Tsunami- Asian Killer Tsunami of Dec 26/2004
Tsunami animation across the globe
Earthquake. -
Magnitude 9.0
on the Richter scale. [a magnitude 9 is ten times stronger than
magnitude
8,
and it releases 32 times more energy than an
earthquake of magnitude 8.]
-
Depth of focus 10 Km (6.2 miles)
-
Epicenter, 160 Km (100 miles), off the coast of Indonesian Sumatra
Island, but
still east of the Java (Sunda) Trench
-
Time, about 7 AM, (midnight GMT) Sunday, Full Moon (Hindu bath, Neap
tide)
Cause of earthquake. Released energy bound in rocks that
resulted from the subduction
of the Australian plate beneath the Eurasian
plate
Damage -
Earthquake, Banda
Aceh near epicenter was heavily damaged. Humans
were
killed and structures were damaged.
Aftershocks
of magnitude 6 occurred up to 4 days, and at different places,
including at
islands owned by India but still on the Indonesian plate.
A magnitude 5.5 aftershock on Thursday
(5th day) started a scare that Tsunami was coming, and people run for
higher
ground. Low level aftershocks were reported up to Jan. 3/05
-
Tsunami, about 11 countries, Indonesia, Malaysia, Thailand, India, Sri
Lanka,
Maldives, and East Africa (Somalia, Kenya, Tanganyika) were affected.
Death
directly from earthquake and tsunami & international aid: Estimates changed from 10,000 on Sunday to
86,0000 on
Wednesday, to 120,000 on Thursday 138,00 by Saturday, to 156,00 on
January 3
(94,000 from Indonesia), death tall increasing as inaccessible areas
were
reached. A third of those killed were kids. Aid from the international
community was immediate, $500 million from Japan, $350 million from the
USA,
etc. Eleven naval vessels from the Indian Navy are now helping clean up
Sri
Lanka. US aircraft carrier Abraham Lincoln has arrived in Sumatra and
helicopters transported food to Sumatrans, (CNN 1/05)].
Only Indonesia, Sri Lanka, Maldives and
Somalia were willing to accept international aid, the rest reported
that they
had enough resources (CNN, Jan. 3/05)
-Diseases:
Diarrhea, respiratory infections, dysentery, hepatitis, dengue fever
malaria
are possible if no intervention is taken ASAP.
Generation of a
Tsunami
(Japanese term for wave in harbor).
--
Earthquake ruptures seafloor, displaces one side of the ruptured floor
upwards by about 10 meters (30
feet), which in turn pushes water upwards starting a wave. Wave energy
propagates by setting water molecules into orbits. Water heaves to crest
and drains away as the trough arrives. The period of the wave
is about 5
minutes. (The wave period is maintained though the speed is slowed on
shore. For example, in Sri Lanka,
a father collected his surviving child that was stranded on a tree
after the
first wave receded. Yet after
saving his kid the father was drowned in the second wave. On Saturday,
heavy
rains brought flash floods and have washed away make shift shelters of
survivors CNN 1/05 TV.)
--Wave
has about 100 km wavelength so wave "feels bottom", and is thus (wave
base = 50 km) a shallow water wave whose speed (C) is directly
proportional to the square root of water depth (D) and the gravitation
acceleration (g) [ C= (g.D)1/2
= 7.1 D1/2 miles per hour, or 3.13 D1/2 meters per second]. Wave moves rapidly
in deep water, about 500 to 700 km per hour. Wave travels great
distances
without loss of energy, because loss of energy is inversely related to
wavelength.
-Wave
near land slows to about 45 km per hour and the waveform is transformed. Depending on the angle of slope of the near
shore
the tsunami might behave like a rising and falling tide, or otherwise
imperceptible wave height in the deep sea is transformed into a
surging
wall-of-water (a bore - with heights reaching 20 feet, because
wave-energy flux depends on wave height and wave speed), or a series of
breaking waves or combinations depending on the topographic relief on
the near
shore.
---
Wave heads on land destroying every thing by its force and the debris
that it
entrains into orbital as it advances forward.
[An
American couple who were scuba diving in deep water off the
coast of
Sumatra reported that the water at depth was murky, and they were being
pulled
down by the force of the water though they surfaced to observe some
debris. They went elsewhere in the
area to attempt another dive, but stopped the effort because of debris. They experienced the Tsunami in deep
water though they did not know of the devastation on shore, which they
noted
only when they returned to shore after the Tsunami event (CNN several
reports
Monday through Wednesday).
Another
group of Americans on a snorkeling expedition to Thailand noted that
the snorkel
zone was shallow and milky. They
inferred that they were in a trough of a tsunami. Initially
they headed toward shore, but were instructed to
sail out to deep water. They
reported having seen may be a wave height measured in inches. Upon returning to shore, they witnessed
the massive devastation brought by the tsunami (CNN. 1/05).
Diving
to coral sites shows devastation of corals and associated nektons in
some
places whereas in others they were not touched (CBS1/4/05).
A
resort hotel in Sri Lanka reported that water advanced to the interior
of the
Hotel. The water was withdrawn and
large areas of the shore and reefs were exposed. Then
came a second wave of water followed by exposure of the
near shore. A third wave arrived. Debris was left all over the shore CNN
1/05). In some areas in
Sumatra, the water was initially withdrawn exposing the shore with
stranded
fishes before the wall-of-water brought the killer wave (CBS 1/4/05)
Earthquake as an
early
warning signal for tsunami.
Inhabitants of the island of Simeulue, 45 km from the epicenter
of the
Dec 26 earthquake benefited by implementing their culture of running to
higher
ground whenever they hear or feel earthquakes. This
culture began in the 1800s when their forebears
instituted it. The result was that many inhabitants were saved from the
death
brought by the December 26/04 Tsunami, except that their schools and
mosques on
the coastal plain were destroyed.
The Andamans
(Indian Island
on the Sumatra side of the earth's plates) suffered little loss of
life, though
their properties were damaged (CNN 3/05).
Presumably, they heeded reactions of animals.
Worldwide
effects of the
earthquake.
On Sunday an
Italian
geophysicist and on Wednesday Caltech geophysicists had reported that
the
subduction of Indo-Australian plate, that resulted in the December 26
earthquake, likely speeded up of the earth's rotation (like an ice
skater
speeds up rotation when arms are pulled in) in microseconds. Also, it has likely resulted in increasing
the wobble of the earth' spin axis by inches.
USGS Geologist,
Atwater warns
that a tsunami could start form the Cascade subduction in the
northwestern
coast of the USA, and it could strike northwestern coastal habitat
within 30
minutes, before the current 6 deep sea sensors of the Pacific can
provide
warnings. A 1700s earthquake (9.0 magnitude) along the Cascade
subduction zone
(about 50 miles offshore) had produced measurable damage in Puget Sound
(AP,
12/29/04).
A more lasting
effect of the
earthquake is the displacement of islands, perhaps along the Sumatra
strike
slip fault.
Ocean basins -
with a view
of understanding the tsunami.
REVIEW
Geologic Time: a
synopsis. Vast geologic time
is divided into 2 Eons,
the Precambrian (from 4600 to 540 million years ago) and the
Phanerozoic (540
Ma to the present. The Phanerozoic
Eon is divided in 3 Eras, the Paleozoic (540 Ma to 245 Ma), the
Mesozoic
(245-65 Ma) and the Cenozoic (65 Ma to the present). Each Era is
divided into Periods
that may be remembered by recalling the following
mnemonic. Come Over Some Day Maybe Play Poker, Two
Jacks Call, Three Queens, for Cambrian, Ordovician, Silurian, Devonian,
Mississippian, Pennsylvanian, Permian (245 Ma), Triassic, Jurassic,
Cretaceous
(65 Ma), Triassic, Quaternary.)
- The Earth is
layered
into the core mantle and crust
(both
oceanic and continental).
- The uppermost
mantle and
crust constitute the lithosphere.
A layer, about 100 km thick, below the lithosphere is partly melted
(magma) and
is called the asthenosphere.
- The earth may be
likened to
an egg with the lithosphere being analogous to the hard shell of an egg.
-The Earth's
lithosphere is
segmented into fragments called plates. The plates may
comprise
of oceanic or continental or combinations of both types of lithospheres.
-
The plates are separated by plate boundaries that are called divergent, convergent or
transform
plate boundary.
- 1) Neighboring
plates slide
alongside each other in a transform plate boundary.
- 2) Neighboring
plates move
apart and away from each other in a divergent plate boundary. In the
rift stage, continental lithosphere is split forming a rift valley. In the drift stage continental
fragments drift away as an ocean basin is developed between them at the
Mid
Oceanic Ridge (MOR). The
largest
mountain chain in the world is the MOR, about 65,000 km long, 50 Km
wide, 3 km
relief with a central rift of about 1 km deep. The ocean basin is
formed by
magma ascending from the asthenosphere, minerals crystallizing from the
magma
and interlocking into rock. Magnetic
domains in the magma are aligned by the Earth's magnetic field as
minerals
form and cool. Consequently, the
igneous rocks that are formed at a divergent boundary have magnetic
polarity
frozen in them. The igneous rocks
so formed are split apart and new magma ascends from which new igneous
rocks
are formed and which may acquire a reverse magnetic polarity if the
Earth's
magnetic polarity has reversed. Thus, magnetic strips characterize ocean basin rocks. Often the
magnetic
strips are displayed on maps by colors, and the color pattern shows
that one
side of the ocean basin is a mirror image of the other, thereby
indicating that
the ocean basin rocks were all formed at the MOR.
-3) Neighboring
plate move
toward each other and collide resulting in one of them being subducted
beneath
the other in a convergent plate boundary. Where plates
collide a
depression, called a trench is developed. For
example, the Java (Sunda) Trench is formed by the
subduction of Australian Plate beneath Eurasian Plate. The subduction
zone
is the contact area between the upper part of the subducted plate
(Australian)
and the lower part of the overriding plate (Eurasian). From the trench
landward, the upper lip of the overriding plate has a topography
characterized
by a fore arc ridge, fore arc basin, volcanic arc and back arc basin. Small islands dot the fore arc ridge
[Fig. 8.1 & 8.2. Java (Sunda)
trench and cross sections].
Sumatra and Java are in the volcanic arc sector, and are dotted
with
volcanoes, Nine volcanoes on Sumatra alone. The
large water covered region east of Java and Sumatra is
the back arc basin. It is also called a foreland basin because it is a water covered, and
because a foreland
is any part of the a stable continent edge adjacent
to a convergent boundary.
What causes
Plate
Movement?
Ridge Push, Slab
Pull and
Slab Suction are the three proposed mechanisms that drive plate
motion.
Ridge Push. Divergence of mantle convection
fractures the overlying lithosphere, lowers the pressure on the
underlying
mantle, and results in decompression melting of the mantle. The
buoyancy
anomaly lifts the mantle into a ridge. The elevation of the ridge
causes an
increase in gravitational potential energy. Gravity slide draws the
ridge
material down and away from the ridge, which further fractures the
lithosphere
at the middle of the ridge and results in mantle material to well up. Ridge push is estimated to be 1/10th as
energetic as slab pull.
Slab Pull. Cold and dense lithosphere is suducted
beneath another at convergent boundaries.
The subducted lithosphere is called a slab. As the slab is
colder and
denser than the mantle, the slab sinks "like lead would in a vat of
molasses". As the slab sinks,
it pulls on the lithosphere. This is slab pull process operates in the
upper
mantle. In the lower mantle, often
the slab is detached or poorly attached to the lithosphere. The slab
sinks in
the lower mantle, and creates slab suction forces in the lower
mantle
that results in drawing neighboring plates toward the trench, "as would
a
drainage outlet to floating toys in a bath tab". Whereas
slab pull affects only the subducting plate, slab
suction affects both the lower and the overriding plate.
However, slab pull generates
counteracting forces in the mantle that reduce the amount of suctioning. Slab pull and slab suction working in
combination appear to explain observed plate movement, that subducting
plates
move 4 times faster than overriding plates. Also,
over the Cenozoic the mass and length of upper mantle
slab has been increasing (Conrad and Lithgoid-Bertelloni, 2004).
Slab suction may
cause back
arc spreading. Tertiary oil deposits are found in the
foreland basin of the Eurasian Plate landward of Java and Sumatra.
Hot
plume tracks as evidence plate movement. Hot
spots are stationary places at which hot rocks ascend, and decompression
melting forms magma (Hot plume) that penetrates the overlying
lithosphere
to form igneous rock edifices, some of which are quite large and are
called Large
Igneous Provinces (LIPs). As
the lithosphere moves over the hot spot early formed igneous rock
edifices are
moved along (conveyor belt style), and new ones form over the hot spot. A series of igneous rock edifices that
are aligned and become young in ages toward a hot spot are called hot
plume
tracks. The following are some
examples. See Fig. 5.28.
1) Hawaiian islands
(ridge)
and Emperor seamounts- Pacific
Ocean
2). Reunion and
Chagos-Laccadive Ridge (CLR), [the Maldives] - Indian Ocean
MOR
separated reunion from CLR about 35 Ma.
3) Kerguelen-
Broken Ridge
and the NinetyEast Ridge --Indian Ocean
MOR
separated Kerguelen from Broken Ridge and the 90E Ridge about 25 Ma.
90E
Ridge , the longest lineament in the ocean, becomes young from 82 to 38
Ma
southwards.
4) Tristan da Cunha, Walvis Ridge and
Etendeka flood basalt of Atlantic Ocean and Africa.
And Tristan da Cunha, Rio Grande
Rise and Parana flood basalt of Atlantic Ocean and South America.
5) Marion, Crozzet
Plateau,
and Thirty-East Spur - Western Antarctica Ocean
6) Ontong Java,
Caribbean,
and kerguelen Plateaus are the largest oceanic LIPs (Arndt, 2003)
7) Traps (or LIPs
on
continents) include, the Deccan, Siberian, Parana, Columbia River
Plateau.
Formation of the
Indian Ocean
over the last 200 Million years.
See animation
182 Ma
-Karoo -Ferrar Plume split Gondwana
132 Ma- Tristan da
Cunha
plume split South America and Africa
Mozambique
Rift is initiated. One side of rift is the edge of Falkland Plateau.
(110 Ma - Kerguelen
Plume
split India from Australia)
88 Ma - Marion
Plume split
Madagascar and India
64 Ma - Reunion
split
Mascarene Plateau from India. (Deccan Trap of India, associated with
earth
cooling, though bested by a bolide impact at Chicxulub, Mexican Gulf,
at the
Cretaceous /Tertiary (K/T) boundary.)-- CO2 - degassed from mantle and
placed
in the troposphere is not removed by the sluggish carbon cycle- causes
earth
warming and Extension.
Formation of the
Java
(Sunda) Trench.
It began as a
subduction zone
when the Tethys Sea was closing. See animation.
-
Igneous rocks of the volcanic arc are generally produced by dehydration
melting of the mantle wedge between the subducted and overriding
plates. Often Andesites are
produced from mixing of magmas.
Volcanic
eruption and
climate.
Copious amount of
lava
extrusion is associated with degassing of the mantle and placing excess
CO2 in
the atmosphere, far more than can be redistributed by the slow carbon
cycle.
This condition might result in global warming, which in turn results in
the
removal of oxygen from the ocean that causes extinction of marine
animals and
also deposition of un-oxygenated black shale (Kerr, 1998).
Some have suggested
that
Reunion hot plume extrusion to form the Deccan Trap is responsible for
the K/T
extinction of dinosaurs and other organisms, though that death is
bested by the
Chicxulub bolide impact.
Some argue that
copious
amount andesite eruption at volcanic arcs leads to earth warming (gases
in the
troposphere), whereas Basaltic eruption at hot plume lead to earth
cooling (
gases in the stratosphere).
History
Vasco
de Gama,
Crossed the Cape of Good Hope in 1498, and set sail to Indian in search
of
Prester John
Portuguese
colonized Sri Lanka (Ceylon), Port Galle.
Search
for
Terra Australis
that was
supposed to counterbalance the continents in the northern hemisphere.
(Utexas.Edu)
Yves
Joseph de
KerguŽlen-TrŽmarac discovered what he called La France Australe
(today's
Kerguelen chain) in 1772, which sent him back with three ships and 700
men to
colonize it in 1773. Upon KerguŽlen's second homecoming to France, he
was
court-martialed, sentenced to 20 years in prison for having mislead his
nation
by making them think of economic benefits.
Captain
James
Cook, also sailed in search of Terra Australis andnamed
Australia, but not the legendary southern
continent. Terra Australis was eventually discovered in the 19th
century. It
was located farther south and its present-day name is Antarctica.
Captain Cook
also landed at La France Australe on Christmas Eve 1776.
Bibliography (incomplete)
-
http://www.scotese.com/ --animation of ocean formation
--http://www.ig.utexas.edu/research/projects/kerg/leg183/leg183.htm
----Results for history-- Kerguelen-
NinetyEast Ridge 38- 82 MA
--
http://www.tsrc.uwa.edu.au/__data/page/28314/pub56.pdf
Lawrence A. LAWVER, Lisa M. GAHAGAN and Ian W.D. DALZIEL-- Indian ocean
--http://www.usna.edu/Users/oceano/pguth/website/so461web/so461_paper_topics.htm
- earth warming from reunion at K/T boundary
--
http://www.earth.cf.ac.uk/people/summaries/116.LIP.htm,
Caribbean LIP
--
http://poseidon.palaeoz.geomar.de/files/AandO/Arndt_ODPLegacy.pdf-,
Ontong
Java, Caribbean, and kergueleun Plateaus LIPs). REE
Pattern similarities- Tholeiites, alkalis and felsics.
Gill,b.
J., 1981.
Orogenic andesites and plate tectonics, Springer-Verlag,New York, p.
390.
Kerr,
W. C. A.,
1998. Oceanic Plateau formation: a cause of mass extinction and black
shale
deposition around the Cenomonian-Tuconian boundary? Journal of
Geological
Society of London, V. 155, pp. 619-626
Strahler,
A. N.,
1998. Plate Tectonics, Geo.Books Publ., Cambridge MA, p. 554.