Fractal models in the earth sciences

271 Earth-ScienceReviews,34 (1993) 271-296 Elsevier Science Publishers B.V., Amsterdam Book Reviews Earth Sciences G. Korvin, 1992. Fractal Models in the Earth Sciences. Elsevier, Amsterdam, 396 pp. Price: US$125.00/Dfl.220.-. ISBN 0-444-88907-8. The first time I looked at this book I was interested yet rather bemused. If they can inspire a delightful, amusing, cultivated and cultured book, admittedly from a delightful, amusing, cultivated and cultured author, fractals are obviously interesting but what are they? They seem to affect or be represented in a wide range of geological topics, but what are fractals? But I then turned to other works for basic definition (Donald Turcotte's GSA Today article, 1991, provides a splendid introduction) and discovered that any object that is scale invariant is a fractal. Once that is clear, Korvin's book became not only delightful but meaningful. Many geological features are scale invariant, that is, they look the same whether they are seen at the molecular, site, regional or continental scale. Fractures, and fracture patterns, streams and stream patterns are obvious examples. Fractal properties have considerable implications for process studies, for example in considering drag and other mechanisms that depend on length of contact. Korvin's discussion is eclectic, ranging from rivers and coasts to sedimentation or rather non-sedimentation rates, from fractures at various scales to rock porosity. Even bornhardts rate amention! He not only draws attention to and discusses these and many more geological examples but indicates real world problems that arise from fracta!s, and with a puckish humour. But just as he does not define fractals so does he not offer much in the way of explanation for the fascinating question as to why shapes are repeated at various scales. Do the same mechanisms operate to give similar patterns at all scales or are fractal patterns convergent? Or, as is the case, according to some authorities, with stream orders and drainage networks, is it all a statistical condition? Here is food for thought, which well summarises Korvin's book for it provides a splendid and stimulating introduction to and development of the fractal theme. C.R. Twidale, Adelaide Volcanology C.A. Wood and J. Kienle (Editors). Volcanoes of North America, United States and Canada. Cambridge University Press, Cambridge, U.K. 1990. Hardcover, 354 pp. Price £40.--/US$70.00. ISBN 0-5-36469-8. On 18 May, 1980, Mount St. Helens in the state of Washington, USA, erupted for the first time since 1857. The mass-media and the public discovered with surprise that most of the west coast of the United States was laden with volcanoes. A swarm of magnitude 6 earthquakes occurred in Long Valley caldera, California, a few days after the climactic eruption of Mt. St. Helens. These earthquakes started a period of unrest that lasted for a number of years and prompted the attention of many volcanologists. These two events have probably contributed to a better appreciation of the volcanic nature of many terrains in western North America, and to the potential hazard of a reawakening of quiescent volcanoes. Volcanoes of North America, United States and Canada. Cambridge University Press,