Sumatra Earthquake & Indian Ocean Tsunami December 26, 2004 Sumatra Earthquake & Indian Ocean Tsunami

Tsunami 101 Tsunami 101: Tsunamis are a series of traveling ocean waves of extremely long length generated primarily by earthquakes occurring below or near the ocean floor. Underwater volcanic eruptions and landslides can also generate tsunamis. A tsunami is a series of ocean waves generated by any rapid large-scale disturbance of the sea water. Most tsunamis are generated by earthquakes, but they may also be caused by volcanic eruptions, landslides, undersea slumps or meteor impacts. The waves radiate outward in all directions from the disturbance and can propagate across entire ocean basins. For example, in 1960 an earthquake in Chile caused a tsunami that swept across the Pacific to Japan. Tsunami waves are distinguished from ordinary ocean waves by their great length between peaks, often exceeding 100 miles in the deep ocean, and by the long amount of time between these peaks, ranging from five minutes to an hour. The speed at which tsunamis travel depends on the ocean depth. A tsunami can exceed 500 mph in the deep ocean but slows to 20 or 30 mph in the shallow water near land. In less than 24 hours, a tsunami can cross the entire Pacific Ocean. In the deep ocean, a tsunami is barely noticeable and will only cause a small and slow rising and falling of the sea surface as it passes. Only as it approaches land does a tsunami become a hazard. As the tsunami approaches land and shallow water, the waves slow down and become compressed, causing them to grow in height. In the best of cases, the tsunami comes onshore like a quickly rising tide and causes a gentle flooding of low-lying coastal areas. In the worst of cases, a bore will form. A bore is a wall of turbulent water that can be several meters high and can rush onshore with great destructive power. Behind the bore is a deep and fast-moving flood that can pick up and sweep away almost anything in its path, such as what happened in Papua New Guinea in 1998 when more than 2,000 people were killed and villages destroyed. Minutes later, the water will drain away as the trough of the tsunami wave arrives, sometimes exposing great patches of the sea floor. But then the water will rush in again as before, causing additional damage. This destructive cycle may repeat many times before the hazard finally passes. Persons caught in the path of a tsunami have little chance to survive. They can be easily crushed by debris or they may simply drown. Children and the elderly are particularly at risk, as they have less mobility, strength and endurance. Tsunamis typically cause the most severe damage and casualties very near their source. There the waves are highest because they have not yet lost much energy to friction or spreading. In addition, the nearby coastal population, often disoriented from the violent earthquake shaking, has little time to react before the tsunami arrives. The largest tsunamis, however, can cause destruction and casualties over a wide area, sometimes as wide as the entire Pacific Basin. These types of Pacific-wide tsunamis may happen only a few times each century. In the deep ocean, the tsunami waves propagate across the deep ocean with a speed exceeding approx. 500 miles per hour and wave height of only about 1 foot or less. They may not be felt by ships at sea. As they reach the shallow waters of the coast, the waves slow down and the water can pile up rapidly into a wall of destruction 30 ft or more in height. Sometimes, coastal waters are drawn out into the ocean just before the tsunami strikes. When this occurs. More shoreline may be exposed than even at the lowest tide. This major withdrawal of the sea should be taken as a warning of the tsunami waves that will follow. Tsunami wave energy extends from the surface to the bottom in even the deepest waters. As the tsunami attacks the coastline, the wave energy is compressed into a much shorter distance and a much shallower depth, creating destructive, life-threatening waves.

How a Tsunami Works A tsunami may be less than a foot in height on the surface of the open ocean, which is why they are not noticed by sailors. But the powerful shock wave of energy travels rapidly through the ocean as fast as a commercial jet. Once a tsunami reaches shallow water near the coast it is slowed down. The top of the wave moves faster than the bottom, causing the sea to rise dramatically.

Indian Ocean Tsunami Wave Propagation in Hours

Indian Ocean Tsunami December 26, 2004 The undersea 2004 Indian Ocean earthquake that occurred on December 26, 2004 produced tsunamis that were among the deadliest natural disasters in modern history. The tsunamis devastated the shores of Indonesia, Sri Lanka, India, Thailand, and other countries with waves of up to 50 feet high, even reaching as far as Somalia on the east coast of Africa, 2,800 miles west of the epicenter. Over 250,000 people are known to have died as a result of the tsunamis, and relief agencies warn of the probability of many more deaths to come as a result of disease and starvation. The plight of the many affected people and countries prompted a widespread humanitarian response. This rare megathrust earthquake took place at 07:58:53 local time in the Indian Ocean off the western coast of northern Sumatra, Indonesia. At a magnitude of 9.3, it was the largest since the 9.2-magnitude Good Friday Earthquake off Alaska in 1964, and one of the largest earthquakes recorded since 1900, when accurate global seismographic record-keeping began.

Tsunami Background A tsunami is not a single wave but a series of waves, also known as a wave train. The first wave in a tsunami is not necessarily the most destructive. • Tsunami waves can be very long (as much as 60 miles) and be as far as one hour apart. They are able to cross entire oceans without great loss of energy. The Indian Ocean tsunami traveled as much as 3,000 miles to Africa, arriving with sufficient force to kill people and destroy property.

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Tsunami Facts The 2004 Sumatra tsunami killed over 123,000 people. The most damaging tsunami on record before 2004 was the one that killed an estimated 40,000 people in 1782 following an earthquake in the South China Sea. In 1883 some 36,500 people were killed by tsunamis in the South Java Sea, following the eruption of Indonesia's Krakatoa volcano. In northern Chile more than 25,000 people were killed by a tsunami in 1868.

Tsunami Dangers Many people were killed by the Indian Ocean tsunami because they went down to the beach to view the retreating ocean exposing the seafloor. Apparently they were unaware that this phenomenon precedes a killer wave. Experts believe that a receding ocean may give people as much as five minutes' warning to evacuate the area. • Because tsunamis can approach the shore as fast as 100 miles per hour it is often too late to get away if you see one. An approaching tsunami is not something to be admired unless you are safely on high ground.

Tsunami Dangers Remember that a tsunami is a series of waves and that the first wave may not be the most dangerous. The danger from a tsunami can last for several hours after the arrival of the first wave. A tsunami wave train may come as a series of surges that are five minutes to an hour apart.

Banda Aceh, capital city of Sumatra

Tsunami - 2004 A Close View of Trinkat Island Pre-Event Post-Event IRS-P6 AWiFS Image of 21-Dec-04 IRS-P6 AWiFS Image of 26-Dec-04 Pre-Event Post-Event

Works Cited BBC National Geographic Oceansonline.com Office of Naval Research Reuters USGS Wikipedia