Geography Reference
In-Depth Information
especially prescient. Just like people farming the fertile soils on the slopes of an active
volcano, people living at or near sea level near an earthquake zone live with risk.
A few weeks later I began to hear and read stories about an English girl named
Tilly Smith, who had been vacationing with her parents at a hotel on the beach at
Phuket and was on Maikhao Beach when she saw the water suddenly recede into the
distance. Tilly had just taken a geography class in her school not far from London,
and her teacher, Mr. Andrew Kearney, had told the class what happens when a tsu-
nami strikes: the huge approaching wave fi rst sucks the water off the beaches and
then the sea foams, rises and returns as a massive, breaking wall that crashes over and
inundates the whole shoreline. Tilly saw what was happening and alerted her par-
ents, her father told hotel security, and they ran back and forth, screaming at beach-
goers to seek shelter on higher ground in the hotel behind them. About a hundred
people followed the Smith family into the building, and they all survived. Of those
who stayed behind, none did. Being aware of some of the basics of physical geog-
raphy has its advantages, and Mr. Kearney clearly had the attention of his students.
Newspaper editors could use some of this awareness. Many headlines referred
to the tsunami as a tidal wave, but a tsunami has nothing to do with the tides that
affect all oceans and seas. A tsunami results from an undersea earthquake involv-
ing a large displacement of the Earth's crust. Most submarine earthquakes do not
generate tsunamis, but in some cases, fortunately relatively rare ones, a large piece
of crust is pushed up or pulled under (or both), and this causes the water overhead
to pile up and start rolling away in all directions. If you were on a cruise ship some-
where in the middle of the ocean, nothing catastrophic would mark the passing of
this tsunami wave; your ship would be lifted up and then lowered, but it would not
overturn. But when such a huge wave reaches a beach, it does what all waves do: it
breaks. Most of us have seen this happen with waves several feet (or even tens of
feet) high. But imagine a wave over 200 feet high approaching a beach. As it begins
to break, it pulls the water away, exposing wide swaths of muddy bottom. Then it
comes crashing into the shore, pushing deep inland.
Tsunamis of the magnitude of 2004 are not common, but as the deadly tsu-
nami that struck the northeast coast of Japan in 2011 reminds us, the hazard is
continuous. As the Earth's human population has grown, so have the numbers of
people vulnerable to such a calamity. As we learn more about the submarine zones
where earthquakes are most likely to occur, we can begin to determine where the
hazards are greatest. Here we combine two major fi elds of study in geography, phys-
ical geography and human geography. Geographers who work in this arena study
human-environmental relationships—the reciprocal relationships between human
societies and natural environments. Both, clearly, are dynamic. The environment is
not a passive stage, and environmental change affects human societies. At the same
time, humans have an impact on their natural environments. The study of hazards,
not just from tsunamis but also from volcanic eruptions, terrestrial earthquakes,
landslides, fl oods, avalanches, and other threats, is a key part of this research.
The tsunami that struck coasts along the Indian Ocean from Indonesia to
Somalia and from Thailand to the Maldives resulted from a violent earthquake
measuring more than 9.0 on the (10-point) Richter scale off the west coast of the
island of Sumatra (Indonesia).
There, two of the planet's tectonic plates are colliding, forcing one beneath
the other (Fig. 13.2). A series of tremors and quakes affects the crust in such sub-
duction zones, but sometimes a major shock occurs. In this case, the towering
wave generated by the December 26 earthquake had but a short distance to travel
to reach northern Sumatra, where it struck in full force. By the time it had done its
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