Determining the Rate of Plate Motion
Adapted from: http://www.ontariogeoscience.net/lessonplans/hot-spots.html
Objectives:
 Calculate the rate and direction of motion.
 Describe features formed by gradual changes such as plate tectonics.
Background:
Mantle hot spots are areas where magma burns a hole through the crust in the middle of a
tectonic plate. Volcanoes form above the hot spot. The interesting thing is that volcanoes
formed by hot spots appear to move. It is actually the plate that is moving, as the hot spot
remains fairly stationary. As the plate slowly moves across the mantle hot spot, a plume of
magma melts it and creates a chain of volcanic islands or seamounts; a volcano that does not
break the surface of the water.
Scientists are able to determine the velocity and direction of plate motion by using the age of the
volcanic islands and comparing it to the location of the mantle hot spot. Over time, scientists
are able to gather a lot of information about plate motion. One of the best examples of this
phenomenon is the Hawaiian Islands.
Procedure:
1. Observe the demonstration by your teacher. This demonstration illustrates how the
Hawaiian Islands formed over a mantle hot spot located beneath the Pacific Plate.
2. Construct a distance/time line graph of the ages (time) and locations (distance) of
the Hawaii-Emperor Volcanic Islands. The data is shown in the table below.
Island / Seamount
Age
(millions of years = my)
Hawaii
Maui
Molokai
Oahu
Niihau
Nihoa
Necker
Midway
Kanmu
Suiko
Meiji
0
0.84
1.48
2.55
3.0
3.5
9.5
17.9
37.5
41.8
67.0
Distance from Hawaii
Island Along Chain
(kilometers=km)
0
200
320
400
680
920
1200
2800
4000
6000
7400
Analysis Questions:
Using the map…
1. Under which island/seamount is the mantle hot spot located today?
2. Look at the shape of the Hawaiian-Emperor Volcanic Islands chain.
What does its shape tell you about the direction of Pacific Plate movement?
Has the plate been traveling in the same direction? If not, about when did it change
direction?
3. Where would you expect to find increased volcanic activity?
4. On the map, mark an “X” to predict the location of the next Hawaiian Island.
Using your graph and the table…….
5. Calculate the average velocity of the Pacific Plate by using the distance and time for
Meijii. (Remember that velocity is speed with direction.)
_____________
Now find the velocities between:
Hawaii and Midway _____________
Kanmu and Meijii
_____________
6. Has the velocity of the Pacific Plate remained constant over geologic time?
What information from the graph supports your answer?
7. Is the motion of the Pacific Plate speeding up or slowing down?
8. What would the graph look like if the motion of the Pacific Plate stopped? (Sketch a
dashed line from Meijii to show what the graph would look like.)
Age (my)
Distance (km)