GEOL 2250 Materials
Tsunami - Asian Killer Tsunami of Dec 26/2004
Tsunami animation local
- 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 subductionof the Australian plate beneath the Eurasian plate
- Earthquake, Banda Aceh near epicenter was heavily damaged. Humanswere 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)
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.
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.
- Neighboring plates slide alongside each other in a transform plate boundary.
- 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.
- 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 basinbecause 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.
- Hawaiian islands (ridge) and Emperor seamounts- Pacific Ocean
- Reunion and Chagos-Laccadive Ridge (CLR), [the Maldives] - Indian Ocean
MOR separated reunion from CLR about 35 Ma.
- 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.
- 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.
- Marion, Crozzet Plateau, and Thirty-East Spur - Western Antarctica Ocean
- Ontong Java, Caribbean, and kerguelen Plateaus are the largest oceanic LIPs (Arndt, 2003)
- Traps (or LIPs on continents) include, the Deccan, Siberian, Parana, Columbia River Plateau.
Formation of the Indian Ocean over the last 200 Million years.
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).
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.
- 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.