Category: Geography

Introduction — Depth of focus (tectonics) Focal depth, or depth of focus, denotes the vertical distance beneath Earth’s surface where seismic rupture begins. Earthquakes are commonly classified by focal depth: shallow-focus events occur <70 km (43 mi), intermediate‑depth events between 70 and 300 km (43–190 mi), and deep‑focus events from 300 to 700 km (190–430…

Introduction — Deposition (geology) Deposition is the process by which loose sediment, soil and rock fragments are laid down and accumulated to form layered deposits that alter surface topography and produce landforms such as beaches, barriers, deltas and floodplains. Material reaches depositional sites after being mobilized by agents including running water, waves, wind, ice and…

Introduction Denudation comprises the suite of surface processes that progressively lower and smooth the Earth’s crust through the action of agents such as flowing water, glaciers, wind, and waves. Conceptually it is broader than erosion: erosion denotes the transport of particulate material, while denudation refers to the aggregate of processes—including weathering, mass wasting and erosion—that…

Introduction — Deep-focus earthquakes Deep-focus earthquakes, also termed plutonic earthquakes, are seismic ruptures whose hypocenters occur at depths greater than 300 km. They are almost exclusively associated with convergent plate margins and the descent of oceanic lithosphere into the mantle; spatially they cluster within the dipping, tabular Wadati–Benioff zones that trace the inclined path of…

Introduction The Dead Sea Transform (DST) is a principal continental transform fault, extending roughly 1,000 km from the Marash triple junction in southeastern Turkey to the northern reach of the Red Sea Rift off Sinai. It marks the plate boundary between the African Plate to the west and the Arabian Plate to the east and…

The geographic cycle, or cycle of erosion, is an idealized temporal framework that interprets the evolution of landform relief as a sequence of uplift and denudational responses rather than as a universal physical law. It frames landscape change in terms of stages through which topography adjusts to shifts in relative elevation and energy gradients. The…

Introduction A craton is the long-lived, tectonically stable portion of the continental lithosphere that commonly forms the structural core of continents. The word derives from the Ancient Greek kratos, “strength,” and is pronounced variously (e.g., /ˈkreɪtɒn/, /ˈkrætɒn/, /ˈkreɪtən/), reflecting its role as a resilient continental nucleus. Cratons consist of ancient crystalline basement rocks capped by…

Convergent plate boundaries are zones where lithospheric plates approach and collide, often forcing one plate to descend beneath the other. This subduction produces a planar band of earthquake foci that marks the downgoing slab and is commonly referred to as the Wadati–Benioff zone. The motions that drive these collisions are ultimately sustained by mantle convection:…

Introduction Convection denotes spontaneous bulk motion of a fluid (single‑ or multiphase) driven by spatial heterogeneity in material properties acted upon by body forces. In most geophysical and engineering contexts the relevant heterogeneity is a density contrast produced by thermal expansion and the principal body force is gravity (buoyancy), so that “thermal convection” serves as…

A convection zone (or convective region) is a stellar layer in which large-scale mass motions carry a significant fraction of the energy flux, in contrast to radiative (or conductive) zones where photon transport dominates. In many stars, notably the Sun and red giants, convective regions reach the surface and give rise to the observed granulation…

Introduction — Convection (heat transfer) Convection, or convective heat transfer, denotes the transport of thermal energy by the bulk motion of a fluid: temperature-bearing fluid parcels move and redistribute heat spatially. This process inherently combines molecular diffusion (conduction), which smooths temperature differences at small scales, with advection, the large-scale conveyance of heat by the fluid’s…

Introduction The continuum hypothesis (CH) is a foundational statement in set theory that concerns the possible sizes of infinite sets, specifically comparing the countable infinity of the integers with the cardinality of the real numbers (the continuum). Informally, CH asserts that no set has cardinality strictly between that of the integers and that of the…

Introduction — Continental margin A continental margin is the submerged perimeter of a continent where relatively thick continental crust abuts thinner oceanic crust, forming the principal transition between terrestrial and deep-ocean domains. Morphologically and functionally it is organized into a shelf–slope–rise system: a shallow, gently sloping continental shelf that extends the landmass seaward; the steeper…

Continental drift is the concept that the positions of Earth’s continents have changed relative to one another through geological time; modern geology subsumes this idea within plate tectonics, which explains continental motion as the transport of continental crust on rigid lithospheric plates. Although now well supported by diverse lines of evidence, the notion that landmasses…

A continent is a conventionally delineated large terrestrial region rather than a unit governed by a single universal criterion; it may be an extensive continuous landmass, a portion of a larger landmass (as Europe and Asia are parts of Eurasia), or a landmass together with adjacent islands lying on the same continental shelf. The number…

Introduction — Complex volcano A complex volcano (also called a compound volcano or volcanic complex) is a single, genetically related volcanic system composed of multiple, spatially associated eruptive centers and their attendant lava flows and pyroclastic deposits, rather than a simple single-vent edifice. The stratigraphy of such complexes commonly alternates effusive lava units and extensive…

Introduction The Cocos Plate is a relatively young oceanic tectonic plate located beneath the eastern Pacific Ocean off the west coast of Central America. It takes its name from Cocos Island, the plate’s sole emergent feature, which is administered by Costa Rica and lies roughly 550 km southwest of the Costa Rican mainland (≈342 mi;…

Introduction Coastal sediment supply is the delivery of mineral and organic material to the shore, principally by rivers (fluvial transport) and, to a lesser extent, by wind (aeolian transport). Fluvial sources provide the vast majority of sediment delivered to the ocean—on the order of 95%—while aeolian fluxes, though much smaller in volume, play a critical…

Coastal morphodynamics — Introduction Coastal morphodynamics examines how seabed geometry and sediment distributions evolve through interaction with fluid forcings — principally waves, tides and wind‑driven currents — to create and modify coastal landforms and sedimentary patterns. Hydrodynamic forcing adjusts essentially instantaneously to changes in bed form, whereas morphological adjustment requires sediment transport over finite timescales;…

Introduction Coastal management encompasses both engineered constructions and regulatory measures aimed at protecting shorelines from flooding and halting or reversing erosion, including projects that reclaim land from the sea. Iconic infrastructure such as the Netherlands’ Oosterscheldekering sea wall illustrates how large-scale engineering is used to shield low-lying territories from storm surge and inundation. Its importance…

Introduction to Coastal Geography Coastal geography examines the dynamic interface between ocean and land as an interdisciplinary field in which marine and terrestrial systems continuously interact and reshape one another. Its physical-geography remit encompasses coastal geomorphology (the origin, evolution and form of coastal landforms), climatology (the role of weather and climate in driving coastal processes…

Introduction Coastal erosion denotes the removal or displacement of land and sediment along shorelines by dynamic agents such as waves, currents, tides, wind‑driven water and ice, and episodic storm impacts. The consequence is a measurable, landward migration of the coastal boundary that can be observed on timescales from individual tides and seasons to longer cyclical…

Introduction Coastal engineering is the branch of civil engineering concerned with the planning, design, construction and maintenance of infrastructure located at or adjacent to shorelines, together with the management of coastal change itself. Practitioners analyse the principal hydrodynamic agents—waves, tides, storm surges and tsunamis—which govern sediment transport, impose structural loads and can produce rapid geomorphic…

Introduction — Coastal development hazards Coastal development hazards arise when human activity concentrates people, infrastructure and economic value in zones that are shaped by inherently dynamic coastal processes. By placing assets on the shoreline, development increases both the potential losses (vulnerability) and the practical probability that naturally occurring coastal phenomena will produce socially significant damage….

Introduction The Coastal and Estuarine Research Federation (CERF) is a U.S.-incorporated, private nonprofit established in 1971 to unite scientists and practitioners concerned with estuarine and coastal systems. Originating from an initiative by members of two regional societies—the Atlantic Estuarine Research Society and the New England Estuarine Research Society—CERF was created to fill a gap for…

Coal has been central to India’s energy system since the late 18th century; commercial coal mining began in 1774 and by FY 2024–25 India produced 1,047 million metric tons, making it the world’s second-largest producer and consumer after China. Domestic output supplies the majority of national demand, but India still imports roughly 15% of its…

India’s climate is exceptionally varied owing to its large latitudinal extent, complex topography and tectonic history; although the Tropic of Cancer bisects the country, much of India functions climatologically as tropical and the Köppen classification records multiple climatic subtypes across the territory. The uplift of the Himalayan chain beginning in the Early Eocene (≈52 Ma)…

Introduction Clastic sedimentary rocks are lithologies in which the dominant constituents are fragments—clasts—derived from pre-existing minerals and rocks by mechanical weathering. A clast denotes any detached piece of geological detritus, from sand-sized grains to larger rock fragments, and the adjective clastic applies both to the lithified rocks and to the unconsolidated particles involved in transport…

Introduction — Cinder cone A cinder cone, or scoria cone, is a small, steep-sided volcanic hill formed by the accumulation of loose pyroclastic fragments around a single vent. These cones result from relatively explosive, gas-rich eruptions that fragment ascending lava into ash, lapilli and scoria; the fragments cool in flight and fall back ballistically to…

Proposed in 1905 by Thomas C. Chamberlin and Forest R. Moulton as an alternative to the nineteenth‑century Laplacian nebular model, the Chamberlin–Moulton hypothesis sought to explain Solar System formation through a tidal interaction between the young Sun and a passing star. In the original formulation a close stellar encounter produced tidal bulges on the solar…

Introduction — Chaman Fault The Chaman Fault is a major active continental fault system exceeding 850 km in length that forms the primary structural boundary between the Eurasian and Indo‑Australian plates across Pakistan and Afghanistan. Its dominant movement is left‑lateral strike‑slip, with the western block shifting southward relative to the east, but the ongoing India–Eurasia…

Introduction The Cascadia subduction zone is a major convergent plate margin extending roughly 1,000 km along the Pacific coast of North America, lying about 100–200 km offshore from northern Vancouver Island, British Columbia, to northern California (representative coordinate ~45°N, 124°W). Along this margin the small oceanic plates—Explorer, Juan de Fuca, and Gorda, remnants of the…

Introduction The Caroline Plate is a minor oceanic tectonic plate in the eastern hemisphere that straddles the Equator and occupies the oceanic region immediately north of New Guinea. Its southern margin forms a plate‑consuming subduction zone with the Bird’s Head Plate and other small plates of the New Guinea region, producing a convergent boundary that…

The Caribbean Plate is a chiefly oceanic tectonic plate occupying approximately 3.2 million km2 (1.2 million mi2) of lithosphere beneath the Caribbean Sea and parts of Central America, lying north of the South American continental margin. As a major structural element of the region’s crust, it forms the foundation for an array of island arcs…

Introduction — Carbon dioxide in Earth’s atmosphere Continuous atmospheric CO2 measurements initiated at Mauna Loa Observatory in 1958, commonly presented as the Keeling Curve, record mole‑fraction in micromoles per mole (ppm) and show an uninterrupted rise from 1958 through 2023. On a molar basis CO2 reached about 427 ppm (0.0427%) by 2024, equivalent to roughly…