Earth science

Halite (rock salt): properties, formation, uses, and distinctions Halite Halite, commonly called rock salt, is the mineral form of sodium chloride. This article covers its physical properties, formation, historical and modern uses, and how to recognize…

Haloarchaea: salt-loving archaea of hypersaline environments Haloarchaea Haloarchaea are a group of salt-requiring Archaea adapted to very salty habitats. This article explains their traits, taxonomy, ecology, history of the name, and practical signific…

Hancock Seamount (Hawaiian–Emperor seamount chain) Hancock Seamount An underwater volcanic mountain in the Pacific that is part of the Hawaiian–Emperor seamount chain; likely extinct and formed by hotspot volcanism. Last eruption is unknown.

Hațeg Island — Late Cretaceous insular ecosystem of Transylvania Hateg Island Hațeg Island was a large offshore landmass in the late Cretaceous Tethys Sea, known for an insular fauna including dwarf dinosaurs and important fossils that have informed studies…

Hydraulic head (hydrology and fluid mechanics) Head (hydraulic) Hydraulic head quantifies the total mechanical energy per unit weight of fluid at a point; used to describe pressure, elevation and flow potential in groundwater and engineered sys…

Hebridean Terrane: geology, structure, and regional significance Hebridean Terrane Summary of the Hebridean Terrane in northwest Scotland: its rocks, stratigraphy, bounds, geographic extent, tectonic history in the Caledonian orogeny, and exploration significance…

HED meteorite (Howardite–Eucrite–Diogenite group) HED meteorite HED meteorites are achondritic rocks—howardites, eucrites and diogenites—linked to asteroid 4 Vesta. They record early planetary differentiation and provide samples of an intact pr…

Hell Creek Formation: geology, fossils, and the end‑Cretaceous record Hell Creek Formation A comprehensive overview of the Hell Creek Formation: its geology, fossil assemblages, K–Pg boundary record, geographic extent, research history and scientific importance.

Hematite (Fe2O3): iron oxide mineral and principal iron ore Hematite Hematite is an iron(III) oxide mineral and the principal ore of iron. It is mined worldwide for steelmaking, has distinctive physical properties, and occurs in diverse geological e…

Hesperornithoides — a small Jurassic troodontid from North America Hesperornithoides Hesperornithoides is a small, bird-like troodontid theropod from the Upper Jurassic Morrison Formation of western North America, known from a relatively complete skeleton that info…

Highland Boundary Fault: Scotland's geological divide Highland Boundary Fault A concise account of the Highland Boundary Fault — its course across Scotland, geological history, landscape effects, and importance to science and people.

History of the Earth: formation, major events, and long-term evolution History of the Earth A concise account of Earth's origin about 4.56 billion years ago, its geological and biological milestones, the geological time scale, and how scientists reconstruct planetary hist…

History of the geologic time scale Overview of how scientists developed the geologic time scale: early stratigraphy, 18th–19th century classifications, fossil correlation, radiometric dating, and modern internationa…

Holocene Epoch Holocene The Holocene is Earth's current geological epoch, beginning about 11,700 years ago after the last major glaciation. It is marked by relatively stable climate, rising seas, the rise…

Hornblende: a common amphibole-group rock-forming mineral name Hornblende Hornblende is a dark, complex amphibole-group silicate name applied to several closely related minerals. Common in many igneous and metamorphic rocks, it is important for petrology…

Hotspot (geology) A geological hotspot is a localized volcanic source often fed by a deep mantle plume or other processes. Hotspots produce island chains, plateaus and geothermal areas and help trac…

Huayangosaurus — an early stegosaur from Middle Jurassic China Huayangosaurus A small, primitive stegosaurian dinosaur from the Middle Jurassic Lower Shaximiao Formation of Sichuan, China, important for understanding early stegosaur anatomy and evolution.

Humboldt Current (Peru Current): Cold, nutrient-rich Pacific current off South America Humboldt Current A cold, low-salinity Pacific current that flows north along South America, driving strong coastal upwelling, exceptional marine productivity and major fisheries, and affecting coas…

Humid continental climate A mid-latitude climate with large seasonal temperature swings: warm to hot summers, cold winters, and year-round precipitation. Common in interior and northeastern regions of North…

Humus (soil organic matter) Humus Humus is the dark, stable organic component of soil formed by decomposed plant and animal residues; it improves fertility, water retention, structure and helps store carbon in ecos…

Huronian glaciation (Paleoproterozoic ice age) Huronian glaciation A prolonged Paleoproterozoic glaciation c. 2.4–2.1 billion years ago, recorded by layered glacial deposits and linked to atmospheric oxygenation and major shifts in the carbon cycl…

Hurricane Andres (2009) Hurricane Andres (2009) was the first named storm and hurricane of the 2009 eastern Pacific season; it formed in June, briefly attained hurricane strength, then weakened and dissip…

Hurricane Belle (August 1976) Hurricane Belle Hurricane Belle was a Category 3 Atlantic hurricane in August 1976 that made landfall on Long Island and southern Connecticut, causing about a dozen deaths and roughly $100 million…

Hurricane Beulah (1967) Hurricane Beulah Major 1967 Atlantic hurricane that crossed the Caribbean, struck the Yucatán, briefly reached Category 5, made landfall in Texas as a major hurricane, spawned 115 tornadoes, caused…

Hurricane Cesar–Douglas: a cross‑basin cyclone of 1996 Hurricane Cesar-Douglas Hurricane Cesar–Douglas was a rare 1996 storm that formed in the Atlantic as Cesar, crossed Central America, and re‑intensified in the Pacific as Hurricane Douglas.

Hurricane Cindy (2005) A short‑lived late‑June/early‑July 2005 storm that became a Category 1 hurricane before striking southern Louisiana; notable for heavy rains, widespread outages and a powerful torn…

Hurricane Cleo (1964) — major Atlantic hurricane affecting the Caribbean and U.S. East Coast Hurricane Cleo Hurricane Cleo was a powerful late‑August–early‑September 1964 Atlantic hurricane that struck Guadeloupe, Hispaniola and the U.S. East Coast, causing over $198 million damage and m…

Hurricane Connie (1955) Hurricane Connie Hurricane Connie was a powerful 1955 Atlantic hurricane that struck the U.S. East Coast, bringing heavy rain, coastal damage, and contributing to widespread flooding in the Mid-Atl…

Hurricane David (1979) Hurricane David Powerful Cape Verde hurricane of 1979 that devastated parts of the Caribbean and struck Florida; caused widespread destruction, thousands of deaths and more than $1.5 billion in da…

Hurricane Diana (1984): Category 4 storm that struck North Carolina Hurricane Diana (1984) Overview of Hurricane Diana (1984), a Major Atlantic hurricane noted for rapid intensification, forecasting difficulties, and its impacts on eastern North Carolina and nearby coast…

Hurricane Earl (2010): formation, track, impact, and aftermath Hurricane Earl (2010) A summary of Hurricane Earl (2010), a long-lived Cape Verde hurricane that reached major intensity, brushed the U.S. East Coast, affected the Leeward Islands, and later struck Atla…

Hurricane Easy (1950) Hurricane Easy was a major September 1950 Atlantic hurricane that hit Cuba and Florida (landfall near Cedar Key), moved inland and dissipated over Arkansas; it caused heavy rain, d…

Hurricane Edith (1971): Category 5 Caribbean storm that struck Central America and Louisiana Hurricane Edith (1971) A powerful 1971 Atlantic hurricane that became a Category 5 in the Caribbean, made landfall in northern Central America, and later hit western Louisiana, producing a Gulf States to…

Hurricane Elena (1985): Gulf Coast major hurricane with looping track Hurricane Elena Category 3 Atlantic hurricane in late Aug–Sep 1985 that executed an unusual loop in the Gulf of Mexico, prompting widespread evacuations and causing heavy damage along the U.S. Gul…

Hurricane Emily (1993) — Atlantic storm overview Hurricane Emily (1993) Atlantic hurricane active Aug 22–Sep 6, 1993. Formed from an African tropical wave, moved near Puerto Rico and toward the U.S. East Coast, producing heavy rain, flooding, and damag…

Hurricane Ernesto (2012) Atlantic tropical cyclone that formed August 1, 2012, crossed Jamaica and the Yucatán Peninsula, made landfall in southeastern Mexico, and dissipated August 10; it caused several d…

Hurricane Florence (September 2018) Hurricane Florence A major Atlantic hurricane that struck the southeastern United States in September 2018, producing catastrophic flooding in the Carolinas and causing widespread damage and disrupti…

Hurricane Frances (2004): Atlantic storm that struck Florida and the U.S. East Coast Hurricane Frances Hurricane Frances was a major 2004 Atlantic hurricane that struck eastern Florida in early September, producing widespread flooding, tornadoes, 49 deaths and about $12 billion in d…

Hurricane Frederic (1979) Hurricane Frederic Powerful 1979 Atlantic hurricane that struck the U.S. Gulf Coast; at landfall it produced major hurricane conditions, causing widespread damage and prompting long-term recovery and…

Hurricane Gaston (2004) Tropical cyclone Gaston affected the U.S. East Coast in late August 2004, making landfall on the South Carolina coast and producing moderate damage from South Carolina northward to…

Hurricane Georges (1998): path, impacts, and aftermath Hurricane Georges A long-lived Atlantic hurricane in September 1998 that struck the northern Caribbean and the U.S. Gulf Coast, causing widespread flooding, infrastructure damage, 604 deaths, and an…

Hurricane Gert (1993) September 1993 Atlantic hurricane that struck Central America and eastern Mexico, producing destructive flooding and landslides; reported peak winds near 105 mph and many casualtie…

Hurricane Gert (1999) Atlantic Cape Verde hurricane in September 1999 that reached Category 4 strength, passed east of Bermuda, became extratropical near Atlantic Canada, and produced notable marine dam…

Hurricane Gloria (1985) Hurricane Gloria Hurricane Gloria was a powerful Atlantic hurricane in late September 1985 that threatened the U.S. East Coast, made landfall near Long Island and southern New England, and caused w…

Hurricane Gordon (1994) A late‑1994, slow‑moving tropical cyclone noted for its erratic track and catastrophic rainfall—especially in Haiti and the central Caribbean—causing widespread flooding, landslide…

Hurricane Gordon (2006) Hurricane Gordon (2006) was a North Atlantic storm that peaked at Category 3, passed through the Azores as a Category 1, and whose remnants affected Western Europe. It was the firs…

Hurricane Hattie (1961) Hurricane Hattie A powerful late‑October 1961 Atlantic hurricane that struck British Honduras (now Belize) and nearby areas, causing widespread devastation, over 300 deaths, and prompting long‑term…

Hurricane Helene (2006) — Cape Verde Category 3 Atlantic Hurricane Hurricane Helene (2006) Hurricane Helene (2006) was a long-lived Cape Verde hurricane that reached Category 3 over the central Atlantic, remained mostly over open water, and produced only minor effects as…