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Rank: 1. Death: 229,866 Date: 2004 Cause: Indian Ocean tsunami Location: Indian Ocean Rank: 2. Death: 100,000 Date: 1755 Cause: Lisbon earthquake/tsunami/fire Location: Portugal, Spain, Morocco, Ireland, and the United Kingdom (Cornwall) Rank: 3. Death: 100,000 Date: 1908 Cause: Messina earthquake/tsunami Location: Messina, Italy Rank: 4. Death: 36,000 Date: 1883 Cause: Krakatoa eruption Location: Indonesia Rank: 5. Death: 30,000 Date: 1707 Cause: Tokaido/Nankaido Location: Japan Rank: 6. Death: 27,000 Date: 1826 Cause: Location: Japan Rank: 7. Death: 25,674 Date: 1868 Cause: Arica earthquake/tsunami Location: Arica, Chile Rank: 8. Death: 22,070 Date: 1896 Cause: Sanriku Location: Japan Rank: 9. Death: 15,030 Date: 1792 Cause: Mount Unzen eruption in southwest Location: Kyushu Japan Rank: 10. Death: 13,486 Date: 1771 Cause: Ryukyu Trench Location: Japan

Causes of earthquakes If seen broadly we can say that earthquakes are caused due to two major reasons. The first reason is the eruption of volcanoes, which are sudden, and as is known volcanoes are seat of inner disturbance and can effect the plates which is the second cause of earthquakes. Earthquakes are caused due to disturbance in the movement of plates, which again can be caused due to various reasons like under crust waves or cracks in the plates. Plate Tectonic Theory The outer layer of the earth is divided into many sections known as plates, which are floating on the molten magma beneath the earth’s crust. Now the movement of these plates is determined by the convection current in the molten magma. The heat makes these plates rise and vice versa. Therefore after intervals there are plates that get submerged in the molten magma and there plates that rise upwards and at times even new crust is formed from the molten magma which in turn forms a new plate until it connects itself with the already existing ones. At times these plates and can be pushed up to form mountains and hills and the movement is so slow that it is really hard to comprehend that there is any movement at all. The movement and the results come out to be visible suddenly. Now these plates are the bases on which the continents stand and when these plates move the continents also move. Most of the earthquakes occur on the edges of the plates where a plate is under one or across. This movement disrupts the balance and position of all plates, which leads to tremors, which are called earthquakes.

The causes of landslides are usually related to instabilities in slopes. It is usually possible to identify one or more landslide causes and one landslide trigger. The difference between these two concepts is subtle but important. The landslide causes are the reasons that a landslide occurred in that location and at that time. Landslide causes are listed in the following table, and include geological factors, morphological factors, physical factors and factors associated with human activity. Causes may be considered to be factors that made the slope vulnerable to failure, that predispose the slope to becoming unstable. The trigger is the single event that finally initiated the landslide. Thus, causes combine to make a slope vulnerable to failure, and the trigger finally initiates the movement. Landslides can have many causes but can only have one trigger as shown in the next figure. Usually, it is relatively easy to determine the trigger after the landslide has occurred (although it is generally very difficult to determine the exact nature of landslide triggers ahead of a movement event). Occasionally, even after detailed investigations, no trigger can be determined - this was the case in the large Mount Cook landslide in New Zealand 1991. It is unclear as to whether the lack of a trigger in such cases is the result of some unknown process acting within the landslide, or whether there was in fact a trigger, but it cannot be determined. Perhaps this is because the trigger was in fact a slow but steady decrease in material strength associated with the weathering of the rock - at some point the material becomes so weak that failure must occur. Hence the trigger is the weathering process, but this is not detectable externally. In most cases we think of a trigger as an external stimulus that induces an immediate or near-immediate response in the slope, in this case in the form of the movement of the landslide. Generally this movement is induced either because the stresses in the slope are altered, perhaps by increasing shear stress or decreasing the effective normal stress, or by reducing the resistance to the movement perhaps by decreasing the shear strength of the materials within the landslide.

The short answer is that earthquakes are caused by faulting, a sudden lateral or vertical movement of rock along a rupture (break) surface.     Here's the longer answer: The surface of the Earth is in continuous slow motion. This is plate tectonics--the motion of immense rigid plates at the surface of the Earth in response to flow of rock within the Earth. The plates cover the entire surface of the globe. Since they are all moving they rub against each other in some places (like the San Andreas Fault in California), sink beneath each other in others (like the Peru-Chile Trench along the western border of South America), or spread apart from each other (like the Mid-Atlantic Ridge). At such places the motion isn't smooth--the plates are stuck together at the edges but the rest of each plate is continuing to move, so the rocks along the edges are distorted (what we call "strain"). As the motion continues, the strain builds up to the point where the rock cannot withstand any more bending. With a lurch, the rock breaks and the two sides move. An earthquake is the shaking that radiates out from the breaking rock.

Tsunamis race across the sea at up to 500 miles (805 kilometers) an hour

A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet (30.5 meters), onto land. These walls of water can cause widespread destruction when they crash ashore.These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate boundary rises or falls suddenly it displaces the water above it and launches the rolling waves that will become a tsunami.

PARIS - THE magnitude 7.0 earthquake that struck Haiti in January, killing a quarter of a million people, also unleashed a string of tsunamis on the country's western coast, scientists reported on Sunday. Several waves measuring up to 75cm were caused by a combination of earth movement and coastal landslides. They included banks of sediment on the sea bed, accumulated at river deltas, which were displaced by the shock and unleashed the waves as they moved, the study says. Waves were reported west, north and south of the epicentre, which was within a few kilometres of the surface on the Enriquillo-Plaintain Garden fault, on the boundaries of two microplates in the Caribbean. Such 'slide-generated' tsunami are rare, but their risk is underestimated, according to the paper, published online in the journal Nature Geoscience. 'Even modest, predominantly strike-slip earthquakes can cause potentially catastrophic slide-generated tsunami,' it says. A strike-slip earthquake occurs when one side of the fault moves along horizontally and in parallel to the other side of the fault, rather than down or up. Vertical displacement, especially of the seabed, is best known for creating tsunamis. The study was led by a team led by Matthew Hornbach of the University of Texas at Austin. The January 12 quake was in tectonic terms a surprisingly complex affair, according to new research. Two-thirds of the movement was strike-slip, and a third was a thrust, or upward, movement. The quake inflicted huge damage to the capital, Port-au-Prince, injuring 300,000 people and leaving 1.5 million homeless. -- AFP

he huge waves moved quickly across the ocean before hitting land. The waves caused a huge amount of destruction to towns and resorts along the coast. Over 150,000 people were killed as the tsunami waves hit the coasts of Indonesia, Malaysia, Myanmar, Thailand, Bangladesh, Sri Lanka, India, and the east coast of Africa. There was very little time to sound alarms and get people away from the coast. The more you know about how the Earth works, the more you can keep yourself and others as safe as possible from natural disasters. We at Windows to the Universe would like to congratulate Tilly Smith, a 10-year-old British girl who used her knowledge about how tsunamis works to save 100 people during the event. Tilly learned about tsunamis at school two weeks before the tsunami hit where her family was vacationing in Phuket, Thailand. She saw the water drawing out quickly from the shore and remembered that this can happen before a tsunami wave hits the coast. Thanks to Tilly, her mother, and the hotel staff, everyone was cleared off the beach minutes before the wave arrived. Last modified May 21, 2008 by Lisa Gardiner.