Natural hazards, extreme events, and mountain topography

The hazard of any natural process can be expressed as a function of its magnitude and the annual probability of its occurrence in a particular region. Here we expand on the hypothesis that natural hazards have size-frequency relationships that in parts resemble inverse power laws. We illustrate that these trends apply to extremely large events, such as mega-land slides, huge volcanic debris avalanches, and outburst flows from failures of natural dams. We review quantitative evidence that supports the important contribution of extreme events to landscape development in mountains throughout the world, and propose that their common underreporting in the Quaternary record may lead to substantial underestimates of mean process rates. We find that magnitude-frequency relationships provide a link between Quaternary science and natural hazard research, with a degree of synergism and societal importance that neither discipline alone can deliver. Quaternary geomorphology, stratigraphy, and geochronology allow the reconstruction of times, magnitudes, and frequencies of extreme events, whereas natural hazard research raises public awareness of the importance of reconstructing events that have not happened historically, but have the potential to cause extreme destruction and loss of life in the future. (C) 2009 Elsevier Ltd. All rights reserved.