Silent tsunami risk in the Tasman Sea

Overview

GNS Science leads this Endeavour-funded research project, which is a collaboration with NIWA, the University of Auckland, the University of Newcastle, Australia and iwi partners Ngāti Tama and Ngāti Mutunga.

The project aims to

• carry out early-stage research examining the link between underwater landslides and tsunami
• understand the tsunamigenic potential of New Zealand’s largest-known underwater landslides
• test new ways to integrate underwater landslide sources into our national tsunami hazard assessments

To achieve these objectives, we will

• study evidence of giant, prehistoric landslides off the coast of Aotearoa New Zealand
• collect new seafloor maps, subsurface geophysical images and seafloor sediment samples to help describe these landslides and the conditions that led to their occurrence
• run numerical simulations of these landslides to study their potential to generate tsunami

The project

Landslides – the #2 cause of tsunami

Underwater landslides are the second-most common cause of tsunami after earthquakes. Scientists estimate that around 10% of tsunami are caused by underwater landslides. During a landslide, a large area of the seafloor is suddenly displaced. This can cause a "drag down" effect, creating a trough in the ocean’s surface. Water rushes in to fill the trough, producing a swell, followed by multiple oscillations that propagated outward – tsunami waves.

Assessing silent tsunami risk

This project will investigate these six underwater landslides, the largest ever found in New Zealand waters. The research conducted by this project will answer these questions:

• What caused these events?
• How frequent are they?
• Is another one likely to happen in the future?
• And, if so, how can we best prepare?

To answer these questions, we will use a mixture of existing subsurface geological information and new data, including seafloor maps and sediment cores, that we will collect using New Zealand’s research vessel Tangaroa.  

The data we collect will inform the likelihood of a future landslide-tsunami recurrence and strategies for hazard risk mitigation. This evidence will be supplemented by pūrākau (historical stories) and mātauranga (traditional scientific knowledge) relating to past tsunami events in the impact regions.

The results will provide a clearer picture of the threat posed by landslide-triggered tsunami in the regions bordering the Tasman Sea, including eastern Australia, and will also improve our understanding of this hazard across the rest of New Zealand, contributing to enhanced hazard assessment and improved resilience.