Hot Water Springs Of Konkan- Geological Significance

During my recent trip to Konkan, just north of the Tural area, I came across a sign for a hot water spring.

This is located in the small settlement of Aaravali. The area around the spring has been converted into a tourist spot where locals and tourists come to enjoy a warm bath.

One interesting feature of Konkan coastal belt is the presence of hot water springs arranged in a fairly narrow linear belt from north of Mumbai to Ratnagiri area in the south. They occur somewhat midway between the Western Ghat Escarpment and the coast. Few names from north to south- Vajreshwari, Akoli kund, Ganeshpuri, Pali, Dasgaon, Unhere, Tural, Aaravali, Rajapur. Satellite image shows the area between Dabhol and Ratnagiri. Hot springs are located within the oval. The dark brown undulating line is the trace of the Western Ghat Escarpment.

What is so special about this area? See the map. Black lines are fracture zones, trending N-S, NW-SE and NE-SW. Hot water springs are located in the vicinity of these fractures roughly within the oval. The depicted area is again between Dabhol and Ratnagiri, but this relationship between fracture systems and location of hot springs applies elsewhere along the entire Konkan coastal region.

Source: Neotectonism in the Indian Subcontinent: Landscape Evolution- K.S Valdiya and Jaishri Sanwal (modified).

Water temperatures are between 50 deg C to 60 deg C. Interestingly, analysis shows significant levels of radon gas at measured sites near Tural. Presence of radon gas hints at the reason why there are hot springs here. It points to deep circulation of water.

The crust in this region is made up of a foundation of older Precambrian age granitic rocks overlain by several hundred meters of younger basalt of Late Cretaceous to Paleocene age (67-65 million years old). Radon forms by radioactive decay of uranium. The Deccan Basalts contain only tiny amounts of uranium. Granites on the other hand are enriched in uranium. Radon emission here imply that these fractures cut through the basalt pile and penetrate the 2 billion years and older granitic rocks underlying these basalts. 

Such fracture systems have provided a passageway for groundwater to percolate to great depths. Cool water comes in contact with hot rocks deep below and gets heated. This warmer buoyant water then rises to the surface, forming a hydrothermal circulation system. The cross section shows fracture/fault systems of the coastal region cutting across basalts and penetrating the underlying granitic basement. I have added a few additional fractures to the figure.

What makes the rocks hot? What is the source of heat?  Deccan volcanism ended 60 million yrs ago. It is unlikely that there is any magma underneath to provide heat. Rocks get hotter at depths due to the natural geothermal gradient. Some geologists think that many of these fractures are actually faults along which there is intermittent movement of the crust. This faulting may be causing friction between crustal blocks, generating additional heat in these zones. These fractures and faults are a legacy of the breakup of the India with Madagascar and later Seychelles during and post Deccan volcanism  68 -60 million years ago. This rifting of the Indian crust resulting in oriented fracture systems.

The schematic shows the evolution of the Western Ghat escarpment and the coastal region. Earlier, perhaps soon after Deccan volcanism ended, the escarpment was a west facing cliff formed when faulting caused the western block to subside . Subsequent erosion has resulted in this cliff retreating eastwards, creating a coastal plain. Orange lines mark the highly fractured Indian crust.

Source:  Western Ghat: The Great Escarpment of India- V.S. Kale 2010. (modified)

Next time you visit Konkan and take a dip in the invigorating warm waters, remember that grand geological forces of continental separation are responsible for the high heat flow and the ground water circulation systems that arise consequently.

Konkan Road Trip Photos: Murud Dabhol Tural

Last week beginning Monday July 15th, I took a four day road trip to Konkan, India west coastal plains. We went first to the small village of Murud and then drove south via Dabhol to Tural highlands.

The phrase 'coastal plains' is something of a misnomer since between the high Western Ghats and the Arabian Sea there are hill ranges with altitudes reaching 50 m to 200 m ASL. Tural is a community living on one of these ranges. We stayed there in the family home of a friend.

The map below shows a portion of the Konkan region through which we traveled.

The region had come alive due to the monsoons, although that week we caught a small break in the rains. It did rain heavily in short bursts, but there were enough interludes to go for long walks and enjoy the sun too.

Some pictures of landscapes that we came across.

1) The coast near Murud. After a brutal summer, the feel of cool winds and sounds of monsoon waves crashing on the shore was very refreshing.

2) Lonely stretch of a shimmering beach near Murud.

3) Loading our car on to the ferry at Dabhol.

4) Colourful fishing boats at Dabhol jetty.

5) Continental erosion writ in mud! River Vashishti meets the Arabian Sea.

6) Rice fields in a quiet community in Tural highlands.

7) Tural highlands is capped by a flat surface.

8) This plateau cap is made up of iron rich laterite. It formed during late Miocene times (~10 million  years ago) by prolonged chemical weathering of the underlying basalt rock and pediment (layer of weathered rock debris) . The picture shows the hard laterite surface, which would have been a low lying peneplain in late Miocene times.

9) Subsequent to lateritization, the western margin (Konkan coastal region) underwent some uplift, resulting in the formation of a plateau or 'table land' as it is commonly called. As the land rose, invigorated streams cut into the laterite surface forming deeply entrenched channels.  The picture below shows a close up of the laterite plateau dissected by a dendritic stream network (blue arrows).

10) The evolution of the Konkan coastal region from a low lying undulating surface undergoing lateritization, to an uplifted and dissected plateau is depicted in the schematic below.

Source: Evolution of Laterite in Goa: Mike Widdowson  2009

11) The laterite is a commonly used building material in this region. Small quarries pockmark these highlands. The picture shows large bricks of laterite. The plateau cap is hard laterite that can't be cut into regular brick shaped pieces. Below this crust though is a softer iron rich soil. This semi indurated material is cut into brick shapes and left to dry. It hardens upon dehydration into a usable stone.

12) We took long walks in cool lush forest patches.

13) Deep in the forest we visited my friend's family temple, a hidden jewel with a spring fed bath. These temples act like a social glue, bringing families and communities together on religious and other occasions.

14) On the way back via Kumbharli Ghat we caught sight of the majestic Western Ghat Escarpment.
 

until next time! 

Geology Excursion To Tamhini Ghat And Korlai - India West Coast

On December 16 and 17, I took part in an excursion to the village of Korlai. This place is about 150 km west of Pune. The trip was organized by Deep Dive India, a venture started by my cousin Shirish Kher. The idea is to offer participants an immersive experience into one or two specialized fields.  On offer for this trip was geology and archaeology. I was the designated geology expert. The accompanying archaeologist was Sachin Joshi, a researcher from Deccan College Pune.

It was a lot of fun!

The group was mostly made up of working professionals with an interest in nature. Many of them came to know of this trip from my Twitter feed.  We drove westwards along the Deccan Plateau. Then, we descended the Western Ghat escarpment along Tamhini Ghat.  On this section, we made several stops to survey the landforms and to examine lava flows. I also gave the  group an introduction to Deccan Volcanism. After crossing the coastal plain we ended up at the village of Korlai, where there was more geology on offer.

We stayed in a home stay in the village of Chaul, a few kilometers away from Korlai.

The next day, Sachin Joshi gave us a fascinating walk-through the Portuguese forts at Korlai and Revdanda. These two villages are on opposite banks of the Kundalika estuary. It is quite a beautiful location. The forts were established by the Portuguese in the 1520's,  a couple of decades after Vasco da Gama rounded the Cape of Good Hope and established trading contacts with rulers and merchants of the Indian west coast.

The satellite image below shows the backwaters of  Mulshi and Varasgaon dams on the edge of the plateau, Tamhini Ghat, the coastal plain and the locations of Korlai and Revdanda villages. The sinuous N-S trending white dotted line seen along the Tamhini Ghat just west of the backwaters is the Western Ghat escarpment.

..and here are more pictures from our trip.

I gave a brief preview of the trip and explained the physiography of our traverse which took us along the Deccan Plateau, down the escarpment and to the coast along a broad coastal plain.

Along the way at Tamhini Ghat, I stopped to point out a lava flow contact. You can see pipe vesicles at the base of the upper flow.

 In Tamhini Ghat, unrolling a satellite imagery, I explained the landforms and structure of the Western Ghat escarpment to geology enthusiasts young and younger!

 At Korlai coast the group is looking down at a dike.

I demonstrated the use of a Brunton compass at this dike.

And here is a view of some of the many dikes intruding the basalts along the west coast.

The rampart and walls of Korlai fort along the rocky coast. You can see a cannon protruding through an opening in the wall.

The group standing on the surface of a lava flow showing columnar jointing. You can make out the polygonal shape of basalt blocks.

Korlai village fishing fleet moored in a back bay with the open Arabian Sea to the right. View from top of Korlai fort.

A beautiful view of Revdanda Fort, built on a sand bar, with waves crashing on to the walls and ramparts.

A watchtower in Revdanda Fort

An entrance with icons of a saint and official markings carved on stone.

 Through a broken wall of Revdanda Fort, a view of the Kunadalika estuary. Korlai Fort is on the stretch of land seen on the opposite side of the river.

The group enjoying themselves, exploring the fractured basalts of the west coast.

A picturesque home in Revdanda village.

This was the first time I had taken a group out on an organized trip like this. I was a bit nervous to begin with. But the atmosphere was informal and the participants enthusiastic and curious. That led to many long and enjoyable discussions on geology and archaeology.

We will be doing a repeat trip along the same route in late January... more pics then.