Category: Geography

The Capricorn plate is a hypothesised minor tectonic entity beneath the Indian Ocean basin (southern–eastern hemispheres) whose formal recognition remains unresolved. It is interpreted as a relatively coherent block of oceanic lithosphere occupying the far western margin of the erstwhile Indo‑Australian plate; in this view Capricorn behaves in many respects like a discrete plate distinct…

Introduction — Burma Plate The Burma plate is a minor tectonic block in Southeast Asia, variably treated as an independent microplate or, for some tectonic syntheses, as part of the broader Eurasian plate. It carries the Andaman and Nicobar islands and northwestern Sumatra, which together form the Andaman–Nicobar–Sumatra island arc that separates the Andaman Sea…

Buoyancy (pronounced /ˈbɔɪənsi, ˈbuːjənsi/), or upthrust, is the net upward force that a fluid exerts on an immersed body or fluid parcel. It originates from the increase of hydrostatic pressure with depth: pressure acting over the submerged surface produces a larger resultant force on the bottom than on the top, yielding an upward resultant. Quantitatively,…

Introduction Consider a plane ruled into parallel strips of uniform width (t). A needle of length (l) is dropped at random; the event of interest is whether the needle intersects one of the parallel bounding lines (illustratively, one needle may straddle a line while another may lie entirely within a strip). Posed by Georges‑Louis Leclerc,…

Introduction A boundary layer is the thin region of fluid immediately adjacent to a solid surface in which the presence of the surface modifies the flow relative to the undisturbed free stream. Within this layer viscous interactions with the boundary alter momentum and, where relevant, scalar properties such as temperature or concentration; beyond the layer…

Introduction — Borders of the Oceans The World or Global Ocean is a single, continuous envelope of saline water surrounding Earth; for practical, navigational and political purposes it is conventionally divided on maps into principal oceanic areas. Most geographers and international bodies recognize five such divisions—Pacific, Atlantic, Indian, Southern (commonly termed Antarctic), and Arctic—whose relative…

Introduction A blowhole, sometimes called a marine geyser, is a coastal landform in which seawater is expelled through a surface opening that links to an underlying sea cave. They form as wave erosion enlarges caves and progressively extends them upward and inland until one or more vertical conduits connect the cave chamber to the surface,…

A blind thrust earthquake arises from slip on a low‑angle reverse (thrust) fault that does not rupture the ground surface; the seismogenic plane is buried, so no surface fault trace is evident. Because the causative structure lacks a visible expression at the surface, blind thrusts typically escape standard geological mapping and remain undetected until subsurface…

The Blasius boundary layer is the canonical steady, two‑dimensional laminar solution describing the viscous shear region that develops along a semi‑infinite flat plate placed parallel to a uniform free stream. Under the assumptions of steady flow, two‑dimensionality, incompressibility, laminar viscosity and a constant external velocity U aligned with the plate, a thin layer adjacent to…

The Bird’s Head plate is a minor but distinct lithospheric block that underlies the Bird’s Head Peninsula at the western end of New Guinea, and forms part of a complex mosaic of plates in eastern Indonesia. Its kinematics remain debated: some authors (e.g., Hillis and Müller) interpret the Bird’s Head as moving coherently with the…

Introduction Bioerosion denotes the biological breakdown of hard substrates—predominantly in marine settings but also on land—by organisms that bore, drill, rasp, scrape or otherwise remove material from coastlines, reefs, vessels and other rigid surfaces. At the microscale this process can be framed as cell‑driven surface degradation: activity of colonizing cells alters or removes surface layers…

Introduction The Big Bang theory is the prevailing physical framework describing the universe’s evolution from an initial state of extreme density and temperature to the present expanding cosmos. It accounts quantitatively for several key observables: the primordial abundances of light elements, the cosmic microwave background (CMB) and its anisotropies, and the emergence of large-scale structure…

Introduction A beach is a coastal or inland littoral landform composed of loose particulate material—derived from rock (sand, gravel, pebbles, shingle) and biological detritus (shells, coralline fragments)—whose grain size, shape, color and stratification record the provenance and transport history of the sediment. The distribution and internal organization of these particles reflect ongoing sedimentary processes: local…

Beach nourishment — Introduction Beach nourishment, also known as renourishment or sand replenishment, is a coastal engineering practice in which sediment—most commonly sand—is placed on eroding shorelines to replace material lost to wave action and alongshore transport. The added sediment is typically sourced from offshore, riverine, or inland deposits and distributed along the foreshore and…

Beach evolution encompasses the continuous interplay of processes that reshape shorelines of seas, lakes and rivers through both loss and gain of sediment. Mechanical breakdown by moving water—waves in marine and lacustrine environments and flow in rivers—wears away bedrock and coarser deposits, creating the sand- and silt-sized particles that constitute much beach material. Fluvial transport…

The Baltic Shield (Fennoscandian Shield) is a major segment of the East European Craton that underlies much of Fennoscandia, northwestern Russia and the northern Baltic Sea, where ancient continental basement rocks are commonly exposed at the surface. Its crust is largely composed of Archean and Proterozoic gneisses and greenstone belts, containing some of Europe’s oldest…

The Azores triple junction, centered at ~39.44°N, 29.83°W, occupies a segment of the Mid-Atlantic Ridge (MAR) west of the Strait of Gibraltar within the Azores archipelago. It marks the mutual boundary of the North American, Eurasian and African (Nubian) plates and is formed where the broadly north–south MAR is intersected by the east–southeast–trending Terceira Rift….

Introduction The Australian plate is a major tectonic plate that comprises not only the continental crust of Australia (including Tasmania) but also adjacent continental fragments and extensive areas of oceanic lithosphere. Its geographic reach extends into parts of New Guinea and New Zealand and across significant tracts of the Indian Ocean basin, so its tectonic…

Introduction An atmosphere is the gravity-bound envelope of gases surrounding an astronomical body; the word derives from the Ancient Greek ἀτμός (atmós, “vapour, steam”) and σφαῖρα (sphaîra, “sphere”). The principal inventory of an atmosphere is established during a body’s primordial epoch, either by direct accretion of nebular material or by outgassing of volatile species from…

The atmosphere is a gravity-bound, mixed envelope of gases and suspended particles that envelops Earth. Its aerosols and particulates give rise to clouds and hazes and create the thin, blue limb visible from orbit above the tropospheric cloud tops. Viewed in clear space imagery, this atmospheric limb contrasts with celestial bodies such as the crescent…

Imagery acquired by the Expedition 29 crew aboard the International Space Station traces a ground track beginning just northeast of Newfoundland, crossing the North Atlantic and continuing southward across the basin into central Africa over South Sudan, illustrating the ocean’s longitudinal extent and north–south orientation. The Atlantic is the planet’s second-largest oceanic division, covering about…

Introduction The Arabian Plate is a relatively small lithospheric plate located in the Northern and Eastern Hemispheres that functions as a discrete structural unit within the global plate-tectonic framework. Over geological time it has moved broadly toward the north, a trajectory it shares with other continental masses such as the African and Indian plates; this…

Introduction — Antarctic Plate The Antarctic Plate is a major tectonic unit encompassing the Antarctic continental landmass, the Kerguelen Plateau, numerous remote Southern Ocean islands, and extensive adjacent oceanic crust. With an area of roughly 60.9 million km², it is the fifth-largest tectonic plate on Earth. Its geological evolution is rooted in the breakup of…

Introduction — Anatolian sub‑plate The Anatolian plate is a continental tectonic plate that underlies most of the Asian portion of Turkey (Anatolia) and constitutes the principal crustal element of the Anatolian Peninsula (Asia Minor). Its northern margin is defined by a major transform boundary with the Eurasian plate along the North Anatolian Fault zone (NAFZ),…

Introduction The Amur (Amurian) Plate is a minor tectonic unit within the northeastern Asian plate mosaic, occupying parts of northeastern China and the Russian Far East. Its name derives from the Amur River, which demarcates a major geopolitical frontier between those two regions and signals the plate’s geographic position at the junction of East Asian…

Amateur geology, commonly practiced as rock collecting, comprises the non‑professional pursuit of locating, extracting and curating rock, mineral and fossil specimens by individuals who are not engaged in formal geological careers. Known regionally as “rockhounding” in North America and “fossicking” in Australia, New Zealand and parts of the UK (notably Cornwall), the activity occurs wherever…

The Alpide belt—often called the Alpine–Himalayan orogenic belt and, less commonly, the Tethyan orogenic belt—is a continuous seismic and mountain‑building system that traces more than 15,000 km along Eurasia’s southern margin, connecting Southeast Asia to the Atlantic. It extends from the islands of Java and Sumatra, across Indochina and the Himalayas, through the mountains of…

Introduction The current consensus age for Earth is 4.54 ± 0.05 billion years (Ga), a chronology that marks the late stages of planetary accretion and the transition to internal differentiation. This estimate is the product of multiple, independent constraints: high-precision radiometric ages of meteoritic material, concordant ages from the oldest terrestrial minerals and lunar samples,…

Introduction Aftershocks are smaller earthquakes that occur in the same region after a larger mainshock, produced as the crust adjusts to the altered stress field generated by the principal rupture. They are an integral element of the fault-system’s post-rupture relaxation and are readily recorded by modern seismometer networks. Large mainshocks commonly give rise to hundreds…

Introduction The African plate, often referred to in tectonic literature as the Nubian plate, is the principal lithospheric plate beneath most of the African continent (excluding its easternmost sector) and includes adjoining oceanic crust to the west and south as well as a narrow continental extension along the eastern Mediterranean coast into parts of Western…

Introduction The Aegean Sea plate (also termed the Hellenic or Aegean plate) is a relatively small lithospheric block beneath southern Greece and western Turkey that forms a discrete tectonic element within the eastern Mediterranean. Its southern margin is defined by the Hellenic subduction zone south of Crete, where the African Plate descends beneath the Aegean…

Introduction An active volcano is a volcanic edifice that is currently erupting or retains the capacity to erupt in the future; in practice volcanologists commonly restrict the label to edifices with confirmed eruptions during the Holocene (the past ~11,700 years). Volcanoes that are not erupting at present are classified on a spectrum from dormant—able to…

Introduction Abyssal plains are extensive, near‑planar regions of the deep seafloor, typically found between about 3,000 and 6,000 m depth. Collectively they make up a majority of the oceanic floor—covering more than half of the Earth’s surface—and rank among the planet’s flattest and least explored geomorphic domains. Physically they occupy the broad basins between continental…

Introduction The tabulated estimates present the mass concentration of each chemical element in Earth’s crust, expressed in milligrams per kilogram (mg/kg), which is numerically identical to parts per million (ppm) by mass. Because 10,000 ppm equals 1% by mass, for example, 100 ppm corresponds to 0.01% of the crust. Reporting abundances in mg/kg (ppm) allows…

Abrasion — Introduction Abrasion is a mechanical weathering process in which moving particles wear down a surface by repeated frictional contact, producing scratches, scuffs, polished surfaces and general removal of material. It is especially pronounced where moving ice interacts with bedrock, but occurs wherever transported solid matter repeatedly rubs against a substrate. Four principal settings…