Short Answer Questions

Question 1

Transform plate boundaries are __________ because they do not involve creation or destruction of lithosphere.

Answer 1

conservative

Question 2

List at least three observations that are explained by the theory of plate tectonics.

Answer 2

• the age of oceanic crust increases when you move away from mid-ocean ridges (youngest crust)
• earthquakes and volcanoes are concentrated along plate boundaries
• there are deep ocean trenches along continental margins and island chains

Question 3

Explain the earthquake depth/distribution pattern seen at subduction zone plate boundaries (can be done in 1-2 sentences)

Answer 3

Along subduction zone plate boundaries, earthquakes are concentrated along the subduction zone (in a chain) and vary in depth but produce many deep earthquakes.

Question 4

If oceanic lithosphere has relatively uniform composition, explain how one piece of oceanic lithosphere can subducted between another piece of oceanic lithosphere. (this will almost certainly appear on one of the exams!)

Answer 4

the heavier and older plate will dive beneath the less dense (younger) plate and sink into the mantle

oceanic lithosphere is more dense then continental lithosphere

Question 5

List and briefly define the five criteria for a substance to be considered a mineral.

Answer 5

To be classified as a mineral, the substance has to be solid, naturally occurring (made geologically), inorganic, have a crystalline structure (lattice arranged atoms), and have a definable chemical composition (chemical formula present).

Question 6

List the sequence of minerals and change in magma composition you would expect during fractional crystallization (Bowen’s reaction series).

Answer 6

Mafic: Olivine, Pyroxene
Intermediate: Pyroxene, Amphibole, Biotite
Felsic: Biotite, Quartz, Muscovite, K-feldspar
If continous, Plagioclase can be any composition but Changs to K-feldspar in low temperature

Question 7

Briefly describe clastic sedimentary rock texture (grain size, roundness, sorting) as a function of the two following factors:

1) sediment transport distance (i.e., distance from source)

2) energy of depositional environment

Answer 7

• Closer to the source: large gain size, less round, and very poorly sorted
• Farther from the source: small grain size, more round, and very well sorted
• high energy environment (fast river and oceans): large grain size, round sediment, and poorly sorted
• low energy environment (lakes and swamps): small grain size, angular sediment, and well sorted

Question 8

List the complete sequence of metamorphic rocks you would expect to form from a shale
or mudstone that experiences increasing metamorphic grade in a continent-continent collision zone.

Answer 8

clay, chlorite, quartz, muscovite, biotite, garnet, staurolite, kyanite, sillimanite

Question 9

What are hotspots and how do they form?

Answer 9

Hotspots are an area of the mantle that is hotter than the rest of the mantle. They form above mantle plumes when the plumes hit the base of the lithosphere and melt.

Question 10

Why does felsic magma usually generate more explosive eruptions than mafic magma?

Answer 10

felsic magma is more viscous (more silica content) and able to trap more gases

Question 11

How do calderas form?

Answer 11

When a magma chamber completely empties and the volcano collapses inside of it

Question 12

What happened in Lake Nyos, Cameroon that caused nearly 2,000 fatalities?

Answer 12

A mass quantity of volcanic carbon dioxide released from a late and concentrated near the ground.

Question 13

List as many factors as you can that contribute to how deadly or destructive an earthquake is.

Answer 13

magnitude, depth, population density, local topography, and building construction

Question 14

List as many factors as you can that contribute to how deadly or destructive a volcanic eruption is.

Answer 14

volcano type, eruption style, explosivity index, magnitude, population density, lava flows, lahars, tsunamis, and gas emissions

Question 15

List and describe all the earthquake hazards that a community located on the coast of a poor country might face.

Answer 15

The community can experience tsunamis, challenging rescue and recovery, and building collapse.

Question 16

What are cratons and how do they form?

Answer 16

Cratons are cold, relatively stable continental lithosphere (large unheated continents) that are formed by accumulating various types of rocks and the buildup of continental crust.

Question 17

What are the causes, consequences, and evidence for the Great Oxygenation Event between 2.4 Ga and 1.8 Ga?

Answer 17

The cause of the event was more oxygen production than rock/ocean absorption due to the origin of photosynthetic life. The consequences were a decrease of oxygen in the atmosphere and biotic evolution. The evidence for this event was the appearance of red sedimentary rocks that were oxidized.

Question 18

What is the most accepted explanation for the end Permian extinction? What type of geological phenomenon?

Answer 18

The most accepted explanation is the Siberian Traps flood basalt eruptions. this geological phenomenon is a hot spot.

Question 19

What is the most accepted cause for the K/Pg extinction? What is the evidence, and what were the consequences?

Answer 19

The most accepted cause is a meteorite impact. The evidence is the Carter in the Yucatan Peninsula and the consequences were sun blockage and acid rain.

Question 20

List and describe the four (or five) major trends exhibited by the Keeling curve.

Answer 20

1) the carbon dioxide concentration is increasing
2) the rate of carbon dioxide emissions is increasing
3) the annual cycle of carbon dioxide decreases in the summer and increases in the winter
4) the amplitude of biosphere flux is increasing

Question 21

What is a tipping point in the context of global climate? Give a real-world example.

Answer 21

A tipping point is a small change in external conditions that can lead to significant environmental and climate impacts. One example of this is the ice melting in the arctic and antarctic can lead to sea-levels increasing.

Question 22

List and define the four main types of reactions involved in chemical weathering.

Answer 22

• solution reactions: dissolving solid materials in naturally formed acids
• oxidation reactions: “rusting” through electron donations
• hydration reactions: combining minerals with water
• hydrolysis reactions: water molecules breaking chemical bonds

Question 23

You probably knew this one was coming: list the five factors of soil development and
describe how each of them influences soil development, including the presence/absence
and thicknesses of the four major soil horizons.

Answer 23

• Climate: high temperatures and moisture can speed up the weathering process and development of soil horizons
• Organic activity: earthworms and bacteria add organic matter composition and plant roots that break rocks can add organic matter
• Relief: a sloped terrain can lead to erosion of soil while flat land can produce more organic material
• Parent material: different types of parent material affects nutrient content in the soil
• Time: the longer soil takes to weather, the more developed it is and the more defined its horizon is

Question 24

List a mineral that is susceptible to chemical weathering, the type of chemical reaction it
undergoes, and the product of that weathering reaction.

Answer 24

A mineral susceptible to chemical weathering is feldspar that undergoes a hydrolysis reaction to produce clay

Question 25

List and describe as many soil problems as you can that are caused or enhanced by poor
agricultural practices.

Answer 25

• Desertification: arid land conditions caused by soil overuse
• Acidification: reduction of soil pH by use of fertilizers
• Deforestation: clearing trees for timber or to create crop land
• Salinization: build up of salts on soil surface by fertilizer overuse

Question 26

Why is soil loss of greatest concern in the region of Africa south of the Sahara Desert? In
other words, what are all the issues that make this region particularly susceptible to soil
erosion?

Answer 26

Soil loss is a great concern because of the periods of drought and heavy rainfall, widespread deforestation, livestock overgrazing, and low organic matter soil that is susceptible to erosion.

Question 27

Explain the relationship between mass wasting and 1) volcanoes and 2) earthquakes.
How do these hazards increase the risk of mass wasting, and what are some ways they
can trigger a mass wasting event?

Answer 27

Volcanoes: volcanoes can produce structures with slopes and large amounts of ash can mix with water to create lahars
Earthquakes: the shaking can trigger a landslide and liquefaction can weaken loose material and trigger debris flows

Question 28

Describe the mechanics of mass wasting in terms of the driving forces and resisting
forces. You can include a sketch to aid your explanation.

Answer 28

The downslope force of the has to be greater than the resistance force that keeps the material from sliding down a slope. The pull of gravity aids in the downhill movement because some of the gravity’s magnitude is in the downslope force direction.

Question 29

What are the most significant risk factors for landslides?

Answer 29

The risk factors are water saturation (heavy rain), increased physical weathering, and vegetation removal.

Question 30

Why are clay-rich materials particularly susceptible to subsidence?

Answer 30

Clay materials have a high capacity to retain water. This causes there to be extra weight on top of the soil and cause the ground to sink.

Question 31

Briefly describe the history of subsidence in Houston in terms of the causes and the areas
most impacted.

Answer 31

During 1906-1943, most subsidence was lost during due to oil and gas removal around the Galveston area. During 1943-1973, there was an oil and gas boom that caused a growth in population and groundwater extraction for drinking water around southeastern Houston. During 1973-1995, the subsidence moved to the northwest due to extraction regulations. Today, most of the subsidence is taking place in north Houston due to groundwater extraction.