## The Rate of Plate Motion (Grades 7-8)

This activity includes a map showing the location of the main islands of Hawaii. The directions provide the age of one island (Niihau) and a series of steps to help determine the rate at which the Pacific Plate has been moving over the Hawaiian hot spot. Rate is distance divided by time. Distance is the number of kilometers from the hot spot (beneath southeast Hawaii) to an island. Use the map scale to estimate distance.

The rate will be in the units of kilometers (km) per million years (Ma). Geologists report the rate of plate motions in centimeters (cm) per year. To convert the rate to cm/yr, follow this conversion:
km 1000 m 100 cm 1 Ma cm
-- X ------ X ------ X --------------- = ----
Ma km 1 m 1,000,000 years year

The rate is 11 cm/year using the distance to and age of Niihau.

To determine how far the plate moves in 50 years multiply the rate by 50. The plate will move 550 cm or 5.5 m in 50 years. Compare this distance to something familiar, e.g., the length of your classroom.

**Directions:**
Use the map and the following information to determine the rate of motion of the Pacific Plate over the Hawaiian hot spot.

The volcano that formed the Island of Niihau is 4.89 million years old.

**Step 1**

Rate is the distance traveled over a period of time. The distance traveled is equal to the distance from the present location of the hotspot (southeast Hawaii) to Niihau. Time is the age of the island.Start by measuring the distance from southeast Hawaii to Niihau.Use the scale on the map.
**Step 2**

To determine the average rate of motion for the Pacific Plate, divide the distance to Niihau by the age of the island.
**Step 3**

Note that your rate is in kilometers/million years (km/Ma). Convert your answer to centimeters per year (cm/yr).
**Step 4**

How far will the plate move in 50 years?