5,021 articles
Orthographic map projection
The orthographic map projection, also called the orthographic projection in cartography, is an azimuthal perspective projection that shows one hemisphere as a globe appears from space.
Osisko Development Corp.
Osisko Development Corp., formerly Ringbolt Ventures Ltd., is a Canadian gold development company incorporated in 2006, holding the Cariboo Gold Project in British Columbia and the Tintic Project in Utah.
Osorno
Osorno (Volcán Osorno) is a 2,659-m glaciated stratovolcano in Chile's Los Lagos Region between Lakes Llanquihue and Todos los Santos; last confirmed eruption 1869, sixth on Chile's volcanic risk ranking, dominantly basaltic unlike nearby andesitic Calbuco.
Otway Basin
The Otway Basin is an onshore and offshore sedimentary basin along the coasts of Victoria and South Australia, a gas province formed during the separation of Australia and Antarctica.
Outburst flood
An outburst flood is a sudden, large release of water from a natural dam, such as a glacier-dammed lake, producing a flood far larger than the river's normal flow.
Outcrop
An outcrop is a visible exposure of bedrock at the Earth's surface, where rock otherwise buried beneath soil or vegetation can be observed and sampled directly.
Outwash plain
An outwash plain is a broad, gently sloping plain of glacial sediment deposited by meltwater streams beyond a glacier's margin, known in Icelandic as a sandur.
Overexploitation of groundwater
Overexploitation of groundwater, also called groundwater overdraft or aquifer overexploitation, is the extraction of water from aquifers faster than they are replenished by recharge, causing declining groundwater storage worldwide.
Overpass myth
The overpass myth, also known as the tornado overpass myth, is the mistaken belief that highway overpasses provide safe shelter from tornadoes, a practice weather agencies warn against.
Overpressure (geology)
Overpressure, also called geopressure, is fluid pressure in a sedimentary basin exceeding hydrostatic pressure at a given depth. It is a drilling hazard behind many well blowouts.
Overshooting top
An overshooting top is the dome-like protrusion of a thunderstorm's cloud top above the anvil, driven by a very strong updraft and used as a satellite indicator of storm intensity.
Overturn
Overturn: in oceanography, the mixing of stratified water due to density instability, and the related global overturning circulation (thermohaline circulation, AMOC) that sinks dense polar water and redistributes heat, salt, and carbon worldwide.
Overturning in the Subpolar North Atlantic Program
The Overturning in the Subpolar North Atlantic Program (OSNAP) is an international program measuring the Atlantic meridional overturning circulation with a moored array since 2014.
Oxford Clay
The Oxford Clay Formation is a Jurassic mudstone rock unit of southern and eastern England, a major source of brickmaking clay and of exceptionally preserved marine fossils.
Oxisols
Oxisols, known as Ferralsols in the World Reference Base, are the most highly weathered of the twelve USDA soil orders, forming in hot, humid tropics with low natural fertility.
Oxygen cycle
The oxygen cycle is the biogeochemical cycle through which oxygen moves among the atmosphere, ocean, biosphere, and rocks, produced mainly by photosynthesis and consumed by respiration and weathering.
Oxygen isotope analysis
Oxygen isotope analysis measures the relative abundance of stable oxygen isotopes in rocks, waters, ice, and biogenic minerals, using those ratios to reconstruct past temperatures and water-cycle history.
Oxygen minimum zone
An oxygen minimum zone (OMZ) is a persistent ocean layer, about 100 to 1,500 m deep, where dissolved oxygen falls far above and below levels of nearby waters, and zones are expanding as the ocean warms.
Oyu Tolgoi
Oyu Tolgoi (Оюу Толгой, "Turquoise Hill") is a large copper and gold mine in Mongolia's South Gobi region, jointly owned by Rio Tinto and the Mongolian government.
Ozone depletion
Ozone depletion is the thinning of the ozone layer caused by CFCs and halons, discovered over Antarctica in 1985 and now slowly recovering under the Montreal Protocol.
Ozone layer
The ozone layer, also called the ozone shield, is the stratospheric region, 15 to 35 kilometers up, that absorbs most of the Sun's harmful ultraviolet radiation.
P wave
The P wave, or primary wave, is the fastest seismic wave an earthquake produces, compressing rock parallel to its direction of travel and arriving first at seismic stations.
P-wave tomography
P-wave tomography is a seismic imaging method that inverts compressional wave travel times from millions of earthquakes to build 3-D models of P-wave velocity variations inside the Earth, from dense arrays to the whole mantle.
Pacaya
Pacaya, also known as Pacaya volcano, is a basaltic stratovolcano in southern Guatemala, about 25 km from Guatemala City, that has erupted nearly continuously since 1961 and dropped ash on the capital in 2010.
Pacific Meridional Mode
The Pacific Meridional Mode is a leading ocean-atmosphere pattern in the northeastern subtropical Pacific, identified in 2004, whose warm anomalies extend from Baja California toward the equator.
Pacific Northwest Seismic Network
The Pacific Northwest Seismic Network (PNSN), run by the University of Washington, monitors earthquakes and volcanoes across Washington and Oregon and feeds the USGS ShakeAlert early warning system.
Pacific Northwest windstorm
A Pacific Northwest windstorm is a strong midlatitude cyclone that hits Oregon, Washington, and southern British Columbia with damaging winds, most often between November and February.
Pacific Plate
The Pacific Plate is the largest oceanic tectonic plate on Earth, underlying most of the Pacific Ocean. Its subduction zones produce most of the world's largest earthquakes.
Pacific storm track
The Pacific storm track is the band over the North Pacific where migrating cyclones and anticyclones are most active, supplying much of western North America's winter weather.
Pacific Tsunami Warning Center
The Pacific Tsunami Warning Center (PTWC) is a National Weather Service facility at ʻEwa Beach, Hawaii, established in 1949 to warn of tsunamis across the Pacific and Caribbean.