Laboratory Manual for Introductory Geology 4e

After watching dramatic images of tsunamis coming ashore near Sendai, Japan,
some of our students asked how “just water” could cause so much damage. The
amount of energy carried by a tsunami is truly unimaginable, but Exercise 11.8
offers a comparison that may help.
EXERCISE 11.8
Why Is a Tsunami So Powerful?
Name:
Course:
Section:
Date:
A cube of water 1 foot on a side (1 cubic foot, or 1 ft 3 ) weighs approximately 62 pounds. Imagine being hit by a 62-pound
weight—it would certainly hurt.
1 ft
1 ft
1 ft
(a) Now imagine a low wall of water 10 feet wide, 1 foot deep, and 1 foot high: it would weigh
(b) A wall of water 30 feet high (like the Sendai tsunami), 1 foot deep, and 10 feet wide would weigh
(c) A wall of water 30 feet high, 5,280 feet wide (a mile), and 1 foot deep would weigh
(d) To approximate a tsunami better: a wall of water 30 feet high, 5,280 feet wide, and “only” 2,640 feet deep would
weigh
lb.
(e) One of the most powerful man-made objects is a modern railroad locomotive. A large locomotive weighs about
200 tons 5 400,000 pounds. The impact of the conceptual tsunami in question (d) is equivalent to being hit
by
locomotives.
lb.
lb.
lb.
This simple calculation should help you understand why “just water” can cause so much damage. And remember that
a tsunami moves much faster than a locomotive.
296 CHAPTER 11 EARTHQUAKES AND SEISMOLOGY