Oceans and Coastal Landforms

2020-04-28 23:36:22

Oceans and Coastal Landforms
Coastal Landforms
- Waves and Current
- Winds
  - Wind Erosional Landform
  - Wind Depositional
    - Sand Dunes

Oceanic mountain ranges and deep trenches are moslty located near Continent Margins.

Sea Floor Spreading Theory

Evidences as proposed by Hess in 1961 are : ^4e69e9
- Volanic eruptions are common around the mid oceanic ridges.
- Rocks equidistant from ridges show similarity and the ones closer to the ridge are young.
- Oceanic crust is younger than continental crust
- Sediment in ocean floor are very thin and young
- Deep trenches have deep seated earthquakes while oceanic ridges are at shallow depths

Water

Water Cycle :
- Evaporation, Transpiration, Condensation, Precipitation
- 59% of water falling returns to atmosphere by Evaporation

Major Division of Oceanic Floor

![[1629895564.jpg]]

Continental Shelf :
- shallowest part, average gradient of 1deg or less
- Average width is 80km, Depth varies from 30m to 600m
- longest shelf is Siberian shelf in Arctic Ocean stretches 1500km.
- sedimentary deposits brought by rivers make them sources of fossil fuels
Continental Slope :
- gradient varies from 2-5deg
- Depth varies from 200mt to 3km
- Canyons and Trenches are observed in this region.
Deep Sea plains
- flat and smooth, Depth Varies from 3km to 6km
- covered with fine grained sediments like silt and clay.
Oceanic Deeps or Trenches
- steep sides, 3-5 km deeper than surrounding
- occur at bases of slopes along, volcanoes and earthquakes are common

Minor Relief Features

Mid oceanic ridge :
- 2 chains of mountains separated by large depression
- islands like Iceland are ex of mountains rising to surface part of mid-Atlantic ridge
Seamounts
- Pointed summits rising from seafloor that does not reach the surface
- Volcanic in origin.
- Flat topped seamount are called Guyots
- ![[Pasted image 20220330110956.png]]
Submarine Canyons
- deep valleys similar to canyons on land ex Hudson Canyon
- ![[Pasted image 20220330111126.png |500]]
Atoll
- ring-shaped reef, island, or chain of islands formed of coral.
- Mostly found in tropical regions around a central depression
- ![[Coastal-Landforms-image3-00090325.jpg|400x300]]

Temperature of Ocean Water

Factors affecting temp distribution of ocean water?

Latitude
Contact of oceans with land : ex Ocena in Northern Hemisphere receive more heat due to more contact w/ land
Prevailing winds : ex blowing from land causes upwelling by driving warm water away from coast, vice versa causes warm waters near coasts
Oceanic currents

Horizontal and Vertical Distribution

Vertical Dist
- First layer : 500 mt thick, 20-25°C temp, always present in tropical region but only in summer in mid latitudes
- Second layer : aka thermocline where temp dec rapidly, 500-1000mt thick
- Third layer : extends upto ocean floor, temp change very slight
Horizontal Dist
- temp gradually dec from equator to poles, highest temp not at equator but slightly north to it
- Avg temp fo Northern Hemisphere more due to more land area

Salinity

24.7 is upper limit to demarcate brackish water

Factors affecting salinity of oceans?

Evaporation and Precipitaion
Fresh water flow from rivers, glaciers
Wind
Ocean Currents

Horizontal Dist

land locked areas show higher salinity, even more in hotter regions
==Salinity in western parts of NH is less due to influx of melted water from Arctic region==
Generally dec northwards but North Sea has high due to saline water influx from North Atlantic Drift
- Baltic sea has low due to rivers draining in it
- Mediterranean sea has high salinity due to high evaporation
IN ocean avg salinity is 35ppm

Veritcal Distribution

Inc at surface due to evaporation
Salinity at depth is fixed
Distinct zone in ocean where salinity increases sharply is called Halocline.

Movement of Ocean Water

Horizontal is Oceanic currents and waves

Waves

are energy not water
features are crest, trough, height, amplitude (half of height), period (time b/w 2 waves), speed and frequency

Tides

Periodical rise and fall of sea level, attraction of sun-moon (more prominent) and centrifugal force is the cause.
Movt of water by meteorological effects viz winds, pressure changes are called surges
Tides based on frequency
- Semi Diurnal Tides are most common tides
  - Has 2 high tides and 2 low tides
  - successive tides are of same height.
- Diurnal
  - have 1 high and 1 low tide during each day
  - successive tides of same height
- Mixed Tides
  - have variations in height mostly along west coast of North America
Tides based on position of Sun, Moon, Earth
- Spring tides
  - all three in straight line, occur twice a month
  - height is higher
- Neap tides
  - Sun, Moon at right angles, counteracting each other
  - Occur after 7 days of Spring tide
Ebb : time between high tide and low tide, when the water level is falling
Flow : time between the low tide and high tide, when the tide is rising aka flood

Ocean Currents

have regular vol, definite path and direction
Strongest near surface, slower at deeper depths

Primary Forces that Influence Currents

Heating by Solar Energy
Wind
Gravity
Coriolis Force

- Large accumulations of water and flow around them is called Gyres which produce large circular currents - Difference in water density affects vertical mobility of currents #PrelimsPYQ

Types Based on Dept and Temp

Surface Currents :
- 10% of all water in ocena
- upper 400m of the ocean
Deep water currents : other 90%

Cold Currents

usually found in the west coast of continents in low and middle latitude in both hemispheres -> causing aridity in the region
in East coast at higher latitudes in Northern Hemisphere.

Warm Currents

East Coast in low and middle latitudes -> results in warm and rainy climates
West Coast at high latitudes in the Northern H -> marine type climate w/ cool summers and mild winters

El Nino #important

El Nino appears once in every 3-7 years.
an extension of warm Peruvian current.
It causes :
- Distortion of equatorial atmospheric circulation.
- irregularities in the evaporation of the sea.
- ==Decrease in phytoplanktons== leading to dec in fishes.

Oceanic circulation pattern corresponds to E’s atmospheric circulation pattern
Air circulation in middle lats is anticyclonic more pronounced in Southern H; cyclonic at higher depths
Mixing of Cold and Warm currents leads to phytoplankton growth, are one of the best fishing grounds

Indian Ocean Dipole IOD

difference b/w temp of Bay of Bengal (Eastern pole) and Arabian Sea (western pole) → pressure diff this difference in temperatures is called Indian Ocean Dipole.
Positive IOD is cooler temp in BoB and warm in Arabian sea; Opposite is vice versa. It brings more rainfall in the western Indian ocean region and cooling of waters in the eastern Indian ocean causing drought like conditions.
Positive IOD causes above avg rainfall, results in more cyclone in Arabian Sea. It is favorable towards bringing Indian ocean.
Negative IOD cause tropical cyclones in BoB
IOD involves a periodic oscillation of sea surface temperatures SST between ‘positive’, ‘neutral’ and ‘negative’.

Coastal Landforms

2020-04-29 00:05:19

Waves and Current

Coastal landforms depends on the *following factors *:
- Action of the waves
- Configuration of land and sea floor
- Whether the coast is advacning seaward or retreating landward.

High Rocky Coasts

Long ridges of sand and/or shingle deposited on the beaches along the shore are called Bars
Bars are submerged features when they show up above water they are called Barrier Bars.
Barrier bar which get keyed up to the headland of a bay is called a spit
When barrier bars and spits form at the mouth of a bay and block it, a lagoon forms.
Lagoons would gradually get filled up by sediments from the land giving rise to a coastal plain.

Low Sedimentary Coasts

Coastal Plains, deltas are common; lagoons, tidal creeks are occassional
Lagoon first forms swam and then coastal plain

Wave Erosional Landform

Wave cut cliffs, terraces are common
Wave-cut terrace are Formed at the foot of the cliff it is a flat or gently sloping platform covered by rock debris derived from sea cliff behind. ![[Coastal-Landforms-image1-00090325.jpg]]
Sea Caves are formed by Lashing and smashing of the waves containing rock debris against the base of the cliff forms.
When sea caves collapse the sea cliffs retreat further inland leaving behing resistant mass of rocks the are called Sea Stacks. ![[Coastal-Landforms-image2-00090325.jpg]]

Wave Depositional Landforms

Beaches: are formed by deposition, Temporary feature, sandunes are common behind a beach
Offshore bars are ridge of sand lying paralled from low tide waterline to seaward.
[[#High Rocky Coasts|Bars, Barriers and Spits]]

Winds

Wind Erosional Landform

Pediments : gently** inclined rocky floors close to the mountains at their foot with or without a thin cover of debris. ![[Landforms-image9-00085771.jpg]]
When pediments extends backwards at the expense of mountain from it gets reduced to an inselberg.
The areas around it are knows as Pediplains.
Due to gradual deposition of sediment from basin margins with mountains and hill, a nearly level plain forms at the centre of the basin, this gets filled by water forming a shallow lake called a Playa.
- most prominent landform in desert, water retained only for short time
Playa plains filled up by salts is called Alkali flats.
Deflation hollows formed due to weathering away of the mantle of rocks by the action of wind.
Deflation creates pits and cavities in rocks leading to the formation of Caves. ![[Landforms-image10-00085771.jpg]]
Mushroom, Table and Pedestal rocks are some other forms

Wind Depositional

Sand Dunes

Crescent shaped dunes called barchans.
Parabolic dunes form when sandy surfaces are partially covered with vegetation. The parabolic dunes are reversed barchans.
Seif is similar to barchan but has only one wing or point.
Longitudnal dunes form when supply of sand is poor and wind direction is constant.
Transverse dunes are aligned perpendicular to the wind direction.

[[kegy204.pdf]] - Distribution of the Oceans and Continents [[kegy213.pdf]] - Water (Oceans) [[kegy214.pdf]] - Movements of Ocean Water