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Books The Geological Triggers of Climate Change Climate Forcing of Geological Hazards. Bill McGuire and Mark A. Maslin, eds. Wiley, 2013. 326 pp., illus. $159.95 (ISBN 9780470658659 cloth). I n the Pacific Northwest, where I live, we have witnessed geologic hazards triggered by climate change. In November 2006, a heavy rainstorm created debris flows, a watery mixture of sediment and boulders, on several of our glacier-clad volcanoes—most notably, Mount Hood (just outside of Portland, Oregon) and Mount Rainier (southeast of Seattle, Washington). The debris flows were initiated in glacial valleys, where the steep valley walls are no longer buttressed by the presence of glacial ice. One consequence of these flows was the closure of a major highway on the east side of Mount Hood for about a month, isolating a major ski area. In Mount Rainier National Park, one road was closed for over a year. With this background, I read Climate Forcing of Geological Hazards with more than just academic interest. The edited volume is geological and geophysical in nature, covering volcanic eruptions, faults, landslides, and methane hydrates in 12 chapters. It does not cover the more geomorphology- oriented processes, such as debris flows, riverine environments, or coastal shorelines, that might be of more direct interest to biologists. However, to understand the long-term (approximately 103 years) trends of geological hazards, this book is a helpful guide. The first two chapters serve as an introduction, providing an overview of the material and a pro forma summary of climate projections through the end of this century. The first chapter argues that geologic conditions on the threshold of stability can be destabilized by relatively small changes in mass distribution (relative to the mass of the rock overburden) in climate-affected landscapes, such as the mass of snow and ice or sea-level change. 68 BioScience • January 2014 / Vol. 64 No. 1 The next three chapters offer details of geological hazards and focus on volcanic events. Mount Etna, in Sicily, is used as a case study about processes that trigger edifice collapses. Much text is devoted to the dating of an ancient edifice collapse, which may be more appropriate for a book on dating techniques, and then attempts to link the timing of the collapse to a wet climatic period, suggesting that the increased infiltration of water into the volcano walls weakened its mechanical strength. The implication is that if glacier-clad volcanoes are subject to increased ice melt caused by climate warming, they, too, would be less stable. The next chapter tries to link volcanic eruptions to shrinking glaciers, the notion being that, as the weight of the ice decreases, the magma vents more easily, and eruptions increase in frequency. Although I am sympathetic to the argument, I think that it is a stretch. The eruptive frequency of volcanoes has not changed over the past 1000 years, which brackets the Little Ice Age, the most glaciologically significant event in the past several thousand years—and a period rich in dated samples. If such a volcanic response exists, the response time is much slower than the variation in the climate (around 102 years). In contrast to the implication in the previous chapter, the following chapter suggests that volcanic activity may be reduced by the shrinking of glaciers. As pressure on the planet’s crust decreases as a result of ice loss, the volume of shallow magmatic chambers increases because of the elastic rebound of the crust; together with fractures created by the rebound, this increased volume reduces the local magmatic pressure. Although the loss of ice may not have a decisive effect on eruptive activity, faulting behavior may be a different story. Both terrestrial and marine fault environments are examined, as are the specific faults in three regions: northern Scandinavia, Utah, and Wyoming. The loading or unloading of the crust changes the pattern of stress accumulation, which causes fault slip. Numerical modeling shows that crustal unloading, due to the disappearance of Pleistocene glaciers and lakes, can cause fault slip and may explain the synchronous increase in postglacial seismicity observed in regions formerly covered by glaciers and ice sheets. Climate Forcing of Geological Hazards next examines whether the relatively small variations in sea level (40 centimeters) due to the El Nino–Southern Oscillation (ENSO) can affect seismicity along the plate boundary at the East Pacific Rise in the southeastern Pacific Ocean, which is highly fractured and relatively weak. Results show a significant correlation between seismic events and the Southern Oscillation Index, and seismic activity is greatest several months after an ENSOinduced lower sea level. Although no direct connections to geologic hazards exist, such changes may help trigger large earthquakes by concentrating stress in faults in a more critical state. Two subsequent chapters address the possible effects of climate change on landslide potential. The first reports on different styles of continental shelf landslides, their global distribution, and their geomorphic setting. Potential http://bioscience.oxfordjournals.org Books landslides exist where thick deposits of stable coarse sediments, deposited during glacial periods, are separated (interbedded) by weak, fine-grained sediments deposited during interglacial periods. The second of these two chapters examines landslides in high-mountain regions related to ice and changing meteorological conditions. On the basis of studies in three different regions—central Alaska, the European Alps, and the Southern Alps of New Zealand—two general (and separate) associations emerge. The first is a period (days) of warm weather prior to a landslide, and the second is a sudden drop in air temperature to below freezing in the hours (to days) before the event. The hypothesis for the former is that meltwater from snow and ice fills the fractures in the rock, reducing the rock strength; for the latter, the freezing of infiltrated meltwater mechanically weakens the rock. The book concludes with a wonderful overview of hydrates, including the history of their discovery (natural deposits were not recognized until the 1970s), their crystalline structure, their role in recent geologic history, and the potential hazards that are associated with them. These ice-like deposits of gas—mostly methane—are stable under high pressure and at low temperatures and are found at the ocean bottom and in permafrost. Were the ocean to warm sufficiently, the clathrate would break down and release methane, a greenhouse gas, which would contribute to accelerated global warming. Thawing hydrate ice may also trigger underwater landslides that could release other methane deposits or even create tsunamis. Identifying the distribution of hydrate deposits and keeping an eye on their stability is in our best interest. Climate Forcing of Geological Hazards thoroughly addresses the volcanic eruptions and landslides that are associated with climate warming. Its informative material will teach even those readers, such as myself, who think they know the subject matter. http://bioscience.oxfordjournals.org ANDREW G. FOUNTAIN Andrew G. Fountain ([email protected]) is a professor of geography and geology at Portland State University, in Portland, Oregon. doi:10.1093/biosci/bit011 TIME AND TIDE Rising Seas: Past, Present, Future. Vivien Gornitz. Columbia University Press, 2013. 360 pp., illus. $40.00 (ISBN 9780231147392 paper). T he specter of sea-level rise is one of the most charismatic consequences of climate change. It is also the subject that is covered admirably, and with an overarching historical context, by Vivien Gornitz in her book Rising Seas: Past, Present, Future. Gornitz has made sea-level studies a focus of her career at the Columbia University Center for Climate Systems Research and the NASA Goddard Institute for Space Studies, and her (1982) article in Science helped usher in the modern era of sea-level-rise research. To understand the movement and the levels of the seas is to gain insight into how the Earth has functioned throughout history. Sea-level change is mostly associated these days with climate change. Rising temperatures are melting glaciers and heating seawater—and increasing the volume of the oceans. Gornitz argues that the factors controlling this warming process are now more numerous than at any other point during human history. At any given time, the levels of the oceans are controlled astronomically: The relative positions of the Earth, the Moon, and the Sun are the principal factors controlling the tides. Indeed, these daily fluctuations are the aspects of sea-level change most commonly experienced. Over much longer time scales, however, the position of the sea is controlled by the tectonic movement of the Earth’s plates, because the rate of seafloor spreading controls an ocean’s temperature and also the buoyancy of those plates. Periods of fast seafloor spreading, such as during the Cretaceous Period, tended to have a buoyant ocean crust and, therefore, higher sea levels, whereas the modern Quaternary Period has a slower rate of seafloor spreading and generally lower sea levels. Sea level is also controlled by changes in the mass and density of the lithosphere with respect to underlying the asthenosphere, a process of equilibrium called isostacy. In many places in North America and Europe, glacially driven isostatic adjustments are one of the major factors influencing sea-level change over the past several thousand years. In locations with soft sediments, such as deltas, sea-level rise is affected by sediment autocompaction, sediment dewatering, and oil and gas production. Rising Seas is written for a wide audience—an academic who is not an expert on the subject but who wishes to learn more or a layman interested in the long-term effects of sea-level rise. The book is enjoyable to read, thoughtfully illustrated and containing artful renderings of climatic processes and presentations of raw data. Schematics are found throughout the pages that explain important sea-levelrelated processes, such as how isostacy functions, how a tide gauge works, and how sand is transported along a beach. In addition, there are data that present temperature changes in ice cores, as well as tide gauge and altimetry data of sea-level change over the past century and a half. January 2014 / Vol. 64 No. 1 • BioScience 69