Download Lab 3. Plate Tectonics DETERMINING RATES OF PLATE

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Lab 3. Plate Tectonics
DETERMINING RATES OF PLATE MOVEMENT IN PACIFIC
While visiting Hawaii in the 1960's, Tuzo Wilson, one of the founders of the theory of plate
tectonics, noticed some interesting features about ocean islands. On a map of the Pacific basin,
he found three linear chains of volcanoes and submarine volcanoes (seamounts). As shown
below, these are the (1) Hawaii Islands -Emperor Seamounts; (2) The Pitcairn Island - Tuamotu
Group; and (3) the Macdonald Seamount - Austral Group. Notice that the eastern most island
or seamount of each chain is volcanically active.
As we can see, although separated by thousands of miles, the three linear chains are parallel
to each other. Of the three, the Hawaii-Emperor seamount chain was the most well known.
Wilson reviewed the reports that had been published on these island chains and recorded
the age of each island in the Hawaiian chain. An interesting pattern emerged. For each chain,
the islands become progressively younger to the southeast. The extreme southeast end of
each chain is marked by active volcanoes.
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Wilson proposed that the Hawaiian islands formed successively over a common source of magma
called a hot spot. The Island of Hawaii is currently located above the hot spot.
Hot, solid rock rises to the hot spot from greater depths (see the sketch below). Due to the
lower pressure at the shallower depth, the rock begins to melt, forming magma. The magma
rises through the Pacific Plate to supply the active volcanoes. The older islands were once
located above the stationary hot spot but were carried away as the Pacific Plate drifted to the
northwest
Image Source:
Eruptions of Hawaiian Volcanoes: Past, Present, and Future: U.S. Geological Survey General Interest
Publication.
Following lab was provided by Steve Mattox,
http://northonline.northseattle.edu/gel101tb/labs/plateslab.html
Directions: Use above maps and the following information to determine the rate of motion of
the Pacific Plate over the Hawaiian hot spot.
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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. You can use
approximate centers of islands to measure distances. Time is the age of the island.
Question #1
Start by measuring the distance from southeast Hawaii to Niihau. Use the scale on the map.
The distance is ________________ km.
Question #2
To determine the average rate of motion for the Pacific Plate, divide the distance to Niihau by
the age of the island. The rate of plate movement is _____________________ km/Ma
(kilometers per millions of years).
Question #3
Convert your answer to cm/yr (centimeters per year). The rate of Pacific Plate movement is
_____________ centimeters per year.
Question #4
Using this rate, how far (in cm) will the Pacific Plate move in 50 years? ____________
Question #5
Repeat the exercise above using the island of Molokai instead. From the distance and age of
this island, the rate of Pacific Plate movement is ___________ centimeters per year.
Question #6
What direction is the Pacific Plate traveling? Explain. _________________
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