IGCP 490

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November 2007

The Krakatau volcanic and tectonic tsunami

5-10 Aug. 2007

Organised by S. Leroy and W. S. Hantoro

The year 5 fieldtrip & workshop of IGCP 490 took place in the region of the Sunda Strait in Indonesia. The aim was to observe the testimonies of the large tsunami caused by the Krakatoa eruption in AD 1883 and also understand what are the monitoring and mitigation systems put in place in Indonesia for earthquakes and tsunamis. Eight scientists (from PhD students to professors) took part in the fieldtrip and the workshop. They were from Indonesia, Belgium and the UK.

The regions visited were the densely industrialised region of NW Java, under the risk of both volcanic and tectonic tsunamis. Emergency plans (with escape routes to the hills) and education of local people as well as workers have been developed to evacuate people and to limit damage to industries. Secondary effects of tsunamis such as pollution (oil and chemicals), fires, destruction of transport are also taken in consideration. A long bridge (> 25 km) is planned to be built across the Sunda Strait. Its resilience to seismic movements has been discussed.

In South-East Sumatra, extremely high run-ups were observed during the tsunami and we visited places where boats and buoys were moved far inland, often along rivers.

Afterwards we climbed the still active Anak-Krakatoa and visited the monitoring station. Back in Java, we moved to the western tip in the national park of Ujung Kulon. We could observe there the reef and the coast in their pristine state. An analysis of the different types of coasts has been made by Indonesian scientists to see which environments resist better to he penetration of a tsunami wave. Indonesian authorities are thinking of implanting artificial reefs where they have been destroyed and to plant a dense curtain of vegetation in order to break the force of any new tsunami. During our visit, we experienced two earthquakes (magnitudes 7 and 5), one with an epicentre in the north coast of Jawa (deep) and one with an epicentre in Ujung Kulon, the natural park we visited (shallow). Our Indonesian colleague working in the monitoring of volcanic and geological hazards, who was participating to the trip, was immediately and automatically made aware by mobile phone of the location, hypocentre, and magnitude of the earthquakes.

During four evenings during the trip, we held a workshop related to IGCP 490. We had 8 talks and feedbacks, as well as a discussion on how to transfer our scientific knowledge to the public and end-users. Some of the presentations will be published in a special issue of Quaternary International on IGCP 490.

In brief, Indonesia is rife with natural hazards, which have shaped its society. An amazing level of monitoring and mitigation measures is been put in place.

The importance to increase the efficiency and capacity of the data and information exchange among scientist in order to obtain better understanding of different hazard mechanism and its mitigation was especially noted during the discussions.

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