Introduction to Natural Hazards
Catastrophic Impacts
Plate Tectonics
Earthquakes
Volcanoes
100
Risk is defined as magnitude of consequences times the probability of occurence. Describe the relationship between frequency and magnitude and give one example to illustrate the relationship.
High magnitude events occur least frequently and low magnitude events occur most frequently. An example is the rarity of magnitude 8 or higher earthquakes. These occur only a few times a year. In contrast, there are several magnitude 4 earthquakes a day.
100
The hazards scale that indicates the risk of a near earth object striking earth is called the ________ scale.
The Torino scale was developed to rank the risk of future impact events. To date, only 1 object has been placed higher than a level 0 on the Torino scale.
100
Identify the layers of the earth, starting from the inner core and working your way out.
Inner core, Outer core, mantle, Asthenosphere, Lithosphere (oceanic and continental crust). (See Keller Figure 2.2)
100
The place where seismic waves appear to originate at he surface is the _______ while the actual break in the rock and location of fault movement is the ________.
Epicenter and focus (See Keller pg 164)
100
Name 4 hazards associated with volcanoes.
Lava flows pyroclastic flows poisonous gases mudflows and lahars
200
Give an example of a slow, intermediate, and fast geologic process.
See table 1.3, page 27 of Keller. Geologic processes tend to be slow!
200
In order for a near earth object to impact earth, its orbit around the sun must do what?
It must cross the Earth's orbit.
200
Describe how convection drives plate tectonic motion.
Heat (stored from the formation of the earth and given off by the radioactive decay of uranium rich rocks) at the core causes magma in the mantle to expand. Expansion causes it to become less dense so it rises toward the asthenoshere. As it rises the magma cools which causes it to contract and become dense again. The now dense magma sinks back toward the core. These cycles of heating and rising then cooling and sinking drive convection cells. The motion of the magma in the convection cells moves the lithospheric plates at the surface of the earth. Where plumes rise up they generate divergent spreading zones that expand oceans. (See Keller page 41)
200
Name the two scales used and explain why we need two different scales to describe the strength of an earthquake.
The magnitude scale describes the actual amount of energy released in an earthquake event. The intensity describes the amount of damages done by the shaking. We need two scales because the rock type, soil type, water content, and focal depth all affect how strong the earthquake feels at the surface and how much damage it does. Thus two earthquakes of equal magnitude do not have equal intensity and vise versa. (See Keller pg. 162-167)
200
How does the pacific Ring of Fire get its name?
Because the edges of the Pacific plate are subducting the surrounding plates, the Pacific is ringed by volcanoes.
300
Name the era, and period that reptiles appeared on earth. (For a question like this I would provide you Table 1.1 so you may wish to consult it now.) How long was this period
Paleozoic era, Permian period. This was between 290 and 245 million years ago so the period of the fossil record where reptiles emerge spans about 45 million years.
300
Describe the differences between an asteroid, comet and meteorite.
An asteroid is a large (10-1000 km diameter) metallic or rocky object. Most asteroids are located in the asteroid belt between Mars and Jupiter. Comets are composed of frozen water and carbon dioxide. They are a few meters to 100 km in scale. Most originate outside the solar system in the Oort cloud. Meteorites are stony or metallic objects that impact the earth's surface and vary from dust to asteroid size. (See Keller Table 11.1)
300
Name the three types of plate boundaries and give an example of each by naming two plates involved.
Divergent - Mid Atlantic ridge, African rift valley, Mid Pacific ridge. Convergent - Nazca and South American plates, Juan de Fuca and N. American plates, Philippine and Pacific plate, Eurasian and Pacific plate, Indo-Australian and Caroline plate, Indo-Australian plate and Fiji plate Transform - perpendicular to mid oceanic ridges, Caribbean and N. American plates, N. American and Pacific plates. (See Keller page 43)
300
Name the type of fault that experiences each of the following stresses -compression -tension -shear -combined
-dip-slip reverse or thrust -dip-slip normal -strike-slip -oblique (See Keller pg 174)
300
Which type of volcano produces highly explosive eruptions that tend to have a dangerous combination of pyroclastic debris and lava flows?
Stratovolcanoes, also known as composite volcanoes tend to have this type of eruption.
400
What does the principle of Uniformitarianism tell us about hazardous earth processes?
The Principle of Uniformitarianism says that earth processes have worked in essentially the same ways since Earth reached its modern form (about 4.6 billion years ago). So, the conditions and types of environments that lead to hazards today also did so in the past. These locations may not have been in the same place due to plate tectonics but the types of locations have been consistent. The frequency of events at a given location may change in response to changing conditions. (See Keller page 24)
400
Describe 3 pieces of evidence that support the hypothesis that an asteroid impact occured 65 million years ago, extinguishing the dinosaurs.
Some evidence you could name includes: -the layer of irridum rich sediments at the stratographic K-T boundary -The sea floor imaging and other geologic evidence of a large crater in the Yucatan -cenotes (a ring of lakes) int he Yucatan -The sudden dissapearance of the dinosaurs from the fossil record 65 million years ago -The loss of many plant species suggesting a halt in photosynthesis 65 million years ago -The sudden proliferation of mammals in the fossil record after 65 million years ago (See Keller page 368-373)
400
Why do volcanoes and volcanic islands appear in a line parallel to a convergent boundary but on the opposite side of the boundary from the subducting plate?
As the subducting plate is pulled under, it melts back into the mantle. This melted magma plus the water in the rock melts a little of the over-riding plate. Together, the magmas travel to the surface and produce a line of volcanoes or volcanic islands on the side of the over-riding plate. (See Keller pg 45)
400
Why is the P-S separation time important?
P waves travel faster than S waves so the farther away from the epicenter, the more separation time between the two types of waves. Because the speed difference is relatively constant, the separation times can be used to determine how far away a seismic measuring center is from the epicenter. With three seismograms the epicenter can be located.
400
Describe the type of location likely to produce each kind of magma: -Felsic rhyolites -Intermediate andesites -Mafic basalts
-Rhyolites are produced in locations where the magma is mostly continental in origin. They are high in silica and feldspar. An example in the US would be the Yellowstone area. -Andesites hav an intermediate composition because the magma is partly melted continental crust and partly melted oceanic crust. These occur at subduction boundaries where an oceanic plate subducts a continental plate. -Mafic rocks are produced at oceanic hotspots and divergent boundaries in oceanic plates. They are high in heavy metallic components such as iron and magnesium.
500
Differentiate between a disaster and a catastrophe. How does population partially determine if a hazardous event is a disaster or catastrophe?
Disasters are hazardous events that cause damages or loss of life while catastrophes are disasters that cause extensive damages and require a long recovery period. As population in an area increases the chance that a hazardous event will be a catastrophe increases because more people can be affected at once.
500
Most craters are not very obvious because vegetation or later geologic events have hidden them. Describe some of the characteristics in the rock record that might indicate a crater forming impact.
Some geologic clues indicating the presence of a crater include: -shocked rocks (melted and rearranged by the pressure of an impact) -melt lenses -fallback ejecta -faults around the edge where material slumped into the crater -broken rock filling a wide basin (see Keller page 364-365)
500
Give at least three examples of evidence that supports the theory of plate tectonics.
-Paleomagnetism of seafloor rocks show regular, symmetric reversals of Earth's polarity at the time the rocks formed (ie when they were once located at the ridge) -the existence of geologic hot spots -the age of sea floor rocks is symmetric and parallel to the mid-ocean ridges -the occurence of similar or related flora and fauna on different continents that are on opposite sides of a divergent boundary -the occurence of geologic strata that are similar in type and sequence on opposite sides (different continents) of divergent boundaries -landforms and continent shapes from opposite sides of divergent boundaries that appear to match as if they were once contiguous (See Keller pg 51-60)
500
What is the seismic gap theory?
The seismic gap theory says that earthquakes happen along sections of faults that have not moved as much as other sections in recent times. In a sense, the section has a gap in motion. Once the earthquake does occur, that section tends to experience numerous earthquakes that fill in the gap. This theory is controversial because there are very few faults with frequent earthquakes and a record of recording earthquakes at different locations to test the theory upon.
500
What are the four types of volcanoes and why do we have different types?
Stratovolcanoes (composite) volcanic dome complexes cinder cones shield volcanoes Volcanoes form in different shapes and sizes because the material ejected at the vent varies depending on the location of the volcano. Lava viscosity, relative amount of water and steam, lava, and pyroclastic debris, and the size of individual flows all affect the final shape and size of the volcano.
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