How Fast is the Pacific Plate Moving? The Hawaiian Islands are part of a long chain of islands and seamounts (including the Emperor Seamounts) extending into the northern Pacific Ocean where they...

How Fast is the Pacific Plate Moving?

The Hawaiian Islands are part of a long chain of islands and seamounts (including the Emperor Seamounts) extending into the northern Pacific Ocean where they terminate at the Kuril trench. This chain of volcanic islands and seamounts was formed as the Pacific plate moved over a relatively stationary mantle hot spot. The current position of the Hawaiian hotspot is assumed to be under Loihi (sites of active volcanism) on the southeast side of the Big Island of Hawaii.

The volcanoes of this chain become extinct as they moved off the mantle hot spot (carried on the Pacific plate) and get progressively older further away from the location of the hot spot. Review section 4.8 (pp. 112-113) in the text. The rate at which the Pacific plate is moving over the Hawaiian hot spot can be easily estimated from geographic and age data. In this activity, you will calculate the rate of motion of the Pacific plate based on data from islands and seamounts in the chain.

The table includes approximate ages for the islands and seamounts. These age data were obtained by
radioisotope geochronology
(we will talk about this in Chapter 11) that gives the formation age of the basalt flows that formed the volcano on each island/seamount.

You will use Google Earth to measure the distances between different locations along the Hawaiian Ridge and Emperor Seamounts.

1. Download the KML file titled Hawaiian-Emperor Chain.kml from Blackboard to your hard drive. The KML file will be used to find the locations of the islands and seamounts.

2. Open the online version ofGoogle Earth
https://www.google.com/earth/
using the Google Chrome browser.

3. In the left navigation panel, click the “Projects” button (see figure).

4. Click the “New Project” button and select “Import KML file from computer.”

5. Select theKML file from your hard drive.

6. In the left panel, you will find the locations for this exercise. If you click one, it will “fly” you to that location where you can read more about it.

7. Measure the distance in kilometers between each location and insert it in the second column of the table. You can determine the distance using the distance tool in the left navigation panel (see figure).

8. In the third column, insert the cumulative distance to the mantle hotspot. Assume that the hotspot is currently located beneath the submarine volcano Loihi.

9. In the fifth and sixth columns, insert the rate of motion of the Pacific plate in km/year and cm/year from the hotspot, respectively. The rate of motion is simply the distance divided by time — in this case the distance from the hot spot and the age of the island/seamount. Be careful about units – the conversion factor is 1 km = 100,000 cm. Hint: the rates of plate motion should be around 10 cm/year.

Complete the data table and answer the questions.

Conversion factor: 1 km = 1000 m = 100,000 cm

1. What is the average rate of motion of the Pacific plate (cm/year)? (Take the average of the values that you determined.)

2. How far will the island of Hawaii move (relative to the hotspot) in 1 million years (give your answer in km)?

3. How far will the island of Hawaii move (relative to the hotspot) in 10 million years (give your answer in km)?

4. What direction is the Pacific plate currently moving relative to the Hawaiian hotspot? Give a compass direction like N, NW, SE, etc.

5. Why do you think there is a bend in the chain of islands and seamounts around Yuryaku seamount?

6. How long ago did the direction of the Pacific plate change relative to the Hawaiian hotspot?

7. What direction had the Pacific plate been moving previously? Give a compass direction like N, NW, SE, etc.