The dreadful moment when the Tsunami of 26 December 2004 hits the Thai coast after travelling ca. 400 km around the northern tip of Sumatra and then WNW across the Andaman sea and the Strait of Malacca. The coast shown in this photograph is "sheltered" (if that is quite the word for it in these circumstances) by Sumatra. The epicentre of the earthquake was on the far side of Sumatra and the tsunami had to work its way around the northern tip of that island, .jpg)
losing a lot of energy in the process. The photograph captures only too clearly the tremendous power that even a weakened major tsunami can have.
The human figure on the left and the boats on the right can give a sense of scale. The unknown photographer did not survive and the same must be assumed for the human being. The camera was found later with the film intact (see Tsunami: the Tragedy in pictures). The exact part of the coast shown has not been identified. The breaking wave appears to be roughly 5-6 m high, which compares with the unimaginable wave of 30 m or even more that hit the town of Aceh much closer and in direct line to the epicentre (for maps see below).
The human figure on the left and the boats on the right can give a sense of scale. The unknown photographer did not survive and the same must be assumed for the human being. The camera was found later with the film intact (see Tsunami: the Tragedy in pictures). The exact part of the coast shown has not been identified. The breaking wave appears to be roughly 5-6 m high, which compares with the unimaginable wave of 30 m or even more that hit the town of Aceh much closer and in direct line to the epicentre (for maps see below).
The Cause: moving geological plates
The Indo-Australian plate moves below the Eurasian plate at around 70 mm per year on average. Plates get locked and move very little for many years, even centuries, pressure builds up - and is then suddenly and catastrophically released in the form of a major earthquake. This happened on 26th December 2004 below Sumatra on the fault line between the Indo-Australian and the Eurasian plates.
The major plates often have smaller plates at their edges. These minor and micro- plates tend to move, more or less, in the same direction as the major plates they belong to but are often the location of specially active geological fault lines.
The major plates often have smaller plates at their edges. These minor and micro- plates tend to move, more or less, in the same direction as the major plates they belong to but are often the location of specially active geological fault lines.
How the tsunami destroys - in principle
The depth and topography of the sea determines the form a tsunami wave takes and how it propagates.
The way a tsunami breaks when reaching a coast is very difficult to predict. It depends on the topography that the wave has passed over on the high seas and on the form, steepness, height and form of the coastline hit. Within a few kilometers the hight of a tsunami wave can vary from lesss than a meter to 20 or more meters.
The way a tsunami breaks when reaching a coast is very difficult to predict. It depends on the topography that the wave has passed over on the high seas and on the form, steepness, height and form of the coastline hit. Within a few kilometers the hight of a tsunami wave can vary from lesss than a meter to 20 or more meters.
Light blue: normal sea level
Dark blue line: normal water surface
Dark blue: tsunami wave reaching higher than normal sea level
brown: land
How the tsunami of 26 December 2004 started
Underwater landslides caused by submarine earthquakes are a major (perhaps usually the only) contributory factor to the formationof a tsunami wave. One enormous landslide off the west coast of Sumatra caused by the the quake of 26 Dec 2004 was discovered by the sonar of the British Navy's "HMS Scott" and is shown on the left. The view is to the south. (Picture courtesy Royal Navy).
How the tsunami of 26 December 2004 spread
The configuration in 3 dimensions of the newly-born tsunami, approx. 15 minutes after its creation. The view is towards north-west. Note that the highest waves (around 37 m) were around the unfortunate city of Banda Aceh at the northern tip of Sumatra.
For more pictures and an animated 17 MB movie of the expanding tsunami, see:
The red lines show the tsunami front at half-hourly intervals. The background shows the sea depth contours and is from Manfred Leier, World Atlas of the Oceans, 2000, Firefly Books, Buffalo NY, USA.
From the epicenter of the primary earthquake (1), the tsunami spreads out at, initially, around 700 km/h and with a starting height of 37 m. By the time the wavefront has reached Banda Aceh (3), its height has already been reduced to "only" 12 m, when reaching the island of Sabang (4) it is 6 m and when reaching the coast near Sigli (5) east of Bandar Aceh it is 5 m in height. The estimates of the tunami's early height are based on the extent and distance from the sea of damage caused. After clearing the northern tip of Sumatra, the tsunami does not lose significant hight anymore but instead slows down in the shallower waters. When the Tsunami reaches the Thai island of Phuket (6) it still produces heights of 4.5 m (Karon beach) and 5.5 m (Patong beach).
Because the power of the tsunami was deflected by Simeulue island (2) immediately to the south of the epicentre and by the west coast of Sumatra, much of the wave energy was deflected to the west and the north. The short time delay between initial and deflected wave energy also caused two tsunamis to move closely together northwards to the Nicobar (7) and Andaman (8) islands.
Coastlines and islands with significant loss of life and serious coastal damage are coloured red.
For photographs of the damage caused by the tsunami, see Pictures
The map below shows just how far and how quickly the tsunami travelled and how far. Human casualties were reported from East African beaches 7-8 hours after the main earthquake near Sumatra. The height of the tsunami had reduced to around 0.5 m by the time it reached the African coast. This may not sound much but if someone is taken completely by surprise, even such a relatively small wave can still be deadly.
The red lines show the progress of the tsunami across the Indian Ocean in half-hourly intervals. It is noticeable that the speed of the tsunami's advance is not significantly slowed down as long as the wave moves in deep waters.
1. Sri Lanka
2. Andaman islands
3. Nicobar islands
4. Simeulue island
5. Nias island
6. Mentawai islands
7. Maldive islands
8. Seychelle islands
The wave hight in meters (m) at any time during the tsunami (modelled)(adapted and simplified from Quirin Schiermeier, "On the Trail of Destruction", Nature 433:350-353, 27th January 2005.
Epicenter
35 to 12 m
12 to 4 m
4 to 2 m
2 to 1 m
1 to 0.6 m
0.6 to 0.4 m
0.4 to 0.2 m
0.2 to 0.1 m
not significantly affected
1 m = 3.28 ft.
The Tsunami spreads: countless local disasters
Sumatra
While in most areas around the Indian Ocean that suffered serious damage from the event of 26 December 2004, it was not so much the earthquake but the following tsunami that caused the horrific loss of life and damage. The western coast of the northern Indonesian province of Aceh and its capital, Banda Aceh, suffered especially grievously. This is the landmass closest to the epicentre of earthquake and tsunami.The loss of life along the western coast of Sumatra (marked in red below) has been enormous and the destruction of infrastructure (houses, bridges, roads , harbours, agricultural land) nearly total. That the province had suffered for decades from a vicious civil war did nothing to improve the situation. That war was stopped only briefly after the disaster and has resumed since makes reconstruction even more difficult.
Height of the tsunami:
Banda Aceh (northeast areas): 9 m
Banda Aceh (southwest areas): 25-31 m
Sabang island: 6 m
Nasi island (northwest of Banda Aceh): 8 m
Sigli (east of Banda Aceh): 5 m
Simeulue island: 15 m
The devastation of Banda Aceh:
yellow line: shore line prior to the tsunami
red line: extent of inundation by the tsunami
red spots: measurement locations of tsunami flow depth and direction
black numbers: representative measurements of tsunami flow depth (in m), in the citxy centre the depath was between 4 and 9 m (1 m = 3.28 feet)
black arrows: direction of tsunami flow
R: runup in the Lhoknga area (in direct line to the epicentre of the earthquake) exceed 25 m and may have reached 31 m
Graphic courtesy Borrero J.C. 2005. "Field Data and Setellite Imagery of Tsunami Effects in Banda Aceh." Science 308:1596 (10 June 2005)
The Andaman and Nicobar islands, including North Sentinel island
Map showing the aftermath of the 26 December 2004 earthquake and tsunami in the Andaman and Nicobar islands:(1) the dead and mis
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