Category: Geography

Introduction A submarine earthquake is a seismic rupture that initiates within the seafloor of a body of water—most commonly an ocean—and is the principal source of tsunamis. The energy released by such events is quantified by moment magnitude, while observed effects on people and built systems are described using intensity scales such as the Mercalli…

Introduction Subduction occurs at convergent plate boundaries where oceanic—and occasionally fragments of continental—lithosphere descends into the mantle, forming a tectonic interface (the subduction zone) and a surface arc–trench complex. The process is driven principally by a density contrast: cold, rigid oceanic lithosphere is denser than the underlying asthenosphere, so once down‑faulting begins the slab largely…

A strand plain is a broad, shore‑parallel sand belt directly attached to the mainland whose surface is dominated by well‑defined, parallel or semi‑parallel sand ridges separated by shallow swales. This ridge‑and‑swale morphology is characteristic of shoreface accretionary systems and records repeated episodes of lateral accretion, migration and episodic reworking by storms and normal wave climates….

Introduction Star formation is the process by which localized over-densities within molecular clouds of the interstellar medium collapse under gravity to produce new stars. Giant molecular clouds act as the principal reservoirs of the cold gas and dust from which collapse is initiated; the balance among cooling, turbulent motions, magnetic support and self-gravity determines whether…

The Sphinx water‑erosion hypothesis is a minority geological claim that reads the pattern of weathering on the Great Sphinx and its surrounding quarry walls as the product of prolonged precipitation and fluvial action, and from that inference argues for a Predynastic or otherwise much earlier construction date than conventionally accepted. Advocates such as John Anthony…

The South Sandwich plate (or Sandwich plate) is a small oceanic microplate located south of the South American plate in the Southern Ocean; the volcanic South Sandwich Islands are situated on this microplate. It is flanked by three larger plates: the South American plate to the east (which subducts beneath the microplate), the Antarctic plate…

Introduction The South Bismarck Plate is a small lithospheric block beneath the southern Bismarck Sea in the southwestern Pacific. It incorporates fragments of continental and island crust, most notably the eastern sector of New Guinea and the island of New Britain, which together constitute the plate’s principal surface expression. Tectonically active, the plate experiences frequent…

The South American plate encompasses the continent of South America and an extensive sector of the adjacent Atlantic seafloor, extending eastward to its divergent contact with the African plate and forming the southern segment of the Mid‑Atlantic Ridge. At its eastern margin this spreading boundary records continuous seafloor formation as the South American plate moves…

The Somali Plate is a minor tectonic plate in the Eastern Hemisphere whose domain straddles the Equator and comprises continental crust, rifted continental margins and adjoining oceanic seafloor along Africa’s eastern flank. Roughly centered on Madagascar, it includes portions of the western Indian Ocean and approximately half of Africa’s eastern coastline; its northern limit extends…

Solifluction denotes a class of slow, gravity-driven downslope movements of soil and loose surface material that are primarily set in motion by recurrent freeze–thaw activity. Repeated freezing and thawing alternately lift, sort and lubricate the uppermost, fine-grained horizon, producing incremental displacement of regolith on gentle to moderate slopes. This process yields a range of surface…

Introduction The Solar System is the gravitationally bound ensemble composed of the Sun and all bodies that orbit it. It formed roughly 4.6 billion years ago when a dense portion of a molecular cloud collapsed to produce the Sun and a surrounding protoplanetary disc from which planets, dwarf planets, moons and smaller bodies accreted. The…

Soil science systematically investigates soil as a critical near-surface natural resource, integrating the processes that create soils, their classification and spatial representation, and the physical, chemical, biological and fertility attributes that determine how soils can be used and managed. Central to the discipline are two complementary perspectives: pedology, which concentrates on pedogenesis, morphology, mineralogical and…

Introduction — Soil horizons A soil horizon is a recognisable, laterally extensive layer within a soil profile, arranged approximately parallel to the ground surface and distinguishable in a cross‑section by measurable differences in physical, chemical or biological properties from adjacent layers. The most commonly used field criteria for delimiting horizons are physical attributes—particularly colour and…

Pedogenesis denotes the suite of physical, chemical and biological processes that convert parent material into soil through interactions among local setting, environmental conditions, and temporal history. These biogeochemical mechanisms both construct and degrade internal order within the developing soil, producing anisotropy—systematic directional and spatial contrasts in properties—as constituents are translocated, transformed, accumulated, or lost over…

Introduction Soil erosion denotes the removal of the upper, nutrient-rich soil horizon by dynamic physical and biological processes, resulting in degradation of the medium that sustains plant growth and soil ecosystem functions. A range of agents produces distinct forms of erosion: flowing water, glaciers and snowmelt, wind (aeolian processes), biotic activity by animals and plants,…

Introduction Sociocultural evolution denotes a family of theoretical approaches in sociobiology and cultural evolution concerned with how societies and cultures transform through time. Beyond narratives of progressive complexity, the concept encompasses reductions in complexity (degeneration), branching diversification without net complexity change (cladogenesis), and qualitative reorganization of social structures. In essence, sociocultural evolution analyzes the processes…

Introduction Slow earthquakes (or silent earthquakes) are fault-slip events that release seismic energy over durations of hours to months, in contrast to ordinary earthquakes whose main energy discharge occurs in seconds to minutes. Initially recognized through long‑term strain measurements, many slow events are now known to produce measurable seismic signals—most notably tremor—when continuous seismometer records…

Introduction Skyquakes are atmospheric acoustic events characterized by sudden, loud noises perceived as originating overhead rather than from obvious terrestrial sources. Observers typically describe an abrupt, forceful sound—most often a sharp “bang” or a brassy, horn‑like blast—that stands out clearly from ambient noise. The acoustic energy of these events can couple into nearby buildings, producing…

Introduction A sinkhole is a natural topographic depression formed when surface material subsides or collapses into voids in the subsurface, and it often marks a direct connection between surface and underground systems. Various terms are used to emphasize different aspects of these features: doline or shakehole for enclosed depressions; ponor, swallow hole or swallet for…

Introduction The Shetland (South Shetland) plate is a small tectonic microplate located off the tip of the Antarctic Peninsula that encompasses the South Shetland Islands and constitutes a distinct crustal block within the Southern Ocean. Bordered on three sides by the Antarctic plate and on the fourth by the Scotia plate, it occupies a relatively…

Introduction Seismology is the branch of geophysics devoted to the study of earthquakes and the elastic waves they generate as they propagate through planetary interiors and across surfaces. The term derives from the Ancient Greek σεισμός (seismós, “earthquake”) combined with -λογία (-logía, “study of”) and is pronounced /saɪzˈmɒlədʒi/ or /saɪs-/. Its scope includes characterization of…

Seismic waves are transient elastic disturbances that transport vibrational energy through Earth and other planetary bodies, generated by abrupt mechanical events such as fault rupture, volcanic activity, magma migration, large landslides, and anthropogenic explosions. They are distinct from the continuous, low-amplitude background vibrations produced by natural and human activity and are characterized by measurable waveforms,…

Seismic velocity structure denotes the spatial distribution of seismic-wave speeds within the subsurface of Earth and other planetary bodies, providing a depth- and laterally varying description of how seismic energy propagates rather than a single bulk value. The principal observables in such profiles are compressional (P-) velocity, shear (S-) velocity, and bulk density; in the…

Introduction Seismic noise denotes the persistent ground vibrations recorded by seismometers that are generally generated at or near the Earth’s surface and are therefore strongly controlled by elastic surface-wave propagation. By convention the ambient field is partitioned by frequency: signals below about 1 Hz are usually labeled microseisms, while those above 1 Hz are called…

Seiche — Introduction A seiche (pronounced /seɪʃ/) is a standing oscillation that occurs in an enclosed or partially enclosed body of water—lakes, reservoirs, swimming pools, bays, harbours, caves and even semi‑enclosed seas—when reflections from basin limits sustain a resonant wave. The phenomenon requires at least partial bounding so that incident and reflected motions interact persistently…

Introduction to sedimentary rocks Sedimentary rocks originate at Earth’s surface through the accumulation, burial and lithification of particulate material derived either from the breakdown of older rocks or from the remains and products of organisms. Sedimentation encompasses any mechanism that leads particles or chemical precipitates to settle and become incorporated into the sedimentary record, whether…

Sedimentary basins are region-scale crustal depressions produced by long-term subsidence that generate accommodation space for accumulation of thick, three-dimensional packages of sedimentary rock. Infill occurs over millions to hundreds of millions of years, largely by gravity-driven transport of eroded material and marine deposition; progressive burial imposes increasing pressure that compacts and lithifies the deposits. Basins…

Introduction A sea is a large body of saline water; in general usage “the sea” refers to the world ocean—the contiguous body of seawater that covers the majority of Earth’s surface—while individual seas include open-ocean marginal seas (for example, the Mediterranean) and large, nearly landlocked basins. In coastal settings such as the Faroe Islands in…

The Scotia Plate is a small tectonic plate occupying the Scotia Sea at the southern margin of the South Atlantic. Its name derives from the steam yacht Scotia, used by the early 20th-century Scottish National Antarctic Expedition that produced the first bathymetric data for the region. Plate genesis is linked to late Eocene tectonics: the…

Sand dunes, whether on coasts or in deserts, are mobile aeolian landforms that serve both geomorphic and ecological functions. They act as dynamic reservoirs of wind-blown sand, provide habitat for specialized—and sometimes rare or endangered—plants and animals, and buffer adjacent shorelines by storing and releasing sediment, thereby reducing coastal erosion. Dune morphology and position strongly…

Introduction Shear or S waves are the transverse elastic body waves that carry information about the Earth’s internal shear response. Particle motion in an S wave is perpendicular to propagation and is restored by shear stresses, in contrast to compressional (P) waves whose motion is parallel to propagation and whose restoring force is volumetric compression….

Rubidium–strontium (Rb–Sr) dating is a radiometric chronometer that exploits the beta decay of 87Rb to 87Sr (half‑life 49.23 billion years) to determine rock and mineral ages. Strontium occurs naturally as four stable isotopes; 87Sr is unique among them because its abundance can increase in a closed system by in‑situ decay of 87Rb while the non‑radiogenic…

Introduction The rock cycle is a central conceptual framework for interpreting how the three principal rock types—igneous, sedimentary and metamorphic—transform into one another over geologic time. It frames these transformations as responses to disequilibrium: rocks are carried into new physical, chemical or biological environments by internal and external forces (for example, tectonic transport, burial, uplift,…

Rocks are naturally forming solid aggregates of minerals or mineraloids that compose Earth’s outer solid shell (the crust) and the greater part of the planet’s solid interior, aside from the liquid outer core and transient magma bodies within the asthenosphere. They are characterized and classified by their mineral constitution, chemical makeup, textures and by the…

The Pacific “Ring of Fire” (also Rim or Circum‑Pacific belt) is an arcuate, subduction‑dominated zone of volcanic and seismic activity that encircles much of the Pacific Ocean. Extending roughly 40,000 km and locally up to about 500 km wide, the belt hosts between 750 and 915 active or dormant volcanoes — roughly two‑thirds of the…