Physical Geology: Caves and Karst, Earthquakes, Geologic Time, Groundwater, Mass Wasting, Rock Structures, Streams, and Fossils

Comprehensive vocabulary flashcards covering the core principles of karst systems, earthquakes, geologic dating, groundwater hydrology, mass wasting, structural geology, fluvial processes, and paleontology.

Karst

A landscape system of above- and below-ground features produced by the chemical dissolution of soluble bedrock (such as limestone) by acidic groundwater.

Sinking Stream

A surface water stream that flows across the land surface for some distance and then disappears underground into a subterranean drainage or cave system.

Sinkhole

A funnel- or bowl-shaped circular depression on the land surface resulting from the subsurface dissolution or mechanical collapse of underlying soluble bedrock or sediment.

Cover-Collapse Sinkhole

A sinkhole that forms abruptly when a subsurface void migrates upward through progressive roof spalling in cohesive sediment (such as clay), causing a sudden collapse of the overlying land surface.

Speleothem

A secondary mineral deposit formed in a cave via the chemical action and evaporation or degassing of mineral-laden water, typically composed of calcite.

Stalagmite

A mound- or cone-shaped speleothem that grows upward from a cave floor as calcite precipitates from mineral-laden water dripping from the ceiling above.

Gypsum Flower

A speleothem characterized by branching, curved crystal petals of the mineral gypsum that grow outward from cave ceilings and walls.

Lava Tube Cave

A non-karst cave formed when the outer crust of an active basaltic lava flow hardens while the interior molten lava drains out, leaving behind a hollow conduit.

Earthquake

The rapid vibration of Earth produced by the abrupt release of accumulated elastic strain energy along a fault plane.

Earthquake Focus (Hypocenter)

The exact subsurface location along a fault plane where seismic rupture initiates and radiates energy outward in all directions.

Epicenter

The geographic point on Earth's surface positioned vertically above the earthquake focus.

Primary Wave (P-Wave)

A compressional body wave exhibiting alternating expansion and contraction; it travels approximately $1.7$ times faster than S-waves and can propagate through both solids and liquids.

Secondary Wave (S-Wave)

A transverse shear body wave that vibrates material perpendicular to its direction of propagation and can travel only through solids.

Rayleigh Wave

A destructive surface wave that causes rock and soil particles to roll in an elliptical, ocean-wave-like retrograde motion.

Modified Mercalli Intensity Scale

A qualitative seismic scale denoted by Roman numerals from I to XII that categorizes earthquake strength based on observed structural damage and human perceptions.

Liquefaction

A secondary seismic hazard wherein unconsolidated, water-saturated ground temporarily loses its shear strength due to intense cyclic shaking and behaves as a viscous fluid.

Seiche

The rhythmic sloshing of water back and forth within an enclosed or partially enclosed water body, such as a lake or reservoir, often generated by seismic waves.

Catastrophism

The historic philosophy pioneered by Archbishop James Ussher suggesting that Earth is only a few thousand years old and was shaped primarily by sudden, worldwide violent catastrophes.

Uniformitarianism

The foundational geological principle developed by James Hutton and Charles Lyell stating that 'the present is the key to the past,' meaning modern geologic processes explain ancient Earth history.

Rule of Superposition

The relative dating law stating that within an undeformed sequence of sedimentary rocks, the oldest strata reside at the base and the youngest strata reside at the top.

Rule of Inclusions

The relative dating principle stating that any rock unit containing xenoliths, clasts, or mineral inclusions must be younger than the fragments enclosed within it.

Principle of Cross-Cutting Relationships

The relative dating principle asserting that any geological feature (such as an igneous dike, joint, or fault) cutting across another rock body must be younger than the unit it transects.

Half-Life

The constant duration required for half of the unstable parent radioisotopes in a sample to decay into stable daughter products ($t = \frac{0.693}{\lambda}$).

Water Table

The subsurface boundary line separating the upper, aerated unsaturated zone from the underlying completely saturated zone.

Porosity

The percentage of total rock or sediment volume occupied by voids or open spaces.

Permeability

A measure of the capacity of a porous rock or sediment to transmit fluids through its interconnected void spaces.

Gaining Stream

A surface stream whose channel bed intersects the regional water table, allowing groundwater to discharge into and sustain the stream's baseflow.

Confined Aquifer

A permeable, saturated geological formation bounded both above and below by relatively impermeable aquitards or aquicludes.

Hydraulic Head

A measure of fluid mechanical energy per unit weight that determines groundwater flow from areas of high potential to low potential, based on water table elevation and pressure.

Cone of Depression

A localized, downward-pointing conical depression in the water table produced around an extraction well due to rapid groundwater pumping.

Mass Wasting

The downslope movement of soil, regolith, or bedrock driven directly by gravity without the continuous transport of water, ice, or wind.

Angle of Repose

The maximum slope angle at which loose, unconsolidated sediment remains mechanically stable without sliding downward ($35^\circ$ for fine sand, $40^\circ$ for coarse sand, and $45^\circ$ for angular pebbles).

Rockfall

The most rapid form of mass wasting, in which rock masses detach from a steep slope or cliff face and free-fall, bound, and roll to the base.

Slump

A rotational slide where coherent blocks of rock or soil move slowly downslope along a distinct, curved, concave-upward rupture surface.

Debris Flow

A rapid, fluid-like mass wasting event consisting of a turbulent, water-saturated slurry in which more than half of the particles are sand-sized or coarser.

Creep

An extremely slow, continuous downslope movement of soil and weathered rock mantle, recognized by tilted trees, leaning utility poles, and displaced fence lines.

Stress

The force applied per unit area acting across a given surface within a solid rock body ($\sigma = \frac{F}{A}$).

Strain

The measure of physical deformation, distortion, or change in size and shape experienced by a rock body in response to applied stress.

Normal Fault

A dip-slip fault caused by tensional extension where the hanging wall block slides downward relative to the footwall block.

Reverse Fault

A dip-slip fault caused by compressional stress where the hanging wall block moves upward relative to the footwall block (classified as a thrust fault if the dip angle is less than $45^\circ$).

Strike and Dip

Geological measurements describing planar rock orientation: strike is the compass direction of a horizontal line on an inclined bed, and dip is the maximum angle of tilt measured downward from the horizontal plane.

Anticline

An up-arched fold in layered strata where the fold limbs dip away from the axial plane, exposing the oldest rocks in the center core.

Syncline

A trough-shaped down-fold in layered rock where the fold limbs dip inward toward the axial plane, exposing the youngest rocks in the center core.

Stream Gradient

The slope of a stream channel expressed as the vertical elevation drop over a specified horizontal distance ($\text{m/km}$).

Stream Discharge

The total volume of water passing through a stream's cross-section per unit of time, calculated as channel cross-sectional area multiplied by average flow velocity ($Q = A \times v$).

Base Level

The lowest downward elevation limit to which a stream can erode its channel, with the ultimate base level being sea level.

Pothole (Stream)

A circular or cylindrical depression ground into bedrock along a stream channel by the rotational swirling action of sand and pebbles trapped in turbulent eddies.

Suspended Load

The portion of a stream's sediment load composed of fine clay and silt particles kept aloft in the water column by turbulent upward currents.

Competence

A measure of the maximum individual particle diameter or clast size that a stream is physically capable of transporting, governed primarily by flow velocity.

Delta

A triangular or fan-shaped depositional landform created where a river debouches into a standing body of water and decelerates, depositing its sediment load.

Fossil

The preserved remains, mineralized hard parts, organic traces, or impressions of past biological organisms preserved in the crust of the Earth.

Lagerstätte

A sedimentary deposit exhibiting extraordinary fossil preservation, frequently conserving soft tissues, complete articulated specimens, or delicate structures.

Permineralization

A mode of fossil preservation where mineral-rich groundwater infiltrates original porous skeletal cavities or cell lumens (such as petrified wood) and precipitates inorganic minerals.

Coprolite

A trace fossil consisting of lithified or petrified animal excrement, useful for reconstructing ancient diets and paleoecological food webs.

Index Fossil

A geographically widespread and readily identifiable fossil organism that existed during a restricted geologic time interval, utilized to correlate and date rock strata.

Ichnology

The branch of paleontology dedicated to the analysis and interpretation of biogenic trace fossils, including trackways, burrows, and feeding impressions.