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.

Graphic Of Engineered Geothermal Energy Projects And India Update

The Economist on Engineered Geothermal Projects...

with a nice graphic...

Here is a graphic summarizing geothermal energy potential from India

 Source: Geothermal Energy Resources and its Potential in India

Gap along the Himalayan axis where high heat flow is associated with granitic intrusives is because the geothermal potential of Nepal is not shown. Within peninsular India all the high heat flow regimes fall along either old Precambrian weak zones which have been reactivated during late Paleozoic -Mesozoic rifting events or coincide with the evolution of the western margin of India during Mesozoic rifting from Africa /Madagascar / Seychelles. This rifting resulted in lithosphere stretching and thinning and hot mantle upwelling.

The focus in India has been on conventional geothermal energy exploration in the vicinity of volcanoes, geysers and hot springs where high heat flow occurs at shallow depths of a few hundred meters. These projects use naturally occurring steam and hot water to generate electricity. The estimate is that these shallow heat flow sites could potentially generate up to 10,300 MW of electricity. Engineered geothermal systems (EGS) projects in which water is circulated along drilled pathways to great depths to heat it up can be located in areas of relatively low heat flow. EGS have not yet been explored in any detail in India. These projects are more expensive but because they don't have to be located near unusually high heat regimes the aggregate energy potential may be even bigger than what is estimated for conventional projects.

Everything right now is still in the "estimates and potential" stage. Not much energy if any at all is being produced from any of these sites. So far at least the government has been neglecting this clean energy resource. We lack the right policies to make both conventional and engineered geothermal energy economically viable.

Geothermal Energy And Earthquakes

Theunis Bates at Sphere has a good write up about the link between geothermal energy projects and earthquakes.

These projects are controversial. The company that started a geothermal project in Basel, Switzerland is facing lawsuits for allegedly triggering earthquakes. Another project in California was recently canceled due to similar earthquake fears.

From the article:

Paul Younger, a professor of energy and environment at Britain's Newcastle University, says that it's not unusual for much smaller tremors to be felt on the surface when pressurized water is forced into rock deep underground. But, he adds, the process is normally only carried out in seismically stable areas, as the shakes caused by hydro-fracturing can interact with existing deep faults and cause larger trembles.

And Basel is anything but stable. The city has a long history of quakes and was all but wiped out in 1356 by an estimated magnitude 6.5 earthquake – the largest ever known to have occurred in Western Europe. "What they were doing was actually fairly conventional," Younger says. "It's where they were doing it that was unconventional. If you go drilling and stimulating near a known active fault, you're asking for trouble."

That may raise a question. Why not just drill in portions of the crust that are known to be structurally very stable and which have no active faults?

....geothermal projects will almost always be located in geologically active areas with lots of faults and which are earthquake prone because the required heat will be found at shallower depths making such locations economically more attractive than drilling deeper in colder more stable parts of the crust.

As our understanding of faults in geologically active regions increase it may be possible in the future to more carefully select sites based on how "stressed out" individual faults are....but there will always be a general overlap between geothermal sites and earthquake prone areas.

Here is the situation for India. Earthquake potential (increases in darker shaded areas) compared with geothermal potential. There is large overlap as expected.

According to a report by D. Chandrasekharam of the Indian Institute of Technology Mumbai, the geothermal provinces of India have a potential to produce around 10,600 MW of power. I haven't seen other government figures for this.  The Ministry of New and Renewable Energy website does not have the numbers for geothermal. 

In any case, if this industry is to have a future, geologists and engineers will have to grapple with the connection between attractive geothermal energy sites and potential earthquake hazards and also importantly develop strong transparent public outreach mechanisms to disseminate information for review and debate.

Tip: Geology.com

Triggering Earthquakes From Geothermal Energy Drilling

There is a very interesting article in NYtimes by James Glanz on the nascent geothermal industry in the U.S. and recent efforts to start projects to recover this energy. The article focusses on the efforts of one company AltaRock, who is currently in the process of getting through various permission to start a project north of San Francisco. They have received permission to drill from the Bureau of Land Management but are awaiting permission to fracture the rock.

And that is what the controversy and fears are about, that hydro-fracturing of the subsurface rocks might trigger damaging earthquakes.

This has happened once before near the town of Basel, Switzerland in 2006 and the article has quite a dramatic description of the events:

The opening of each fracture is, literally, a tiny earthquake in which subterranean stresses rip apart a weak vein, crack or fault in the rock. The high-pressure water can be thought of loosely as a lubricant that makes it easier for those forces to slide the earth along the weak points, creating a web or network of fractures.

Mr. Häring planned to use that network as the ultimate teapot, circulating water through the fractures and hoping it emerged as steam. But what surprised him that afternoon was the intensity of the quakes because advocates of the method believe they can pull off a delicate balancing act, tearing the rock without creating larger earthquakes.

Alarmed, Mr. Häring and other company officials decided to release all pressure in the well to try to halt the fracturing. But as they stood a few miles from the drill site, giving the orders by speakerphone to workers atop the hole, a much bigger jolt shook the room.
“I think that was us,” said one stunned official.

Analysis of seismic data proved him correct. The quake measured 3.4 — modest in some parts of the world. But triggered quakes tend to be shallower than natural ones, and residents generally describe them as a single, explosive bang or jolt — often out of proportion to the magnitude — rather than a rumble.

Triggered quakes are also frequently accompanied by an “air shock,” a loud tearing or roaring noise.

You can just imagine the panic in the nearby community after this sequence of events. The project was shelved.

AltaRock claims it has learned from Basel and has a developed superior method that minimizes risk. They say that the area they have chosen in Lake and Sonoma counties has a history of only small earthquakes and their project will steer clear of large faults.

Its not clear though how they or any other company could stop small tremors from cascading into a larger earthquake. The situation is not at all similar to say capping a well if you want to stop production. I am not a seismologist but I don't think we know enough about stress initiation and propagation through fracture networks to be confident about thresholds. Stop hydro-fracturing if earthquakes reach say 1.5 on the Richter because anything above that is a potential trigger for a larger one. I doubt if we are confident about the science to use arbitrary thresholds to minimize earthquake risks.

Another point I wanted to put out is that such geothermal projects will necessarily be located in areas of high earthquake risk. Geologically active regions will be the ones with enough heat nearer the surface and it makes economic sense to take advantage of this shallow natural heat and avoid drilling too deep. Which mean that the geothermal industry if it has to grow rapidly without getting tangled in litigation and protests must have a transparent and honest dialogue with various stakeholders about the current state of the science of earthquakes and the risks hydro-fracturing entails. For the people living near these project areas, this is not just a Not In My Back Yard because it spoils my view kind of a protest situation.

In this regard AltaRock has not made a good start. At least going by the NYtimes article the company has been less than forthright about the risks involved. For example in the seismic risk report it filed it did not give due importance to the connection between the Basel earthquake and the geothermal drilling despite Swiss seismologists agreeing that the drilling and fracturing of the rock did cause the earthquake. Even senior BLM engineers involved in giving permissions were unaware of the Basel incident and acknowledged that this information should have been disclosed.