Page 83 - Laboratory Manual in Physical Geology

ACTIVITY 2.8 Hot Spots and Plate Motions

Name: ______________________________________ Course/Section: ______________________ Date: ____________

As a lithospheric plate migrates across a stationary hot spot, a volcano develops directly above the hot spot. When the plate
slides past the hot spot the overlying volcano becomes dormant, and over time, it migrates many kilometers from the hot
spot. Meanwhile, a new volcano arises as a new part of the plate passes over the hot spot. The result is a string of volcanoes,
with one end of the line located over the hot spot and quite active, and the other end distant and inactive. In between is a
succession of volcanoes that are progressively older with distance from the hot spot.

A. FIGURE 2.7 shows the distribution of the Hawaiian Islands chain and Emperor Seamount chain. The numbers indicate age in
millions of years old or ago (Ma), obtained from the basaltic igneous rock of which each island is composed.

1. In general, how is the Emperor Seamount chain related to the Hawaiian Islands chain?

2. What was the rate in centimeters per year (cm/yr) and direction of plate motion of the 2300 km long Emperor Seamount
Chain from 20 to 40 Ma?

3. What was the rate in centimeters per year (cm/yr) and direction of plate motion in the Hawaiian region from 4.7 to
1.6 Ma?

4. What was the rate in centimeters per year (cm/yr) and direction of plate motion from 1.6 Ma to the present time?

5. Go to the JPL-NASA GPS Time Series website at http://sideshow.jpl.nasa.gov/post/series.html . The map
displays each GPS station as a green dot and yellow line. The yellow line points from the green dot to the
direction that the GPS station (and lithospheric plate to which it is anchored) is moving. Look at Hawaii.
JPL-NASA GPS station “NPOC” is located there, and you can see its direction of motion.

a. How does the current motion of NPOC on Hawaii compare to the direction of Pacific Plate motion
over the past 40 million years?

b. The NPOC GPS station on Hawaii, and the Pacific Plate to which it is attached, has the following motion: Latitude
vector direction & velocity: +1.4825 cm/yr, Longitude vector direction & velocity: –5.1612 cm/yr

Using the formula in FIGURE 2.3 , Part E, what is the current velocity (in cm/yr) of Pacific Plate motion at Hawaii?
Show your work.

B. REFLECT & DISCUSS Based on all of your work above, explain how the direction and rate of Pacific Plate movement
changed over the past 60 million years.

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