Lab 3 – Plate Tectonics and the Seafloor
Instructor Guide

In this activity, students will use bathymetry and OOI earthquake data to explore the relationship between plate interactions and bathymetric features on the seafloor. Students should come away from this having used real data to make interpretations for themselves about what earthquakes tell us about the seafloor, as well as the potential hazards that are associated with these processes.

The exercise consists of three activities that will lead students from simple observations to plate tectonic interpretations to hypothesizing about potential hazards.

Approximate time involved: Activity 1 – 15-20 minutes, Activity 2 – 20 minutes, Activity 3 – 25 minutes.

Video Introduction to Lab 3

Learning outcomes

  • LO1. Students will identify seafloor features and their relationships using earthquake data.
  • LO2. Students will successfully determine plate tectonic settings by connecting real-world relationships to background knowledge.
  • LO3. Students will be able to articulate some of the challenges that are faced when data does not fit simple models.
  • LO4. Students will successfully identify a reasonable hypothesis for the potential natural hazards in the studied area.
Learning outcome Activity 1 Activity 2 Activity 3
Outcome 1 Introduced  and guided practice Guided practice Guided practice
Outcome 2 Applied
Outcome 3 Guided practice, Applied Applied
Outcome 4 Guided practice Guided practice

Materials needed

computer

Lab 3 Student Answer Form v2.0

What students should know before this activity

  • Students should have some basic map reading skills (Data skill preparation: Lab 1.2 and Lab 1.3) and be familiar with using widgets. Widget use could be introduced as part of the lab exercise.
  • Students should be familiar with general plate tectonic processes as well as 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.).
  • Students should be familiar with ocean basin bathymetric features.
  • Students should know the basic cause and process of earthquake formation and the relationship between tsunami formation and earthquakes.

What instructors should know before this activity

Instructors should cover plate tectonics (plate boundaries, plate interactions, topographic fetures related to plates) and seafloor features (Continental shelf, slope, and rise, trenches, seamounts, volcanoes, mountains, mid-ocean ridges, and faults) in a lecture or enganging exercise prior to this lab.

  • As the instructor you should understand and be familiar with the basics of plate tectonics, how seafloor features are related to tectonic processes, and the relationship between earthquakes and plate tectonics.
  • You should also understand the cause of earthquakes and how earthquakes are able to generate tsunamis.
  • Please review the introduction material in the student activity – It is important that you read through the same materials that the students will be using and that give a summary of basic plate tectonic, earthquake, and tsunami concepts.
  • Related to the students, it is important to give time to the students to explore the widgets on their own before guiding them. After introducing them to the widget, let them experiment a bit.

Scientific 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 thus broken into sections called tectonic plates, much like the thin shell of an egg is brittle and can be broken. These plates float on top of a more fluid, but still solid, layer called the asthenosphere.  The plates of the lithosphere ride on top of the asthenosphere and move due to convection within the earth. These plates move relative to each other, sometimes colliding (forming deep-sea trenches, mountains, and explosive volcanoes), sometimes pulling apart (forming rift valleys and mid-ocean ridges), and sometimes sliding past each other (forming strike/slip faults and transform zones between mid-ocean ridge segments).These interactions are directly related to many of the features that we find on the seafloor, such as volcanic seamounts, mid-ocean ridges, transform and fracture zones, and deep-sea trenches.

Image of egg shell broken as an analogy for plates on the earth and 2 images of earth with lines representing tectonic plates.Much like the shell of the egg in this image, the outer layer of the earth, or lithosphere, is a brittle layer that is broken into section. These sections are called tectonic plates (image copyright: Benjamin R. Jordan, used with permission; Earth images Google Earth 2021.
Image of egg shell broken as an analogy for plates on the earth and 2 images of earth with lines representing tectonic plates.
Image of egg shell broken as an analogy for plates on the earth and 2 images of earth with lines representing tectonic plates.
The lithosphere is the outermost layer of the earth. It sits on another, softer (but still solid) layer, called the asthenosphere. Although solid, the rocks within the earth still move in slow convection cycles. This movement is directly connected to the movement of the lithosphere’s tectonic plates (image copyright: Benjamin R. Jordan, used with permission).
The lithosphere is the outermost layer of the earth. It sits on another, softer (but still solid) layer, called the asthenosphere. Although solid, the rocks within the earth still move in slow convection cycles. This movement is directly connected to the movement of the lithosphere’s tectonic plates (image copyright: Benjamin R. Jordan, used with permission).
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.
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.
Ocean map with divergent plate boundaries identified .
Ocean map with divergent plate boundaries identified .
Diagram of subduction zone of Nazca plate subducting under the South American Plate resulting in a trench between the plates off the west coast of South America and the Andes mountains along the west coast of South America.
Diagram of subduction zone of Nazca plate subducting under the South American Plate resulting in a trench between the plates off the west coast of South America and the Andes mountains along the west coast of South America.

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. By examining the size and location of earthquakes, we learn something about the behavior of tectonic plates.  For example, the deepest earthquakes occur in convergent settings, where one plate subducts beneath another. If, as part of the earthquake, the seafloor is disturbed, either by direct movement of the seafloor or by the generation of an underwater landslide, the energy from this disturbance can be transferred to the ocean itself, forming a tsunami.  Thus, areas of active plate interactions within the ocean present a significant natural disaster hazard.

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.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 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.
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.
A tsunami wave moves radially out from its source, much like the ripples from a rock tossed into a pond.  A tsunami usually consists of multiple waves, not just one.  In fact, the largest wave of a tsunami is often NOT the first one that reaches land
A tsunami wave moves radially out from its source, much like the ripples from a rock tossed into a pond.  A tsunami usually consists of multiple waves, not just one.  In fact, the largest wave of a tsunami is often NOT the first one that reaches land
Once a tsunami wave reaches shore, it can arrive as a massive surge of water, several meters high.  The bottom, center image denotes the height of the tsunami wave that is shown in the other two images.  This wave hit Hilo, Hawaii in 1946
Once a tsunami wave reaches shore, it can arrive as a massive surge of water, several meters high.  The bottom, center image denotes the height of the tsunami wave that is shown in the other two images.  This wave hit Hilo, Hawaii in 1946

A tsunami wave moves radially out from its source, much like the ripples from a rock tossed into a pond. A tsunami usually consists of multiple waves, not just one. In fact, the largest wave of a tsunami is often NOT the first one that reaches land. Once a tsunami wave reaches shore, it can arrive as a massive surge of water, several meters high.

 

Teaching notes

In addition to a basic understanding of plate tectonic theory, students should know the basic, physical layers of the earth and their characteristics (lithosphere, asthenosphere, mesosphere, outer core, inner core). It might also be helpful to familiarize students with the basic concept of earthquakes and their causes (see the Invitation section below). If you are going to have the students work through all of the steps or activities, then it would be helpful to the students to also know of the connection between earthquakes and tsunamis, and to be familiar with the concept of a natural hazard. They should also know what it means to form a hypothesis.

Optional pre-lab activities:

  • Prior to the start of the exercise, ask students to briefly discuss if they know about plate tectonics. Review with them the three basic types of plate boundaries (convergent, divergent, and transform) and what are the typical features associated with each type of boundary.
  • Show students a global map of plate boundaries. Discuss the impacts that plate movement and interactions can have on human populations and the natural environment.
  • Data skill preparation: Lab 1.2 and Lab 1.3

Intro page 3.0:

This exercise can be used for both introductory and upper-level oceanography (or geology) courses. It is set up as a series of steps in which students can progress as far as you want to guide them. However, it is presumed that students who use this exercise have, at a minimum, been introduced to the basic concepts of plate tectonics, including plate boundaries and interactions. The introduction to this lab reviews the basics of plate tectonics but is not meant to replace lecture on these topics.

  • Block models can be used to demonstrate plate boundary interactions and earthquake formation.
  • YouTube videos describing plate tectonics and plate boundary processes can also be shown. Bozeman Science Plate Tectonics is a good overview for the topic.

Activity 3.1:

In this lab activity, students will first observe and label features on the seafloor. It is important that the students understand plate tectonics and seafloor features prior to this activity.

  • Prior to the start of the exercise, ask students to briefly discuss with a partner, or in a small group, what they know about plate tectonics.  After giving them a short time do this, lead a whole group review of the three basic types of plate boundaries (convergent, divergent, and transform) and the typical features associated with each type of boundary.

Activity 3.2:

The first portion of this exercise asks students to explore the location where data in this exercise were collected.  Zoom in and out of the map to develop familiarity with the highlighted feature, as well as nearby features. In this activity students will overlay earthquake location data and relate that data to the features they observed and labeled. Using the relationship between the topography and earthquake data, students will determine the various plate boundaries and types. The students should be able to independently identify the divergent boundaries (mid-ocean ridge) and transform zone and identify the subduction zone, which does not have a distinctive trench, making it a challenge to identify the process of subduction. Students, with your guidance, should be able to determine the subduction zone based on the depth of the earthquakes.

This is a good place to introduce the relationship between plate movement and earthquake formation by demonstrating the breaking of a wooden pencil (the hexagonal kind, not the round kind).  As you slowly bend the pencil, talk about how energy is built up within the pencil (and lithosphere) as force is applied.  Have the students listen quietly as you slowly bend the pencil.  There should be some small cracking sounds before the pencil completely breaks.  Ask the students what they think is happening to cause the sounds (correct answer: bonds breaking within the pencil).  Finally, bend the pencil enough to break it completely.  Explain to the students this break is a “pencil quake” and that earthquakes occur in the same way, as plate tectonic forces store energy in the earth’s lithosphere until the rocks break, causing an earthquake.  This exercise can be done at any time during the exercise – wherever you think it would be most appropriate.

Activity 3.3:

Lastly, in thinking about the subduction zone, the comparatively limited number of earthquakes, and what happened in the Tohoku region of Japan in 2011, students will hypothesize about the earthquake and tsunami hazards that potentially exist in the area discussed in this exercise (spoiler: they are significant).

  • Using Google Earth, show the students the area around Japan, including the Japanese Trench, and then remind the students of the events related to the 2011 Tohoku Earthquake and Tsunami.  If not already seen, show the students footage of the tsunami (Recommended Video: Japan Tsunami 3/11/2011 shows real footage of the tsunami
  • Ask the students, what is the potential for such an event occurring in the area that they have explored?  What plate tectonic similarities exist between Japan and the Pacific Northwest?  What does the earthquake data indicate about the build-up of tectonic energy (refer back to the breaking pencil demonstration)?
  • Ask students whether residents in the Pacific Northwest should be worried?  What additional data might be helpful to clarify the potential threat (data such as occurrence interval (link 1and link 2) vs the length of the record from the USGS and OOI)?  Why does it matter?
  • Explain to the students that this exercise will introduce to them the type of information that can help them to determine if a similar event has the potential to occur at other locations.
  • Ask the students what they would need to know in order to determine if a similar hazard exists at another location.  Have them write down these ideas. (ANSWER: Three very important things are: volcanoes, earthquakes, and a trench – be aware that the Pacific Northwest has the volcanoes and earthquakes, but not the trench due to the fact that the Juan de Fuca Plate is subducting at a very shallow angle.  It is important to help the students to recognize subduction without the obvious presence of a trench).

Extensions:

  • Continue to LAB 4 – Sea Floor changes in a volvanically active setting.
  • Talkabout the Boxing Day 12/26/2004 Tsunami in Indonesia
  • Show students a global map of plate boundaries and have them discuss with a partner, or in a small group, what they think are the impacts that plate movement and interactions can have on human populations and the natural environment.  Lead a whole group discussion afterwards, of their ideas and add information and clarification as needed.
  • After showing the following video to the students, you might do the following:
    • Video: https://www.newsflare.com/video/118479/other/57-magnitude-earthquake-underwater (if that page doesn’t work, here is a YouTube version: https://www.youtube.com/watch?v=V-KA_3nAi94).  This is a video of the impacts of an earthquake underwater.  The video was taken by Jan Paul Rodriguez in the Mabini (Batangas Province), Philippines in early April 2017.  The magnitude of the earthquake was 5.7.
      • Ask the students to describe their observations.  What might have caused the motion of disturbance of the water? (Answer: an earthquake)
      • What might have caused the earthquake? (Answer: movement along a fault and breaking of rock).
      • Ask them to discuss the impacts the motion of the seafloor might have on the shape of the seafloor, marine organisms, and/or coastal areas.  What predictions can you make about the impacts from an even larger earthquake?
  • You could also show them this video of the tsunami impacts on Crescent City, California
  • Real-world application: https://www.dnr.wa.gov/programs-and-services/geology/geologic-hazards/Tsunamis.
  • Compare the area of this exercise with other areas of the world using Google Earth.  Ask the students if they know of or have experienced earthquakes for a given location.  What was the experience like?  Where was it?  How was the area similar to the one in the data exploration?
  • For more advanced students, an emphasis on earthquake patterning in time vs space is recommended.  Discussions could revolve around:
    • Having the students calculate earthquake recurrence intervals for various ranges of earthquakes.
    • Focusing on larger clusters of earthquakes and the features that they may be associated with.
    • Why does the subduction of the plate beneath Japan form a much deeper trench than the subduction beneath the Pacific Northwest?  Students can calculate distance (and age) between the subduction zones and the mid-ocean ridge.

Advanced Extensions

  • For an advanced-beginner to intermediate try OOI Data Exploration: Exploring Tectonics & Seamounts with OOI Data
  • For advanced extensions see OOI Data nugget: 2015 AXIAL SEAMOUNT ERUPTION. The Data Nuggets are curated data sets and visualizations from OOI and include direct access to the underlying data as well as Python notebooks for producing the visualizations. They are particularly suited for an advanced application in an introductory class or for an upper-level oceanography course.

Post-lab Questions for Reflection

  • Have the students reflect and think about what they have learned.  Ask questions like:
    • Do you think any differently now about the relationship between features on the seafloor and plate tectonics?
    • How about between earthquakes and seafloor features?
    • Why do we care about collecting the type of data used in this exercise?
    • What is the potential for such an event occurring in the area that they have explored?
    • What plate tectonic similarities and differences exist between Japan and the Pacific Northwest?
    • Describe what the earthquake data indicates about the buildup of tectonic energy.
    • What are the limits to what the data does or doesn’t tell us?
    • What additional data would be useful to have?
  • Ask the students to consider how the knowledge that they have gained in this exercise applies to them.  In what ways?
    • What specific skills did they gain or find useful in the exercise?
    • How else might those skills be applied in their lives?
    • Was there anything that they found new or surprising?
    • What was difficult or challenging about this exercise?
    • What additional information would have made things clearer or more understandable.
  • What is the value of monitoring earthquakes on the seafloor?
  • How might such information help individuals and communities?

Associated resources

Additional Resources