Jyotirao Phule On Watershed Management

Jyotirao Phule (1827-1890) was a social reformer from Maharashtra who worked for the emancipation of the lower castes and for improving the lives of peasant agriculturists. In Shetkaryacha Asud (The Cultivator's Whipcord), written in 1883, he describes the plight of poor farmers and offers some advice on improving yield through land management practices. 

An excerpt- 

The essence of leaf, grass, flower, dead insects and animals, is washed away by summer rain, therefore our industrious government should, as and when convenient, use the white and black soldiers and the extra manpower in the police department to construct small dams and bunds in such a way that this water should seep into the ground, and only later go and meet streams and rivers. This would make the land very fertile , and the soldiers in general, having got to working in [the] open air, will also improve their health and become strong. 

.....Therefore the government should maintain these bunds in good condition, especially the backwaters. The government should conduct surveys of all the lands in its territory, employing water specialists, and wherever it is found that there is enough water to be drawn from more than one source, these places should be clearly marked in the maps of the towns, and the government should give some awards to farmers who dig wells without its assistance. Also the government should allow the farmer to collect all the silt and other things extracted from rivers and lakes, as in the older times, and it should also return all the cow pastures to the villages, which it has included in its 'forest'. 

Phule covers many of the interventions that are recommended by watershed management specialists today. The last line of the passage I have quoted is telling. Preventing villagers from using what was traditionally considered 'village commons' has always been contested by the people. Phule also called for the destruction of the "oppressive Forest Department". The conflict between agriculturists, forest dwellers, pastoralists, and the forest department continues to this day. 

This essay, translated from Marathi to English by Aniket Jaaware, has been republished in Makers of Modern India, a compilation of essays written through the 19th and 20th century by influential Indian political activists and social reformers. The collection is edited and introduced by historian Ramachandra Guha.

Map: Paris Olympics Purple

I was hoping that this 1874 geological map of the Paris area was the inspiration behind the startling purple color theme for the recently concluded Paris Olympics. The map was shared on X (formerly Twitter) by the Geological Society of London.

The sedimentary strata are folded into an arc that looks like the purple athletics track! 

Alas, no. The purple color was selected because the organizers wanted a unique identity for the games. And apparently it made for better television viewing.

There is a geology connection to the athletics track though. A big component of the flooring is calcium carbonate usually obtained by grinding down quarried limestone. For these games, in keeping with the theme of sustainability promoted by the organizers, the purple track was made up of discarded mussel shells obtained from an Italian fishing cooperative. 

Oh well. I like my geology connection story better.

Remotely India: Bundelkhand Mafic Dikes and Quartz Veins

Remotely India #14

Do you see anything striking (pun intended) about this geologic map of the Bundelkhand craton?

Source: Sarada Mohanty 2023- Proterozoic Basins of the Bundelkhand Craton

Notice that the green lines are predominantly oriented in a NW-SE direction. The pink lines are predominantly striking NE-SW. These are magmatic and fluid intrusions into the Bundelkhand granitic crust. The green lines represent mafic dikes (Mg and Fe rich basaltic magma), and the pink lines represent quartz veins. 

The Bundelkhand craton is an Archean age block of continental crust. Like other Archean age terrains, it has a long history of magmatism, volcanism, and sedimentation. The oldest rocks, a suite of granitic rocks going by the term 'tonalite–trondhjemite–granodiorite', and associated volcanics and chemical sediments are as old as 3.4 billion years. Through the Archean the crust grew by repeated injections of magma. Voluminous magmatism petered out by around 2. 4 billion years ago with the formation of the Bundelkhand granodiorite batholith, an enormous subsurface body of congealed magma. Granodiorite is a calcium feldspar bearing variant of granite. This younger rock type covers most of the surface area of this terrain.

Geologic activity continued for hundred of millions of years after the emplacement of this batholith with the intrusion of these impressive dike swarms and quartz vein clusters.

Staying true to the objective of this series on Indian geology as seen from satellite imagery, the emphasis here will be on the field features of these intrusive bodies.

Giant Quartz Veins:

Locality- Northeast of Mauranipur, Uttar Pradesh.

The quartz vein stands out as a high long ridge. Steep sided blocks of quartz make up the spine of the ridge. Weathered boulders shed from the quartz vein have formed the surrounding slopes. This distinctive landform is instantly recognizable in the imagery as you explore this region.  

Locality: Southeast of Mohangarh, Madhya Pradesh.

Here you can observe the intrusive relationship between the giant quartz vein and the older Bundelkhand granite (BG) which crops up as low hills made up of a light toned fractured rock. The linear vein can be traced cutting across the host rock.

Locality: Southeast of Mauranipur, Uttar Pradesh.

At this location you can observe an unusual feature. Two quartz veins have split to form a tuning fork shaped geomorphic feature.

These quartz veins intruded the crust around 2.15 to 2 billion years ago. The quartz crystals contain bubbles of gas and minuscule amounts of liquid trapped inside them. They inform us about the temperature and pressure during precipitation of the crystals and about the salinity of the fluid. There are also tiny crystals of other hydrous minerals like chlorite and epidote found inside the quartz. These reveal the source of the fluid. Such studies conducted by Duttanjali Rout and colleagues identify two distinct sources of fluids involved in the formation of these veins. A hot moderate salinity fluid derived from the Bundelkhand granodiorite mixed with meteoric water percolation downwards through fractures. The deeper fluids were sourced from not more than 5 km in the subsurface.

A drop in the temperature and pressure of the rising silica saturated fluid as it encountered the colder meteoric water resulted in decrease of silica solubility and the precipitation of quartz. The giant quartz veins are the product of a vigorous Proterozoic geothermal system that lasted tens of millions of years. The researchers have drawn a comparison with Broadlands-Ohaaki geothermal system in Northland, New Zealand, and the Kakkonda geothermal system in NE Japan. Both are in granitic terrains and could be loose analogs for the processes in operation during the formation of the Bundelkhand quartz veins.  

There are differences in what we can observe in these ancient and modern systems. In the Proterozoic example, the surface expression of the silica rich geothermal system, the hot springs and geysers, have long since eroded away. We can study only the subsurface plumbing system. In the modern settings, the surface processes are apparent and the underground patterns of fluid flow have to be inferred. 

Mafic Dikes:

Locality- Northeast of Lalitput, Uttar Pradesh,

A NNW-SSE trending dike is exposed near Tera village. The surface expression of mafic dikes is very different from the quartz veins. The dikes weather away faster and are exposed as low relief hills with extensive boulder fields derived from the weathering of the dolerite rock. In the satellite imagery, you can see the dark toned nature of the boulders hinting at its mafic composition. Due to the spread of boulders around the dike, the width of the intrusion appears far more that its true width. 

Locality- Mahoba , Uttar Pradesh

An ENE-WSW trending mafic dike is surrounded by Mahoba town. As with the NW-SE trending cluster, these E-W trending intrusions also appear as dark toned low relief boulder strewn hills.

Locality- Mahoba, Uttar Pradesh.

This is a synoptic view of the E-W trending dike, captured by ISRO Cartosat. The white rectangle in the lower left of the image is the bounding area covered by the previous imagery. It is quite an extensive intrusion, and to the eastern end it can be seen cutting across outcrops of the Bundelkhand granite. 

Geochronologic work on these mafic dikes shows that the NW-SE trending dike swarm intruded around 1.9 to 1.8 billion years ago. The E-W trending group of dikes are much younger, dated to about 1.1 billion years ago. 

The geochemistry of these dikes point to an upper mantle source of the magma. The dikes are a variety of thoeliitic basalt, not too much different from the basalts of the Deccan Traps in Maharashtra. Unlike the shallow sourced fluid of the quartz veins, the source magma of the dikes was generated at least 50 km down in the mantle lithosphere.

The crisscrossing lines you see on a geologic map of the Bundelkhand craton are a record of geologic activity that continued long after voluminous granitic magmatism ended. In rare exposures, mafic dikes are seen cutting across quartz veins, indicating that they are the younger of the intrusives. Most of the geochronology data collected so far supports this field observation. Studies of the spatial patterns of the dikes and quartz veins too hint that they represent two independent deformation events. The formation of both these systems required extensive fracturing and faulting  of the crust by extensional forces. Geologists are still working out the reasons for these crustal disturbances. 

In the case of the quartz veins, the fracture systems tapped relatively shallow sources of heat and fluids. In the subsequent reactivation of the crust, much deeper fracture systems cutting across the crust tapped upper mantle sources of heat,  providing conduits for the passage of mafic magma to shallower crustal levels. 

These deep crust penetrating fractures and Proterozoic mafic dike swarms tell another story about the strength of the crust and the advent of plate tectonics, but that is fuel for another post!

I am having fun resurrecting my Remotely India series. Stay in touch for more explorations of Indian geology on this blog.

Ganga Earthquake, Nile, Deep Sea Habitats

Some readings over the past few weeks:

1) An Earthquake Changed the Course of the Ganges. Could It Happen Again?  Sediment load carried by big rivers like the Ganga often choke up channels and force the river to cut another path. Sudden channel shifts can also occur due to tectonic movements. A recent survey of the Ganga about 100 km south of Dhaka, Bangladesh , identified an old channel of the Ganga. Exploring this area, researchers came across veins of sand cutting across the sediment layers. These veins or sand dikes were  injected into the surrounding sediment. They are a sign of major ground trembling triggered by a large earthquake. Ground motion may pressurize buried sand and inject it  upwards. Further studies showed that this event may have been a 7-8 magnitude earthquake that occurred 2500 years ago. Kevin Krajick writes about this discovery and the larger geologic context.

2)  Lessons from the Nile about rivers and society. The Nile river has sustained agriculture, human habitation, and royal dynasties for millennia. A Nature Geoscience editorial summarizes a collection of sedimentological and geomorphologic studies that track the evolution of the Nile through the Holocene. Phases of the river cutting a deep valley changed to phases of the river flooding laterally and building fertile floodplains. This geomorphological evolution driven by climate change and more recent dam building have influenced agriculture and social systems in the past as well as the present. 

3) Ocean Exploration: Meet The Deep. I highly recommend this site. National Ocean and Atmospheric Administration, U.S.A., has compiled some stunning photographs and videos of deep sea habitats and the diverse forms of life that inhabit this little understood world. Corals, sponges, brittle stars, molluscs, worm tubes- attached to the bottom, living around energy sources such as hydrothermal vents and cold seeps. It is an absolutely fascinating exploration of the biodiversity of the deep sea. 

Octocoral and Brittle Star: Source NOAA Ocean Exploration

As a bonus, these images make great wallpaper for your mobile phone!

Field Photo: Unusual Himalaya Metamorphic Rock

My friend Emmanuel Theophilus, who spends a lot of time wandering in the high Kumaon Himalaya, sent me this photo of a feldspar rich gneiss.,

He observed this loose boulder near the small settlement of Bugdiyar in the Goriganga valley, north of Munsiyari town. Bugdiyar is located in the Greater Himalaya. This is a high grade metamorphic rock terrain. As you walk along the many trails that lead to places like Nandadevi Base Camp and Milam Glacier,  you can observe mica and amphibole rich schist with gleaming garnets, quartz and feldspar rich gneiss, migmatite gneiss (partially melted gneiss), and leucogranite (quartz and feldspar rich magma) intruding this high grade ensemble. 

This traverse takes you into the core of the Himalaya orogen, where high temperature and pressure during mountain building that took place 35 to 15 million years ago transformed the sedimentary protolith into metamorphic rocks. 

This particular gneiss rock has an extraordinary texture. I have never before seen such large feldspar (white crystals) in a metamorphic rock. Judging by the pebbles and other rocks strewn by the side, these are inches long feldspar grains. 

I want to introduce two terms used to describe texture in metamorphic rocks; porphyroblastic and porphyroclastic. Both these terms describe rocks with very large crystals surrounded by fine grained minerals. These are rocks with two distinct crystal size classes. 

Porphyroblastic texture forms when one mineral grows more quickly than other minerals during metamorphism. Large crystals of the rapidly growing mineral are set in a finer crystalline matrix. Both the large and small sized minerals have recrystallized, but at different rates.  

In contrast, porphyroclastic texture forms when there is a size reduction of some minerals , leaving one unaffected mineral larger than the rest. This situation occurs most commonly in fault zones where softer minerals may get crushed more easily leaving the resistant mineral as a large porphyroclast. These types of rocks have a broken appearance. The softer minerals become aligned to give the rock a prominent streaky banded texture. The more competent mineral may also develop an elongated shape.

Which of the above is the rock Theo found? My guess is that it is a porphyroblastic gneiss. Take a closer look at the beautiful large grains. They seem to be the result of growth during metamorphism, in the process engulfing small pockets of mica in their interiors. The rock lacks the streakiness and the often broken, bent, and stretched large grains characteristic of a porphyroclastic texture.

However, there is a subtle sign of deformation too. Have a look at this close up. 

The black arrows point to rugby ball shaped feldspar grains. They have a long axis and a short axis and appear to be stretched in one direction. Also notice the grey cracks running along the longer axis of many of these crystals and continuing into the rock. These are paper thin zones where force or stress was localized. The change in shape (strain) in the feldspar grains follows these very narrow zones of deformation. 

All of the above is my reasoned speculation on the origin of this texture. The next step is to meet up with Theo near Bugdiyar and walk along the Goriganga in search of the outcrop.

The Goriganga near Bugdiyar. It is spectacular out there!