[hide]ScienceDaily (June 1, 2012) — The current theory of continental drift provides a good model for understanding terrestrial processes through history. However, while plate tectonics is able to successfully shed light on processes up to 3 billion years ago, the theory isn't sufficient in explaining the dynamics of Earth and crust formation before that point and through to the earliest formation of planet, some 4.6 billion years ago. This is the conclusion of Tomas Naæraa of the Nordic Center for Earth Evolution at the Natural History Museum of Denmark, a part of the University of Copenhagen. His new doctoral dissertation has just been published by the journal Nature.

"Using radiometric dating, one can observe that Earth's oldest continents were created in geodynamic environments which were markedly different than current environments characterised by plate tectonics. Therefore, plate tectonics as we know it today is not a good model for understanding the processes at play during the earliest episodes of Earths's history, those beyond 3 billion years ago. There was another crust dynamic and crust formation that occurred under other processes," explains Tomas Næraa, who has been a PhD student at the Natural History Museum of Denmark and the Geological Survey of Denmark and Greenland -- GEUS.

Plate tectonics is a theory of continental drift and sea floor spreading. A wide range of phenomena from volcanism, earthquakes and undersea earthquakes (and pursuant tsunamis) to variations in climate and species development on Earth can be explained by the plate tectonics model, globally recognized during the 1960's. Tomas Næraa can now demonstrate that the half-century old model no longer suffices.

"Plate tectonics theory can be applied to about 3 billion years of the Earth's history. However, the Earth is older, up to 4.567 billion years old. We can now demonstrate that there has been a significant shift in the Earth's dynamics. Thus, the Earth, under the first third of its history, developed under conditions other than what can be explained using the plate tectonics model," explains Tomas Næraa. Tomas is currently employed as a project researcher at GEUS.

Central research topic for 30 years

Since 2006, the 40-year-old Tomas Næraa has conducted studies of rocks sourced in the 3.85 billion year-old bedrock of the Nuuk region in West Greenland. Using isotopes of the element hafnium (Hf), he has managed to shed light upon a research topic that has puzzled geologists around the world for 30 years. Næraa's instructor, Professor Minik Rosing of the Natural History Museum of Denmark considers Næraa's dissertation a seminal work:

"We have come to understand the context of the Earth's and continent's origins in an entirely new way. Climate and nutrient cycles which nourish all terrestrial organisms are driven by plate tectonics. So, if the Earth's crust formation was controlled and initiated by other factors, we need to find out what controlled climate and the environments in which life began and evolved 4 billion years ago. This fundamental understanding can be of great significance for the understanding of future climate change," says Minik Rosing, who adds that: "An enormous job waits ahead, and Næraas' dissertation is an epochal step."
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http://www.sciencedaily.com/releases/201...120606.htm

A tsunami (Japanese for harbor wave) can be caused when a large volume of water in a sea or ocean is displaced. Tsunamis can happen most anywhere that there is an ocean or giant body of water. They especially happen where major natural events like underwater earthquakes or volcanoes can happen.

A tsunami can be generated when convergent or destructive plate boundaries abruptly move and vertically displace the overlying water. There is usually a movement underwater, like an earthquake, where the earth's plates push together, or a landslide, which causes a wave to be generated. When tectonic plates slide on each other, that's when an earthquake may happen. Because they can slide under the ocean, the impact can make the water form a giant wave. This wave is massive - nothing like what a surfer seeks. The wave can be meters high, and as it rushes closer to the coast it gains enough momentum to wreak massive damage on land. The momentum slows upon reaching land, but it is still a major force.

Get in a pool or the bath tub and put your hand a good ways down and then pull it up quickly but not out of the water, pull up strong but don't break the surface and watch the result. Not exactly a tsunami, but a simple version of the science.

Tsunamis can be caused from different kinds of events, including, but not limited to:

Sea bed earthquake, displacing water (the most likely cause).
Distance landslides into the ocean or sea.
Tropical storms or hurricanes.
Volcanic disruption.
Meteor striking the ocean or sea.


More details

"Most tsunamis occur when there are underwater seismic events such as an underwater earthquake or volcanic eruption. This normally occurs along plate boundaries. Subduction in convergent boundaries account for most tsunamis. This will cause shock waves to be radiated out of the epicenter. There will be a rise or fall of the seabed. This displacement will create a wave which cannot be clearly detected from shore. These waves can travel at speeds up to 700 mph (i.e. the speed of sound in water). As the wave gets nearer to the shore, the wave will compress and gain height in the shallower water. The waves can be up to 100 ft. (30 m) or more when they come ashore.

Tsunamis can also occur because of landslides. When land subsides into water bodies (usually extremely large landslides), they can create a wave that resembles a tsunami. The wave of these kinds of tsunamis will not be very high, unless a huge volume of rock or ice is involved.

Tsunamis can also occur when asteroids fall into the water bodies. This is extremely rare, and they must be extremely large to cause a large water displacement to form a wave. Meteorites will not cause high waves as they are usually much smaller than asteroids.

Some meteorological storm conditions such as deep depressions causing cyclones, hurricanes, strong winds and other similar occurrences can generate a storm surge, which can be several metres above normal tide levels. This is due to the low atmospheric pressure within the centre of the depression. As a storm surge comes ashore, it can resemble a tsunami, inundating vast areas of land."


http://wiki.answers.com/Q/How_do_tsunamis_happen

ScienceDaily (July 6, 2011) — Bringing fresh insight into long-standing debates about how powerful geological forces shape the planet, from earthquake ruptures to mountain formations, scientists at Scripps Institution of Oceanography at UC San Diego have identified a new mechanism driving Earth's massive tectonic plates.

Scientists who study tectonic motions have known for decades that the ongoing "pull" and "push" movements of the plates are responsible for sculpting continental features around the planet. Volcanoes, for example, are generally located at areas where plates are moving apart or coming together. Scripps scientists Steve Cande and Dave Stegman have now discovered a new force that drives plate tectonics: Plumes of hot magma pushing up from Earth's deep interior. Their research is published in the July 7 issue of the journal Nature.

Using analytical methods to track plate motions through Earth's history, Cande and Stegman's research provides evidence that such mantle plume "hot spots," which can last for tens of millions of years and are active today at locations such as Hawaii, Iceland and the Galapagos, may work as an additional tectonic driver, along with push-pull forces.

Their new results describe a clear connection between the arrival of a powerful mantle plume head around 70 million years ago and the rapid motion of the Indian plate that was pushed as a consequence of overlying the plume's location. The arrival of the plume also created immense formations of volcanic rock now called the "Deccan flood basalts" in western India, which erupted just prior to the mass extinction of dinosaurs. The Indian continent has since drifted north and collided with Asia, but the original location of the plume's arrival has remained volcanically active to this day, most recently having formed Réunion island near Madagascar.

The team also recognized that this "plume-push" force acted on other tectonic plates, and pushed on Africa as well but in the opposite direction.

"Prior to the plume's arrival, the African plate was slowly drifting but then stops altogether, at the same time the Indian speeds up," explains Stegman, an assistant professor of geophysics in Scripps' Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics. "It became clear the motion of the Indian and African plates were synchronized and the Réunion hotspot was the common link."

After the force of the plume had waned, the African plate's motion gradually returned to its previous speed while India slowed down.

"There is a dramatic slow down in the northwards motion of the Indian plate around 50 million years ago that has long been attributed to the initial collision of India with the Eurasian plate," said Cande, a professor of marine geophysics in the Geosciences Research Division at Scripps. "An implication of our study is that the slow down might just reflect the waning of the mantle plume-the actual collision might have occurred a little later."

http://www.sciencedaily.com/releases/201...134139.htm

For the first time, scientists have found a link between climatic events and the movement of tectonic plates.

LONG-TERM, NATURAL CLIMATIC events can alter the motion of the earth's tectonic plates, according to new research.

An international team - led by researchers from the Australian National University - found that intensifying monsoon activity has sped up the motion of the Indian plate, which crunched into the Eurasian plate to form the Himalayas 40 to 50 million years ago.
Tectonic plate motion linked to weather

Over the past 10-15 million years, monsoons - which increase rainfall in northeast India by 4m annually and cause erosion - have sped up the anti-clockwise motion of the Indian plate by almost one centimetre per year, the researchers say. This is quite fast, considering tectonic plates move about the same rate at which fingernails grow.

"We were very excited," ANU's Dr Giampiero Iaffaldano told Australian Geographic. "This is the first time we have been able to make the link between what naturally happens to climate over millions of years and the motion of tectonic plates," he says.

"While it was already known that plate tectonics can affect climate through events such as mountain uplift altering wind and rainfall patterns," Giampiero says. "Now we know that it can also operate the opposite way".
Erosion leads to faster tectonic plate movement

Monsoonal rain, says Giampiero, causes erosion of mountains, which reduces frictional forces along the plate boundary. This essentially allows the plates to move against each other more quickly - although he is quick to stress that it remains, nevertheless, a very slow process, taking millions of years.

Dr Jo Whittaker, a geophysicist at the University of Sydney, says the work has "implications for how scientists understand the forces driving the motion of the tectonic plates" - in particular, it is hoped the results may help to unlock the secrets of earthquake-prone regions.

"Ultimately we aim at understanding what forces caused plate motions to change in the past and which regions are currently more prone to large earthquakes. To that end, we may also have to consider, among other factors, the history of climate over the past million years", says Giampiero.

The findings were published in the journal, Earth and Planetary Science Letters.

http://www.australiangeographic.com.au/j...plates.htm