Computer simulations show that, far from protecting coastal communities, islands can dramatically amplify the damaging impact of tsunamis

Islands close to a coast can provide significant protection from waves. For that reason, coastal communities often thrive in areas that are protected by nearby islands.

But what happens in the event of a tsunami? There is a long-standing belief that tsunamis are most destructive when they hit long, straight coastal stretches. So its natural to assume that nearby islands may offer significant protection by acting as natural barriers.

But there is some anecdotal evidence that, far from protecting coastal areas, islands may actually amplify the devastating effect of a tsunami. And oceanologists have long known that tsunamis behave very differently from wind-generated waves. Nevertheless, convincing scientific evidence about the way tsunamis interact with islands is thin on the ground.

Today that changes thanks to the work of Themistoklis Stefanakis at University College Dublin and a few friends who have simulated the effect that islands have on tsunamis and how this changes the impact of the tsunami on a straight beach behind.

This kind of computer simulation is by no means simple. Stefanakis and co simplified the problem by considering the presence of a small conical island some hundred metres high in front of a straight stretch of beach several kilometres behind it.

One of the big challenges for computer scientists doing this kind of work is to perform the simulation accurately but with minimal computational cost.

One problem is that the cost of a simulation increases dramatically with the complexity of the model. Stefanakis and co cope with this by taking data from a specially selected set of points in the model rather than from all over it.

Whats more, they use a learning algorithm to examine the experimental results from one simulation and then use this to fine tune the selection of data points in the next simulation, an approach known as active experimental design.

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Islands And The CounterIntuitive Effect They Have on Tsunamis