Mud-rich coastline made 2011 Japan tsunami far more destructive, study finds | Japan disaster

IIt’s been just over 15 years since the devastating Tohoku earthquake and tsunami struck Japan, killing nearly 20,000 people and triggering the Fukushima Daiichi nuclear disaster. A new analysis of video footage of the wave has revealed that the mud-rich coastline made the tsunami far more destructive than it otherwise could have been.

Patrick Sharrocks, from the University of Leeds, and colleagues studied helicopter video footage, as well as before and after images from Google Earth, to estimate the speed, shape and strength of the tsunami flow front. They found that as the wave passed through mud-rich rice fields, it changed from a clear, fast-moving flow of water to a thick, slimy, mud-laden flow.

Writing in the Journal of the Geological Society, they explain how a dense, fast-moving mudflow would have exerted a considerably greater force than its clear-water counterpart, resulting in greater damage to buildings in its path and a much higher number of injuries and deaths.

This type of flow is similar to the destructive mudflows that sometimes form on the sides of volcanoes when water mixes with sediment. The authors recommend that tsunami risk assessments be updated to reflect the amplified risk posed by mud-rich coastal environments and used to inform coastal land use decisions in tsunami-prone regions.