Angle of repose unconsolidated sediment figure 1 the

Info icon This preview shows pages 100–103. Sign up to view the full content.

View Full Document Right Arrow Icon
Angle of Repose unconsolidated sediment Figure 1 : The angle of repose is the steepest angle a sediment pile can form.
Image of page 100

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Lab #7: Geologic Hazards of Whatcom County 99 II. Earthquakes The origin of an earthquake is call the hypocenter (focus), and the surface point directly above the hypocenter is called the epicenter . Earthquakes are an exceptionally important geologic hazard in the Pacific Northwest since the Juan de Fuca plate subducts beneath the North American plate, resulting in a relatively constant stream of earthquakes. Additionally, as the oceanic lithosphere of the Juan de Fuca plate sinks into the asthenosphere, it compresses from the high pressure and creates deeper earthquakes. Furthermore, the transform boundary of the San Andreas Fault to the south, the extension of the basin-and-range province to the southeast, and the tectonic activity to the northeast all serve to twist and tear the continental crust in the Pacific Northwest. There are many factors that control how much the ground moves during an earthquake. The two most important controls are the amount of energy released from the earthquake ( magnitude ) and the distance from where the rock actually ruptured. Another crucial factor is the rock that seismic waves pass through. Earthquake waves travel differently through different rock types, and looser, less tightly bound rock or sediment slows down the seismic waves. This will increase the amplitude of the waves, which increase shaking and results in greater damage (Fig. 2). In general, sedimentary rock is less dense and less compacted than igneous or metamorphic rock, and unconsolidated sediment is even less dense and structured than sedimentary rock. One of the biggest problems with unconsolidated sediment is the additional hazards of liquefaction , which occurs when saturated sediment is shaken (Fig. 3). Water trapped in pore space rises to the surface, and as it accumulates, the sediment become less stable and flows like a fluid. Figure 2. Collapse of I-880 in San Francisco from the M6.9 Loma Prieta Earthquake in 1989 Figure 3. Liquefaction causes apartment buildings to sink into the ground during an earthquake in Japan, 1964.
Image of page 101
Lab #7: Geologic Hazards of Whatcom County 100 III. Volcanoes The driving mechanism for the vast majority of volcanic eruptions is volcanic gases that are trying to escape from the magma. At depth, these gases are dissolved in the magma. But as the magma rises, the pressure that confines the gases in the magma is reduced ( decompresses ), allowing the gases to form bubbles. As the magma rises, decompression allows more bubbles to form and existing bubbles to expand, which in turn drives the magma to rise and so forth. This positive feedback loop can sometimes lead to an volcanic eruption.
Image of page 102

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 103
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern