic magma - it tends to be cooler and more viscous, tends to erupt violently and form pyroclastic material such as tuff and breccia
40
What are the two types of magma?
1. Pahoehoe - made of hotter, runnier, mafic magma which hardens to form a coiled, "ropy" texture
2. Aa - made of cooler, slower, felsic magma - tends to be "blocky" in texture
41
What are pillow lavas?
Pillow lavas resemble pillows and are formed underwater when magma either flows into the water, or exits through tube ends. The texture is typically GLASSY, from quenching or quick cooling by the water.
42
What is a Nuee Ardente? Where does the name comes from, and what is it also known as?
Nuee Ardente = glowing cloud - also known as a PYROCLASTIC FLOW
These are extremely destructive, and occur when a cloud of gas, hot ash, and magma races down a volcano - they can wipe out a whole city at once.
43
What is pyroclastic material, and what are some examples?
Pyroclastic material = fire fragments
Formed by magma ejected into the air. Can range from fine ash, to streamlined bombs, to large blocks.
44
What is a lahar?
A lahar is pyroclastic material, mixed with snow, mud, rain, and ice.
45
What is the most common type of volcano? What is it made up of?
A composite cone - made up of pyroclastic material as well as lava flows - medium in size with a crater
46
Describe the three types of volcanoes, and their compositions.
1. Shield volcano - very large, ranging in hundreds of km, has a caldera at the top, much wider than it is tall - and made up of successive lava flows
2. Cinder cone - very small, with a crater, made mainly of pyroclastic material
3. Composite cone - medium sized, made of pyroclastic material and lava flows
47
What is the difference between a crater and a caldera? How is a caldera formed?
Crater \< 1 km
Caldera \> 1 km
Calderas are formed by the collapse of the underlying magma chamber as it empties
48
What leads the magma to the caldera or the crater?
A conduit or pipe
49
What are fissure eruptions? What do they form?
Fissure eruptions occur when magma flows out of fissures in the crust, plateaus are formed by the magma that flows from the fissure
50
Where do volcanoes tend to occur?
They tend to occur at convergent boundaries at subduction zones, where denser, oceanic lithosphere melts to form basaltic/gabbro rich mafic magma
51
What type of magma does melted oceanic lithosphere generate?
Basaltic magma
52
Around what geological structure do subduction zones and volcanoes tend to occur?
Around the Pacific Ring of Fire
53
What is a seamount?
A location in which and underwater volcano produces basaltic magma which flows out onto the sea floor
54
What is an intraplate volcano and what causes it?
An intraplate volcano occurs in the middle of a continent/lithospheric plate - it is caused by deep mantle plumes which protrude
55
What are the two types of weathering that forms sedimentary rock?
1. Mechanical
- frost wedging, sheeting, biological
2. Chemical
- hydrolysis, dissolution, oxidation
56
What is mechanical weathering also known as?
Disintegration
57
What is chemical weathering also known as?
Decomposition
58
What is the relationship between mechanical and chemical weathering?
They work together to enhance erosion - mechanical weathering increases surface area for chemical weathering to work on
59
Describe the types of mechanical weathering.
1. Frost wedging - water enters rock fractures as a liquid, it expands 9% as it freezes splitting the rock apart
2. Sheeting - occurs when material is unloaded from a batholith, allowing for rock expansion, as the rock expands slabs break off
3. Biological activity - vegetation grows roots in rock fractures - the roots grow and expand, splitting rock apart
60
Describe the three types of chemical weathering, and their effects on the rock.
1. Dissolution - CO2 + H2O ---\> H2CO3
- this carbonic acid dissolves some rocks, making them stable at surface conditions
2. Oxidation - ferromagnesian rocks have metals which react with oxygen in the atmosphere forming metal oxides, rust, and CLAY MATERIALS
3. Hydrolysis - occurs when K+ in orthoclase is replaced by hydrogen, because hydrogen is much smaller, it causes collapse of the mineral, forming clay
61
What type of rock does hydrolysis occur in?
Granitic rock, rich in orthoclase and potassium
62
What are the rates of weathering like for different rocks?
Rocks that form at low T/P are more stable at the surface - ex. quartz, biotite, etc. Rocks that form at high T/P are less stable at the surface - ex. olivine and pyroxene
63
In general, are light or dark silicates more stable at the surface?
Light, as they are formed nearest to surface conditions
64
What is the most weathering-resistant type of rock? Why?
Quartz, because it is the last mineral remaining in the magma melt, closest to surface temperature and pressure with strong, covalent bonds of silicate tetrahedra
65
Between marble and granite, which is more stable? Why? What is their common use?
Granite is more stable, predominantly formed of quartz, marble is soluble in carbonic acid and very susceptible to hydrolysis.
They are commonly used for headstones, however granite is the better choice.
66
How does climate effect the rate of rock weathering?
Tropical climates that are warm and wet tend to cause an increase in weathering rate, while polar climates tend to decrease the rate.
67
What is soil? What are the two main components of it?
Soil is the result of rock weathering (inorganic) with organic components.
Inorganic component = regolith
Organic component = humus
68
What are the five factors in soil formation?
1. Parent soil - the type of bedrock and sediment determines the rate of soil formation and its fertility - parent rock maintains many of the mineral properties
2. Time - the more time that passes, typically the more soil that is produced
3. Climate - soil forms fast in greater amounts in the tropics, and slower and in lesser quantities in polar regions
4. Plants and animals - both plants and animals decompose to humus, releasing nutrients into the soil, and increasing the soil's water retention
5. Topography - sleep slopes erode easily and do not hold moisture or vegetation
69
What are the letters that represent a soil profile? What is each layer comprised of?
O = the organic layer, with lots of humus
A = a mix of organic matter and minerals
E = eluviation layer - transportation from upper layers to lower layers, leaching of ions in solution
B = accumulation of oxides and clays (in wet climates)
C = regolith and parent material
70
How does rain cause soil erosion?
Causes soil to be eroded into rills, then gullies, and then streams
71
What are some ways that soil is eroded? What are the consequences of soil erosion?
Rain, deforestation, farming, wind, etc.
Consequences = decreased lake holding capacity causing flooding, lack of fertile soil for food production, vegetation reduction
72
What does the word sedimentary mean? What percentage of the rock on earth is sedimentary?
Sedimentary = to settle - contains high levels of quartz and clay minerals
75%
73
What is the formation of sedimentary rock from sediment known as?
Diagenesis and lithification
74
Describe the two types of diagenesis and lithification in the formation of sedimentary rocks?
1. Compaction - pressure on sediment forces grains close together, expelling water whcih binds the grains together
2. Cementation - fluid with ions (the cement) coats the sediment grains, causing them to stick together
75
What is clastic sedimentary rock also known as? Describe the types and where they're formed.
Detrital rock
1. Conglomerate - solidified gravel formed in flowing rivers, landslides or in wave actions with rounded rocks (breccia if angular), close to the source.
2. Sandstone - made up of sand grains and quartz, if it is well-sorted the grains are of the same size, if not = poorly sorted
3. Arkose - sandstone with a large amount of feldspar
4. Shale - made up mostly of silt and clay, deposited in quiet waters, and floodplanes
76
Describe shale.
Shale is made up of silt and clay grains that are packed very closely together, formed in quiet waters. It is impermeable to water, and makes GOOD CAP ROCK for oil and gas. Also used for pottery, tiles, etc.
77
Describe the different types of limestone.
Limestone is formed with CALCITE
1. Micrite - formed in sea water
2. Fossiliferous limestone - formed in coral reefs
3. Chalk - formed by dead plankton on deep sea floors
4. Coquina - formed in shallow waters and at beachy shorelines of shells and fossils, loosely cemented together
5. Travertine - formed in karst and cave environments
78
What are the other types of chemical sedimentary rocks? (Non-limestone, mostly inorganic)
1. Dolostone (replaces Ca with Mg in limestone)
2. Chert - formed from microorganisms that use silica
3. Coal (ORGANIC) - formed in ancient swamps from the remains of animals and vegetation
4. Evaporites - formed in ancient sea basins - ex. Halite and Gypsum
79
Describe the four types of sedimentary structures.
1. Strata - strata is layered by different deposition events
(ex. CROSS-BEDDING, GRADED BEDDING)
2. Mudcracks - cracks in the mud formed by evaporation
3. Ripple marks - reveal the location of ancient seas and wind over loose sediment
4. Fossils - mainly found in sedimentary rock
80
What is graded bedding?
Graded bedding is the settling of particles with the coarser, larger ones on the bottom and smaller, finer pieces on the top. Occurs in TURBIDITIES after deposition by turbidity currents.
81
What are the four controlling factors that produce metamorphic rock?
1. Parent rock - the metamorphic rock maintains the majority of the composition of the parent rock
2. Heat - heat drives chemical reactions
- produced from PLUTONIC INTRUSIONS, as well as by the geothermal gradient
3. Pressure - two types, confining and directed
4. Chemically acitve fluids - water can be important as it often has a high concentration of ions - also, water is released upon heating through evaporation whivh causes rock dehydration
82
What are the two types of pressure involved in the formation of metamorphic rock? How do they work, and what rock texture does it cause?
1. Confining pressure - occurs in all directions and increases with depth (ex. swimming pool water pressure)
2. Directed pressure - occurs at convergent boundaries of colliding lithospheric plates
Causes a foliated rock texture
83
What is metamorphic grade, and what causes it mainly? Name the rocks from low to high grade.
Metamorphic grade is the intensity of metamorphism - increases with TEMPERATURE
Low grade - chlorite, muscovite, biotite, garnet, staurolite, sillimanite - High grade
84
What is contact metamorphism also known as? What kind of pressure occurs? What kind of heat change occurs? Give an exampe of a type of rock it produces.
Thermal metamorphism, occurs above intrusions into cooler parent rock - causes recrystallization, but NOT reorientation of crystals (ex. no foliation). Only pressure that occurs is confining pressure.
ex. Sandstone is baked into granite
ex. Limestone is baked into marble
85
What is the effect of contact metamorphism surrounding the intrusion?
An aureole = a golden halo
Decreases with distance (temperature) away from the intrusion
86
What is regional metamorphism? Where does it occur? What kind of heat/pressure is present? Give an example of a rock it produces.
Regional metamorphism occurs at convergent plate boundaries in the CORES OF MOUNTAIN BELTS where directed pressure is most intense, near subduction zones. It involves directed pressure, and the only heat present is due to the geothermal gradient. It casues both recrystallization and reorientation of crystals into a foliated rock.
Ex. shale
87
What are the grades of shale metamorphism, and where do they occur?
1. Slate (lowest grade, farthest from the core)
- slaty cleavage, very fine partings
2. Phyllite
- wavy partings
3. Schist
- mica and chlorite schist with schistose texture (ex. mica on the outside, amphibole in the centre)
4. Gneiss
- highest level of foliation found in mountain roots
- light and dark mineral segregation
88
What are the four ways in which geological time is deciphered?
1. Superposition
2. Original horizontality
3. Cross-cutting relations
4. Inclusions
89
What is the principle of superposition?
States that every rock is older than the rock above it and newer than the rock below it.
90
What is the Original horizontality theory?
States that sediment is deposited horizontally, therefore any rock that has sediment that is not completely horizontal has undergone some sort of change
91
What does the Cross-cutting relations theory state?
That a **fault** is newer than the rock it cuts, and a **rock** must be younger than the rock it cuts
92
What do inclusions tell us about the age of a rock?
The intrusive rock must be older than the rock it intrudes
93
What is an unconformity? What are the two causes of unconformities.
An unconformity is a gap in a rock's geological time - missing rocks are typically due to NONDEPOSITION or EROSION within rock sequences.
94
What are the three types of unconformities? Describe them.
1. Angular Unconformity - flat strata, resting on tilted strata
2. Nonconformity - occurs when sediment is deposited onto igneous rock or metamorphic rock
3. Disconformity - layers of horizontal, parallel strata, with a change in sediment that is often difficult to recognize
95
What is used to determine correlation between rocks in different outcrops?
Fossil succesion, using a fossil index.
Fossil succession - animals evolved at different times in earth's history
Fossil index - some fossilized organisms are widespread around the world and are known to have existed at a certain time
96
How is radioactive dating used? What is the definition of a half-life?
With radiometric methods - parent, radioactive isotopes decay to daughter atoms.
Half-life = the amount of time it takes for an original sample to decay to half of its amount
Comparing the amount left to the half-life allows for the amount of time since formation to be deduced
97
How was the age of the earth determined?
Using radiometric measures
98
What is carbon dating, and how does it work?
Works only on matter that was once living (carbon-based). Living organisms take in both C12 and C14 while living from the environment. C12 is consistently present in living things. C14 is constantly decaying to N14, and is taken in from the environment only when the organism is alive. Therefore, when alive an organism has a ratio of C14/C12 that is constant. When the organism dies, C14 decays to N14, and the ratio of C14/C12 decreases.
C14 has a half-life of 5730 years. Therefore, using this half-life and the ratio of C14/C12, the time since the organism has died can be deduced.
99
How far back can carbon dating be used to detect the amount of time since an organism has died?
~50,000 years
100
What is crustal deformation? What materials may be yielded from crustal deformation?
Rocks can become deformed to produce strctures that can
a) PRODUCE ENERGY
b) OIL RESERVES
101
What three types of stress cause rock deformation?
1. Compressional stress - shortens rock, squeezes rock together
2. Tensional stress - pulling rock apart, lengthens it
3. Shear stress - causes sideways slip of the crust
102
What is strain?
The result of stress
ex. stress = force, strain = result
103
What is elastic deformation?
Occurs before elastic limit is reached - no permanent rock damage is done
104
What two types of deformation are the result of the elastic limit being reached?
1. Brittle deformation (strong rock) - occurs to crustal rock near the surface, fracturing
2. Ductile deformation (weak rock) - flowing which occurs higher temperatures and pressures, ex. rock sagging
If given enough time, all rocks will undergo ductile deformation due to gravity - all rock will flow eventually!
105
What are the two components used to uniquely define a rock in geological space?
1. Dip: AZIMUTH of a horizontal line on the surface of a plane - the angle the rock forms with the horizontal
2. Strike: perpendicular to the dip, horizontal
106
What type of pressure/stress causes folds in a rock? What is the anatomy of a fold?
Caused by compressional stress
- fold has two limbs on either side, as well as a fold axis, and an axial plane
- Anticline - the arch of a fold
- Syncline - the trough of a fold
107
Describe the different types of folds.
1. Overturned = the anticline is overturned in a fold
2. Plunging = when the fold axis is facing downwards in comparison to the horizontal
3. Symmetrical - limbs are mirror images
4. Asymmetrical - limbs are NOT mirror images
108
What is a monocline?
A gentle "step" inthe crust, often caused by and underlying fault
109
What is a dome rock deformation? What is a basin?
Dome = oldest strata on the inside, newest on the outside
Basin = oldest strata on the outside, newest on the inside
110
What is a joint rock deformation?
A fracture in which no displacement occurs - it is a parallel pattern of fractures, caused by the cooling of igneous rock
111
What type of stress causes joints? What material is often found between joints?
- tensional stress causes joints
- ores deposits are often found during joint fractures
112
What is a fault? What does the friction cause?
A type of rock deformation in which fracture and displacemet both occur. Friction causes the formation of a slickenslide.
113
What are the two types of dip-slip faults? What type of stress causes them?
Slippage along the dip of the fault plane
1. Normal = hanging wall moves down, due to tensional stress
2. Reverse = hanging wall moves up in comparison to the footwall, due to compressional stress
114
What are the types of strike-slip faults?
A strike-slip fault is slippage along the strike of a fault
1. Left-lateral - left side of the fault moves down
2. Right-lateral - right side of the fault moves down
3. Transform faults - occurs at oceanic lithospheric paltes, breaking up oceanic ridges, allowing for them to spread through divergent boundaries, ddue to tensional stress
115
What type of fault occurs along the Californian San Andreas Fault?
Strike slip transform faults
116
What causes an earthquake?
Elastic rebound of the crust as stress builds up, causing slippage or crustal deformation
-DIP-SLIP OR STRIKE-SLIP crustal deformations both cause earthquakes
117
What is the hypocentre of the earthquake? What is the epicentre? Where do seissmic waves propogate from?
Hypocentre = the location of the slippage, seissmic waves propogate from here
Epicentre = the spot on the surface of the crust, directly above the hypocentre
118
Where do earthquakes typically occur?
At plate boundaries, often convergent
119
How does a seissmograph work?
It has a weight with a pen on the end, and a paper scroll beneath it. At the time of an earthquake, the shaking causes the weight to move, "drawing" on the paper creating a seissmograph.
120
What are the three different types of waves formed by an earthquake, and how fast do they each travel?
1. SURFACE WAVES - l waves, slowest, largest amplitude on a seissmograph
2. BODY WAVES
a) P waves - primary waves, the fastest, arriving first, undergoing push-pull wave actions (like a slinky!)
b) S waves - slower than P waves, they are shear, and travel perpendicular to the direction of oritentation
121
How is the epicentre of an earthquake located?
Each wave (p, s, and l) travel at different speeds; their unqie velocities can be intersected to find the distance to the epicentre from one seissmograph. The distance forms the radius of a circle. The distance from the epicentre fromthree different seissmographs are used, and circles are formed using the distance as the radius. The location of the intersection is the epicentre of the earthquake.
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What is the primary focus of the Richter scale? How does it work? Is there a maximum?
Richter scale mainly measures the energy released by the earthquake.
It is exponential and limitless. Each sequential number is 10x the ampitude of the previous and releases 32x the energy. Therefore, two away, the amplitude of the wave is nearly 100x larger, and the energy is nearly 1000x larger.
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What was the highest recorded rating of an earthquake on the Richter scale to date?
8.9
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What is moment magnitude? What does it take into consideration, and which kind of earthquakes is it best for?
Moment magnitude is best for larger earthquakes. It takes rock strength, the size of the fault, and the displacement all into consideration.
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What was the highest rating on the Moment magnitude scale? How about the Tsunami on boxing day?
9.6 was the highest, 9.5 on boxing day
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What are the five ways by which earthquakes cause destruction?
1. Ground vibrations
- buildings have trouble withstanding horizontally propogating waves - sediment does not withstand it well, hard bedrock is better at withstanding it
2. Liquifaction
- normally soft sediment becomes unstable and turns to MUD, buildings sink, submerged rock emerges, etc.
3. Tsunamis
A seissmic sea wave may be caused following the rupture of the sea floor. Wave grows as it reaches towards the shoreline and the ocean floor becomes shallower
4. Landslides/Ground subsidence
- ground lowers, and landslides may occur if there are sedimentary hilly areas around
5. Fire
- often caused by rupture of electrical lines and broken gas lines, worsened by broken water lines
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How are earthquakes predicted in the short-term? How about in the long-term?
Short-term - not yet technology to predict them
Long-term - seissmic gaps = earthquake is overdue due to a lack of seissmic activity/buildup of strain
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How do seissmic waves propgate through the earth's interior?
Crust-mantle (Liquid) - p and s waves both accelerate
Mantle - core (Liquid) - p waves slow down, s waves disappear
Inner core (solid) - p waves accelerate once again
NOTE: all waves propogate from the epicentre
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How is the ocean floor mapped?
Through the use of multibeam sonar, and satellite imaging.
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What is the passive continental margin, and what three components is it made up of?
Passive continental margin = not associated with boundaries, volcanoes, or earthquakes
1. Continental shelf - approximately **130 m deep**, average of **80 km** wide a gentle slope, valuable for OIL and GAS, FISHING, and SAND/GRAVEL DEPOSITS.
2. Continental slope - approximately **20 km** wide, with a steeper slope than the continenta shelf. IT IS THE BOUNDARY BETWEEN OCEANIC AND CONTINENTAL LITHOSPHERE.
3. Continental rise - formed due to deposits of sediment, in GRADED BEDDING. Caused by turbidities from turbidity currents and deep sea fans.
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What is a submarine canyon and how is it caused? What does it do and where is it found?
Occurs at the continental slope. Submarine canyons are caused by ancient glaciation, when rivers flowed through the slope. Turbidity currents of sediment are caused by the canyons which form turbidity deposits. Turbidites currents form the continental rise.
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What is an active continental margin?
Active subduction zones, with an accretionary wedge formed of deformed sediment and fragments of oceanic plates.
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What is a deep ocean basin, and what percentage of the earth's surface does it make up? What three components make up a deep ocean basin?
Deep ocean basin makes up ~30% of the earth's surface
1. Deep ocean trenches - formed at subduction zones, most occur around the Pacific margin
2. Abyssal plains - some of the flattest areas of earth, hide rugged terrain with deposits of graded bedding strata from turbidity deposits
3. Seamounts - underwater volcanoes, common near OCEANIC RIDGES, form pillow lavas, cause sea floor spreading
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What is a coral reef? What is an atoll?
Coral reef - the skeletalremaisn of ancient corals, cemented by ALGAE SECRETIONS over thousands of years, up to **45 meters deep**, require warm water as well as sunlight
Atoll - formed around the remains of a seamount that becomes inactive - seamount sinks into the sea floor, and coral grows upwards to remain in the sun
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What is the longest topographic feature on earth?
The Mid-Ocean Ridge
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What is an oceanic ridge and what two components make it?
1. Rift valleys - rise **2-3 km** above the ocean floor
2. Transform faults - cut through the rift valleys
Magma protrudes through the fault, causing sea floor spreading
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Within what time period was paleomagnetism discovered?
During WWII
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What type of rock displays paleomagnetism?
Basaltic rock
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What is paleomagnetism?
Magnetic minerals in basalt point to the existing magnetic poles at the time of ROCK CRYSTALLIZATION
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What is polar wandering?
Over the past 500 million years the magnetic poles of the earth have been reversed - shows diverging paths, poles have only migrated a little bit, therefore it can be used as a reference to deduce how much the continents have shifted
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What is sea floor spreading? How quickly does it occur?
Sea floor spreading occurs at sea floor ridges, in which material in the mantle is upwelled, causing se floor to MOVE TOWARDS THE TRENCHES, which CONSUME sea floor. Typically occurs approximately 5 cm/year, although faster in some places than others
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What are geomagnetic reversals?
Due to frequent reversal of the earth's poles, the ocean floor has regions of basalt with different polarities. APPEARS LIKE A STRIPED MIRROR IMAGE, COMING OUT FROM THE OCEANIC RIDGE. Stripes get older further away from the ridge
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Which Canadian discovered the striped-mirror image of geomagnetic reversal?
Lawrence E. Morely
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Who came up with the theory that the earth's continents are cut up into 7 different tectonic plates?
J.T. Wilson
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How many lithospheric, tectonic plates are there?
7
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What are the three types of plate boundaries?
1. Divergent - cause sea floor spreading by the formation of ridges, which are formed by magma upwelling
2. Convergent - occurs at subduction zones, oceanic lithosphere is consumed
3. Transform faults - faults that cut across oceanic lithosphere, where plates slide past each other - cuts ridges, perpendicular to their direction
BETWEEN TWO CUTS OF A TRANSFORM FAULT = ACTIVE
BEYOND RIDGE SEGMENTS = INACTIVE
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Where does the epicentre of a deep earthquake tend to be? Where does the epicenter of a shallower one tend to be?
Deep = near subduction zones
Shallow = near trenches and oceanic ridges
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What evidence exists for J.T. Wilson's tectonic plate model of the lithosphere?
1. Earthquakes - tend to occur at plate boundaries
2. Ocean drilling - sea floor gets deeper and older away from oceanic ridges, maximum age = **180 million years old**, sea floor continuously moves away from ridges, towards deeper trenches
3. Hotspots - seamounts and volcanic islands form a chain on a palte continuously moving over a MANTLE PLUME
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What is the cause of the movement of lithospheric plates?
Convection in the asthenosphere, caused by unequal heat distribution
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