Extinct undersea volcanoes squashed under Earth's crust cause tsunami earthquakes

New research has revealed the causes and warning signs of rare tsunami earthquakes, which may lead to improved detection measures.

Tsunami earthquakes happen at relatively shallow depths in the ocean and are small in terms of their magnitude. However, they create very large tsunamis, with some earthquakes that only measure 5.6 on the Richter scale generating waves that reach up to ten metres when they hit the shore.

A global network of seismometers enables researchers to detect even the smallest earthquakes. However, the challenge has been to determine which small magnitude events are likely to cause large tsunamis.

In 1992, a magnitude 7.2 tsunami earthquake occurred off the coast of Nicaragua in Central America causing the deaths of 170 people. Six hundred and thirty seven people died and 164 people were reported missing following a tsunami earthquake off the coast of Java, Indonesia, in 2006, which measured 7.2 on the Richter scale.

The new study, published in the journal Earth and Planetary Science Letters, reveals that tsunami earthquakes may be caused by extinct undersea volcanoes causing a "sticking point" between two sections of Earth's crust called tectonic plates, where one plate slides under another.

The researchers from Imperial College London and GNS Science in New Zealand used geophysical data collected for oil and gas exploration and historical accounts from eye witnesses relating to two tsunami earthquakes, which happened off the coast of New Zealand's north island in 1947. Tsunami earthquakes were only identified by geologists around 35 years ago, so detailed studies of these events are rare.

The team located two extinct volcanoes off the coast of Poverty Bay and Tolaga Bay that have been squashed and sunk beneath the crust off the coast of New Zealand, in a process called subduction.

The researchers suggest that the volcanoes provided a "sticking point" between a part of Earth's crust called the Pacific plate, which was trying to slide underneath the New Zealand plate. This caused a build-up of energy, which was released in 1947, causing the plates to "unstick" and the Pacific plate to move and the volcanoes to become subsumed under New Zealand. This release of the energy from both plates was unusually slow and close to the seabed, causing large movements of the sea floor, which led to the formation of very large tsunami waves.

All these factors combined, say the researchers, are factors that contribute to tsunami earthquakes. The researchers say that the 1947 New Zealand tsunami earthquakes provide valuable insights into what geological factors cause these events. They believe the information they've gathered on these events could be used to locate similar zones around the world that could be at risk from tsunami earthquakes. Eyewitnesses from these tsunami earthquakes also describe the type of ground movement that occurred and this provides valuable clues about possible early warning signals for communities.

Dr Rebecca Bell, from the Department of Earth Science and Engineering at Imperial College London, says: "Tsunami earthquakes don't create massive tremors like more conventional earthquakes such as the one that hit Japan in 2011, so residents and authorities in the past haven't had the same warning signals to evacuate. These types of earthquakes were only identified a few decades ago, so little information has been collected on them. Thanks to oil exploration data and eyewitness accounts from two tsunami earthquakes that happened in New Zealand more than 70 years ago, we are beginning to understand for first time the factors that cause these events. This could ultimately save lives."

By studying the data and reports, the researchers have built up a picture of what happened in New Zealand in 1947 when the tsunami earthquakes hit. In the March earthquake, eyewitnesses around Poverty Bay on the east coast of the country, close to the town of Gisborne, said that they didn't feel violent tremors, which are characteristic of typical earthquakes. Instead, they felt the ground rolling, which lasted for minutes, and brought on a sense of sea sickness. Approximately 30 minutes later the bay was inundated by a ten metre high tsunami that was generated by a 5.9 magnitude offshore earthquake. In May, an earthquake measuring 5.6 on the Richter scale happened off the coast of Tolaga Bay, causing an approximate six metre high tsunami to hit the coast. No lives were lost in the New Zealand earthquakes as the areas were sparsely populated in 1947. However, more recent tsunami earthquakes elsewhere have devastated coastal communities.

The researchers are already working with colleagues in New Zealand to develop a better warning system for residents. In particular, new signage is being installed along coastal regions to alert people to the early warning signs that indicate a possible tsunami earthquake. In the future, the team hope to conduct new cutting-edge geophysical surveys over the sites of other sinking volcanoes to better understand their characteristics and the role they play in generating this unusual type of earthquake.

Can coral save our oceans? Soft coral tissue may help protect reefs against the hazardous effects of climate change

Coral reefs are home to a rich and diverse ecosystem, providing a habitat for a wide range of marine animals. But the increasing acidification of ocean water is jeopardizing the calcified foundations of these reefs, endangering the survival of thousands upon thousands of resident species.

Reefs and environmental change

Acidification is caused by increased carbon dioxide emissions in the atmosphere due to global change, fossil fuel burning, and other pollution. These emissions dissolve in the ocean, resulting in a slight lowering of oceanic pH levels. This produces changes to ocean water's carbon content, destroying the calcification of reef-building stony coral.

"The rise in temperature and ocean acidification are the main concerns of environmental change," said Prof. Benayahu, the Israel Cohen Chair in Environmental Zoology, whose TAU laboratory is home to one of the world's only soft coral (octocoral) research centers. "We know the value of reefs, the massive calcium carbonate constructions that act as wave breakers, and protect against floods, erosion, hurricanes, and typhoons. While alive, they provide habitats for thousands of living organisms, from sea urchins to clams, algae to fish. Reefs are also economically important in regions like Eilat or the Caribbean."

At first, the researchers examined the effects of lowered pH levels on living colonies of soft corals. Observing no significant effects on their physiology, Gabay thought it would be interesting to consider the effects of acidification on the skeleton of these soft corals.

"We really wanted to know if something could survive dropping pH levels in the future," said Gabay. "I was curious as to whether coral tissue could protect the inner coral skeleton, which is of most use in terms of reef construction, so I conducted an experiment using live soft corals and soft coral skeletons, which were placed in tanks containing ocean water with manipulated pH levels."

Using state-of-the-art microscopy, Gabay then scanned the tissue-covered skeletons and bare skeletons of soft corals exposed to experimental acidic conditions, the same conditions the International Panel of Climate Change predicts will occur 100 years from now if carbon dioxide emissions continue to rise. She found that the bare soft coral skeletons exhibited acidic stressed symptoms -- large pockets burned into their microscopic corpuscular subunits -- whereas the tissue-covered skeleton revealed almost no damage to its microscopic subunits.

"We found that the soft coral's tissue may indeed protect the skeleton from declining pH levels," said Yasmin Gabay. "The organism's internal environment apparently has a mechanism that protects against the acidic conditions."

The future of "the orchestra"

According to Prof. Benayahu, the future of soft-coral reefs isstill unclear. Soft corals are not primary reef builders, because their skeletons are slow to calcify. Stony corals provide the massive skeletons that create reefs. Soft corals are replacing these reef builders, because they are somehow able to survive and live under extreme environmental conditions.

"A reef is like an orchestra. Many organisms interact to create harmony," said Prof. Benayahu. "Thousands of species live together and create life together. It is hard to predict what will happen if only soft corals survive, because they simply do not calcify at same rate as stony corals."

The researchers are currently studying the potential effects of soft coral displacement of stony coral species and the subsequent ramifications for reefs.

Plate Tectonics

 Learn About the History and Principles of Plate
Tectonics Plate tectonics is the scientific theory that attempts to explain the movements of the Earth's lithosphere that have formed the landscape features we see across the globe today. By definition the word "plate" in geologic terms means a large slab of solid rock. "Tectonics" is a part of the Greek root for "to build" and together the terms define how the Earth's surface is built up of moving plates. The theory of plate tectonics itself says that the Earth's lithosphere is made up individual plates that are broken down into over a dozen large and small pieces of solid rock. These fragmented plates ride next to each other on top of the Earth's more fluid lower mantle to create different types of plate boundaries that have shaped the Earth's landscape over millions of years. History of Plate Tectonics Plate tectonics grew out of a theory that was first developed in the early 20th century by the meteorologist Alfred Wegener. In 1912, Wegener noticed that the coastlines of the east coast of South America and the west coast of Africa seemed to fit together like a jigsaw puzzle. Further examination of the globe revealed that all of the Earth's continents fit together somehow and Wegener proposed an idea that all of the continents had at one time been connected in a single supercontinent called Pangaea. He believed that the continents gradually began to drift apart around 300 million years ago - this was his theory that became known as continental drift. The main problem with Wegener's initial theory was that he was unsure of how the continents moved apart from one another. Throughout his research to find a mechanism for continental drift, Wegener came across fossil evidence that gave support to his initial theory of Pangaea. In addition he came up with ideas as to how continental drift worked in the building of the world's mountain ranges. Wegener claimed that the leading edges of the Earth's continents collided with each other as they moved causing the land to bunch up and form mountain ranges. He used India moving into the Asian continent to form the Himalayas as an example. Eventually Wegener came up with an idea that cited the Earth's rotation and its centrifugal force toward the equator as the mechanism for continental drift. He said that Pangaea started at the South Pole and the Earth's rotation eventually caused it to break up, sending the continents toward the equator. This idea was rejected by the scientific community and his theory of continental drift was dismissed as well. In 1929 Arthur Holmes, a British geologist, introduced a theory of thermal convection to explain the movement of the Earth's continents. He said that as a substance is heated its density decreases and it rises until it cools sufficiently to sink again. According to Holmes it was this heating and cooling cycle of the Earth's mantle that caused the continents to move. This idea gained very little attention at the time. By the 1960s Holmes' idea began to gain more credibility as scientists increased their understanding of the ocean floor via mapping, discovered its mid-ocean ridges and learned more about its age. In 1961 and 1962 scientists proposed the process of sea floor spreading caused by mantle convection to explain the movement of the Earth's continents and plate tectonics. Principles of Plate Tectonics Today Scientists today have a better understanding of the make-up of the Earth's tectonic plates, the driving forces of their movement, and the ways in which they interact with one another. A tectonic plate itself is defined as a rigid segment of the Earth's lithosphere that moves separately from those surrounding it. There are seven major plates (North America, South America, Eurasia, Africa, Indo-Australian, Pacific and Antarctica) as well as many smaller, microplates such as the Juan de Fuca plate near the United States' state of Washington (map of plates). There are three main driving forces for the movement of the Earth's tectonic plates. They are mantle convection, gravity and the Earth's rotation. Mantle convection is the most widely studied method of tectonic plate movement and it is very similar to the theory developed by Holmes in 1929. There are large convection currents of molten material in the Earth's upper mantle. As these currents transmit energy to the Earth's asthenosphere (the fluid portion of the Earth's lower mantle below the lithosphere) new lithospheric material is pushed up toward the Earth's crust. Evidence of this is shown at mid-ocean ridges where younger land is pushed up through the ridge, causing the older land to move out and away from the ridge, thus moving the tectonic plates. Gravity is a secondary driving force for the movement of the Earth's tectonic plates. At mid-ocean ridges the elevation is higher than the surrounding ocean floor. As the convection currents within the Earth cause new lithospheric material to rise and spread away from the ridge, gravity causes the older material to sink toward the ocean floor and aid in the movement of the plates. The Earth's rotation is the final mechanism for the movement of the Earth's plates but it is minor in comparison to mantle convection and gravity. As the Earth's tectonic plates move they interact in a number of different ways and they form different types of plate boundaries. Divergent boundaries are where the plates move away from each other and new crust is created. Mid-ocean ridges are an example of divergent boundaries. Convergent boundaries are where the plates collide with one another causing the subduction of one plate beneath the other. Transform boundaries are the final type of plate boundary and at these locations the no new crust is created and none is destroyed. Instead the plates slide horizontally past one another. No matter the type of boundary though, the movement of the Earth's tectonic plates is essential in the formation of the various landscape features we see across the globe today.

The El Nino Cycle Indeed El Nino, and the role it plays in periodic droughts which hit the Indian subcontinent, was one of the foundational questions that drove modern weather research. In his book on Victorian famines, writer Mike Davis calls the El Nino Southern Oscillation (or ENSO to give it its full name) the "elusive great white whale of tropical meteorology for almost a century". And despite more than a century of research, it still, in a sense, remains that way. El Nino arises in the eastern Pacific, along the coast of South America. In 'normal' years, there exists both a temperature and air pressure difference between the oceans there, and the western Pacific, thousands of miles on the other side, near Indonesia and Southeast Asia. The waters of the eastern Pacific near South America are colder, and are associated with higher atmospheric air pressure over them, as compared with the waters of the western Pacific which are warmer, and are associated with lower atmospheric pressure. As we learnt in high school geography, wind always blows from a region of high pressure to a region of low pressure, and this is what happens over the Pacific, with winds blowing from the east to the west. In turn, the air over the western pacific rises into the atmosphere and then cycles back east, and the whole process starts again. http://articles.economictimes.indiatimes.com/2014-06-22/news/50772456_1_indian-monsoon-eastern-pacific-high-pressure