Tropical landforms Flashcards
(14 cards)
Hydrolysis
- Chemical weathering
- Water reacting with feldspar (granite) to produce kaolin
Exfoliation
- Large diurnal temperature differences
- Rocks expand during day and contract during as they cool
- Creates stress and cracks on outer layers of rock
What is a tropical weathering profile?
Three main zones:
Residual soil – leached by water (eluviation), rich in clays and oxides
Weathered rock (saprolite) – permeable, contains unweathered corestones
Unweathered bedrock – feldspars/micas mostly intact
Inselbergs
Steep-sided residual hills rising from tropical plains
Inselbergs include:
- Hills of sedimentary rocks
- Castle kopjes/ Tors of residual core stones
- Bornhardts
Tors/ Castle kopjes
- Tors are ridges or piles of rounded weathered boulders that have their bases in the bedrock and are surrounded by weathered debris
- Formed by chemical weathering of the rock along joints and bedding planes beneath the surface
Inselberg formation
Two main theories:
Two-stage model:
- Deep weathering forms soft regolith
- Regolith is later stripped, leaving resistant rock
Simultaneous weathering and erosion: - Both processes happen together depending on local conditions
Bornhardts
- Large, dome-shaped inselberg
- Steep vertical slopes and a convex top
- Little vegetation
- At least 100 feet high
- Common in granite plateaux of African savannas and humid tropics
- Formed in igneous or metamorphic rocks (esp. granite)
- Can evolve into castle kopjes (rocky residual hills
Bornhardt formation
Main formation theories:
- gradual deep chemical weathering + erosion strips away weathered material+ uplift
- Stripping/ exhumation theory – removal of regolith reveals unweathered rock
- parallel retreat theory – valley sides erode, leaving isolated hills
- Bornhardts have different processes → same landform
Cockpit karst
Cockpit karst is a tropical landscape with star shaped depressions and smooth conical hills
- eg. Cockpit Country, Jamaica
- Up to 100 metres deep
- Forms in areas with high tectonic uplift and intense river erosion
Formation processes include:
- Solution along joints and stream networks
- Cave collapse theory: caves migrate upward and collapse, raising floors and deepening depressions
Cone karst
- Cone karst – A subtype of cockpit karst with limestone conical hills
- eg. Gunung Sewu, Java, Indonesia
- Lots of vegetation
- around 100m tall
Tower karst
Tower karst consists of steep-sided, isolated limestone blocks rising from lowland plains.
eg. Guanxi, China / Phang Nga, Thailand
- Heights vary from a 30-330m high
- Iregular and uneven, bare rock, too steep for vegetation
Forms in areas with:
- Limited tectonic uplift
- High water table
- Limestone close to other rock types
Processes include:
- Lateral erosion by rivers
- Differential solution and erosion along lines of weakness
- Possibly formed by the retreat of cockpit karst slopes
China karst
- large amounts of rainfall – over 2000 millimetres per
year - long periods of slow uplift exposing broad, plateaus
- thick beds of limestone, up to 3000 metres deep
Underground features
- Caves and tunnels formed by carbonation-solution and river erosion in limestone.
- Carbonation dissolves calcium carbonate, which is later re-deposited.
- Stalactites hang from cave ceilings (formed from slow-dripping water)
- Stalagmites grow from the cave floor (formed from faster-dripping water)
- Deposition is slow – about 1 mm every 100 years
- Precipitation of dissolved calcium carbonate from dripping water
- Lower water table causes deeper depressions
Blue hole, Bahamas
Blue holes are deep, circular, water-filled sinkholes formed in limestone by carbonation solution and later submerged by rising sea levels.
- Formed during times of lower sea level (~130 m lower, 10,000 years ago)
- As sea level rose, limestone caves and sinks were flooded
- Some are inland, others open into the sea or reefs
- Over 200m deep in the Bahamas
- Major tourist attraction
