Coastal Red Sand Dunes

In News

• Recently, Scientists urged the Andhra Pradesh government to protect glacial-period coastal red sand dunes of Visakhapatnam.

Key Points

• About: 
  • The city of Visakhapatnam is blessed with a number of sites that have geological importance. One among them is the coastal red sand dunes, popularly known as ‘Erra Matti Dibbalu’.
• Location and Spread: 
  • The site is located along the coast and is about 20 km north-east of Visakhapatnam city and about 4 km south-west of Bheemunipatnam.
  • The Erra Matti Dibbalu are spread across an area of about 20 sq km and the entire area has been notified as a Geo Heritage Site.
• Geo Heritage Site:
  • This site was declared as a geo-heritage site by the Geological Survey of India (GSI) in 2014 and the Andhra Pradesh government has listed it under the category of ‘protected sites’ in 2016.
  • This site has much significance geologically, archaeologically and anthropologically and it needs to be protected for further study and evaluation. 
• Uniqueness in the Site:
  • The red sediments are a part of the continuation of the evolution of the earth and represent the late quaternary geologic age. 
  • With a height of up to 30 m, they exhibit badland topography with different geomorphic landforms and features, including:
    • Gullies, 
    • sand dunes, 
    • buried channels, 
    • beach ridges, 
    • paired terraces, 
    • the valley in the valley, 
    • wave-cut terrace, 
    • knick point and 
    • waterfalls.
• Depicts real time effects of Climate Change:
  • About 18,500 years ago, the sea (Bay of Bengal) was at least 5 km behind from the present coastline. 
  • Since then it has been undergoing continuous active changes till about 3,000 years ago and still the changes are on.
• Geochemically unaltered
  • The top light-yellow sand unit, which is estimated to have been deposited around 3,000 years ago, could not attain the red colouration as the sediments were geochemically unaltered. 
  • These sediments are unfossiliferous and deposited over the khondalite basement. 
  • The dunes consist of light yellow sand dunes at the top followed by a brick red sand unit, a reddish brown concretion bearing sand unit with yellow sand at the bottom. 
    • This bottom-most yellow sand unit is fluvial while the other overlying three units are aeolian in origin.

Significance of the Site

• Study the impact of climate change, as Erra Matti Dibbalu has seen both the glacial and the warm periods.
• The site is about 18,500 to 20,000 years old and it can be related to the last glacial period and will tell about the archaeological history.
• The site also has archaeological significance, as studies of artefacts indicate an Upper Palaeolithic horizon and on cross dating assigned to Late Pleistocene epoch, which is 20,000 BC.
• The site was home to the prehistoric man as the excavations at several places in the region revealed stone implements of three distinctive periods and also the pottery of the Neolithic man.
• Such sand deposits are rare and have been reported only from three places in the tropical regions in south Asia such as Teri Sands in Tamil Nadu, Erra Matti Dibbalu in Visakhapatnam and one more site in Sri Lanka. 
  • They do not occur in equatorial regions or temperate regions due to many scientific reasons, which make it geologically very important.

Source: TH