James Goltz and Katsuya Yamori
Tsunamis are natural hazards that have caused massive destruction and loss of life in coastal areas worldwide for centuries. Major programs promoting tsunami safety, however, date from the early 20th century and have received far greater emphasis following two major events in the opening decade of the 21st century: the Indian Ocean Tsunami of December 26, 2004, and the Great East Japan Earthquake and Tsunami of March 11, 2011. In the aftermath of these catastrophic disasters, warning systems and the technologies associated with them have expanded from a concentration in the Pacific Ocean to other regions with significant tsunami vulnerability. Preparedness and hazard mitigation programs, once the province of wealthier nations, are now being shared with developing countries. While warning systems and tsunami mapping and modeling are basic tools in promoting tsunami safety, there are a number of strategies that are essential in protecting lives and property in major tsunami events. Preparedness strategies consist of tsunami awareness and education and actions that promote response readiness. These strategies should provide an understanding of how tsunamis occur, where they occur, how to respond to warnings or natural signs that a tsunami may occur, and what locations are safe for evacuation. Hazard mitigation strategies are designed to reduce the likelihood that coastal populations will be impacted by a tsunami, typically through engineered structures or removing communities from known tsunami inundation zones. They include natural or constructed high ground for evacuation, structures for vertical evacuation (either single purpose structures specifically for tsunami evacuation or existing buildings that are resistant to tsunami forces), seawalls, breakwaters, forest barriers, and tsunami river gates. Coastal jurisdictions may also use land-use planning ordinances or coastal zoning to restrict development in areas of significant risk of tsunami inundation. The relative efficacy of these strategies and locations where they have been implemented will be addressed, as will the issues and challenges regarding their implementation.
Maria Papathoma-Köhle and Dale Dominey-Howes
The second priority of the Sendai Framework for Disaster Risk Reduction 2015–2030 stresses that, to efficiently manage risk posed by natural hazards, disaster risk governance should be strengthened for all phases of the disaster cycle. Disaster management should be based on adequate strategies and plans, guidance, and inter-sector coordination and communication, as well as the participation and inclusion of all relevant stakeholders—including the general public. Natural hazards that occur with limited-notice or no-notice (LNN) challenge these efforts.
Different types of natural hazards present different challenges to societies in the Global North and the Global South in terms of detection, monitoring, and early warning (and then response and recovery). For example, some natural hazards occur suddenly with little or no warning (e.g., earthquakes, landslides, tsunamis, snow avalanches, flash floods, etc.) whereas others are slow onset (e.g., drought and desertification). Natural hazards such as hurricanes, volcanic eruptions, and floods may unfold at a pace that affords decision-makers and emergency managers enough time to affect warnings and to undertake preparedness and mitigative activities. Others do not. Detection and monitoring technologies (e.g., seismometers, stream gauges, meteorological forecasting equipment) and early warning systems (e.g., The Australian Tsunami Warning System) have been developed for a number of natural hazard types. However, their reliability and effectiveness vary with the phenomenon and its location. For example, tsunamis generated by submarine landslides occur without notice, generally rendering tsunami-warning systems inadequate.
Where warnings are unreliable or mis-timed, there are serious implications for risk governance processes and practices. To assist in the management of LNN events, we suggest emphasis should be given to the preparedness and mitigation phases of the disaster cycle, and in particular, to efforts to engage and educate the public. Risk and vulnerability assessment is also of paramount importance. The identification of especially vulnerable groups, appropriate land use planning, and the introduction and enforcement of building codes and reinforcement regulations, can all help to reduce casualties and damage to the built environment caused by unexpected events. Moreover, emergency plans have to adapt accordingly as they may differ from the evacuation plans for events with a longer lead-time. Risk transfer mechanisms, such as insurance, and public-private partnerships should be strengthened, and redevelopment should consider relocation and reinforcement of new buildings. Finally, participation by relevant stakeholders is a key concept for the management of LNN events as it is also a central component for efficient risk governance. All relevant stakeholders should be identified and included in decisions and their implementation, supported by good communication before, during, and after natural hazard events.
The implications for risk governance of a number of natural hazards are presented and illustrated with examples from different countries from the Global North and the Global South.
How big, how often, and where from? This is almost a mantra for researchers trying to understand tsunami hazard and risk. What we do know is that events such as the 2004 Indian Ocean Tsunami (2004 IOT) caught scientists by surprise, largely because there was no “research memory” of past events for that region, and as such, there was no hazard awareness, no planning, no risk assessment, and no disaster risk reduction. Forewarned is forearmed, but to be in that position, we have to be able to understand the evidence left behind by past events—palaeootsunamis—and to have at least some inkling of what generated them.
While the 2004 IOT was a devastating wake-up call for science, we need to bear in mind that palaeotsunami research was still in its infancy at the time. What we now see is still a comparatively new discipline that is practiced worldwide, but as the “new kid on the block,” there are still many unknowns. What we do know is that in many cases, there is clear evidence of multiple palaeotsunamis generated by a variety of source mechanisms. There is a suite of proxy data—a toolbox, if you will—that can be used to identify a palaeotsunami deposit in the sedimentary record. Things are never quite as simple as they sound, though, and there are strong divisions within the research community as to whether one can really differentiate between a palaeotsunami and a palaeostorm deposit, and whether proxies as such are the way to go. As the discipline matures, though, many of these issues are being resolved, and indeed we have now arrived at a point where we have the potential to detect “invisible deposits” laid down by palaeotsunamis once they have run out of sediment to lay down as they move inland. As such, we are on the brink of being able to better understand the full extent of inundation by past events, a valuable tool in gauging the magnitude of palaeotsunamis.
Palaeotsunami research is multidisciplinary, and as such, it is a melting pot of different scientific perspectives, which leads to rapid innovations. Basically, whatever is associated with modern events may be reflected in prehistory. Also, palaeotsunamis are often part of a landscape response pushed beyond an environmental threshold from which it will never fully recover, but that leaves indelible markers for us to read. In some cases, we do not even need to find a palaeotsunami deposit to know that one happened.