geomorphic processes and landforms notes upsc geomorphological processes and landforms pdf

geomorphic processes and landforms notes upsc geomorphological processes and landforms pdf

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geomorphological processes and landforms pdf geomorphic processes and landforms notes upsc ?

Geomorphic processes 1
Geomorphic processes
Earth’s surface is exposed to gradation processes by exogenic forces, but they’re not
able to overcome the endogenic land building forces.
Endogenic
processes that work/derive energy from below the surface (primordial heat,
subsurface radioactive decay, tidal friction etc)
constructive: lead to continuous elevation (of mountains and plateaus) or deepening
(of trenches)
can be diastrophic (results over time – rise in mountain height etc) or sudden
(volcanic activism etc)
Examples in nature:
1. folding of crust due to compressive forces
symmetrical, asymmetrical, isoclinal, monoclinal, overturned, recumbent,
plunging, fan, open and closed
2. faulting: cracks along rocks move due to tension/compression forces,
types of fault:
normal (tension) fault: rift valley, block mountains
reverse (compressive) fault: ramp valley, block mountains
strike-slip fault (horizontal slipping)
horst is the raised block, graben is the subsided block
3. volcanic landforms: refer Volcanic below
Geomorphic processes 2
Exogenic
processes that work over the surface of earth, deriving energy ultimately from the
sun
destructive: work to level the terrain differences – lower mountain heights, fill craters
and seas etc
weathering, erosion, mass wasting, transportation
Examples of exogenic forces
1. weathering: decomposition of rocks; aids concentration of certain minerals and
ores by leaching away soluble impurities
physical: frost wedging, diurnal contraction cycles, unloading, salt expansion,
friction due to wind and water
chemical: dissolution (aided by CO2), carbonation, hydration (repeated
expansion), redox (depending on O2 presence)
biological: burrowing and digging by rodents, insects, earthworms,
anthropogenic disturbance, plant roots, actions of lichens
benefits: soil formation, leaching of soluble impurities and enriching mineral
deposits like Mn, Fe, Al
exfoliation: dome (unloading), tor (thermal expansion)
2. mass wasting
large scale movements of soil, rocks, earth etc due to gravity,
can be slow: slump, soil creep,
or fast: earth flow, debris slide, mudflow, avalanche, landslides
aided by:
reduction in material support from below,
overloading,
excess water seepage,
disturbances like explosions and quakes,
Geomorphic processes 3
structural weaknesses like joints and faults,
removal of vegetation: deforestation, overgrazing
3. erosion: removal of top layer of soil (refer Land and soil for management)
water: splash, sheet, rill, gully
wind: saltation, suspension, surface creep
glacial action
4. deposition: into depressions and craters levelling them up
Landforms and evolution
Volcanic landforms
volcanic (basalt) and plutonic (granite) rocks
batholith: large domes of cooled magma concave downwards, appear to surface
after denudation
lacolith: concave down, smaller volcanic landform
lopolith: dome concave upwards
phacolith: wavy structure of solidified magma
sheets, sills: flat slabs of solid magma, called differently depending on thickness
dyke: vertical walls of magma, solidified perpendicular to surface as magma rushed
upwards through fissures and cracks
refer types of volcanoes in Interior of earth
dyke, batholith are discordant: don’t form along existing bedrock
laccolith, lopolith, phacolith are concordant: form along existing bedrock
geysers and hot springs are usually associated with volcanism
Geomorphic processes 4
Fluvial landforms
1. Young stage:
rills → gullies → deepen into V-shaped valleys, gorges and canyons
gorge: narrow and deep, steep and straight sides
Geomorphic processes 5
canyon: broader, wider at top than bottom, may be as deep as gorge
interlocking spurs
potholes: rock fragments cause abrasion on bed → depressions in bed
pebbles and rocks might enter; depressions widen into plunge pools
meanders unlikely to form; but would get entrenched (if formed) due to
aggressive down cutting (eg Colorado Valley)
irregular outcrop of rock → rivers jump (rapids)
waterfalls
drainage divides are broad and irregular
2. mature stage: down cutting lowered, lateral erosion prominent; tributaries increase
water volume
alluvial fans and bajadas formed as rivers break into plains
V shaped valleys are deeper, divides become narrow, some streams integrate
irregularities like waterfall and cascades disappear
meanders: lateral erosion, Coriolis force, irregularities in alluvial deposits can
make one side more susceptible to erosion
oxbow lakes: lateral erosion → river curvature can accentuate; during floods,
river might straighten course, leave behind horseshoe shaped lake (eg:
Kanwar)
3. old stage: gentle gradient, freely meandering streams, nearly at sea level
divides are flat and broad with marshes, swamps, lakes etc
meander and oxbow lake formations
levees and point bars formed
due to deposition of sediments in small ridges perpendicular to riverbanks
levees on concave side, point bars on convex side
carrying capacity reduces → sediments deposited → braided channels and
delta plains formed
Geomorphic processes 6
Karst topography
action of ground water in areas where limestone and dolomite dominate in landform
dissolution of CO2 from atmosphere in rain, and later from carbonate based rock
accelerates the dissolution
as underground drainage system develops, it allows more water to pass,
accelerating the process
Erosional
sinkhole/swallow holes – round depressions largely due to solution
circular at top, funnel shaped towards bottom
might collapse to form collapse sink/doline
might combine to form long trenches (uvalas)
points, grooves, ridges/lapies form on limestone slab as most of the surface is eaten
away,
eventually forming smooth limestone pavement
in areas where dolomite/limestone is prominent, eating away by GW could lead to
cave and tunnel formation
cave: open from one end; tunnel: open from both ends
Depositional
evaporation → carbonate salts deposited as icicles reaching down from ceiling
(stalactites) or narrow salt structures reaching up from floor (stalagmites)
could join and form salt pillars
Glacial landforms
Due to sheer size, they carry material picked up on the way, damaging the floors and
sides of valleys greatly by abrasion.
Erosional
Geomorphic processes 7
cirque: steep deep long wide troughs formed as glaciers slide down the slopes of
mountains
leave behind tarns(cirque lakes) once the glacier disappears
horn: At the point of meeting of multiple cirque, sharp structures with steep sides
(serrated ridges) form
Glacial valleys/troughs: moraine filled, might get filled with water to form fjords
bergschrund: point of separation of glacier from firm static ice
truncated spur: ridge extending towards valley that got eroded by glacier
kettle: ice pockets left behind as glacier recedes → lake formed
Depositional glacier
moraines: debris brought by glacier into the valley;
medial moraines: formed by multiple glaciers joining,
lateral moraines: deposited along edges of glacier, parallel to flow
terminal moraines: deposited at end of glacier, perpendicular to flow
horseshoe moraines: lateral moraines joined by terminal moraine
eskers: when some ice melts, water flows beneath ice in a channel depositing
coarse materials → trail of deposits left after snow completely melts
outwash plains: glacio-fluvial deposits in the form of alluvial plains
drumlins: smooth oval shaped ridge formed out of glacial till, blunted on one side
due to ice push; indicates direction of glacial flow
Geomorphic processes 8
Waves on retreating coast
high hard rock retreating coast with steep slope, like western coasts
erosional features are dominant here, eroded material deposited
indented coasts, with rivers abruptly meeting the sea, seas entering land via fjords,
narrow coasts
steep rocks → rock cliff → sea cave → sea arch → sea stacks
sea stacks: as cliffs recede, resistant parts of rock may be left behind
wave cut terrace + wave built terrace (gentle platform) → bars, barrier bars → spit
→ lagoon → coastal plains
sediments deposited parallel to coast → offshore bar
can be exposed with addition of sand and sediments → barrier bar
gets keyed onto coast from one side → spit
eventually keyed on from both sides → lagoon formed
over time becomes a coastal plain
Waves on emerging coast
low sedimentary coasts with gentle slope, like eastern coasts
Geomorphic processes 9
rivers in mature stage, forming deltas and coastal plains
depositional activity dominant due to availability of sediment from rivers
marshes, swamps, lagoons, creeks common
depending on supply of material, bars → lagoons → swamps → coastal plains
sand lifted from the beach forms sand dunes along the coast
Wind action
Devoid of vegetation, heat up faster setting up fast moving unrestricted winds which
lead to weathering, erosion, deposition. Extreme diurnal variations make the rocks more
exposed to weathering due to torrential pouring in short periods too.
Erosional
piedmont plateau: formed due to parallel retreat of slopes through back-wasting:
mountain front moves backwards, leaving rocky structures behind
pediplains: over time, mountains -> pediment plateau -> pediplains
zeugens: mushroom rocks with resistant material over slender less resistant
material
friction by particles flying at low heights
upper rock of tough material, lower pedestal softer
yardangs: composed of alternate strong and weak rocks
inselberg: hill of resistant material rising from softer eroded rocks of plain
ventifacts: rocks smoothened by wind action
Depositional
playas: in basins surrounded by mountains, drainage is towards centre of basin ->
deposits of sediments -> level plain at centre of basin
can become a shallow water body in wet times
sand dunes in varying shapes depending on wind speed and direction:
Geomorphic processes 10
barchans: crescent shaped dunes
parabolic: reversed barchans due to vegetation
seif: longitudinal dunes; barchans with one wing
transverse dunes: form when wind blows perpendicular to sand supply
star shaped: wind in multiple directions
loess: deposits of fine silt and dust

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