Determining the Rate of Plate Motion

Adapted from:

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-EmperorVolcanicIslands. The data is shown in the table below.

Island / Seamount / Age
(millions of years =my) / Distance from Hawaii Island Along Chain
(kilometers=km)
Hawaii / 0 / 0
Maui / 0.84 / 200
Molokai / 1.48 / 320
Oahu / 2.55 / 400
Niihau / 3.0 / 680
Nihoa / 3.5 / 920
Necker / 9.5 / 1200
Midway / 17.9 / 2800
Kanmu / 37.5 / 4000
Suiko / 41.8 / 6000
Meiji / 67.0 / 7400


Analysis Questions:

Using the map…

  1. Under which island/seamount is the mantle hot spot located today?
  1. Look at the shape of the Hawaiian-EmperorVolcanicIslands 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?

  1. Where would you expect to find increased volcanic activity?
  1. On the map, mark an “X” to predict the location of the next HawaiianIsland.

Using your graph and the table…….

  1. 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______

  1. Has the velocity of the Pacific Plate remained constant over geologic time?

What information from the graph supports your answer?

  1. Is the motion of the Pacific Plate speeding up or slowing down?
  1. 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.)