Earth systems

quick clay

primarily found in glaciated regions of the northern hemisphere.

• Freshwater clay

• Marine clay

• many years later the marine structure remains, but salts are gone.

freshwater clay

no support, so the structure is compact.

marine clay

has a “house of cards” structure held together by precipitated salts in the pore space.

surface runoff

After precipitation, water is absorbed by vegetation or can become ____ _____

• overland flow (unchanneled, unorganized)

• stream flow (channeled, organized).

splash erosion

The collision of raindrops with the ground is strong enough to blast fine soil particles upward and outward.

sheet erosion

water flows across the surface as a thin sheet, transporting material already loosened by splash erosion.

Rill erosion

as overland flow gains in turbulence, sheet flow gets separated into tiny channels, or rills, this concentrated flow picks up more material and grooves the slope.

gully erosion

coalesces into fewer, larger channels called gullies, and then they get incorporated into the drainage systems of a valley and change to streamflow.

volume and velocity

Once surface flow is channeled, the ability to erode and transport material increases with _____ __ ______ of water

rates and effectiveness

Erosion ____ ____ _____ vary by speed, turbulence of streamflow, and resistance of bedrock.

direct hydraulic power

Erosion by ____ ____ ____ of moving water along bottom and sides of the channel.

abrasive debris

Erosion can be increased by ______ ______ transported in streamflow, contributes to further fragmenting by collision.

chemical weathering

Some ____ _____ also helps erode the channel through corrosion.

valley

a portion of terrain where drainage system is clearly established, including both valley bottom to a rim at the top.

interfluve

the higher land above the valley walls that separates adjacent valleys.

drainage basin

The _____ ______ of a stream is all the area that contributes to overland flow, streamflow, and groundwater

• It consists of the valley bottom, sides, and interfluves draining into valley.

• It ends at a drainage divide, which is the line of separation between runoff that descends in the direction of one drainage basin and runoff that descends toward an adjacent basin.

stream orders

describes the arrangement and organization of streams within a watershed.

• First-order streams are the smallest with no tributaries, join to form second-order streams, which join to form third-order streams

channel cross section

streamflow is confined to channels, which gives it a 3D nature.

• friction on bottom and sides slows flow, while center moves fast.

• deep and smooth channels exhibit laminar flow in parallel paths.

turbulence

downstream flow is interrupted by irregularities in direction and speed

Reasons for turbulence

• Friction

• Internal shearing stresses between currents within the flow

• Surface irregularities in the channel

• Stream speed

turbulence creates

• results in eddies, whirlpools, and whitewater rapids

• a great deal of frictional stress

stream channel patterns

• Straight

• Sinuous

• Meandering

• Braided

Straight channels

short and uncommon.

• From where streams are confined by topography or follow geologic structures.

  • Generally, mountain streams.

• deepest parts of the channel, called the thalweg, usually wanders back and forth across the channel.

• Deposits are likely opposite the place where the thalweg approaches one bank.

ex. Colorado river, Grand Canyon

sinuous channels

are more common than straight channels and have winding curvatures that are gentle and irregular.

• even a stream with a steep slope will likely be sinuous

• low gradients have more sinuosity and begin to meander.

Colorado river, Canyonlands

meandering channels

exhibit intricate pattern of smooth curves.

• streams follow serpentine course, twisting and turning back on itself.

• occurs when the land is flat and the gradient is low.

• meandering shift location continuously through erosion on outside of curves and deposition on inside of curves.

Little Missouri River, Theodore Roosevelt National Park.

braided channels

consists of multiple interwoven channels separated by low bars or islands of sand, gravel, or other loose debris.

• when very flat stream channel has heavy sediment load

• Generally near mountain fronts

• Also, in regions with prominent dry season with low stream discharge

Denali National Park, AL

Geologic topographic factor

The most important in shaping stream development:

• Consequent stream

• Subsequent streams

• antecedent stream

• superimposed stream

Consequent stream

follow the initial slope of the land

subsequent streams

exploit zones of structural weakness

antecedent stream

predate geologic activity was able to down cut and keep pact with the uplift.

superimposed stream

initial structure controlling the drainage has been eroded, no resemblance to the current surface structure.

drainage patterns

Entire systems can form into conspicuous drainage patterns in response to land surface structure and slope:

• Dendritic pattern

• Trellis pattern

• Radial pattern

• Centripetal pattern

• Annular pattern

dendritic pattern

• Treelike, branching dendritic drainage pattern consists of random merging of streams

• is more common than all other patterns and is found almost anywhere

• develop as a response to underlying structural control: alternating bands of tilted hard and soft strata.

• parallel streams flow in valleys between ridges, with short, right-angled connections cutting through ridges

radial pattern

is usually found when stream descends from a concentric uplift, like an isolated volcano

centripetal patterns

is opposite of radial pattern, usually associated with streams converging into a basin

annular pattern

• ring-shaped

• develops on domes or in a basin where erosion exposes concentric bands of tilted hard and soft rock

transportation

• Any water moving downslope can transport rock.

  • overland flow carries a smaller load

• Eventually overland flow reaches to valley bottoms as material collected in the stream load

• 3 components:

  • dissolved load

  • suspended load

  • bedload

dissolved load

Some minerals, mostly salts, are carried in water solution as the ___ ___

suspended load

very fine particles of clay and silt carried as ___ ___ without ever touching streambed

bedload

Sand, gravel, and larger rock fragment constitute the _____

• Saltation: smaller particles

• Traction: coarser pieces

Competence

A measure of the largest particle size a stream can move, transport

• increases by the square of its speed

capacity

A measure of the amount of solid material a stream has the potential to transport

• varies tremendously over time, depending on fluctuation in volume, flow speed, and stream load

deposition

Transported material is set down as the flow speed or water volume decreases.

Alluvium is the term for stream-deposited sediments:

• Smooth and round

• Display layers or strata

• Sorted by size

perennial steams

in humid regions, most are ___ ___ with permanent streamflow

intermittent and ephemeral

• ______ streams or seasonal streams flow only part of the year

• _____ streams only flow during and just after rains

stream discharge

the volume of flow per unit time

fluctuations in discharge

from place to place and from time to time, most streams have variable flow regimes wihe pronounced ___ ___ ___

flood events

bring large increases in stream discharge and in denudation

valley deepening

wherever stream has rapid speed or large volume, energy used for downcutting as streambed is lowered

• generally, produces a deep, steep-sided v-shaped valley

• more prevalent at upper reaches of stream where gradient is steeper.

lower limit to how much downcutting a stream can do is its base level.

ultimate base level

sea level is absolute or ___ ___ ___ as lower limit of downcutting

local base level

__ ___ ___ can be imposed by structural or drainage conditions that limit downcutting

Knickpoint

irregularities in a channel from change in bedrock resistance

• form steeper sections where waterfalls and rapids are found

• eventually moves ____ upstream as _____ migration

Graded streams

In equilibrium, it shows a balance between its transporting capacity and the amount of material supplied to it, and thus between degradation and aggradation in the stream channel.

valley widening

As downcutting diminishes, the stream gradient reduces, and stream energy diverts to meandering flow pattern.

As the main flow of the current swings from one bank to the other, lateral erosion begins:

cut banks

erosion of outside of curves forming cut banks occurs where flow speed is greatest

point bar

alluvium is deposited on the inside of the curves forming ___ ___ where flow is slowest.

headward erosion

by rill and gully cuts into interfluve at upper end of gully or valley

• results in decrease of interfluve area and increase in valley area

• stream capture

stream capture

when a portion of the drainage basin of one stream is diverted into the basin of another stream.

reduces a drainage divide, cuts the channel, and captures flow of beheaded or captured stream and may have a bend called an elbow of capture,

delta formation

• valley is lengthened at seaward end by deposition

• flowing water slows down when it enters lake or ocean, deposits its stream load into a depositional landform called a delta.

• creating a maze of parallel channels called distributaries

• sediments sorted during deposition and forming layered beds:

  • coarsest, sloping foreset beds

  • flood-depositied topset beds

  • finest sediment as bottomset beds

deposition in valleys

When a stream loses power to transport, alluvium can be deposited on the valley bottom in a process of aggradation.

• In high-water periods, when flow is fast, most of sediment is shifted downstream.

• In low-water periods, flow is slowed, sediment more likely to settle and will fill in the channel, in some cases, raise the streambed.

floodplains

Low-lying, nearly flat alluvial valley floor that is periodically inundated with floodwaters.

• cutoff meanders

• oxbow lake

• meander scars

• natural levees

• backswamps

• yazoo streams

bluffs

on the outer educe of floodplain usually bounded by higher elevation slopes called bluffs.

stream rejuvenation

Occasionally, elevation of continent changes relative to sea leavel

• by drop in sea level

• by tectonic uplift of land surface

when such uplift occurs, it “rejuvenates” streams in the area by stream’s downcutting ability is ___ ____

stream terrace

the remnants of previous valley floor

entrenched meanders

form when an area with a meandering stream is uplifted slowly while the steam incises downward, retaining its meandering course.

weathering

• mechanical ___ is dominant, especially salt wedging

• slower rates of weathering produce more angular particles.

soil and regolith

• are thin or absent in most deserts

• Bedrock is exposed directly to weathering and erosion

• Soil creep is rare

sand

• not all deserts are covered in sands, yet some deserts are

• sand is easily moved by rain and can be transported and redeposited by winds

rainfall

limited overall, yet falls in intense storms with high, rapid runoff, so fluvial erosion and deposition are remarkably effective.

impermeable surfaces

resistant bedrock and harden subsurface soil that do not readily absorb water, leading to high runoff

fluvial deposition

almost all streams are ephemeral and effective agents of erosion; transportation is short distance, depositional features are common.

wind

• Not all desert landforms are shaped by ____

• Yet most deserts have high winds, easily shifting sands, and dust.

basins of interior drainage

many deserts contain underdeveloped drainage networks that end in inland basins or valleys with no outlet.

cactus

reduces water loss

• no leaves,no transpiration

• waterproof skin to reduce evaporation

• spines to control temperature and water

• slow growth and great age

water storage and capture

• fleshy stem to store water

• shallow and long roots

some species have deep roots: example mesquite tree

animals

Reduce water loss/avoid heat

• Gila woodpecker: uses nest holes in large cactus.

• Lizards: do not sweat; can tolerate very high body temperatures.

• Nocturnal animals: many are active at night (e.g., owls, rattlesnakes, scorpions) to avoid daytime heat

Water capture

• Gambel’s quail: gets most of its water from plants; stays in the shade

• Ground squirrel: can tolerate salty water

rain shadow

a dry area of land on the leeward (downwind) side of a mountain range, where precipitation is significantly reduced because the mountains block moist air, forcing it up, cooling it, and causing it to drop its rain/snow on the windward (upwind) side, leaving the other side dry and often desert-like as the now-dry air descends and warms.

interior desert

too far away from moisture (gobi desert)

antartica

extremely low temperature, very little evaporation, very low precipitation. Also, sinking air.

atacama

coastal desert with rain shadow, subtropical high, and cold ocean current.

running water

Desert geomorphology holds ___ ___ as the most important external agent of landform development.

• on lightly vegetated ground, erosion by rain splash or streamflow is very effective

• rare, but the intensity of rainfall on impermeable desert surfaces produces runoff capable of moving great volumes of sediment in a very short time.

ghost water

evidence in dry steams and lake beds

arid mountain streams

• large amounts of alluvium rest in dry steams beds awaiting next rains

• slopes of mountains have thin or no surface material

where slopes are gentle

stream channels develop braiding, much silt and sand left on surface

exotic steams

• Rare permanent streams in dry lands, an ____ ____ is sustained by water originating outside the desert from an adjacent wetter area or higher elevation area

• Flow of exotic rivers in dry land diminishes downstream.

ephemeral streams

• vast majority of all deserts streams ____ _____ that carry water only seasonally or after a rainstorm

• brief periods of stream flow are marked by intense erosion, transportation, and deposition

dry lake beds

• relatively common, occupying areas of lowest elevation

• called salina if a heavy concentration of salts are in lake-bed sediments

• surface forms a claypan

• and if enough flow of water, forms a temporary playa lake, which overtime settles into a flat surface.

saline lakes

• Many permanent desert lakes are saline lakes

• High rate of evaporation relative to inflow leads to accumulation of dissolved salts

• Many of the largest desert lakes are remnants of larger bodies of water formed in a wetter climate.

fluvial erosion

• Desert areas with significant relief have large expanses of bedrock exposed.

• During rare rains, bedrock is mechanically weathered and eroded by running water, leaving steep and rocky slopes.

• Following a thunderstorm, rapid runoff occurs into dry ephemeral stream and develops flash flood or debris flow (dangerous).

another name in Africa: Kopje (islands in the sea of grass)

differential weathering and erosion

• Resistant rocks form cliffs, pinnacles, spires, and other sharp crests

• Softer rocks tend to wear away more rapidly, producing gentler slopes.

• Common in sedimentary landscapes, often producing vertical escarpments of steep, cliff-like slopes, and abrupt changes in slope angle.

residual surfaces and features

isolated landforms left by differential weathering and the removal of rock

• inselbergs

• bornhardt

inselbergs

steep sided mountains or ridges

bornhardt

composed of highly resistant rock and has a rounded form

residual surfaces and features

Isolated landforms left by differential weathering and the removal of rock.

• Along the lower slopes of desert mountains or hills, a gently inclined bedrock plateau forms, called a pediment.

  • Weathered bedrock surface

  • Detachment faulting

piedmont

is a generic term for any zone at the foot of a mountain range

• piedmont zone

• alluvial fans

• desert basins

piedmont zone

the ___ ____ of a desert mountain range is prominent area of fluvial depositon

• pronounced change in slope

• break in slope slows speed of sheetwash, stream flow, or debris flow into the ____ ____

alluvial fans

• As a stream leaves a mountain canyon, its flow slows and loose alluvium is deposited

• Flow breaks into distributary channels

• Forms ___ ___ as a moderately sloping, fan-shaped landform

• Sediment is sorted by size, largest boulders at “apex” and finer material at margins

desert basins

interior basins covered with a considerable depth of finest alluvium

limited

• effect of wind as sculptor of terrain is very ____

• motion of air passing over ground is similar to that of water flowing over a steambed

• aeolian processes - those related to wind action

  • most pronounced, widespread, and effective where fine-grained, unconsolidated sedimentary material is exposed, without vegetation, like deserts

deflation

• when loose particles blown in air or alon thre ground, mostly duct and sand grains

• blowout or _____ hollow, is a shallow depression form which fine material has been deflated