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Identification and Mitigation of Geologic Hazards

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Identification and Mitigation of Geologic Hazards AIPGprofessional geologists in all specialties of the science Identification and Mitigation of Geologic Hazards An important and practical application of and because earthquakes geology is identifying hazardous natural are of such a scale that phenomena and isolating their causes in they can affect several order to safeguard communities. According communities si-multane- to the USGS, the average economic toll ously, the risk to human life from natural hazards in the United States is is obvious.2 The largest approximately $52 billion per year, while recorded earthquake to hit the average annual death toll is approxi- the North American conti- mately 200.1 The primary causes are nent had a magnitude of earthquakes, landslides, and flooding, but 9.2, which occurred on other events, such as subsidence, volcanic March 27, 1964 in eruptions, and exposure to radon or asbes- Anchorage, Alaska. It dev- tos, also pose considerable danger. astated the town and sur- Awareness of the potential hazards that rounding area, and could persist in areas under consideration for be felt over an area of half Figure 2. Volcano Zones both private and community development a million square miles.2 is critical, and so geological consultants Land-slides caused most of the average global temperature by 2 and engineers are called in to survey land the damage, while a 30-foot high tsunami degrees Fahrenheit for 2 years.3 development sites and assist building con- generated by an underwater quake leveled tractors in designing structures that will coastal villages around the Gulf of Alaska, The role of geologists in mitigating such stand the test of time. killing more than 100 people.2 hazards is difficult. While great progress has been made in predicting the incidence Less frequent, but just as destructive are of volcanic eruptions, our ability to predict EARTHQUAKES AND volcanic eruptions. Approximately 700 earthquakes is inadequate. Despite these potentially dangerous volcanoes are active difficulties, generalities can be made. VOLCANOES in the world today, collectively initiating Earthquake occurrence is concentrated 3 In the average year, some 12 million approximately 50 eruptions each year. around, but not confined to, the rim of the earthquakes occur worldwide but most of Surprisingly, the United States is ranked Pacific Ocean in an area known as the cir- them are low in magnitude.1 Earthquakes third most volcanically active country in the cum-Pacific belt; this also happens to be are generally concentrated along tectoni- world, with most of the activity being con- the area of greatest volcanic activity (the cally active plate boundaries where numer- centrated along the Pacific coast (part of Pacific Ring of Fire). The geologic activity ous faults exist (normally near the edges of the Pacific Ring of Fire, Fig. 2). In addition in this region is produced by the movement continents, Fig. 1). As nearly half of the to lava flows, other volcanic hazards of the Pacific plate underneath the conti- world’s population resides in coastal areas, include lahars, which are mud and ash nents surrounding the Pacific Ocean. The flows (either hot or understanding of plate tectonics within the cold), and clouds of field of geology explains how and why poisonous gas and these earthquakes and volcanoes take 3 dust. Unlike most place. other natural disas- ters, volcanic erup- tions can affect the LANDSLIDES AND entire planet; for example, the 1815 SUBSIDENCE eruption of Tambora Landslides are a group of hazards that (in Indonesia) ex- include both fast- and slow-moving debris ploded with the flows associated with the onset of other energy of 10,000 natural phenomena, such as earthquakes, atomic bombs, re- volcanic eruptions, floods, and wildfires, as leasing a layer of well as slope instability created by industri- ash that shrouded alization processes.1 Landslides and ava- the earth and lanches produce over $2 billion in building Figure 1. Quake Zones caused a lowering of and highway losses and about 25-50 American Institute of Professional Geologists [email protected] • www.aipg.org AIPG Fact Sheet FS-04-003 July 2016 areas. Assessing the risk of large living in older homes may be most at risk floods is very difficult because of because of the types of materials used in the unpredictable nature of weath- the construction of the building. er patterns. Radon is a radioactive gas formed by The most intense form of flood- the decay of the element radium from ing, called flash flooding, results rocks that have a high uranium content, from tremendous amounts of water such as granites, shales, and metamor- raining down over a localized area phic varieties of these rocks.5 According in a short amount of time. Heavy to the EPA, radon is considered a carcino- runoff can pick up loose material gen to humans, and its presence in indoor and transport it quickly downslope air is estimated to cause between 15,000- in the form of mudflows, another 20,000 lung cancer deaths each year in 6 Photo by J. T. McGill, USGS geologic hazard. the United States. Radon can affect both new and old homes alike, as it is due to 4 deaths annually in the United States. The Geologists look back through the infiltration of the gas through cracks in vulnerability of future landslide occurrence the rock record to determine where and basements, or the transmittal of radon to is directly related to the location and fre- when floods have historically taken place. the home in contaminated water, which 5 quency of past slide events. The four Examination of landforms, types of soil has been in contact with high uranium- most landslide-active locations in the and sediment, signs of erosion, and flood- content rocks. Radon problems are solv- United States are California, Alaska, scarring recorded in tree rings, allow the able, and tests are available for its detec- 1 Washing-ton, and Utah. flood history of an area to be pieced tion. together. Geologists combine this data Subsidence, or the localized sinking of with contemporary knowledge about the Today’s geologist is well trained for the land surface, can be induced by a area in order to predict the likely-hood of identifying those forms of asbestos that number of factors, including tectonic shift- future flooding. are considered hazardous to human ing, collapse of soluble rock (karst topog- health. As such, geologists are used to raphy), removal of underground water diagnose asbestos problems. Since only supplies, earthquakes, and underground ASBESTOS AND RADON certain types of rocks containing high mines.3 Soil expansion due to the absorp- Two other hazards can be found inside quantities of uranium are presently linked tion of water, can cause homes and build- the home; they are asbestos and radon to most radon gas production, geologic ings to heave or buckle, and in the United gas. While presently on the decline due to maps can be used to identify areas of States, causes more than $2 billion in recent public abatement, exposure to cer- greatest risk. damages to highways and buildings annu- tain types of asbestos can result in severe ally.3 and fatal lung disease. The term “asbes- Field evaluation of slope stability tos” has evolved from being used to REFERENCES through the examination of materials and describe any fibrous mineral, to being 1. USGS, FS-61-95, http://water.usgs.- processes that comprise and affect them, reserved exclusively for use in describing gov/wid/html/HRDS.html#HDRO allows geologists to estimate their poten- a few fibrous minerals considered to be 2. Erickson, J., 1994, Quakes, Eruption, tial hazard and suggest ways to counter- health hazards by federal statutes.2 Most and other Geologic Cataclysms: New act or minimize their occurrence. Geologic varieties of asbestos do not pose a major York, Facts on File, Inc. maps already in existence can be used to health threat, and those that do, require detect areas where swelling soils, subsid- prolonged contact with the tissue of the 3. AIPG, 1993, Citizens’ Guide to 3 ence, and landslides may be problematic. lungs. Inhalation and the body’s inability Geologic Hazards. to break down certain types of asbestos fibers results in irritation and the eventual 4. AIPG, 1996, Home Buyers’ Guide to FLOODING production of cancerous cells.3 People Geologic Hazards. More than 3 million 5. USGS, http://energy.cr.usgs.gov-/ miles of rivers and streams radon/georadon.html flow throughout the United 6. EPA, www.epa.gov/iaq/radon/radon- States, resulting in nearly qa1.html 10 percent of the land sur- face to be prone to flood- ing.2 Average annual flood losses in the U.S. are more than $3 billion today, a substantial in-crease from the less than $100,000 at the beginning of this cen- tury.2 This rapid rise can be attributed to population growth and an unaware- ness of the inherent dan- gers of building on flood- plains and in flood-prone Geologic Radon Potential.
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