Geography Chap 11 (Goh Cheng Leong + NCERT)

CHAPTER 11

Islands and coral reef

Types if Island:
1) Continental   2)Oceanic

1)Continental Island
--Formation = subsidence of land / Rise in sea level.
--Identification= similar type of structure, flora, fauna with diff surface features.
--Type = a) Individual Island b)Archipelago Island c)Festoon Island.
a) Individual Island:
>Lie just outside the continent.
>almost same features as of parent continent.
>Ex- Newfound land= strait of Belle Isle;

         Madagascar= by Mozambique channel;
         Sril lanka= Pak strait;
         Tasmania= Bass strait;

          Formosa= Formosa strait;



Note: Strait= narrow water body connecting two large water body.
            Channel= large water body it also connects two large water body, but due to lack of narrowness it appears as if its separating two landmass.

b)Archipelagoes:
>group of island.
>Ex- British isle; Balearic Island of Mediterranean Sea and Islands of Aegean Sea.
>belaric islnd--Image ↓


--Islands of Aegean Sea. ↓


c)Festoon or island arc
>Archipelago = mountain ranges are continuation from continent to island.
>Ex- East indies, Alutian island(Berring strait), Ryuku island, Kurile islands and other island arc of pacific coast
>Ryuku island ,..Image ↓


--Kuril island (Russia dispute) Image ↓:


2) Oceanic island:
--not connected from continent.
--Different flora and fauna.
--Type= a)Volcanic island  b)Coral island.

a)Volcanic island:
>Pacific :
  >>Hawai (Mauna Loa in hawai rises from sea bed unlike other volcano that rises from ridges in ocean)
  >>Galapagos
  >>South sea island.

>Atlantic:
  >>Azores
  >>Ascension
  >>St Helena
  >>Madeira
  >>Canary island

>Indian Ocean:
  >>Mauritius
  >>Reunion island

>Antartic:
  >>South sandwich island
  >>Bouvet island.

b) Coral island:
>Pacific:
  >>Gilbert and Ellice island
  >>Marshall island

>Atlantic:
  >>Bermuda

>Indian ocean:
  >>Laccadives
  >>Maldivies

Coral reefs
--Tropical sea
--Coral animals + Marine animals= Coral polyps, Calcareous algae, shell forming creatures and lime secreting plants.
--They live in colonies and grows below water level
--Polyps are most important/ abundant.
    >Polyps live in a cup of coral-à dies à forms coral reef after getting cemented.
--Not all coral forms reef ===Example=”Precious coral” in Pacific; “Red coral” in Mediterranean
                          >>these can survive low temp and deep water.
The reef building corals:
--Water temp = 20 °C
--Water depth= 200 feet = beyond less light.
                        >Absence of light= no microscopic algae= food of corals.
--Salty water.
                        >Not shallow enough to bring them to surface= they will die.
--water free from sediment >>>> therefore not near delta producing river|| always near moving ocean water. || sea ward side of reefs.

Types of Coral Reefs:

--Fringing reefs:
  >close to the shore……extending outward from land…….seperated by  many times = Lagoons.

  >Slope= steeply downward in seaward …compared to landward
  (Image ↓):


--Barrier reef:
  >separated from coast by a much wider and deeper channel or Lagoon.
  >barrier reef= have narrow gaps…..allows ships.
  >Image ↓:


--Atolls:
  >circular in shape
  >enclosing a lagoon------without any land in centre.
  >Inside of reef = sand + limestone debris---collected==palm can grow.
  > provides air bases .
  >Ex- Suvadiva in Maldives;  west of Ceylon.
--Image ↓:


Explanattion of coral island formation:

1) Darwins “theory of subsidence.”….subsidance of middle land forming atolls
2)R.A Daly’s “Glacial control theory”. …..erosion of middle land forming attols.

Modern belief= combination of Both.

Image ↓: