On the Bay of Bengal coast, to the south of the Bhimunipatnam ridge, an area comprising deeply gullied red sand dunes of around 4 km length and 2 km width near Visakhapatnam. It is bounded by streams Chittigadda in the North-West and Peddagadda in the South-West. This area is referred to as Erra matti dibbalu. They are unique because of the gullied red dunes formations.
How the Erra matti dibbalu formed and what gave the sand its unique red color? questions have challenged geologists since more than a century. Some scientists are of the opinion that the initial chapter of this epic story took place in the “Pleistocene” period from around 1.8 million years ago to around 10,000 years ago. During that time the sea level rose to as much as 50 meters above the current level and fell away below the current level many times. Between these oscillating sea levels, the coast was submerged and exposed over and over again.
When the sea receded it left behind huge volumes of clay and silt. Subsequently, the beach sand swept over the clay and silt, and over time this Aeolian sand covered the earlier soil forming large sand dunes. The clay and silt under the sand then “baked” in the sun much like a brick gets baked in a kiln leading to the peculiar red earth. Later, the action of the wind and flowing water caused the deeply gullied characteristic landscape. The red color of the dunes is said to be due to the terrorization of haematite. This simply means that iron-rich material hematite coated the loose sand grains and when it got exposed to the elements the stuff oxidized over a period of time. Just like a nail exposed to salty air would get corroded and appear red in color.
Other theories suggest that the main cause of the formation is mainly due to Fluvial meaning action caused by flowing water. And that it happened in a period of tectonic quiescence – a quiet period without too much tectonic activity. Yet others are convinced that much of what we see today is due to the Neotectonic activity, this fancy word simply means the tectonic activity that took place in the recent past, which is around 6,000 years ago. Dr. Srinivas Madabhushi points out that the sudden change in the flow of the Gosthani River, the gap in the Bhimunipatnam ridge, the pattern of fractures and several other clues clearly indicate a series of recent tectonic activities.
It is possible that the theories converge at a point to explain the surreal Erra matti dibbalu landscape, but the jury is still out on the exact process that caused these formations. That is why it is even more important that these dunes be preserved in its original form for future generations to study and to admire. It is a tourist place especially during the cooler season tourists and casual visitors visit Erra matti dibbalu. It is obvious that the predominant number of visitors to the site do not visit the site to marvel at its beauty or wonder at the geological phenomena that caused the awe-inspiring landscape.