Geology: Surface Water Systems, Earthquakes, and Geologic Time

Vocabulary practice flashcards covering surface water dynamics, fluvial geomorphology, Great Lakes glacial evolution, seismology, earthquake hazards, stratigraphic principles, and geochronology.

Drainage Basin

An area of land (also known as a catchment or watershed) where all surface runoff and groundwater drains through a network of tributaries into a common trunk stream.

Drainage Divide

A topographic high ridge or elevated boundary that separates adjacent drainage basins, dictating the direction water flows into separate river systems.

Dendritic Drainage Network

A branching, tree-like river drainage pattern that typically forms on uniform, homogeneous substrates with gentle regional slopes.

Radial Drainage Network

A stream pattern in which tributaries flow outward in all directions away from a central elevated structure, typically developing on isolated volcanic cones or domes.

Rectangular Drainage Network

A drainage pattern characterized by numerous right-angle bends developed along intersecting sets of geological joints or faults.

Permanent River

A river whose channel floor lies at or below the local water table, receiving regular groundwater baseflow and flowing year-round in humid, temperate settings.

Ephemeral River

A river whose bed is situated entirely above the regional water table, only conveying surface runoff during or directly following intense precipitation events in dry or high-evaporation regions.

Cut Bank

The steep, cliff-like outer bank of a meandering stream where high water velocity causes maximum active erosion.

Point Bar

A low, crescent-shaped deposit of river sediment (alluvium) formed on the inside bend of a meander where the stream velocity slows down.

Oxbow Lake

A curved lake created when a meander neck is breached via avulsion during a flood, isolating the former channel loop from the main river.

Braided River

A stream consisting of an intricate web of interwoven, dividing, and rejoining channels separated by temporary sand and gravel bars, common where sediment load is exceptionally high.

Stream Discharge

The total volume of water passing through a stream cross-section per unit time ($\text{ft}^3/\text{s}$ or $\text{m}^3/\text{s}$), determined by multiplying cross-sectional area by average flow velocity ($A_c \times V$).

Saltation

A process of bedload sediment transport where sand and gravel grains skip and bounce along the river bottom, colliding with and dislodging other clasts.

Longitudinal Profile

A cross-sectional graphic depicting the decrease in stream elevation and gradient from its steep headwaters downstream to base level at its mouth.

Slot Canyon

A very narrow, deep canyon with near-vertical walls formed by rapid stream downcutting through resistant bedrock governed by vertical rock joints.

Nickpoint

A sharp change in stream channel gradient, such as a waterfall lip, which migrates upstream over time as soft underlying strata are undercut and collapse.

Finger Lakes

A cluster of elongate, deeply carved glacial troughs in Upstate New York, comprising lakes such as Seneca Lake ($632\,\text{ft}$ deep) and Cayuga Lake ($435\,\text{ft}$ deep).

Isostatic Rebound

The gradual uplift of the continental crust in response to the removal of heavy glacial ice sheets, which altered outlet spillways and maintained high lake levels ($605\,\text{ft}$) in the Great Lakes between $4{,}000$ and $6{,}000$ years ago.

Hypocenter (Focus)

The specific subterranean location on a fault plane where slip initiates and earthquake energy is initially released.

Epicenter

The geographic point on the surface of the Earth positioned directly above an earthquake's hypocenter (focus).

Fault Scarp

A steep surface step or cliff generated when dip-slip displacement along a fault plane breaks and offsets the ground surface.

Strike-Slip Fault

A near-vertical fault along which adjacent blocks displace horizontally past one another parallel to the strike direction due to lateral shear stress.

Stick-Slip Behavior

The recurring earthquake cycle in which friction locks a fault and builds elastic strain ("stick") until the friction is overcome, generating sudden rupture and displacement ("slip").

Primary (P) Wave

The fastest compressional body wave that displaces rock particles back and forth parallel to the direction of wave propagation, capable of traveling through solids, liquids, and gases.

Secondary (S) Wave

A shear body wave that shakes material perpendicular to the path of wave propagation; it travels more slowly than a P-wave and propagates exclusively through solid media.

Love (L) Wave

A surface seismic wave that causes horizontal, side-to-side shearing of the ground surface perpendicular to the direction of propagation.

Rayleigh (R) Wave

A surface seismic wave that causes ground particles to trace an elliptical rolling trajectory in a vertical plane, resulting in rolling surface undulations.

Seismogram

The physical or digital tracing made by a seismograph that records the arrival sequence of seismic energy: P-waves first, S-waves second, and surface waves last.

S-P Travel-Time Interval

The time delay between the arrival of the P-wave and the subsequent S-wave, which increases systematically with distance from the earthquake source.

Modified Mercalli Intensity Scale

A qualitative assessment scale (I through XII) based on eyewitness accounts, the severity of ground shaking, and observed structural damage.

Richter Magnitude Scale

A logarithmic measurement scale derived from the maximum recorded wave amplitude on a standard seismograph corrected for distance to calculate released energy.

Wadati-Benioff Zone

A planar dipping zone of earthquake foci extending from shallow depths to down to $670\,\text{km}$, tracing the trajectory of a cold, brittle oceanic plate descending into the mantle.

Pancaking

A mode of structural earthquake failure in which vertical support columns crush, causing multi-level building floors to collapse flat on top of one another.

Liquefaction

The transformation of loosely packed, water-saturated sand or mud into a fluid-like slurry caused by an increase in pore pressure during strong seismic shaking.

Tsunami

A giant sea wave or series of surges produced by abrupt vertical movement of the seafloor (e.g., along subduction thrusts), disturbing the entire ocean water column and traveling at hundreds of kilometers per hour.

Principle of Uniformitarianism

The foundational geological principle introduced by James Hutton asserting that natural physical laws and processes observed today operated identically in the past ("the present is the key to the past").

Principle of Original Horizontality

The geological rule stating that sediment layers are originally deposited in nearly flat, horizontal sheets; any folding or tilting must have taken place subsequent to deposition.

Principle of Superposition

The stratigraphic principle establishing that within an undeformed sedimentary sequence, the oldest layers reside at the bottom and progressively younger layers are deposited above.

Principle of Cross-Cutting Relations

The rule of relative dating stating that any geologic feature (such as an igneous dike, pluton, or fault) that interrupts or truncates other rocks is younger than the rock bodies it cuts.

Principle of Inclusions

The relative dating concept stating that any fragment of rock (clast or xenolith) enclosed inside another rock mass must be older than the surrounding host rock matrix.

Principle of Baked Contacts

The principle stating that an invading molten igneous body thermally metamorphoses (bakes) the pre-existing rock around it, demonstrating that the intrusion is younger than the adjacent rock.

Index Fossil

A fossil belonging to an organism that had an extensive geographic distribution but survived over a brief, distinct duration of geologic time, used to correlate and date strata.

Angular Unconformity

A surface of erosion or non-deposition that separates tilted or folded older sedimentary strata below from younger, flat-lying sedimentary beds above.

Nonconformity

An unconformity where layered sedimentary strata are deposited directly on an eroded surface of crystalline plutonic igneous or metamorphic basement rocks.

Disconformity

An erosional contact separating parallel layers of sedimentary rock, representing missing geologic time without structural tilting, often detected through fossil gaps.

Geologic Time Scale

A chronological calendar dividing the $4.57\,\text{billion-year}$ history of the Earth into Eons, Eras, Periods, and Epochs based on stratigraphy, mass extinctions, and radioactive decay.

Phanerozoic Eon

The eon representing "visible life" from $542\,\text{Ma}$ to the present, subdivided into the Paleozoic, Mesozoic, and Cenozoic Eras.

Cambrian Explosion

The rapid evolutionary diversification event roughly $542\,\text{Ma}$ at the start of the Paleozoic Era when diverse multicellular marine organisms with hard shells and skeletons first emerged.

Half-Life ($t_{1/2}$)

The precise length of time required for half of the unstable radioactive parent atoms in a mineral sample to decay into stable daughter products.

Zircon Dating

A radiometric dating method applied to durable zircon crystals that dated Earth's oldest known continental crustal materials to $4.1$ to $4.2\,\text{Ga}$, helping estimate the total age of the Earth at $4.57\,\text{billion years}$.