Indonesia Tsunami Impacts in Aceh Provence and North Sumatra
(2007)
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Indonesia Tsunami Impacts: Aceh Provence and North Sumatra
The huge earthquake and resulting tsunami which occurred on December 26, 2004 off the west coast of Sumatra resulted in regionally variable patterns of impact in and around the Indian Ocean basin. The coast of Sumatra was close to the earthquake epicenter and was the first to be struck, within one hour of the event. A collaborative expedition between the Khaled bin Sultan Living Oceans Foundation, Reef Check International and IUCN (World Conservation Union) to the northwest coast of Sumatra and Aceh Province, Indonesia, was conducted in October 2005.
Reef surveys were conducted using two methods: Manta Tow and the Reef Check Plus protocol. A total of 9 sites (8 offshore island sites and 1 mainland Aceh site) were surveyed over a distance of 650 km. Typically tsunami damage was observed as overturned coral colonies and tree debris on the reef. Over half of the reefs surveyed indicated that there had been no tsunami damage and only 15% of the sites surveyed indicated a high level of damage. However, even in areas where severe tsunami damage was recorded and corals were killed as a result of the event, there were still large areas of intact reef present, which will be able to repopulate the damaged reef in the future. Similar post-tsunami surveys in Thailand suggest that full recovery of these reefs should occur within the next 5-10 years.
There was evidence that the earthquake caused both uplift and subsidence of some islands. These processes have resulted in three impacts on reefs:
- extensive mortality of uplifted reef-flat corals,
- the bringing of reef-front corals into the reef-flat zone and
- the relocation of reef-flat communities to the reef-front. Both uplift and subsidence therefore have implications for near-future reef ecosystem dynamics in the region.
INTRODUCTION
On December 26, 2004 an earthquake measuring 9.3 in magnitude (Bilham, 2005) occurred at latitude 3oN, off the west coast of Sumatra where the northward moving Indo-Australian plate is subducted below the continental Eurasian plate. This earthquake was the most severe event since the Alaskan earthquake of 1964 and was the second largest since modern seismographic recording began over a hundred years ago. The energy it released was as much as all the global earthquakes combined between 1976 and 1990. This huge earthquake triggered tsunami waves, which caused devastation throughout the Indian Ocean basin. The coast of Sumatra was the first to be struck, within one hour of the event. The tsunami waves reached Sri Lanka and India in 2-3 hours, Seychelles and Mauritius in 7 hours, East Africa in 9 hours and South Africa in 11-14 hours. This tsunami event was the most catastrophic such event in recent history resulting in the deaths of over 300,000 people (Spencer, 2007).
The effects of hurricanes and cyclones on coral reefs have been well documented for more than 20 years (e.g. Woodley et al., 1981; Bythell et al., 2000) but there are no such reports on the effects of tsunami waves on coral reefs. At the International Coral Reef Initiative’s (ICRI) 10th Anniversary meeting in the Seychelles in April 2005, a review of post-tsunami reef damage assessments was made. The review revealed that numerous reef surveys had been conducted throughout the Indian Ocean (e.g. Thailand,Seychelles, Maldives, Sri Lanka) to observe coral-reef damage following the December 2004 tsunami, but there was an evident lack of surveys along the west coast of Sumatra, the coastline closest to the epicenter of the earthquake. Northwest Sumatra experienced very severe terrestrial tsunami damage; water inundation reached 3-4 km inland and wave scour and coastal subsidence set back the shoreline by 1.5 km (Borrero, 2005). The aim of this expedition was to survey a 650 km stretch of the west coastline and offshore islands of Sumatra, Indonesia, from Sibolga to Banda Aceh (in Aceh Province) (Fig. 1) in order to document the state of the reefs in this area following the December 2004 tsunami and to fill a gap in the knowledge of the impacts of the tsunami around the Indian Ocean basin…
