Graphical Determination of the Rate of Plate Motion (Grades 9-12)

The diagram for this activity is a plot of "Distance from Kilauea" (the approximate location of the hot spot) versus "Age (Ma, millions of years)" of selected islands and seamounts. Directions for the activity are provided on the diagram. Note that the answer will vary with the best-fit line drawn by the student. A reasonable answer is 12-13 cm/yr. The conversion from km/Ma to cm/yr is given in activity 2. According to the rate the student determines, the plate will move about 6-7 m in 50 years. This rate differs differs slightly from the rate (11 cm/yr) in the previous activity. Ask your students for possible explanations. The methods used to determine the rates are different. This exercise is an average over the entire length of the volcanic chain. In activity 3 the rate was based on a single data point. The different rates also suggest that the rate of plate motion is not constant.

The age of the islands and seamounts increases with distance away from the Hawaiian hot spot. This activity determines the average rate that the Pacific Plate has moved over the last 65 million years.

Seamount or
Island		     Distance (km)	       Age
------               -------------             ---
Suiko			 4,860			65
Koko			 3,758			48
Midway 			 2,432			28
Necker			 1,058  	     	10
Kauai			   519			 5
  1. Plot the data on the graph.
  2. Draw a best-fit line through the data points.
  3. Determine the slope of the line. The slope is equal to the rate of plate motion.
  4. Convert your answer from kilometers/million years to centimeters per year.
  5. How far does the plate move in 50 years?

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