THE GREAT WAVES OF 26 DECEMBER 2004 The tsunami was brought on by a massive undersea earthquake of the magnitude of 9.0 (one recent study has suggested 9.3) on the Richter scale, caused by tectonic activity resulting in the sudden faulting of a part of the contact zone between the Indian and Burma plates. Although the epicentre of the quake is described as having been just off the north-western coast of Sumatra, near the island of Simeulue, it was in fact a rupture along a 1,200 km fault line, in which a section of the Indian plate slipped about 15 m below the Burma plate, at a depth of between 1 km and 5 km below the surface of the sea. The origins of the quake are thought to be at a depth of 30 km below the seabed. In its intensity it is the second strongest earthquake in recorded history. The main quake took place at 00.58.53 hrs UTC followed by 15 aftershocks which took place between .58.53 and 11.05 hrs UTC. Seismic activity and, in particular, great sea waves of this nature are not as frequent in the Indian Ocean as they are in the Pacific. Thus one of the most traumatic aspects of the disaster was that it was not seriously anticipated. Experts, however, were not unaware of the possibility in this region of a tsunami of this magnitude and had even modelled such an event to a degree fairly coincident with what actually happened. Tsunamis are virtually ‘unknown’ in Sri Lanka, although at the very beginnings of the country’s Historical Period in the 2nd Century BC, the great chronicle records a famous event in which ‘the sea-gods made the sea overflow the land’ (Mahavamsa, 32.22) in the early kingdom of Kälaniya, centred in the Kelani Ganga basin immediately north of Colombo. Records however show a number of tsunamis in the Indian Ocean region over the last 150 years, although none seem to have affected Sri Lanka to a significant extent or had such a widespread impact on the region as whole. The recorded Indian Ocean tsunamis include the following: 326 BC – Indus delta, near Kachch (one of the world’s oldest records of a tsunami; an earlier record comes from a 100 m or 150 m high tsunami at Santorini, Greece, in 1650 or 1600 BC). 1524 AC – near Dabhoi, Maharasthra, 2 April 1762 – Arakan coast, Myanmar 16 June 1819 – Rann of Kachch, Gujarat 31 October 1847 – Great Nicobar Island 31 December 1881 – Car Nicobar 26 August 1883 – Krakatoa Volcano eruption, Indonesia (?) 1907 – Simeulue Island, Indonesia 26 June 1941 – Andaman Islands (Magnitude Richter 8.0) 28 November 1945 – Mekran Coast, Baluchistan Of these, the 1883 and 1941 tsunamis affected Sri Lanka, but the highest waves were not more than about 1 m. There seem to have been no casualties in 1883 and only one death in 1941 in Arugam Bay on the south-east coast.

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The tsunami of 26 December was in fact a series of waves, which struck Sri Lanka less than 2 hours after the main earthquake, which took place at 6.59 am (Sri Lanka time – i.e.0.58.53 hrs UTC). The first wave struck Kalmunai in the Ampara District, Eastern Province, at about 8.27 am and ‘curved’ around the south coast and struck as far north as Negombo about 45 minutes to one hour later. Eye witness accounts∗ from various locations indicate that there were three (or four) main waves, with one or two ‘troughs’, in which the water level fell and the sea receded a considerable distance from the normal shoreline. Wave timings. The earliest wave (or wave sequence) at Galle was at about 9.18 am followed by two other waves reported to be at about 10.30 and 11.30. At Ahungalla, ~40km north of Galle, a report says that the first wave was at 9.30 a.m. and gives precise times for the receding of the sea level: 35 minutes of retreat and 7 minutes for the second wave to reach its peak, at about 10.10 a.m. The situation at Kosgoda, ~45 km north of Galle, was similar, except that the period between the first and second wave is reported to have been less than circa 70 minutes, and closer to the ~40 minutes interval reported from Unawatuna. The report from Dehiwela-Mt Lavinia, just south of the Colombo Municipal limits, is the same, though no precise times are available All three locations also report that the second wave was the most powerful one, Source: The Sunday Times, Colombo. 2 January 2005 although the first wave at Unawatuna and at Dadalla, just south and north of the city centre of Galle, was powerful enough to sweep away cars and buses. As in many other eye witness accounts from the south, Kosgoda reports that the second wave came ‘with a roaring sound’ and was the most powerful. This applies also to the east coast, as at Nilavali. Elsewhere, there are alternate accounts which place the first wave and the third as the most destructive, but these are not so well authenticated. It is reported that the main wave at Koralawella, Moratuwa, about 18 km south of Colombo, was at about 11.30 am, and presumably therefore the ‘third wave’. Careful observations at Nilavali (just north of Trincomalee) by an engineer who was nearly drowned in the tsunami were as follows: First wave: 8.55 am – wave height 4 to 5 ft Second wave: 915-9.20 am – wave height 14 to 15 ft (with a roaring sound) Third wave: 9.45 am – wave height not observed (also noisy) A 4th, 5th and 6th wave are also reported, but not observed _____________________________ ∗ Eye-witness accounts are from Ravi Abeywardene, Nilu Abeyaratne, Cecil Balmond, Chris Chapman, Jimi Hensman, Samitha Manawadu, and Varunika Hapuwatte Ruwanpura. Five of them are personal communications, while two are published accounts

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The waves at their maximum seem to have reached a height of 8 metres, though most heights were much less. The wave height at Peraliya, where hundreds were killed when the tsunami struck a train, is said to have been ~7.5 m. A table prepared by the seismologist, Dr. W. Kehelpannala of the Institute of Fundamental Studies, Kandy, gives the following heights (all measurements are of the location height of the inundation water level – the wave crests were sometimes much higher):

South Coast

East Coast

Hambantota Godalla 7 m (MSL) Hambantota Town 6.8 m MSL Kirinda 5.6 (fr. floor level of house) Kottegoda 6.2 (MS L) Tangalle 4 (MSL) Yala (Butawapitiya) 2.85 (from ground ~600m from shore) Yala (Buttawa) 5.4 (from beach surface) Yala (Patanangala) 6.2-6.5 (MSL)

Kalkudah 6.7 (MSL) Kinniya (nr. Police Post) 2.2 (MSL) Kinniya 5.13 (MSL ~50 m fr. shore line) Kinniya (nr. District Hospital) 4.6 (MSL) Kuchchaveli 5 (MSL) Maradamunai 3.45 (ground level 200 m fr. shore line) Maradamunai 1.35 (ground level 800 m fr. shore line) Nilavali 5 (MSL) Onthachimadam 3.09 (250 m fr. shore line) Pasekudah 4.0 (35 m fr. shore line) Potuvil (Arugam Bay) 8.9 (MSL) Potuvil 4.6 (fr. floor level of house) Trincomalee (nr. the Fort) 4.6 (MSL) Trincomalee (China Bay) 3.36 (MSL) Trincomalee (nr. SSP Office) 3.13 (MSL)

As we would expect, the impact of the wave varied from place to place, and there were variations even in the same location. Sea bed topography, coastal morphology, reefs, dunes, lagoons, mangroves and other aspects of natural landscape and the built environment were all factors in the impact of the wave on human settlements. No detailed survey of this has been published but the damage to infrastructure, shops and other business enterprises, hotels and especially urban, rural ands coastal housing has been carried out by various agencies, but is not featured in this preliminary survey.

Source: The Sunday Times, Colombo. 20 March 2005

The short and long term human and material costs of the disaster are immeasurable, but some indicators for Sri Lanka according to published figures and estimates record about 35,000 dead, 5,000 missing, 15,000 injured, 88,000

houses destroyed, 26, 000 houses damaged, 150,00 vehicles destroyed or badly damaged, 580,000 people displaced and the livelihoods of even more than that number affected.

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