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Tsunami

Tsunamis are waves initiated by large and sudden forced displacements of the sea water, with characteristics intermediate between tides and swell waves. They are generated by various mechanisms, including submarine earthquakes, submarine landslides, collapsing/exploding volcanoes, terrestrial rockfalls, asteroid impacts, meteoric conditions and nuclear explosions. Tsunamis generated by large earthquakes in subduction zones along the major plate boundaries contribute most significantly to the global tsunami hazard.

Historical and recent evidence exists for five tsunami events which have affected (or been recorded) along the South African coast. These mostly modelled imminent threats from sources of remote submarine seismicity along subduction zones, but the possibility that submarine slumps and slides, as well as volcanic activity on the surrounding Reunion and Marion Islands constitute additional potential tsunami sources. The passive margin of the west coast and the broad Agulhas Bank spanning the south- and southeast coasts of South Africa has resulted in increased susceptibility to adjacent low-lying coastal areas in these regions.

The report by Cawthra (2011) describes tsunami triggering mechanisms and the potential hazard from tsunamis along the South African coastline. It also details the techniques used in prediction and modelling tsunami hazard and risk.

Reference:
Cawthra, H. 2011. An initial investigation into potential geological hazard of Tsunamis in South Africa: Insights into vulnerable coastal areas. Council of Geoscience Report number: 2011-0014.

Download the report.