Geomorphology Flashcards
What can rocks be in? (3)
Horizontal strata (layers)
Inclined strata
Massive igneous
What are the horizontal strata?
Hilly landscapes
Basaltic plateau/lava plateau
Canyon landscape
Karoo landscape
How are hilly landscapes formed?
In HUMID regions
Mass wasting and sheet erosion cause gentle slopes and a hilly landscape forms.
SUITABLE FOR FARMING
Chemical weathering has taken place forming thick grained soil.
E.g. valley of a thousand hills
In ARID regions
Only mechanical weathering, so soil is thin and coarse-grained and the slopes are rugged and steep.
LITTLE FARMING takes place
How are Basaltic plateau/lava plateau formed?
Drakensburg is an e.g. of a landscape where lava poured through long narrow cracks and layers built up to form a plateau.
The strata are horizontal and uniformly resistant.
GOOD for TOURISM, NOT farming
How are canyon landscapes formed?
Horizontal strata of hard and soft layers erode at different rates.
The hard rocks results in steep slopes while less resistant rock forms more gentle slopes.
A plateau formed through tectonic uplift and rejuvenated rivers cut deep steep-sided valleys.
E.g. Grand Canyon, fish river
Uses:
DAMS,
not farming-too dry
Forms a barrier to transport routes
Tourist attraction
Hydro-electric
How are Karoo landscapes formed?
Valleys widen through backwashing and scarp retreat.
The plateau is protected by a resistant hard layer.
Rivers erode weaknesses vertically to form canyons.
Scarp retreat or backwasting is lateral erosion where rocks of differing resistance maintain their angles. This results in mesas and buttes forming. The hard cap rock forms a flat, protective layer.
Once this layer is removed a conical hill forms.
When does a homoclinal terrain develop?
If the strata of alternating resistance to erosion have been uplifted and tilted then a homoclinal terrain develops.
The alternating strata DIP by the SAME DEGREE and in the SAME DIRECTION.
Describe homoclinal ridges and hogsbacks and cuestas.
A group of slopes is referred to homoclinal ridges but the STEEPLY tilted strata form HOGSBACKS while the GENTLY tilted strata are called CUESTAS.
…..
How are basins and domes formed?
When layers bend they form anticlines and synclines.
When these become eroded they can result in basins and domes forming.
Uses of basins and domes:
Hard layers form less fertile soil
Slopes used for forestry
Cuesta plains agriculture
Cuestas can trap water that is underground, and oil and gas
What are massive igneous rocks?
Rocks with no layers, usually igneous intrusions like batholiths, laccoliths and lapaliths.
What happens when magma cools?
It forms joints and cracks.
Along these, erosion takes place.
What is exfoliation?
When the outer layer peels away due to extreme heating and cooling.
When does a Granite dome form?
When a batholith becomes exposed.
Batholith
Largest
Granite
No apparent base
Laccolith
Mushroom shaped
Pushes areas of strata up
Lopolith
Saucer shaped (inverted mushroom)
Layers cannot support weight
Dyke
Wall like vertical intrusion
Sill
Horizontal intrusion and spreads between layers
Pipe
Chimney shaped
What is a tor?
A pile of unconsolidated core stones-often granite.
What’s the most popular theory for tor formation?
While the rock was still below earths surface, chemical weathering took place along joints.
When the rock became exposed eventually, the weathered material would be eroded away leaving the core stones behind.
If joints widely spaced, core stones would be large.
Concave
Cave in
Convex
Rounded
Crest
Convex top of the slope
Soil creep
Cliff/scarp
Almost vertical
Vertical too steep for material to collect rockfall
Talus/scree
Weathered debris collects at a constant angle.
Disposition.
Pediment
Plain base of the slope
Concave
Thin sails
Knickpoint
Distinct change in the angle of the slope
Parallel slope retreat
Slope angle and length remain constant as slope retreats parallel to itself for each part of the slope.
The pediment increases in length over time (backwasting)
Mass movement
Movement of weathered material down a slope under force of gravity
Whether the movement is gradual or sudden is determined by (3)
Gradient of slope
Weight of debris
Presence of any lubricating moisture
What can trigger mass movement? (5)
Earthquakes
Modification of slopes by humans
Undercutting of cliffs by waves or rivers
Heavy rain
Volcanic activity
Which slopes are most unstable?
Slopes that are
Saturated
Sediment
Dipping downslope
Extensive development
Little vegetation
Permeability
The ability of a rock to allow water to pass
Types of mass movement? (6)
Soil creep
Solifluction
Landslides
Rock falls
Mudflow
Slumps
Soil creep
Most gradual
Rate of 1mm/year
Solifluction
Soil slides on water-saturated ground.
5-20cm/year
Occurs after heavy rain or in tundra region after spring thaw.
Landslides
Sudden moments of large land masses break loose.
Often along fault zone.
Damage to roads, railways and dams.
Rock falls
Most rapid form of mass wasting
Slopes steeper than 40*
Rocks break loose from weathering, frost action and earthquakes.
Mudflow
Rapid
Streams of mud flow down steep slopes after heavy rain.
1km/hour
In arid regions after heavy rain
Slumps
Slopes failures caused by rotational movement.
Downward and outward
In areas where softer materials overlie more resistant rock.
Environmental impact of mass movement (4)
Natural erosion carrying materials from high to low ground.
Landslides block a river forming a lake or causing a flood.
Destruction of vegetation and animal life.
Landslides can travel far, getting bigger and picking up material along the way.
Human impact of mass movement (3)
Loss of life.
Damage to railroads, buildings and underground pipes-long term economic damage and loss of industrial productivity.
Reduces real estate value and causes road closures.
Minimising effects of mass movement (10)
Restrict activities along slopes.
Plant vegetation on slopes.
Engineering techniques to prevent landslides.
Safety nets to stop rockfalls.
Stabilising slopes by cutting and filling.
Remove excess water by drainage and runoff channeling structures.
Retaining walls.
Reduce deforestation.
Use rock bolts to fasten unstable rocks.
Gabions.
