<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="531" name="hazards" parent="1174" scope="Potential dangers from both natural processes (e.g., earthquakes, floods, and climate change) and human impacts on the environment."/><uf><usefor name="catastrophes"/><usefor name="coastal hazards"><usewith><term thcode="2" code="1799" name="coastal processes" parent="101" scope="Processes unique to coastal areas including longshore transport, beach erosion, storm surge, shoreline change, delta formation, barrier island migration, beach stabilization by vegetation"/></usewith></usefor><usefor name="disasters"/><usefor name="earthquake hazards"><usewith><term thcode="2" code="304" name="earthquakes" parent="451" scope="Ground shaking caused by the sudden release of accumulated strain by an abrupt shift of rock along a fracture in the earth or by volcanic or magmatic activity, or other sudden stress changes in the earth."/></usewith></usefor><usefor name="emergency management resources"/><usefor name="environmental hazards"/><usefor name="geologic hazards"/><usefor name="harmful algal blooms"><usewith><term thcode="2" code="30" name="algal blooms" parent="310" scope="Exceptional growth of algae and cyanobacteria in lakes, rivers or oceans due to excessive nutrients or climatic conditions."/></usewith></usefor><usefor name="ocean hazards"><usewith><term thcode="2" code="816" name="ocean processes" parent="101" scope="Recurrent natural changes that are physical, biological, or chemical, actively affecting the seas and oceans."/></usewith></usefor></uf><bt><term thcode="2" code="1174" name="topics" parent="1" scope="Themes, subjects, and concerns for which USGS information resources are relevant."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><rt><term thcode="2" code="30" name="algal blooms" parent="310" scope="Exceptional growth of algae and cyanobacteria in lakes, rivers or oceans due to excessive nutrients or climatic conditions."/><term thcode="2" code="769" name="contamination and pollution" parent="1174" scope="Introduction of harmful substances into the environment by human action or natural processes."/><term thcode="2" code="246" name="desertification" parent="168" scope="The alteration of arable land to dry, barren land due to prolonged drought or the deleterious effects of human intervention including overgrazing, overpopulation, or destructive agricultural practices."/><term thcode="2" code="284" name="droughts" parent="63" scope="Extended periods of moisture deficit over a sizeable area sufficient to have an adverse effect on vegetation, animals, or man."/><term thcode="2" code="304" name="earthquakes" parent="451" scope="Ground shaking caused by the sudden release of accumulated strain by an abrupt shift of rock along a fracture in the earth or by volcanic or magmatic activity, or other sudden stress changes in the earth."/><term thcode="2" code="320" name="ecotoxicology" parent="650" scope="Scientific study of causes, dispersal, and effects of contaminants on the environment."/><term thcode="2" code="384" name="fires" parent="101" scope="Combustion, marked by flames or intense heat, in natural settings, often ignited by lightning or human activities.  For fires set as part of natural resource management, use 'controlled fires'."/><term thcode="2" code="398" name="floods" parent="1667" scope="Relatively high water that overflows the natural or artificial banks of a stream or coastal area that submerges land not normally below water level."/><term thcode="2" code="548" name="human impacts" parent="1174" scope="The effects, intentional or unintentional, beneficial or harmful, direct or indirect, which human activities have upon the environment and living things."/><term thcode="2" code="1718" name="impact cratering" parent="101" scope="Impact of extraterrestrial objects such as asteroids, comets, and meteorites on Earth."/><term thcode="2" code="639" name="landslides" parent="1736" scope="Downslope movement of rock, soil, or artificial fill under the influences of gravity."/><term thcode="2" code="661" name="liquefaction" parent="2284" scope="Physical process which can occur during an earthquake.  Clay-free soil deposits (primarily sands and silts)temporarily lose strength and behave as viscuous fluids, resulting in ground failure."/><term thcode="2" code="1721" name="magnetic storms" parent="451" scope="A period of time during which the earth's magnetic field varies rapidly.  During magnetic storms, satellite electronics can be damaged through the build up and subsequent discharge of static electric charges and astronauts and high-altitude pilots can be subjected to increased levels of radiation."/><term thcode="2" code="750" name="mining hazards" parent="548" scope="Dangerous conditions which result from the extraction of naturally occurring mineral deposits.  Includes tunnel collapses, fires, and explosions."/><term thcode="2" code="1687" name="scour" parent="1667" scope="Erosion of sediment in a stream bed, often occurring at manmade structures such as bridge supports."/><term thcode="2" code="1075" name="social sciences" parent="1019" scope="Sciences concerned with the structure and interrelationships of human societies, human institutions and organizations, and human culture over time."/><term thcode="2" code="1102" name="storms" parent="63" scope="Atmospheric disturbances with winds of unusual force or direction. Accompanied by rain, snow, hail, or sleet, and often by thunder and lightning."/><term thcode="2" code="1195" name="tsunamis" parent="822" scope="Sea waves generated by submarine earthquakes, volcanic eruptions, or landslides, which are generally imperceptible in deep water but may be very destructive when striking the shoreline."/><term thcode="2" code="1286" name="volcanic activity" parent="451" scope="Episodes during which gases, ash, and lava (molten rock) escape from vents in the earth's crust, accompanied by minor tremors."/></rt></descriptor>