Fluvial Landform (13. FloodPlain)

                                                                                                                                                      Back to Fluvial Landform

•  A floodplain is 

                            Land adjacent to a stream / river

                            Near a river/stream which floods when the water level reaches flood stage.

• That stretches from the banks of its channel.

• Flood plains are made by a meander.

• When a river breaks its banks & floods, it leaves behind layers of rock and mud.

• Floodplains generally contain unconsolidated sediments.

• Extending below the bed of the stream.

• These are accumulations of :

                                    sand                      gravel

                                    loam                      silt/clay

• The floodplain during its formation is marked by meandering or an astomotic streams:

                                   ox-bow lakes

                                   bayous

                                   marshes/stagnant pools

Historically, many towns have been built on floodplains, where they are highly susceptible to flooding, for a number of reasons:

• access to fresh water;

• the fertility of floodplain land for farming;

• cheap transportation, via rivers and railroads, which often followed rivers;

• ease of development of flat land

Fluvial Landform (12.Exhumed river Channel )

                                                                                                                                                      Back to Fluvial Landform

• An exhumed river channel is a ridge of sandstone.

• The softer flood plain mudstone is eroded away.

• The process :

                     1. The deposition of sand within a river channel & mud on the adjacent floodplain.
                     2. Eventually the channel is abandoned.
                     3. Over time becomes buried by flood deposits from other channels.
                    4. Because the sand is porous 
                    5. Groundwater flows more easily through the sand than through the mud of the floodplain deposits.

• Minerals can cement the grains together converting the loose sand into sandstone. 

• Millions of years later, erosion can remove the softer, less cemented mud stone.

• An exhumed river channel is a form of inverted relief.

• Exhumed channels are important indicators for ancient stream flow direction.

Fluvial Landform (11.Endorheic Basin )

                                                                                                                                                      Back to Fluvial Landform

Caspian Sea

• An endorheic basin is a closed drainage basin.

• That retains water.

• Allows no outflow to other external bodies of water, such as ;

                                   rivers

                                   oceans

• Water accrued in a drainage basin eventually flows out through rivers or streams.

• An endorheic basin, rain that falls within it does not flow out.

•  The bottom of such a basin is typically occupied by a salt lake or salt pan.

Great Salt Lake

• Endorheic water bodies include some of the largest lakes in the world, such as;

                      Aral Sea
                     Caspian Sea

• Endorheic lakes are bodies of water do not flow into the sea.

• Endorheic lakes are usually in the interior of a body mass, far from an ocean.

• Watersheds are often confined by natural geologic land formations .

• The inland water flows into dry watersheds .

• endorheic lakes are usually more sensitive to environmental pollutants inputs than water bodies that have access to oceans.

Uureg Nuur

examples:

• Lake Tanganyika in Africa.
• Lake Lahontan in North America.
• Salar de Atacama, in the Atacama Desert, Chile.
• Lake Trasimeno, in Italy.
• Lake Velence, in Hungary.
• Bolsón de Mapimí, in northern Mexico.
• Willcox Playa of southern Arizona
• Qattara Depression, in Egypt.
• Chott Melrhir, in Algeria.

Wfm tarim basin

Fluvial Landform ( 10. Drainage Basin )

                                                                                                                                                      Back to Fluvial Landform 

• A drainage basin is land surface water from ;

                                               rain

                                               melting snow

                                               ice

• The waters join another waterbody, such as;

                                            river                                   lake

                                            reservoir                           estuary

                                            wetland                              sea

                                            ocean

• Drainage basin are called as;

                                         Catchment                             Catchment area

                                         Catchment basin                  Drainage area

                                         River basin                            Water basin

• In closed drainage basins converges to a single point inside the basin.

• It become permanent lake, dry lake.

• It includes streams & rivers.

• The drainage basin acts as a funnel.

Largest river basins

• The Amazon basin
• The River Plate basin
• The Congo basin
• The Nile basin
• The Mississippi basin

Endorheic drainage basins

• Inland basins ,do not drain to ocean.
• Around 18% of all land drains to lakes, seas/sinks.
• The largest drains;

                         Caspian Sea

                         Aral Sea

                         Great Basin,United States

                        Okavango River (Kalahari Basin)

                        African Great Lakes

Catchment Factors

1. Topography

•  Determines speed.
• Clearly rain falls in steep mountainous areas will reach the river faster than flat or gently sloping areas.

2.Shape 

• Contribute speed .
• A long thin catchment will take longer to drain than a circular catchment.

3.Size

• Determine amount of water reaching the river.

4.Soil type 

• Determine how much water reaches the river.
• Certain soil types such as;

                                            sandy soils

                                            clay 

5.Land use

• Contribute to the volume of water reaching the river, in a similar way.

Fluvial Landform ( 09.Cave )

                                                                                                                                                      Back to Fluvial Landform

Lava tube,Hawaii.

• A cave/cavern is a natural underground space.
• It is large enough for a human to enter.
• Caves form naturally by the weathering of rock extend deep underground.
• Cave refer to,such as;

                                       -sea caves

                                      -rock shelters

                                      -grottos.

• Caves are formed by;

                                 -A combination of chemical processes

                                 -Erosion from water

                                 -Tectonic forces

                                - Microorganisms

                                 -Pressure

                                 -Atmospheric influences

                                - Digging

• Most caves are formed in limestone by dissolution.

                 

Lechuguilla Cave, New Mexico

solutional caves

• Frequently occurring caves.
• Formed in rock.
• Soluble as;

                                              limestone                         chalk

                                             dolomite                            marble

                                              salt                                    gypsum

• Rock is dissolved by natural acid in groundwater.
• The largest & abundant solutional caves located in limestone.
• Limestone dissolves under the action of;

                                  -rainwater
                                  -groundwater charged with H₂CO₃ (carbonic acid)
                                  -naturally occurring organic acids

• The dissolution process  landform known as karst.
• characterized by sinkholes.
• Limestone caves are adorned with calcium carbonate.
• Slow precipitation. 

e.g.

        Lechuguilla Cave,New Mexico

        Carlsbad Cavern

Large sea cave, Santa Cruz Island, California

Primary caves

• Lava tubes formed volcanic activity.
• Lava flows downhill.
• The surface cools and solidifies.
• The hotter lava continues to flow under that crust.
• The liquid lava beneath the crust flows out, a hollow tube remains, thus forming a cavity.
•  Examples

                           Canary Islands, Hawaii

                           Kazumura Cave,Hilo

• Other caves formed through volcanic activity include;

                               -rift caves

                              -lava mold caves

                             -open vertical volcanic conduits

                             -inflationary caves

Ogof Craig a Ffynnon, South Wales.

Sea caves

• Found along coasts.
• Littoral caves formed by wave action.
• Some wave-cut caves are above sea level .
• In places such as;

                                   -Thailand's Phang Nga Bay

Erosional caves

• Formed by erosion.
• These can form in any type of rock.
• There must be some zone of weakness to guide the water,as a fault,joint.
• A sub type of the erosional cave is the wind/aeolian cave.

Fracture cave

• Glacier caves occur in ice & under glaciers.
• Formed by melting.
• Influenced by very slow flow of the ice.
• These are called ice caves.

Fracture caves

• Formed by layers of more soluble minerals.
• Dissolve out from between layers of less soluble rock.
• These rocks fracture & collapse in blocks of stone.

Talus caves 

• It called as talus.
• Openings between rocks.
• That fallen down into a pile at the bases of cliffs.

Anchialine caves 

• Usually in coastal areas.
• Containing a mixture of freshwater & saline water.
• Contain highly specialized and endemic fauna.

Branchwork caves

• They are made up of passages.
• That join downstream as tributaries.
• Formed near sinkholes 
• Converges into other higher order branches downstream.

Angular Network caves

• Formed by intersecting fissures of carbonate rock.
• that have fractures widened by chemical erosion.
• These fractures form high, narrow, straight passages.
• That persist in widespread closed loops.

Anastomotic caves

• Largely resemble surface braided streams.
• Their passages separating.
• They usually form one bed/ structure.
• Only rarely cross into upper or lower beds.

Spongework caves

• Formed by solution cavities are joined by mixing of chemically diverse water.
• The cavities form a pattern.
• That is three-dimensional & random, resembling a sponge.

Ramiform caves

• Form as ;

                        irregular large rooms

                        galleries

                        passages

• These randomized three-dimensional rooms
• Form from a rising water table.
• Erodes the carbonate rock with hydrogen-sulfide enriched water.

Pit caves 

• Called as;

                       vertical caves

                       potholes cave

• Consist of a vertical shaft
• They may or may not be associated with one of the above structural patterns.

World's five longest surveyed caves

1. Mammoth Cave, Kentucky, USA
2. Sistema Sac Actun/Sistema Dos Ojos, Mexico
3. Jewel Cave, South Dakota, USA
4. Sistema Ox Bel Ha, Mexico
5. Optymistychna Cave, Ukraine