Earth System Exam 4

Lee side

(facing away from the direction from which the ice came) is shaped largely by plucking, which produces a steeper and more irregular slope

Fluvial Deposition in Arid Lands

Depositional features more prominent than erosional ones in a desert landscape Depositional features: Talus accumulations at foot of steep slopes; deposits of alluvium in ephermeral stream channels

kettles

Depressions when large blocks of ice are left by a retreating glacier becomes surrounded by glacial drift After ice block melts, morainal surface collapses leaving a depression

Impermeable surfaces in deserts

Desert surfaces impermeable to infiltrating water, permitting little moisture to seep into the ground Caprocks - resistant bedrock surfaces Hardpans - hardened and generally water-impermeable subsurface soil layers High runoff when it rains

Basins of interior drainage in deserts

Deserts contain watersheds that do not drain into any ocean Drainage networks typically underdeveloped

recessional moraines

Develops as the glacier recedes Ridges that mark where the ice front was temporarily stabilized during the first retreat of the glacier Concave arc that bulges in direction of ice movement Indicates ice sheets advance as a connecting series of tongues of ice

Hydrograph

Discharge of stream plotted over time on a graph

Pleistocene Glaciation

Dominant environmental characteristic of Pleistocene Glaciation is cooling of high-latitude and high elevation areas so fast that ice accumulated in many places Consisted of an alternation of glacial periods (times of ice accumulation) and interglacial periods (times of ice retreat) 20 glacial episodes took place during the Pleistocene

Deepening of valleys

Downcutting Knickpoint migration

Playas

Dry lake beds Salina - unusually high concentration of salt in lake bed sediments Claypan - if a playa surface is heavy impregnated with clay Playa are among the flattest and most level of all landforms develops from sediment settling when full of water and than evaporating and leaving dry mud

Melt Streams

During warmer months, streams of meltwater normally flow along with moving ice Streams may run along surface of the glacier until they reach cracks or crevasses Moulins - steep drainage shafts Streams transport rock debris

Drumlins

Elongated hills or deposited till The long axis is parallel to the direction of the glacier flow

Downcutting

Erosion by moving water ○ Removes material ○ Abrasion by bedload Deepens the channel Most effective in upper reaches of drainage basin Typically results in V-shaped valleys

Deposition

Erosion followed by deposition when either flow speed or water volume decreases Diminished flow result of a change in gradient, change in channel width or direction

Glaciers: Slow rivers of ice

Form on land Part of it may float on the ocean as ice shelves Snowpack over years turns to ice Glaciers are not stationary Slow movement under its own weight and the pull of gravity Large impact on shaping the environment

Glaciers

Form on land Part of it may float on the ocean as ice shelves Snowpack over years turns to ice Glaciers not stationary Slow movement under its own weight and the pull of gravity Large impact on shaping the environment

Natural Bridges

Form when the rock over which water flows changes from an erosion resistant type to a less resistant type Forms where an entrenched meander wears away the rock in a narrow neck between meander loops

Moraines

Formed by till deposited by the glacier Much longer than they are wide Till unsorted material deposited by glacier

River Deltas

Forms at the mouth of a river where it reaches the ocean Here the stream velocity is reduced and sediments are deposited As new sediments are deposited the delta grows Coastal currents Human modification of sediment load

Radial pattern

Found when streams descent from some sort of concentric uplift (i.e. isolated volcano)

Moraines

Glacial deposits are laid in a defined pattern Longer than they are wide Distinct ridges When originally formed, moraines tend to have smooth and gentle slopes Become uneven over time

Depositional landforms

Glacial erratic's Unsorted debris (till) Glaciofluvial deposits

Secondary deposition by meltwater

Glacial stream runoff has several peculiarities - peak flows in midsummer, distinct day-and-night differences in volume, large silt content, and occasional floods Much of debris is deposited or redeposited by meltwater Subglacial streams carrying sediments from glacier Glaciofluvial deposition - occurs around margins, meltwater deposition involving debris that was originally deposited by ice, picked up, and redeposited by meltwater beyond the outer margin of the ice

Glaciofluvial below

Glacier meltwater stream Sorted Finer material

Glacier formation and movement

Glaciers are open systems with inputs and outputs of both material and energy As glaciers retreat due to higher temperatures, surface albedo decreases and the decreased reflectance results in greater solar energy absorption which can lead to higher temperatures Glacier may develop with a net year to year accumulation of snow Glaciers depend on the right combo of temperature and moisture

Rates of movement

Glaciers move very slowly Few cm a day Fastest moving ice is that at and near the surface Speed decreases with depth

Where on Earth has temperature increased the most?

Global temperature increase most dramatic in Arctic Majority of earth's glaciers loosing mass Ice sheet mass loss

Lengthening of valley

Headward erosion Delta formation

Development and Flow of Mountain Glaciers

Highland icefield can extend broadly across the high country Individual alpine glaciers usually form in sheltered depression near the heads of stream valleys

Landforms from Continental Glaciation

Erosional Valley deepening Lakes Rounded hills - Roche Moutonnee

Butte

Erosional remnant that has a very small surface area and cliffs that rise above their surroundings Formed from mass wasting of mesas

glacier plucking

Erosive power of ice is greater than that of flowing water Friction between ice and rock causes lowermost ice to melt and the layer of water created reduced the pressure on the rock Water can refreeze around rock Glacial plucking - rock fragments beneath ice grasped when meltwater refreezes; as ice moves along, these particles are plucked out and dragged along Roughens the surface

Erosion by Ice Sheets

Except in mountainous areas of great initial relief, the principal topography resulting from erosion caused by an ice sheet is a gently undulating surface Valley bottoms gouged and deepened by moving ice

Headward Erosion

Fast moving water from slope breaks between interfluve and valley wall causes material collapse Results in decrease of interfluve area and increases in valley area Causes a headward extension of the valley into the interfluve area Interfluve - area between streams

Aeolian Transportation

Finest particles carried in suspension as dust Strong turbulent winds lift and carry suspended dust Particles larger than dust are moved by wind through saltation and traction Wind uplifts particles larger than grain size and carries a short distance Larger particles roll across surface with traction

Modifying rivers for flood control

Flat land, abundant water and productive soils attract humans to valley bottoms People have tried to mitigate potential flood damage

Deposition in desert basins

Flatter portions have significant accumulation of alluvium - not enough stream flow to carry sediments far from mountain front Large rock fragments rarely transported into middle of basin - middles are covered with fine particles of sand

Yazoo tributary

Flows parallel to main channel because of natural levees

How much has sea levels changed because of the mass change 2002-2017?

10mm

Sea levels

130m lower at peak glaciation Different drainage patterns Migration across bering straight

split

A linear deposit attached to the landsplit at one end and extending into open water in a down current direction Most are straight, sandy peninsulas projecting out into a bay or other coastal indentation, variations in local currents, winds, and waves often give them other configurations

barrier island

A long, narrow island built up in shallow offshore waters Always oriented parallel to shore Believed to result from the deposition of sediment where large waves (particularly storm waves) begin to break in the shallow waters of continental shelves Barrier islands often become the dominant element of coastal terrain

Cutoff meander

A meander loop is cut off and by passed by a cutoff meander

horns

A steep-sided, pyramid-shaped mountain peak formed by expansive quarrying of the head walls where three or more cirques intersect

How does ablation and accumulation vary over a typical year?

Ablation increases peaks in summertime and dips in winter Accumulation dips in summertime and peaks in winter

Contemporary Glaciation

About 10% of earth's land surface is covered with ice today ○ 96% in Antarctica and Greenland ○ More than 2/3 of all freshwater is at this moment frozen into glacial ice Antarctic ice sheet ○ Antarctic ice by far the most extensive ice sheet on earth ○ 98% of its surface in Antarctica covered with glacial ice ○ E Antarctica contains about 9 times the volume of ice of W Antarctica Greenland ice sheet ○ Greenland ice much less extensive than Antarctica Mountain glaciers ○ Remainder of world's present-day glaciers are concentrated in high mountain areas Climate change and contemporary glaciation. Antarctica's temperature has been warming at a rate of about 0.12 degrees C per decade over the last 50 years

Increase in CO2 from 1850 to 2018

About 280 ppm in 1850 and 405.91 ppm in 2018

Knick point migration

Abrupt changes in bedrock resistant Hard bedrock slow down erosion Waterfalls -> turbulent water -> eventually knick point will be eroded away Ex.) Niagara Falls Hard limestone on top on softer material

Glacier Mass Deposits

Accumulation (Snow inputs) Mass balance Ablation (runoff, evaporation, sublimination, and calving losses)

Retracting Alpine Glacier

Accumulation in winter Ablation in summer Ablations larger than accumulation Glacier is still moving

Causes of the Pleistocene Glaciations

Accumulation of ice masses more of less simultaneously at various latitudes in both hemispheres but without uniformity Apparently concurrent development of pluvial conditions in dry land areas Multiple cycles of ice advance and retreat including both minor fluctuations over decades and centuries and major glaciations and deglaciations over tens of thousands of years Milankovitch cycles Ocean circulation patterns Atmospheric circulation changes Changing continent positions Reductions in insolation

Drainage basin (watershed)

All area that contributes to overland flow, streamflow, and groundwater to that stream Consists of valley bottom, valley sides, and surrounding interfluves Terminates at a drainage divide

coastal submergence

Almost all oceanic coastlines show evidence of submergence over the last 15,000 years or so As water from melting glaciers returned to the oceans, rising sea level caused widespread submergence of coastal zones

Processes that shape the topography of oceanic coastlines are similar to the processes acting on lakeshores with 3 exceptions:

Along lakeshores the range of tides is so small they are insignificant to landform development The causes of sea-level fluctuations are quite different from causes of lake-level fluctuations Coral reeds are built in tropical and subtropical oceans only to in lakes

Erosion by Glaciers

Amount of erosion caused by a glacier is roughly proportional to the thickness of ice and its rate of flow Depth of erosion is limited in part by the structure and texture of the bedrock ad in part by the relief of the terrain

barrier island lagoons

An extensive barrier island isolates the water between itself and the mainland forming a body of quiet salt water called a lagoon Overtime lagoon becomes increasingly filled with water-deposited sediment from coastal streams, wind-deposited sand from the barrier island, and tidal deposits if the lagoon has an opening to the sea Unless tidal inlets across the barrier island permit vigorous tides or currents carry lagoon debris seaward the lagoon is to be slowly transformed After a barrier island becomes a certain size it often begins to migrate slowly shoreward as waves wear away its seaward shore and sediments accumulate building up its landward shore

waves of translation

As waves roll into shallow water metamorphis occurs \When water depth become equal to about half the wavelength, the wave motion begins to be affected by frictional drag on the sea bottom Wave of translation results in significant horizontal movement of the surface water Friction slows and bunches waves, decreasing wavelength, while increasing height

Basal slip

At bottom of glacier, the entire mass slides over its bed on a lubricating film of water Glacier molds itself to the terrain it is riding over

Extent of Pleistocene glaciations

At its max Pleistocene extent, ice covered 1/3 of land area of earth Greatest total area of ice-covered land was in N America

Fringing reefs

Attached reef to a volcano

Hamada - barren bedrock

Barren surface of consolidated material Consists of exposed bedrock but it is sometimes composed of sedimentary material that has been cemented together by salts evaporated from ground-water Fragments formed by weathering are quickly swept away by the wind so little loose material remains Restricted to plains areas

Glacial abrasion

Bedrock is worn down by rock debris being dragged along in the moving ice Polishes surfaces when bedrock is of highly resistant material and striations (fine parallel indentations) and grooves (deeper indentations) in less resistant bedrock

Cirques

Broad amphitheater hollowed out at the uppermost head of a glacial valley Has a steep often perpendicular head and side walls and a floor that is fatteningly sloping or deepened enough to form a basin Marks the place where an alpine glacier originated First landform feature produced by an alpine glacier By middle of summer a large crevice known as a bergschrund opens at the top of the glacier exposing part of the head wall to frost wedging Tarn - cirque lake

ria shorelines

Coast along which numerous estuaries project Long, narrow inlet of a river that gradually decreases in depth from mouth to head If a hilly or mountainous coastal area is submerged, numerous off-shore islands may indicate the previous location of hilltops and ridge crests

coastal depositional landforms

Coastal deposition occurs wherever the energy of moving water is diminished Deposits along coastlines tend to me more ephemeral than those farther inland Due to small particle size of coastal deposits and b/c sand tends not to be stabilized by vegetation cover

longshore currents

Coastal topography is affected most by longshore currents Water and sediment move roughly parallel to the shoreline Longshore currents develop just offshore and are set up by the action of the waves striking the coast at a slight angle b/c most waves are generated by wind, the direction of a longshore current typically reflects the local wind direction

Pluvial (increased rain) developments

Considerable increase in amount of moisture available Creation of many lakes - Pleistocene lakes

Coral Reefs

Coral polyps can build coralline formations almost anywhere in shallow tropical waters where a coastline provides a stable foundation

Fossil sand dunes

Cross bedding develops when wind blown sand slides down the slip face of a dune leaving thin layers inclined relative to the ground surface

glacial troughs

Cross-sectional profile often changed from a stream cut V shape to an ice eroded U shape

Wineglass canyons

Cup is an open area of dispersed headwater tributaries high in the range Stem is the narrow gourge cut through the mountain front Base is the alluvial fan

Flood controls on the Mississippi River

Dams Artificial levees Living on the floodplain Diversion or bypass channels can be constructed to divert floodwaters out onto an artificial floodplain Restoring floodplains

Smallest to largest types of glaciers

Ice cap Ice berg Ice sheet Alpine glacier Ice field

How do we know past climates?

Ice cores

Glacier movement

Ice is brittle substance; however, ice under confining pressure deforms rather than breaks Partial melting aids in the movement of glacier

Glacier

Ice must be moving or flowing to be considered a glacier

highland glaciers

Ice must be moving or flowing to be considered a glacier

Barchan

Individual dune migrating across a nonsandy surface, although barchans are also found in groups Cresent shaped with the horns pointing downward Sand movement over the crest, from windward side to slip face, and from around the edges of the crest Form where strong winds blow consistently from one direction Fastest moving of all dune types Not found in Australia

Badland

Intricately dissected and barren terrain Formed in areas underlain by horizontal strata or clay formations that are poorly consolidated Rains are an erosive agent

Kettles

Irregular depression in the group created as a block of ice deposited by the glacier melts

Impacts of glaciation and deglaciation

Isostatic adjustments Sea levels Geomorphology

How has the Greenland ice sheet mass changed between 2002 and 2017?

It has decreased

Erg - A Sea of Sand

Large area covered with loose sand generally arranged in some sort of dune formation by wind Accumulation of vast amount of sand necessary to produce an erg explained by periods of humid climate These products carried by streams into an area of accumulation When climate becomes drier, wind becomes principal agent of transportation and deposition of sand

Star dunes

Large pyramid shaped dunes with arms radiating out in 3 or more directions Develop where wind frequently changes direction

Last glacial maximum vs. today

Last glacial max: 30% land surface coverage Today: about 10% of earth's surface is covered by glaciers

Widening of valleys

Lateral erosion

Transverse dunes

Less uniformly cresent shaped than barchan Occurs where entire landscape is sand covered Convex side faces the prevailing wind direction All crests are perpendicular to the wind direction and the dunes are aligned in parallel waves across the land Migrate downwind as barchans do

Unsorted till on top of glaciers

Limited water action Unsorted material Angular

Seifs

Linear or longitudinal dune Long, narrow dunes that usually occur in abundance and in generally parallel arrangement Lengthy parallel orientation represents an intermediate direction between two dominant wind directions - blowing from one direction part of the year and from another direction the rest of the year Rare in American deserts

Eskers

Long sinuous ridges of stratified drift Composed of glaciofluvial gravel and are thought to have originated when streams flowing through tunnels in the interior are the debris As ice stagnates and melts these subglacial streams deposit much of their load in the tunnel Eskers are the debris that is exposed once the ice melts

Drumlines

Low elongated hill Smaller than moraines and composed of similar unsorted till Long axis is parallel to the direction of ice movement End of drumline faces the direction where ice came Blunt and steeper than opposite end Configuration reverse of the Roche moutonne Origin result of ice readvance into an area of previous glacial deposition Occur in groups

Floodplain

Low-lying near flat valley floor that is periodically inundated with floodwaters At any given time the stream will occupy a small portion of the floodplain Changes over time as the channel meanders

Piedmont zone

Marks the change from the ranges' steep slopes to the near flatness of the basin floors Covered with unconsolidated sand Area of fluvial deposition During rains, flash floods break onto piedmont zone resulting in deposition

Deposition

Material dropped far from origin

Desert weathering

Mechanical weathering dominant in deserts Water needed for chemical weathering Salt wedging more common in arid regions than humid ones Slower rate of total weathering in deserts and the production of more angular pieces of weathered rock

Factors that increase sea levels

Melting of glaciers and ice sheets glacier calving thermal expansion of ocean water

Dissolved load

Minerals dissolved in water and carried as a solution

Depositional landforms

Moraines Kettles Drumlines Glaciofluvial Outwash plains Eskers Kames

Terminal or end moraines

Moraines formed at the front of glaciers Indicate where a glacier has been stationary for some time

Lateral moraines

Moraines formed at the sides of glaciers

The Ranges

Most are sharp Mountain ranges long, narrow, and parallel to each other Seamed by numerous gullies, gorges, and canyons that rarely have flowing streams Narrow and steep sided and have V-shaped cross section Channel bottom filled with sand and other loose debris

Outwash plains

Most extensive glaciofluvial features are outwash plains which are smooth, flat alluvial aprons deposited beyond recessional or terminal moraines by streams issuing from ice Streams heavily loaded with reworked till or with debris washed directly from melting ice form a braided patter of channels across the area beyond the glacial front As they flow away from the ice, these braided streams, choked with debris, rapidly lose their speed and deposit their load Beyond the outwash plain a lengthy deposit of glaciofluvial alluvium may be confined to a valley bottom = valley train

tsunami formation

Most tsunami are a consequence of abrupt movement along an ocean floor fault - especially from the vertical displacement caused by reverse or thrust faulting along the subduction zone May also result from underwater volcanic eruptions and major underwater and coastal landslides When it reaches shallow water, the tsunami changes considerably - slows down causing wavelength to decrease and the wave height to increase

Transport

Move material on top, within, and below

sediment budget

Must be in balance if the deposit is to persist Removal of sand must be offset by the addition of sand Most have a continuing sediment flux with sediment arriving in some places and departing in others During storms balance is upset - coastal deposits are significantly reshaped or removed and replaced when calmer conditions prevail

Postglacial landscape

Produced by ice sheets is one of low relief but not absolute flatness Ice-scoured rocky knobs and scooped-out depressions Soil and weathered materials are largely absent with bare rock and lakes dominating the surface Stream patterns are erratic and inadequately developed b/c preglacial drainage system was deranged by ice erosion

Piedmont zone

Prominent area of fluvial deposition Pronounced change in slope at mountain base with steep slope giving way abruptly to a gentle one Break in slope greatly reduces the speed of sheetwash, streamflow, or debris flow that travels into zone

Abrasion

Requires "tools" in the form of airborne sand and dust particles Wind drives these particles against rock and soil surfaces to form natural sandblasting Does not construct landforms but sculpts them Pitting, etching, faceting, and polishing of exposed rock surfaces

glacial steps

Resistant rock on valley floor is gouged less deeply than weaker or more fractured rock Down-valley profile of a glacial trough is marked by an irregular series of rock steps or benches separated by steep cliffs on the down-valley side - glacial steps Postglacial stream that flows out of a cirque and down a glacial trough usually has a relatively straight course but includes rapids and waterfalls Paternoster lakes - small lakes on benches

terminal moraine

Ride of till that marks the max advance of a glacier Forms as an end moraine when a glacier reaches its equilibrium point As ice melts around the margin, till is deposited and morain grows

Direct deposition by glacial ice

Rock debris deposited directly by moving or melting ice with no meltwater redeposition involved = till Direct deposition by ice ensues when melting occurs around the margin of an ice sheet or near the lower end of a mountain glacier but it is also accomplished whenever debris is dropped on the ground beneath the ice Most fragments are angular Glacial erratic's - Driftenormous fragments

Basin-and-Range Landforms

SW interior of US Land without external drainage with only a few exotic rivers flowing through or out of the region Extensive normal faulting Aridity due to rain shadows Principals features - ranges, piedmont zones, and basins

Aeolian Deposition

Sand and dust eventually deposited when wind dies down Finer material laid down as a thin coating of silt and has little landform significance Coarser sand deposited locally Sometimes spread across the landscape as an amorphous sheet called a sandplain Sand dune

What explains the zig zag pattern seen in the time series?

Seasons

Coastal Emergence

Seaward of the cliff face, the pounding and abrasion of the waves creates a broad erosional surface called a wave-cut platform usually slightly below water level The combo of wave-cut cliff and wave-cut platform produces a profile that resembles a letter "L" with the steep vertical cliff descending to a notched base and the flat horizontal platform extending seaward Most of the debris eroded from cliff and platform is removed by the swirling waters ○ Larger fragments are battered into smaller and smaller pieces until they are transportable ○ Some of the sand and gravel produced in this fashion may be washed into an adjacent bay and become at least temporarily a part of the beach ○ Much of the sediment is shifted directly seaward where it may be deposited ○ As time passes the cliff wears away by weathering and erosion, these deposits may eventually cover the wave-cut platform, resulting in a beach that extends to the base of the cliff

Deposition in Valleys

Sediment continuously rearranged in the channel and when the flood plain overflows

Straight channels

Short and uncommon

beach drifting

Short-distance shifting of sand directly onshore by breaking waves and the retreating water from the beach A zigzag movement of sediment that results in a general downwind displacement Parallel to coast Nearly all waves approach the coast obliquely rather than at a right angle Return of flow brings sand back to the sea Repetition of movement shifts sand further along the coastline

Eskers (glaciofluvial)

Sinuous ridges Glaciofluvial gravel Probably deposited in subglacial channels

Kames

Small hills or poorly sorted sand and gravel Meltwater deposit in stagnant ice Probably formed in crevasses

Hanging glacial troughs

Small tributary glaciers When ice melts valleys are of different depths Mouths of tributary valleys are perched high along sides of major troughs forming hanging valleys/troughs

Kames

Small, steep mounds or conical hills or stratified drift are found sporadically in areas of ice-sheet deposition Diverse in origin but associated with meltwater deposition in stagnant ice

First order stream

Smallest stream with no tributaries First order streams and valleys more numerous than all others combined

Outwash plains (glaciofluvial)

Smooth and flat Sorted sediment Created by braided rivers carrying meltwater and sediment from the glacier May cover huge areas

Transformation of snow to glacial ice

Snow (90% porosity) Granular ice (50% porosity) Firn (20%) Glacial Ice (0% except bubbles)

Changing Snow to Ice

Snow crystallizes directly from water vapor in atmosphere and floats to earth as lacy, hexagonal crystals Crystalline snow is compressed by overlying snow into granular form ○ Density doubles ○ With time and more compression, granules begin to coalesce into a material called neve/firm Density approaches 90% of that of liquid water

Conditions for glacier formation

Snowfall - enough moisture in the atmosphere to produce significant snowfall Cold

forded coasts

Spectacular coastlines often occur where high-relief coastal terrain has undergone extensive glaciation Troughs once occupied by valley glaciers or by continental ice sheets may be so deep that their bottoms are presently far below sea level In some localities these deep, sheer-walled coastal indentations (fjords) are so numerous that they create an extraordinary irregular coastline, often with long, narrow fingers of saltwater

wave erosion

Spray as fast as 115km Speed and mass of waves leads to coastal erosion Along a rocky shoreline, air is forced into cracks in the rock as the wave hist the shore Resulting compression is released as water recedes allowing an expansion of air Loosens rock particles Chemical action Seawater crystallizes in the crevices and pores of onshore rocks and cliffs Salt wedging

Dating the ice age

Start of Pleistocene 2.58mm years ago By the start of the Pleistocene the amplitude of climate fluctuations from glacial period to interglacial period has increased and some parts of the N Hemisphere were covered by glaciers Pleistocene ended 11700 years ago

4 types of Stream Channel Patterns

Straight Sinouous Meandering Braided

Valley lengthening

Stream can lengthen its valley in two ways 1) Headward erosion - upper end 2) Delta formation - lower end

Graded streams

Streams might reach a steady over time Sediment input = sediment output Stream profile is adjusted to only transport the same amount of sediment out of the system as it receives

Temperature increase on average

Temperatures on average have risen by 1.3 degrees F in the last century Fastest rise within the last 1000 years

Elbow of capture

The abrupt bend in the stream channel where the capture took place

Mississippi Today

The army corps of engineers is keeping the river in its current channels Channels allow for shipping Manmade levees prevent flooding and also deposition on the flood plain Upstream dams capture sediment that would flow downstream The net result ○ Less sediment deposition in the flood plain ○ The delta is not growing, but eroding

Base level of valleys

The lower limit of stream downcutting Gentle slope towards sea level (has to maintain some stream flow)

Bedheaded stream

The lower part of the stream overtaken by the captor stream

Oxbow lake

The part of the meander that was cut off,, initially filled with water, fills with sediment over time

Meandering Stream

The simultaneous deposition and erosion at different parts of the meandering river results in looping patterns in the landscape

tides

The tides rise and fall in a cycle that takes about 12 hours producing two high tides and two low tides a day on most seacoasts Tides significant agents of erosion in narrow bays, around the margin of shallow seas, and in passages between islands, where they produce currents strong enough to scour the bottom and erode cliffs and shorelines

Reg - Stony deserts

Tight covering of coarse gravel, pebbles, and/or boulders from which wind and water have been removed Stony desert Finer material removed through surface erosion - pebbles fit closely together Desert pavement Desert varnish - dark shiny coating that forms on the surface of pebbles, stones, and larger outcrops after long exposure to the desert air Characterized by a high content or iron and manganese oxides along with wind-delivered clay

valley glaciers

Tongues of ice that travel down mountain valleys If the leading edge of a valley glaciers reaches a flat area and escapes from the confines of it valley walls it is called a piedmont glacier

Plateaus

Top platforms Bounded on one side by a prominent encarpment

Entrenched meanders

Topographic features formed when an area containing a meandering stream incises downward while retaining its course

Dendric pattern

Treelike branching dendrictic drainage pattern Random merging of streams Tributaries join larger streams irregularly but always at an angle smaller than 90 degrees Underlying structure does not control the evolution of the drainage pattern - underlying rocks are more or less equally resistant to erosion Most common

Erosional landforms

Turning V-valley into U-valley Formation of sharp ridges horns Cirques: carved out hollows

Desert Sand Dunes

Unanchored dunes are deformable obstructions to airflow that can move, divide, grow, or shrink Develop sheltered air pockets on their leeward sides that slow down and baffle the wind so deposition is promoted there Moved by local winds that erode the windward slope of the dune forcing sand grains up and over the crest Then deposited over the steeper leeward side (slip face) Slip face - angle of 32-34 degrees. Angle of repose of dry sand. Not all dunes unanchored - could be anchored by vegetation and won't shift with wind Dunes provide little nourishment for plant growth so when it manages to gain a foothold it may anchor the dunes Dune patterns are almost infinite in their variety

Penck's Theory of Crustal Change

Uplift stimulates erosion immediately and that slope form is significantly influenced by the rate of uplift. Slopes tend to maintain a constant angle as they erode retaining their steepness as they retreat rather than being worn down at a continuously lower slop angle.

backshore

Upper part of the beach, landward of the high-water line Dry, covered by waves during severe storms only Contains one or more berms which are flattish, wave-deposited sediment platforms The foreshore is the zone that is regularly covered and uncovered by the rise and fall of tides The nearshore extends seaward from the low-tide mark □ Nearshore is the place where waves break and surf action is greatest The offshore zone is permanently underwater and deep enough that wave action rarely influences the bottom Along irregular shorelines, beach development may be restricted largely or entirely to bays Beaches are built up slowly during quiet weather and removed rapidly during storms

Cirque glaciers

Very small alpine glaciers confined to the basins where they originate

Wave motion

Water waves wind generated - set in motion by friction of air blowing across water Some water waves are generated directly by wind stresses on the water surface Water waves become swells when they travel beyond the location where they were generated by wind

wave-cut cliffs and platforms

Wave-cut cliffs, sea stacks, and wave-cut platforms comprise one of the most common coastal landform complexes As we discussed earlier, as waves erode away at a rocky headland, steep wave-cut cliffs form; these cliffs receive the greatest pounding at their base, where the power of the waves is concentrated Combo of hydraulic pounding, abrasion, pneumatic push, and chemical solution at the cliff base cuts a notch at the high-water level As the notch enlarges the overhang sporadically collapses the cliff recedes as the ocean advances Where wave action cuts through the bottom of a cliff-topped headland, a sea arch may form, while sea stacks develop where wave erosion leaves towers of rock isolated just offshore from the coastal cliff

wave refraction

Waves change direction as they approach the shore Occurs when line of waves does not approach exactly parallel to the shore As a result wave line bends as it pivots toward the obstructing area Wave energy tends to be concentrated in the vicinity of an obstruction

Lateral moraines

Well-defined ridges of till built up along sides of valley glaciers Where a tributary glacier joins a main valley glacier their lateral moraines unite at the intersection

Plastic flow of ice

When a mass of ice attains a thickness of ~50m the plastic flow of ice begins in response to overlying weight Entire mass does not move uniformly Ice oozes outward from around the edge of an ice sheet or down-valley from the toe (the end) of an alpine glacier

Marine terraces

When a wave-cut platform is uplifted along a tectonically rising cost, a marine terrace forms Appears the fluctuations of sea level during the Pleistocene played a part in the formation of at least some marine terraces When sea level drops during a glacial period, the wave-cut platform is left well above sea level; gradual tectonic uplift during the period of low sea level leaves the terrace high enough to be preserved after sea level rises during the subsequent interglacial period

Sea-level change

When continents were covered with ice, less water was available to drain from the continents into the oceans Causes significant difference in drainage patterns and topographic development on seashores and coastal plains

effects of tsunami

When they strike a shoreline, tsunami arrive as a very rapidly advancing surge of water up to 40m high

proglacial lakes

Where ice flows across a land surface, natural drainage is blocked and meltwater from ice can become dammed by the ice front forming a proglacial lake Most are small and temporary

Lateral erosion

Widening slow when above the base level As gradient decreases, stream flow meanders and lateral erosion occurs Water moves fastest on outside of curves Slowest water on inside of curves accumulates alluvium Alluvium - material transported and deposited by flowing water

Loess

Wind deposited silt that is fine grained and buff colored Not associated with dry land Despite depositional origin, loess lacks horizontal stratification Most distinctive characteristic is its great vertical durability, which results from its fine grain sand, high porosity, and vertical, joint like cleavage planes Tiny grains have great molecular attraction for one another, making the particles very cohesive Particles are angular, which increases porosity Loess accepts and holds large amounts of water Relatively soft and unconsolidated loess maintains almost vertical slopes when it is exposed to erosion because of its structural characteristics Prominent bluffs Most loess deposits are in midlatudes where some are very extensive Provide fertile possibilities for agriculture

Sinuous channels

Winding and occur in almost all topographic settings Curvature is gentle and irregular

Coastal dunes

Winds are active in dune formation along many stretches of ocean and lake coasts whether the climate is dry or not On flattish coastlines, ocean waves deposit sand along the beach Onshore wind can blow some of the sand inland often forming dunes Parabolic dunes develop - vegetation becomes established in dune

Erosion of Escarpment Edge

Worn back by weathering, mast wasting, and fluvial erosion Cliffs retreat maintaining their perpendicular faces as they are undermined b the more rapid removal of the less resistant strata Much of undermining accomplished by sapping - groundwater seeps and trickles out of the scarp face, eroding fine particles and weakening the cohesion of the face Blocks of the caprock break off usually along vertical lines Harder rocks are cliff forms and less resistant beds develop more gently inclines slopes Talus accumulates at base

tombolo

a depositional feature that connects a near-shore island with the mainland

Aretes

a ridge produced where several cirques have been cut back into an interfluve from opposite sides

Cols

a sharp-edged pass of saddle through the ridge formed when two adjacent cirques on opposite sides of a divide cut back enough to remove part of the arte between them

groin

a short wall or dam built outward from a beach to impede the longshore current and force sand deposition on the up current side of the structure

Antecedent stream

a stream that predates the uplift

Equilibrium line

accumulation = ablation

Accumulation

addition of ice by incorporation of snow

Yardangs

align parallel with dominant wind direction

eustatic sea-level change

an increase or decrease in the amount of water in the oceans

Piedmont

any zone at the foot of a mountain range

Swash

breaking wave rushes toward shore carries sand and rock particles onto beach momentum of the surging swash overcome by friction and gravity

Glaciofluvial features

composed largely or entirely of gravel, sand, and silt b/c meltwater is really capable of moving larger material

Medial moraine

dark band of rocky debris

Stratified drift

deposits that resemble alluvium in that they may appear both layered and somewhat sorted b/c they were carried along by the meltwater

Alpine glacier

describes glaciers that develop individually, high in the mountains rather than as part of a broad icefield, usually at the heads of valleys

Undercut bank

erosion on the outside of meander curves

beach

exposed deposit of loose sediment adjacent to a body of water Sediment relatively homogenous on a given section of the beach

Stross side

facing in the direction from which the ice came of a Roche moutonnee is smoothly rounded and streamlined by grinding abrasion as the ice rides up the slope

Pinnacle

final spire of resistant caprock protecting weaker underlying beds

Mesa

flat topped surface

Consequent stream

follows slope of the land

Arches

form when the lower portions of a narrow fin of sedimentary rock weaken and collapse leaving more resistant rock

End moraine

forms along the active edge of a glacier

Continental ice sheets

glaciers that form in nonmountainous areas of the continents

Glacier flour

heterogenous collection of particles of all sizes that makes up glacier's load

ice shelf

ice reaches ocean along a massive front

Baymouth bar

if the spit becomes extended clear across the mouth of a bay and connects with land on the other side transforming the bay into a lagoon

Intermittent streams

impermanent streams in arid regions

Fluvial processes

involve running water

ground moraine

large quantities of till are laid down from underneath the glacier rather than from its edge usually means rolling plains across the landscape

estuaries

long fingers of seawater projecting inland

outlet glaciers

long tongues of ice around margin of the sheet extend between rimming hills to the sea

Ablation zone

lower portion; new ice added each year is less than the amount lost

tsunami

major oceanic wave systems are triggered by a sudden disruption of the ocean floor

Two types of glacier outlets

marine terrestrial

Accumulation zone

new ice from snowfall added each year exceeds the amount lost from melting and sublimation (upper portion)

Indirect effects of Pleistocene glaciations

periglacial processes sea-level changes crust depression pluvial (increased rain) dev.

Calving

process of chunks of ice frequently break off from ice shelfs and fall into the sea

Roche moutonnee

produced when bedrock hill is overridden by moving ice

Atoll

ring-shaped structure formed when the top of the volcanoes sinks below the water surface forming a landless lagoon

Scarp

steep vertical cliffs

Trunk glaciers

system of merging glaciers typically develops in the main valley joined by tributary glaciers from smaller valleys

Drift

term for all material moved by glaciers

Till plain

uneven deposition produces an irregularly undulating surface of broad, low rises, and shallow depressions

jetties

usually built in pairs on either side of a river or harbor entrance

patterned ground

various geometric patterns repeatedly appear over large areas in arctic

Ablation

wastage of ice through melting and sublimation

Bajadas

when alluvial fans overlaps and become a larger one

Coral Polyps

Anthozoan animals called stony corals Critical element in the development of coral reefs These tiny creatures live in colonies of countless individuals, attaching themselves to one another Most massive corals grow 0.5-2 cm per year Can take up to 10,000 years for a coral reef to become established Some coral reefs began forming 30. Each individual coral polyp extracts calcium carbonate from seawater and secretes a limy skeleton around the lower half of its body Most polyps withdraw into their skeletal cups during the day and extend their arm like feeding structures at night At the top of the body is a mouth surrounded by rings of tentacles which gives them a blossom-like appearance Feed on minute animal and plant plankton Reef-building hard corals are hosts to symbiotic algae that provide additional food for the coral polyp through photosynthesis The ubiquity of coral reeds in shallow tropical waters is a tribute to the remarkable productiveness of the polyps b/c they are not very hardy creatures Can't survive in water that is very cold, very fresh, or very dirty Require considerable sunlight

waves of oscillation

As a wave passes a given point on the water surface, the water at that location makes a small circular or oscillatory movement As the wave passes the water moves upward producing a wave crest Crest formation is followed by a sinking of the surface that creates a wave trough Horizontal distance from the crest to crest or from trough to trough is called the wavelength Vertical distance from crest to trough equivalent to the diameter of the circular orbit of the surface water as the wave form passes is the wave height Height of wave depends on the wind speed, wind duration, water depth, and fetch (area of open water) Influence of wave movement diminishes rapidly with depth

Glacier Flow vs. Glacier Advace

As long as glacier exists ice in it is flowing either downward or laterally outward Ice in glacier always moves forward but outer margin may or may not be advancing depending on balance of accumulation and ablation Even in a retreating glacier ice moves forward During wetter or cooler period when there is greater accumulation, glacier will flow further During warmer or drier periods rate of ablation increases and glacier wastes away sooner

Barrier reefs

As new layers are laid down over old the coral builds upward around the volcano as a cylinder of irregular height At the same time, the volcano is sinking and pulling the original reef base downward When the coral has been built up enough and the volcano has sunk enough the result at the water surface is a coral ring separated by a lagoon from the part of the volcano still above water - barrier reef Ring of coral may be a broken circle b/c of the varying thickness of the coral, appearing to "float" around a central volcanic peak

Point bar

Net deposition of alluvium where stream slows down at the inside of meander curves

Periglacial processes

Never touched by glacial ice but was indirectly influenced by the ice Erosion and deposition of done by the enormous amounts of meltwater released as the glaciers melted Frost weathering caused by the low temperatures in the periglacial zone and associated soilfuction of frozen subsoil Extended over more than 20% of earth's land area

Structure of Mesa-and-Scarp Landforms

Normally associated with horizontal sedimentary strata Most resistant layers to weathering/erosion are limestone and sandstone Broad and irregular stair shaped pattern

The Basins

Playa found in low point where gentle slopes from all slides end Damage control in rains and flash floods Drainage terminal for all overland and streamflow from near sides Salt accumulations commonplace Water is usually abundant enough to flow across outer rim of basin floor and onto player but after water evaporates away, salts remain Saline lakes are clear Basin floor covered with fine grained material b/c streams too weak to transport large particles Denudation process tends to raise floor of basins

Development of Pleistocene ice sheets

Pleistocene ice sheets (except for ones in Antarctica) did not originate in polar regions Developed in subpolar and midlatitude and then spread outward

Erosion

Plucking by refreezing Abrasion by frozen debris Subglacial meltwater

Equilibrium Theory

Slopes adjust to geomorphic processes such that a balance of energy exists - the energy provided is just adequate for the work to be done Harder rock develops steeper slopes and higher relief Applied when land is simultaneously uplifted and eroded fluvially If in equilibirum, slopes denuded by mass wasting and erosion at same rate as they are being regenerated by uplift General form remains same over time

Fluvial deposition in deserts

Almost all streams in desert are ephemeral - flow only during and immediately after rain Effective agents of erosion - shift large amount of material in short time

Deposition in Valleys

Any time a stream loses power to transport is load, alluvium can be deposited almost anywhere in a valley bottom Aggradation - process of deposition During high water periods where flow is fast and voluminous the stream scours its bed and shifts most of sediment downstream In low water periods sediment settles to the bottom and results in filling of the channel

Alluvial fans

As stream leaves narrow confines of a mountain gorge and emerges onto the open piedmont zone, its flow slows Flow breaks into distrubutary channels that end their way down the piedmont slope sometimes cutting shallow new channels in the loose alluvium but frequently depositing more debris atop the old A moderately sloping fan-shaped landform builds up at the mouth of the canon When one part of the fan is built up the channeled flow shifts to another section and builds that up The entire fan is eventually covered more or less symmetrically with alluvium Large boulders are dropped near the apex (top) of fan and finer material accumulates near the margins As deposition continues the fan extends outward across the piedmont zone and onto the basin floor

Headward erosion

Basis of a rill, gully, and valley formaton and extension Upper perimeter of valley is a line where the gentle slope of an interfluve changes to the steeper side of a valley side Overland flow from the interfluve drops abruptly over this slope break Fast moving water tends to undercut the rim of the interfluve, weakening it and causing a small amount of material to collapse Result is a decrease in interfluve areas and a corresponding increase in valley area As the overland flow of the interfluve becomes part of the streamflow of the valley there is a distinct extension of rolls and gullies into the drainage divide of the interfluve - a headward extension of the valley

Soil and regolith in deserts

Covering of soil and regolith thin or absent in deserts Exposes bedrock to weathering and erosion and contributes to the stark, rugged, rocky terrain Soil creep is a relatively minor phenomenon on most desert slopes

Subsequent streams

Develop along zones of structural weakness Trend at right angles to other drainage channels

Trellis pattern

Develops as a response to underlying structural control - alternating bands of tilted hard and soft strata Long parallel streams are linked by shirt, right-angled segments Ridge and valley section of Appalachian Mountains and Ouachita Mountains

Differential weathering and erosion in deserts

Differential weathering and erosion produces differences in slope and shape of the resulting landform Mark of differential weathering most striking in desert b/c of lack of plant coverage Rocks resistant to erosion form cliffs, pinnacles, spires, and sharp crests Softer rocks wet more rapidly - gentler slopes Common in sedimentary landscapes

Streamload has 3 components

Dissolved load Suspended load Bedload

Stream Rejuventation

Drop in sea level or tectonic uplift can rejuvenate streams in an area by increasing their gradients which causes the stream to flow faster, providing renewed energy for downcutting

Erosion by streamflow

Erosion and transportation ability enhanced by increased volume and velocity of water Also enhanced by abrasive 'tools' that pick up and carry material (i.e. rock fragments) Rock fragments become smaller and rounder from frequent collisions Chemical action in streamflow Chemical weathering processes help erode through corrosion (dissolution of soluble rock by water) Erosive effectiveness determined by speed and turbulence of the flow and the resistance of the bedrock Flow speed governed by gradient (slope angle), shape of channel (the narrower the channel the faster the flow), and the volume of water (more water = higher speed) Degree of turbulence determined by flow speed (faster flows more turbulent) and the roughness of the stream channel (irregular channel increases turbulence)

Superimposed stream

Existed when the landscape was higher but this older landscape has since eroded away Original drainage pattern incised into underlying rocks with different structure

Saline lakes

Few desert lakes Smaller ones product of subsurface structural conditions that provide water from a permanent stream or exotic streams or from streams from nearby mountains Saline lakes - high rates of evaporation relative to the inflow and or basins or interior drainage lead to the accumulation of dissolved salts Many large lakes are the remains of larger bodies of water formed from wetter previous climates

Suspended load

Fine particles of clay and silt carried in suspension, moving along with the water without ever touching the streambed

Nature levees

Floodplain slightly higher along the banks of the stream channel than elsewhere As the stream overflows during a flood friction with the floodplain surface slows the current when it leaves its normal channel Causes deposition to take place along the margins of the main channel producing natural levees on each side of the stream Natural levees merge outwardly and almost imperceptibly with the less well-drained lower portions of the floodplain known as backswamps Sometimes tributary stream entering a floodplain cannot flow directly into the main channel because it encounters prominent natural levees Tributary then flows down-valley in the backswamp zone running parallel to the main stream until it finds an entrance - yazoo stream

Erosion by Overland flow

Fluvial erosion begins when rain starts to fall Collection of raindrops with ground is strong enough to blast fine soil particles up and out (splash erosion) On sloping ground, particles move downhill Much of water infiltrates the soil (little runoff) Water not absorbed by soil moves across surface as a thin sheet, transporting loosened material (sheet erosion) As overland flow moves downslope, its volume increases, resulting in turbulence that breaks up the sheet flow into tiny channels called rills Picks up more material (rill erosion) Rills coalesce into fewer and larger channels called gullies (gully erosion) As gullies get larger and larger they become incoperated into drainage systems and the flow changes from overland flow to stream flow

Floodplain landforms

Frequent shifting of stream meanders produces an increasingly broad flattish valley floor largely covered with alluvium left by periodic floods At any given time, a stream is only likely to occupy a small portion of the flatland During periods of flood flow, the entire floor may be flooded Valley bottom = floodplain Outer edges of the floodplain bounded by an increase in slope sometimes marking the outer limit of lateral erosion and undercutting where the flat terrain abruptly changes to a line of bluffs

Channel cross section

Friction along bottom and sides of channel causes water to move most slowly there and faster in the center of the stream Amount of friction determined by width and depth of the channel and the roughness of the surface Shallow channel with rough bottom has greater retarding effect on streamflow than a deep, smooth-bottom one

Turbulence

General downstream movement interrupted by irregularities in the direction and the speed of water Produce momentary currents that can move in any direction including upward Caused partly by friction, partly by the internal shearing stresses between currents within the flow and partly by surface irregularities in the channel Faster streams more turbulent Eddies and whirlpools results of turbulence Creates frictional stress that dissipates much of the stream's energy, decreasing the amount of energy available for erosion

Pediment

Gently inclined bedrock platform Residual surface left by weathering and removal of rock rather than the deposition Extends outward from mountain front Some pediments may be the result of deep subsurface weathering After overlain weathered material is removed by erosion a flat or gently sloping bedrock surface remains Other pediments formed as consequence of detachment faulting in areas undergoing tectonic extension whereby blocks of crust are displaced along nearly horizontal fault planes

Sand in deserts

High proporation of sand has three important influences on topographic development A sandy cover allows water to infiltrate the ground and thereby reduces runoff by way of both streams and overland flow Sand is readily moved by heavy rains Sand can be transported and redeposited by wind

Wind in desert

High winds characteristic of most deserts

Interfluve

Higher land above valley walls that separates adajcent valleys Some consist of ridgetops or mountain crests Others broad and flattish divides between drainage systems

Stream terraces

If a stream is occupied by a broad floodplain prior to rejuvenation, renewed downcutting the stream carves a new valley floor The old floodplain becomes an abandoned stretch of flat land overlooking the new valley - stream terrace Often come in pairs

Stream orders

In drainage basin, small streams come together to form larger ones Stream order refers to arrangement of all streams within a watershed Average stream length generally increases with increasing order Average watershed area generally increases with increasing order Average stream gradient (elevation change over a given distance) decreases with increasing order

Measuring streamflow

Influenced by local factors (i.e. climate and area of drainage) Data gathered from a network of stream gages

Residual surfaces and features

Inselbergs - steep-sided mountains or ridges Island mountains) Bornhardt - composed of highly resistant rick and has rounded form Differential weathering and erosion lower surrounding terrain and leave resistant bornhardt standing high

Meandering channels

Intricate patterns of smooth curves Serpentine course forms tightly curves loops Occurs where land is flat and gradient is low Tend to shift down-valley producing rapid changes in the channel

Vegetation in deserts

Lack of continuous cover of vegetation Widely spaced shrubs or sparse grass Provides little protection from the force of raindrops and inadequately bind surface material with roots making it easier to transport material during rainfall The less vegetation a desert has the greater the rate of weathering

Three geomorphic factors show how streams shape valleys

Length of geologic time - countless repetitions of movement of water Role of mass wasting in moving weathered rock down to valleys Effectiveness of floods

Transportation

Load carried by overland flow likely to be small relative to streamflow Eventually material reaches valley bottom where it is added to the material contributed by mass wasting to constitute the stream load

Graded streams

Longitudinal profile of a stream is restricted by base level but the profile at any given time depends on a number of factors Stream has steepest gradient near top and gentler toward the mouth In long term stream has a tendency to approach a dynamic equilibrium - channel slope adjusts, changing the water velocity, such that the amount of sediment entering a stretch of the stream is equal to the amount exiting

Stream capacity

Measure of amount of solid material a stream has the potential to transport normally expressed as the volume of material passing a given point in the stream channel during a given time interval Varies over time Depends on fluctuation in volume in flow speed as well as characteristics of the load

Stream competence

Measure of the particle size a stream can transport expressed by the diameter of the largest particles the stream can move Depends on flow speed Flow speed doubles - the size of the largest movable particle increases fourfold (2^2 = 4x)

Ephemeral streams

More than 99% of rivers in desert are ephemeral Carry water only seasonally or after rainstorm Dry beds of ephermeral streams have flat floors, sandy bottoms, and steep sides

Cuttoff meanders

Most conspicuous feature of floodplain is the meandering channel of its river Often a meander is bypassed as the stream channel shifts by lateral erosion, cuts a new channel across its neck, and starts meandering again, leaving the old meander loop as a cutoff meander The cutoff portion of the channel may remain filled with water for a period of time as an oxbow lake Eventually dry up leaving meander scars

Floodplains

Most prominent deposition landscape A low-lying, nearly flat alluvial valley floor that is periodically inundated with floodwaters Frequently form where a meandering stream flows across a wide, nearly level valley floor

Stream discharge

Most streams have variable flow regimes with pronounced fluctuations in discharge (volume of flow per unit time) Q = wdv w = width of channel d = depth of channel v = velocity of stream Inceases during a flood Speed of flow increases - competence of stream increases

Wind

Motion of air passing over the ground is similar to that of water flowing over a streambed - thin layer right as ground surface has wind speed of zero but increases with distance above the ground Wind turbulence caused from different layers of air moving at different speeds and from warming from below that causes air to expand and rise

Rainfall in deserts

Much of rain comes from intense convective thunderstorms (results in high and rapid runoff) Fluvial erosion and deposition are sporadic and rare but remarkably effective and conspicuous

Braided channels

Multiple interwoven channels separated by low bars or islands of sand, gravel, and debris Very flat stream channel with heavy sediment load Regions with prominent dry seasons and periods of low stream discharge

Fluvial Erosion in Aris Lands

Occurs in small portion of year Happens rapidly and effectively Large expanses of exposed bedrock are common - mechanically weatheres and eroded by running water, leaving steep, rugged, rocky surfaces Flash floods and debris flows

Centripetal pattern

Opposite of radial Associated with streams converging in a basin

Exotic streams

Permanent streams in dry lands are few Exotic streams - sustained by water that originates outside of the desert Water comes from an adjacent wetter areas or higher mountain area Ex.) Nile River - Flow of exotic rivers diminishes downstream b.c water seeps into the riverbed, evaporates, or is diverted for irrigation

Stream capture

Portion of the drainage basin of one stream is diverted into the basin of another stream by natural processes Relatively uncommon in nature

Valley

Portion of the terrain in which a drainage system is clearly established Includes the valley bottom and valley walls Upper limit conceptualized as a lip at the top of the valley walls above which drainage channels are indistinct or absent

Flood recurrence intervals

Probability of a given sized flood occurring

Annular pattern

Ring-shaped annular drainage pattern Can develop on a dome or in a basin where erosion has exposed alternating concentric bands of tilted hard and soft rock Principal streams follow curving courses on softer material occasionally breaking through harder layers in short right angled segments

Running water in waterless regions

Running water is b far the most important external agent of landform development Erosional and depositional work of running water influences the shape of the terrain surface almost everywhere outside of areas of extensive sand accumulation Intensity and presence of impermeable surfaces produces abrupt runoff Steep gradients of mountain streams increase the capacity of these streams for carrying large loads, but the flow of mountain streams in arid lands is sporadic At any given time, large amounts of alluvium sit at rest in the dry streambed of a desert mountain, awaiting the net flow Most resistant strata stands out as caprocks and cliff faces Where slopes are gentle in arid land, stream rapidly become choked with sediment as a brief flood subsides

Bedload

Sand, gravel, and larger rock fragments Smaller particles moved with general streamflow in a series of jumps/bounces (saltation) Coarser pieces moved by traction (riding or sliding along streambed) Moved spasmodically - debris transported some distance, is dropped, and picked up later and carried further

Base level

Stream excavates its valley by eroding the channel bed If only downcutting involved, the resulting valley would be a narrow steep-sided gourge Lower limit to how much downcutting a stream can do - base level Base level is an imaginary surface extending beneath the continents from sea level at the coasts Sea level is an absolute or ultimate base level Local or temporary base levels for particular streams or sections of streams No tributary can cut deeper than its level of confluence with the higher-=order stream it joins so the level of their junction is a local base level for the tributary Lake can also serve as a temporary base level for the streams that flow into it Some valleys below sea level and can produce a temporary base level lower than the ultimate base level Can occur because the stream does not reach the ocean but terminates in an inland basin

Alluvium

Stream-deposited sediment Deposits include all sizes of rock debris Typically smooth and round due to battering of rock Often display distinct strata layers Often sorted - consist of rocks of just about the same size Occurs when speed of water flow diminishes Heaviest rocks deposited first

Davis's Geomorphic Cycle

Structure - type and arrangement of underlying rocks and surface materials Process - internal and external process that shaped landforms Stage - length of time of process Development of landforms has several stages: ○ Youth - Initial flat surfaces is dissected by streams, which begin to incise deep, narrow, steep-sided, V-shaped valleys separated by flattish interfluves. Streams flow rapidly and are marked by waterfalls and rapids ○ Maturity - Streams approach an equilibirum condition having worn away the falls and rapids and developed smooth profiles. Stream gradient is reduced. Streams meander and floodplains form. Drainage system expands, dissecting all of the interfluves. ○ Old age - Erosion reduces the entire landscape to near base level. Region is dominated by extensive floodplains over which a few major stream meander broadly and slowly. Leave flat, featureless landscape with minimal relief. ○ Rejuvenation - Regional uplift creates new period of downcutting and a restart in the cycle.

Captor stream

The stream that breaks through the drainage divide and overtakes the other stream

Captured stream

The upper part of the stream overtaken by the captor stream

Delta formation

Valley lengthened at its seaward end by deposition Flowing water slows down whenever it enters the quiet water of a lake or ocean and deposits its load Most of this debris is dropped right at the mouth of the river in a landform called a delta Stream slows down losing competence and capacity and drops much of its load which partially blocks the channels and forces the stream to seek another path Deltas consist of a maze of roughly parallel channels called distributaties where water flows slowly toward the sea Coarser sediments tend to be deposited immediately where the stream enters the water in sloping foreset beds Forset beds become covered with thin horizontal topset beds during floods The finest sediments settle in bottom set beds on the ocean floor beyond the above water portion of the delta Rich alluvial sediments and water favor vegetation which provides a base for further expansion of the delta Stream valley extends downstream

Knickpoint migration

Waterfalls and rapids often found in valleys where downcutting is prominent Occurs in steeper sections of the channel Faster more turbulent flow intensifies erosion Irregularities in channel called knickpoints Result of abrupt changes in bedrock resistance The more resistant material inhibits downcutting and as water plunges over the waterfall or rapids, the increased speed tends to scour the channel above and along the knickpoint and fill the channel immediately downstream Intensified action erodes the harder material so the position of the knickpoint migrates upstream with a successively lower profile until it finally disappears and the channel gradient is smoothed Knickpoint migration rapid is berock is made of soft sediments

Deflation

When loose particles are blown through the air or along the ground they are shifted by deflation Blowout - shallow depression from which an abundance of find material has been deflated

Valley deepening

Whenever there is rapid speed or relatively large volume, stream expends most of energy downcutting Lowering of the streambed involves the hydraulic power of moving water, the lifting capabilities of turbulent flow, the abrasive effect of the stream's bedload as it rolls, slides, and bounces along the channel Most prevalent in the upper reaches of a stream where the gradient is steep and the valley is narrow Produces a deep valley with steep sides and a V-shaped cross section

Valley Widening

Where a stream gradient is steep and the channel is well above the local base level, downcutting is usually the dominant activity - valley widening likely to be slow Downcutting diminishes with time as the stream gradient is reduced or wherever the stream course flows down a gentle slope Streams energy diverted into a meandering flow pattern As main flow of current flows from one side to other, lateral erosion begins and erosion on the outside of the curves begins Alluvium is deposited on the inside of the curves forming a point bar where the speed is the slowest Channel shifts position often so undercutting is not concentrated in just a few locations - over long period of time most parts of valley sides are undercut Mass wasting will wear back valley walls as valley floor widens through lateral erosion

Ephemeral streams

carry water only during and immediately after a rain

Stream

channeled flow of water

Streamflow

channeled movement of water along a valley bottom

Perennial streams

permamnent

Ventifacts

rocks facested by such "sandblasting

Overland flow

unchanneled downslope movement of surface water

Second order stream

where first order streams unite

Third order stream

where second order streams unite