The devastating Tsunami (a.k.a. ocean surge, or tidal wave) which hit
Indonesia, India, Sri Lanka, Thailand, and many other countries in the region
was triggered by a massive earthquake in Indonesia. Earthquakes are often created when two
rigid tectonic plates, which are grinding against each other, suddenly rupture.
The largest earthquakes, those capable of triggering a Tsunami, occur at subduction
zones where one plate dives underneath the edge of an adjoining plate.
Tsunamis, earthquake, plate movements and ruptures are not protective of humans,
or antagonistic towards us, or even aware of our existence; they just happen.
Our job is to prevent loss of life and damage by the future tsunamis.
About tectonic plates:
Until the mid 19th century, scientists assumed that the continents were fixed
in place and subjected to only vertical movements such as those motions which
create mountain ranges. By the mid 19th century, when the coastlines of the
Atlantic Ocean had been accurately mapped, geologists noticed that the East
coasts of North and South America could be closely fitted against the West coast
of Europe and Africa. Some scientists suggested that all of the present
continents once formed a single, very large land mass which had split into many
pieces eons ago. Two parts pulled apart to create the Atlantic Ocean. Like most
scientists who propose radical new ideas, these geologists were initially
ridiculed. However Alfred Wegener, a German meteorologist, did a careful
analysis of the continental fit early in the 20th century. He revived the
concept that the continents once formed a single land mass, which he
called Pangaea. He noted "many striking similarities between the fossil
plants and reptiles on the opposite coasts" of the Atlantic ocean. 1 He showed that the same
formation of three layers of rock occurs in many areas of the world: a glacial
deposit called tillite at the bottom, a layer composed of sandstone, shale and
coal; and a basalt lava flow on top. He speculated that the layers were formed
in a part of Pangaea, which later broke up and drifted apart to form some of the
continents we see today. 2
Few geologists accepted this theory until two discoveries were made in the
The study of paleomagnetism -- magnetism in rocks: The magnetic
field of molten rock forms when it has cooled down sufficiently to pass through its Curie temperature. It preserves the direction
of the earth's magnetic field as it existed at that time. By drilling a hole
through undisturbed rock, the top layer will be found to be magnetized in
the current direction of the earth's magnetic field. But layers underneath
are found to be magnetized in alternating directions. This showed that the
earth's magnetic field reverses directions every few hundred thousand years.
The discovery of a continuous ridge of undersea mountains in the
middle of the Atlantic and Pacific oceans: Molten material from deep in
the earth "heaps up to form the ridge, and it also moves out sideways
from the ridge like a pair of giant conveyor belts." As it cools, it is
magnetized in the direction of the Earth's magnetic field. Every few hundred
thousand years, the Earth's field is reversed. This can be detected in the
form of "alternating regions of normal and reversed magnetic directions
symmetrically disposed on both sides of the ridge." 1 The sea floor is spreading
as new material continually wells up from within the earth. "...if one
were to push the continents bordering the Atlantic together (reversing the
drift that is going on at present), the continents would meet at the
Mid-Atlantic Ridge and close up on the ocean that now separates them."
The current theory, accepted by most geologists, is that the earth has an
outer shell made up of six to eight large tectonic plates and many smaller ones.
"Tectonic" comes from the Greek world "tekton" which means
"builder." These relatively rigid masses of rock slide over the mantle. The
mantle is composed of hot, soft rocks underneath the plates. Some geologists
suggest that the mantle is in motion and carries the plates along with it.
About the South Asian tsunami:
Near Sumatra Island in Indonesia, there is a complex structure of tectonic
plates involving the Burma plate, with the India and Australia plate to the west
and the Sunda and Eurasian plates to the east. These plates are continually
grinding against each other. They move very slowly -- only at about the rate, on
average, that a human fingernail grows. Serious problems happen at subduction zones
where one plate dives underneath the edge of an adjoining plate. Force builds up
-- sometimes over hundreds of years -- until a rupture occurs and generates a
violent earthquake. On 2004-DEC-26 -- the day after Christmas -- at 0758 local time (0058 GMT), an
unusually powerful rupture occurred
which generated a magnitude 9.15 earthquake "about [100 miles] 160 kilometers...off the coast of Indonesia's Sumatra Island at a depth of about
[6.2 miles] 10 kilometers...."3
It was the strongest earthquake anywhere on earth since the magnitude 9.2 quake
which hit Prince William Sound, Alaska, in 1964. "The strongest quake on
record hit Chile in 1960 and measured 9.5 on the Richter scale."
4 The energy in earthquakes
increases by a factor of ten for each one point increase in the open-ended
Richter scale. Thus a magnitude 9 earthquake contains a thousand times the energy of a magnitude 6 earthquake.
The earthquake was detected by sensors at earthquake observatories round the world.
Quakes approaching 9 on the Richter scale are capable of generating a tsunami.
This earthquake sent a sea surge in the Indian Ocean which probably reached speeds of 270 mph (450 km/hr) in open
water. After about three hours, it approached Sri Lanka. It slowed down to perhaps 27 mph (45 km/hr) as it
land, where it was squeezed upwards to produce a wave capable of massive destruction.
The first sign from land of a tsunami is that water is sucked away from the
beach. In some areas, this tsunami exposed the ocean bottom near the shore,
stranding fish. Many villagers rushed to collect the fish, were hit by the sea
surge, and killed.
In early 2005-FEB, scientists at NASA said that the earthquake that caused
the tsunami disrupted the Earth's rotation and shaved 2.68 microseconds from the
length of each day. The North Pole shifted by about one inch. The planet is now
slightly less oblate -- that is, not quite as flattened at the poles. 8
It is quite impossible to rearrange tectonic plates, prevent earthquakes, or
prevent tsunamis. But there are ways to minimize some of the devastation and
loss of life:
Where possible, establishing a green belt of trees at the shore to
adsorb some of the force of the sea surge.
Educating people who live near the ocean to be aware that the first sign
of an oncoming tsunami may be a retraction of the water from the shore. If
they see that happening again, they need to move inland as fast as possible.
Developing evacuation programs to evacuate to higher floors of strongly
constructed buildings and/or a sufficient distance from the shore line.
Develop a warning system such as the one that currently exists in the
countries bordering the Pacific Ocean. Such a system is being implemented worldwide.
Benefits of the motion of the tectonic plates:
It is difficult to talk about the benefits of tectonic plates with the
realization that their motion created a tsunami which recently snuffed out the lives of
about 155,000 people. However, the same shifting of tectonic plates that causes
earthquakes and generated the South Asia tsunami is also partly responsible for
life on earth.
Dr. Donald J. DePaolo, a geochemist at the University of California,
"It's hard to find something uplifting about 150,000
lives being lost. But the type of geological process that caused the
earthquake and the tsunami is an essential characteristic of the earth. As
far as we know, it doesn't occur on any other planetary body and has
something very directly to do with the fact that the earth is a habitable
tectonic plates existed elsewhere in the solar system's approximately 70 planets
and moons, they would have produced mountain ranges of the type seen on Earth.
None have been seen.
Dr. Frank Press, the lead author of "Understanding Earth"
6 and a past president of the
National Academy of Sciences, said:
"On balance, it's possible that life
on earth would not have originated without plate tectonics, or the atmosphere,
or the oceans."
Plate movement "builds mountains, enriches soils....concentrates gold and
other rare metals and maintains the sea's chemical balance."
7 Plate movement also recycles carbon
dioxide, thus regulating the earth's temperature. Evolution of the
species is enhanced when the long-term temperature of the earth is stable.
Dr. William H. Schlesinger,
dean of the Nicholas School of the Environment and Earth Sciences at Duke
"Without a relatively constant temperature enhanced by the movement of the
tectonic plates, life might not have evolved on earth beyond simple organisms.
Having plate tectonics complete the cycle is absolutely essential to
maintaining stable climate conditions on earth. Otherwise, all the carbon dioxide would disappear and the
planet would turn into a frozen ball." 7
Dr. Jelle Zeilinga de Boer, a geologist at Wesleyan University says
that evidence from earlier tsunamis suggests that they can distribute rich
sediments from river systems across coastal plains, making the soil richer. He
"It brings fertile soils into the lowlands. In time, a more fertile
jungle will develop."
Robert S. Detrick Jr., a geophysicist at the Woods Hole
Oceanographic Institution, said that in spite of the staggering loss of
"... there's no question that plate tectonics rejuvenates the planet."
The following information sources were used to prepare and update the above
essay. The hyperlinks are not necessarily still active today.
J. Tuzo Wilson, "Continental Drift," Colliers Encyclopedia CD-ROM, Vol. 7, (1996-FEB).