Gr.11 Geomorphology 🌍 Flashcards
What is topography?
The shape or relief of the land
What does the structure of rocks determine ?
The type of landforms and therefore the landscape of an area
What are horizontal rock layers called?
Strata/ stratified rock
What are bedding planes?
The planes separating horizontal rock layers.
What is the difference between exogenic forces and endogenic forces?
Exogenic forces: originate at the earth’s surface and decrease relief by, e.g. weathering and erosion.
Endogenic forces: originate within the earth’s surface and increase the relief, e.g. uplift
What does it mean if rock is uniformly resistant to erosion?
Rocks erode at the same rate.
What are 4 horizontally layered rock formations?
Hilly landscapes
Basaltic plateaus
Canyons
Karoo landscape
Which is more resistant: dolerite or basalt?
Why?
Dolerite. It cools slowly underground. Basalt cools faster on the earth’s surface
What are the 2 types of hilly landscapes that may form?
Series of rounded slopes
Hills with narrow gullies and sharp ridges (called badlands)
What causes rounded slopes? Give an example
Humid climates: sheet wash occurs and removes the surface material.
Eg. Valley of 1000 Hills, KwaZulu-Natal
What is sheet wash?
Gushing run-off
What causes badlands? Give an example
Arid regions: sheet wash washes over slopes with little/ no vegetation. Erosion takes place quickly.
E.g. Death Valley, California
What is a basaltic plateau?
A lava plateau with steep cliffs.
Give an example of a basaltic plateau
The Drakensberg
What causes a basaltic plateau to form?
Upward movement of the earth’s crust
Or fissures forming and magma welling up to surface over a long time
How do basaltic plateaus erode?
Vertical joints and cracks in the basalt erode to from deep cliffs
Why does a plateau have a flat top?
Lava pours onto the surface of the earth. This forms a hard cap rock which is uniformly resistant to erosion.
What is another name for a canyon?
A gorge
How does erosion take place in a canyon landscape?
Water finds weak places in layers and erodes vertically. The more resistant the layers, the steeper the slopes.
How do canyon landscapes differ in different climates?
Dry regions: steep, rugged, cliff-like slopes
Wet regions: hilly with more vegetation
Give an example of a canyon landscape
Fish River Canyon, Blyde River Canyon, Grand Canyon
Decide into resistant and less resistant to erosion:
Sandstone, shale, clay, granite, limestone, quartzite
Resistant: sandstone, granite, quartzite
Less resistant: shale, clay, limestone
Out of what do Karoo landscapes develop?
Canyon landscapes
Describe the rock in a Karoo landscape
Resistant hard layer (sill) such as dolerite on top of layers of sandstone and softer shale. Flat topped hills and wide, flat plains
What is a mesa?
A flat-topped table mountain wider than it is high
What is a butte?
A flat-topped hill higher than it is wode
What is a pointed butte?
A narrow hill with a sharp peak
What is a conical hill?
A small, pointed hill
Know how to draw and label a mesa, butte etc. 🌻On diagram sheet
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Who “discovered” scarp retreat?
King
What are 2 other names for scarp retreat?
Parallel retreat/ scarp recession
Where does scarp retreat occur?
In semi-arid regions
What is scarp retreat?
Initially a river erodes into an uplifted landmass. As back washing occurs, the landform retreats on itself. This occurs with stratified rock where the layers of rock are of a different resistance to the cap rock. The pediment becomes a large, flat pediplane.
Who “discovered” slope decline?
Davis
Where does slope decline occur?
In humid climates
What is slope decline?
Rivers erode into uplifted landmasses to form steep slopes. As water rushes down the slope, it becomes less steep until it’s almost flat (peneplane). The upper convex slope becomes concave.
Who “discovered” slope replacement ?
Penck
What is slope replacement?
Uniform rock with equal weathering over the slope. Scree/talus accumulates at the base of the cliff. Slope becomes gentler
How can a hilly landscape be useful to people?
Humid: contour farming on slopes
Arid: no agricultural value
How can a basaltic plateau be useful to people?
Tourism
On Deccan plateau: farming on fertile (basalt) soil
How can a canyon landscape be useful to people?
Tourism- hiking , photography, canoeing
How can a Karoo landscape be useful to people?
Sheep farming. Tourism.
Know how to label a laccolith, dyke, batholith etc.
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What is a batholith ?
A large, dome-shaped intrusion with no bedding planes that occurs deep within the earth
What is a laccolith ?
Smaller, mushroom-shaped intrusions connected by a pipe, causing the overlying sedimentary strata to dome upwards.
What is a lopolith?
Saucer-shaped intrusion causing the sedimentary layers beneath it to bend downwards
What are dykes?
Vertical sheets of dolerite that have intruded between vertical cracks in sedimentary rock.
What are sills?
Horizontal layers of dolerite that have intruded between the bedding plane and sedimentary layers.
How does a granite dome form?
Igneous intrusions (batholiths) are exposed to the earth’s surface when the surface material is removed by erosion before chemical weathering takes place below the surface.
How do granite domes erode?
Exfoliation occurs. Sheets peel off in layers due to contraction and expansion along pressure joints.
When will a batholith become a tor?
The surface above the batholith erodes slower than the rate of chemical weathering that breaks down the rock underneath the ground.
What will happen if the underground chemical weathering of a batholith is too rapid?
Only a pile of loose rocks will remain
What are the 4 slope elements?
Crest
Freeface/ scarp
Talus/ scree/ debris slope
Pediment
Describe a crest?
The convex-shaped slope. It has a thin covering of soil. Soil creep takes place here.
Describe a freeface/ scarp?
This is more than 80 degrees, so it’s almost vertical. Rock is exposed here and it’s too steep for any weathered material to accumulate on. It has joints and cracks that widen as it weathers.
Describe a talus/ scree slope?
Has a constant angle. Material accumulates at a similar rate as it is eroded away so this slope is never buried.
What is a crest?
The top of a slope
What is a freeface/scarp?
A cliff near the top of a slope.
What is a pediment?
The plain at the base of a slope
Know how to draw how a batholith becomes a granite dome/ tor. 🌻on diagram sheet
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Label contractual joints and pressure release joints on tor
How are homoclinal ridges classified?
According to the gradient at which the layer dips
the angle between the dip slope and the horizon
At what angle does a homoclinal ridge dip?
25-45 degrees
At what angle does a Cuesta dip?
10-25 degrees
At what angle does a hogsback ridge dip?
More than 45 degrees
Give an example of a hogsback ridge
Hogsback, Eastern Cape
Know how to draw a homoclinal ridge. 🌻 On diagram sheet
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How can areas with inclined strata be used by people?
Eroded dip slope (hard layers) can be used for forestry
Cuesta plains provide valuable agricultural soil
Underground water can be trapped in cuestas
Oil and gas can be trapped in cuestas
What is a syncline versus an anticline
A dip. An anticline is a peak. (Not definitions)
What is exfoliation?
When a granite dome becomes exposed, the extreme cooling and heating causes expansion and contraction of the rock. This causes the peeling of layers on the surface of the rock.
What is mass movement?
The movement of weathered materials down a slope
Put soil creep, landslides, mudflow, rock falls and solifluction in order of speed
Soil creep Solifluction (water-saturated soil) Landslides Mudflow Rock falls
What must one take into account when building on a slope? (4)
Slope angle, ecology, geology and rainfall of an area
What can be done to control mass movement? (7)
Vegetation maintained/ planted
Cuttings on the side of a mountain stabilised using concrete or wire mesh.
Stakes inserted into the slope
Drainage instituted
Development on slopes limited
Risk analysis and risk assessment-hazardous areas mapped
Arrangements for landslide disaster management
What are the 6 types of mass movement?
Soil creep, solifluction, landslides, rock falls, mud flows, slumps
Solifluction
A very slow down-slope movement of water-saturated soil.
Landslide
When a large mass of land breaks loose and plunges down a slope.
Rockfall
Very rapid movement of material on slopes exceeding 40 degrees
Mudflow
Stream of mud on steep slopes after heavy rain.
Soil creep
The slow, down-slope movement of soil.
Slumps
Slope failure caused by rotational movement
Where does soil creep occur?
A range of climates
Where does solifluction occur?
In regions where debris becomes saturated after heavy rain or in tundra regions when ground thaws in spring.
When do landslides occur?
Slopes exceeding 40 degrees with weathering, frost action or earthquakes.
When do mud flows occur?
On steep slopes in arid regions after heavy rain
Where do slumps occur?
In areas where softer materials overlie more resistant rocks
What are the effects of mass movement on the environment? (4)
Major factor in natural erosion
Landslides Block rivers, forming lakes
Landslides Destruction to vegetation and animal life
Landslides Flooding due to damming up of bodies of water
What are the effects of mass movement on people? (5)
Soil creep damages railroads, building structures and underground pipes.
Landslides damage structures and property. Real estate values are reduced in landslide-prone areas.
Landslides reduce productivity of agricultural lands.
Landslides interrupt transportation systems, causing a loss of industrial productivity
Road closures force road users to take detours
On which slope element do boulders and stones collect?
The pediment
How does an Atlantic air mass flow?
From the Antarctic towards the Equator
Describe the Benguela current
A very cold and very dry body of air
What is the main agent of erosion in a Karoo landscape?
Rain/rivers
How does water contribute to mudslides?
It adds weight and volume
