Fluvial Geomorphology, Weathering, and Sedimentary Processes

Comprehensive vocabulary flashcards covering the hydrologic cycle, fluvial processes, stream landforms, sediment classification, physical and chemical weathering, mass movement, and sedimentary rock genesis.

Hydrologic Cycle

The natural cycle that describes the continuous movement of water throughout the Earth system among atmospheric, surface, subsurface, and organic reservoirs.

Global Freshwater Proportion

Freshwater accounts for only $2.5\%$ of all water on Earth, with oceans comprising $96.5\%$ and saline groundwater and lakes comprising $1\%$.

Runoff

Water that flows downslope across the land surface due to gravity.

Sheetwash

A broad, thin sheet of unconfined water spreading across the ground surface during rain or runoff events.

Downcutting

The deepening of a channel through erosion as water cuts through exposed bedrock, aided by gravity.

Sheet Erosion

Erosional removal of surface material in thin layers by sheetwash, often creating little rock pedestals.

Rill Erosion

The development and expansion of very small, distinct incision channels carved into soil by concentrated surface runoff.

Gully Erosion

Advanced erosion where expanding water channels exacerbate into deep, wide ravines.

Drainage Network

An array of interconnecting stream channels whose specific geometric pattern (such as dendritic, trellis, radial, parallel, or rectangular) is controlled by regional geology and underlying structure.

Drainage Divide

A highland, mountain ridge, or topographic boundary that separates one drainage basin (watershed) from an adjacent basin.

Continental Divide

A major continental highland boundary that directs water flow into entirely different oceans or major seas on either side of a continent.

Permanent Stream

A stream that flows year-round because the elevation of the streambed lies below the local water table.

Ephemeral Stream (Dry Wash)

A stream channel that flows only temporarily after precipitation and remains dry most of the time because its bed lies above the water table.

Stream Discharge

The volume of water passing through a stream cross section over a given time interval, which increases as flow velocity increases.

Stream Stage

The elevation of the water surface of a river or stream above an established datum at a given location, measured in feet.

Turbulence (Stream Flow)

Chaotic, irregular fluid flow that occurs when flowing water encounters physical obstacles such as boulders, generating swirling eddies and whirlpools.

Scouring

A stream erosion process in which moving water lifts and carries away loose, unattached sedimentary particles.

Breaking and Lifting

A stream erosion mechanism where the physical pressure and force of flowing water separates and lifts intact blocks or chunks of rock from the streambed.

Dissolution (Stream Erosion)

The process by which flowing water chemically dissolves soluble rock and mineral matter directly into solution.

Abrasion

The mechanical wearing down and grinding of streambed rock surfaces caused by the sandblasting-like action of sediment transported by moving water.

Dissolved Load

The portion of a stream's sediment load consisting of ions carried completely in chemical solution.

Suspended Load

Tiny mineral and sediment grains that swirl and stay aloft within the water column without settling to the streambed.

Bed Load

Larger sedimentary clasts that slide, roll, or saltate along the floor of the channel.

Base Level

The lowest elevation to which a stream channel can downcut, where sea level serves as the ultimate base level and lakes or resistant rock layers act as local base levels.

Alluvium

General term for loose, detrital sediment deposited by a flowing stream or river.

Stream Bar

An accumulation of coarser alluvium (such as sand or gravel) deposited along the bed or margin of a stream where flow velocity diminishes.

Floodplain

A broad, low-gradient, flat area of land adjacent to a stream channel that is inundated when the stream overspills its banks during flooding.

Braided Stream

A channel pattern consisting of numerous dividing and reuniting shallow paths separated by temporary bars, forming when streams transport abundant sediment during high flow and deposit it as velocity slows.

Meandering Stream

A stream pattern characterized by wide, sweeping, sinuous curves that snake across a valley or floodplain.

Cut Bank

The steep, cliff-like outer edge of a meander loop subject to active erosion due to faster water velocities.

Point Bar

A wedge- or crescent-shaped deposit of sand and gravel formed on the inside curve of a meander where slower water velocity permits deposition.

Oxbow Lake

A curved, U-shaped body of water formed when a meander neck is breached by a cutoff and the abandoned meander loop is separated from the active channel.

Alluvial Fan

A fan- or cone-shaped accumulation of sediment deposited where a steep mountain torrent abruptly emerges from a narrow canyon onto a flat valley or plain.

Delta

A triangular or fan-shaped alluvial sediment body formed where a sediment-laden stream empties into standing water, such as an ocean or lake.

Mesocosm

An experimental outdoor system that approximates natural environmental conditions while permitting researchers to manipulate and control variables.

Emergence Rate

The percentage of fish eggs in an experimental or natural setting that successfully hatch and survive to reach the free-swimming fish life stage.

Effect Size (Emergence Study)

The statistical impact of an experimental treatment on fish emergence rate; positive values indicate an increase relative to the control, while negative values indicate a decrease.

Physical Weathering

The mechanical disintegration and breaking apart of solid rock into smaller pieces without altering its chemical composition.

Chemical Weathering

The chemical decomposition and transformation of minerals within rock into new minerals and dissolved ions through reactions with water and air.

Biological Weathering (Bioweathering)

The breakdown of rock and mineral substrates driven by organisms, operating through physical fracturing (e.g., root wedging) or chemical processes (e.g., acid secretions by fungi and bacteria).

Exfoliation

A physical weathering process in which broad, curved slabs or sheets of rock crack and spall off parallel to the surface due to pressure unloading and thermal expansion.

Frost Wedging

A physical weathering mechanism wherein liquid water seeps into joints, freezes, expands, and exerts outward tensile stress that splits rock apart.

Tafoni

Cavernous, pitted, or honeycomb-like weathering structures hollowed into rock surfaces through the coupled action of wind, moisture, and salt crystallization.

Dissolution (Chemical Weathering)

A chemical weathering reaction in which minerals dissociate completely in solution, such as calcite dissolving in carbonic acid ($H_2O + CO_2 \rightarrow H_2CO_3$).

Hydrolysis

A chemical decomposition reaction where the ions of water decompose silicate minerals into secondary clay minerals, such as albite decomposing into kaolinite: $2NaAlSi_3O_8 + 2H_2CO_3 + 9H_2O \rightarrow 2Na^+ + 2HCO_3^- + 4H_4SiO_4 + Al_2Si_2O_5(OH)_4$.

Differential Weathering

The phenomenon where adjacent rock layers weather at contrasting rates due to differences in mineral composition and physical durability, such as weak shale eroding faster than resistant sandstone.

Sediment

Loose, unconsolidated fragments of rocks or minerals produced by weathering processes and transportable by erosion.

Boulder

A detrital clast diameter size defined as more than $256\,mm$ ($10\,in$).

Cobble

A detrital clast diameter size defined as between $64\,mm$ ($2.5\,in$) and $256\,mm$ ($10\,in$).

Pebble

A detrital clast diameter size defined as between $2\,mm$ ($0.08\,in$) and $64\,mm$ ($2.5\,in$).

Sand

A sediment grain diameter size defined as between $\frac{1}{16}\,mm$ ($0.0025\,in$) and $2\,mm$ ($0.08\,in$).

Silt

A sediment grain diameter size defined as between $\frac{1}{256}\,mm$ ($0.00015\,in$) and $\frac{1}{16}\,mm$ ($0.0025\,in$).

Clay (Grain Size)

The finest sediment grain diameter category, defined as less than $\frac{1}{256}\,mm$ ($0.00015\,in$).

Mass Movement

The downslope transfer of rock, regolith, or soil under the direct pull of gravity, classified by material type, velocity, mass character, and environment.

Slumping

A mass wasting process where an intact block of regolith slips downslope along an underlying curved failure surface, leaving a distinct slump scar at the head.

Creep

The extremely slow, gradual downslope migration of surface soil and regolith.

Solifluction

The slow downslope flow of water-saturated soil over an impermeable substrate layer, such as permafrost.

Lahar

A specialized, fast-moving volcanic mudflow or debris flow of saturated volcanic ash, water, and rock fragments.

Clastic Sedimentary Rock

A sedimentary rock formed from mineral or rock fragments that have accumulated, compacted under overburden weight, and cemented together by precipitation of ions from groundwater.

Evaporite

A chemical sedimentary rock formed when standing water evaporates from a basin, supersaturating the brine and causing dissolved minerals (such as halite and gypsum) to precipitate.

Chert

A dense, hard biochemical or chemical sedimentary rock consisting of cryptocrystalline quartz.

Coal

An organic sedimentary rock formed through the compaction, dewatering, and carbon concentration of accumulated ancient plant material.