Decolonising Science Series: Resisting Earthquakes in Pre-Columbian Peru

When we think about earthquake resilience, we imagine the sky scrapers and we think about high-tech infrastructure. We visualise the colossal tuned mass damper (in the form of a giant metal sphere) in the Taipei 101, the trusses used to resist torsional forces by Transamerica Pyramid in San Francisco or even the seismic absorbers built into the foundation of skyscrapers such as the Mori Tower in Tokyo. Our thoughts generally turn to futuristic methods of protecting our modern buildings from large earthquakes. But the Earth has been experiencing quakes at least since plate tectonics dictated the crustal dynamics and our ancestors have been learning how to cope with them for thousands of years.

Ancient Ingenuity 

The first time I came across ancient methods of earthquake resilience was during my trip to Peru in Lima. We visited the Huaca Pucllana sight in Miraflores, which is thought to be a religious site built by people from the “Lima Culture” (named as such because they lived in the region of present day Lima not because this was the name of their society) approximately 1600 years ago. The structure itself is formed like a stepped pyramid made from nine million mud bricks.

The old and the new: Huaca Pucllana in the foreground, Miraflores in the background

The curious aspect of the building is that the bricks are stacked vertically, like books, with deliberate spaces between each brick such that the whole structure looks like a book shelf. A young boy in our tour group asked the guide why the bricks were stacked like that instead of the conventional horizontal style we’re used to seeing outside of this area. Our guide explained that this was how the Lima people mitigated the seismic activity that frequented the country: the space between the bricks dampened (i.e. reduced the energy of) the waves travelling through the structure thus preventing the pyramid from collapsing.

A closer look at the brick work at Huaca Pucllana

It is likely that this technique is a modified version of that used in earlier structures. Huaca Huallamarca in San Isidro is another stepped pyramid structure also located in Lima but this site was built approximately 1,800-2,000 years ago. The main difference between this religious site and Huaca Pucllana is that the bricks were rounded. Yet the “inter-void” technique, seen later in Huaca Pucllana, was also seen in Huaca Huallamarca, evincing its earlier use here. Sadly, it’s difficult to judge just how successful this technique was because Huaca Pucllana was neglected, allowing damage to the site. While the individual bricks may have been squeezed out of shape, the fact that the overall structure survived is a testament to this ingenuity.

This had me thinking: what other evidence is there of seismic resistance in history?

Now that is a nebulous question so let's go back to Peru for now. 

The Indestructible City  

Further north in Peru lies the ancient city of Chan Chan, the capital of the Chimor Empire from 900-1470 AD, that was located at the mouth of the Moche Valley. In the centre of the twenty square kilometre city are nine large independent “citadels” or “palaces” separated by thick high mud walls that were decorated with friezes. This political centre was surrounded by 32 “semi monumental” compounds and four production sectors. It is believed that at the height of its kingdom, the ancient city was home to 50000-100000 people and it was the largest city in Pre-Columbian South America. Yet all of this was abandoned when the Incans defeated the Chimu people in a bloody battle! So how did the world’s largest ancient mud citadel survive the seismic activity of Peru?  

The iconic Chan Chan walls are thought to withstand seismic activity due to their shape and size. The walls are tapered and thickened to 2.5 m wide at the base. They may have also been reinforced with “Guadua angustifolia” bamboo vertically and horizontally within the walls. There was also a suggestion that the adobe walls were strengthened with the use of expansion joints at every 5 meters. However, it is very likely that the width to height ratio plays the most crucial factor in the survival of the city walls and buildings.

Incan Innovation 

Then we have the Inca Empire which created the most spectacular architecture that still survives in Peru today. There were subtle techniques the Incans adopted to mitigate earthquakes. The windows, doors and rooms were built in a trapezoidal shape where the sides inclined inwards from the bottom up. It is likely that the Incans recognised that triangles are a “stronger” shape than rectangles because they help to disperse the stress during seismicity thus stabilising the overall structure. This is like the use of tapered walls in Chan Chan, but it is not the only technique that is reminiscent to previous kingdoms! Walls were built as two parallel lines of stone blocks that were filled with mud in between, which are thought to have a dampening effect on the seismic waves.

 The ruins at Ollantaytambo are the legacy of Emperor Pachacuti 

Tambomachay shows a range of Inca construction designs 

And then there were large scale construction methods… The cities and towns of the Incas Kingdom that were built on highlands were typically buttressed by farming terraces. The farming terraces are an iconic part of Incan Architecture: each terrace is several meters deep, several meters tall and they were made by digging into the mountains. The main way this helped withstand seismic activity is that the steep sided mountains were replaced by flat stepped shape steps which reduced the chance of mass wasting (e.g. landslides), which stabilised the region it supported above.

During the Spanish conquest, Ollantaytambo became the fortress of the Inca Resistance led by Manco Inca 

The farming terraces surrounding the Pisac Ruins

However, it is their masonry skills that give the Incas the fame in the world of civil engineering. Buildings were made from rocks that were uniquely cut and fit together like a jigsaw puzzle in such a precise manner, mortar was not needed to hold the structure together. This mortar-less construction prevented collapse during an earthquake: the bricks were free to shake but once the seismic activity subsided, the bricks would be forced back into place because they were specially cut to be in a certain position. The blocks were cut differently to each other in shape and size, compared to conventional bricks, but they fit perfectly with each other that it is often joked that you cannot even fit a paper between two stone blocks. Everything about this masonry technique of interlocking bricks, how the bricks were cut, transported and fit, continues to marvel people today.

Sacsayhuaman: A fortress, which overlooks the present day city of Cusco, hosts some of the best masonry work by the Incas

The streets of Ollantaytambo: The buildings use the stonework foundation built by the Incas

Macchu Picchu hosts the best examples of methods adopted to resist seismic activity. The Spaniards never discovered Machu Picchu, which is likely because the city was abandoned before the invaders arrived to the region; hence it escaped the destruction they brought with them. The Spanish destroyed as much of the Inca culture after the conquest. Buildings constructed by the Incas were taken down and individual stones would be transported to build new structures for the colonisers. Sometimes the Inca stonework would be used as foundation and the Spanish would build directly top, so even today when you travel through Peru, you can see buildings with a clash of Inca and colonial architecture.  The superiority of Incan civil engineering against contemporary western constructions were brought head to head during the 1950 Cusco earthquake: the Spanish church of Qoricancha was destroyed while the Inca base that it was built on remained intact. It's just one of the ways that the Incas were more technologically advanced than the primitive Europeans.

Machu Picchu: The Lost City in the Clouds

The Andes is the host of one of the cradle of civilisation, where "civilisation" was thought to have first developed, so it's no surprise that Peru is scattered with the ruins from a large range of time. The subduction of the Nazca plate under the South American plate makes Peru prone to Earthquakes so many kingdoms have had to adapt to these hazardous conditions. There are great examples of both small and large scale methods of mitigating earthquakes throughout Peru from the Pre-Columbian times and their survival today attests to their success today!

If you ever wanted to break a geologist's heart...

Credits to Rishi Dutta & Jazmin Scarlett for editting. 

EGU: A First Impression

The European Geosciences Union (EGU) is the most established geosciences organisation in Europe. Created in September 2002 as a merger of the European Geophysical Society and European Union of Geosciences, EGU now hosts over 17 different scientific journals and has over 12,500 members from students all the way up to retired seniors. However, EGU is probably most well known for its Annual General Assembly, which is the biggest geosciences event in Europe. Held in April every year, it attracts over 1,100 scientists to attend its event from all over the globe. This year, I had the chance to attend EGU as a representative of Bristol Earth Science's Diamond group. This was my first multidisciplinary international conference and with just six weeks of planning (I was asked to attend at fairly short notice), I couldn't wait to tick this off my academia bucket list.  

In 2017, EGU brought together 14,496 scientists from 107 countries (two from Bangladesh, woo!) to Vienna, Austria. Since the first General Assembly in France, it has now always been held in the Austria Centre Vienna (the largest conference centre in Austria). Participants are in charge of arranging their own accommodation and transport but luckily EGU provides a free public transport pass during the days of the conference and it's easy to get to the centre via the U-Bahn (stop Kaisermuhlen). I actually made the mistake of thinking that the conference was held at the Vienna International Centre so when I exited the station, I saw a huge crowd turning left and walking into the "visitor" entrance of the VIC. So like a fool, I followed them into the security check. This should have set alarm bells in my head but instead I was naive enough to think "Huh, this is pretty high level security for a geology conference". None of the guards thought my presence was odd even though everyone else in the queue was at least twenty years older than me and it wasn't until I made it all the way through that I realised I was in the UN centre... d'oh! After a smooth exit and a lost in translation moment (damn, five years of German did not pay off), I found myself at the correct venue.

At the entrance of the EGU General Assembly

With almost 5,000 oral presentations and over 11,000 posters, EGU can be overwhelming for newcomers, especially early career scientists. The EGU General Assembly website posts the programme on their website and you can filter the events by division, date and time. The best part of the website is that you are able to build your own personal programme by "starring" the talks you are interested in. The only criticism I have for the personal programme is that if you have quite a few sessions you are interested in and they overlap in time, the list design can make it difficult to plan. If I had more time, I would have made a timetable but perhaps it's something the EGU web designers can integrate into the website.

It was the session titled "What do diamonds and their inclusions tell us about processes in the deep Earth" that lured me to the EGU General Assembly. Although it was a small session, it had speakers from the US, France, Italy and Amsterdam. Conferences are a great way to see the current research and progress that has been made in your subject but also to keep check of what you know: when you're a PhD student, it can be easy to focus your reading in a certain direction. In the recent years of diamond research, there's been a lot of progress in the understanding of diamond forming fluids-melts (DFFM) and Graham Pearson's talk showed that DFFM found in fibrous diamonds have also been found in monocrystalline diamonds, suggesting that both the diamonds were formed through the same process(es) and went on to suggest that perhaps trace elements in fluid inclusions can be used to "identify" diamonds.  

I also took advantage of exploring other fields and dropped into talks ranging from studies into craters on Ceres to the impact of North Atlantic warming on European Summers in the early 20th century and even more familiar topics such as evidence of magmatism in Burma during the Cretaceous and Cenozoic. How much I gained from the talks really depended on the level of technicality and enthusiasm of the speaker, for example I didn't enjoy much of the talks on Kimberlites as I expected to (despite being the sessions most related to my field) but quite a few geophysical talks were really insightful. Regardless of your scientific background, I would encourage everyone to attend as many of the talks presented by EGU medal and award winners. I'm not sure if they aim for their presentations to be accessible to general audiences but I found all the ones I attended really easy to follow and every speaker was so passionate about their subject which reverberated in their talks. I would warn members next year to get to your favourite talks early because there were a number of cases where a talk was too popular and members were blocked from attending.

"Make Facts Great Again" symposium

As it has such a large attendance with members from a range of experiences, EGU is able to hold quite a few "union wide" events everyday and these include sessions on outreach, networking and debates. Initially, I never investigated these events because I was so focused on the academic talks but while I was at EGU, I was kicking myself for missing out on certain talks or prioritising one event over another. Some of the great debates and symposiums are based on how the scientific community can progress (such as the "Make Facts Great Again" symposium about how the scientist can engage with the general public - I was very unsatisfied with this talk, more on it another time) while others are about changing the structure of academia (group debate about if ECS should be judged on their publications). There are also chances to meet fellow Earth Scientist bloggers and tweeters as well as opportunities to explore your creative side with poetry and photography sessions. The special scientific events are really what makes EGU enjoyable.

Obligatory selfie with my first poster presentation in an International Conference

Every day, the Exhibition Halls host posters of the sessions that were held earlier in the day. You can view the posters any time of the day but if you want to speak to authors, the best time to come drop in is between 5 - 7 pm when scientists are required to stand by their posters. This was my moment to shine because I was specifically at EGU to present my results on lithospheric diamonds. Although a poster isn't as prestigious as a talk, the main advantage is that you're more likely to interact and receive feedback from other scientists. Speakers are only given 15 minutes to present including Q&A and I noticed that the majority of speakers actually didn't have enough time to answer any questions. During the poster session, I managed to personally meet quite a few scientists in my field and discuss my work and have the odd debate over a contentious summary. I actually found this the best way to network especially as someone who is very shy and didn't have their supervisor to introduce them to others.

One of the many networking events at the General Assembly

For some, EGU is their favourite conference while for others it's an experience only worth one visit in their academic career. The types of sessions are so diverse and how much you will get out of it will depend on your field of research: for a petrologist like me studying silicates in diamonds, there was only one session relevant to me but volcanologists on the other hand may find there is a lot to gain from the conference. This could make networking very difficult - every young scientist I met prior to my session was a Climate Scientist. The EGU conference however is great if you have a broad interest in Geosciences and would like to understand what is happening in a variety of fields or you are interested in extra-curriculum activities such as outreach. It is a conference that is definitely worth considering if you have the opportunity.

When my supervisor asked me to attend EGU in his place, I was very apprehensive. No one in my department was going to attend the General Assembly as a participant and there was only one small session I was interested in. In the end, I do not regret going at all and I found myself most times as giddy as a child in a candy store as I ventured into all the different sessions. In all honestly, there is so much going on at the conference that it doesn't feel lonely at all (though having lunch by yourself can feel a little awkward, you can go check out some stalls, posters or even work to ease the feeling). I spent two full days at the General Assembly and I felt exhausted by the second day - if you're going for a full week, I recommend breaking up the time with a bit of sight seeing - after all, EGU General Assembly is held in a very beautiful city.

I'm not sure if I would attend EGU conference as a PhD student again but if anything, it has prepared me for future multidisciplinary conferences I may attend in the near future.

A weekend in... Ireland

I knew I would kick myself if I didn't take advantage of Bristol's proximity to Ireland and Wales to explore the west side of the British Isles. We didn't manage to get decent flight prices last year because we always remembered to book flights when it was too late but this year we were prepared. Now planning a city break in Easter isn't very easy and with the added conservative nature of Ireland's Catholicism, it's necessary to plan your stay ahead of time. 

The weekend away began with an early flight from Bristol's airport to Dublin on Thursday. Our first stop was Beanhive Cafe for some brunch: I had the vegetarian brunch and James had the standard Irish breakfast. Both of us struggled to finish the meal, but only because they were excessively generous with their portions. We headed straight to Trinity College to walk around the college grounds (and to walk off our breakfast). I couldn't help but be surprised how small the university felt, like the size of just one college in Cambridge University, but I had to remind myself that the whole university was still spread across the city. Nevertheless, it felt a little familiar while walking around. We also went ahead to see the Book of Kells and the beautiful Old Library Exhibition also hosted in Trinity College. 

We wandered around Temple Bar area a little, crossing the River Liffey via Ha'penny Bridge and stepping into Temple Bar itself for a drink. We were still too stuffed from our brunch to have any food (that's how generous the portion was!) so we took a bus to Kilmainham Gaol. The jailhouse itself cannot be explored without a tour and as it is so popular, I strongly recommend booking ahead of time. We completely overlooked this and as I was scrolling through top sites of Dublin on the Tripadvisor app on our bus from the airport, I saw the warnings from previous tripadvisor reviewers. We instantly went on the Kilmainham Gaol website and saw that the next four days were booked out and only a few places were available on Thursday. Lesson learnt. The tour itself was excellent and gave us so much insight into the independence and partition of Ireland. On our way back to the city centre, we took a stroll through Phoenix Park.   

No one can escape Dublin without a night in the Temple Bar area so we went back there for dinner at a Spanish tapas place The Port House Pintxo. Now if we fell in love with one thing in Ireland, it was this place. From the cheese and honey dishes, the burgers and especially the empanadillas... We couldn't get enough of the menu. The restaurant itself had a pretty cool vibe to it, perfect for a date night. James was convinced that we had found the place and that we should have all our meals here. Even though we didn't return, because I'm pretty strict on trying as many different places as I can on a short city break, my tongue still dreams of this place.  

We started promptly on Friday as we were driving up to Belfast. Good Friday is considered a "dry" day because of a ninety year old law banning alcohol on particular christian holidays. This meant that all the pubs, and restaurants serving alcohol, would be closed and all the other restaurants and museums were likely to have shorter opening hours. Northern Ireland doesn't have the same laws and any information we found online suggested that everything was going to be open as normal, so we thought we would be making the most of our time spending the next two days in Belfast and around.

We couldn’t leave without having some breakfast and the cute little bakery Queen of Tarts near the Temple Bar area was on the top of our list. I opted for the smoked Irish salmon with free range scrambled eggs and toasted home-made brown soda bread and James tried the smoked bacon and leek potato cakes with poached eggs and roasted cherry tomatoes. Of course we needed something sweet from the bakery and we had the chocolate pecan tart and apple crumble to complement our savoury dishes (both were double YUM).

I wish I could say more of the drive up to Belfast, but in all honesty, I was asleep for most of it. We drove straight to the Titanic Belfast museum for the “Titanic Experience” exhibition. We originally planned to stay there for two hours…. Three at most, but we ended up staying til 6 pm (four hours!). It’s a very detailed museum, giving you details from how Belfast changed as a city during the industrial revolution to what the different class of rooms looked like on the Titanic. We drove a little around the harbour side to see the famous port that made Belfast what it is today.

The city still faces strong tension between the Catholic and Protestant communities and one of the ways this manifests is through the Peace Walls that have been built in a number of cities to separate the two and reduce "inter-communal" violence. The first Peace Wall was built in 1969 as a temporary solution to the Northern Ireland Troubles and the 1969 riots. However, they've only increased in number and size since then and approximately 109 Peace Walls are thought to exist across the country. The biggest and longest Peace Wall separates Shankill Road and Falls Road, which is the one we went to see. Although a poll in 2012 showed that 69% of residents believe the Peace Walls are still needed, the first Peace Wall was broken down in 2016 on Crumlin Road. The Northern Ireland Executive Committee has promised that by 2023, all the Peace Walls will be broken down (with permisson)! Alongside the Peace Lines, many murals and other street art can be seen around Northern Ireland as a result of the political nature of the city.

In the evening, we walked around Cathedral Quarter to find a place for dinner. A few places were already pre-booked, which again we didn’t expect for Belfast as it never looked busy, but they had a table for two in The Strip Joint where I tried the Hannon 35 day Himalayan salt beef steak. We stayed in Cathedral Quarter in the evening especially as I was pleasantly surprised how beautiful this area looked. We walked across the alleys and popped into Dirty Onion for the live music.

Saturday started with us walking around Dublin’s town centre. We went past the infamous Europa hotel, which is supposedly the most bombed hotel in Europe, on our way to breakfast at the Harlem Café (sorry, but the decor here put me at constant unease) and then strolled around the City Hall. Then in the late morning we visited Stormont Estate to see the Parliament buildings. 

We headed to Giant’s Causeway in the afternoon and had a little lunch at the National Trust café before enduring the harsh winds and rain on our walk to the rocks. Around 50-60 Ma, the region experienced intense volcanism. Basaltic magma intruded through the older chalk beds which formed part of the Thulean plateau, Europe's most "extensive" lava field. As the lava cooled, they contracted horizontally forming the polygonal pillars that makes the Giant's Causeway famous. The large igneous province that was broken up during the opening of the North Atlantic ocean making Giant's Causeway one of the few remants of the Thulean Plateau. I’ve seen many volcanic columns around the world but the best part of Giant’s Causeway is that you can climb the columns and see the actual polygonal features up close. 

A quick drive from Giant's Causeway is the Carrick-a-Rede Rope Bridge that is famous for its small 20 m rope bridge that connects the mainland to Carrickarede. The bridge was first built in 1755 to help Irish fishers to catch Atlantic Salmon. Since then, it has be altered and reconstructed several times to make it safer. Salmon fishing has stopped in the region because of the dwindling population of the fish and now the bridge is solely a tourist site. Sadly, there were high winds on the day we visited and so the bridge was off limits to cross. As a compromise, we didn't have to pay an entrance fee, so we still committed ourselves to seeing the little rope bridge and the stunning geology that continued on from Giant's Causeway.  

I was feeling a little down on Sunday so I ended up having a lie in while James tried to find breakfast. I didn’t leave the hotel until after midday but we knew it was the only day we had left to visit the Chester Beatty Library on the grounds of Dublin Castle. While Lonely Planet likes to boast that this is one of the best museums in Europe, one cannot help but feel wary that this is just a white man's obsession with the orient during the late British Empire.

The rest of the late afternoon was spent exploring St. Patrick's Cathedral. We had dinner at the "mexican" restaurant 777, where every item of the food menu was unsurprisingly priced at £7.77. From the outside, the restaurant looks closed, we even walked away to find another restaurant because it looked shut down but we saw people coming out. We were lucky not to have missed out because everything on this menu was great (James recommends the Bisrec Tostados)!

After breakfast at Lemon Crepe on Monday, we meandered through St. Stephen's Green. You cannot have a city break without a tour of one of its brew houses or distilleries. Never a huge alcohol fan, we chose to go to the Guinness Storehouse on Monday as it seemed the more bearable one out of whiskey and beer. Even if I didn't consider the expensive price of the ticket, I would say that I felt a little disappointed, I expected to see a part of the actual factory but all you see is a replica of a few of the machines in a tour very detached from the actual brewhouse and very basic information about Guinness itself. There's an exhibition on the history of Guinness's advertising but even that feels limited. I would say a tour of the whiskey distillery would probably be more worthwhile. 

James insisted we visited Smithfield Square, the Hipster neighbourhood of Dublin, but the Cruinniu na Casca event had taken over the Smithfield Stage so we were pretty much getting a different vibe from what we expected. I wish we explored all the street food (we found a Stormzy mural just hidden behind them!) that was around but we decided to give ourselves a challenge at Meat Wagon. The late after noon was spent walking through the city centre, past the General Post Office (the headquarters of the rebel leaders of the 1916 Easter Rising) and Grafton Street. Of course we thought the best way to tie up our Ireland trip was a drink at the Stag's Head and an Irish Stew at Hairy Lemon. 

Road Trip Across Ladakh: When India met Eurasia

Formation of the Greater Ranges of Asia 

The Himalayas and Karakoram are two of the highest mountain ranges in the world. The Himalayas stretches across 2900 km, passing through six countries, and contains the highest mountain on Earth (Mt Everest if you're wondering) yet it is one of the youngest ranges. On the other hand, Karakoram is only 500 km across but it has the densest concentration of high peaks (over 8000 m) and it is one of the most glaciated parts outside of the polar regions. The Himalayan mountains continue to grow because the region is still very tectonically active, resulting in a high frequency of earthquakes. The formation of the mountains has caused global impact from changing oceanic circulation patterns to inducing the South Asian Monsoons, just in case the heights of the mountain ranges weren't impressive enough!

The two mountain ranges share the same drive of formation: the collision between India and Eurasia. If we wind back to the early Mesozoic, during the time of Pangaea, India was neighbouring Africa, Antarctica and Australia in the southern hemisphere while Eurasia was located in the north. The two landmasses were separated by the Tethys Ocean. This arrangement was disrupted approximately 175 Ma years ago when Pangaea started to break apart and the Indian plate began to move towards Eurasia. This plate movement was due to convergent plate boundaries. The key plate boundary was located along the southern margin of the continental Eurasia plate where the oceanic plate, which is denser than continental plate, was being subducted into the mantle. The subduction zones started to close the Tethys ocean and India moved at a rate of 10-20 mm per year until around 50 Ma, when the two continental plates collided.

The plates continued to converge but the rate India travelled northwards was reduced to 5 mm per year. As the Indian plate and Eurasian plate are both light density continental rocks, the continents began to uplift creating some of the world's greatest mountain ranges. The collision caused the rocks to buckle and fold over, creating the stunning geology. This process continues today as the crust of the Indian plate carries on thrusting under that of the Eurasian plate causing the crustal thickness of the region to be twice the average. Ladakh, located in the state of Kashmir and Jammu in India, is dominated by the geology that created the two mighty mountain ranges. The five main geotectonic units from south to north are: Tethys Himalaya, Indus-Tsangpo Suture Zone, Ladakh arc, Shyok Suture Zone and the Karakoram block. During our road trip from Manali to Leh and around, we were able to have a glimpse of the beautiful landscape the region had to offer.

Starting our journey in the Himalayas

Our road trip officially started in Manali. Technically we took an overnight coach leaving Delhi at 7 pm and arriving in the town of Manali at around 9 pm so you could say our road trip started further south but as I spent most of this journey either yearning for that Blue and Gold Sari I didn't have time to buy or trying to find a comfortable position to sleep in, the excitement did not start until the day after. By then I had already missed half of the Himalayan tectonic units: The clastic sediments (sourced from the Himalayas as they eroded) of the Sub-Himalayan unit and metamorphosed sedimentary rocks (sourced from the Indian platform) of the Lower Himalayas unit. Unfortunately the trip only improved a little as we had to pass the apparently majestic Rohtang Pass in complete cloud cover (damn that Monsoon season).

The start of the road trip took place within the High Himalayan Crystalline Sequence: The Climax of the Himalayan orogeny. The rocks here were originally Precambrian to Mesozoic sedimentary rocks that were metamorphosed into medium to high grade metamorphic rocks during the peak of the Himalayan formation in the mid-Tertiary (though the rocks have undergone many phases of deformation). Here, mica schists, quartzites and gneiss that represent up to amphibolite facies can be found. The HHCS was intruded by leucogranites in the Miocene which also formed migmatites in the process. In fact, Manali is located on one of these High Himalayan Leucogranites. Our four hour drive was spent completely in the HHCS as we spent the night in Keylong. The view of homes on mountain tops was one of the best views among the many others.

The sky cleared the next day just in time for us to enjoy the Tibetan Tethys Zone in its full glory. The TTZ is the most northerly zone of the Indian plate and the numerous formations within it show how much the environment has changed! This zone represents a sedimentary shelf facies that formed in the passive northern margin of the Indian plate, which has been divided in two by Carbiferous-Permian volcanic rocks. The earlier Precambrian to Carboniferous Lahoul Supergroup moves from shallow water sedimentary rocks to terrestrial formations (continental molasse, aeolian sandstones) back to marine formations (limestones, evaporites, deltatic clastics).  The Panjal Traps are the continental flood basalts from the Carboniferous to Permian period that occurred from the break up of Gondwana. Post volcanism, the Zanskar Supergroup represents a return to marine setting with carbonate platforms, carbonate sediments, shales, sandstones and limestones that eventually evolved into shallow water setting. The TTZ is largely unmetamorphosed and contains abundant fossils indicating the rich biodiversity that once existed in the Tethyan Sea.

Driving through the Indus Tsangpo Suture Zone

The Indus Tsangpo Suture Zone (ITSZ) separates the Indian plate from the Eurasian plate. The three units within the the ITSZ show a progression from a deep marine setting to shallow waters progressing into a delta and then finally a continental collision facies. The two earlier main units in the ITSZ are the Lamayuru Complex and the Nimdam-Dras Volcanic Group. The shales, sandstones and limestones of the Lamayuru, which were deposited during the Triassic to Jurassic period, represent the "deep water" marine setting. The Dras Volcanic group (of the Nimdam-Dras unit) comprises of basalt, andesites and dacites that show island arc tholeiitic and primitive calc alkaline geochemistry. The Nimdam group contains volcanoclastic materials, limestone blocks and volcanic blocks. The Dras Group represents an island arc while the Nimdam group suggests a forearc basin which received and deposited sediments from the island arc.

The most dominant and youngest group in the ITSZ are the Cenozoic Indus Basin sedimentary rocks, also known as the Indus Molasse. These rocks are carbonate or clastic sediments that originated from the Eurasian plate and were deposited south of the Kohistan-Ladakh Batholith. The earlier group of IBSR, the Tar group, shows an evolution into a shallow marine (shales, fine sandstones, limestones) and delta dominated with fluvial deposits (coarse sandstones, conglomerates). The later group, the Indus Group, shows a switch from a marine to a terrestrial setting. The arrival of Indian sediments into the sequence has been used to date the collision of the two continental masses. During the final leg of the Manali-Leh roadtrip, the highway curves through the vibrant maroon and green shales and sandstones and this was the highlight of the trip. It was the first time that I made my driver stop so I could run over to examine the outcrops while James awkwardly tried to explain that I am a geologist through the language barrier (it didn't work).

Settling in the Ladakh Batholith

Once we crossed the Indus River on the highway route, the sedimentary units stopped abruptly and we were greeted by valleys and mountains made of crystalline felsic igneous rocks. This is the Ladakh Batholith, part of the Trans-Himalayan batholith, which stretches 600 km between the Indus Suture Zone in the south and Shyok Suture Zone in the north. The batholith is mostly made of biotite and hornblende granodiorite and granite but there is presence of mafic components in the form of ol-norite and gabbro. Leh sits comfortably within one of these granitic valleys that was shaped by glaciers.

The Ladakh Batholith resulted from the Andean-type magmatism that occurred during the subduction of the Tethys Ocean under Eurasia. The label "Andean type" refers to a subduction of an oceanic plate under a continental plate. As the oceanic lithosphere subducts into the mantle, it partially melts and dehydrates allowing some of the volatiles, especially the water, to percolate to the mantle of the overlying plate. This lowers the melting temperature of the mantle wedge and can cause some melting leading to magmatism, which in this context manifested as mainly plutonism with some volcanism. The Ladakh Batholith is a result of multiple pulses of intrusion of calc-alkaline material that has been uplifted and eroded to its current form today.

The batholith has been dated several times as another way of understanding and timing the formation of the mountain ranges and the beautiful geology surrounding it. Weinberg and Dunlap (2000) used U-Pb and K-Ar dating techniques on zircons and samples of subvolcanic dike respectively. They found that magmatic activity occurred in Leh between 70-50 Ma and the last magmatic event occurred around 49.8 Ma, just around the time when the sedimentary rock suggests collision with India. This suggests that magmatism stopped soon after the collision due to the change in plate boundary (from oceanic-continental to continental-continental) "disrupting" the magmatic system.

Exploring the Nubra Valley in the Shyok Suture Zone

The zone between the Ladakh Batholith in the south and the Karakoram units (Eurasian plate) in the north is messy, less studied and not well understood compared to the other geological units. However, there's one thing for sure, it's another collision zone! James and I couldn't wait to drive off to another part of Ladakh and we chose to see the Nubra Valley before Pangong Tso (saving the sunshine for the best part of the trip). Our car drove over the Khardung-La pass and headed to the Nubra Valley within the Shyok suture zone in the northwest.

The Shyok Suture Zone represents the collision between the Ladakh-Kohistan Arc and the Karakoram Block. This second convergent boundary was located south of the Eurasian subduction zone as an intra-oceanic island arc. The geology of SSZ is composed of ophiolitic melanges (sections of the oceanic crust that have been obducted onto continental crust), metamorphosed volcanic rocks and sedimentary rocks. The Shyok Suture Zone represents a "complete section through an oceanic island arc". There is a disagreement between the direction of subduction, the features of an island arc the units represent and the timing of (the Shyok ocean) closure. Moreover, there is still an on going debate today whether the Ladakh-Kohistan island arc collided with the Asian or Indian plate first though it was generally understood that the Ladakh-Kohistan Island Arc collided the the Karakoram Block in the Cretaceous period before the Indian collided with Eurasia in the Tertiary period.

Rolland et al (2000) suggested that the SSZ in Ladakh shows signs of a NW-SE evolution from a back arc to arc formation i.e. the back arc basin was opening in the northwest of the Ladakh Arc and closing eastward. The suggestion comes from the presence of basaltic blocks and tuffs with a geochemistry between mid-ocean ridge basalts and island arc basalts in the northwest and arc setting volcanic rocks in the southwest. The sedimentary and volcanic rocks also suggest a change in the geodynamic setting from west to east: limestones with pillow basalts and lava flows found in the west suggest a effusive eruption in a marine setting while pelites, sandstones and conglomerates with ignimbrite layers suggest a continental setting with a "catastrophic" aerial eruption in the east.

Dipping into Pangong Tso & looking onto the Karakoram Block

The first time I wanted to visit Pangong Tso was, unsurprising to any desi readers out there, after I watched "3 Idiots". It wasn't the first time I've seen the beautiful lake in a bollywood movie (Dil Se and Jab Tak Hai Jaan were also shot there to name a few) but the scenery in "3 Idiots" was particularly stunning. My dad leaned over to me in the cinema and told me that the lake was in Ladakh and that he'll take us there one day. So I got a little impatient and went there before he had the chance (I hope I'll take them there one day).

Pangong Tso is located in the Karakoram Block, the final geotectonic unit of our Ladakh trip! The Karakoram terrane extends from Hindu Kush, Afghanistan in the west to Tibet in the east. The terrane can be divided into three major lithologies. The most northerly unit is the Karakoram Tethys Zone which is, as you can guess, a sedimentary sequence that records the travel of the Karakoram as it left Gondwana to make the Asian plate: from deep water sediments in the Carboniferous to shallow marine carbonates in the mid-Jurassic. The sedimentary sequence was then intruded by diorites from a pre-collision event. The south of the KTZ is the Karakoram Batholith and this comprises of granites that range from monzogranite to garnet-two mica-leucogranite composition formed by both pre and post collisional events. Karakoram Metamorphic complex lies between the Karakoram Batholith and SSZ. It's made of metasedimentary rocks, amphibolites and gneiss-migmatites which have have been intruded by granitic bodies too!

The Pangong Metamorphic Complex can be found south of the lake and we had a peek of it on our way back from Pangong Tso to Leh. This complex comprises of, as described by Rolland et al (2000, 2002 and 2009), "a granulite facies core and an amphibolitic cortex". The granulite core is mainly made of garnet-bearing gneiss, metabasite and limestone while the amphibolite facies contains metapelitic schists and gneiss along with the presence of metabasic rocks. This complex is bounded by the Karakoram fault and earlier papers suggest that this block has been exhumed from a 18 km depth and moved southwards. The garnets in garnet-kyanite-starulite gneiss show multiple stages of growth implying that the complex underwent many stages of deformation. Thanh (2001) suggested that the garnet cores formed during the subduction setting induced prograde metamorphism, which were then "abruptly" uplifted during the Karakoram-Ladakh Arc collision, and the overgrowth were formed during the continental collision between India and Eurasia.

Looking Back

I had a wonderful time in Ladakh. Before I jumped on a coach to Manali, I knew that Ladakh would be a geologist's paradise. It wasn't until we were in the Himachal Pradesh - Jammu and Kashmir border (when the clouds and mist shifted a little and the temperatures became a little warmer) that I fell in love with my subject again. This was the first time I tried to explore the geology and apply my course to the real world on my own. I gained a new found love for geological field work. I found myself naturally pouring into the literature to put together the pieces I saw. I understood more about the Himalayas now then during my second year course! My only regret is not reading the papers before I left, it would have been great to drive over to the ophiolites or having a closer inspection of the Pangong Metamorphic Complex. Alas, maybe next time!

References

1. Searle, Mike P. Geology and tectonics of the Karakoram Mountains. John Wiley & Sons Inc, 1991.
2. Garzanti, Eduardo, Aymon Baud, and Georges Mascle. "Sedimentary record of the northward flight of India and its collision with Eurasia (Ladakh Himalaya, India)." Geodinamica Acta 1.4-5 (1987): 297-312.
3. Henderson, Alexandra L., et al. "Geology of the Cenozoic Indus Basin sedimentary rocks: Paleoenvironmental interpretation of sedimentation from the western Himalaya during the early phases of India‐Eurasia collision."Tectonics 29.6 (2010).
4. Henderson, Alexandra L., et al. "Constraints to the timing of India–Eurasia collision; a re-evaluation of evidence from the Indus Basin sedimentary rocks of the Indus–Tsangpo Suture Zone, Ladakh, India." Earth-Science Reviews 106.3 (2011): 265-292.
5. Phillips, Richard J., Randall R. Parrish, and Michael P. Searle. "Age constraints on ductile deformation and long-term slip rates along the Karakoram fault zone, Ladakh." Earth and Planetary Science Letters 226.3 (2004): 305-319.
6. Phillips, Richard J. "Geological map of the Karakoram fault zone, eastern Karakoram, Ladakh, NW Himalaya." Journal of Maps 4.1 (2008): 21-37.
7. Rolland, Y., A. Pecher, and C. Picard. "Middle Cretaceous back-arc formation and arc evolution along the Asian margin: the Shyok Suture Zone in northern Ladakh (NW Himalaya)." Tectonophysics 325.1 (2000): 145-173.
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9. Schärer, Urs, Copeland Peter, Harrison T. Mark, and Searle Mike P. "Age, Cooling History, and Origin of Post-Collisional Leucogranites in the Karakoram Batholith; A Multi-System Isotope Study." The Journal of Geology 98.2 (1990): 233-51. Web.
10. Searle, M. P. "Structural evolution and sequence of thrusting in the High Himalayan, Tibetan—Tethys and Indus suture zones of Zanskar and Ladakh, Western Himalaya." Journal of Structural Geology 8.8 (1986): 923-936.Sinha, Anshu K., et al. "Contribution to the geology of the eastern Karakoram, India." SPECIAL PAPERS-GEOLOGICAL SOCIETY OF AMERICA (1999): 33-46.
11. Streule, M. J., et al. "Evolution and chronology of the Pangong Metamorphic Complex adjacent to the Karakoram Fault, Ladakh: constraints from thermobarometry, metamorphic modelling and U–Pb geochronology." Journal of the Geological Society 166.5 (2009): 919-932.
12. Thanh, N. X., et al. "Multiple garnet growth in garnet–kyanite–staurolite gneiss, Pangong metamorphic complex, Ladakh Himalaya: new constraints on tectonic setting." Lithos 127.3 (2011): 552-563.
13. Thanh, Ngo Xuan, et al. "A Cretaceous forearc ophiolite in the Shyok suture zone, Ladakh, NW India: Implications for the tectonic evolution of the Northwest Himalaya." Lithos 155 (2012): 81-93.
14. Weinberg, R. F., and M. P. Searle. "The Pangong Injection Complex, Indian Karakoram: a case of pervasive granite flowthrough hot viscous crust."Journal of the Geological Society 155.5 (1998): 883-891.Weinberg, Roberto F., and William James Dunlap. "Growth and deformation of the Ladakh Batholith, northwest Himalayas: implications for timing of continental collision and origin of calc‐alkaline batholiths." The Journal of Geology 108.3 (2000): 303-320.