Multi-risk assessment and cascading effects analysis conducted as part of a cooperation between Indonesia and Germany - Joint research on tsunamis induced by volcanoes and landslides

Why do tsunamis still occur seemingly without warning? In 2018 alone, Indonesia experienced not one but two tsunamis that claimed numerous lives. Both tsunamis followed a chain (cascade) of events, with landslides triggering tsunamis. New detection and early warning strategies need to be developed for tsunami events like these. The TSUNAMI_RISK project takes mapping and monitoring as its starting point and will investigate how geoscientific findings can be used to inform social discussions and disaster risk management in Indonesia.

Background and motivation

Following the catastrophic Indian Ocean tsunami on Boxing Day in 2004, Germany developed new methods for identifying and characterising earthquake parameters and tsunamis as part of its humanitarian support, and based on this, established innovative early warning capacities in the region. Since 2011, this system has been in operation at the Meteorological, Climatological and Geophysical Agency (BMKG) in Indonesia and has been successfully incorporated into the warning and decision-making chain on several occasions.

And yet the question remains: why do tsunamis occur seemingly without warning? In 2018 alone, Indonesia experienced two tsunamis that caused numerous casualties. Both tsunamis followed a chain (cascade) of events: On 28 September in Palu, on the island of Sulawesi, the cascade consisted of a sequence of earthquakes – landslides - while on 22 December, after a prolonged period of volcanic activity, a flank failure occurred on Anak Krakatau, which in turn triggered a tsunami. In both cases, the resulting tsunamis caught the local population largely unawares, leading to a high death toll. The existing tsunami early warning system, designed to detect tsunamis triggered directly by earthquakes, was unable to provide efficient warnings in these cases. This raises questions in society and the relevant authorities regarding appropriate strategies for improved precautions, early warning systems and mitigation for events like these as well.

Solutions

Applied research can contribute significantly to answering the wide range of unanswered questions related to cascading geohazards that threaten our societies. The two tsunami events in Palu and Anak Krakatau can serve as an extremely well-documented basis for in-depth research into the underlying processes, providimg possible solutions for similar scenarios involving cascading events both in Indonesia and throughout the world. New detection and early warning strategies need to be developed for tsunami events like these. Unlike earthquakes, landslides often show precursors and can be detected by detailed measurements made with the aid of modern seismic and remote sensing methods; in addition, it is possible to estimate their localization on steep flanks as well as the amplifying effects in narrow bays. The TSUNAMI_RISK project described here therefore takes mapping and monitoring as its starting point, investigating the processes during landslides and the resulting tsunamigenic effects. In close cooperation with Indonesian partners, the project aims to identify unstable slopes; to measure mass movements with state-of-the-art satellite observations and geodetic and seismic methods; to investigate their dynamics in simulations and experiments; and thus to investigate their relevance and precursors in geoscientific and technical terms. The project will test the seismic detection of landslides, which can be used as a concrete early warning method; however, these signals are more subtle than those of tsunamigenic earthquakes, and the work planned for this project will help develop possible warning strategies for this class of events. Furthermore, TSUNAMI_RISK will explore how geoscientific findings can be used to inform societal discussions and disaster risk management in Indonesia. To ensure that knowledge and technologies are developed in line with societal needs, the project aims to achieve a better understanding of the underlying social and socio-political causes of vulnerability of the affected population; to determine what kind of knowledge and information can actually be used by whom and in what way; and how these findings can be translated into concrete actions.

The work is carried out by thematically and methodologically leading working groups at German universities and Helmholtz institutes in close cooperation with Indonesian authorities and research groups.

Overall scientific and technical objectives

The TSUNAMI_RISK project aims to contribute to three different key areas:

• Geoscientific research
• Social scientific research
• Policy recommendations and their transfer into practice

With respect to geoscientific research on the physical processes of tsunamis caused by non-seismic sources, the project will (a) identify areas potentially at risk from tsunamis induced by volcanoes and landslides; (b) conduct analyses at selected localities to better understand the underlying physical processes and driving forces that cause a tsunami; and (c) conduct experimental and numerical modelling studies of tsunami generation and propagation through volcano-induced landslides, including the analysis of land management options (e.g. the protective effects of coastal vegetation).

Furthermore, the project will investigate how geoscientific findings can be used to inform societal discussions and disaster risk management in Indonesia. Therefore, the social scientific research questions deal with (a) the culture of handling different hazards, risks and disasters; here, the team has planned background studies on the historical, social, cultural and political framework; the risk perception of the population and institutional actors; spirituality; norms and values; institutional trust; confidence in the population; (b) the analysis of the institutional framework and the current state of disaster risk management (DRM); early warning and crisis response; behaviour of authorities at local, regional and national levels; and will assess Standard Operating Procedures; and (c) eliciting an understanding of local conditions and the range of possible community responses to events like these, and investigating the population’s awareness and understanding of tsunami risks prior to the two events, with a focus on the challenges associated with the warning process.

In terms of recommendations for disaster risk management and their transfer to practice for policy makers at all levels as well as to inform civil society ("science to practice"), the project will consider some specific aspects, such as (a) the importance and applicability of geoscientific knowledge for disaster risk management; (b) the improvement of warning procedures, warning chains and evacuation plans; (c) administrative and societal strategies for dealing with such risk scenarios; (d) the implications for training at an administrative level; and strengthening awareness and knowledge in society.

Finally, the research results as well as the conclusions and recommendations will be made available and transferred to practical application. This requires training and qualification measures as well as corresponding training concepts.