GEOG 2051 Exam 2 Namikas - LSU

Weathering

The breakdown of Earth materials into smaller components.

Angular Debris

The sharp-edged rock fragments covering hillslopes, created by weathering processes attacking underlying bedrock.

Physical Weathering

The mechanical breakdown of Earth materials through physical forces like pushing, pulling, prying, and cracking without altering chemical composition.

Chemical Weathering

The decomposition of rocks and minerals through chemical reactions that alter them into new substances or break them into component materials.

Weathering Sequence (3 Stages)

Bedrock (Parent Material) -> Regolith (broken rock fragments) -> Soil (regolith mixed with organic matter and organisms).

Parent Material

The original underlying bedrock whose characteristics (like hardness and jointing) directly affect weathering rates.

Jointing

Cracks or fractures in a rock that increase surface area, allowing weathering processes to act more rapidly.

Mineral Hardness Weathering Rule

Harder minerals (e.g., Diamond) resist weathering efficiently, while softer minerals (e.g., Talc, Gypsum) weather quickly.

Moisture Climate Effect

Dry climates result in slow weathering; wet climates result in rapid weathering.

Temperature Climate Effect

Warm climates cause chemical weathering to dominate; cold climates cause physical weathering to dominate.

Hydrology Weathering Effect

Areas where water ponds/remains experience rapid weathering; areas where water runs off quickly weather much slower.

Northern Hemisphere Slope Aspect

South-facing slopes receive more sunlight (warmer/drier); North-facing slopes are cooler and retain snow longer.

Orographic Precipitation Weathering Effect

Heavy rain/weathering occurs on the windward side of a mountain (moist rising air); dry conditions/slow weathering occur on the leeward side (rain shadow).

Vegetation (Enhancing Weathering)

Plant roots physically crack rocks (root wedging), and decaying organic matter/lichens release acids that chemically dissolve rock.

Vegetation (Reducing Weathering)

Dense plant canopies intercept rainfall before it hits the ground, limiting water exposure and slowing weathering rates.

Frost Action (Freeze-Thaw)

Physical weathering where water enters rock cracks, expands by ~10% upon freezing, and exerts pressure that widens the fractures.

Crystallization

Physical weathering where salt water evaporates inside rock pores, leaving behind growing crystals that exert force and break the rock apart.

Root Wedging

Physical weathering where plant roots grow into existing rock fractures, expanding and prying the rock apart over time.

Exfoliation (Pressure Release/Spalling)

Physical weathering where deeply formed intrusive igneous rocks expand, crack, and peel off in sheets like an onion after overlying weight is eroded.

Oxidation

Chemical weathering where metallic minerals react with oxygen and water to form weaker oxides (e.g., iron rusting), making rock easy to break.

Hydrolysis

Chemical weathering crucial to granite where feldspar chemically reacts with water and transforms into a much weaker clay mineral.

Carbonation

Chemical weathering where carbon dioxide dissolves in rainwater to form weak carbonic acid, which dissolves limestone (calcium carbonate).

Historic Carbonation Targets

Famous limestone/marble structures highly susceptible to carbonation and acid rain damage (e.g., Notre-Dame, Parthenon, Pyramids of Giza).

Karst Topography

A unique surface and underground landscape formed globally on limestone bedrock primarily through the chemical weathering process of carbonation.

Solution Sinkhole

A round surface depression formed by water collecting in a low spot and gradually dissolving the limestone bedrock from above.

Collapse Sinkhole

A round surface depression formed suddenly when the roof of an underground limestone cave collapses into an empty void.

Disappearing Stream

A surface river that flows along the ground and suddenly plunges underground through a sinkhole or karst opening.

Karst Valley

A dry, riverless valley formed in karst landscapes when multiple individual sinkholes expand and merge together.

Cave/Cavern Formation

Formed underground via erosion when a high water table allows acidic groundwater to dissolve hollow spaces out of limestone.

Dripstone (Speleothems)

Cave formations created via deposition when water evaporates and leaves behind mineral deposits (calcium carbonate).

Stalactite

A dripstone formation that hangs tightly from the Ceiling of a cave (T for Top).

Stalagmite

A dripstone formation that grows upward from the cave Ground (G for Ground).

Column

A vertical cave structure formed when a stalactite growing down and a stalagmite growing up meet and merge.

Soda Straw

A thin, hollow, elongated stalactite that structurally resembles a drinking straw hanging from a cave ceiling.

Drip Curtain

A long, wavy, vertical sheet of rock formed when water drips along a continuous crack in a cave ceiling.

Slope System

A dynamic, inclined landform boundary with material inputs (upper weathering) and material outputs (downslope mass movements).

Angle of Repose

The steepest maximum angle that loose granular material can maintain naturally without collapsing.

Slope Driving Force vs. Resisting Force

If driving forces (gravity/weight) exceed resisting forces (friction/cohesion), slope failure occurs; if resisting forces are greater, it remains stable.

Gravity Components on Slopes

Divided into a parallel driving force (pulls material downhill) and a perpendicular resisting force (holds material to the slope).

Slope Angle Effect

Gentle slopes feature higher perpendicular resisting forces (stable); steep slopes feature higher parallel driving forces (unstable).

Friction Factors (Slope)

Rough, angular particles provide high friction (stable); smooth, rounded particles provide low friction (unstable).

Cohesion

Any binding force causing soil/rock particles to stick together (e.g., roots, moisture, organic matter, retaining walls), increasing slope stability.

Lubrication & Buoyancy

Water mechanisms that destabilize slopes by reducing particle friction and reducing effective sediment weight.

Waxing Slope

The topmost convex portion of a slope where steepness increases; serves as the main zone of weathering.

Free Face

The steepest, near-vertical cliff portion of a slope; acts as a bare zone of transport where debris cannot accumulate.

Waning Slope (Debris Slope)

The lowermost concave portion of a slope; acts as the zone of deposition where material builds toward the angle of repose.

Mass Movement

The downslope transfer of rock, soil, or debris as a single mass driven primarily by gravity, classified by speed and moisture.

Mass Movement Speed Ranking

Fastest to slowest: Falls -> Avalanches -> Flows -> Slides -> Creep.

Fall

The fastest, driest type of mass movement where rock or debris completely loses contact with the slope and drops through the air.

Avalanche

An extremely fast mass movement where material bounces and rolls down a slope, losing small amounts of energy to friction.

Flow

A fluid-like mass movement (Earthflow, Mudflow, Debris Flow) that requires large amounts of water to saturate fine or coarse sediment.

Slide (Landslide)

A mass movement where material shifts downslope as a single, large, cohesive, intact block along a distinct failure plane.

Soil Creep

The slowest form of mass movement (mm/year), caused by freeze-thaw cycles that heave soil particles up perpendicularly and drop them vertically via gravity.

Fluvial

A scientific term referring to anything related to, produced by, or found in a river or stream.

Hydrologic Cycle Water Balance

Land receives excess precipitation compared to evaporation; oceans lose excess water via evaporation. Rivers return the excess land water back to oceans.

Drainage Basin (Watershed)

The total land area that catches precipitation and supplies runoff water and sediment to a specific river system.

Drainage Divide

A line of elevated topography (e.g., mountain ridge) that separates neighboring drainage basins from one another.

Major U.S. Drainage Regions

Pacific Drainage (west of Continental Divide), Gulf Drainage (central U.S.), and Atlantic Drainage (east of Appalachian Divide).

Dendritic Drainage Pattern

The most common, branch-like, energy-efficient river network; indicates uniform rock types and irregular topography.

Parallel Drainage Pattern

A river network where channels run parallel in the same direction; indicates a highly consistent, uniform regional slope.

Radial Drainage Pattern

A network where streams flow outward in all directions from a high central point; indicates a volcano, isolated mountain peak, or geologic dome.

Trellis Drainage Pattern

A network where main streams run parallel in valleys and smaller

Stream Capture (Piracy)

A process where a stream erodes backward through a ridge, breaching a boundary and stealing the water of a neighboring basin stream.

Deranged Drainage Pattern

A chaotic, disorganized river network with random channels and marshy hollows; indicates a landscape heavily disrupted by historical glacial activity.

Stream Discharge (Q)

The total volume of water flowing past a given point in a river channel per unit of time, calculated as Q = Width x Depth x Velocity.

Perennial Stream

A stream or river channel that experiences continuous, reliable water flow year-round (e.g., Mississippi River).

Intermittent Stream

A seasonal stream channel that flows during wet periods or snowmelt seasons but goes completely dry during part of the year.

Ephemeral Stream

A desert or arid channel that remains dry for long periods, flowing briefly only after rare, intense localized precipitation events.

Downstream Discharge Trends

As a typical river moves downstream, width, depth, velocity, and total discharge all increase due to accumulating tributaries.

Exotic Stream

A rare river whose discharge decreases downstream because of heavy evaporation or human diversion while crossing a desert (e.g., Nile, Colorado).

Dissolved Load (Solution Transport)

Chemical ions dissolved completely within river water and transported downstream (accounts for ~40% of the Mississippi River's load).

Suspended Load (Suspension)

Fine particles like clay, silt, and fine sand held aloft in the moving water column by turbulent flow without settling.

Bed Load

Large, coarse sediments (gravel, pebbles, boulders) that move along the bottom of a stream channel.

Traction vs. Saltation

Bed load transport types: Traction involves rolling/sliding along the bed; Saltation involves moving in short hops and bounces.

Stream Competence

The largest individual particle size a river can physically move, controlled completely by the river's velocity.

Stream Capacity

The maximum total volume of sediment a river can physically carry, controlled completely by the river's discharge.

Braided River

A multi-channel river network that splits and rejoins around sediment bars; indicates a massive sediment supply and highly variable discharge.

Meandering River

A single, highly sweeping river channel that snakes back and forth across a flat floodplain, driven by continuous outer erosion and inner deposition.

Cut Bank

The steep outside loop of a river meander where water velocity is highest, resulting in active erosion.

Point Bar

The gently sloping inside loop of a river meander where water velocity drops, resulting in sediment deposition.

Oxbow Lake

A crescent-shaped lake formed when a tightening meandering river cuts a straight path through a narrow neck, abandoning the old loop.

Meander Scar

A dry, marshy, low-lying depression left behind on a floodplain after an oxbow lake fills completely with sediment.

Longitudinal Profile

A side-view graph plotting a river's elevation vs. distance from headwaters to mouth, showing available potential and kinetic energy.

Graded Stream

A river in a state of dynamic equilibrium where the sediment input into the system perfectly matches the river's transport capacity.

Aggradation vs. Downcutting

Base level drop or land uplift causes a river to erode downward (downcutting); base level rise (sea level rise) causes sediment to pile up (aggradation).

Stream Rejuvenation

A process where tectonic uplift increases a river's gradient and energy, forcing it to downcut rapidly and carve deep canyons or entrenched meanders.

Nickpoint

An abrupt irregularity or steep drop-off in a river's longitudinal profile, typically visible as a waterfall or rapids.

Waterfall Migration

The upstream movement of a waterfall over time due to continuous erosion of the resistant rock layer at a nickpoint.

Recurrence Interval

A statistical tool calculating the average time gap between flood events of a specific magnitude based on historic annual peak discharge records.

Flood Hydrograph

A graph displaying river discharge over time following a rainfall event, illustrating peak discharge and lag time.

Hydrograph Lag Time

The time delay between peak rainfall and peak river discharge as runoff travels across a drainage basin.

Urbanization Hydrograph Effect

Impermeable surfaces (concrete, roofs) cause a dramatically shorter lag time and a much higher, faster, more destructive peak flood discharge.