Honeycomb Weathering - Rock Swiss Cheese

After a very long hiatus (almost a decade I guess) just like geological unconformities, I am back and I am going to make a conscious effort to post at least one blog (my geological encounters) per month. Let see how it goes....

Wondering the reason for the hiatus - Well a lot of things have been happening at my end, and I guess I did not know how to cope, but I am seeking help and this blogs are my effort to get back to my natural self, and keep pinning things that I really love and passionate about - that is to keep learning from the geological record and sharing with people who would like to read my geological rambling.

So I have been looking at some of my fieldwork diaries, and one thing that I came across was the honeycomb weathering patterns on cretaceous Basalts from the western coastal belt of Deccan Volcanic Province.

 Small cavities separated by thin septa of unweathered basalt rock, making it highly porous.

The longer the cheese is fermented, the bigger the eyes or cavities will be. Something similar happens along the rocky coast, where regular onslaught of sea lashing on the rock with long duration of salt spray, sand-laden wave & wind crashing on the rock surface abrades to sculpt a beautiful pattern resembling a honeycomb structure, isn't that cool!! These amazing Swiss 🧀-like patterns are a result of honeycomb weathering a.k.a Tafoni, a form of cavernous weathering that arises from a combination of physical factors such as moisture absorption, marine-laden sand abrasion, wind corrosion and salt crystallization, and chemical processes like oxidation and dissolution acting on rock surfaces, like these basalts along the Konkan rocky shores for very long geological time (post-dating the basalt outpouring of 62 mya). These small cavities separated by thin septa of unweathered rock continue to evolve and when you fast forward time these patterns continue to coalesce to form bigger and more complex cavities. The continued onslaught by salt, wind, and waves abrades the surface forming cavities sometimes as big as 0.8 meters wide. 

The small cavities coalesce into bigger ones over time by the continued battering of physical and chemical agents. 

Just as bees meticulously construct hexagonal cells to efficiently store honey and pollen, natural processes like wind, water, and chemical weathering act on basalt to create these distinctive patterns. Most importantly, when extensive patterns exist they provide storage for freshwater in otherwise impervious hard rock basalts along the coastal belt, and is a source aquifer rock for natural springs along the coast. Also, these cavities are also home to many crustaceans along the rocky beaches of western Konkan plains.

A closer look at the honeycomb structure. (Telescopic leveling rod for scale)

Disclaimer: So if you see such patterns next time on a rock thinking of it as a 🧀 because I said so, and risk of biting into it. I can not guarantee the structural integrity of your 🦷. Cheers! 🤓😆

Landslide engulfs Malin village

The news is all around about the massive landslide that occurred in Malin village on 30 July, located in northwest part of Pune district, Maharashtra. It was triggered by torrential rains, where around 150 people are still trapped and missing in those slushy debris, and 31 now being reported dead. The rescue work is being hampered by the continuous downpour in that region. I hope rescue workers are able to pull out survivors, as now it is race against time. Really heart moving images from the disaster site on the news channels.   

Village lady lamenting over the loss of her dear ones and the house that has been totally devastated . (Photo source: www.firstpost.com)

Landslide debri that swept over the village burying 40 houses. (Photo source: www.firstpost.com)

Location of the village - Malin from Google Earth.

The landslide hit the village in the night when the locals where asleep. It seems it took hours to raise the alarm when a local bus driver alerted officials on discovering that Malin and the road leading to it were no longer to be seen - (source BBC). From the images and videos online it looks to me that they contain loose soil, weathered basalt rock fragments, vegetative matter (trees,plants, etc), water and air; which have formed a mixture of slurry that moved down slope. That gives little or no time to escape, indicating that the speed of the slide would have been really fast. Such kind of debris flows are common after a sustained period of intense rainfall, which is supported by the Met department data of 152 mm rainfall that occurred in the past 48 hrs. Apart from the intensity of rain - inherent nature of the slope forming weak or low strength rock/soil, highly weathered rock material and presence of some rock structures (joints and fractures), slope parallel cracks, interface between rock and overlying weathered rock/soil, etc. are one of the reasons for the slope failure uphill. The landslide can also be attributed to different reasons like the role of development (like ground leveling, road construction) and deforestation up-slope, excessive grazing and annual wild fires that make the slope more prone to landslide during heavy rains.

Cattle tracks along slopes while grazing also destabilize the slope during monsoons. (Photo credit: R. Thomas)

Areas that are especially close to the edge of the Western Ghats escarpment are more vulnerable to landslides. Though landslide occurrence is very common during the monsoon along the western ghats of Maharashtra, this occurrence surely highlights the unpreparedness or plans that are required especially for vulnerable communities located along the slopes. Areas prone to landslide occurring along roads that snake through the western ghats are in many places secured by retro-fitting with rock-bolts and geonets. But, what about those villages that are nestled in the valleys of the western ghat escarpments??

A blog article on AGU by Dr. Dave Petley, highlights the use of NASA TRMM landslide warning tool in forecasting potential areas of landslide. The tool - Tropical Rainfall Measuring Mission provides an accurate estimates of the rainfall over the strong-monsoon areas. This information is fed into atmospheric and oceanic models to help in delineating likely places for landslides. In the article, he also points out a geomorphic feature - 'topographic hollow' above the village as a likely feature for concentrating intense rainfall during overland and soil flow, resulting in increase pore water pressure in the soil and later breaking as a debris flow that engulfed the village. 

TRMM data for the Malin landslide, accessed 31st July, the orange colour indicating likely places for landslide.

The disconnect between economy and agriculture

Agriculture is supposed to be the backbone of the Indian economy. But, we do not see agriculture actually contributing to growth of the economy in a big way. There are several reasons for the bad performance of this sector, of which the disconnect between the market and the agriculture is one of the reason, and the least attention given especially in those drought prone areas, where the farmers have to face the uncertainties of rainfall. 

The picture below just gives the glimpse of the loss that I am talking about. It is a story of Mr. Nitin Gofne, who is a farmer from Jaoli village in Phaltan - a taluka (block) from the Satara district of Maharashtra. The area has been in the grip of severe drought for the last two years. His Ox is left free to graze his farm plot, in which he had grown tomatoes. A commodity that requires a lot of water. You might be wondering, why did he grow where water is already so scarce? Well most of the people in the village do not have other source of income apart from farming. Two years of continuous drought (and probably being a drought area) has left them with no income from farming. He grew tomatoes with a hope that it will give him those additional cash to grow other crops from the sale of tomatoes, and help him revive his financial situation. But the fall in tomato price in the market left him in a loss, so the result he being unable to make those additional cash and make up for the loss of income during the drought. 

How did I end up meeting him? I was there with an organisation to help them assess the groundwater aquifer in that village, ended up talking to him and getting to know his sad story. But what can be the solution to this? There is no fixed price and all those water used in growing those tomatoes is all gone waste. Such situations cannot help to strengthen our agriculture nor is it a sustainable use of our natural resource. It will keep fueling the never ending cycle of migration of people from rural to urban. I feel we need to bridge this gap by bringing market to these farmers, so that they get the right price for the products they grow, right advise at the right time on the type of crop to be grown based on available water resource; especially when they use those valuable resource of water from the ground. Is it not possible to use the current mobile technology/ revolution for making that connect!?!

Mr. Nitin, a young farmer from Joali village, Satara.

Pillow Basalt lava structures of Karnataka

Pillow Basalt - A feature seen today forming only in oceans along active rift margins or submarine volcanoes. But the Pillow basalt lava structures of Karnataka are far away from any active submarine volcanoes or mid-oceanic ridges (see the white down arrow showing the location of Pillow basalt far away from any active submarine volcano vents or oceanic ridges). 

Position of Mardahalli Pillow basalt w.r.t to the active Andaman Sea Back-Arc Basin (BAB) in the east and mid-oceanic Carlsberg ridge (diverging spreading center) in the south west.  (Image courtesy: Google Earth)

They were formed ~2.8 billion years ago, and provides an important clue to the evolution of precambrian peninsular India. I visited the site during my masters study in 2009, and this small mound hosts an important clue to submarine volcanic activity of Peninsular India during the Precambrian times. 

You might be wondering how does it look like? They look like buns or pillows - a feature formed when hot molten basaltic magma slowly erupts under water and solidifies so rapidly to form roughly spherical or rounded pillow-shape. Such pillow basalts can be seen forming even today along the mid-oceanic ridges or where sub-marine volcano erupts in the ocean. The lava gets chilled so fast that part of the flow separates into discrete rounded bodies a few feet or less in size. The pillow basalts when erupted under water forms a chilled rind on all sides of the extrusion. 

Features of pillow structure - rind, vesicle zone and core seen on pillow lava cliff section at Mardihalli hill (marker pen for scale). (Photo by: R. Thomas)

The hot rind is solid but elastic (like a balloon), and continuous injection of lava into it leads to bulbous, spherical, or tubular lobes that eventually solidify to form pillow-shaped masses of basalt. Have a look at the video of pillow lava formation.

The pillow lavas structures of Mardihalli hill in Karnataka is one of the featured national geological monument on the Geological Survey of India website. It is located near Maradihalli, a small village situated in Chitradurga District, Karnataka. But not many know about it or is not part of the travel itineraries of many tourist. It is nestled within Chitradurga schist belt of Dharwar Group and is one of the best preserved of its kind in the world. However, there is another similar pillow lava monument located in the Iron ore belt of Nomira, Keonjhar District, Odisha. To get there is very easy, it can be approached by a metalled road via Ayamangala which is about 180 km from Bangalore. Maradihalli is 16 km southeast of Chitradurga town and 4 km north of Ayamangala village, along the NH-4 (Bangalore –Pune).

Pillow lava location just south of Maradihalli village. (Image courtesy: Google Earth)

The visit to the site was part of geological mapping study exercise together with Geological survey of India. What I remember so fondly is standing beside this cliff with my chisel end hammer, and being carried away in the geological past, imagining the under sea eruption. But what has made this moment come alive once again is the paper by Duraiswami et. al. published last year in the Journal of Volcanology and Geothermal Research on the 'Emplacement of pillow lavas from the ~2.8 Ga Chitradurga Greenstone Belt, South India: A physical volcanological, morphometric and geochemical perspective'. 

Stacked pillow lava structure at Mardihalli hill- a national Geological Monument. (Hammer for scale)  (Photo by: R. Thomas)

How were they placed there? The research article attributes its placement to marginal shallow marine inter/ back arc basin. The study also shows repeated budding of larger pillows, producing a series of interconnected pillow units indicating fluid lava that was emplaced on steeply dipping flanks. 

Budding (indicated by black arrow) of a pillow lava /basalt at Mardihalli hill. (Photo by: R. Thomas)

The study was also carried on another hill along the road northwest of Mardihalli near Kunchiganalu marked as Chitradurga hill in the literature, which shows individual pillowed flows alternating with massive submarine sheet flows that are devoid of any vesicles (I did not visit this one). Both Mardihalli and Chitradurga hills are part of the north-south trending hills of the Chitradurga greenstone belt that mimics a back arc submarine basin. The main outcomes of the study of the pillow lavas shows - they were emplaced at low to moderate effusion rates (≤ 5 m3/s), and erupted as tholeiites (not as andesites as previously interpreted). The study shows Back Arc-Basin affinities based on the geochemistry, and envisages that the Chitradurga basin witnessed distinct episodes of submarine tholeiite eruptions that produced pillowed lavas, that later variably interacted with sea water to produce spilitized geochemistries. The field and stratigraphic relationships of the volcanics and associated clastic sediments suggest that the pillow lavas were emplaced in a shallow marine marginal inter/back arc basin.  - excerpts from the paper. For further read on this interesting article (only abstract available)  - Duraiswami, R.A., et al. (2013)

A plant whose smell mimics rotten flesh / animal excrement

It was last month, when I came across a strange smelling plant at Panchgani. I was in a midst of an open air discussion on 'Spring conservation in Western Ghats'. Suddenly I could smell something horrid, disgusting and unbearable smell in the air, something like a dog pooh or decaying animal. I could see also other participants looking at each other making disgusting faces and covering their nose. In the first place, I thought it might be some dead decaying animal around in some bush but when searched for it, to my surprise it was a small wild plant. I was really intrigued by its smell mimicking dead decaying flesh.

When asked about it to a botanist friend, I was told this "This plant is common in deciduous forests. It has a bulb in the ground. It flowers in March/ April. The photo is showing the flower. The middle stem like thing has pollen grains on the upper portion and female flowers on the lower portion enclosed by the spotted spathe (Petal like thing). The dirt loving flies are attracted by the foul smell and pollens get stuck to their legs, when they visit other flower they pollinate it. As soon as the rain comes the leaves come up though the ground. The pollinated flowers may turn into a fruit. It looks like corn cob dark green turning to sparkling red on maturity. In marathi it is called as Nurki (due to its smell). Botanical name is Typhonium venosum. Synonym is Sauromatum venosum family is Araceae. The plant is poisonous, but is planted as ornamental plant in some parts of the world"

Typhonium venosum plant (Image courtesy: wikipedia)

The fact that this plant/herb whose smell mimics dead decaying flesh or to some noses dog excrement leaves me pondering - how this plant/herb might have evolved in the wild to draw some specific insects to pollinate its species esp. the flies? So, if any of you happen to smell something horrid in the wild don't be carried away like I did.    

The horrid smelling plant in the wild. Notice the three flies sitting on the plant. (Image credit: R. Thomas)

Oldest known microscopic Zircon crystals confirms Earth's crust formation to 4.4 billion years ago

A very tiny Zircon crystals extracted from a remote rocky outcrop from Western Australia's Jack hills region has been confirmed to be formed 4.4 billion years ago - a recent study published in the journal Nature Geoscience. 

Prof. John W.Valley from University of Wisconsin-Madison spearheading a team of international scientist, have used a new technique called atom - probe tomography in conjunction with secondary ion mass spectrometer to establish accurately the age and thermal signatures of the zircon crystals by determining the mass of individual atoms of lead collected in the sample after radioactive decay of Uranium. The findings have been build on an earlier study by Prof. Valley and others, published in Nature journal that used lead isotopes to date zircon.

These tiny Zircon time capsules play an important role in radioactive dating of rocks, as they contain Uranium atoms, which sets the clock on as they start decaying into Lead. In addition they have also measured oxygen isotope ratios that sheds some light on the cooling of the Earth. This present findings will help in understanding formation of the Earth's hydrosphere and in understanding how other habitable planets form. 

Indeed we have come a long way from 4004 B.C. for the age of the Earth given by James Ussher to 4.4 billion years that comes out from this present study. 

Place of Jack hills zircon crystal (4.4 Ga) in context to the Earth's time - line.
Image credit: Andree Valley/ University of Wisconsin

Reference and Further Reading:
1. University of Wisconsin-Madison. "Oldest bit of crust firms up idea of cool early Earth." Sciencedaily. ScienceDaily, 23 February 2014.

2. John W. Valley, Aaron J. Cavosie, Takayuki Ushikubo, David A. Reinhard, Daniel F. Lawrence, David J. Larson, Peter H. Clifton, Thomas F. Kelly, Simon A. Wilde, Desmond E. Moser, Michael J. Spicuzza. (2014): Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography. Nature Geoscience.

3.Wilde, S. A., Valley, J. W., Peck, W. H. & Graham, C. M. (2001) Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago. Nature 409, 175–178.

Geo-spotlight: Observations of first ever advancing rhyolitic obsidian flow at Puyehue-Cordón Caulle volcano in Chile

A team of geologists from Lancaster University in United Kingdom, University of Mainz in Germany and Victoria University of Wellington in New Zealand have reported for the first time a slow advancing lava flow of rhyolitic (more sticky and viscous lava than the usual red hot flowing basaltic lava) obsidian down the slopes of Puyehue-Cordón Caulle volcano in Chile, in their recent research article in Nature Communications. The most fascinating observation of this flow is that after almost a year from its last eruption in April 2012, when the lava from the vent had ceased to extrude; the flow is still progressing when visited by the team in January 2013.

Puyehue-Cordón Caulle volcano and its obsidian lava flow, still going nearly a year after the volcano stopped erupting. Credit: NASA Earth Observatory.

The reason for the slow flow is attributed to the thick carapace of solidified rubble strewn slabs, which has kept the lava core insulated from losing heat to the surrounding. Dr. Hugh Tuffen, a researcher from Lancaster University adds, “The effectiveness of the insulation provided by the ~10 m-thick upper crust is staggering - these things may keep moving for years to come. Viscous heating and latent heat of crystallisation in the interior can also help to keep them warm.”

Their results demonstrate how efficient thermal insulation by the shell of solidified lava crust allows prolonged advance of compound rhyolitic flow fields, and reveals unexpected resemblance with processes at basaltic lava flow fields elsewhere. This very unique flow is under the 'Geo-spotlight' and further similar studies of active lava fields will shed lights on the strange motion and emplacement of lava flows in general.

Photo images of the flow in concert with satellite images were used in constructing a 3D animation of the thick flow front. The animation created by a team member Dr. James Mike can be viewed on the BBC news website.