5,021 articles
Uniformitarianism
Uniformitarianism, or the principle of uniformity, is the geological principle that processes observed today, like erosion and volcanism, shaped Earth in the past; James Hutton proposed it in 1788.
Unimpaired runoff
Unimpaired runoff, also called full natural flow, is the flow a river would carry without dams or diversions, estimated by removing human effects from measured flows.
Union of Concerned Scientists
The Union of Concerned Scientists (UCS) is an American nonprofit science advocacy organization founded at MIT in 1969, working on climate, energy, and nuclear weapons policy.
Unit hydrograph
A unit hydrograph is the direct runoff hydrograph resulting from one unit depth of rainfall excess falling uniformly over a watershed, introduced by LeRoy Sherman in 1932.
United Kingdom Hydrographic Office
The United Kingdom Hydrographic Office is a Ministry of Defence agency founded in 1795 that publishes ADMIRALTY charts used by over 90% of large international ships.
United Nations Climate Change Conference
The United Nations Climate Change Conference, commonly called COP, is the annual UNFCCC climate summit where government delegates have negotiated agreements such as the Kyoto Protocol and Paris Agreement since 1995.
United Nations Framework Convention on Climate Change
The United Nations Framework Convention on Climate Change (UNFCCC) is a 1992 international treaty requiring countries to report greenhouse gas emissions, with heavier duties on industrialized ones.
United States Drought Monitor
The United States Drought Monitor (USDM) is a weekly map showing where drought is occurring and how severe it is across the United States, first issued in 1999.
United States Geological Survey
The United States Geological Survey (USGS) is a federal science agency of the Department of the Interior, created in 1879 and headquartered in Reston, Virginia.
United States Hydrographic Office
The United States Hydrographic Office, also known as the U.S. Naval Hydrographic Office, was the U.S. Navy's charting agency from 1866 until 1962, chiefly for foreign waters.
Universal Soil Loss Equation
The Universal Soil Loss Equation (USLE) is an empirical model that estimates long-term average annual soil loss from sheet and rill erosion using six factors for rainfall, soil, topography, cover, and support practices.
Universal Thermal Climate Index
The Universal Thermal Climate Index (UTCI) is an equivalent temperature that folds air temperature, humidity, wind, and radiation into one measure of heat stress on the body, released in 2009.
University-National Oceanographic Laboratory System
The University-National Oceanographic Laboratory System, or UNOLS, is a consortium of 61 academic institutions that coordinates access to the U.S. Academic Research Fleet, founded in 1971.
Unmanned underwater vehicle
An unmanned underwater vehicle (UUV), also called an underwater drone or robotic submarine, is a robot operating underwater without a human aboard, either tethered and remotely piloted or autonomous.
Upper mantle
The upper mantle is the outermost part of Earth's mantle, extending from the Moho down to the 660-km discontinuity and hosting the lithosphere and asthenosphere that carry tectonic plates.
Upper-atmospheric lightning
Upper-atmospheric lightning, also called transient luminous events or high altitude lightning, is short-lived glowing discharge above large thunderstorms, seen in forms like sprites, blue jets, and elves.
Upsweep
Upsweep is a long-running, unidentified underwater sound in the South Pacific, recorded by NOAA's hydrophones since August 1991 and loud enough to be heard across the Pacific.
Upward continuation
Upward continuation is a potential-field technique that recalculates gravity or magnetic data at a higher elevation, acting as a low-pass filter that suppresses shallow-source noise.
Ur Schatt
The Ur Schatt, also written Ur-Schatt or Ur-Shatt, was the combined Tigris-Euphrates-Karun river that flowed along the exposed Persian Gulf floor into the Gulf of Oman about 15,000 years ago.
Uraninite
Uraninite, also known as pitchblende, is a radioactive uranium oxide mineral (UO₂) and the most important ore of uranium, from which Marie and Pierre Curie isolated polonium and radium in 1898.
Uranium mining
Uranium mining, the extraction of uranium ore from uranium mines, is the first stage of the nuclear fuel cycle, supplying reactors and, historically, nuclear weapons programs.
Uranium ore
Uranium ore is rock with uranium concentrated enough for economic extraction, mined by open pit, underground, and in situ leaching methods, then milled into yellowcake for nuclear fuel.
Uranium–thorium–helium thermochronology
Uranium–thorium–helium ((U-Th)/He) thermochronology is a geochronology method dating minerals by radiogenic helium from uranium and thorium decay, used to study exhumation, fault slip, and landscape evolution.
Urban heat island
The urban heat island is the excess warmth of a built-up city over its rural surroundings, up to 12 °C warmer on a clear, calm night.
USArray
USArray is a continental-scale seismic observatory and component of NSF's EarthScope program, funded in 2003 to record earthquakes and image the structure beneath North America with dense seismograph networks.
USDA Soil Taxonomy
USDA Soil Taxonomy is a hierarchical soil classification system developed by the United States Department of Agriculture under Guy Smith, published in 1975 and used worldwide.
Ushkovsky
Ushkovsky (formerly Plosky) is a 3,943 m compound volcano at the NW end of Kamchatka's Kliuchevskaya group, with an ice-filled 4.5 x 5.5 km caldera and last eruption in 1890 CE.
Utica Shale
The Utica Shale is an Upper Ordovician black shale in the Appalachian Basin, a major natural gas and oil drilling target in eastern Ohio since about 2011.
V-notch weir
A V-notch weir is a sharp-crested, thin-plate weir with a triangular notch used to measure small water flows in open channels, its triangular shape giving it sensitivity at low discharges.
Vaalbara
Vaalbara is a proposed Archean supercontinent, or supercraton, joining the Kaapvaal Craton of southern Africa and the Pilbara Craton of Western Australia; its existence remains debated.