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Philosophy, sociology and religion

Philosophy, sociology and religion

Nature’s unknown unknowns

22 Jan 2015
Taken from the January 2015 issue of Physics World

The Dynamics of Disaster Susan W Kieffer 2013 W W Norton £18.99/336pp

A seismic hazard map
Assessing hazard: Seismic hazard maps predict the expected ground shaking from earthquakes, with varying degrees of success. (Courtesy: GSHAP/Science Photo Library)

US university students who want to tick the “science” box on their list of graduation requirements without much effort often choose courses on natural hazards. Such students frequently describe these earthquake and volcano (“shake and bake”) courses as “mics” (from Mickey Mouse), “guts” or other terms indicating “a course your dog could pass”. As one student-created wiki page (www.yalewiki.org) puts it, “A gut class is a class that is known to have a light workload, easy grading, or both.”

Textbooks for such classes make heavy use of spectacular images of destruction and nicely explain natural processes in simple terms. However, they are often misleading, in that they imply that the science of disasters is well understood and that it is obvious what society should do to avoid, mitigate or manage disasters when they occur. In doing so, they fail to convey the humility in the face of the complexities of nature that natural-hazard scientists relearn after most major disasters. Although we can use complicated algorithms to draw pretty-coloured pictures and maps of potential hazards, the Earth is not obligated to comply with them, and often doesn’t. A spectacular example is the great 2011 earthquake and tsunami off Japan’s Tohoku coast, which were much bigger than expected from the national hazard map. As Science magazine explained afterwards, “The seismic crystal ball is proving mostly cloudy around the world.”

Susan Kieffer’s book The Dynamics of Disaster is quite different from these simplistic texts. In it, Kieffer, a professor emerita at the University of Illinois, uses her deep expertise in the physics of geological processes to give an unconventional and insightful treatment of natural hazards, including volcanoes, earthquakes, tsunamis, rogue waves, hurricanes and landslides. Her approach – explaining sophisticated physical concepts using non-technical language – works surprisingly well. A passage in which she explains the book’s title nicely encapsulates her style. “Disasters are dynamic,” she writes. “They occur when energy stored in the earth in one form or another is suddenly unleashed in a way that harms humans. The release is episodic and often unpredictable. For a few brief moments of geological time, the normal processes of the earth seem to go crazy as their usually staid pace changes abruptly and briefly to a vigorous, forceful, and catastrophic tempo.”

Kieffer describes these processes as involving a change in conditions that sets in motion a change of materials. As an analogy, she describes what happened as her husband overinflated a bicycle tyre: the rising pressure suddenly changed the tyre from a stressed whole to flying pieces. Each discussion begins with descriptive examples and then discusses the mechanics.

Perhaps the best section involves landslides. Using examples from Norway, Switzerland, China, Italy, Alaska, California, Wyoming and even Mars, Kieffer explains that although all landslides involve material sliding under the influence of gravity and overcoming friction, they are very variable in terms of the materials involved and how they behave. The chapter ends with the humble admission “Geoscientists have come up with such a bewildering array of proposals for how [landslides] move that it may sound as if we simply don’t know what we are talking about. Some of the processes proposed almost certainly occur some of the time in some of the landslides. Not all of the processes occur all of the time or in all places. The large number of hypotheses and mechanisms proposed is simply testimony to the awesome complexity of our world, not to our ignorance.”

The book explains that natural-hazard science often involves what Donald Rumsfeld, the former US secretary of defence, once called “unknown unknowns – things we don’t know we don’t know”. In large part, our knowledge is incomplete because the most destructive events are so rare. For the same reason, deciding how much of our limited resources we should invest in mitigating these risks is a difficult question. Here, Kieffer uses the analogy of car crashes; the (relatively high) probability that one may happen doesn’t affect our willingness to use cars. Hence, she asks, “If you lived on a coastline and learned there was a probability that a tsunami would sweep away your house roughly every thousand years, would you sell it immediately and move away?”

This book is part of a recent trend – one that is just beginning, but is likely to grow – in which scientists, especially young ones, seek to move beyond the “disasters are bad” view presented in beginner classes to a more sophisticated and nuanced view. The challenge is to honestly assess what we know, admit what we don’t, and try to both learn more and make sensible policies given the limits of our knowledge. This book is a good place to start for anyone interested in these challenges, either from general interest, a desire to teach better or a wish to make a career in this important and exciting field.

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