Purpose

Students will develop the basic Plate Tectonic model using a constructivist approach. They will acquire data from sites available via the Internet, and plot and interpret these data. Concepts which they will learn during this project include map projections, plotting, 3D visualization via cross-section construction, location and origin of earthquakes and volcanoes, and Earth structure. Ohio Science Model Goal 1: The Nature of Science, Goal 2: The Physical Setting, and Goal 5: Thematic Idea [Earth System].

Proficiency Outcomes

4th Grade Test

1. Create and/or use categories to organize a set of objects, organisms or phenomena.
4. Use a simple key to distinguish between objects.

6th Grade Test

3. Make inferences from observations of phenomena and/or events.
5. Evaluate conclusions based on scientific data.
10. Identify simple patterns in physical phenomena.
11. Describe simple cycles of the earth, sun, and moon.

Materials Needed

  • Large color world map for display, preferably showing topography of ocean floor and continents; latitude/longitude necessary; preferably laminated (for example: World Physical Map, 1:30,000,000 from American Map - ISBN 0-8416-8996-2; The World Physical Map, 1:32,000,000 from Kummerly & Frey - ISBN 3-329-04063-3)
  • Washable markers
  • Computer(s) with Internet link: minimally, need access to one

For Each Student

  • Ruler, pencil (3H), eraser
  • Tracing paper, plain white or graph (metric preferred) paper
  • World map, including topography if possible, and latitude/longitude, on one sheet, less than desk size (for example, Rand McNally Outline Maps of World, 11"x15", has outline map on one side/relief on other; 50 map package $11)

Introduction

Students will each gather data on earthquake and volcanic eruption occurrence worldwide from sites on the Internet. They will plot the earthquake epicenters and active volcanicity locations on world maps. This project can use current events, gathered daily over several weeks or months, and/or make use of archived data available on web sites.

Activities deriving from the tectonic data maps will allow each student to build towards the development of the basic plate model, which include lithospheric structure, plate boundary types and geological characteristics of the plate boundaries.

Background Knowledge

The students will need to learn the following concepts for this project. These form the basis upon which their work will build to a more detailed and complete understanding of their physical world.

1. Locating Events on a Map
Demo: globe and the world map

We define position on Earth’s surface by latitude and longitude. Latitude is measured in degrees north and south of the equator (equator = 0°; north pole = 90° N; south pole = 90°). On a globe, circles drawn parallel to the equator = parallels. We use parallels to measure latitude.

Longitude is measured in degrees east or west of the Prime Meridian (= 0°), chosen to pass through Greenwich, England. Since there are 360° in a circle, longitude is measured from 0° to 180° E of PM, and 0° to 180° W of PM. 180° E and W of PM = International Date Line. On a globe, circles drawn through the N and S poles to determine the longitude of points = meridians.

Map projection is the transfer of position on Earth’s surface (globe) to a 2D map. There are many different map projections. All involve distortion because there is a loss of dimension between a globe and a map. Parallels indicate east - west direction, and on some maps are straight lines; meridians run north - south, and on some maps are straight lines. However, on a world map, such a Cartesian grid (i.e. a rectangular grid) results in increasing distortion as one moves to higher latitudes, and so parallels and meridians are usually curves.

Plotting locations: Each point on Earth’s surface is uniquely defined by its latitude and longitude designations. The earthquake Internet site gives lat./long. locations decimally, to hundredths of a degree. At the scale of the maps used, tell the students to use whole degrees, ignoring the numbers to the right of the decimal point, or, for older students, you can use this exercise for practice rounding to the appropriate whole degree value. To plot, first find the line which represents the latitude of the epicenter, and then move along it to the longitude value of the epicenter (or vice versa).

2. Locating and Quantifying Earthquakes

  • focus = actual location of earthquake; given as depth below a surface location.
  • epicenter = point on surface directly above the focus; latitude/longitude.
  • magnitude = “size” of quake; different methods of quantifying; expressed on a logarithmic scale.

The Richter Magnitude Scale is based on the maximum amplitude of the shear waves recorded at seismograph stations. It is most useful for smaller earthquakes relatively close to the recording station, and so is also called the local magnitude (ML ). For large, more distant quakes, the magnitude is based upon surface wave amplitude (MS ), and for deep-focus quakes, on compressional waves (Mb). The Moment Magnitude Scale (MW ) is based on the size of the source, and give a better estimate of the size of the largest earthquakes. On the Internet site, these symbols are used to indicate the method of determination of the magnitude for each quake. For the purposes of this plotting activity, the method is not important.

Optional Activity: Earthquakes and the Behavior of Earth Materials

3. Volcanoes

  • active = currently is erupting, or geologically recently has erupted.
  • dormant = has not erupted recently but has the geological conditions present which could lead to eruption in the future.
  • extinct = no longer has potential to erupt.

4. Earth Structure and the Basic Plate Tectonic Model

Earth’s layered structure

  • compositional layers: crust, mantle, core. These layers are distinguished from each other on the basis of composition.
  • strength layers: lithosphere, asthenosphere. These layers are distinguished by differences in behavior. The lithosphere, the outermost strength layer, is relatively cool and strong and primarily exhibits brittle behavior. The asthenosphere, below the lithosphere, is hotter and weaker and exhibits ductile behavior.

* Demo

Rock hammer & rock: hit the rock with the hammer (use safety glasses) and break it. This is brittle behavior, like the lithosphere.

Silly putty: pull gently on the silly putty - it stretches without breaking; this is ductile behavior. To show the students that materials are not inherently brittle or ductile, show how silly putty can behave brittlely, by pulling it quickly so it breaks. Likewise, if rocks are put under asthenospheric conditions (higher temperature and confining pressure) they behave ductilely, and flow under applied stress.

Students don’t “like” that the layer boundaries do not coincide, but it is important that they understand that the crust is the upper part of the lithosphere, and that the lower part of the lithosphere is compositionally mantle, i.e. the lithosphere/asthenosphere boundary is at about 100 km depth, while the crust/mantle boundary varies from about 7 km (under the oceans) to a range of about 35 km to about 70 km on the continents.

Lithospheric structure

The lithosphere is broken into a relatively small number of plate-like portions which are in motion relative to the underlying, ductile asthenosphere.

Optional Activity: Plate Tectonics and the Surface of the Earth

Student Project

The students will need to learn the following concepts for this project. These form the basis upon which their work will build to a more detailed and complete understanding of their physical world.

1. Data collection, recording, and plotting.

Students use archived data for a defined period of time, or project can take place over several weeks/months with periodic collection of data. I prefer the latter, so that students experience that science takes place over time with accumulation of observations, and they can think about what the developing data set represents and puzzle out interpretations rather than presenting science as a set of known facts.

Earthquakes (http://geology.usgs.gov/index.shtml): All recorded quakes versus some defined minimum magnitude record data on Earthquake Log (see handout). Plot epicenters (latitude/longitude) on world map.

Volcanoes: (http://volcanoes.usgs.gov/): All reported activity, or some defined minimal activity level record data on Volcano Log (see handout). Plot volcano locations (latitude/longitude) on world map

The display world map can be used to plot selected events; use different color marker for volcanoes and earthquakes; also can indicate focal depth of earthquakes using different colors: eg. shallow: surface to 100 km depth; intermediate: 100 - 200 km; deep: >200 km.

2. Written description of map pattern

After sufficient data have been plotted, students write descriptions of any earthquake and volcano patterns which emerge on their maps. (Curvilinear bands (= possible plate boundaries) will emerge as data accumulate; there will also be “rogue” occurrences in the interior of plates, for earthquakes because there are weaknesses within the lithosphere that quake, although less frequently than at boundaries; and for volcanoes, there are mantle “hotspots” which cause volcanoes at the surface unrelated to plate structure). Students should identify possible plate boundaries based on their plotted data.

Students can prepare a plate boundary overlay of the map: place a piece of tracing paper over the map. Trace map edges or corners so overlay can be easily repositioned. Draw locations of possible plate boundaries as defined by plotted data.

3. Interpretation of plate boundary types

Each student chooses a possible plate boundary, from their map, to interpret.

Construct a cross-section (= vertical section) of the possible boundary, using earthquake depth data and epicenter location, and any volcanic occurrences in the boundary vicinity.

  1. use graph paper if available, otherwise plain white paper
  2. choose a convenient, enlarged with respect to map, scale: horizontal scale = vertical scale
  3. choose the line of section: this will be perpendicular to the selected plate boundary
  4. plot latitude/longitude points along top edge of cross-section

Write a description of the cross-section pattern of earthquakes and volcanoes. Answering the following questions should aid in your interpretation:

  1. Do the earthquake foci define a vertical or a sloping boundary?
  2. What is the maximum foci depth? Is this consistent with a “normal” 100 km thick lithosphere, or does it suggest the occurrence of brittle material at greater than “normal” depth?
  3. Are any volcanoes associated with this boundary? If not, what does that indicate about boundary processes? If so, where are the volcanoes with respect to the earthquake locations? eg. coincident; all to one side? What styles of eruption are associated with this boundary? What do the occurrence of such eruption styles and locations suggest about boundary processes?
  4. What type of motion is indicated for this plate boundary, based on these observations?
    • divergent: plates move away from each other; shallow quakes define vertical zone; basaltic, effusive volcanoes
    • transform: plates move parallel to each other but in opposite directions; shallow quakes define vertical zone; no volcanoes
    • convergent: subduction zone - ocean plate moves under continental or oceanic plate; quakes (all depths) define sloping boundary; andesitic to rhyolitic, often violent, eruptions; collision of two continents - shallow to medium depth quakes in diffuse zone; no volcanoes

Class summary: Ask each student (or groups of students who worked on same boundary) to describe their results. Plot the results on the display map, using different line symbols or colors for the different boundary types. Class discussion of the relationship of topography to plate boundary types. If you have one, show the class a world tectonic map, or pull one up from the internet (available at these earthquake and volcano sites); compare the boundaries the students discovered to the boundaries delineated on the published tectonic map.

Other Activities

  1. Each student choose one earthquake or volcano. Find media reports of human effects of the earthquake/volcano. Give short class presentations.
  2. Extension activities for math skills (thank you to Jamie Sadler, MIST workshop participant, for age-appropriate ideas):
    • Have different groups of students plot different days of world earthquake activity
    • Graph the number of quakes per day for a given period of time, eg. week
    • Compare/contrast quake magnitude by location, eg. different boundary types or boundary vs. not on a boundary

Links

Karen H. Fryer
Professor of Geology