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Islands sharing same lagoon affected worst by tsunamis

Bluepeace

The tsunamis’ impact on islands of the Maldives is presumably highly individualistic for each island, but a broad pattern of geomorphologic impact can be observed, writes Ali Rilwan, co-founder of Maldives’ first environmental NGO Bluepeace Maldives.

Kandholhudhoo in Raa Atoll, which was evacuated after the waves hit

Extreme events, particularly high waves and storms, play a vital role in the pattern of island accumulation and island erosion in the atolls of the Maldives.

The morphology and dynamics of islands are thus a function of prevailing pattern of extreme events. However, there appear to be few instances where atolls in the Maldives were affected by storms and high waves.

It is also believed the depth of the surrounding seas, and slopes to shores of an atoll and tide level, determine height and strength of the tsunamis that hit the islands of the Maldives on 26 December 2004. In addition, low-tide at the time of the tsunamis striking the islands could have played an important role in minimizing the destruction on the islands.

Islands in an atoll separating each others with deep channels reduce the devastating impact of tsunamis and many such islands escaped without much or any damage. In deep channels, the tsunamis simply rushed through the channels, and waves did not even reach high tide marks on islands adjacent to deep channels.

This was observed in Raa Atoll where most of the islands are situated with relatively small lagoons and deep channels separating each other. Kandholhudhoo in Raa Atoll, which was evacuated after the waves hit, is an exceptional case. The island had already suffered monsoon flooding and swells due to the combination of reclaimed shoreline and mined reef. The large population pressure on this island has led to the reclamation up to the coastal area in all directions beyond the local reef, known as the “house reef”. A handful of islands in different atolls in the Maldives affected by the killer tsunamis can also be listed in the same category as Kandholhudhoo as these islands have reclaimed and modified its coastal zone. Like Kandholhudhoo, the coastal area of the capital island of Male has been reclaimed. However, the seawall and the breakwaters may have reduced the devastating impact of the tsunamis.

When the tsunamis struck the islands, dense coral reefs in large lagoons could not help to reduce the devastating impacts of tsunamis by absorbing some energy of the waves. Islands that were worse affected are islands that are in a same lagoon and islands with a large lagoon. Large lagoons have acted as big land masses on which waves can crest resulting in them hitting the islands in the same lagoon with greater force and height, destroying homes and infrastructure. The human tragedy in these islands has been horrendous. Quite apart from the terrible loss of life, means of livelihood of thousands have been destroyed. Almost two-thirds of the fatalities were in Meemu, Laamu, Thaa and Dhaalu atolls. Most of the islands in these atolls are either in a same lagoon or with a very large lagoon.

It is also believed the depth of the surrounding seas also determined the height and strength of the tsunamis. And many believe that it was the main reason why, on some islands especially in the far South with deep seas, escaped with minor or no damage at all. Due to these geological features, the tsunamis hit the islands in Huvadhu Atoll and Addu atoll more like a tidal surge of less than a meter’s height.

Ecological damages to some of these islands throughout the archipelago are catastrophic. There is also fear that the substructures of many islands have been damaged. Crops and introduced vegetation on many islands were totally destroyed by salt water.