|Executive Summary: GSC Seychelles Tsunami Expedition
7 February 2005
Dr. Irwin Itzkovitch,
Dear Dr. Itzkovitch,
It is our pleasure to inform you that the GSC Indian Ocean Tsunami Expedition to the Republic of Seychelles (RS) returned to Canada this past weekend. We consider our expedition, which was to investigate the tsunami that struck that island archipelago nation on 26 December 2004 , an unqualified success.
Reports will be completed and submitted to you, UNESCO affiliated agencies, and the Republic of Seychelles Government by the end of next week. We have much of it already written and we are waiting for the reduction and plotting of GPS and other survey data. In the interim, we would like to give you a brief summary of our activities and findings.
We arrived in RS the morning of 22 January and departed the morning of 3 February. We investigated the tsunami and its impact on the two largest granitic islands, Mahé and Praslin, where most of the population of about 80,000 reside.
The tsunami resulted in significant property damage but only two fatalities in RS. Two factors worked in RS's favor: the tsunami struck during low tide and it was a Sunday so most businesses in the commercial and industrial areas of Victoria , the capital, were closed. These areas were extensively flooded and boats and debris were driven ashore. Furthermore, children were not in school. Had the tsunami struck at high tide on a normal working day, the death toll could have been scores or hundreds.
We expected to find that damage occurred on coasts facing the source of the tsunami to the east but we were surprised to find areas of significant damage on leeward coasts that we assumed would have been protected. Also, damage occurred on some of these protected coasts hours after the most energetic tsunami waves had already struck in other areas. Other parts of the islands and other islands in the archipelago, depending on orientation and bathymetry, were unscathed because the tsunami waves at those sites did not exceed high-tide levels.
The most significant damage resulted from erosion associated with the draining of tsunami flood waters. On Praslin, this included the destruction of hotel buildings and infrastructure. On Mahé, it included breaching of a causeway carrying the main road to the airport and the lateral spread failure of a fill that forms part of the docking facilities for the fishing fleet in the inner harbour of Victoria .
We did not see tsunami deposits covering the entire extent of runup. In most cases the deposits covered only part of the area affected by the waves. This has become a topic of discussion on the west of coast of Canada , where modelling suggests runup heights approximately twice the extent that would be predicted from observations of deposits. Obviously this has major implications for residents of coastal British Columbia . As a result, we can say that our observations from RS will have direct applicability to ongoing research and assessment of the tsunami hazard for British Columbia and other coastal areas in Canada .
Throughout our stay in RS, we worked closely with and were extensively supported in our work by senior officials in the RS Government and state corporations. These officials included the Principal Secretaries of Environment, of Land Use, and of Transportation, the Director of the Meteorological Service, and the Principal Secretary to the President of RS. The Seychelles Nation, the national newspaper, and the Seychelles Broadcasting Corporation (SBC) also interviewed us. The television exposure greatly facilitated our work (a copy of the Nation press coverage will be forwarded to your office). Furthermore, at the request of the Central Bank of RS, we were asked to present our preliminary findings (to 31 January) to a delegation representing the IMF and the World Bank. To us, such a level of trust speaks volumes about the positive relationship that we developed with the Government of RS.
We have amassed a substantial number of interviews and documentary photographs taken by witnesses, as well as video imagery. The Director of the Centre for GIS in the Ministry of Land Use and Habitat, with approval of the Principal Secretary, provided us with GIS vector data, as well as high- and low-resolution orthophoto coverage. Part of this will be used to prepare the report of our findings. These assets will be made available to other researchers on a request basis.
Lastly, we were able to obtain tidal data recorded during the Krakatoa tsunami of 1883 from the RS National Archives in Victoria and from the 1888 Royal Society report that we examined in the British Library in London . This data set can be compared with the water level records from the 2004 tsunami, which appears to have been larger and more damaging that the Krakatoa event. The archival investigation also uncovered evidence of another tsunami that struck the islands ca. 1833 and may have been comparable to the 2004 event.
The report that we will soon forward to you will be preliminary to subsequent work that we feel is warranted to explain the damage distribution. This will involve numerical modeling of the wave train propagating across and around the shelf of the Seychelles micro-continent. This would be vital to a proper understanding of tsunami hazards in RS and would aid in preparation for future tsunami events.
Yours very truly,
GSC Seychelles Tsunami Expedition