Tsunami: The Underrated Hazard

  • Edward Bryant
Cambridge University Press: 2001. 320 pp. £19.95, $27.95 (pbk)

A tsunami, one of the few internationally understood Japanese terms, is a water wave in an ocean or lake. It can be generated by various submarine geological processes, such as earthquakes, volcanic eruptions, landslides and even meteorite impacts. In the deep ocean, a tsunami travels at jet-liner speed without raising or lowering the sea surface by more than a few metres. In shallow water, however, the wave becomes slower and bigger, sometimes rising to more than 10 metres and causing extensive damage to coastlines.

Waves of destruction: tsunami events have caused 5,000 deaths in the past decade. Credit: DAVID NEWTON

In 1960, a great earthquake off the Chilean coast sent a tsunami to Hawaii and Japan that resulted in many fatalities. Such waves threaten not only the Pacific Rim but also the shores of the Atlantic Ocean and the Mediterranean and Caribbean seas. In the past decade alone, some 5,000 deaths have been caused by 10 tsunami events.

Edward Bryant provides a wide-ranging review of tsunamis. His book starts with five stories of tsunamis, pieced together from legends, historical documents and eyewitness accounts. The book ends with another five scenarios of future potential tsunami damage around the globe. Although the latter collection verges on scientific fiction, it carries the author's message that tsunami hazards are underrated. The intervening chapters explain the nature and context of the tsunamis described in the stories. The book contains vivid descriptions of past tsunamis, and makes effective use of graphics, photographs and imaginative illustrations.

Recent advances in tsunami science have come from many fields. Broad-band seismic records help seismologists to estimate the space–time distribution of tsunami- generating seafloor displacements. Coastal and ocean-bottom gauges now monitor the progress of tsunamis and improve the accuracy of tsunami warnings. Physical and numerical models simulate the generation of tsunamis and their interactions with coastal structures such as breakwaters. Fast computers help to identify areas that are at greatest risk from tsunamis, as does the identification of onshore deposits of past tsunamis. The Internet has increased the rate at which information on tsunami events and research can be exchanged. Large tsunamis attract international, multidisciplinary survey teams.

Bryant became interested in tsunamis when he was investigating the origin of boulders in Australian coastal rock platforms. The book, in both its scope and its wealth of citations, demonstrates that he has read widely. And the case studies and research results he cites are up to date. That alone makes the book useful as a reference work. However, in quality and depth, the book varies greatly from chapter to chapter.

The section headed “Tsunami-formed landscapes” will interest scientists studying prehistoric tsunamis or coastal geomorphology. These chapters deal with deposition and erosion resulting from tsunamis — a topic that has received attention only in the past decade or so. Bryant describes tsunami deposits worldwide, drawing particular attention to boulders he found in southeast Australia, atop cliffs and dunes tens of metres above the current sea level. He repeatedly distinguishes between tsunami deposits and storm deposits, although the criteria used for this are not always obvious. In fact, such criteria have been a hot research topic. A summary of storm deposits would have been a useful addition. Bryant reviews reports of tsunami deposits in Hawaii, although without due attention to attendant controversies on their origin.

Bryant also explores ways in which tsunamis can shape coastal landscapes, particularly by 'scouring' bedrock. He thereby revives Sir James Hall's postulation of 1812 that Edinburgh's landscape was shaped by a tsunami, and draws an analogy to scouring by subglacial streams. This unique idea, so far untested, states that high-speed rotation of water creates a whirlpool which then scours rocky coastlines. But it requires a quantitative explanation involving factors such as angular velocity and energy source, whereas Bryant simply invokes cavitation. A modern example of bedrock scouring would also have made Bryant's arguments more convincing.

Other parts of the book are written for the general reader. Some chapters barely go beyond student-notebook level and often mix established theory with speculation. Although any separation of the two would be subjective, these sections need to be read with a critical eye. When discussing tsunami dynamics, Bryant presents equations without providing sufficient background on concepts such as the intrinsic difference between deep- and shallow-water waves or finite-difference methods. Also weak are the sections on seismic gaps and earthquake (and tsunami) prediction. And it would have been helpful to have described the conflicting arguments on earthquake predictability.

Bryant's book has lofty goals — summarizing a diverse and rapidly emerging field is not easy. The book succeeds in organizing and providing examples of many facets of tsunami studies, but falls short of portraying these facets accurately. It will therefore be most useful to tsunami researchers who can identify its technical and factual errors. Parts of the book lack rigour and consistency; especially needed are a more comprehensive and better-organized index and a glossary of tsunami jargon from the many fields involved. With these revisions and peer review, a second edition of this book could be an authoritative, multipurpose textbook for newcomers to tsunami research.