Father of Plate Tectonics
truly revolutionary scientific theories may take years or decades to win general
acceptance among scientists. This is certainly true of plate tectonics one of
the most important and far-ranging geological theories of all time. When
'Continental Drift' the forerunner of the now well established science of plate
tectonics was first proposed, it was ridiculed, but steadily accumulating
evidence finally prompted its acceptance, with immense consequences for geology,
geophysics, oceanography, and paleontology. Although it had been suggested by
Taylor and other earlier scientists, the man who should be given the title of
'The Father of Plate Tectonics' was a brilliant interdisciplinary scientist, Alfred
Born on November
1, 1880, Alfred Lothar Wegener earned a PhD in astronomy from the University of
Berlin in 1904. However, he had always been interested in geophysics, and also
became fascinated with the developing fields of meteorology and climatology.
During his life, Wegener made several key contributions to meteorology: he
pioneered the use of balloons
to track air circulation, and in 1911, wrote a
textbook that became standard throughout Germany. In 1906 Wegener joined an
expedition to Greenland to study polar air circulation. Returning, he accepted a
post as tutor at the University of Marburg, taking time to visit Greenland again
in 1912-1913. (The photograph of Wegener on the right was taken during this
expedition). In 1914 he was drafted into the German army, but was released from
combat duty after being wounded, and served out the war in the Army weather
forecasting service. After the war, Wegener returned as a lecturer to Marburg,
but became frustrated with the obstacles to advancement placed in his way.
He was finding it very difficult to obtain a professorship in any German
University because of his theory of continental drift which was at the time
considered to be 'scientific heresy'.
Marburg, in the autumn of 1911, Wegener was browsing in the University Library
when he came across a scientific paper that listed fossils of identical plants
and animals found on opposite sides of the Atlantic. Intrigued by this
information, Wegener began to look for, and find, more cases of similar
organisms separated by great oceans. Orthodox science at the time explained such
cases by postulating that land bridges, now sunken, had once connected far-flung
continents. But Wegener noticed the close fit between the coastlines of Africa
and South America. Might the similarities among organisms be due, not to land
bridges, but to the continents having been joined together at one time?
Such an insight,
to be accepted, would require large amounts of supporting evidence. Wegener
found that large-scale geological features on separated continents often matched
very closely when the continents were brought together. Wegener also found that
the fossils discovered in a certain place often indicated a climate utterly
different from the climate of today: for example, fossils of tropical plants,
such as ferns and cycads, were found on the Arctic island of Svalbad or Spitsbergen. All of
these facts supported Wegener's theory which he called continental Drift In 1915 the first edition of The Origin of Continents and
Oceans, a book outlining Wegener's theory, was published; expanded editions
were published in 1920, 1922, and 1929. About 300 million years ago, claimed
Wegener, the continents had formed a single mass, called Pangaea (from the Greek
for "all the Earth"). Pangaea had rifted, or split, and its pieces had been
moving away from each other ever since. Wegener was not the first to suggest
that the continents had once been connected, but he was the first to present
extensive evidence from several fields.
Modern reconstruction of Pangaea, ca. 255 million years ago.
Wegener's theory was almost uniformly hostile, and often exceptionally harsh and
scathing. Many speakers were sarcastic to the point of insult. Part of the problem was that Wegener had no convincing mechanism for
how the continents might move. Arthur Holmes another famous maverick geologist
supported Wegener and in fact suggested mechanisms similar to sea-floor
spreading which is accepted to-day as part of the plate tectonics theory. There
were other scientists who supported Wegener: the South African geologist
Alexander Du Toit supported it as an explanation for the close similarity of
strata and fossils between Africa and South America, and the Swiss geologist
Émile Argand saw continental collisions as the best explanation for the folded
and buckled strata that he observed in the Swiss Alps. Wegener's theory found
more scattered support after his death, but the majority of geologists continued
to believe in static continents and land bridges.
the revival of
continental drift? In large part it was increased exploration of the Earth's
crust, notably the ocean floor, beginning in the 1950s and continuing on to the
present day. By the late 1960s,
plate tectonics was well supported and accepted by almost all geologists.)
In 1930 Wegener mounted another trip
to Greenland. The expedition reached a place which they named Eismitte
at an elevation of about 3000 meters (about 10,000 feet). There on
November 1 they celebrated Wegener's fiftieth birthday. Because supplies
were low Wegener and his team member Rasmus Villlumsen set out for the
coast. Their friends never saw them again. On 12 May 1931 Wegener's
frozen body was found fully dressed in his tent. His eyes were open and
the expression on his face was calm and peaceful. The picture on the right
courtesy Wegener Institute of Wegener with an Inuit companion was taken on the
fatal expedition to Greenland where Wegener met his death. (Photo - Courtesy
By 1930 Wegener's theory had been
almost universally rejected and sank into obscurity. It was not until the
1960s that his ideas began to receive acclaim. Despite some differences in
detail Wegener was proved right in all his major concepts.
We now know that Wegener's theory was wrong in one point: continents do not
plow through the ocean floor. Instead, both continents and ocean floor form
solid plates, which "float" on the
asthenosphere, the underlying rock that is under such tremendous heat and
pressure that it behaves as an extremely viscous liquid. This is
why the older term "continental drift" is not quite accurate -- both continents
and oceanic crust move.
Plate Tectonics was born and Alfred
Wegener's work was acclaimed as one of the greatest advances in the Earth
Sciences. It is a vindication of his life that an important Institute is
named after him. In my opinion Wegener's name should rank among the
greatest along with Galileo, Newton, Darwin and Einstein for his contribution to
day, scientists have mapped and explored the great system of oceanic ridges, the
sites of frequent earthquakes, where molten rock rises from below the crust and
hardens into new crust. We now know that the farther away you travel from a
ridge, the oolder the crust is, and the older the sediments on top of the crust
are. The clear implication is that the ridges are the sites where plates are
moving apart. Where plates collide, great mountain ranges may be pushed up, such
as the Himalayas; or if one plate sinks below another, deep oceanic trenches and
chains of volcanoes are formed. Earthquakes are by far most common along plate
boundaries and rift zones: plotting the location of earthquakes allows
seismologists to map plate boundaries and depths. Paleomagnetic data have
allowed us to map past plate movements much more
precisely than before. It is
even possible to measure the speed of movement of continental plates extremely accurately,
using satellite technology. Nevertheless, Wegener's basic insights remain sound,
and the lines of evidence that he used to support his theory are still actively
being researched and expanded.
Although Wegener's great achievement
was not fully appreciated in his lifetime he was a appreciated for his work in
meteorology and has been honoured in his own country and throughout the world by
having an Institute named after him. The photograph on the left is by
courtesy of the Wegener Institute
The Alfred Wegener Institute
institute for polar and marine research
It was established as a public foundation in 1980 The
Institute conducts research in the Arctic, the Antarctic and at
temperate latitudes. It coordinates Polar research in Germany
the major role played by these regions within the Earth's climate
system, global change is the central focus of the research effort of
The Institute collaborates closely with international
and maintains close contacts with many universities and institutes
in Europe and farther afield. It sends scientists to other
institutes throughout the world, to other research ships and
stations, and invites scientists from other nations to cruises
aboard the research ship Polarstern (Pole Star) About a
quarter of quarter of those participating in Polarstern expeditions
are scientists from abroad.
Plate Tectonics - Modern Aspects
Plate tectonics deals with the
dynamics of the Earth's outer shell which is called the CRUST or LITHOSPHERE.
The lithosphere consists of about a dozen large plates and several smaller ones.
The continents sit on the plates. The plates rest on the semi-molten
asthenosphere of magma and move slowly across the asthenosphere relative to each
The lithosphere is the rigid outer layer of the Earth. It differs
from the underlying asthenosphere in terms of its mechanical (or rheological,
ie, 'flow') properties rather than its chemical composition. Under the influence
of the low-intensity, long-term stresses that drive plate tectonic motions, the
lithosphere responds essentially as a rigid shell whilst the
asthenosphere behaves as a highly viscous liquid.
The weaker mechanical properties of the asthenosphere are attributable to the
fact that, within this part of the upper mantle, the temperature lies close to
the melting temperature. The base of the lithosphere is conventionally defined
as the 1,300 degrees Celsius isotherm since mantle rocks below this
temperature are sufficiently cool to behave in a rigid manner
Plates can drift apart
(sea floor spreading), push into each other or slide past each other.
Sea Floor Spreading
The ocean plates diverge from each
other and produce a ridge of under ocean volcanoes, such as the mid-Atlantic
Ridge. This produces sub-marine volcanic mountains the tops of which form
islands such as the Canaries, Iceland the Azores etc. This
phenomenon is called sea floor spreading Along
the mid Atlantic ridge, there are diverging plates (North American and
Eurasian). There are many earthquakes along the ridge. They are moving apart and
therefore causing North America and
Eurasia AND South America and Africa to drift further and further apart.
Picture two giant conveyor belts, facing each other but slowly moving in
opposite directions as they transport newly formed oceanic crust away from the
ridge crest. There
are many earthquakes along the ridge. A huge earth quake occurred in 1755 in
which Lisbon was destroyed partly by the earthquake and partly by the tsunamis
and fires which followed it.
The Mid-Atlantic Ridge is known as a divergent boundary. There is a submerged mountain range,
extending from the Arctic Ocean to beyond the southern tip of Africa. The rate
of spreading along the Mid-Atlantic Ridge averages about 2.5 cm’s per year, or
25 km in a million years. Seafloor spreading over the past 100 to 200 million
years has caused the Atlantic Ocean to grow from a tiny inlet of water between
the continents of Europe, Africa, and the Americas into the vast ocean that it
Where plates collide pushing into each
other earthquakes and volcanoes occur. The 'ring of fire' is very active
in the Pacific particularly in Indonesia and Japan. In some cases plate
collisions result in the building of mountain ranges. The building of a
mountain range is called an OROGENY. The description below
together with the map is also shown in another page of this web-site
The Himalayas: Two continents collide
Plates were very much on the move during the Cainozoic. The subcontinent of India was on its
way to Asia. Australia and Antarctica parted and
cruised away from each
other. South America was on its own.
About 225 million years ago, India was a large island still situated off the
A vast ocean (called
the Tethys) separated India from the
Asian continent. When Pangaea broke apart about 200 million years ago, India
began to forge northward. By studying the history -- and ultimately the
closing-- of the Tethys, scientists have reconstructed India's northward
About 80 million years ago, India was located roughly 6,400 km south of
the Asian continent, moving northward at a rate of about 9 m a century. When
India began to ram into Asia about 40 to 50 million years ago, its northward advance
slowed by about half. The collision and associated decrease in the rate of plate
movement are interpreted to mark the beginning of the rapid uplift of the
Himalayas. The final collision of the land masses took place in the
Among the most dramatic and visible creations of plate-tectonic forces are the
lofty Himalayas, which stretch 2,900 km along the border between India and
Tibet. This immense mountain range began to form between 40 and 50 million years
ago, when two large landmasses, India and Eurasia, driven by plate movement,
collided. Because both these continental landmasses have about the same rock
density, one plate could not be subducted under the other. The pressure of the
impinging plates could only be relieved by thrusting skyward, contorting the
collision zone, and forming the jagged Himalayan peaks.
India was once situated well south of the
Equator, near the continent of Australia.
The progress of the last 6,000-km part of the journey of the India landmass (Indian Plate) before its
collision with Asia (Eurasian Plate) about 40 to 50 million years ago is shown
in the illustration. Map Courtesy United States Geological Service
An excellent example of plate migration
leading eventually to an orogeny is the formation of the Himalayas
Sometimes plates grind up against one
another. Volcanoes are not formed but severe earthquakes may occur an
example being the San Andreas Fault in California. The December 2005 Asian
Tsunami was caused by two plates pushing against one another causing a large
earthquake and a devastating tsunami.
- The Earth's surface is made up of a series of large
plates (like pieces of a giant jigsaw puzzle).
- These plates are in constant motion travelling at a few
centimetres per year.
- The ocean floors are continually moving, spreading from
the centre and sinking at the edges.
- Beneath the plates
there are convection currents which move the
plates in different directions.
- The source of heat driving the convection currents is
radioactive decay which is happening deep in the Earth.
The map which
is shown above illustrates how the lithosphere is segmented into plates like a
massive jig-saw. Credit due to Moorland School web-site Dr Paul
The concepts of Plate Tectonic activity are admirably illustrated in the
diagram which is reproduced below by kind permission of Professor L.S.Fichter of
James Madison University in Harrisonburg VA USA.
With the exception of hot spots all volcanic
activity takes place at convergent and divergent plate boundaries. A convergent
plate boundary is where two plate are pushing against one another. Fractional
melting takes place at convergent plate boundaries. These are called
subduction zones. A volcano is formed. Most volcanoes on land are of
At divergent plate boundaries, as in sea floor
spreading, magma is brought up from deep in the mantle toward the surface via
convection cells. This material is very hot, and under enormous pressure.
There are massive amounts of volcanic activity but most of it is not obvious
because it takes place under the sea
The Lisbon Earthquake
The Lisbon Earthquake struck on the morning of
the first of November 1755. Contemporary
reports state that the earthquake lasted between
three-and-a-half and six minutes, causing gigantic fissures
five metres (16 ft) wide to appear in the city centre. The
survivors rushed to the open space of the docks for safety and
watched as the water receded, revealing a sea floor littered by
lost cargo and old shipwrecks. Several tens of minutes after the
earthquake, an enormous tsunami engulfed the harbour and
downtown, It was followed by two more waves. In the areas
unaffected by the tsunami, fire quickly broke out, and flames
raged for five days.
shockwaves of the earthquake were felt throughout the whole of
Europe as far away as Finland. Tsunamis up to 20 metres
(66 ft) in height swept the coast of North Africa and even hit
Martinique and Barbados. Even the coast of southern England and
the west coast of Ireland were hit by three metre high tsunamis.
Of a Lisbon population of 275,000, up to
90,000 were killed. Eighty-five percent of Lisbon's buildings
were destroyed. Another 10,000 people were killed in
Morocco. It is said that many animals sensed danger and
fled to higher ground before the tsunamis struck The
Lisbon quake is the first documented reporting of such a
phenomenon in Europe.
This is all very reminiscent of the disaster
which struck South East Asia in December 2005.
A third major category of
volcanic activity has little to do with plate tectonics. Hot
spot volcanoes often (but not always) occur within plates. They
are generated by isolated, stationary, plumes of magma that
arise deep in the mantle. Common examples are the shield
volcanoes of the Hawaiian islands, the Galapagos Islands and
Yellowstone Park in Wyoming.
There are essentially three types of volcanoes:-
1) Where two or three tectonic plates converge.
An example of this is found in the Pacific Ring of Fire.
One of the most volcanic parts of the world is the Indonesian
2) Where tectonic Plates diverge.
An example of this is the Mid-Atlantic Ridge.
3) Hotspots. These are caused by
the upwelling of magma from deep in the mantle. These so
called mantle plumes are found in places far from plate
boundaries and can produce very high mountains. Mauna Kea
in the Hawaiian islands is higher than Mount Everest if you
measure it from its base deep in the Ocean and not from sea
level. As a plate moves across a hot spot it can create
over millions of years whole chains of islands as found in
Hawaii and in the Galapagos Islands. Hotspots are found
elsewhere in the Solar System - examples being Mars and Venus.
Acknowledgement USGS (United States Department of the Interior - United States
Throughout the history of the Earth there
have been particularly violent periods of volcanic activity. One of these
was in Permian Times in the Siberia. Another was in the Deccan Traps in
the Indian Plates.
The existence of massive volcanic activity was
one of the theories advanced as the cause of the dinosaur extinction. This
suggests that huge volcanic activity involving the formation of massive volcanic
plumes and immense basaltic lava flows could have brought about the Cretaceous
Extinction. The volcanic activity that produced the huge lava flows that formed
the Deccan traps in India was sited as a possible culprit. There are still many
earth scientists who consider that, as well as the impact, the volcanic activity
contributed very considerably to the demise of the dinosaurs.
There can be little doubt than considerable
volcano activity did take place at the end of the Cretaceous /beginning of the
Tertiary. A huge outpouring of the earth's interior that
occurred over much of present-day India 65 million years ago came from the
boundary between the earth's lower mantle and its molten iron core some 1,800
miles beneath the surface, scientists have determined. The same lower
mantle signature also typifies several "hot spots," volcanic areas beneath
earth's plates responsible for forming chains of volcanoes as the plate
gradually slides above. Reunion Island in the Indian Ocean is thought to be the
hot spot that formed the Deccan Traps. the volcanic activity
occurred as the Indian Plate was making its way northward and at the time
'India' was migrating from the southern to the northern hemisphere in its 'mad
rush' geologically speaking towards its eventual collision in the Miocene Epoch
when it collided with Asia to form the Himalayas.
Toba the Terrible
Sometime long ago the tropical island of Sumatra lay bathed in the
eternal summer and the birds and animals pursued their lives as
usual. Hundreds and even thousands of kilometres away one of
natures latest creations had emerged. The men and women of
those times may have led a simple life but they used tools, had
discovered fire and could talk to each other -they were human beings
of the species Homo sapiens and were our direct ancestors. They had
no knowledge that deep beneath the surface a huge mantle plume was
about to erupt. At a place we now call Toba the largest
super-volcano for 28 million years was about to explode.
To-day a beautiful lake, which has become a tourist resort, marks
the place where the terrible event occurred together with genetic evidence
scientists have proved
that all 6 billion of us of every ethnic group including the Australian
Aborigines (who arrived in Australia ten thousand years after the disaster) owe
our existence to the few survivors of the
super-volcano. The evil myths of racism have been
scientifically proved TO BE TOTALLY AND UTTERLY WRONG.
Some scientists estimate that many humans were killed by the event as a direct
result at the time - volcanic ash several meters deep was scattered for hundreds
of kilometres from the explosion. Many of those that survived the
explosion died as a result of the appalling weather conditions and famines that
It is estimated by a number of authorities in the field that
only 10 to 20 thousand people over the whole world survived the disaster.
That means that every man and every woman alive to-day are the descendants of the few
The evil myths of racism have been scientifically proved TO BE TOTALLY AND
Lake Toba to-day
Credit Tri Jay Tour and Travel
According to a recent hypothesis our
species came very close to extinction because of the eruption of a
super-volcano in Sumatra about 73,000 years ago. Evidence is
emerging from a number of different fields - geological, anthropological, climatological and genetic that this event not only caused enormous damage over
the whole area of Indonesia, South East Asia, India, the Middle East and
parts of Africa but led to a 'volcanic winter" that lasted for about six years and caused
a 1000 years of the coldest ice age on record. It has been estimated that the eruption lasted around 9-14 days
(ref. Ledbetter M. et al, 1979) and took place in the northern
summer. The pyroclastic ash fall is estimated at 800 cubic
kilometres which gives an average thickness of 10 cm over the whole
Earth. As far away from the epicentre of
the eruption as Vansadhara and other places in India there is
evidence of ash falls between 1.5 and 6 metres 5-20 ft.) deep occurred.
Using the estimated eruption time of 9-14 days (ref. Rose W.I.,
1990) and an eruption volume of 2,800 cu. km, an average eruption
rate of 8 million metric tons of material per second has been calculated. The areas directly affected by ash fall from the Toba explosion must be
speculative but one site in central India, for example,
today has a thickness of no less than 6 m (20 ft) (ref. Acharya S.K. et al.,
1993). It is possible that this thickest of deposits found so far represents an
accumulation of wind-blown or water-driven ash, but even if it does, most of
Southeast Asia, parts of Sunda, the Andaman and Nicobar islands, along with all
of the Indian subcontinent and Sri Lanka were covered in deep ash.
Such a heavy fall would have exterminated most plant and animal life in
the affected areas. The deepness of the ash reduces gradually towards
the west but can still be expected to have been substantial in the
Middle East and parts of East Africa.
In addition, it
is thought that the staggering amount of 1010 metric tons of H2SO4
(sulphuric acid) was blown into the atmosphere by the Toba event (Huang
et al. 2001).
Prior to the eruption of 73,000 years ago, Toba had produced at least two
earlier major eruptions 800,000 and 500,000 years ago. The earlier outbreaks
were not as large as the colossal eruption of 73,000 years ago which is the only
eruption of class VEI 8 to have taken place since primates have appeared on
It was of an order of
magnitude vastly more than Laki in 1783, Tambora in 1815
and Krakatao in 1883 three
of the greatest Holocene eruptions. The Toba eruption may have caused about 3 to
4 degree C cooling at the surface (Sigurdsson, 1990).
The Toba Eruption is what volcanologists call a
VEI-8 volcanic event. The last four such super-volcanoes
Lake Taupo North Island New Zealand
26,500 years ago
Volume of erupted material 1,170 cubic kilometres
Lake Toba Sumatra Indonesia 75,000 years ago Volume of erupted material 2,800 cubic
500,000 years ago
800,000 years ago
Yellowstone Caldera Wyoming USA 640,000
years ago Volume of erupted material 1,000 cubic
Yellowstone Caldera Wyoming USA 2,200,000 years
ago Volume of erupted material 2,500 cubic kilometres
La Garita Caldera Colorado USA
27,000,000 years ago Volume of erupted material 5,000 cubic
Very Mild by Comparison!
The Laki eruption in Iceland
eight months during which time about 14 cubic km of basaltic lava and some
tephra were erupted. Haze from the eruption was reported from Iceland to Syria.
In Iceland, the haze lead to the loss of most of the island's livestock (by
eating fluorine contaminated grass), crop failure (by acid rain), and the death
of one-quarter of the human residents (by famine). The climatic and atmospheric effects of the Laki eruption are
impressive. In the eastern United States, the winter average temperature was 4.8
degrees C below the 225 year average. The estimate for the temperature decrease
of the entire Northern Hemisphere was about 1 degree C.
Note after this page of the
web-site was written there was a most interesting and
informative programme on BBC 2 television on Timewatch 19 January 2007about the
Laki eruption and its effects. Apart from the 10,000 people in Iceland who
died, a very large number of people in Western Europe perished from the toxic
cloud of sulphur dioxide that swept in an arc across Norway then down to Poland,
Czechlands, Germany France and finally to the British Isles. Crop failure
and famine and a terrible winter ensued. The famous book the Natural History of
Selbourne was mentioned in ther programme including the national hero of Iceland
who led his people through the time of their tribulation
The site of the eruptions has recently been investigated by Thor Thordardson see
hyperlink at end of this chapter of the web-site.
Tambora erupted in 1815 killing 92 000 people.
1816 became the year without a summer as the global climate effects were felt.
Aerosols from the Tambora eruption blocked out sunlight and reduced global
temperatures by 3 deg C. Europe missed a summer, and India had crop failures
following the Tambora eruption. 100 cubic km of magma was erupted. Tambora is a stratovolcano, forming the Sanggar peninsula of Sumbawa Island. The
diameter of the volcano at sea-level is about 38 miles (60 km). Prior to the
1815 eruption, the volcano may have been as tall as 13,000 feet (4,000 m). The
1815 eruption formed a caldera about 4 miles (6 km) in diameter. The caldera is
3,640 feet (1,110 m) deep.
The paroxysmal explosion at Tambora was heard 1700 km away, and
Madura Island (500 km away) was in darkness for 3 days. Rock fragments 15 cm in
diameter were ejected 40 km from the volcano
Krakatao is situated between the islands of Java and
Sumatra in Indonesia. The 1883 eruption ejected more that
six cubic miles of rock and ash and generated the loudest sound ever reported.
Atmospheric shock waves reverberated around the world seven times and were felt
for five days. Near Krakatoa, according to records, villages and towns were
destroyed and many seriously damaged, more than 36,000 people died, and many
thousands were injured by the eruption, mostly in the tsunamis, which followed
Credit Lonely Islands The Andaman and Nicabar Islands George Weber and
Simron Jet Singh
Map of Central Sumatra
Credit Lonely Islands The Andaman and Nicabar Islands George Weber and
Simron Jet Singh
Earth - The
Genesis of a Living World