HAWAII AND PLATE TECTONICS
Figure 3.18 on page 63 in your text shows both a cross section and a
map view of the Hawaiian Islands, which have formed as a result of volcanic activity
caused by a
mantle hot spot
(note that the entire chain includes both the submerged
Emperor Seamounts and
the Hawaiian
Islands). The estimated age for each island (in millions of years) is shown in
the cross section. These ages, based on the radiometric
dating of ancient lava flows, are given as ranges because the islands were not created
instantaneously but over an extended period of time (note that the
age range given
for Maui should be 0.8 - 1.3 Ma). The U.S.G.S.
Hawaiian Volcano Observatory Site has more information on the history of these islands,
and pages 34-35 in your textbook provide background information on the radiometric dating of earth
materials.
The table below shows distances (in kilometers) between
adjacent Hawaiian Islands (as measured between volcanic peaks), their average
age differences, and the rates of plate movement inferred from this
information (note: one kilometer equals 100,000 cm).
Island Sequence |
Separation Distance |
Age Difference |
Rate of Plate Movement |
From Kauai to Oahu |
181 km |
1,900,000 years |
9.5 cm/yr |
From Oahu to Molakai |
123 km |
1,250,000 years |
9.8 cm/yr |
From Molakai to Maui |
81 km |
700,000 years |
11.6 cm/yr |
From Maui to Hawaii |
124 km |
1,000,000 years |
12.4 cm/yr |
1. Notice that the Pacific Plate is apparently moving
faster today than it did in the past.
What does this tell us about the geologic principle of
uniformitarianism?
2. How does the most recent rate compare to
other rates around the Pacific Plate?
Is
there an apparent pattern to the variation in rates of
plate movement? Explain.
3. The chain of Hawaiian Islands provides evidence that the
Pacific Plate moves to the
northwest. What
auxiliary
assumptions are made by using this chain of islands as
evidence for plate movement?
4. If the Pacific Plate has been moving continuously to the northwest
over a mantle hot
spot, why has this produced a chain of discrete
islands (separated by water) instead
of one, long, continuous island?
5. Some geologists have suggested that the older Hawaiian Islands are
smaller islands
because they have been exposed to wave erosion for longer
periods of time. What is
the auxiliary assumption behind this
hypothesis?