Final days of fieldwork

After Dr Chris Stokes had left, it was time for us to return to Tierra del Fuego for our final ten days in the field. We worked hard and managed to achieve a great deal, though the weather became steadily worse as the Patagonian autumn properly arrived.

We started by finishing our project looking at soil depths in the area (see our last blog post). Many, many soil pits later, we felt at one with the Fuegian earth and had it well and truly ingrained in our skin, our ears, our hair and under our nails. Continually sticking our heads down small soil pits, with the wind eddying around, meant there was silt everywhere!

Chris at one of the enormous boulders.

Chris at one of the enormous boulders.

We also spent some time at another of the groups of giant erratic boulders, which are thought to have been carried down from Cordillera Darwin by an ice-lobe in the past. Like before, we were studying their location, size and physical properties to assess how they might have come to be deposited and what the weather has done to them since. These boulders were the most impressive yet – they are so large that you can see them from many kilometers away. However, the terrain was much tougher to traverse and spiky bushes and dense, waist-high shrubs were everywhere so that our legs are now scratched and scarred from traipsing from boulder to boulder. Luckily, we found a cracking spot for our tent, and left it there for several days to return to in the evenings. We were treated to stunning sunsets, looking out over the vast, low expanse of northern Tierra del Fuego whilst we ate our dinner. As the sun sank low beneath the clouds, the yellow grass turned a golden orange against the grey skies – always a perfect way to finish a long day. (For anyone interested, our dinner was always a variation on pasta or instant mashed potato and always hit the spot nicely!)

The rest of the days were spent checking Chris’ mapping of the glacial geomorphology, and in particular focusing on more complex areas where the ice-lobe might have retreated but then re-advanced over the same position in the past. Then, all-too-suddenly, Sunday arrived and that was it, we had finally reached the end of our seven weeks of fieldwork. We said goodbye to Tierra del Fuego in driving rain. A pity, but then it saved Chris from getting sentimental – he now has a year and a half back in Durham to complete his Ph.D.!

Will enjoying an evening sunset.

Will enjoying an evening sunset.

However, the challenges were not quite over. Firstly, we had to negotiate a non-time-change. That is to say, the clocks were not supposed to go back…but did. On Sunday, every electronic device and computer went back by one hour for the winter period. However, we later discovered that the Chilean government had decided that the time should not change for a couple of weeks! Confused? We certainly were, and so were the Chileans. Apparently, even the national news channel was broadcasting the wrong time for most of the day!

We also had the heart-wrenching task of deciding which samples to ship back to the UK for analysis. Moreover, we had to actually get the samples shipped, which was by no means simple. Amid a lengthening queue at the courier service, we explained in our very best Spanish that we wanted to send two cool-boxes full of gravel back to the UK. This raised many questions from the staff – most pressing of which being why on earth we wanted to do it! Chris was heard to mutter “las rocas son muy importantes para mí” (the height of his Spanish abilities) though we figured an explanation of past glacial processes was probably a bit much for both sides.

Eventually, the samples were sent, the vehicle was returned to the rental company and everything was packed away. Needless to say, after several weeks of almost non-stop work, we are now shattered. But we have a few days to rest, recuperate and see a little bit more of Patagonia before our flights back home. The plan is to go and find some real ice…

Glaciofluvial fans and touring with Dr Chris Stokes

Our last blog post was from Ushuaia in Argentina, where we were due to meet with local academics. We met with Profesora Andrea Coronato of the CADIC-CONICET research institute the next day and then spent another day working with her and Diego (her PhD student) in an area further north that they know very well.

From left to right: Will, Andrea, Diego and Chris (and behind us, some very nice outwash in a glaciofluvial fan).

From left to right: Will, Andrea, Chris and Diego (and behind us, some very nice outwash in a glaciofluvial fan).

We showed them how we take the samples for dating glacial outwash and in return they showed us some of the key geomorphology that they have been working on. We were particularly interested in a couple of glaciofluvial fans that Andrea has written about. These are deposits of outwash that form a fan-shape as they spread out over the land surface and are thought to be linked to ice-lobe meltwater. It was fantastic to work with other people who have worked in this area and know it so well, and will prove invaluable to our own research. It was also great to renew the friendly bond between Durham University and academics all the way down in Argentina – long may it continue!

We then returned to Chilean Tierra del Fuego and spent a bit of time looking at soils. When a glacier or ice-lobe advances, it removes all of the soil and vegetation from the landscape. Then, once the ice has retreated, plants will return to the area and soil will start to develop again.

Chris using a Munsell Soil Colour chart to describe the colour of the soils.

Chris using a Munsell Soil Colour chart to describe the colour of the soils.

This means that the more time that has passed since ice retreated, the deeper the soil should be. If you dig a hole and measure the soil depth at the top of hills or moraines, it can help to give a rough idea of relatively how long that place has been ice-free. So we spent a couple of days trundling around the landscape armed with a spade, a tape measure and a Munsell colour chart (which is a bit like a book of paint-colour swatches, but for soils). It seems like everything we do must look rather bizarre to passers-by.

Finally, during this last week, we have been joined in the field by Dr Chris Stokes of Durham University. He is one of Chris Darvill’s PhD supervisors and is a particular expert in Drumlins (hills that have been shaped and elongated by a glacier or ice-sheet). Naturally, he was very excited to see the fantastic drumlins that you get down here – there are a group north of Punta Arenas which are arguably some of the most spectacular in the world!

Chris Stokes next to an information board about drumlins. You can just about see some real drumlins behind him.

Chris Stokes next to an information board about drumlins. You can just about see some real drumlins behind him.

Chris is also an expert at remotely mapping glacial geomorphology from satellite imagery, so it was nice for him to be able to see the area on the ground and help us to interpret the landscape. We showed him almost everything in our study area in the few days that he was here (which is an awful lot!), and in return he treated us to a couple of much-needed meals and nights in a hotel in Punta Arenas. This was gratefully received, particularly a hot shower. But even without the steak and chips and comfy beds, it has been great having him out here!

A bit of geomorphology, a goodbye to Harold and a trip to Ushuaia

Harold in a cheery mood - last seen by a boulder in Madrid

Harold in a cheery mood – last seen by a boulder in Madrid

Harold has left since our last post, which means marginally more space and less smell in the car (only kidding, he shall be missed!). We hear that he had an interesting departure from Punta Arenas. He was bought copious drinks by a trumpeter in the Chilean Navy then slept rough in the airport. Things must have really got to him as he was reported to be trying to sample boulders in Madrid on the way home!

In the meantime we (Chris and Will) have been focusing on checking geomorphology and looking for lake sediments.

The cosmogenic exposure dating of the outwash plains requires us to be really sure about how different parts of the landscape relate to one another and how this geomorphology may have changed through time. We want to be clear about exactly where the outwash sediments originated so that we know how our dates will correspond to the former ice lobe. For our latest samples, this meant trekking into a remote area (which looked a lot like Scotland!) in order to make sense of where the sediments that we collected had come from.

A 'dropstone' in laminated silts and clays deposited by a former lake.

A ‘dropstone’ in laminated silts and clays deposited by a former lake.

The important thing was to try to understand how moraine ridges, outwash plains, mountains and rivers fitted together over time to leave the landscape that we can see today.

We have also been searching for clues left by old lakes. We think that all of the former ice-lobes in this area may have once had lakes in front of them (called glacial lakes), which would have collected sediment over time. To be more sure, we have been searching for sands, silts and clays: fine sediments that are often found in the middle of large lakes. Another good indicator is the presence of stones which have been randomly dropped by icebergs. The presence of these stones in layered fine sediments is very good evidence that a glacial lake once existed (and tends to get us very excited!).

Yesterday, we travelled down to the far south of Tierra del Fuego in order to meet other academics at a research institute in the Argentine city of Ushuaia (apparently the world’s southermost city).

The journey down to Ushuaia.

The journey down to Ushuaia.

The journey passed through the snowy peaks of the southernmost part of the Andes and on the horizon we could see the Cordillera Darwin, where glaciers reach down into the Beagle Channel. These mountains were once the source of our ice-lobes, and the distance that we covered and change in landscape that we saw helped us to appreciate the awesome scale of the former Patagonian ice sheet.

Tomorrow, we will be working back up north with Andrea Coronato from Ushuaia and Diego, her PhD student. We are hoping to visit some of their field sites and learn about the work that they have been doing, looking at even older glaciations. Then we will travel back to Chile and return to camping in the winds.

Boulder trains

One of the key aspects of our fieldwork is investigating the impressive boulder trains of Tierra del Fuego. A boulder train is a long, linear group of large rocks that can look out of place in the landscape due to their size and rock type, which is often different to the local geology. Rocks like these are sometimes called glacial erratics given that transportation and deposition by ice is the only probable means by which they can have ended up in their present location.

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The Bahia Inutil boulder train.

Northern Tierra del Fuego has several impressive boulder trains which are both large and incredibly well-preserved. The size of some of the individual boulders is staggering: they can be seen clearly on satellite imagery and on the ground. Indeed, some are as large as houses! Over the last week, we have been focussing on two of the trains near Bahía Inútil and San Sebastián, and the latter required us to cross the border into Argentina for the first time.

 

It is thought that these Argentine boulders may be several hundreds of thousands of years old. However, scientists recently used a cutting-edge technique called cosmogenic exposure dating and found that most of them gave ages that were much younger.

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Will on one of the Argentine boulders.

This is a bit of a puzzle, and may be explained by the high winds here. We are trying to look at this in a bit more detail by measuring various properties of the rocks that may be linked to weathering and erosion.

We were kindly granted permission to work on the land in Argentina by the family at Estancia Sara. The owner also allowed us to camp in his back garden which offered welcome shelter from the strong, incessant winds which our tents have now become accustomed to. We stayed there for two nights. On the first, we shared the garden with a French Canadian unicyclist (obviously) who was unicycling her way northward through Patagonia. Needless to say, we were rather impressed, though we certainly weren’t going to try it ourselves!

On to Tierra del Fuego

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A long, long queue for the ferry to Tierra del Fuego.

Any hopes of a smooth transition from the Chilean mainland to the island of Tierra del Fuego were quickly shattered when we encountered a monumental hold-up at the ferry port.
Strong winds were preventing the ferry from crossing the Strait of Magellan (yep, even in Patagonia!) so we were forced to wait for over five hours. In this time we occupied ourselves in a number of ways. These included people-watching and listening to old episodes of Desert Island Discs on an i-pod. Harold even spent a good half-hour cleaning his nails (they are sparkling now).

Much of our initial work on the island was similar to that of the week before but this time associated with the moraine limits and outwash of the former Magellan ice-lobe. It was whilst exploring this landscape that things took an unnerving turn when we inadvertently found ourselves locked into the land of an Estancia (a Patagonian ranch). Initially we thought we might be in a spot of trouble but we soon came across the owner, Pedro, who proceeded to give us some cake and juice and show us Google Earth imagery of his Estancia land.

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Chris and Will with Pedro at Estancia Domenica.

He even kindly took the afternoon off work to give us a comprehensive tour of Estancia Domenica. Not only was this extremely generous of him, but it gave us the opportunity to see much more of the land in an area that is critical to the geomorphological mapping work that we are doing. Pedro was as fascinated by the landscape as we were (he is a specialist in agricultural soil science!) and overall it was an amazing afternoon that was both useful for our research and in affirming the warmth of the Chileans we have encountered.

 

The Skyring and Otway ice-lobes

We moved eastwards from the Fitzroy channel into the areas formerly occupied by the Skyring and Otway ice-lobes. The evidence for these is extremely well-preserved as ridges of glacial material (moraines) separated by extensive, gently sloping plains formed by glacial meltwater (outwash).

Harold enjoying the view from a glacial drumlin on the ground (during a very nice sunset!).

Harold enjoying the view from a glacial drumlin on the ground (during a very nice sunset!).

This landscape documents the different positions of these glaciers throughout the Quaternary period (the last 2.6 million years or so). It was of particular interest to Harold as he spent a year mapping it from satellite imagery for his Masters thesis in a dingy room in Durham three years ago. Consequently, it was nice for him to finally see what it looked like on the ground!

Our main goal was to collect samples from the outwash, which will be analysed when we are back in the UK. This may help us to work out the age of the outwash, which is linked to the time when a glacier deposited a particular moraine (we will explain a bit more about how exactly this works in a future blog post…).

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Pali Aike on a very windy morning.

We spent our last night in the area before heading to Tierra del Fuego in the Pali Aike National Park. Located right on the Chilean-Argentine border, the park provided a brief respite from studying glaciers in an eerie, almost lunar-like volcanic landscape. It was stunning, though we were on our guard after the warden kept saying the word “Puma”(!)

The Fitzroy channel

It seems like we have been in Patagonia for much longer, yet we have only been here for a little over two weeks. We have driven more than 1500 km, eaten countless packets of Tritons (a Chilean take on Oreos, and very nice!), and collected loads of field data, all the while met by many friendly faces in Chile and Argentina. Best of all, we still haven’t been blown away!

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Will enjoying a still morning by the Fitzroy channel.

Our first port of call was the Fitzroy channel, a narrow waterway connecting the large embayments of Seno Otway to the south and Seno Skyring in the north. As the glaciers that once occupied these bays retreated, large lakes were trapped in front of them. It has been suggested that the channel was cut by water draining catastrophically from one lake to the other.

The purpose of our visit was to investigate this idea by examining the sediments exposed along the eastern side of the channel. One of the techniques we used was measuring the direction and slope (strike and dip) of the beds of sands and gravels deposited during the drainage (known as palaeocurrent analysis).

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Chris and Harold looking at the strike and dip of sands (very closely!).

We were working and camping beside a very dusty road for three days and among the passers-by (many of whom were Chilean oil-truck drivers who always gave a friendly honk of their horn) was Jonathan Wills, a bird-watcher from the Shetland Isles who was once taught by the eminent J.B. Sissons (quite a name in British glaciology) – it was a bizarre but brilliant coincidence indeed!