Download Determine the Speed of the Pacific Plate

Name_______________________
Oceanography—Mr. Nelson
Determine the Speed of the Pacific Plate
According to the theory of plate tectonics, the Earth's lithosphere, or outermost layer
consisting of the crust and part of the mantle, is made of interlocking pieces, much like the
cracked shell of a hard-cooked egg. The pieces of the lithosphere are known as lithospheric
plates. The plates float across the surface of the hot, soft, flexible layer of mantle that lies
beneath them. (Scientists call this underlying layer the asthenosphere.)
Most of the Earth's volcanoes are found at the boundaries of the plates. But a few
volcanoes are found, surprisingly, in the center of the plates. Such volcanoes are thought to
be caused by "hot spots" located deep within the Earth-perhaps in the lower parts of the
mantle or even in the core itself. Superheated molten material rises from a hot spot and
"burns through" the plate, creating a volcano.
Because hot spots are stationary, a chain of volcanic islands may be formed as an
oceanic plate moves over a hot spot. See the diagram below. By determining when the
islands in the chain were formed, it is possible to calculate how- fast the plate is moving
over a hot spot. In this activity you will determine how fast the Pacific plate is moving over
the hot spot that formed the Hawaiian Islands. The Hawaiian Islands are the most recent
additions to the Hawaiian chain of volcanoes, which extends 3500 km northwesterly across
the floor of the Pacific Ocean.
The following diagram illustrates the eight main Hawaiian Islands. Approximate age is given for the
larger island.
1. Using the scale shown on the diagram, determine the distance between the five major
islands. Enter your answer in the km column of the data table.
2. Convert each distance from kilometers to centimeters by multiplying the value in
kilometers by 100,000. Enter this new data in the cm column of the data table.
3. Calculate the approximate age difference between the islands.
Enter this in the years column of the data table.
Distance Between the Two Islands
Islands
Hawaii and Maui
Maui and Molokai
Molokai and Oahu
Oahu and Kauai
Hawaii and Kauai
(km)
(cm)
Difference in Ages of
the Two Islands
(years)
4. Using the following formula, calculate the approximate speed at which the pacific plate is moving between the
times that each island formed. Enter your data in the data table.
Speed of crustal
movement (cm/yr)
Distance between two islands (cm)
Difference in age between two islands (yrs)
Islands
Speed of Crust (cm/yr)
Hawaii and Maui
Maui and Molokai
Molokai and Oahu
Oahu and Kauai
Hawaii and Kauai
Questions:
1. Calculate the average speed of the Pacific Plate._______________________________
2. In which compass direction is the Pacific plate moving? _________________________
Explain your answer.
3. According to your data, did the Pacific plate always move at a constant rate? _______________
Explain your answer.
3) Draw on the map where you would expect the next Hawaiian Island to form, in the future, when Hawaii moves
off the hot spot. Label this island Loihi. Explain why you located Loihi there.
4) What do you think will happen to Kauai in a couple million years?
5) What do you think would happen if you had a Hot Spot
under the continent?