Reference no: EM133101297
Geology
Discussion: Visit Geology to learn more about major earthquakes in the middle part of the United States and their risk factors. After viewing the website, summarize your ideas.
Exercise 1 - Earthquake Hazards
Part I - Earthquakes and Plate Tectonics
Each year, the vibrational (seismic) waves from earthquakes cause buildings to fail somewhere in the world, resulting in the death of large numbers of people. In addition to buildings, earthquakes cause considerable damage to human infrastructure, such as utility lines and transportation systems. Seismic waves also can trigger highly destructive tsunamis and landslides. Although humans cannot prevent earthquakes, we can use science and engineering to help minimize the hazards. In this exercise we will explore some of the earthquake hazards and ways we can reduce the loss of life and property damage.
1) The map in Figure 3.1 shows the location of earthquake epicenters that occurred over a 35- year period. Note how the epicenters clearly define the edge of Earth's tectonic plates.
a) Using a red colored pencil, place a set of arrows at the plate boundaries listed below so as to indicate whether the boundary is dominated by compressional, tensional, or shearing forces (i.e., indicate whether the boundaries are convergent, divergent, or transform.
mid-ocean ridge in the Atlantic Aleutian Islands of Alaska western coast of South America Japan western coast of North America Islands of Indonesia
b) What is the name of the geologic process that takes place along the plate boundary running through the Atlantic basin?
c) What geologic process occurs along the convergent boundaries you identified on the map?
d) What is the name of the earthquake hazard that can develop along convergent boundaries which is capable of bringing death and destruction to distant shorelines?
e) Explain why large magnitude earthquakes are relatively rare along divergent boundaries, but quite common along convergent boundaries.
Exercise 2 - Volcanic Hazards
Part I - Magma Chemistry and Lava Flows
In general, basaltic magmas originate from the upper mantle and are relatively hot, rich in iron and magnesium, but poor with respect to silica (SiO2). Andesitic and rhyolitic magmas, on the hand, are relatively cool, poor in iron and magnesium, but rich in SiO2. These so-called SiO2 rich magmas form in a variety of ways. One is when basaltic rock (oceanic crust) undergoes partial melting in a subduction zone. Another is when granitic rock (continental crust) melts, or is incorporated into a basaltic magma. Finally, SiO2-rich magmas can form when iron and magnesium rich crystals within a basaltic melt become separated from the magma.
The SiO2 content of magmas is important because it helps control the fluid property known as viscosity. As illustrated in Figure 4.1, magmas that are relatively rich SiO2 have more resistance to flow, hence are more viscous. Temperature is also important because as magmas become cooler their viscosity increases. Consequently, relatively hot, SiO2-poor basaltic magmas are much less viscous than the cooler, SiO2-rich andesitic and rhyolitic magmas.
1) Lava flows are one of the more obvious types of volcanic hazard. Which magma, basaltic or rhyolitic, would likely pose the greatest threat to communities in the area surrounding a volcano? Explain why.
2) Shown below are topographic profiles of the two basic types of volcanoes, shield and composite cone.
a) Label which profile corresponds to a shield volcano and which is a composite cone.
b) Label which volcano would contain mostly basaltic flows, and which would have mostly andesitic/ rhyolitic flows.
c) Explain how the topographic profiles of the volcanoes above are related to the viscosity of their respective magma types. In other words, how does magma viscosity affect a volcano's topographic profile?
3) When an oceanic (basaltic) crustal plate collides with a continental (granitic) plate at a convergent plate boundary, the oceanic plate almost always undergoes subduction. Describe how the difference in chemical composition between basalt and granite (rhyolite) determines which plate undergoes subduction.
4) Volcanism has taken place on all of the rocky planets of the inner solar system in the geologic past. Olympus Mons (now extinct) is the largest volcano on Mars, and on Earth, Mauna Loa is the largest. Their topographic profiles are shown below.
a) Based on its topographic profile, what type of volcano is Olympus Mons?
b) What does the topographic profile of Olympus Mons indicate about the chemical composition of its lava flows. Explain how you know.
5) As measured from its base on the sea floor, Mauna Loa is 5.1 miles high and has radius of 68 miles. Olympus Mons is 15.5 miles high and its radius is 171 miles. Because the volcanoes are cone shaped, we can use the following formula to estimate the volume rock making up each volcano:
V = 1/3Πr2h
where r = the radius at its base, and h = the height.
a) Using the equation above, estimate the volume of rock (in miles3) making up Mauna Loa.
b) Estimate the volume of rock (in miles3) in Olympus Mons.
c) In terms of volume, how many times larger is Olympus Mons than Mauna Loa?
6) Convert the heights of Mauna Loa and Olympus Mons from miles to feet.
Mauna Loa = 5.1 miles high x = feet
Olympus Mons = 15.5 miles high x = feet
For comparison, Mt. Everest is about 29,000 feet above sea level. Note that because Mauna Loa here is measured from its base on the sea floor, approximately 14,000 feet of its total height lies below sea level.
Attachment:- GEOLOGY_Discussion.rar