took 5 hours to reach Western Australia, 7 hours to reach the Arabian Peninsula, and did not reach the South African coast until nearly 11 hours after the earthquake The sudden vertical rise of the seabed by several metres during the earthquake displaced massive volumes of water, resulting in a tsunami that struck the coasts of the Indian Ocean. A tsunami that causes damage far away from its source is sometimes called a
teletsunami and is much more likely to be produced by the vertical motion of the seabed than by horizontal motion. The tsunami, like all the others, behaved differently in deep water than in shallow water. In deep ocean water, tsunami waves form only a low, broad hump, barely noticeable and harmless, which generally travels at the high speed of ; in shallow water near coastlines, a tsunami slows down to only tens of kilometres per hour but, in doing so, forms large destructive waves. Scientists investigating the damage in Aceh found evidence that the wave reached a height of when coming ashore along large stretches of the coastline, rising to in some areas when travelling inland. Radar satellites recorded the heights of tsunami waves in deep water: the maximum height was at two hours after the earthquake, the first such observations ever made. According to
Tad Murty, vice-president of the Tsunami Society, the total energy of the tsunami waves was equivalent to about , which is more than twice the total explosive energy used during all of World War II (including the two atomic bombs) but still a couple of
orders of magnitude less than the energy released in the earthquake itself. In many places, the waves reached as far as inland. Because the fault affected by the earthquake was in a nearly north–south orientation, the greatest strength of the tsunami waves was in an east–west direction.
Bangladesh, which lies at the northern end of the
Bay of Bengal, had few casualties despite being a low-lying country relatively near the epicentre. It also benefited from the fact that the earthquake proceeded more slowly in the northern rupture zone, greatly reducing the energy of the water displacements in that region. Coasts that have a landmass between them and the tsunami's location of origin are usually safe; however, tsunami waves can sometimes
diffract around such landmasses. Thus, the Indian state of
Kerala was hit by the tsunami despite being on the country's western coast, and the western coast of Sri Lanka suffered substantial impacts. Distance alone was no guarantee of safety, as Somalia was hit harder than Bangladesh despite being much farther away. Because of the distances involved, the tsunami took anywhere from fifteen minutes to seven hours to reach the coastlines. The northern regions of the Indonesian island of Sumatra were hit quickly, while Sri Lanka and the east coast of India were hit roughly 90 minutes to two hours later. Thailand was struck about two hours later despite being closer to the epicentre because the tsunami travelled more slowly in the shallow
Andaman Sea off its western coast. The tsunami was noticed as far as
Struisbaai in South Africa, about away, where a tide surged on shore about 16 hours after the earthquake. It took a relatively long time to reach Struisbaai at the southernmost point of Africa, probably because of the broad continental shelf off South Africa and because the tsunami would have followed the South African coast from east to west. The tsunami also reached Antarctica, where tidal gauges at Japan's
Showa Base recorded oscillations of up to a metre (), with disturbances lasting a couple of days. Some of the tsunami's energy escaped into the Pacific Ocean, where it produced small but measurable tsunamis along the western coasts of North and South America, typically around . At
Manzanillo, Mexico, a tsunami with a wave height of was measured. As well, the tsunami was large enough to be detected in
Vancouver, Canada, which puzzled many scientists, as the tsunamis measured in some parts of South America were larger than those measured in some parts of the Indian Ocean. It has been theorized that the tsunamis were focused and directed at long ranges by the
mid-ocean ridges which run along the margins of the continental plates.
Early signs and warnings at 10:25 a.m., prior to the third—and strongest—tsunami wave Despite a delay of up to several hours between the earthquake and the impact of the tsunami, nearly all of the victims were taken by surprise. There were no
tsunami warning systems in the Indian Ocean to detect tsunamis or to warn the general population living around the ocean. Tsunami detection is difficult because while a tsunami is in deep water, it has little height and a network of sensors is needed to detect it. Tsunamis are more frequent in the Pacific Ocean than in other oceans because of earthquakes in the "
Ring of Fire". Although the extreme western edge of the Ring of Fire extends into the Indian Ocean (the point where the earthquake struck), no warning system existed in that ocean. Tsunamis there are relatively rare despite earthquakes being relatively frequent in Indonesia. The last major tsunami was caused by the
1883 eruption of Krakatoa. Not every earthquake produces large tsunamis: on 28 March 2005, a magnitude 8.7 earthquake hit roughly the same area of the Indian Ocean but did not result in a major tsunami. The first warning sign of a possible tsunami is the earthquake itself. However, tsunamis can strike thousands of kilometres away where the earthquake is felt only weakly or not at all. In the minutes preceding a tsunami strike, the sea sometimes recedes temporarily from the coast, which was observed on the eastern earthquake rupture zone such as the coastlines of Aceh,
Phuket island and
Khao Lak in Thailand,
Penang island in Malaysia, and the
Andaman and Nicobar islands. This rare sight reportedly induced people, especially children, to visit the coast to investigate and collect stranded fish on as much as of exposed beach, with fatal results. However, not all tsunamis cause this "disappearing sea" effect. In some cases, there are no warning signs at all: the sea will suddenly swell without retreating, surprising many people and giving them little time to flee. an hour after the earthquake One of the few coastal areas to evacuate ahead of the tsunami was on the Indonesian island of
Simeulue, close to the epicentre. Island folklore recounted an
earthquake and tsunami in 1907, and the islanders fled to inland hills after the initial shaking and before the tsunami struck. These tales and oral folklore from previous generations may have helped the survival of the inhabitants. On Maikhao Beach in north
Phuket City, Thailand, a 10-year-old British tourist named
Tilly Smith had studied tsunamis in geography at school and recognised the warning signs of the receding ocean and frothing bubbles. She and her parents warned others on the beach, which was evacuated safely.
John Chroston, a biology teacher from Scotland, also recognised the signs at Kamala Bay north of Phuket, taking a busload of vacationers and locals to safety on higher ground.
Anthropologists had initially expected the
aboriginal population of the Andaman Islands to be badly affected by the tsunami and even feared the already depopulated
Onge tribe could have been wiped out. Many of the aboriginal tribes evacuated and suffered fewer casualties, however. Oral traditions developed from previous earthquakes helped the aboriginal tribes escape the tsunami. For example, the folklore of the Onges talks of "huge shaking of ground followed by high wall of water". Almost all of the Onge people seemed to have survived the tsunami.
Indonesia Aceh The tsunami devastated the coastline of
Aceh province, about 20 minutes after the earthquake.
Banda Aceh, the closest major city, suffered severe casualties. The sea receded and exposed the seabed, prompting locals to collect stranded fish and explore the area. Local eyewitnesses described three large waves, with the first wave rising gently to the foundation of the buildings, followed minutes later by a sudden withdrawal of the sea near the port of
Ulèë Lheuë. This was succeeded by the appearance of two large black-coloured steep waves which then travelled inland into the capital city as a large turbulent bore. Eyewitnesses described the tsunami as a "black giant", "mountain" and a "wall of water". Video footage revealed torrents of black water, surging by windows of a two-story residential area situated about inland. Additionally, amateur footage recorded in the middle of the city captured an approaching black surge flowing down the city streets, full of debris, inundating them. '', a 2,600-ton vessel, was flung some to inland. In the years following the disaster, it became a local tourist attraction and has remained where it came to rest. The level of destruction was extreme on the northwestern areas of the city, immediately inland of the aquaculture ponds, and directly facing the Indian Ocean. The tsunami height was reduced from at Ulèë Lheuë to a further to the north-east. The inundation was observed to extend inland throughout the city. Within of the shoreline, houses, except for strongly-built reinforced concrete ones with brick walls, which seemed to have been partially damaged by the earthquake before the tsunami attack, were swept away or destroyed by the tsunami. The area toward the sea was wiped clean of nearly every structure, while closer to the river, dense construction in a commercial district showed the effects of severe flooding. The flow depth at the city was just at the level of the second floor, and there were large amounts of debris piled along the streets and in the ground-floor storefronts. In the seaside section of Ulèë Lheuë, the flow depths were over . Footage showed evidence of back-flowing of the
Aceh River, carrying debris and people from destroyed villages at the coast and transporting them up to inland. A group of small islands: Weh, Breueh, Nasi,
Teunom,
Bunta,
Lumpat, and
Batee lie just north of the capital city. The tsunami reached a run-up of on the western shorelines of
Breueh Island and
Nasi Island. Coastal villages were destroyed by the waves. On
Weh Island, strong surges were experienced in the port of
Sabang, yet there was little damage with reported runup values of , most likely due to the island being sheltered from the direct attack by the islands to the south-west. The second wave was the largest; it came from the west-southwest within five minutes of the first wave. The tsunami stranded cargo ships, barges and destroyed a cement mining facility near the
Lampuuk coast, where it reached the fourth level of the building. survived the tsunami in
Ulèë Lheuë,
Banda Aceh Meulaboh, a remote coastal city, was among the hardest hit by the tsunami. The waves arrived after the sea receded about , followed by an advancing small tsunami. The second and third destructive waves arrived later, which exceeded the height of the coconut trees. The inundation distance is about . Other towns on Aceh's west coast hit by the disaster included
Leupung,
Lhokruet,
Lamno, Patek,
Calang, and
Teunom. Affected or destroyed towns on the region's north and east coast were
Pidie Regency,
Samalanga,
Panteraja, and
Lhokseumawe. The high fatality rate in the area was mainly due to lack of preparation of the community towards a tsunami and limited knowledge and education among the population regarding such a natural phenomenon. Helicopter surveys revealed entire settlements virtually destroyed, with destruction extending miles inland. Only a few mosques remained standing. The greatest run-up height of the tsunami was measured at a hill between Lhoknga and
Leupung, on the western coast of the northern tip of Sumatra, near Banda Aceh, and reached . The tsunami heights in Sumatra: The tsunami first struck the eastern coastline and subsequently refracted around the southern point of Sri Lanka (
Dondra Head). The refracted tsunami waves then inundated the southwestern part of Sri Lanka after some of its energy was reflected from impact with the Maldives. Civilian casualties here were second only to those in Indonesia, with approximately 35,000 killed. The eastern shores of the country were the hardest hit since it faced the epicentre of the earthquake, while the southwestern shores were hit later, but the death toll was just as severe. The southwestern shores are a hotspot for tourists and fishing. The
degradation of the natural environment in Sri Lanka contributed to the high death tolls. Approximately 90,000 buildings and many wooden houses were destroyed. In
Hambantota, run-ups measured with the greatest inundation distance of . Run-up measurements along the Sri Lankan coasts are at . Estimates based on the state of the shoreline and a high-water mark on a nearby building place the tsunami above sea level and higher than the top of the train. boat stranded almost inland • in Khao Lak • along the west coast of Phuket island • along the south coast of Phuket island • along the east coast of Phuket island • on the Phi Phi Islands • at Ban Thung Dap • at Ramson • at Ban Thale Nok • at Hat Praphat (Ranong Coastal Resources Research Station) • at
Thai Mueang District • at Rai Dan The province of Phang Nga was the most affected area in
Thailand. The quiet resort town of
Khao Lak is located on a stretch of golden sandy beach, famed for its hotels overlooking the
Andaman Sea and hilly
rainforests. A video, taken by a local restaurant manager from a hill adjacent to the beach, showed that the tsunami's arrival was preceded by a sudden retreat of the sea exposing the seafloor. Many tourists and locals can be seen trying to gather fish. Moments later, the tsunami arrives as a wall of foaming water that slams into the coast, washing away numerous people who had no time to escape. Another amateur video, captured by a German family at beach level, showed the tsunami appearing as a white horizontal line in the distant horizon, gradually becoming bigger (bore-like), engulfing a jet skier and lifting two police boats. A maximum inundation of approximately was measured, the inundated depths were and there was evidence that the tsunami reached the third floor of a resort hotel. The tsunami in Khao Lak was bigger due to offshore coral reefs and shallow seafloor which caused the tsunami to pile-up. This was similar to eyewitness accounts of the tsunami at
Banda Aceh.
Khao Lak also experienced the largest tsunami run-up height outside of
Sumatra. The highest-recorded tsunami run-up was measured at Ban Thung Dap, on the south-west tip of
Ko Phra Thong Island and the second-highest at at Ban Nam Kim. The tsunami runup height measured in mainland India by Ministry of Home Affairs includes: The shrine's compound, nearby villages, hundreds of shops, homes and pilgrims were washed away into the sea. About 600 pilgrims died. Rescue teams extricated more than 400 bodies from the sand and rocks in the vicinity and large number of unidentified bodies were buried in mass graves. Kerala experienced tsunami-related damage in three southern densely populated districts,
Ernakulam,
Alappuzha, and
Kollam, due to diffraction of the waves around
Sri Lanka. Conversely, the southernmost district of
Thiruvananthapuram experienced negligible impact, a result of the wide-angle turn required for diffracted waves to reach the peninsular tip. The most severe destruction was concentrated along narrow land strips situated between the
Arabian Sea to the west and the
Kerala backwaters to the east, where the geography restricted inland evacuation. Initial tidal recession preceded the surge, with the highest fatality rate recorded in the
Alappad panchayat—including the villages of
Cheriazheekkal and
Azheekal—where waves reached heights of 4 m (13 ft) and caused approximately 131 deaths. Many villages in Andhra Pradesh were destroyed. In the
Krishna District, the tsunami created havoc in
Manginapudi and on
Machalipattanam Beach. The most affected was
Prakasam District, recording 35 deaths, with maximum damage at
Singarayakonda. Given the enormous power of the tsunami, the fishing industry suffered the greatest. Moreover, the cost of damage in the transport sector was reported in the tens of thousands. The tsunami varied in height from to based on survivors' accounts. The tsunami travelled at its maximum inland at Karaikal,
Puducherry. At
Port Blair, the water receded before the first wave, and the third wave was the tallest and caused the most damage. Results of the tsunami survey in South Andaman along Chiriyatapu, Corbyn's Cove and Wandoor beaches: • in maximum tsunami height with a run-up of at Chiriyatapu Beach • in maximum tsunami height and run-up at Corbyn's Cove Beach • in maximum tsunami height and run-up of at Wandoor Beach Meanwhile, in the Little Andaman, tsunami waves impinged on the eastern shore about 25 to 30 minutes after the earthquake in a four-wave cycle of which the fourth tsunami was the most devastating with a wave height of about . The tsunami destroyed settlements at
Hut Bay within a range of from the seashore. Run up level up to have been measured. The significant shielding of Port Blair and Campbell Bay by steep mountainous outcrops contributed to the relatively low wave heights at these locations, whereas the open terrain along the eastern coast at Malacca and
Hut Bay contributed to the great height of the tsunami waves. Reports of tsunami wave height: • at
Diglipur and
Rangat at North Andaman Island • high at Campbell Bay on
Great Nicobar Island • high at Malacca (in Car Nicobar Island) and at Hut Bay on
Little Andaman Island • high at Port Blair on South Andaman Island
Maldives The tsunami severely affected the
Maldives at a distance of from the epicentre. Similar to Sri Lanka, survivors reported three waves with the second wave being the most powerful. After the tsunami, there was some concern that the country might be submerged entirely and become uninhabitable. However, this was proven untrue. The highest tsunami wave measured was at
Vilufushi Island. The tsunami arrived approximately two hours after the earthquake. The greatest tsunami inundation occurred at
North Male Atoll,
Male Island at along the streets. Local footage recorded showed the tsunami flooding the streets up to knee level in town, while another video taken at the beach showed the tsunami slowly flooding and gradually surging inland. The Maldives tsunami wave analysis: Tsunami survey heights: • around the Irrawaddy delta • at
Dawei area • around
Myeik • around
Kawthaung Interviews with residents indicate that they did not feel the earthquake in Taninthayi Division or the Irrawaddy Delta. The 71 casualties can be attributed to poor housing infrastructure and additionally, the fact that the coastal residents in the surveyed areas live on flat land along the coast, especially in the Irrawaddy Delta, and that there is no higher ground to which to evacuate. The tsunami heights from the earthquake were not more than along the Myanmar coast, the amplitudes were slightly large off the Irrawaddy Delta, probably because the shallow delta caused a concentration in tsunami energy. The Puntland coast in northern Somalia was by far the area hardest hit by the waves to the west of the Indian subcontinent. The waves arrived around noon local time. Bangladesh escaped major damage and deaths because the water displaced by the
strike-slip fault was relatively little on the northern section of the rupture zone, which ruptured slowly. In
Yemen, the tsunami killed two people with a maximum runup of . The tsunami was detected in the southern parts of east Africa, where rough seas were reported, specifically on the eastern and southern coasts that face the Indian Ocean. A few other African countries also recorded fatalities; one in Kenya, three in
Seychelles, ten in Tanzania, and South Africa, where two were killed as a direct result of the tsunami—the furthest from the epicentre. Tidal surges also occurred along the
Western Australian coast that lasted for several hours, resulting in boats losing their moorings and two people needing to be rescued. ==Impact==