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Page WEB13-1
Practice Problems
Problem W13.1. Tectonic Strain Rate. As the old supercontinent Pangaea broke
apart, South America moved substantially westward over a period of about 220
million years. During that time it is estimated South America became about 38
km narrower in its east-west dimension due to strain.
WQ13.1. If we take the width of the continent to be 3800 km, what has been the
average strain rate experienced by South America? Because your answer will be
small, express it per year, rather than in the more conventional per seconds.
Problem W13.2. Geology of the Island of Hawaii. Study the geologic map of the
island of Hawaii (Figure WS13.1). Things to note:

the ticks for latitude and longitude around the edge of the map.

the ocean around the island appears in white, as do areas of the island that
have not been mapped at the level of detail shown in color.

colors for the different lava flows represent the age of the rock. ka means
thousands of years before 1950.

a type of volcanic rock called aa (a Hawaiian word) appears as stippled areas
on the map.
After studying the map, please answer the following questions.
WQ13.2. Assuming that the city of Hilo straddles both lava rocks shown in
green and blue, what is the age range for the rocks in the city? (Remember to
include units.)
WQ13.3. What appears to be the source of the lava flows younger than 1843?
(Give the name of the feature.)
WQ13.4. Do the younger-than-1843 lava flows reach the sea?
WQ13.5. Have the younger-than-1843 lava flows reached the ocean shore within
the city of Hilo?
WQ13.6. What is the age of the rocks at the southernmost tip of the island?
(Remember to give units.)
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Figure WS13.1 Geologic map of the island of Hawaii. (From J. P. Lockwood
and P. W. Lipman, 1987, Holocene eruption history of Mauna Loa Volcano,
Chapter 18 in R. W. Decker et al., editors, Volcanism in Hawaii, USGS Prof.
Paper 1350)