Study Guide Exam2

GLG110 Dangerous World Exam2 Study Guide 1. Be able to make a comparative sketch of Earth’s compositional layers with respect to its rheological layers. Layers include continental crust, oceanic crust, mesosphere, core, outer core, inner core, asthenosphere, lithosphere, and mantle. Compositional layers should include a description of the chemical constituents (i.e., silica content or metal alloy content) that differentiate the layers, whereas rheological layers should include physical characteristics (i.e., plastic, liquid, solid, brittle solid) that differentiate the layers. 2. Be able to make a sketch of the three different types of plate boundaries (convergent subduction, divergent, transform) showing relative plate movement. Be able to compare and contrast the different earthquake and volcanic hazards associated with each. Divergent: light to moderate earthquakes, nonexplosive volcanic eruptions (small volcanos). Convergent: Great earthquakes, explosive volcanic eruptions. Transform: strong to major earthquakes. 3. Be able to explain the differences in the age of the sea floor vs the age of the continental crust. The age of the sea floor is way younger than the age of the continental crust this is because of seafloor spreading that occurs at the mid-ocean ridges making the ocean floor no more than 200 million years old while continental crust is several billion years old. 4. Explain in a sentence the process of convection (cooling process) and how this process is analogous to plate tectonic theory. Convection is a heat transfer mechanism through mass movement driven by density differences. This is analogous to plate tectonic theory because it is assumed that it may be involved in driving plate tectonics within Earth’s mantle and crust. (Temperature-driven circulation pattern) 5. Be able to explain plate motion with respect to Hot Spot volcanism as evidenced by the age of volcanic rocks that form. Hot spots are plumes of hot rock that rise from deep in the surface and cause volcanoes above the Earth’s surface. Hot spots are fixed and do not require moving tectonics but as the plates move across the hotspot, a chain of volcanoes is formed. The further the volcanic rocks from the hotspot the older the rock is. 6. Be able to identify locations on a Plate Tectonic map where you might find andesitic (intermediate silica content) volcanoes vs basaltic (low silica content) volcanoes. Andesitic volcanos form around the ring of fire and above subduction zones. Basaltic volcanoes are located along the mid-ocean ridge. 7. Be able to make a sketch of a reverse and normal fault, which shows the “stress” direction and type of stress that results in the different types of fault movement. Also, be able to label “hanging wall” and “footwall” on each sketch and show the relative movement of each that results from the different types of stress applied. 8. Know the differences between the different types of seismic waves (P-, S-, and Surface waves) with regard to their velocities, arrival times, and the relative hazard posed by each. Know how earthquake foci are located (triangulation). Primary waves (p-waves) are the fastest waves (5-8 km/s) and are felt first. Shear (secondary waves (s-waves) are the second fastest wave (2-5 km/s) and are felt second. Surface waves are horizontal and vertical orbital waves of the ground, they are the third fastest and are extremely destructive. Triangulation is the process of locating a feature using distances from three points. 9. Explain the earthquake cycle (elastic rebound theory) as it pertains to generating seismic waves that cause devastation. Elastic rebound theory is a sudden release of elastic strain energy that is stored in rocks that have accumulated for over 100s to 1000s years. The rocks deform elastically until a critical point is reached and the fault slips, releasing the stored elastic. This release is seen in form of seismic waves (P, S, and surface waves) 10. Be able to explain seismic amplification and duration of shaking based on the local composition of the building substrate (igneous rock, silt, sedimentary rock, water-saturated sediment, etc.). Hard igneous rock has low amplification of shaking (surface waves), sedimentary rock has intermediate shaking, alluvium is slightly higher while silt and mud are the highest. Material amplification is highest in water-saturated sediment. 11. Know the differences between the different ways to assess earthquake magnitudes (Richter, Mercalli, Moment), and the strengths and weaknesses of each of the scales. Richter Magnitude scale is a logarithmic scale based on the peak amplitude of the S-wave. It is used to record ground shaking direction and magnitude; it is the best quantitative measure of ground shaking. It is not an absolute measurement of the

size of an earthquake, and it is not well suited for comparing sizes around the world. Mercalli Intensity Is based on EQ interactions between humans and their environment, it has 12 categories. Building codes are not the same worldwide so it’s not applicable to every country and may take weeks to complete. The moment magnitude is an absolute scale. Average displacement x area of movement (fault length) x rock properties 12. Be able to explain the primary hazards related to earthquakes (liquefaction, fire, building collapse, ground shaking) and how these hazards may be different depending on where you live. Liquefaction is land sinking due to shaking so the rock underneath us turns into water because the water has nowhere to go. This occurs far away from the epicenter; long surface waves cause this. Fires occur because pipelines burst due to movement. Building collapses could be different depending on building codes and how far you are from the epicenter, surface waves cause the most destruction and lead to this. Ground shaking causes the most damage and is the cause of major damage; fires, liquefaction, and building collapse. 13. Be able to discuss the 5 fundamental concepts as it pertains to Japan’s earthquake readiness, risk, and ability to forecast and prepare for the 2011 Tohoku Earthquake. 1. Subduction zone near Tohoku, Japan. The early detection system. 2. Common place for earthquakes since it is near an active subducting zone. Japan’s investment in early detection systems, updated building codes, and community preparedness drills. 3. Tsunamis, major coastal flooding, liquefaction, and landslides. 4. High population density. 5. $1 billion dollar investment into research and development in their early detection system. Investment into retrofitting older buildings and infrastructure to sustain shaking. Japan has the densest sensorimotor network system to forecast, locate and study earthquakes. 14. Know the different causes of melting at different tectonic settings and the primary cause of a volcanic eruption (i.e., what drives the magma out of the subsurface). Decompression (divergent) melting occurs when pressure on rocks close to their melting temperature is decreased due to thinning of the overlying lithosphere during tectonic extension and when superheated rocks up well from deep within Earth’s mantle as part of a hotspot. Melting occurs at convergent boundaries (subduction) due to the addition of volatiles to the asthenosphere, which is released from the down-going oceanic plate. The addition of heat to rocks will induce melting if the temp exceeds the melting temperature of the rocks at that depth 15. Be familiar with the five types of volcanoes discussed in class including their: silica content and rock name, the viscosity of the melt, explosive character, and volatile content. Shield Volcano /----\: Low SiO2, Basalt rock, low viscosity, low volatile, low explosive (far-traveling lava flows). Stratovolcano /\ : high SiO2, Andesite rock, high viscosity, high volatile content, a combination of lava flows, and pyroclastic activity. Lava Dome (dome-shaped, steep-sided): Andesite to rhyolite, low to moderate SiO2, low to moderate volatile content, mostly effusive with lavas piling up near vent, but can be explosive. Cinder Cone (cone-shaped with steep sides and summit crater): low to moderate SiO2, low to moderate volatile content, mildly explosively (tephra ejection lava flows). Continental Calderas (broad uplift with large summit depression): high SiO2 content, rhyolite rock, high viscosity, high volatile content, very explosive. 16. Be able to summarize the different hazards (e.g., ash fall, lahar, etc.) associated with volcanoes, including the processes driving them as well as their dangerousness with a focus on their proximity to the volcano. Pyroclastic Material (tephra): explosive fragments; ash, lapilli, bombs, and blocks come from within the eruption column, near the volcano. Ash Fall/Scoria Fall: cooled ash can be thick, comes from the eruption cloud close to the volcano, and can extend worldwide. Lava flow: a minimal hazard to life but can be devastating to infrastructure, paths are predictable, and they move slowly enough to avoid coming from down the side of the eruption column. Pyroclastic flow (Plinian eruption): high-hazard, fast-moving hot ash deposits that flow down the side of the volcano, within 10 miles of the volcano. Lahar (hot mudflow): high-hazard, fast- moving hot water, mud, ash, and debris that runs down river canyons many 10s of miles. 17. Understand how volcanoes erupt. Specifically, what is it that causes the molten rock to be propelled onto the surface, and fragmented into bombs, cinders, and ash? Volcanoes erupt because of the melting of molten rock called magma that rises to the surface. It is less dense than surrounding rock, so it rises buoyantly toward the surface. When the magma hits the surface, it solidifies to form different volcanic rocks. The volatile content is what causes the molten rock to be propelled to the surface and fragment into bombs, cinders, and ash.

channels that help control flooding and fix drainage problems. This can be considered anti-ethical to the production of fish and wetland wildlife. 25. Be familiar with the 5 fundamental concepts as it pertains to the 2010 Pakistan flood. 26. Understand the differences and similarities between the 9 main types of mass wasting and the mechanisms by which they move (Table 7.1 and Figure 7.4). Falling- rockfall: rock detaches from a free face and cascades downward bouncing off the slope below or falling through the air before impacting the talus slope below. Sliding- Rockslides are the result of inherent planar weaknesses in the underlying bedrock, such as bedding planes in sedimentary rocks. Failure of the rocks along these weaknesses results in rocks sliding down dip. Soil slips occur when the unconsolidated soil that overlies the coherent bedrock becomes mobilized sliding down the planar interface. Rock slump- the key characteristic of a rock slump is the downward movement of soil and the underlying bedrock in a semi-coherent mass occurs along a curved, concave-up detachment surface. Because the surface is curved the downward motion results in the rotation of the slide mass and back-tilted benches. Slumps are sometimes referred to as rotational slides for this reason. Flowing- An earthflow occurs when unconsolidated sediment and/or soil moves at slow to moderate speeds downslope in a turbulent mass, flowing. A debris flow occurs when unconsolidated sediment becomes saturated by water and begins to flow downslope rapidly as a high-density fluid. An avalanche occurs when unconsolidated snow and ice flow downslope in a turbulent mass. Soil creep is a very slow, imperceptible turbulent movement of unconsolidated sediment and soil downslope. Complex- The upper part of the slide is more of a slump and then the lower part is more of a flow. 27. Know the effects of Earth’s material, slope/topography, climate, vegetation, water, and time on mass wasting. More steepness (slope) and the topography create more mass wasting and are associated with rock falls, avalanches, and soil slips. Vegetation stabilizes the sediment on the floor and prevents it from weakening. Climate: in arid/semi-arid climates vegetation tends to be sparse, soils are thin, and bare rock is exposed so rockfall, debris flow, and shallow soil slips are common. In subhumid to humid regions, there is lots of vegetation and thick soils cover most slopes so complex landslides, earth flows, and soil creeps. Water affects mast wasting by affecting the slope, it decreases stability by adding weight and weakening the plain. Earth material can make landslides hazardous because of weak zones if they intersect the slope of a hill or mountain. Over time the forces acting on the slope change which weakens the slope because of the weathering of rocks due to soil and water contact. 28. Understand how humans can increase the hazard from mass wasting by interacting with the landscape. Development and urbanization in landslide-prone areas, removing vegetation, and tree cutting in prone areas. Humans build homes and urbanize areas that are prone to mass wasting and hazards increase because more people are being affected by it and even increasing the likeliness overall. 29. Be able to provide several examples of how Mass Wasting hazards can be minimized. Mass wasting can be minimized by building structures and improving drainage on naturally sensitive slopes. Also, by recognizing areas that are of high potential, and prohibiting urbanization that may worsen the slope strength, adding retaining walls in logical ways, adding benches, and anchoring slopes. 30. Be familiar with the 5 fundamental concepts as it pertains to the 1995 and 2005 La Conchita landslides. 1. Cracking of sea cliff, rock material of the sea cliff is unconsolidated beach sand, heavy rainfall contributed to the previous landslide, the sea cliff was uplifting because of the red mountain fault. 2. 1995 slump above the community, lots of previous ancient slides, steep cliffs above the community, active ocean erosion. 3. Heavy Rainfall, and coastal erosion. 4. Avocado orchard added water mass and made plain weaker. 5. Retain the wall and dewater.