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;…
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Metal
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,…
Megathrust Earthquake
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
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…
Mariana Plate
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…
Maoke Plate
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…
Mantle Plume
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
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…
Magnetic Field
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…
Magmatism
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…
Magmatic Underplating
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…
Mafic
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…
Lwandle Plate
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…
Longshore Drift
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…
Lists Of Volcanoes
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…
List Of Tectonic Plates
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…
List Of Tectonic Plate Interactions
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…
List Of Rock Formations
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,…
List Of Natural Phenomena
Introduction Natural phenomena are observable events produced by Earth’s physical, chemical, and biological systems rather than by human action. They range from luminous atmospheric displays such as the aurora to commonplace cyclical events like sunrise, and are unified by their origin in natural processes and energy exchanges within the environment. These phenomena are conventionally organized…
List Of Geological Phenomena
Introduction Geological phenomena comprise the natural features and processes that geology seeks to explain: they record Earth’s material composition, the operative physical and chemical mechanisms, temporal evolution, and the resulting landforms. These phenomena arise from internal Earth dynamics, surface agents, or their interactions, and are therefore central to reconstructing past environments and assessing present-day hazards….
Limestone Pavement
Introduction Limestone pavements are a distinctive karst morphology in which an exposed, flat limestone surface is incised into a regular, block‑like pattern that resembles man‑made paving. The pattern arises where chemical weathering preferentially dissolves carbonate rock along pre‑existing joints and fractures, producing an orthogonal or sub‑orthogonal network of slabs (clints) separated by deeper fissures (grikes)….
Lava
Lava is the molten or partially molten rock expelled from a planet or satellite interior onto the surface—via volcanic vents or crustal fractures—and may be emplaced subaerially or submarine. Typical eruptive temperatures lie between about 800 and 1,200 °C (1,470–2,190 °F); this thermal range governs lava rheology, crystallization kinetics and the development of volcanic landforms….
Lava Dome
Introduction A lava dome is a roughly circular, mound‑shaped volcanic landform produced by the slow extrusion of highly viscous lava that, because of limited lateral mobility, accumulates over the vent to form a prominent protrusion. Dome‑building eruptions are most common where magmas are chemically evolved—notably at convergent plate margins—and account for roughly 6% of volcanic…
Laurasia
Introduction — Laurasia Laurasia was the northern continental mass of the late Paleozoic–Mesozoic supercontinent Pangaea, occupying the northern hemisphere portion of the united landmass from the assembly of Pangaea (approximately 335 Mya) until the early stages of its breakup (around 175 Mya). The name reflects its constituent cratons—principally Laurentia and the Eurasian plate—whose amalgamation produced…
Laramide Orogeny
Introduction The Laramide orogeny was a principal mountain‑building episode across western North America that initiated in the Late Cretaceous (roughly 80–70 Ma) and waned during the early Paleogene (somewhere between ~55 and 35 Ma); precise onset, termination and cumulative duration remain debated and the deformation occurred in episodic pulses separated by relative quiescence rather than…
Landforms#Coastal And Oceanic Landforms
Introduction A landform is a discrete morphological feature of the solid surface of a planetary body—on Earth or elsewhere—formed or modified by natural processes and, in some cases, by human activity. Together, landforms make up the physical fabric of a terrain, whose pattern of elevation, slope and relief is captured by the concept of topography….
Kuroshio Current
Introduction The Kuroshio Current (Japanese: 黒潮, “Black Tide”; also Japan or Black Current, 日本海流) is a warm, northward western-boundary current on the western flank of the North Pacific, named for its deep blue waters. As the Pacific analogue of the North Atlantic’s Gulf Stream, it carries tropical heat poleward as the western limb of the…
Jura Mountains
Introduction The Jura Mountains (IPA: /ˈdʒʊərə, ˈʒʊərə/; anglicized JOOR‑ə, ZHOOR‑ə) are a sub‑alpine chain lying immediately north of the Western Alps. They form a conspicuous physiographic element that largely traces a long segment of the French–Swiss boundary and provides a continuous upland link from the Alpine foreland into northern Switzerland and southwestern Germany. Geomorphologically the…
Isostasy
Introduction Isostasy denotes the gravitational equilibrium in which Earth’s crust or lithosphere “floats” on the denser, deformable mantle or asthenosphere, producing and maintaining variations in surface elevation through buoyancy. The elevation of a crustal block is determined quantitatively by its thickness and density: relatively thick or low-density crust attains greater buoyant heights, whereas thin or…
Ionosphere
Introduction The ionosphere is the ionized region of Earth’s upper atmosphere, occupying a vertical extent roughly from 48 km to 965 km above mean sea level; it includes the thermosphere and overlaps the upper mesosphere below and the lower exosphere above. Solar extreme ultraviolet and X‑ray radiation ionize neutral constituents, producing populations of free electrons…
Intraplate Earthquake
Introduction Intraplate earthquakes are seismic events that originate within the interior of a tectonic plate rather than along plate boundaries. Although less frequent than interplate earthquakes, they may concentrate on pre‑existing zones of mechanical weakness far from active margins. Because regions distant from plate boundaries are often not engineered or retrofitted for seismic loading, intraplate…
Intraplate Deformation
The topography of central East Asia is dominated by an elevated region comprising the Tibetan Plateau and adjacent ranges such as the Tien Shan; this broad swath of high relief reflects extensive crustal shortening and uplift across the continental interior rather than isolated orogenic fronts. The pervasive nature of these landforms indicates that the mechanical…
Interplate Earthquake
Introduction Interplate earthquakes originate at the contacts between tectonic plates, where accumulated stress is released as relative displacement across faults and radiated as seismic waves through the Earth. These boundary events account for the vast majority of global seismic energy release—over 90 percent—and include the largest known earthquakes, particularly those that occur on subduction interfaces…
Internal Structure Of Earth
Introduction Earth’s interior (excluding atmosphere and hydrosphere) is organized in concentric shells: a silicate crust and overlying lithosphere, a mechanically weaker asthenosphere, the solid mantle, a convecting liquid outer core whose motion sustains the geomagnetic field, and a solid inner core. This stratification is routinely represented in geological cross‑sections and underpins models of heat and…
Inland Sea
An inland sea (also called an epeiric or epicontinental sea) is a shallow, continental-scale body of marine water that occupies broad interior basins or epicontinental platforms and differs fundamentally from ordinary lakes by its partial marine character and large areal extent. Such seas may be entirely surrounded by land or retain one or more hydrological…