The ability to predict and determine the probability

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The ability to predict and determine the probability of hazardous events is crucial for risk analysis, and understanding how a natural hazards will affect people, communities, and infrastructure. The same hazardous events that produced disasters in the past are now creating catastrophes. Poor land use, increasing populations, and more expensive building practices are resulting in significantly greater damage from modern hazards in terms of both human and financial losses. In order to reduce the impact of natural hazards, there must be cooperation between scientists, politicians, engineers, land-use planners, and disaster management personnel. Risk vs. Hazard The terms hazard and risk are often used incorrectly. A hazard is the actual phenomenon that will cause damage to people or property. Risk is the likelihood of being affected by a hazard. Therefore, it is important to identify potential hazards for a given area, and equally important to assess the risk for those hazards. Mitigation Mitigation is the effort to lessen the impact of natural disasters on people and property. Mitigation techniques vary for each hazard. Nearly all mitigation plans include an educational component, because even the greatest hazard mitigation plan will fail if no one knows what the hazards are and what should be done when they occur. Examples of mitigation techniques include evacuation routes, engineering, education, and planning ahead. Western Washington Geologic Hazards There are many hazards that pose a risk to residents of Whatcom County. We will be investigating three of these geologic hazards: mass wasting, earthquakes, and volcanoes. Other hazards are very important, and more information can be found at the Whatcom County Division of Emergency Management: . wa.us/dem/pdf/natural_hazards.pdf . I. Mass Wasting Ground failure and subsequent movement of earth materials downhill is called mass wasting . Mass wasting includes many different types of ground failure, and range from small instantaneous events (e.g. a rock falling off a cliff), to large instantaneous events (e.g. an extensive mass of sediment flowing downhill due to slope failure), to large gradual events (e.g. slow movement of upper soil layers, known as creep ). There are several types of mass wasting that have dramatic impacts and occur in numerous regions, the most common being debris flows . Debris flows occur when loose or uncompacted sediment flows turbulently downhill. Before we can learn to avoid debris flows, we must first understand some important concepts. The most important of these is called the angle of repose , which is steepest angle at which a sloping surface composed of loose, unconsolidated material will remain stable (Fig. 1). Angle of repose only pertains to loose sediment, and varies with the size and shape of the sediment, as well as the amount of fluid present. Slopes gentler than the angle of repose are stable. However, if the angle is increased at all, the sediment fails and slides down slope.
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