Friday, January 29, 2021

Andaman and Nicobar Islands - Physiography

 


The Andaman–Nicobar Islands is an archipelago in the Bay of Bengal. The Islands is the extended part of the Arakan Yoma mountain ranges of Myanmar into the sea. The islands are known by different names like “The Islands of the Marigold sun” and “The Bay Islands”. There are about 572 islands in the Andaman and Nicobar archipelago covering the area of 8279 sq. km. But including all the Islands, smaller Islets and rocky outcrops they are 836 in number. (Andaman Government Website). The two main groups i.e. Andaman Islands and Nicobar Islands are separated by the 160 km wide Ten Degree Channel.

Andaman Islands -

In the Andaman group of Islands, the central islands have been divided into three i.e. North Andaman, Middle Andaman and South Andaman. South of these three islands there are Rutland Island followed by Little Andaman. Baratang is another main Island east of Middle Andaman Island. Ritchie’s Archipelago is another group of smaller Islands, NNE of Port Blair in Andaman Sea, including important tourist islands like Havelock, Neil and Henry Lawrence Island. These Islands are separated by passage and straits like –

Duncan Passage - Little Andaman from Great Andaman.
The Austin Strait - The Middle and North Andaman;
The Humphrey Strait - The Middle and Baratang islands;
The Middle Strait - Baratang and South Andaman;
The Macpherson Strait - The South Andaman and Rutland islands.

Nicobar Islands -

Lying south of the Andaman Islands, separated by Ten Degree Channel are the Nicobar Group of Island covering an area of 1841 km2. Moving from north to south, the main islands in the group are Car Nicobar Island in the North; followed by Katchal, Camorta, Nancowry and other smaller Islands; and Little Nicobar and Great Nicobar further south. Indira Point on the south coast of Great Nicobar Island is the southernmost point on India’s territory.

Physiography of Andaman and Nicobar Island –

Andaman Islands has most of the relief in the eastern part whereas the western part has gentle and low elevation. Great and Little Nicobar have hilly topography. The highest point in the Andaman–Nicobar Group is Saddle Peak (733 m from sea level) on North Andaman. Mount Thullier (642 m) on Great Nicobar Island is another higher peak.

Barren Island, the only active volcano of India, is an Island in Andaman Group located in Andaman Sea. Andaman Islands also have presence of Karst landscapes in the Neil Island and Baratang Island.

References – 

Bandopadhyay, Dr. P. & Carter, Andrew. (2017). Chapter 2 Introduction to the geography and geomorphology of the Andaman–Nicobar Islands. Geological Society, London, Memoirs. 47. 9-18. 10.1144/M47.2. Available at -https://www.researchgate.net/publication/313266512_Chapter_2_Introduction_to_the_geography_and_geomorphology_of_the_Andaman-Nicobar_Islands. Assessed on 25/01/2021.

Census of India 2011: Andaman and Nicobar Islands - District Census Handbook , New Delhi: Office of the Registrar General, India, 2005. Available at -https://censusindia.gov.in/2011census/dchb/3500_PART_B_DCHB_ANDAMAN%20&%20NICOBAR%20ISLANDS.pdf.

NASA/METI/AIST/Japan Space Systems, and U.S./Japan ASTER Science Team. ASTER global digital elevation model V003, 2018, distributed by NASA EOSDIS Land Processes DAAC, https://doi.org/ 10.5067/ASTER/ASTGTM. 003.


Thursday, January 14, 2021

Mangroves of India

 

Mangrove are the dense shrubs or forests found along tidal estuaries and deltas, salt marshes, and on muddy coasts in the tropical and sub-tropical regions. These are mostly found in Asia, Africa and South America. The largest area of mangroves are found in Indonesia, followed by Brazil, Australia, Nigeria, and Mexico. 

The areas where mangroves are found poses many challenges for the plant community like high salinity, tidal inundation twice a day, low oxygen etc. However, mangroves are equipped with varied morphological and physiological adaptations to survive these conditions. They have complex root system that extend above and below the water line with amazing filtration system to sieve out or exclude salt. This allows them to survive in saline sea water as well as in fresh water. Mangrove have additional benefits for environment like they prevent coastline erosion, protect inner areas from tsunamis, storms and high waves and also provide habitat, breeding, and feeding grounds for aquatic and other organisms. They are important carbon sinks also known as blue carbon.

As per the Indian State of Forest Report of 2019, mangrove cover in the country is 4,975 square km, which is 0.15% of the country’s total geographical area. The largest area under mangroves is in West Bengal. Indian mangroves consist of 46 species representing about 57% of the world's mangrove species (Ragavan et al, 2016)


In India, the mangroves are mostly located in the river estuaries and deltas; backwaters and islands. Therefore, the mangroves of India are broadly classified into three regions, as (Mandal and Naskar, 2008) -

1. Deltaic or Eastern Coast Mangroves,

2. Estuarine & Backwater or Western Coast Mangroves and

3. Insular mangroves or Andaman & Nicobar Islands. 
 

Deltaic or Eastern Coast Mangroves

West Bengal - Sunderbans (Ganga-Brahmaputra)

Odisha - Bhitarkanika (combined delta of the Mahanadi, Brahmini and Baitarani)

Andhra Pradesh - Coringa wetland (the Gautami-Godavari river), Krishna (three islands located between Gollamattapaya and Nadimeru distributaries, and the Krishna river).

Tamil Nadu - Pichavaram and Muthupet mangrove (Cauvery)

Puducherry mangroves

Estuarine & Backwater or Western Coast Mangroves

Gujarat - Gulf of Kachchh; Saurashtra coast or Kathiawar; Gulf of Khambhat (estuaries like the Sabarmati, the Mahi, the Narmada, and the Tapti); South Gujarat coast (small tidal creeks and few minor estuaries.

Maharashtra – Mumbai, Thane creek and small patches in Raigarh, Ratnagiri and Sindhudurg district.

Goa coast - Zuari and Mandovi estuary

Kerala - Mangroves in Kannur and Kasaragod, Kozhikode (Kadalundi), Ernakulam (Pithuvypin, Mangalvanam Bird Sanctuary and Kundannur area.), Allepey.

Daman and Diu mangroves

Insular mangroves or Andaman & Nicobar Islands.

The mangrove forests of these islands are situated along the tidal creeks, inland channels and in shores (bays).

References -

India State of Forest Report, 2019. Forest Survey of India, Ministry of Environment, Forest & Climate Change, Government of India

Mandal, R.N. and K.R. Naskar. (2008). Diversity and classification of Indian mangroves: a review. Tropical Ecology 49, 131–146.

Ragavan, P., Saxena, A., Jayaraj, R.S.C., Mohani, P.M., Ravichandran, K., Saravanan, S., and A. Vijayaraghavan (2016). A review of the mangrove floristics of India. Taiwania, 61 (3), 224‒242.

Selvam, V. (2003). Environmental classification of mangrove wetlands of India. Current Science. 84.