Geology Review Q3

MOUNTAIN BUILDING, GEOLOGIC TIME, STREAMS & FLOODS

Recurrence Interval

Statistic probability of flood exceeding certain size (R=(n+1)/m)

Flood Zone (Floodplain)

Flat area of land next to a river, erodes w/ river meanders

Surface Runoff/Overland Flow

Water cannot penetrate soil, rolls over surface and may collect contaminants

Subsurface Flow

Movement of water under Earth’s surface through rocks, soil, or sand

Incised Meanders

Stream valley development: carved into bedrock channels vertically, topographic uplift

Stream Terraces

Stream valley development: step-like landforms above streams/floodplains, strath/fill varieties

Headward Erosion

Stream valley development: uphill growth of valley through mass wasting, sheetwash, gullying

Lateral Erosion

Stream valley development: widening of stream valley from erosion, meandering, mass wasting

Graded Stream

Stream valley development: smooth, concave upward profile, shows balance w/ sediment deposition/transport

Knickpoint

Stream valley development: sharp break in profile (waterfall), imbalance in sediment load bearing, migrates upstream

Downcutting

Stream valley development: deepening valley by erosion of stream bed, may make walls collapse to form V-shaped valley

Base Level

Stream valley development: Theoretical limit for erosion, elevation of mouth of stream to sea level/global base level

Alluvial Fans

Stream deposition: sediment deposited where steep mountain stream emerges into flat plain, multiple = ‘bajada’, found near river avulsions

Delta

Stream deposition: Body of sediment deposited at mouth of river when river velocity decreases

Wave-dominated (delta)

Morphology: Delta containing barrier islands on ocean side (Nile Delta)

Tide-dominated (delta)

Morphology: Delta containing tidal bars parallel to tidal current (Ganges River Delta)

Stream-dominated/Birdfoot (delta)

Morphology: Delta contains larges amount of sediment deposited into quiet water, creates new channels (avulsions) (Mississippi River Delta)

Distributary

Morphology: river that flows away from channels to divide sediment deposition

Levee (natural)

Sediment deposited adjacent to channel, erodes and accumulates w/ flooding on floodplains

Cutoff

Process of new meanders from migrating streams over time, creates oxbow lakes as a result

Cut Bank

Erosion of the outer edge of a meandering stream

Point Bar

Deposition along inner bend of a meandering stream

Meandering Stream

Stream deposition: sinuously flowing streams, fine-grained sediment, well-defined channels, tilted water surface

Braided Stream

Stream deposition: Flows around a series of bars and rivulets, coarse-grained, load exceeds capacity

Bar

Stream deposition: ridge of sand or gravel deposited in the middle or along the banks of a stream

Sediment Load

Amount of sediment transported in a stream

Bed (Load)

Sediment load: heavy particles that travel along streambed, traction/saltation (boulders/rocks)

Suspended (Load)

Sediment load: light enough to be carried in stream forever (clay/silt, loess)

Dissolved (Load)

Sediment load: Soluble products of chemical weathering (calcite)

Hydraulic Action

Stream erosion: ability of water to pick up and move sediment

Solution

Stream erosion: dissolution of rock in water (slow)

Abrasion

Stream erosion: grinding away of stream channel by friction

Losing Stream

Water is lost from stream to groundwater, discharge/velocity decreases downstream

Gaining Stream

Water is gained from groundwater to stream, discharge/velocity increase downstream

Discharge

Volume of water flow over a given period of time over a given point, calculated Q=Area*Depth*Velocity

Gradient/Channel Slope

Overall slope of stream from headwater to mouth, affects velocity

Channel Roughness

Obstructions to flow caused by rocks, debris, humans…, affects velocity

Maximum Velocity

Region with the highest velocity, occurs at thalweg, does the most work

Thalweg

Deepest part of stream where maximum velocity occurs, displaced on outer bend in meandering stream

Flow Velocity

Distance water travels in a stream unit per unit time, creates energy

Settling (Velocity)

Velocity: grains settle out after being transported

Erosional (Velocity)

Velocity: unmoved particle begins moving

Decreasing Stream Characteristics

From headwater to mouth: discharge and channel roughness tendency

Increasing Stream Characteristics

From headwater to mouth: flow velocity, channel size, and discharge tendency

Dendritic (Drainage)

Drainage: branching pattern of streams, intricate w/ tributaries, drains into single body of water

Radial (Drainage)

Drainage: streams flow outwards from central elevated point in all directions

Rectangular (Drainage)

Drainage: streams flow in right-angled bends w/ sharp turns, common among fault lines

Trellis (Drainage)

Drainage: parallel to main tributaries w/ small, sharp turns, grid-like pattern

Drainage Basin

Stream anatomy: total area that stream and related tributaries drain into, defined by topography

Drainage Divide

Stream anatomy: separates drainage basins, usually high ridges

Longitudinal Profile

Stream anatomy: graphical representation of stream elevation along length, tends toward a smooth equilibrium

Hydrologic Cycle/Water Cycle

Continuous movement of water along Earth’s surfaces (Evaporation, Condensation, Precipitation)

Half-life

Time required for ½ of total radioactive substance to decay (N=Noe^(-Yt))

Radioactive Isotope

Isotope w/ unstable nucleus that undergoes radioactive decay (spontaneous change)

Radioactive Decay

Spontaneous change underwent by radioactive isotopes

Fossils

Remnants/traces of buried and preserved ancient organisms after lithification (body/trace)under anoxic conditions

Faunal Succession

Fossils: succession under fossil species through layers in a predictable order

Stratigraphic Correlation

Determination of time equivalency of rock units regionally, continentally, globally

Unconformity

Surfaces that represent a gap in geologic record

Disconformity

Unconformity: separates beds parallel to one another, usually erosion of older rocks

Angular Unconformity

Unconformity: younger strata on erosional surface on folded layer rock

Nonconformity

Unconformity: erosional surface on metamorphic rock covered by younger rock

Principle of Inclusion

Relative dating: fragments included in host rock are older than host rock

Cross-cutting Relationship

Relative dating: disrupted pattern is older than cause of disruption (fault lines are younger than affected sediment)

Lateral Continuity

Stratigraphic principle: sediment layer extends laterally until tapers at edge

Superposition

Stratigraphic principle: oldest sediment is at the bottom and youngest at the top

Original Horizontality

Stratigraphic principle: beds of sediment in water are formed as horizontal layers

Eons

Phanerozoic, Precambrian

Cenozoic Era

Geologic time: Quaternary, Tertiary (Neogene/Paleogene)

Mesozoic Era

Geologic time: Cretaceous, Jurassic, Triassic

Paleozoic Era

Geologic time: Permian, Pennsylvanian, Mississippian, Devonian, Silurian, Ordovician, Cambrian, Precambrian

Uniformitarianism

Idea that geologic processes today are the same processes as in the past

Catastrophism

Idea that Earth was formed through short, sudden events (volcanism, meteors)