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Factors Affecting Landform Development (SEASONALLY HUMID (MACRO (CLIMATE :…
Factors Affecting Landform Development
SEASONALLY HUMID
MACRO
CLIMATE
: Geomorphic Processes
Most developed in
Aw climates
w high annual rainfall totals of
800mm/yr
and high temps of
25°C
throughout the year → active carbonation-solution
Higher temperatures
↑ rate of decomposition of vegetation, increasing acidity of water underground and ↑ removal of limestone through carbonation
Intense rainstorms
facilitate slope wash processes (gullying action) and fluvial action (lateral erosion)
Seasonal migration of WT (due to rainfall seasonality in Aw & thus GW recharge) affects cockpit characteristics:
width & depth
Dry season
→ vertical deepening where WT is lower
Wet season
→ widening where WT is higher
Continual widening / deepening forms landforms w certain widths & depths but does NOT determine eventual landform type
Past climates
also influence karst development
TECTONIC UPLIFT
: Exposure of limestone rock
Responsible for uplift of limestone bed
:sunrise_over_mountains:
Guilin 320mya
Differential rates of tectonic uplift affects height of WT , nature of geomorphic processes at work and eventual landform formed
Is not a seasonal variation but a long phase of uplift
Rapid
tectonic uplift → rate of water recharge cannot keep up with pace →
low WT
→ gullying occurs frequently → downcutting occurs, dolines deepen → formation of
CK
Slow
tectonic uplift→ rate of water recharge keeps up →
high stable WT
at base level → limited downcutting → when doline floors reach base level, lateral erosion and slope retreat occurs → formation of
TK
Can also affect relief of areas by creating uplands/lowlands, causing WT height to vary with relief and thus type of karst formed
MESO
VEGETATION
Reliant on water availability from ppt totals
Presence of abundant decomposing vegetative matter in the tropics releases large amounts of biogenic CO2 that ↑ dissolution
LOCAL
LITHOLOGY
Rock composition
influences
rate of weathering
Pure limestone is weathered fast and results in vast landforms of easy surface lowering
Limestone w impurities leave a layer of clastic sediment, impeding surface lowering, favouring TK
Joint pattern
determines
location of cockpits
Where greatest dissolution & gullying occurs at areas of highest joint density, leaving unweathered limestones as hills
Doline distribution in CK is controlled by
spacing
and
density of joints
HYDROLOGY
Groundwater
: influences karst development through WT migration where weathering is more active around the the WT at the epiphreatic zone
Autogenic
water is enough for CK development but TK requires
large supply of water
of both auto (existing basin) and allogenic water to facilitate lateral erosion & isolation due to greater fluvial action & gullying
Type of
landform
: tectonic (rate) & hydrology (auto/allo)
Type of
specific features
on landform: climate (WT), lithology (joints) & hydrology
Scale of landscape dvlpmt is reliant on the interaction btwn tectonic, climate & local factors (lithology & hydrology)
Greatest scale of limestone dvlpmt is when limestone is of great thickness, high purity & highly jointed
PAST CLIMATES
: Coastal Karsts
Strong influence on coastal karst dvlpmt due to changes in sea level
Last glacial maximum of Pleistocene
: lowered sea level exposed limestone beds & allowed for karst formation (only during cool
glacial periods
where water froze to become ice)
Early Holocene
: rise in sea level submerged the karst landscape leaving only the karst hills visible above sea level (
interglacial period
)
Criteria:
Scale
climate macro scale & most imp factor in affecting vegetation (meso) and hydrology (local)
but macro factors only have a broad influence, eventual landform & characteristics depend on local factors
don't discuss local factors alone!
Time
: Past climates inactive dunes
Space
Humid vs arid
Relief: Lowlands, uplands, coastal
(include diagrams for landform essays!)
ARID / HYPER ARID
MACRO
TRADE WINDS
Forms both erosional and depositional landforms (yardangs , dunes and loess)
Unidirectional constant winds can promote continual development of landform
Especially strong trade winds in hyper arid or arid regions
CLIMATE
Lack of rainfall thus lack of soil moisture
High temperatures
LOCAL
SURFACE & LITHOLOGY
Erosion
Abundant supply of unconsolidated fine grained sediments due to lack of vegetation (promotes loess)
Important for
erosional
landforms as resistance of materials determine the rate of erosion and thus shape of landform
Constant supply of sands for abrasion
Deposition
Supply of sediments deposited determines size of landform
Coarse or fine sediments determines how far sediments are transported and type of landform
TOPOGRAPHY
Landforms formed by wind are usually on the
lowlands
, encouraging strong wind action
MESO
VEGETATION
Sparse vegetation due to lack of moisture, thus surface materials are loose and easily lifted by the winds
PAST CLIMATES
: Relic Dunes
Relic dunes were formed in glacial phases of the Pleistocene where strong trade winds dominated, accounting for large areal distribution of loess and dunes in areas of wetter conditions in the present
Holocene's wetter conditions ↑ vegetation growth and limited wind action and landform development
SEMI-ARID
MACRO
CLIMATE:
Rainfall
Regular, high intensity rainfall
Erosion
Forms rills & gullies due to erosive action of water
Promotes for some vegetation, but sparse and full intensity of rain reaches surface
Water > Wind action
due to presence of some vegetation but intense rainfall
Deposition
Regular rainfall encourages deposition through
wet deposition
, where fine silts are deposited due to raindrops (forms loess)
MESO
VEGETATION
Presence of scrubby vegetation
Erosion:
Surface vegetation protects loose fine materials from being lifted from the surface
Deposition:
Reduces wind velocities and acts as an obstacle for deposition (stabilizes dunes too)
LOCAL
SURFACE & LITHOLOGY
Erosion
Surface crust may form due to presence of rainfall (thus clay formed) which
impedes deflation
as loose materials at the surface may be bound to it
Important for
erosional
landforms as resistance of materials determine the rate of erosion and thus shape of landform
Constant supply of sands for abrasion
For fluvial erosion: thin regolith and surface crusting discourages infiltration and large surface runoff generated causing easy erosion of surface to form rills
Deposition
Supply of sediments deposited determines size of landform
Coarse or fine sediments determines how far sediments are transported and type of landform
TOPOGRAPHY
Landforms formed by wind are usually on the
lowlands
, encouraging strong wind action
Water eroded landforms are on the
hillslopes
, encouraging surface runoff
Erosion
Erosivity of the agent
Surface erodibility