Lab 4 – Plate Tectonics

If you could travel anywhere in the United States, where would you go? Would you visit the dynamic coast of California, with rocky sea cliffs and stunning views? Perhaps you would relax on the broad sandy beaches of the Carolinas, tour beautiful farms in the Midwest, ski the Mountains of Colorado, cruise through fjords in Alaska, or even summit the peaks of volcanoes in the Pacific Northwest. Regardless of where you’d choose to explore, you’d experience the consequences of one of Earth’s most long-standing geological processes–Plate tectonics! Although we owe a debt of gratitude to plate tectonics for shaping some of our favorite places (the West Coast, mountains, and volcanoes), we must also acknowledge the hazardous consequences–earthquakes, tsunamis and volcanic eruptions. In this lab, we explore the relationship between plate tectonics, the dynamic landscapes it shapes, earthquakes, tsunamis, and volcanic eruptions, with a keen eye on one of the most hazard prone areas in the United States–the Pacific Northwest.

[HALEY – Insert Figure Here]

Learning outcomes

  • LO1. Determine plate tectonic boundaries by connecting real-world relationships to background knowledge. 
  • LO2. Correlate earthquakes depths and plate boundaries (Activity 3.2)
  • LO3. Articulate how tsunami waves are generated, and how they are detected to inform early warnings and evacuation orders (Activity 3.3)
  • LO4. Develop an earthquake/tsunami Action Plan (Activity 3.3)

Background information

  • Key terms: earthquake, epicenter, seamount, mid-ocean ridge, transform fault, subduction, tsunami

Data collection sources:

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Locations of the OOI data stations and cabled arrays (left). The red box indicates the location of the cabled array that collected the data in this lab. Map of the OOI cabled array near Oregon and Washington (right)
Map of the OOI cabled Array near Oregon and Washington.
Figure 3.0.2 Locations of the OOI data stations and cabled arrays (left).  The red box indicates the location of the cabled array that collected the data in this lab.  Map of the OOI cabled array near Oregon and Washington (right).

 

Geologic Background

The theory of plate tectonics is the grand, unifying theory of Earth science. The basic idea is that the outermost, physical layer of the Earth, the lithosphere, is brittle and is broken into pieces called tectonic plates, like the broken, brittle egg in the image below.

NOTE: I deleted the egg figure and was asked to add it back. I’m not able to –

Figure 3.0.3 FIX

  • These plates float on a more ductile but still solid layer called the asthenosphere, which behaves similarly to hot plastic, and allows the overriding lithosphere to move very slowly about the surface of the Earth. These plates move relative to each other, pulling away from each other at divergent plate boundaries, pushing towards each other at convergent plate boundaries, or sliding past each other at transform plate boundaries.
  • Tectonic plate interact in three main ways: divergence (away from each other), convergence (colliding into each other), and transform motion (sliding past one another). the black arrows indicate the direction of movement (image copyright: Benjamin R. Jordan, used with permission; right image USGS.

    Figure 3.0.4 Tectonic plates interact in three main ways: divergent, convergent, and transform motion. The black arrows indicate the direction of movement (image copyright: Benjamin R. Jordan, used with permission; right image USGS.

    Some of the most dynamic landscapes on Earth are located at plate boundaries. Here, steep mountains and volcanoes form and waves crash on rocky cliffs, rather than wide, sandy beaches. In addition, most geological activity on Earth occurs at plate boundaries, and the processes occurring here are responsible for causing geological hazards like earthquakes, tsunamis, and volcanic eruptions. As a result, locations far from plate boundaries tend to have flatter topography and fewer geologic hazards.

    Use the widget below to explore some of our favorite places in the United States in the greater context of plate tectonics!

 

  • These interactions between tectonic plates lead to earthquakes as tremendous amounts of energy are built-up and then released, much like energy is built up within a pencil as it is bent. Eventually, the strength of the wood will be overcome by the energy and the pencil will break.
    Image of no stress as pencil, bending pencil as stress, elastic strain and then the pencil broken as no more stress.Graph indicating increasing stress as pencil is bent maximizing stress just before the pencil is broken, and then as the stress is released, the energy is released with an earthquake.

    Figure 3.0.5 Much like bending a pencil will eventually lead to breaking it, Tectonic forces within the lithosphere will lead to the breaking of rock, forming an earthquake (image copyright: Benjamin R. Jordan, used with permission).

    • Image of 6 ocean bottom seismometers (OBS) ( look like metal pan with very high rounded lid with sensos and cables attached) getting ready for deployment on the seafloor.

      Figure 3.0.6 Image of ocean bottom seismometers (OBS) getting ready for deployment on the seafloor.

      Sensors: The OOI cabled array uses many instruments to monitor the Axial Seamount Volcano. These instruments collect data on such things as ocean salinity and ocean chemistry, seawater pressure, as well as changes in hydrothermal vents. For this activity, data was collected by ocean bottom seismometers (OBSs), which detect and monitor earthquake events (see sidebar).

    • Ocean Bottom Seismometers: Seismometers are instruments that detect shaking and vibrations at the surface of, or within, the earth. The farther an earthquake wave travels, the weaker and harder to detect it becomes. OBSs are designed to be placed on the seafloor, close to the areas that are being studied, in order to collect reliable data. They are used throughout the world’s oceans by oceanographers and marine geologists and geophysicists to answer questions about plate tectonic movement, underwater volcanic processes, and the behavior of the deep earth.
    • Other need-to-know scientific background: Students should be familiar with general plate tectonic processes, the types of plate boundaries and the specific geologic features associated with those boundaries (i.e. mid-ocean ridge = divergent boundary, explosive volcanoes and/or deep sea trench = convergent boundary, etc.), the basic cause and process of earthquake formation, and the relationship between tsunami formation and earthquakes.

     

    Activities in this Lab

    Instructor Guide

     

     

    Next LAB 4.1 ⇒

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