Consideration has been given to the advisability of a tsunami warning system for Ireland in the aftermath of the disastrous consequences of the Indian Ocean Tsunami of December 2004. The historical and modelling evidence, although incomplete, is considered sufficiently robust to indicate that Ireland could be subject to future tsunamis of significant proportions. In order to protect life and property from this low-probability risk, it is essential that an effective warning system be installed and an educational programme put in place. The Geological Survey of Ireland is currently co-ordinating a national initiative to develop a proposal for an early warning system within international frameworks.
Historical records and geological evidence indicate that significant tsunamis have occurred in the past in the Atlantic Ocean, caused by earthquake and landslide events. A tsunami triggered by the magnitude 8.6 Lisbon earthquake in1755 had a catastrophic effect on Lisbon and its effects were felt as far away as Ireland and the West Indies. The fault structure responsible, on the Azores-Gibraltar Fracture Zone, remains seismically active and could potentially suffer another tsunami-generating earthquake in the future. The Geological Survey of Ireland has commissioned a modelling study of the potential threat from a repeat of the Lisbon earthquake. Preliminary results suggest that such an event could produce waves of 3-5m height at the Irish coastline, with a propagation time of 5-8 hours from their source west of Gibraltar. Such waves would be magnified on entering shallow water or narrow channels or bays.
Geological evidence exists for tsunamis caused by submarine landslides that originated on the European shelf of the North Atlantic. The Storegga Slide off Norway, 8,200 years ago, generated a tsunami that had run-up heights of at least 20m in the fjords of Northern Europe and reached Scotland and, probably, Ireland. The Southeast Rockall Slide offshore Ireland, evidently about 12,000 years old, also occurred on a significant scale and the resultant tsunami would have had significant impact on Ireland’s coastlines. Recent research in UCD and Norway suggests that these submarine landslides were related to rising sea levels at the end of the last glaciation and are unlikely to recur at present sea levels. However, the most recent significant tsunami in the North Atlantic was caused by a major landslide on the Grand Banks of Canada in 1929, which claimed about 30 lives on Newfoundland, demonstrating that it would be prudent to consider them a possibility on this side of the Atlantic.
Considerable publicity was generated in 2001 by predictions that a future eruption of Cumbre Viejà volcano on La Palma, Canary Islands, might cause a major coastal landslide that might trigger a major tsunami. This would impact on both European and North American coastlines.
It is essential that an Irish response to tsunami threats has both international and national elements. The international perspective is required to ensure that best practice is incorporated in all aspects of a warning system while at the same time providing the most cost effective approach. The International Oceanographic Commission of UNESCO recently decided to establish an Intergovernmental Coordination Group for a tsunami early warning system in the northeast Atlantic, Mediterranean and related areas (ICG/NEAMTWS) and that this system be developed within its global framework. In developing its system, Ireland would seek to be part of this.
An effective national warning system for Ireland would ideally have the following components:
• A seabed seismic network capable of providing warnings of events thousands of kilometres as well as more locally.
• A network of tsunameters, sophisticated seafloor pressure gauges that can detect the passage of tsunami waves overhead and transmit information in real-time to a central control unit.
• A risk management strategy involving international monitoring and coordination, ongoing risk assessments and a programme of geophysical, geological and oceanographic research.
• A central control unit, which would receive real-time information from the seismic and tsunameter networks, and would be responsible for identifying potential tsunami events.
• A public warning system would be managed by the central control unit.
• A programme of education developed to make the public aware of tsunami risk and the appropriate action in case of an alert.
GSI is currently liaising with the Dublin Institute for Advanced Studies, the Marine Institute, the Office of Public Works and the Engineering Division of the Department of Communications, Marine and Natural Resources to develop a proposal for these different strands of an early warning system as appropriate to current areas of responsibility.