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Greensburg tornado
The Greensburg tornado was a violent EF5 tornado that struck Greensburg, Kansas, on May 4, 2007, destroying about 95 percent of the town and killing 11 people.
Greenschist
Greenschist is a schistose metamorphic rock whose green color comes from chlorite, epidote, or actinolite; it forms by low-grade regional metamorphism of shale or basalt.
Greenstone belt
A greenstone belt is a curving belt of volcanic and sedimentary rocks altered to green minerals, mostly in Archean terranes of the oldest continents, and rich in gold.
Greenstone Gold Mine
Greenstone Gold Mine is an open-pit gold mine near Geraldton, Ontario, wholly owned by Equinox Gold, on the historic Hardrock deposit. First gold poured in May 2024.
Greta Thunberg
Greta Thunberg, born in Sweden in 2003, is a climate activist who began a school strike outside the Swedish Parliament in 2018 that grew into Fridays for Future.
Greywacke
Greywacke, also spelled graywacke (German Grauwacke), is a dark gray, hard, poorly sorted sandstone deposited by underwater density currents in deep ocean water near mountain ranges.
GRIB
GRIB, or General Regularly-distributed Information in Binary form, is a binary format defined by the World Meteorological Organization for exchanging gridded weather and climate data.
Gridpoint Statistical Interpolation
The Gridpoint Statistical Interpolation (GSI) is a NOAA data assimilation system, developed at NCEP and operational since 2007, that generates initial conditions for weather forecast models.
Griggs
Mount Griggs (formerly Knife Peak) is a 2,317-m andesitic stratovolcano in Katmai National Park, Alaska, the cluster's highest peak, lying about 10 km behind the volcanic front, active since about 292 ka, fumarolically active, last eruption about 1790 BCE.
Grímsvötn
Grímsvötn, also known as Grimsvotn volcano, is Iceland's most active subglacial volcano, lying beneath the Vatnajökull ice cap. Its 2011 eruption sent ash over 20 km high and disrupted air travel across northern Europe.
Grossular
Grossular is a calcium aluminum silicate mineral of the garnet group, the most varicolored of the six common garnets, including gem varieties hessonite and tsavorite.
Ground-penetrating radar
Ground-penetrating radar (GPR), or georadar, is a nondestructive geophysical method that transmits radio-frequency pulses into the ground and records reflections to map buried features and their depths.
Groundwater
Groundwater, also called subsurface water or phreatic water, is water held in cracks and spaces of rock and sediment below the Earth's surface, the largest store of liquid freshwater.
Groundwater age dating
Groundwater age dating is the estimation of the time since water recharged an aquifer, inferred from dissolved tracers like CFCs, tritium, and carbon-14 rather than measured directly.
Groundwater discharge
Groundwater discharge is the outflow of water from the saturated zone back to the land surface or to streams, lakes, wetlands, and, in coastal areas, the ocean floor.
Groundwater model
A groundwater model, also known as a groundwater flow model, is a computational method that predicts hydraulic heads, flows, and solute concentrations in aquifers, most often with the USGS MODFLOW code.
Groundwater pollution
Groundwater pollution, also called contaminated groundwater, is the contamination of underground aquifers by pesticides, fertilizers, sewage, and industrial waste, which threatens the drinking water of half the U.S. population.
Groundwater protection
Groundwater protection: preventing aquifer contamination through vulnerability mapping, protection zones, land-use controls, and SDWA, EU, and managed recharge programs worldwide.
Groundwater recharge
Groundwater recharge, also called deep percolation or aquifer recharge, is the downward flow of water from the surface to the water table; managed recharge deliberately adds water to aquifers for storage and recovery.
GRUAN
GRUAN, the GCOS Reference Upper-Air Network, is an international network of sites measuring climate variables from the surface into the stratosphere, envisaged by the WMO in 2007 to calibrate satellites and radiosonde data.
Guiana Shield
The Guiana Shield, also called the Guayana Shield, is a Precambrian rock formation underlying Venezuela, Guyana, Suriname, French Guiana, and parts of Brazil and Colombia.
Gully
A gully, also known as a voçoroca, is a channel or miniature valley cut into soil by concentrated runoff, too deep for ordinary tillage to smooth over.
Guntur (landform)
Guntur (Gunung Guntur), "thunder," is a 2,251 m complex stratovolcano in West Java near Garut, last erupting in 1847 after 24 eruptions since 1690; it drives the Kamojang and Darajat geothermal fields.
Gust factor
The gust factor is the ratio of a peak wind speed over a short duration, such as 3 seconds, to the mean wind speed over a longer period.
Gust front
A gust front is the leading edge of gusty surface winds produced by a thunderstorm's downdrafts, often marked by a shelf cloud, that produces wind shear hazardous to aircraft.
Gutenberg discontinuity
The Gutenberg discontinuity is the seismic boundary about 2,900 km down where Earth's solid mantle meets its liquid iron outer core, named for Beno Gutenberg.
Haboob
A haboob (Arabic habūb) is a wall of dust or sand pushed by thunderstorm outflow winds that can cut visibility to zero; the term began in Sudan and now covers similar storms worldwide, especially in Arizona.
HadCRUT
HadCRUT is a series of global historical temperature datasets produced jointly by the Met Office Hadley Centre and the University of East Anglia's Climatic Research Unit since 1850.
Hadean
The Hadean, formerly the Priscoan, is the earliest eon of geological time, spanning Earth's formation about 4.567 billion years ago to 4.031 billion years ago, known almost entirely from zircon grains.
Hadley cell
The Hadley cell, or Hadley circulation, is an atmospheric circulation in which air rises near the equator and descends near latitude 30° in each hemisphere.