After working on earth surface features on land the opportunity to collect and use cutting edge marine geophysical survey data drew him to a PhD in submarine geomorphology.
Joshu is working on understanding the range of processes that control the movement of large scale submarine landslides. These can move enormous amounts of material – literally mountain size. We know that submarine landslides can cause tsunami but we still have much to learn about the details of landslide motion and the risks they can pose to coastal areas.
Over the last fours years Joshu has led a project in Wellington’s Cook Strait canyons mapping the landslides there and modelling the probability of landslide tsunami from collapse of the canyon walls. The results show that significant tsunami waves could occur from multiple locations within the canyon and arrive in Wellington within minutes. This information is being fed into risk assessment models to determine the likely costs and fatality/injury associated with these events. These same methodologies are being applied in Kaikoura and Lake Tekapo.
A major project now underway, and one of huge international interest, is an investigation of large slow moving landslides directly offshore Gisborne. These landslides appear to move so slowly that, although similar in size to Mahia Peninsula, they are unlikely to fail catastrophically and cause large tsunami. This type of failure is well known onland but this is the first example identified offshore. We have state-of-the art 3D geophysical surveys of the seafloor and up to 1 km below the seafloor and in 2016 will carry out robotic scientific drilling to determine what is controlling these intriguing and important landforms.
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