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.
Mineralogic phenomena
Mineralogic phenomena concern where and how minerals form, their crystal structures and chemistries, and the environmental conditions that govern their stability. Observations of mineral assemblages, primary versus secondary growth, textural habits and mineral reactions driven by pressure–temperature–fluid changes inform petrogenesis and can identify concentrations of economic value (ore deposits) that preserve the physicochemical history of formation.
Lithologic phenomena
Lithologic phenomena describe the origin, transformation and classification of rock types. Igneous rocks record processes of magma generation, ascent and solidification (including fractional crystallization, assimilation and cooling-rate effects on texture); sedimentary rocks document transport, deposition and diagenesis of clastic and chemical sediments (with transient phenomena such as liquefaction and quicksand where saturated grains lose strength); and metamorphic rocks arise from recrystallization under elevated temperature, pressure and fluid activity that reequilibrates mineralogy and texture.
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Endogenic phenomena
Endogenic processes are driven by Earth’s internal heat and mantle dynamics. Plate tectonics—the horizontal motion of lithospheric plates propelled by mantle convection—produces continental drift, seismicity through fault slip, and subduction-related trenches; these processes generate major topography, concentrate volcanism, and structure the architecture of continents and oceans.
Magmatism and surface expression
Magmatic activity links deep processes to surface phenomena: hydrothermal circulation above magmatic bodies produces hot springs and geysers; gradual inflation and deflation of magmatic or hydrothermal reservoirs causes bradyseism; and volcanic eruptions, controlled by magma composition, volatiles and conduit dynamics, construct volcanic landforms and create acute hazards.
Geomagnetism
Earth’s magnetic field, generated by convective motion in the electrically conducting outer core (the geodynamo), varies on multiple timescales. Secular variation and geomagnetic reversals are recorded in rocks as paleomagnetic signatures, which serve as key constraints on seafloor spreading rates, the timing of oceanic crust formation, and past continental latitudes.
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Exogenic phenomena
Surface (exogenic) processes are powered by external energies—solar radiation, gravity, atmosphere, hydrosphere and cryosphere—and include mass movements (landslides, slumps) governed by slope stability, material strength and pore-water pressures, as well as weathering and erosion, whereby physical, chemical and biological agents break down rock and transport sediment to reshape landscapes.
Glacial and periglacial phenomena
Ice-driven processes reshape terrain through glacial erosion and deposition: ice flow carves valleys, forms moraines and leaves features such as hanging valleys where tributary glaciers erode less deeply than main trunks. Periglacial processes in cold climates, including freeze–thaw and frost-driven sediment transfer, further modify slopes and sediment budgets.
Impact and coupled interactions
Extraterrestrial impacts produce craters, shock metamorphism and ejecta that locally reorganize crustal structure. Many landscape features reflect coupled endogenic–exogenic interactions: orogeny combines tectonic convergence, crustal thickening and surface denudation to build mountains, while drainage reorganization (e.g., stream capture) results from the interplay of uplift, erosion and base-level change to reconfigure fluvial networks.