Lab 1 Exercises

Activity I: Plate Boundary Characteristics

In this activity, you will learn to identify types of plate boundaries based on the characteristics that they exhibit. This activity is based on the “Discovering Plate Boundaries” activity by Dale S. Sawyer at Rice University and has been modified based on teaching experiences in the Department of Earth and Environmental Sciences at Mount Royal University, Canada.

In groups, we will examine five types of plate boundaries today:

• • Ocean-Ocean Divergent (the boundary between two plates where oceanic crust is being pulled apart)
  • Ocean-Ocean Convergent (where two plates of oceanic crust are moving toward one another leading to the subduction of one plate)
  • Ocean-Continent Convergent (where oceanic and continental crust are moving toward one another leading to the subduction of the oceanic crust)
  • Continent-Continent Convergent (where two plates of continental crust are moving toward one another)
  • Ocean-Ocean Transform (where oceanic crust is moving horizontally in opposite directions across a transform fault)

To start, examine the plate boundaries map. Seven plate boundaries are highlighted and numbered on your map. You will also be assigned a paper copy of map displaying one of four data sets: volcanoes, earthquakes, topography/bathymetry, and seafloor age.

You will each, individually, study your data set and attempt to draw conclusions about what geological features and processes characterize each of the numbered plate boundaries.

Later in lab today, you will gather in small groups to share your observations with your groupmates. You will be asked to summarize your observations, so write down your conclusions and be prepared to teach your peers!

Step 1

Examine your assigned map.  Start by locating all the numbered plate boundaries on your assigned map. Are they easy or difficult to find? Looking closely at your data type, start making notes about the spatial distribution of the data points. Exactly what you look for will vary with data type. For the point data (volcanoes and earthquakes) you are looking for distribution patterns. For surface data (topography and seafloor age) you are looking for where the surface is high and where it is low, where it is old and where it is young. In this activity you are focusing on observations, not interpretations, meaning that you do not need to worry about why there is or is not a pattern, you just need to observe and record what you see. You are analyzing the data, not interpreting them!

Step 2

Now focus your attention on the numbered plate boundaries on the plate boundaries map. Identify the nature of your data near each of the numbered plate boundaries. Is it high or low, symmetric or asymmetric, missing or not missing, varying along the boundary or constant along the boundary, etc. Complete Table 1.1 below to classify the plate boundaries based on your observations of your assigned data, using the tips below for guidance. Right now, you will only fill in the column for your assigned data set. Remember: do not try to explain the data; just observe!

Below are some suggestions for the kinds of observations that are useful for each data set. Compare your boundary to the types of boundaries on the map as you do this. Remember, the goal is to find unique characteristics for each boundary type.

Volcanoes: Observe and make notes on the distribution patterns. Are the volcanoes near a given boundary randomly distributed, tightly clustered, or do they define a linear trend?

Earthquakes: Observe and make notes on the distribution patterns and depth of the earthquakes. Note both the range of depths (extremes) and the more typical or average. For example, a given boundary might have all shallow earthquakes (0- 33 km) with rare deeper earthquakes between 33 -70 km depth. Earthquakes might be randomly distributed, tightly clustered, or may define a linear trend.

Topography/bathymetry: Look for any topographic features that seem to be related to the boundary, such as nearby mountain chains, deep sea trenches, broad gradual highs or lows, offset (broken and shifted) features, etc. Briefly describe how extreme they are (e.g., a very high or wide mountain chain). Make sure that you understand how the colour scale on the map represents elevations above sea level. For example, your should recognize that bright fuchsia colours correspond to large negative values and represent the deepest parts of ocean where the seafloor is far beneath sea level.

Seafloor age: This data set can be tricky; be careful not to see patterns where there are none! For example, you might observe that in some places, the seafloor age changes from place to place along the boundary. In this case, there is no clear pattern, and this indicates no relationship between seafloor age and the boundary (though this is still a good observation!). Alternately, the seafloor age may be the same everywhere along the boundary, or it may change in a consistent pattern. Do your best to describe what you see, and whether or not your observations fit a clear, consistent pattern.

Step 3

Everyone has been randomly assigned to a group (the number on the map that you were given is your group number). You will now meet with other classmates with the same group number to discuss your observations in real time. Each group has at least one representative of each data set. Consider yourselves a group of experts gathering to compare observations. In your group, introduce yourself and summarize type of data you have been analyzing. Taking turns, each group member will share their observations about their assigned data set from Step 2. Your instructor will periodically stop by each group meeting to check in while you complete this part of the activity.

Work together in your group to complete Table 1.1 by summarizing your observations on the characteristics of each type of plate boundary. By the end of this activity, each member of your group should have a completed Table 1.1. Each group member should be able to describe the characteristics of each type of plate boundary using all four data types.

Activity II: Hot Spot Volcanoes and Plate Motion

In 1963, J. Tuzo Wilson of the University of Toronto proposed the idea of a mantle plume or hot spot—a place where hot mantle material rises in a stationary and semi-permanent plume, and affects the overlying crust. He based this hypothesis partly on the distribution of the Hawaiian and Emperor Seamount island chains in the Pacific Ocean (Figure 1.1). The volcanic rock making up these islands gets progressively younger toward the southeast, culminating with the island of Hawaii itself, which consists of rock that is almost all younger than 1 Ma. Wilson suggested that a stationary plume of hot upwelling mantle material is the source of the Hawaiian volcanism, and that the ocean crust of the Pacific Plate is moving toward the northwest over this hot spot.

In addition to his contributions on mantle plumes and plate motion, Wilson also introduced the idea that the crust can be divided into a series of rigid plates in a 1965 paper, and thus he is responsible for the term plate tectonics.

Practice Exercise 1.1 Volcanoes and the Rate of Plate Motion

The Hawaiian and Emperor volcanoes shown in Figure 1.1 are listed in the table below along with their ages and their distances from the centre of the mantle plume under Hawaii (the Big Island).

Ages of Hawaiian and Emperor volcanoes and their distances from the centre of the mantle plume. Calculate their rate of movement in centimetres per year. 

Island	Age	Distance	Rate
Hawaii	0 Ma	0 km	–
Necker	10.3 Ma	1,058 km	10.2 cm/y
Midway	27.7 Ma	2,432 km
Koko	48.1 Ma	3,758 km
Suiko	64.7 Ma	4,860 km

Plot the data on Figure 1.2, and use the numbers in the table to estimate the rates of plate motion for the Pacific Plate in cm/year. (The first two are plotted for you.)

There is evidence of many such mantle plumes around the world (Figure 1.3). Most are within the ocean basins—including places like Hawaii, Iceland, and the Galapagos Islands—but some are under continents. One example is the Yellowstone hot spot in the west-central United States, and another is the one responsible for the Anahim Volcanic Belt in central British Columbia. It is evident that mantle plumes are very long-lived phenomena, lasting for at least tens of millions of years, possibly for hundreds of millions of years in some cases.

In this activity, you will use data from chains of hot spot volcanoes to make a rough estimate of the rate of motion of the Pacific Plate, and to determine the direction of plate motion for several different tectonic plates. This activity and the data provided are based on the “Determining Plate Rates From Hot Spot Tracks Using Google Earth” activity developed by Susan Schwartz and Erin Todd at the University of California-Santa Cruz.

Examine the map with the Hawaii-Emperor seamount chain data that your instructor provided you with. Each place marker on each map indicates a location where a volcanic rock was sampled and dated. This type of dating uses radioactive elements in the rock to give geologists a precise age of when the lava cooled and solidified to form a volcanic rock. The number next to each place marker is the age of the rock in millions of years (Ma). The current location of the hot spot at Kilauea Volcano in southeast Hawaii is shown by the marker labeled 0 Ma.

Hot Spot Volcanoes and Plate Motion Exercise Questions

1. Using your ruler, measure the distance between the present location of the hot spot at Kilauea Volcano and Midway Island in kilometres (these locations are marked with blue points on the map). Measure the distance as a line from the centre of each point and round to the nearest whole km. (hint: you may need a calculator to convert between the measurement you get from your ruler and the true distance – consider the map scale!)

2. Make a rough estimate of the average rate of motion for the Pacific Plate in kilometres per million years. To do this, divide the distance between two volcanoes along the chain by their difference in ages (shown in millions of years, Ma). The rate is calculated as the distance over time. Round to the nearest tenth.

3. Most plate rates reported in scientific literature are measured in cm/yr. Convert your estimated rate to cm/yr. Again, round your result to the nearest tenth. Remember this calculation is a rough estimate!

4. Examine the entire length of the Hawaii-Emperor chain. What do you think might have caused this chain to form such a distinctive “elbow-like” shape?

Examine the other map that you were provided by your instructor (this is the “hot spot volcanism” map). Notice that this map includes the locations of boundaries between tectonic plates, as well as place markers and ages for volcanoes along several hot spot chains (or tracks) in various parts of the world.

5. Based on the hot spot tracks shown on the map and the ages of the volcanoes, determine the direction of plate motion for the African, Nazca, North American, and Pacific plates. Match the plate name to the arrow that most closely illustrates the vector (direction) of motion.

6. Predict whether the plate boundary between the following pairs of plates is convergent or divergent based on the plate motion determined from the hot spot tracks:

a) Pacific & Nazca Plates

b) South American & African Plates

Media Attributions

• Maps of plate boundaries, topography/bathymetry, seismology, volcanology, seafloor age by Dale S. Sawyer, Discovering Plate Boundaries activity. All rights reserved. Used with permission.
• Figure 1.1: “Hawaii Hotspot” by National Geophysical Data Center. Adapted by Steven Earle. Public domain.
• Figure 1.3: “Hotspots” by Ingo Wölbern. Public domain.
• Google Earth kmz file by Susan Schwartz and Erin Todd, CC-BY-NC-SA 3.0
• Determining Plate Rates From Hot Spot Tracks Using Google Earth activity by Benjamin Daniels, CC-BY-NC-SA 4.0. Derivative of Determining Plate Rates From Hot Spot Tracks Using Google Earth activity by Siobhan McGoldrick, CC-BY-NC-SA 4.0 and Student Handout for Plate Rate Assignment by Susan Schwartz and Erin Todd, Determining Plate Rates From Hot Spot Tracks Using Google Earth activity, CC-BY-NC-SA 3.0
• Arrow figure, adapted by Siobhan McGoldrick, CC-BY-NC-SA 4.0. Derivative of figure by Susan Schwartz and Erin Todd, Determining Plate Rates From Hot Spot Tracks Using Google Earth activity, CC-BY-NC-SA 3.0