Category: Geography

Introduction The North Atlantic Current (NAC), often termed the North Atlantic Drift or North Atlantic Sea Movement, is the northeastward continuation of the Gulf Stream and functions as a major warm western‑boundary current in the North Atlantic. As the initial poleward branch of the North Atlantic Subpolar Gyre, the NAC conveys western‑boundary flow from subtropical…

North American Plate — Introduction The North American Plate is a principal tectonic plate with an area of approximately 76 million km² (29 million mi²), making it the second-largest plate on Earth. Its surface encompasses most of the North American continent, Greenland, portions of northeastern Siberia, and several adjacent island territories including Cuba, the Bahamas,…

Newton’s law of universal gravitation posits that every pair of mass elements attracts each other with a force proportional to the product of their masses and inversely proportional to the square of the distance between their centers of mass. In its usual quantitative form, F = G m1 m2 / r^2, where F is the…

The New Madrid seismic zone (NMSZ), also described in the literature as the New Madrid fault line, fault zone, or fault system, is a principal source of intraplate earthquakes in the conterminous United States. Unlike plate-boundary seismicity, intraplate earthquakes originate within a tectonic plate; the NMSZ exemplifies how reactivated crustal structures well inland from plate…

Introduction The neural tube is the embryonic structure that gives rise to the central nervous system—the brain and spinal cord—in chordates, including all vertebrates. Its formation begins with the appearance of a neural groove flanked by paired neural folds; as morphogenesis proceeds the groove deepens, the folds elevate and converge at the midline, and their…

Introduction — Nebular hypothesis The nebular hypothesis, originally proposed by Immanuel Kant and later reformulated by Pierre Laplace, is the foundational cosmogonic model in which the Solar System originates from a rotating disk of gas and dust surrounding a young Sun. Its modern incarnation, the solar nebular disk model (SNDM), retains the core idea of…

The Nazca (Nasca) plate is an oceanic tectonic plate located in the eastern Pacific basin immediately offshore of western South America. Bounded to the west by the Pacific Plate and to the south by the Antarctic Plate, these margins are expressed respectively by the East Pacific Rise and the Chile Rise. Along its eastern boundary…

Introduction India’s land and water endowments remain central to its natural-resource profile. In 2020 the country possessed approximately 155.37 million hectares of cultivable land, equivalent to about 52.3% of its territorial area; however, this agricultural land is under pressure and showing contraction due to intensive cropping, expanding livestock grazing, deforestation, urban expansion and an increase…

Introduction A natural arch (also called a natural bridge or rock arch) is a freestanding, arch‑shaped rock formation defined by a span of rock with an opening beneath. Such landforms arise where erosional agents remove weaker rock beneath a more resistant caprock, leaving an overhead arch and a void. They commonly occur on inland and…

Introduction Mud volcanoes are eruptive landforms produced by the ascent and surface discharge of mud slurries, water and associated gases; smaller, localized seepage features of the same process are often called mud‑pots. Individual edifices span a broad morphological spectrum, from shallow seeps under a metre high and a few metres across to extensive mud‑dome complexes…

Mountain ranges arise from large‑scale movements of the Earth’s crust and are produced by multiple, interacting orogenic processes — notably folding, faulting, volcanic activity, igneous intrusion and metamorphism. These mechanisms operate together to thicken, deform and build topography rather than acting in isolation. Under compressive regimes at convergent plate boundaries, brittle failure generates low‑angle thrusts…

Beaches are continually reshaped by hydrodynamic forces: waves, currents, tides and fluvial flows erode coastal and terrestrial materials and redistribute the resulting sediment along the shore. Over long intervals, repeated physical weathering and transport reduce bedrock and coarser deposits to sand-sized grains that accumulate onshore and generate the characteristic cross-shore beach profile. Fluvial systems contribute…

Introduction Mining constitutes a significant component of India’s economy, contributing roughly 2.2–2.5% of national GDP and a markedly larger share—about 10–11%—of the industrial sector’s output. Artisanal and small-scale operations exert a measurable influence on the sector’s cost structure, accounting for approximately 6% of total mineral production costs, while direct employment in mining is reported at…

Introduction (Minerals) A mineral is a naturally formed, crystalline chemical element or compound produced by geologic processes, characterized by a reasonably well‑defined chemical composition and an ordered crystal structure. By convention the geologic definition normally excludes substances known only from living organisms, yet exceptions exist: some minerals are biogenic (e.g., calcite produced by organisms), some…

Introduction The Milky Way is a barred spiral galaxy that contains the Solar System and, when seen from Earth, appears as a luminous, unresolved band produced by the combined light of innumerable stars concentrated in its spiral arms. Morphologically a barred spiral, its optically defined D25 isophotal diameter is estimated at 26.8 ± 1.1 kpc…

Introduction — Mid‑ocean ridge A mid‑ocean ridge (MOR) is a linear, submarine mountain system formed where tectonic plates diverge and new oceanic lithosphere is created. Typically found at depths near 2,600 m and standing roughly 2,000 m above the adjacent abyssal plains, these ridges are the topographic highs of the ocean floor produced as mantle…

Metamorphism denotes the transformation of a pre‑existing rock (the protolith) into a new lithology through changes in mineralogy and texture while the rock remains solid; melting to form magma does not occur. These transformations typically take place at temperatures above ~150 °C and commonly under elevated pressures and in the presence of chemically active fluids,…

Introduction Metamorphic rocks form when an existing “protolith”—which may be igneous, sedimentary, or previously metamorphosed—undergoes recrystallization and chemical re-equilibration in the solid state in response to elevated temperature and/or pressure. Typical metamorphic conditions begin at roughly 150–200 °C (300–400 °F) and commonly involve lithostatic pressures on the order of 100 MPa (≈1,000 bar) or greater;…

A metal is a material class characterized by a lustrous appearance when freshly cut or polished and by high electrical and thermal conductivity that arises from delocalized electronic states at the Fermi level. These mobile electrons enable metallic conduction and related thermal transport and are the electronic basis for many distinguishing properties of metals. Mechanically,…

Introduction Megathrust earthquakes are the largest class of interplate seismic events that originate where one lithospheric plate is forced beneath another at a subduction zone. They result from abrupt rupture on the shallow thrust fault that separates the overriding and subducting plates, most commonly located at the base of oceanic trenches. When such rupture occurs…

Mass wasting, or mass movement, denotes gravity-driven downslope displacement of consolidated and unconsolidated Earth materials in which the moving mass remains coherent rather than being transported within a separate fluid phase (water, air or ice). Processes range from imperceptibly slow soil creep and solifluction—seasonally saturated, slow flows common in cold environments—to abrupt failures such as…

Introduction The Mariana plate is a small tectonic plate that underlies the Mariana Islands immediately west of the Mariana Trench and constitutes the crustal foundation of the Izu–Bonin–Mariana Arc. Its western margin meets the Philippine Sea plate along a divergent boundary that is segmented by numerous transform faults; these strike‑slip offsets compartmentalize the western edge…

The Maoke Plate is a small tectonic element beneath western New Guinea that underlies the Sudirman Range, the mountain chain that hosts Puncak Jaya, the island’s highest summit. Its eastern margin was initially interpreted as a convergent contact with the Woodlark Plate, but more recent models reassign this interaction either to an expanded Solomon Sea…

Introduction — Mantle Plumes Mantle plumes are hypothesized upwellings of anomalously warm, buoyant mantle material that rise from depth and are invoked to account for volcanic activity not readily explained by plate-boundary tectonics. At larger scale, broad upwellings termed superplumes are inferred from seismic imaging as extensive low-velocity zones (LVZs), which indicate regions of elevated…

Mantle convection — Introduction Mantle convection is the slow, heat‑driven creep of Earth’s solid silicate mantle that transports internal heat to the surface and provides the primary driving force for plate tectonics. The rigid lithosphere overlies a weaker, ductile asthenosphere; together these constitute upper‑mantle components, with the lithosphere broken into tectonic plates that are continuously…

A magnetic field is a vector (more precisely a pseudovector) field that describes the magnetic influence experienced by moving electric charges, electric currents and magnetized matter. A charge moving through the field is subject to a force perpendicular to both its velocity and the local magnetic-field vector; permanent magnets exert forces on ferromagnetic materials and…

Introduction — Magmatism Magmatism encompasses the emplacement of molten rock within and atop a planet’s outer layers and the subsequent cooling and solidification that produces igneous rocks. Large intrusive bodies such as the Gangdese batholith—mapped as an extensive pluton emplaced ~100 Ma—illustrate how subsurface magmatic processes generate broad volumes of crystalline crust and record the…

Introduction Magmatic underplating describes the emplacement and accumulation of mantle-derived basaltic magmas at the base of the crust—commonly at the Mohorovičić discontinuity (Moho) but also at shallower crustal horizons—where they stall, pond in sills or layered bodies, and ultimately cool and crystallize. Stalling is controlled principally by buoyancy contrasts between ascending magma and the surrounding…

Introduction Mafic describes silicate minerals and igneous rocks whose chemistry is dominated by magnesium and iron rather than silica. This ferromagnesian composition commonly yields darker-colored rocks and minerals. Typical mafic mineral assemblages include olivine, pyroxene, amphibole, and biotite, which together control the textures and physical behavior of mafic igneous rocks. Common rock types—basalt (volcanic), diabase/dolerite…

Introduction — The Lwandle plate The Lwandle plate is a recently recognized, predominantly oceanic microplate situated in the southwestern Indian Ocean between roughly 30°E and 50°E, immediately offshore of Africa’s southeast margin. It constitutes a distinct lithospheric block separate from the adjacent Nubian and Somali plates and also abuts the Antarctic Plate, so that its…

Introduction Longshore drift denotes the along‑shore transport of sediment within the surf and swash zones, driven by the nearshore flow commonly called the longshore current. It encompasses a broad suite of material — from clay and silt through sand to pebbles, shingle and shell — that is mobilized and redistributed parallel to the shoreline. The…

Introduction Global compilations that overlay volcanic locations on plate boundary maps demonstrate a pronounced spatial clustering of volcanism at plate margins. Tectonic processes at convergent, divergent and—less commonly—transform boundaries govern the generation and character of magmatism, so that most volcanic centers align with these structural zones rather than with continental interiors. At convergent margins, subduction…

Introduction The planet’s rigid outer shell is partitioned into a system of major tectonic plates—commonly rendered on global plate‑tectonic charts (for example, NASA’s Plate Tectonics map)—each representing a coherent segment of the lithosphere that moves as a mechanical unit. Individual plates are on the order of 100 km thick, a thickness defined by the rigid…

Plate boundary interactions are conventionally sorted into three principal types—convergent, divergent, and transform—each defined by the relative motions of adjacent lithospheric plates and by characteristic geomorphological and tectonic expressions. Convergent (compressional) boundaries encompass several distinct modes of plate collision and recycling: subduction of dense oceanic lithosphere beneath an overriding plate; continental‑continental collision producing extensive orogenic…

Introduction A rock formation is a distinct, often visually striking exposure of bedrock produced and revealed by geologic processes; in stratigraphy and petrology the term also denotes a formal, mappable rock unit or sedimentary stratum used to describe layered sequences. At the Earth’s surface such formations arise where differential breakdown and removal of material—by physical,…