Thursday, November 24, 2022

Mid Oceanic Ridges: Geodiversity And Biodiversity

Mid Oceanic Ridges. Unlike continental mountain chains, these undersea mountain ranges are invisible to our day to day gaze. 

Yet, they are among the most dynamic of geologic features. They form where tectonic plates split and move apart, and new ocean floor is generated by upwelling magma. Sea water percolates through the cracks in this new crust, heats up in the subsurface and then rises carrying with it gases and metals. These vigorous hydrothermal circulation systems provide a link to exchange chemicals between the mantle and the crust. Varied microbial and macrofaunal communities colonize these environments depending on proximity to magma, the strength and chemistry of hydrothermal systems, and the nature of bedrock composition and fault controlled topography. 

Some specific geologic settings, those with serpentinite rocks,  have recently attracted great interest because they are thought to have provided the right combination of heat and chemicals to stimulate pre-biotic chemistry and the origin of life.

Gretchen L. Früh-Green and colleagues review this fascinating underworld, bringing out, both, the diversity of geologic processes at work and the resulting biodiversity that depends on this varied geology and energy supply. The introductory paragraph shared below gives an idea of the importance of this geological environment.

"Mid-ocean ridge (MOR) systems extend approximately 60,000 km around the globe and are the most dynamic and continuous tectonic feature on the planet (Fig. 1). On average, about 3.3 km2 yr−1 of new oceanic crust is generated at global spreading centres, which account for >70% of the total volcanism, and where about 60–70% of the Earth’s surface has been produced over the past 160–180 Myr (ref.2). Mantle melting, volcanism and faulting at MORs drive hydrothermal circulation that allows the transfer of heat, chemical compounds, metals and volatiles from the asthenosphere to the hydrosphere and biosphere. Approximately 75–80% of the Earth’s total heat flux occurs as the oceanic crust ages, and it is most pronounced at ridge flanks, where low-temperature fluid flow continues off axis for millions of years and contributes to global biogeochemical cycles. It is estimated that the volume of the ocean circulates through the oceanic ridge system in much less than 1 Myr (ref.6).

Spreading centres are one of the most extreme environments on Earth that can support oases of life at high temperatures and thriving in perpetual darkness. Microorganisms obtain energy from magmatic gases and chemical compounds of altered oceanic crust, rather than from light, through a process called chemosynthesis. In turn, many of these microorganisms symbiotically sustain macrofaunal communities that populate hydrothermal vent environments. The microorganisms with the highest known growth temperature on Earth are found within MOR hydrothermal systems and investigation of their genetic diversity has changed the current view of the tree of life".

I have put the last sentence of the first paragraph in bold to highlight the scale of this geological system. This is rich and rewarding reading. The paper is open access.

Gretchen L. Früh-Green, Deborah S. Kelley, Marvin D. Lilley, Mathilde Cannat, Valérie Chavagnac & John A. Baross: Nature Reviews Earth & Environment- Diversity of magmatism, hydrothermal processes and microbial interactions at mid-ocean ridges.

Thursday, November 10, 2022

Milam Glacier Trail - Geology

Geology enthusiasts will find the Milam Glacier trail captivating. The river Goriganga emerges from the glacier and flows in the Johar valley in this region. I walked the trail in Mid October, and came across a variety of geological features of interest. The trail begins in the village of Lilam, just north of the town of Munsiyari in the Kumaon region of Uttarakhand. It passes through the steep Greater Himalaya, and later northwards, through the Tethyan Himalaya.

The map below, intended more to show the geological set up, shows the trail as a red line. It depicts the trail only until Rilkot. Milam, the end of the trail,  is about 20 km north of the extent of this map.  

The Greater Himalaya (GH) and the Tethyan Himalaya  (TH) are two thick slices of the Indian crust which were moved southwards by great thrust faults as India collided with Asia about 50 million years ago. Both the GH and TH are made up of sequences of rocks that formed on the northern margin of the Indian plate over a vast period of time. The rocks range in age from the Proterozoic to the Eocene (1.8 billion to ~50 million years old) The GH consists of rocks which were buried to great depths during the India-Asia collision and metamorphosed at high temperatures and pressures. On the other hand, the TH rocks experienced only shallow burial and show a light metamorphic imprint while retaining many of their primary sedimentary characteristics. 

This post is mainly a visual journey intended to help trekkers make sense of the geology they will encounter along the trail. Short explanations accompany the pictures and videos. 

The map above shows three major fault zones. All three dip (tilt) north.  In Munsiyari, while you wait for your trekker permit to get processed, walk down the main bazaar road towards the petrol station. Keep a watch for the rock outcrops on your right. These are limestones of the Lesser Himalaya caught up in the Munsiyari Thrust Zone, the southernmost of the faults in this area. 

The picture collage shows the deformation in the fault zone rocks. Shearing along the fault has produced a shiny smooth surface and a mica like character to the bedding surfaces. They will feel like talc to the hand, or like porcelain. Sedimentary layers also show folding and striations, two typical deformation features along faults.

This rock below,  know as augen gneiss,  is one of the iconic rocks of the Munsiyari area. It is among the oldest dated rocks in the Himalaya, estimated to be between 1.9-1.8 billion years old. While the limestones near the petrol station are positioned below the fault plane (footwall), the augen gneiss is part of the hanging wall (above the fault plane) of the Munsiyari Thrust. Notice how the white feldspar grain (porphyroclast) is deformed into a sigmoidal shape. The feldpar is an inch in length. White arrows denote the sense of motion along the fault.The Munsiyari Thrust, as is the case with other major thrust faults in the Himalaya, shows a primarily "top to the south up" sense of shear. This means that the thrust direction is southwards.


 From Lilam, at the start of the trail, you will pass through another great fault zone known as the Vaikrita Thrust or the Main Central Thrust. The MCT carry the Greater Himalaya rocks in its hanging wall. Due to soil, scree and vegetation it is hard to see fresh rock outcrops. The picture shows the general disposition of the GH and their appearance (taken from a construction site near Lilam). These banded rocks are called gneiss and they formed when sedimentary rocks were subjected to high temperatures and pressures.


A few kilometers ahead near Bugdiyar, the Goriganga has cut a narrow gorge. It is an awe inspiring site! Check out this video. Permanent link - Goriganga Near Bugdiyar

A road is being constructed between Lilam and Milam. Sections of it coincide with the old trail, while in other parts you can avoid the road and walk the old route. Ahead of Bugdiyar, from Nahardevi to Laspa, I walked along the new road which has exposed some amazing rocks. Here, you are walking along rocks which were buried to 20-25 kilometers depth and then exhumed! Conditions were so extreme, reaching more than 800 deg C,  that the sedimentary/metamorphic rocks partially melted to form a rock with igneous and well as metamorphic features. These mixed rocks are known as migmatites. 

The video shows a rock wall with migmatite gneiss. Notice the white bands which is the melt (leucogranite), while the darker layers are the source metamorphic rock. The video spans about 25 feet. Permanent Link - Migmatite Gneiss Nahardevi


Another close up of leucogranite cutting across (dike) gneiss layers. The leucogranite magma then gets injected parallel to the layering or foliation, forming a sill (topmost light colored layer).The gneiss layers are about 2-3 feet thick. 

Ahead, in the Laspa area, you walk across the northernmost of the great fault zones, the South Tibetan Detachment System, also referred to as the Trans Himadri Fault. Across this zone, you will notice a change in the metamorphic grade. The gneiss and migmatites give way to low grade metamorphic rocks like slate and phyllite and quartzites. 

The pic shows an outcrop of carbonaceous slates and quartzites intruded by leucogranite (vein is 6-10 inches in width).  The dikes and sills of leucogranites become rarer as you walk northwards and finally disappear by the time you reach Rilkot village. The rocks from hereon along the trail are part of the Tethyan Sedimentary Sequence.


From Rilkot you enter a landscape profoundly shaped by glaciers. The advance and retreat of glaciers since the Last Glacial Maximum (20,000 years ago) has left behind characteristic glacial deposits. The two prominent types of glacial deposits seen throughout this part of the trail are lateral moraines and glacial outwash terraces. Lateral moraines is debris carried by glaciers along the walls of the valley. They are recognizable as linear ridges. Outwash terraces form when glaciers retreat and the meltwater carry and deposit sediment across the valley forming a plain. Subsequently, the river cuts down through these deposits, leaving flat topped terraces high above the active river bed. For more reading on this topic do refer to Nawaz Ali and colleagues work on the glacial history of the Goriganga Valley.

The pic below shows the Goriganga at Rilkot. LM denotes a lateral moraine of the Shalang Glacier (from a side valley near Martoli). Its age is uncertain but some scientists estimate it to be a relict of a glacial advance that took place before the Last Glacial Maximum. T refers to a glacial outwash terrace formed during a period of deglaciation about 12,000 years ago. 

 

Deglaciation between 16,000 years ago and 8,000 years ago resulted in two pulses of sediment deposition. Near Tola village remnants of these two episodes of terrace formation can be clearly seen, marked T1 (younger) and T2 (older).


 The video below shows a delightful steep climb up the Martoli terrace, a few km north of Tola. Erosion along the sides of the terrace has carved out the pinnacles you can see at the top. Permanent Link - Martoli Terrace.  

There are some structurally interesting outcrops of Tethyan strata near Milam. The picture shows steeply dipping near vertical beds which are folded (bracketed by yellow lines). This location is just before Milam village.


 Ahead of Milam village is this nice closeup of folds in slates and phyllite grade rocks. The picture spans about 15 feet in width. The Tethyan Sedimentary Sequence is part of a fold and thrust belt that formed in the early stages of Himalaya mountain building. 

Keep an eye towards the path from Milam village to the glacier. Strewn higgledy-piggledy is multi-colored rubble from various types of sedimentary and low grade metamorphic rocks. These are affected by multiple sets of fractures. I suspect that they come from a fault zone high up and unfortunately inaccessible to most trekkers. I have put together a collage of these pretty looking boulders.


Here is a map of the trail between Rilkot and Milam along with the geological divisions. You can use this to anticipate what type of terrain you are on. Expect to see high grade metamorphic rocks and leucogranites if you walk westwards, as for example towards Nandadevi Base Camp. And you will see sedimentary and low grade metamorphic rocks if you explore the side valleys to the east. 

Source: Nawaz Ali et.al. - Chronology and climatic implications of Late Quaternary glaciations in the Goriganga valley, central Himalaya, India

 As you gaze towards Milam village from a distance two distinct outwash terraces can be clearly seen. Here marked T1 (younger) and T2 (older).

This photo of Milam Glacier shows two beautiful lateral moraines. Notice these have a sharp crest suggesting there are young in age (compare with the LM near Rilkot). They are thought to have formed as recently as the Little Ice Age just a few hundred years ago!  

This trail is a gift to geologists. I did a rather quick nine day walk through the main trail and noticed so much interesting geology. Along this path are vestiges of processes that occurred at different times and at different levels of the crust, from rocks that formed in a seething hot metamorphic cauldron that existed during the peak of Himalaya orogeny 20 million years ago, to glacial deposits from the historical Little Ice Age when children skated on the frozen  Thames River and much of the northern hemisphere experienced intense cold phases.  

A final nod to this fantastic journey. Spectacular leucogranite dikes and sills intruding gneiss on the stretch between Nahardevi and Laspa. 

There is much left to explore. I will be surely going there again.

Monday, October 31, 2022

Milam Glacier Trail - Landscapes

Earlier in the month from October 10th to October 18th, I walked the Milam Glacier trail in the Kumaon Himalaya, Uttarakhand. A four day walk through the Johar Valley from Lilam village near Munsiyari to Milam took me past some fantastic landscapes and geology. 

After an initial breathtaking climb which takes you from about 6000 feet at Lilam to more than 9,000 feet at a high ridge known as Mainsingh Top, the trail descends towards the Indo-Tibetan Border Police outpost at Bugdiyar. After this, a gradual ascent takes you higher, with the rest of the walk undulating between 10,000 to 11,000 feet ASL. I was lucky with the weather. After walking the first two days in belting bone chilling rain the skies cleared and I was treated to some gorgeous views of the High Himalaya. 

I am posting a few pictures of the landscapes along this scenic route. The pictures are roughly ordered from the start towards the end of the trail.

The Greater Himalaya near Bawaldhar, a small resting stop which we came across on the first day.

Another view of the Greater Himalaya in the vicinity of Bugdiyar. Notice the steep slopes, narrow valleys and the sheer rock faces and the cascading Goriganga river. 

A lovely rough trail near the Laspa area. The October colors really makes the landscape radiant. 

After Laspa, the Greater Himalaya made up of high grade metamorphic rocks give way to the low grade metamorphic and sedimentary terrain of the Tethyan Himalaya. You do notice a change in the topography from the sheer steep slopes and narrow valleys typical of the Greater Himalaya to the wider valley forms and gentler gradients of the Tethyan domain. 

The Goriganga at Rilkot. The river is more serene here making a soothing gurgling sound as it flow past. Also check out the gorgeous longitudinal gravel bars in the river channel. Permanent Link: Goriganga at Rilkot.  


The high meadows of Martoli. This is a beautiful if desolate place with stunning views of the high Himalayan all around. 

A lone resident of Burfu surveys his kingdom. Most of the villages were empty of people as residents had migrated to lower altitudes for the winter. The flat plateau seen in the background is a glacial outwash terrace. It was formed by streams redepositing debris that accumulates in front of a glacier. Thick layered river deposits create a plain in front of the glacier. At a later point in time, the river cut through its own deposits, forming flat terraces stranded high on the valley slopes. 

Encounter on a lonely trail. After walking alone for hours, it is always fun to meet the locals travelling between villages. We met this small caravan between the settlements of Burfu and Bilju. Permanent link: Encounter at Bilju.

 A house in Milam village basks in the October sun. 

The Goriganga snakes its way down Milam Glacier through the fabled Johar Valley. This location is a few kilometers downstream of the glacier. 

Near Milam Glacier! The actual glacier is about 4-5 km upstream of this location, but this is a good photo spot along the trail.

What a trip! I think late September to early October is really the best time to visit this area. The countryside is lush and you get clear views of the Himalaya. The local residents have still not migrated to lower altitudes and you can get to enjoy their company in the many hamlets along the way. However, this year, rains continued well into the second week of October. I feel with climate change there will be a greater unpredictability to October weather in the future.

Finally, a big thank  you to Emmanuel Theophilus, Malika, Kamala Pandey, and Munna Singh Nitwal for being such gracious hosts and making my trip so memorable.

A post on geology tips for trekkers is coming soon... 

Monday, September 26, 2022

Readings: Earth's Ice, Neanderthal Women, Indian Monsoons

Some good stuff from the past few weeks.

1) How much of the Earth's Ice is Melting? Sid Perkins writes about the variety of methods of estimating ice loss from the high latitudes. These methods are showing where and how much melting is taking place, in turn, helping scientists make predictions of future sea level rise. The overall scenario is rather gloomy. 

2) The Lives of Neanderthal Women. "Archaeology is no exception to biases against women’s interests across science and the humanities". Archaeologist Rebecca Wragg Skykes expertly constructs a picture of what the lives of Neanderthal women might have been like.

3) Indian Monsoon Across Millennia. Stalagmites from a cave in Meghalaya, NE India are giving paleoclimatologists information about monsoon variability over a thousand years. Their geochemistry points to periodic deadly droughts that coincide with phases of major social and political turmoil in India. Paper authors Gayatri Kathayat and Ashish Sinha describe their research. 

 

Wednesday, August 31, 2022

LInks: India Aquifers, Early Bipedalism, Mars Geology

 Here are some interesting articles I read recently.

1) Mapping India's Aquifers.  Indian agriculture depends heavily on groundwater. To understand and manage this resource we need a good idea of the nature and extent of aquifers. Subodh Yadav, Joint Secretary, Department of Water Resources, River Development and Ganga Rejuvenation, Ministry of Jal Shakti, has written an informative article on the National Aquifer Mapping Program. Detailed reports are available to the public through the Central Ground Water Board, Aquifer Information and Management System page. Mapping and report availability is still work in progress.

2) Is Sahelanthropus the earliest biped? A good article by Brian Handwerk on the many questions spawned from a recent analysis of a 7 million year old femur fossil. Fossil remains named Sahelanthropus tchadensis were found nearly 20 years ago in Chad, and various studies have come to conflicting conclusions on whether Sahelanthropus could walk on two legs. Bipedalism is considered to be one of the key traits distinguishing members of the human branch from other apes and so there is a vital interest in understand the timing and circumstances of its evolution. 

3) Ground Penetrating Radar images from Mars Perseverance Rover. The indefatigable Mars Rover loaded with geological instruments is currently exploring the edge of the Jezero Crater on Mars. Here, rivers emptied into a large lake depositing sediment and building a delta. The first radar images show inclined sedimentary layers which could be the classic sign of a delta architecture or something else, scientists suspect. Read on! By Holly Ober, University of California, Los Angeles.