Looking at a globe you can see
that most of the continents seem
to fit together like a puzzle: the
west African coastline seems to
snuggle nicely into the east coast
of South America and the
Caribbean sea; and a similar fit
appears across the Pacific.
Alfred Wegener suggested that:
All continents were one large land
mass called Pangaea (meaning “all
lands”). About 200 million years ago,
it broke apart and the continents
moved to their current location. This
is called continental drift.
Searching for evidence: 1. Fossil
Paleontologist observed that the same
fossilized plants and animals from the
same time period were found in South
America and Africa. The same was true for
fossils found in Europe and North America,
and Madagascar and India. Many of these
organisms could not have traveled across
the vast oceans that currently exist.
Wegener's drift theory seemed a plausible
2. Glacial evidence
Another observation favoring continental
drift was the presence of evidence for
continental glaciation in the Pensylvanian
period. Striae left by the scraping of
glaciers over the land surface indicated that
Africa and South America had been close
together at the time of this ancient ice age.
The same scraping patterns can be found
along the coasts of South America and
3. Wegener's drift hypothesis also provided an
alternate explanation for the formation of
Wegener's explanation was that as the
continents moved, the leading edge of the one
continent would encounter the leading edges of
another continent, compressing the land and
folding it upwards forming mountains. The
Sierra Nevada mountains on the Pacific coast
of North America and the Andes on the coast of
South America were cited. Wegener also
suggested that India drifted northward into the
Asian continent thus forming the Himalayas.
Convection moves continents?
In 1929, Arthur Holmes elaborated on one of
Wegener's many hypotheses; the idea that the
mantle undergoes thermal CONVECTION. This
idea is based on the fact that as a substance is
heated its density decreases and rises to the
surface until it is cooled and sinks again. This
repeated heating and cooling results in a
current which may be enough to cause
continents to move. Arthur Holmes suggested
that this thermal convection was like a conveyor
belt and that the upwelling pressure could break
apart a continent and then force the broken
continent in opposite directions carried by the
The main features of plate tectonics
The Earth's surface is covered by a series of
The ocean floors are continually, moving,
spreading from the center, sinking at the edges,
and being regenerated.
Convection currents beneath the plates move
the crustal plates in different directions.
The source of heat driving the convection
currents is radioactivity deep in the Earth’s
The Earth’s rigid crust and mantle are
called the lithosphere. The
lithosphere is broken into sections
called plates. Plates carry a
continent or an ocean or both. The
plates “float” and move around on the
plastic-like layer beneath the
lithosphere called the asthenosphere.
Plates move between 1-12 cm per
When plates move, they can interact in
Move apart----divergent boundary, crust is
created (example: seafloor spreading on the
Move together----convergent boundary, crust
is destroyed (example: Mt. St. Helens
volcano, Andes mountains in S. America,
Himalaya mountains in Asia, Islands of
Slide past each other---transform boundary
(earthquakes at San Andreas Fault, CA)
A crack in the earth’s crust is a
fault. When plates slide along
each other at the fault line,
tremendous pressure builds up.
When the pressure is released, it
produces vibrations or seismic
waves called earthquakes.
Point on the Earth directly above
earthquake is epicenter.
Instrument used to measure
earthquakes is seismograph.
Intensity or magnitude of
earthquake is measured on
An ocean wave caused by an
Japanese word tsunami means
Tsunamis are often mistakenly
called "tidal waves" when, in fact,
they have nothing to do with tidal
How an earthquake causes a tsunami
During a major earthquake, the seafloor can
move several meters. An enormous amount
of water is suddenly set into motion, sloshing
back and forth for several hours. The result
is a series of waves that race across the
ocean at speeds of more than 800 km/hr
(500 mi/hr), comparable to the speed of
commercial jets. The energy and momentum
of these transoceanic waves can take them
thousands of kilometers from their origin
before slamming into far-distant islands or
Not the 1st time tsunami has hit the
lands of Southeast Asia.
The 1883 eruption of Krakatau Volcano,
located in the Sunda Straits between the
islands of Sumatra and Java, Indonesia,
provides an excellent example of an
eruption-caused tsunami. A series of
tsunamis washed away 165 coastal villages
on Java and Sumatra, killing 36,000 people.
The larger tsunamis were recorded by tide
gauges as far away as the southern coast of
the Arabian Peninsula-more than 7,000 km
Tsunami of December 26, 2004
The cause of the disastrous tsunami lies deep
beneath the ocean, where two tectonic plates
collided. The Indian-Australian plate slid under
the Philippine plate in a “subduction zone” 750
miles long and more than 300 miles wide.
The movement is jerky, as the submerging plate
tends to drag the upper plate down with it. But
as pressure builds, the upper plate breaks free,
springing back to its original position. The
movement in the Indian Ocean was just 16½
yards at a depth six miles below the seabed, but
it was more than enough.
The seabed lifted, displacing the ocean. The
water had to find somewhere to go, so began to
flow outwards in a huge wave, or tsunami. Dr
Roger Musson, a seismologist with the British
Geological Survey in Edinburgh, said that
similar events had been taking place in the
region for several million years and would
happen again over the next few million years.
“The effect of the earthquake is like throwing a
stone in a pond, except that you are throwing it
from below. You get the equivalent of a splash
and water is displaced with waves spreading
outwards,” he said.
Over the ocean, the waves of a tsunami
are small, probably no more than a few
centimetres to a metre high. Fisherman 20
miles out at sea barely notice their
Their speed depends on the depth of the
water, but is typically several hundred
miles an hour. The deeper the water, the
faster the waves travel and at the bottom
of the deepest ocean they can keep pace
with a jet aircraft.
As the Dec. 26 tsunami approached
the coasts of Sri Lanka, Indonesia,
India, Thailand, Malaysia and the
Maldives, it slowed. The more it
became compressed, the more it
grew in height. As it reached the
shore it grew into a monster.
“The scale of the waves will vary from
place to place, depending on the
topography of the coast,” Dr Musson
map of tsunami
2004 Sumatra Earthquake
To someone on a ship in the open ocean, the
passage of a tsunami wave would barely
elevate the water surface. However, when it
reaches shallower water near the coastline
and "touches bottom," the tsunami wave
increases in height, piling up into an enormous
wall of water. As a tsunami approaches the
shore, the water near shore commonly
recedes for several minutes -- long enough for
someone to be lured out to collect exposed
sea shells, fish, etc. -- before suddenly rushing
back toward land with frightening speed and
Then click Refresh and be patient!
From the Times of London (online) 1 January 2005
Girl's sea warning saved a hundred
A GIRL aged ten saved a hundred fellow tourists from the
tsunami because of a geography lesson about the giant
waves. Tilly Smith urged her family to get off Maikhao beach
in Thailand after seeing the tide rush out and boats on the
horizon begin to bob violently.
The youngster, recalling a recent school project on quakes,
turned to her mother Penny and said: "Mummy, we must get
off the beach now. I think there is going to be a tsunami."
Penny and her husband Colin alerted others and they cleared
the Phuket beach just in time. It was one of the few beaches
where no one has been reported killed or seriously injured.
Last night Tilly, from Oxshott, Surrey, told The Sun that credit
for her quick-thinking should go to Andrew Kearney, her
geography teacher at Danes Hill Preparatory School.
Tsunami warning system
Because of past killer tsunamis, which
have caused hundreds of deaths on the
Island of Hawaii and elsewhere, the
International Tsunami Information Center
was created in 1965. This center issues
tsunami warnings based on earthquake
and wave-height information gathered
from seismic and tide-gauge stations
located around the Pacific Ocean basin
and on Hawaii.
But governments have not invested in one
for the Indian Ocean, partly because events
like this are far less common.
International Coordination Group for the
Tsunami Warning System in the Pacific
“85 percent of all tsunamis occur in the Pacific Ocean,
generated in the regions where the main tectonic plates
forming the floor of the Pacific collide against themselves or
against the continental plates that surround the ocean basin,
in an area known as the Ring of Fire. The Mediterranean
and Caribbean Seas also have histories of some locally
destructive tsunamis. Tsunamis in the Indian Ocean have
been rare and far part in time. This might explain why no
tsunami warning system has been developed in the Indian
“The Indian Ocean tsunami is now reported to be one of the
strongest in the world for the past 40 years. More than
100,000 lives have been lost and material damage is
Aftermath in Sri
Destroyed City in
Dust and smell of
Elephants in Thailand
used as vehicles to
Fishing pier in India
Flooding in Sri Lanka
destruction in India
Among the rubble in
After “tidal wave”
Young boy outside
destroyed home in
Cleanup effort in
Amid smell and
destruction in Sri
Local army helps
clean up in Sumatra
Remains of Thai
Home destroyed as
boat is carried
ashore by tsunami
Baby “Tsunami Roy”
born 3 weeks early as his
parents headed for the
cliffs in the wake of the
Among the ruins in
Military aids relief
US students help
clean up the beach
Water remaining in
Beach returns to
Where Are All the Dead Animals?
Sri Lankan wildlife officials are stunned --
the worst tsunami in memory has killed
over 120,000 people along the Indian
Ocean island's coast, but they can't find
any dead animals.
"The strange thing is we haven't recorded
any dead animals," H.D. Ratnayake,
deputy director of the national Wildlife
"No elephants are dead, not even a
dead hare or rabbit," he added. "I
think animals can sense disaster.
They have a sixth sense. They know
when things are happening."
Quake May Have Made Earth Wobble
The deadly Asian earthquake may
have permanently accelerated the
Earth's rotation -- shortening days
by a fraction of a second -- and
caused the planet to wobble on its
axis, U.S. scientists said on
Tuesday, December 28, 2004.
Richard Gross, a geophysicist with
NASA 's Jet Propulsion Laboratory in
California, theorized that a shift of
mass toward the Earth's center
during the quake on Sunday caused
the planet to spin 3 microseconds, or
one millionth of a second, faster and
to tilt about an inch (2.5 cm) on its
When one huge tectonic plate beneath the
Indian Ocean was forced below the edge
of another "it had the effect of making the
Earth more compact and spinning faster,"
Gross said changes predicted by his
model probably are too minuscule to be
detected by a global positioning satellite
network that routinely measures changes
in Earth's spin, but said the data may
reveal a slight wobble.
The Earth's poles travel a circular
path that normally varies by about 33
feet, so an added wobble of an inch
(2.5 cm) is unlikely to cause long-
term effects, he said.
"That continual motion is just used to
changing," Gross said. "The rotation
is not actually that precise. The Earth
does slow down and change its rate
When those tiny variations
accumulate, planetary scientists must
add a "leap second" to the end of a
year, something that has not been
done in many years, Gross said.
Scientists have long theorized that
changes on the Earth's surface such
as tide and groundwater shifts and
weather could affect its spin but they
have not had precise measurements
to prove it, Caltech seismologist
Hiroo Kanamori said.
"Even for a very large event, the
effect is very small," Kanamori said.
"It's very difficult to change the
rotation rate substantially."