Fluvial Geomorphology
19th October
TERMINOLOGY:
Abrasion
Abrasion is a process of erosion which can happen in four different ways.
The first type of abrasion is caused by ice or glaciation. As a glacier
moves, it erodes away at the land surrounding the ice. This is a slow
process.
The second type of abrasion is caused by rivers. Flowing water hits the
channel walls and causes erosion. Pebbles or stones in the river also
cause erosion when they hit the channel walls.
The third type of abrasion is through the action of waves. As waves
break on the shore, the water, stones, and the energy of the waves
cause erosion.
The final type of abrasion is caused by wind. The wind can transport
sand and small stones, blowing them strongly against rocks and land.
Over time, this causes erosion as you can see in the picture.
Attrition
Attrition is an erosional process. Rocks and pebbles are carried in the flow of a river.
They repeatedly knock into each other, which causes the rocks to erode or to break.
As the rocks continue to collide, they erode more and more, getting smaller and
smaller until they are only sediment
Abrasion refers to the way in which the suspended load, transported by the flow
collides with the bed and bank.
Hydraulic action
Refers to the force of the water flow against the banks and bed. Sometimes the bank
becomes over saturated and just slumps into the river.
Confluence
Confluence of rivers is defined as a meeting point of two or more rivers. In other
words, it usually refers to the point where a tributary joins a major river, called the
mainstream
Watershed
a higher lying area that splits water basins (drainage basin)
Delta
wetlands that form as rivers empty their water and sediment into another body of
water
Alluvium
is one in which the bed and banks are made up of mobile sediment and/or soil.
,Illuvial fan
a triangle-shaped deposit of gravel, sand, and even smaller pieces of sediment,
such as silt.
Suspension -> solution -> traction -> saltation
Solution
minerals are dissolved in the water and carried along in solution.
This typically occurs in areas where the underlying bedrock is
limestone.
Suspension
fine light material is carried along in the water.
Saltation
small pebbles and stones are bounced along the riverbed.
Traction
large boulders and rocks are rolled along the riverbed.
Terms:
Oxbow lake
Delta
Flood
Mouth
Tributary
Origin
Meander
Alluvial fan
Waterfall
Fast/slow
Abrasion/attrition
Deposition
TRANSPORTATION:
Note:
Rivers need energy to transport material, and levels of energy change as the river
moves from source to mouth.
, When energy levels are very high, large rocks and boulders can be
transported. Energy levels are usually higher near a river's source when its
course is steep and its valley narrow. Energy levels rise even higher in times
of flood.
When energy levels are low, only small particles can be transported (if any).
Energy levels are lowest when velocity drops as a river enters a lake or sea
(at the mouth).
DRAINAGE PATTERNS:
What is a drainage pattern?
Stream channels create a variety of drainage patterns on the surface of
the Earth.
This network is visible on aerial photographs and satellite images.
Drainage patterns are responsible for the drainage run-off to the sea.
The pattern of streams and their tributaries is indicated on a topographic
map by means of blue lines.
By learning drainage patterns, one can learn about underlying structures
and rock types.
Dentric pattern
Most common stream patterns
Greek word = dendron meaning tree
Tributaries join at acute angles, like the branches of a tree
Where does dentric drainage develop?
Over uniform ricks of similar hardness, usually massive igneous rock, or sedimentary
rock.
The slope on which this stream pattern is found is usually uniform
Example in South Africa:
In mountainous terrain
The Cape Fold belt
Ariel sketch:
19th October
TERMINOLOGY:
Abrasion
Abrasion is a process of erosion which can happen in four different ways.
The first type of abrasion is caused by ice or glaciation. As a glacier
moves, it erodes away at the land surrounding the ice. This is a slow
process.
The second type of abrasion is caused by rivers. Flowing water hits the
channel walls and causes erosion. Pebbles or stones in the river also
cause erosion when they hit the channel walls.
The third type of abrasion is through the action of waves. As waves
break on the shore, the water, stones, and the energy of the waves
cause erosion.
The final type of abrasion is caused by wind. The wind can transport
sand and small stones, blowing them strongly against rocks and land.
Over time, this causes erosion as you can see in the picture.
Attrition
Attrition is an erosional process. Rocks and pebbles are carried in the flow of a river.
They repeatedly knock into each other, which causes the rocks to erode or to break.
As the rocks continue to collide, they erode more and more, getting smaller and
smaller until they are only sediment
Abrasion refers to the way in which the suspended load, transported by the flow
collides with the bed and bank.
Hydraulic action
Refers to the force of the water flow against the banks and bed. Sometimes the bank
becomes over saturated and just slumps into the river.
Confluence
Confluence of rivers is defined as a meeting point of two or more rivers. In other
words, it usually refers to the point where a tributary joins a major river, called the
mainstream
Watershed
a higher lying area that splits water basins (drainage basin)
Delta
wetlands that form as rivers empty their water and sediment into another body of
water
Alluvium
is one in which the bed and banks are made up of mobile sediment and/or soil.
,Illuvial fan
a triangle-shaped deposit of gravel, sand, and even smaller pieces of sediment,
such as silt.
Suspension -> solution -> traction -> saltation
Solution
minerals are dissolved in the water and carried along in solution.
This typically occurs in areas where the underlying bedrock is
limestone.
Suspension
fine light material is carried along in the water.
Saltation
small pebbles and stones are bounced along the riverbed.
Traction
large boulders and rocks are rolled along the riverbed.
Terms:
Oxbow lake
Delta
Flood
Mouth
Tributary
Origin
Meander
Alluvial fan
Waterfall
Fast/slow
Abrasion/attrition
Deposition
TRANSPORTATION:
Note:
Rivers need energy to transport material, and levels of energy change as the river
moves from source to mouth.
, When energy levels are very high, large rocks and boulders can be
transported. Energy levels are usually higher near a river's source when its
course is steep and its valley narrow. Energy levels rise even higher in times
of flood.
When energy levels are low, only small particles can be transported (if any).
Energy levels are lowest when velocity drops as a river enters a lake or sea
(at the mouth).
DRAINAGE PATTERNS:
What is a drainage pattern?
Stream channels create a variety of drainage patterns on the surface of
the Earth.
This network is visible on aerial photographs and satellite images.
Drainage patterns are responsible for the drainage run-off to the sea.
The pattern of streams and their tributaries is indicated on a topographic
map by means of blue lines.
By learning drainage patterns, one can learn about underlying structures
and rock types.
Dentric pattern
Most common stream patterns
Greek word = dendron meaning tree
Tributaries join at acute angles, like the branches of a tree
Where does dentric drainage develop?
Over uniform ricks of similar hardness, usually massive igneous rock, or sedimentary
rock.
The slope on which this stream pattern is found is usually uniform
Example in South Africa:
In mountainous terrain
The Cape Fold belt
Ariel sketch:
