part ii (8-14)

Question 1

Illustrate why the inclination of a compass needle varies with latitude (distance north/south of the equator)

Answer 1

Cooled layers of rock with magnetic properties are parallel to Earth’s magnetic field lines. The closer the rocks are to the poles, the stronger the inclination (positive dip, negative dip)

Question 2

Explain how paleomagnetic data can constrain the past motion of tectonic plates

Answer 2

The magnetism of the rocks now are not the same as rocks from 100 years ago as the Earth’s magnetic field lines, the poles, have moved. Paleomagnetic data can be used to locate where the poles and the continents used to be.

Question 3

List the several major discoveries about the sea floor that were made in the 1950s-1960s, and describe how they led to/supported the theory of plate tectonics

Answer 3

(1) As the ocean floor formed, rocks containing magnetite would point at the pole. But as the magnetic poles would move, new rocks would point at this new location. As a result, since the ocean floor is stripped with rocks that reference the current and past location of the magnetic poles, this is used as evidence that the ocean floor is spreading and of tectonic plates.

(1.5) Using sonar data, Marie Tharp mapped the ocean floor and found all these mid-ocean ridges along the middle of the ocean, therefore theorized that the pieces of the ocean are pulling apart.

(2) Using a big global seismometer network, geologists were able to accurately and precisely locate earthquakes and found that those earthquakes sit right on these plate boundaries including those rift valleys

Question 4

Illustrate how earthquakes release stress that has built up along a fault that was “locked”, and relate this stress buildup to plate-tectonic motions

Answer 4

(awaiting response from professor)
Earthquakes release stress that has built up along a fault that was “locked” by “snapping” (horizontal and vertical separation), releasing seismic waves through the earth

Stress builds up because of movement by plate tectonics. As plates diverge, converge, and/or transform, plates catch onto each other due to friction which builds stress

Question 5

Define the terms “epicenter”, “focus”, and “fault scarp”, and identify them on a diagram of an earthquake

Answer 5

“Epicenter”: the point on the Earth’s surface where the earthquake begins; vertically above the hypocenter

“Focus”: the underground focus point of where an earthquake really happens

“Fault scarp”: feature on the surface of the earth that looks like a step caused by slip on the fault

(see iPad for diagram)

Question 6

Contrast P-waves, S-waves, and surface waves, and explain how P- and S-waves can be used to locate the epicenter of an earthquake

Answer 6

P-waves are the first (and fastest) waves of an earthquake, where when the rock is compressed, in a slinky-like manner the rock will expand/”push” back hence it can be compressed by any medium except liquids.

S-waves are the slower secondary waves of an earthquake, which shakes the ground side-to-side perpendicular to the direction it is traveling. Can only travel through solids.

Surface waves can only travel along or parallel to the surface of the planet in an overall circular motion.

The delay between P- and S- waves indicate how far away the earthquake is, and given at least three stations to locate an overlap, this information can pinpoint the earthquake’s epicenter.

Question 7

State the difference in amplitude, and the difference in energy released, for two earthquakes with a magnitude difference of 1 (for example, a M6.0 vs a M7.0)

Answer 7

Because the magnitude is using a logarithmic scale, a magnitude increase of +1 represents 10x the amplitude of shaking and 32x the energy released

Question 8

Discuss the extent to which earthquakes can be predicted, and the extent to which they cannot

Answer 8

The extent to which where and when earthquakes will occur can be predicted by analyzing general trends. We know that earthquakes are more likely to happen at plate boundaries, and that we can look to the “average” for frequency predictions/estimations. Also determining how often a fault has moved in the past (law of superposition and cross cutting section) and recency of earthquakes, this can be used as an indicator of how strong the next earthquake will be.

However, these are all broad assumptions. The crust’s response to changing stress is dynamic. Thus it is difficult to predict specific times, locations, and strength of the next earthquake.

Question 9

Briefly explain how liquefaction can occur during an earthquake

Answer 9

Loosely packed, water-logged sediments at or near the ground surface lose their strength in response to strong ground shaking

Question 10

List different construction techniques for improving earthquake resistance, and briefly explain how they work

Answer 10

Reinforced concrete: steel skeleton embedded inside concrete that can bend without snapping, hence is able to hold a lot of weight that can shift together

Base isolation: by separating the structure from its base, the amount of energy that is transferred to the superstructure during an earthquake is reduced significantly

Tuned mass damper: with its out of phase motion, the inertial force of the TMD mass abates the resonant vibration of the structure by dissipating its energy

Question 11

Outline what can be done before an earthquake to prepare for it

Answer 11

Secure all heavy and tall items, prepare first-aid kit, food, water, and emergency necessities

Question 12

State what one should do during an earthquake in various common situations (in a building, outside, in a car, in bed, in a high-rise, near steep slopes), and common misconceptions about what one should do

Answer 12

In a building… drop, cover, and hold onto any sturdy furniture; do not run outside until shaking stops

Outside… go to an open area away from trees, telephone poles, and buildings. Once in the open, get down low and stay there until the shaking stops

In a car… stop in a clear area that is away from buildings, trees, overpasses, underpasses, and utility wires

In bed… stay there and cover neck with pillow

In a high-rise… drop, cover, and hold onto any sturdy furniture; do not run outside until shaking stops

Near steep slopes… be alert for falling rocks and landslides

Common misconceptions: run outside or to other rooms during shaking if inside building

Question 13

List things one should do/check after an earthquake

Answer 13

Expect aftershocks, check yourself for injuries, go outside as soon as possible after shaking stops, do not enter damaged buildings, save phone calls for emergencies

Question 14

Illustrate the difference between an anticline and a syncline

Answer 14

Anticline: the strata dips away from the crest
Syncline: the strata dips towards the trough of the fold

(illustration on iPad)

Question 15

Distinguish between hanging wall and the footwall of a fault

Answer 15

The footwall is the block of rock that lies on the underside of an inclined fault; the hanging wall the block of rock that lies above an inclined fault

(illustration on iPad)

Question 16

Explain the difference between a normal fault, a reverse fault, and a strike-slip fault; and indicate which kind of fault is associated with each kind of plate tectonic boundary

Answer 16

Normal faults: as plates diverge from one another, hanging wall moves down (divergent)

Reverse faults: as plates are being pushed together, the hanging wall slides up (convergent)

Strike-slip fault: plates move side-to-side (transform)

Question 17

List the types of subatomic particles that make up an atom, and explain the difference between different elements

Answer 17

Protons (positively charged), electrons (negatively charged), neutrons (neutral, just mass)

The number of protons and electrons in an atom determine what element it is.

Question 18

State the difference between ionic and covalent bonds

Answer 18

Ionic bonds is the process in which atoms will “give up” one electron in order to have stability and transfer to other atom. Bonds by charges being attracted to one another

Covalent bonds is the process in which atoms will “share” its electrons with each other enough for each to have full orbital; connected by shared electrons.

Question 19

Define “mineral”, and use this definition to categorize substances as either a mineral, or not a mineral

Answer 19

“Mineral”: a naturally occurring, solid (at room temperature), abiotic (not formed by life), crystalline substance (set arrangement), with a specific chemical composition.

Substances must fit all the categories above, emphasis on naturally occurring.

(see lecture for examples/practice)

Question 20

List the common physical properties that can help identify minerals, and explain the difference between crystal form/habit and cleavage

Answer 20

Different colors, streaks, hardness, crystal form, cleavage

Crystal form/habit is a reflection of how a mineral grows (the ideal shape of crystal faces), while cleavage describe how it breaks.

(complete additional examples/practice)

Question 21

Define “volcano”, list the plate-tectonic settings in which volcanoes typically form, and explain how magma is generated in such settings

Answer 21

“Volcano”: a rupture in the crust that allows hot lava, volcanic ash, and gasses to escape from a magma chamber below the surface.

Divergent (reduces pressure on asthenosphere, allowing magma to rise) and convergent (subducting plates pushes water trapped in minerals down = metamorphoze (release of water) → lowers melting point causing asthenosphere to melt = allowing magma to expand to lithosphere) plate boundaries.

Question 22

State the key compositional and mechanical differences between mafic magma and felsic magma, and relate these to the different ways these magmas typically erupt and flow

Answer 22

Mafic magma: low in silica (less gas) and contain more dark-colored, magnesium and iron rich mafic minerals; erupts less viciously because magma is more dense; flows easily to the surface because it is not as hot, hence has a low viscosity

Felsic magma: higher in silica (more gas) and contain lighter-colored minerals; erupts explosively because of hot, gas-rich magma churning within its chamber increasing pressure; does not flow easily because it is too vicious to move

Question 23

List the common types of volcanoes, the type of magma (mafic vs intermediate or felsic) that forms them, and how these volcanoes form from these magma types

Answer 23

Mafic lava: (1) shield volcanoes: repeated low viscosity, runny lava that spreads too far from its source to form a volcano with gentle slopes; (2) cinder cones; develop from explosive eruptions of mafic which fall as cinders around the vent to form the volcano

caldera, lava domes

Intermediate lava: composite volcanoes: successive eruptions of intermediate lava flows and pyroclastic flows

Question 24

Outline the rock cycle

Answer 24

(illustration on iPad)

Question 25

Explain where intrusive and extrusive rocks form, and how and why the texture of the types is different

Answer 25

Intrusive rocks form when magma is trapped deep inside the Earth (within Earth); the slow cooling process allows crystals to grow large, giving the intrusive igneous rock a coarse-grained texture

Extrusive rocks form from erupting volcanoes and oozing fissures (Earth’s surface); the cooling lava did not have enough time to grow large crystals hence resulting in fine-grained texture

Question 26

Describe the special textures that can form in extrusive rocks, and how they form

Answer 26

Porphyritic: magma that has been slowly cooling and crystallising within the Earth’s crust is suddenly erupted at the surface, causing the remaining uncrystallised magma to cool rapidly

Volcanic glass: when magma is rapidly cooled below its normal crystallization temperature

Bubbles: as magma rises to the surface the pressure on it decreases, allowing gasses dissolved in the magma to come out of solution, forming gas bubbles (the cavities) inside it

Pyroclastic: forms directly from the fragmentation of magma and rock by explosive volcanic activity

Coarse-grained: the cooling lava did not have enough time to grow large crystals

(illustrate as well; to memorize what each texture looks like)

Question 27

Classify igneous rocks, given their composition (felsic, intermediate, or mafic) and texture (course-grained, fine-grained, porphyritic, glassy, or pyroclastic)

Answer 27

(illustration on iPad)

Question 28

Illustrate how a single intrusion of magma can produce a body of igneous rock that has layers of different mineralogy (different mineral composition)

Answer 28

This is due to magnetic differentiation.
(As the molten material cools, chemical compounds in the melt crystallize into minerals at different temperatures, with “high temperature” minerals crystallizing first. These high temperature minerals are denser than the molten material and tend to settle out in the bottom of a magma chamber (pluton). As the melt continues to cool, the composition of the melt changes as more crystals form and settle out. Finally the melt completely cools with the composition of the rock enriched in low temperature minerals.)

(mafic is lower in silica, felsic is higher)

Question 29

Explain why mafic volcanism is not so dangerous

Answer 29

Although mafic volcanism erupts less viscously, it is less explosive than felsic volcanoes

Question 30

Describe the deadliest processes associated with composite volcanoes (pyroclastic flows and lahars)

Answer 30

Pyroclastic flows are superheated clouds of pyroclastic material that can travel at speeds up to 100 mph.

Lahars, a debris flow that originates on the slopes of a volcano, can happen when old volcanic debris gets mobilized during heavy rain or snow melt or eruptions (and pyroclastic flows) triggering such melting. Due to their density, lahars can destroy infrastructure and homes and bury towns (and people) rapidly.

Question 31

Describe how large eruptions can have negative consequences even in other parts of the world

Answer 31

Volcanic eruptions can impact climate change through emitting volcanic gases like sulfur dioxide, which causes global cooling, and volcanic carbon dioxide, which has the potential to promote global warming.

causes acid rain and famine

Question 32

List some useful resources that form by igneous processes, and an example of something that is made from them

Answer 32

Diorite: a base material in the construction of roads, buildings, and parking areas; also used as a drainage stone and for erosion control.

Granite: used in bridges, paving, and a range of interior projects (decoration)

Silicon: used for microchips, glass, cement, and pottery

Pumice: an abrasive in cleaning and polishing

Question 33

Explain why so much farming takes place near volcanoes

Answer 33

Volcanic deposits are enriched in elements such as magnesium and potassium. When volcanic rock and ash weathers, these elements are released, producing extremely fertile soils.