Erra Matti Dibbalu: Coastal Red Sand Dunes of Visakhapatnam

By: D Rajasekhar Reddy
Picturesque and rare, the Late Quaternary Red Sand Dunes—Erra Matti Dibbalu is spread over 10 sq km between the coasts of Visakhapatnam and Beemunipatnam in Andhra Pradesh. Owing to its geological significance, the Geological Survey of India declared it as a National Geoheritage Site in 2014 while state government notified it as a Protected Area in 2016. Attempts are now underway to establish a Visakhapatnam Geopark by combining several geological and cultural sites in the region.
History Life

The spectacular Erra Matti Dibbalu that stretches between Visakhapatnam and Bheemunipatnam along the coast is a marvelous gift of nature. The low-lying dunes with a maximum elevation of 90 m above mean sea level (msl) is located 20 km to the northeast of Visakhapatnam and 4 km southwest of Bhimunipatnam. The width of the dunes vary from 200 m to 2 km, running for 5 km along the coast in an east-west direction. Besides being unusual, the rare sand dunes have an important and interesting history of evolution. Such sand deposits have been reported only from three low latitude tropical regions in South Asia—the Teri Sands of Tamil Nadu, the Erra Matti Dibbalu in Andhra Pradesh and Red Coastal Sands of Sri Lanka. They do not occur in any other equatorial or temperate regions across the world (Gardner 1995).

Geomorphology of the Site 
The gullies in the sand dunes are features that adds mystique to aesthetic appeal of the site. Erra Matti Dibbalu also showcases migrating sand dunes near the coast and parabolic (U-shaped) sand dunes extending up to 2 km landward from the shoreline indicating the intensity of wind action. The area records various landforms and features of different dimensions including gullies, buried channels, beach ridges, paired terraces, valley in valley, wave cut terraces, knick points and waterfalls which aid the understanding of geomorphic evolution of the area (Vaidyanadhan 2012).

Origin of the Red Sand Dunes
William King, a geologist from the Geological Survey of India, discovered the significance of Erra Matti Dibbalu at Bheemunipatnam for the first time, more than a century ago and described them as badlands to represent the denudational remnants of great sand banks or isolated banks formed around sunken or depressed hills. Subsequently, many researchers have contributed on various aspects of Erra Matti Dibbalu. The red sediments are deposited over the basement of khondalite rocks (garnetiferous sillimanite gneiss) and comprise of yellow sands at the bottom followed upward by reddish brown concretion bearing sand unit, brick red sand unit and light-yellow sand unit. The thickness of the sand units is not uniform throughout the area due to the variation in the basement configuration (Rao et al. 2006).

The study of the dune sediments indicate that the bottom-most yellow sand unit is fluvial (transported by rivers joining the sea) while the other overlying three units are aeolian (windblown) in origin. Geological evidence indicates that the sands of the top three units were transported during different periods by prevailing winds which was exposed due to the sea level fall during the Last Glacial Maxima (LGM), 18,500 years ago.

Subsequently, a shift in climate caused in-situ geochemical alteration of the iron bearing minerals in the sands, resulting in the reddening of the dunes. The top light-yellow sand unit however, estimated to have been deposited only around 3000 years ago, were not subjected to such a weathering and hence the sediments could not attain the red colouration. Also of significance is the calcareous concretions that are recorded in the red sediments. The age of these concretions, determined by radiometric dating ranged from 5810 ± 120 years to 5840 ±170 years ago (Rao et al. 1982). The mineralogical and geochemical studies of these sediments indicate that they are mainly derived from the khondalite suite of rocks from hinterland Eastern Ghats (Murali Krishna et al. 2016). Based on the remote sensing and field geological studies, Madabhushi (1995) revealed that the area was active tectonically between 2.5 million and 11,000 years ago.

Archaeological Signatures
Archaeological excavations of artefacts found in the compact dark yellow Erra Matti Dibbalu indicate undisputedly, an Upper Paleolithic horizon and on cross dating assigned to Late Pleistocene Epoch 20,000 BCE. Mesolithic and Neolithic cultural materials were also unearthed from the red sediments at different locales denoting their continued formation till almost recent times. These geoarchaeological evidence indicates erosion even subsequent to Neolithic period, which could be dated to 2,000 BCE. Thus, the region was also home to prehistoric man,  ascertained through excavations at several places, which revealed stone tools of three distinctive periods as also pottery fragments belonging to Neolithic cultures (Reddy et al. 1999).

Erra Matti Dibbalu – A National Geoheritage Site
The red sand sediments of Erra Matti Dibbalu are unconsolidated and loose. Every monsoon the sediments are washed away, turning the sea a bright red. Further degradation due to human interference such as digging, climbing, littering etc. are affecting their stability and exacerbating erosion. As such, we face the danger of losing a rare and picturesque record of nature.

Following a national workshop jointly organised by the Geology Department of Andhra University and INTACH in 2012 the site was declared a National Geoheritage Monument in 2014 by the Geological Survey of India (Reddy and Sarma 2012). The state government of Andhra Pradesh notified the site as a Protected Area two year later, in 2016.

However, the Erra Matti Dibbalu is a valuable asset and its importance needs to transcend national borders. The scope of its study for understanding past environmental indicators is significant, enabling further research into past climate, sea level oscillations, monsoon variability etc. This needs to be utilised by the global scientific communities. If these red sand dunes are disturbed and eroded, valuable natural scientific documents will be erased forever, rendering further work impossible. Hence, there is an urgent need to protect and preserve the Erra Matti Dibbalu from any potential threat including unregulated tourism and construction activities.

Way Forward
The Visakhapatnam region is replete with many exquisite geological features. Study of ancient natural arch of Shilathoranam formed 1500 million years ago atop the Tirumala Hills; or that of the magnificent limestone caves with stalactites and stalagmites at Borra; and research about the volcanic ash deposit in Patal valley at Araku which is said to have originated from the volcanic eruption of Toba in Indonesia 73,000 years ago—are all indeed magnificent repositories of the earth’s history. It is therefore important to establish a Visakhapatnam Geopark Circuit by combining the myriad geological, cultural and archaeological sites such as Thotlakonda, Bavikonda, Pavurallagutta etc. Geoparks can significantly help promote scientific knowledge apart from encouraging tourism, thereby, contributing to the economy of the region.

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