ESC1000 Final Yang Wang
Explain the contrasts among the different scales used to describe the size of an earthquake.
-Mercalli intensity scale: focuses on the severity of damage at a location. -Magnitude Scale: focuses on the amount of ground motion at specific distances from the epicenter, measured by a seismograph
What is the age of the oldest rocks on Earth? What is the age of the oldest rocks known? Why is there a difference?
4.03 Ga, 4.57 Ga. They come off of different planets, so they can be older than Earth rocks
What is a tsunami, and why does it form?
A tsunami is a giant wave traveling at speeds of about 800 km/hr (500mph). They are formed by the rise of the sea floor shoving up overlying water. Then the water from above the upthrust sea floor moves outward from above the fault zone.
Compare the deposits of an alluvial fan with those of a typical river environment and with those of a deep-marine deposit.
Alluvial fans are wedge-shaped deposits occurring at the foot of an eroding mountain range. The sediments are typically coarse (sand, pebbles, or cobbles) and contain substantial amounts of feldspar (physically weathered from a typically granitic montane source).Deep-marine deposits are dominated by the skeletons of planktonic microorganisms(chalk derived from foraminiferans and bedded cherts derived from diatoms and radiolaria)and clay (which settles to form finely laminated mudstone).
How does an unconformity develop
An unconformity occurs when sedimentary layers are deposited on top of a surface of erosion or nondeposition. Three kinds of unconformities are recognized: nonconformities, disconformities, and angular unconformities. Nonconformities arise when sedimentary strata are deposited on top of crystalline (metamorphic or igneous) rock. Disconformities occur when strata are deposited on top of an erosional surface that was horizontal at the time, so that layers above and below the unconformity are parallel. Angular unconformities arise when the new strata are deposited on top of older layers that have been tilted out of horizontality, so that, regardless of future tilting, layers on opposite sides of the unconformity are not parallel.
How does plate tectonics explain the peculiar combination of low-temperature but high-pressure minerals found in blueschist?
Blueschists form at the base of thick accretionary prisms, sediments scraped off of the downgoing slab at subduction zones. Because the subducting slab is relatively cool, it adds little heat to the prism, allowing for the relatively high pressures but low temperatures in which the blueschist mineral assemblage is stable.
Clastic Rock
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering.
Clastic and chemical sedimentary rocks are both made of material that has been transported. How are they different?
Clastic rocks have been transported as SOLID MATERIALS in water. Chemical rocks are transported in water as DISSOLVED IONS. The rocks form when the water evaporates.
What factors determine the nature of soils in different regions?
Climate - Amount of water and warmth. Substrate composition - Soil parent minerals. Slope steepness - Soils develop best on low slopes. Drainage - Wet soils are more organic-rich. Time - Older soils are more developed. Vegetation - Controls type of organic matter added.
Describe how cross beds form. How can you read the current direction from cross beds?
Cross beds form from sediment deposited on the leeward side of dunes and ripples. These angled beds dip downward in the downstream direction (parallel to the lee side of the dune or ripple).
Describe the geologic settings where thermal, dynamic and dynamothermal (regional) metamorphism takes place.
DYNAMIC- when faults shear past one another and the minerals in the rock recrystallize and requires no change in pressure or temperature THERMAL- caused by igneous intrusion to emphasize that it develops in response to heat without a change in pressure and without differential stress DYNAMOTHERMAL- otherwise known as regional metamorphism because it affects a large region, includes heat and compression and shearing.
How is dolostone different from limestone, and how does it form?
Dolostone is composed of the mineral dolomite (CaMg[CO3]2), whereas limestone is composed of calcite, CaCO3. Dolostone contains more magnesium (a trace impurity in natural calcite) and has a different crystalline structure.
What happens during diagenesis, and how does diagenesis differ from metamorphism?
During diagenesis, sediments are compacted and new minerals precipitate from porewater to cement grains together. Further, chemical reactions may alter some of the mineral makeup of the sediment or sedimentary rock, and the weight of overlying layers of rock and sediment may lead to the dissolution of some grains (pressure solution). -Metamorphism takes place at greater depths in sedimentary basins. -Metamorphism refers to changes taking place at higher pressure and temperature than diagenesis.
How does physical weathering differ from chemical weathering
During physical weathering, intact rocks break into pieces. During chemical weathering, rocks react with water and air to produce new minerals such as clay and ions in solution.
Describe elastic rebound theory and the concept of stick-slip behavior.
Elastic-rebound theory is the concept that earthquakes happen because stresses build up, causing rock to bend elastically until slip on a fault occurs. Stick-slip behavior describes when earthquakes occur due to slip on a preexisting fault. Faults act like scars, they remain weaker than the surrounding crust. When stress builds up the fault slips before the stress becomes great enough to fracture surrounding intact rock.
What kinds of conditions are required for the formation of evaporites?
Evaporite formation requires a fluid with dissolved ions (typically seawater) to beevaporated to such an extent that the ions will precipitate out, typically as halide, carbonate,or sulfate minerals. Hot, dry conditions with extensive subaerial exposure are conducive to evaporite formation; these include warm, broad, shallow seas with little riverine influx and restricted circulation.
Feldspars are among the most common minerals in igneous rocks, but they are relatively rare in sediments. Why are they more susceptible to weathering and what common sedimentary minerals are produced from weathered feldspar?
Feldspars are more susceptible to weathering because they undergo hydrolysis in the presence of carbonic acid. Quartz and feldspar most common in igneous rocks
What is metamorphic foliation, and how does it form?
Foliation is the presence of parallel planar surfaces or layers in metamorphic rock. Under sufficiently differential stress, platy or elongate grains are broken down and regrown in a preferred orientation perpendicular to maximum compressive stress.
How does a schist differ from a gneiss?
Gneiss is compositionally banded, with alternating bands or swirls of light- and dark-colored minerals, including additional minerals besides mica (quartz, feldspar, amphibole).
Explain how liquefaction occurs in an earthquake, and how it can cause damage.
Liquefaction occurs in beds of wet sand or silt where the ground is shaking and causes the sediment grains to try to settle together. But because of the spaces(pores) between grains are filled with water, water pressure in the pores increases and pushes the grains apart, and the wet silt or sand because of a fluid-like slurry. It can cause damage because buildings whose foundations lie in liquefaction material may sink or even tip over.
Describe two different methods for correlating rock units. How was correlation used to develop the geologic column? What is a stratigraphic formation?
Lithologic correlation is the use of physical and chemical characteristics of rocks to determine that spatially isolated strata were once continuous (through original lateral continuity). Fossil correlation uses fossils with known stratigraphic ranges to determine the approximate temporal equivalence of two bodies of rock (which may be of disparate lithologies). Because a single locality does not provide strata that span in age throughout Earth's history, fossil correlation was required to provide time equivalence for units that are geographically isolated. With successful correlation, rock sequences from all parts of the world could be brought together to form an accurate sequence of relative time: the geologic column. A stratigraphic formation is a recognizable layer of a specific (usually sedimentary) rock type or set of types that were deposited within a certain time interval and can be traced over a broad region.
What kind of minerals tend to weather more quickly?
Mafic silicates like olivine and pyroxene tend to weather much faster than felsic minerals like quartz and feldspar.
What two features characterize most metamorphic rocks?
Metamorphic mineral assemblages (minerals uniquely produced under the temperature and pressure regimes of metamorphism) and metamorphic texture (grain arrangement, often involving foliation: a preferred alignment of platy grains or alternating light and dark mineral bands) are characteristic of most metamorphic rocks Foliation and texture, particular minerals
How are metamorphic rocks different from igneous and sedimentary rocks?
Metamorphic rocks are the result of heat and stress causing an alteration of texture, mineralogy, or both, within a preexisting rock, without the rock having undergone melting. Many metamorphic (but no igneous or sedimentary) rocks possess foliation
On the seismograph of an earthquake recorded ar a seismic station in Paris, the S-waves arrive 6 minutes after the P-wave. On the seismogram obtained by a station in Mumbai for the same earthquake, the difference between P-wave and S-wave arrival times is 4 minutes. Which station is closer to the epicenter? From the information provided, can you pinpoint the location of the epicenter?
Mumbia, India, is closer to the epicenter because the time between the arrival of the P and S waves is shorter. The further away from the epicenter the larger the time between the arrival of the P and S waves. You cannot pinpoint the location of the epicenter because you need a third location to find an epicenter.
Compare normal, reverse, and strike-slip faults
Notes from lab
Compare numerical and relative age
Numerical age for a rock is a number estimating the time of the rock's formation in years before the present. Relative age is a statement of ordinal timing; for example, Ordovician sedimentary rocks were deposited after those of the Cambrian but before those of the Silurian.
Describe the different horizons in a typical soil profile. (Other Animals Eat Beef and Cheese)
O Dark organic matter- rich surface layer. A Organic and mineral matter . E Transitional layer leached by organic acids. B Organic-poor mineral-rich layer. C Slightly altered bedrock. (top to bottom)
Describe the motions of the four types of seismic waves. Which are body waves, and which are surface waves?
P-waves: compressional waves can be generated by pushing and pulling on the end of a spring. The vibration direction is parallel to the direction of wave movement. Body waves S-waves: shear waves can be produced by moving the end of a rope up and down. As the waves pass through rock, the vibration direction is perpendicular to the direction of the wave movement. Body waves L-waves: as it passes, the ground surface moves back and forth like a slithering snake. Die out with increasing depth. Surface waves. R-waves: make the ground surface go up and down. Die out with increasing depth. Surface waves.
Why is radiocarbon dating useful in archaeology, but useless for dating dinosaur fossils?
Radiocarbon dating is used for dating organic matter. Dinosaurs are possibly too old to contain any more carbon to effectively use radiocarbon dating.
How does a phyllite differ from a schist?
Schist differs from phyllite in that, as a result of greater heat and pressure, its mica grains are large, visible discrete plates, unlike the smooth sheen of tiny mica grains within phyllite.
How is a slate different from a phyllite?
Slate and its characteristic slaty cleavage arise from the preferred orientation of clay minerals resulting from the relatively low-temperature and low-pressure metamorphism of a body of shale. Phyllite arises when significantly higher temperatures and pressures cause clay grains within slate to be recrystallized to form mica grains, which retain a preferred orientation. Unlike slate, which is rather dull, mica gives phyllite a silky luster.
What types of structures are most prone to collapse in an earthquake? What types are most resistant to collapse?
Structures built on land underlain by weak mud that could liquefy are prone to collapse in an earthquake. Also, structures built on top of, on, or at the base of steep escarpments could fail and produce landslides. Also, buildings downstream of dams are dangerous because they could crack and collapse causing a flood. Buildings that are resistant to collapse include ones that are wider at the base and that have cross beams added for strength. Wrapping a bridge's support columns in cable and bolting the span to the columns will prevent the bridge from collapsing so easily. Placing buildings on rollers or shock absorbers lessens the severity of the vibrations.
How does prograde metamorphism differ from retrograde metamorphism?
The changes in mineral assemblage and mineral composition that occur during burial and heating are referred to as prograde metamorphism, whereas those that occur during uplift and cooling of a rock represent retrograde metamorphism.
Why can't we date sedimentary rocks directly?
The mineral component of sedimentary rocks are generally older than the rock itself (Inclusion)
How does the principle of fossil succession allow us to determine the relative ages of strata
The predictability of fossil distribution which allows geologists to arrange fossil species in a progression from older at the bottom to younger at the top, (The sequence contains a definable succession of Fossils (A,B,C,D,E,F), that the range in which a particular species occurs may overlap with the range of other species, and once a species becomes extinct, it does not reappear higher in the sequence. (With the Principle, we can define the relative ages of strata by looking at fossils.)
How are growth rings and ice cores useful in determining the ages of geologic events?
They can help determine how long an organism survived. Ice cores can keep track of what the climate was like, and the temperatures.
Explain how biochemical sedimentary rocks form.
They form from shells of organisms and plant fragments
Describe how a turbidity current forms and moves. How does it produce graded bedding?
Turbidity currents form when sediment becomes unstable on a subaqueous slope and tumbles downward, pulling a current of water with it. After a while, the velocity of the turbidity current slows. The heaviest (largest) particles settle out first, whereas smaller, lighter particles stay in suspension for longer periods. Ultimately these smaller particles settle atop the coarser grains to produce graded bedding, a grain-sized gradient from coarse(near the base of the bed) to fine (at the top of the bed).
Is seismic risk greater in a town on the west coast of South America than on the east coast?
West coast because it is a subduction zone unlike the east which is a passive zone
Why does metamorphism happen at the site of meteor impacts and along mid-ocean ridges?
When a meteorite slams into the Earth, the heat and the pressure from it are definitely sufficient to cause metamorphic changes to the rock. Mid-ocean ridge settings provide ample opportunity for relatively cool water to interact with hot, recently formed rock.
Where would you go if you wanted to find exposed metamorphic rocks? How did such rocks return to the surface of the Earth after being at depth in the crust?
You would go look for the site of an ancient, greatly eroded mountain range. Metamorphism is strongly active in the lower portions of mountain ranges. As overlying layers of sediment and rock are weathered and eroded away, isostatic pressure causes the basement to be buoyed upward, until finally these rocks are exposed at the surface.
How does seismicity on mid-ocean ridges compare with seismicity at convergent or transform boundaries? Do all earthquakes occur at plate boundaries?
mid-ocean ridges: seismicity occurs at shallow depths convergent/transform: shallow and intermediate and deep seismicity only about 5% occur within plates
Describe how a clastic sedimentary rock is formed from its unweathered parent rock.
weathering>erosion>transportation>deposition>lithification
