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

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

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!)

TECTONIC UPLIFT : Exposure of limestone rock

  • Responsible for uplift of limestone bed
    🌄 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

ARID / HYPER ARID

MACRO

LOCAL

MESO

SEMI-ARID

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

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

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

MACRO

MESO

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)

LOCAL

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)

VEGETATION

  • Sparse vegetation due to lack of moisture, thus surface materials are loose and easily lifted by the winds

CLIMATE

  • Lack of rainfall thus lack of soil moisture
  • High temperatures

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

TOPOGRAPHY

  • Landforms formed by wind are usually on the lowlands , encouraging strong wind action

Erosion

  • Erosivity of the agent
  • Surface erodibility

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)