Waiting for the next jumbo-jet wave

Tsunami
April 19, 2002

Natural hazards are fast becoming part of our everyday lives and are no longer confined to strange lands far away. In the first year of the new millennium, one in 30 people on the planet was affected by natural hazards, including many in the United Kingdom who were flooded out by some of the most intense rains for more than three centuries. Our television screens and newspapers regularly disclose the terrible devastation wrought by flood, cyclone, earthquake or volcanic blast, and most of us, as a result, are quite familiar with the staggering destructive potential of Mother Nature's shock troops - barring those, it seems, caused by the giant sea waves that go by the name of tsunami. Our blissful ignorance of this terrifying natural phenomenon has now, however, been ably and admirably tackled by Edward Bryant, whose new book reveals the awesome facts about these watery hazards.

Tsunami is a Japanese word derived from tsun - for harbour - and ami - for wave. It reflects the fact that in deep water, tsunami are barely detectable, perhaps being only a few tens of centimetres high. When they enter shallow water, however, they build rapidly to form towering walls of water as high as a 15-storey building. Countless Japanese fisherman have returned home to find their harbour, their homes and their loved ones obliterated by a huge wave that they did not even notice as it passed beneath their boats.

Tsunami and earthquakes often go hand in hand, the waves typically being generated when a submarine quake gives a sharp jolt to the sea bed. They can also be formed in other ways, including as a result of submarine landslides, collapsing or exploding volcanoes or as a consequence of an asteroid or comet crashing into the ocean. In an introductory chapter that addresses the basics, Bryant warns that no coastline on the planet is safe from tsunami, but they most favour the Pacific rim, where the Earth is constantly shaking. Here, tsunami have taken at least 500,000 lives over the past 2,000 years.

Like the ripples that form when a stone is cast into a lake, tsunami spread rapidly - with the speed of a jumbo jet in deep water - and can traverse an ocean within 24 hours. As they travel they lose little energy and hang on to their destructive potential. The great Chile earthquake of 1960, for example, generated tsunami that took lives and destroyed property as far afield as Hawaii, New Zealand, Japan and along the coast of Chile itself.

Bryant's interest in tsunami, he reveals in the preface, arose from a Saul-like conversion after seeing spectacular boulders that had been washed up onto the New South Wales coast by tsunami possibly exceeding 130m in height. His enthusiasm comes over well throughout the book, despite the fact that it is in essence an academic text, aimed primarily at earth and environmental science tutors and their students.

The book is clearly and logically laid out in four parts, addressing tsunami as known hazards, tsunami-formed landscapes, causes of tsunami and the modern risk of tsunami. The introductory chapter includes a taster that focuses on five tsunami from legend and history, while succeeding chapters take a comprehensive look at tsunami dynamics (warning - this chapter contains mathematical equations), their "signatures" on coastlines and the various ways in which they can be generated. Of particular interest to me, as a hazard scientist, is the last part of the book, which looks at the current and future threat.

The closing decade of the last millennium saw the generation of ten major tsunami, and it is clear the problem is not going to go away. In fact, rising sea levels associated with global warming can only exacerbate the threat.

Most worryingly, we have yet to experience - in modern times - a really big tsunami, and it is a shame that this book was published too soon to incorporate research that reveals that a gigantic chunk of a volcano on La Palma in the Canary Islands is poised to slide into the North Atlantic. Were this huge mass of rock - the size of the Isle of Man - to crash into the ocean, the word tsunami would be on everyone's lips and Bryant's excellent book would no doubt sit at the top of the bestseller lists.

Bill McGuire is professor of geohazards, University College London.

Tsunami: The Underrated Hazard

Author - Edward Bryant
ISBN - 0 521 77244 3and 77599 X
Publisher - Cambridge University Press
Price - £55.00 and £19.95
Pages - 320

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