Erebus fieldwork – gas sampling

Erebus fieldwork – gas sampling

We are now back at McMurdo after two and a half weeks in the field. This post was started partway through our season. Unfortunately, I didn’t get a chance to finish and post it in the few hours that the internet connection was up – apologies to our readers for the delay (it’s a harsh continent!)

Our campsite at Lower Erebus Hut

Our campsite at Lower Erebus Hut

Our field camp was at Lower Erebus Hut (LEH), on the north side of Erebus. Most of our work, however, was a half hour snowmobile drive around the caldera, at Ice Tower Ridge. This is a line of ice towers and caves that extends southwest from an old Erebus caldera rim up to the summit area. We are looking at gas compositions from this area to see how they vary with distance from the main crater – but this first post will focus more on the practicalities of our work.

Ice Tower Ridge, Erebus

Ice Tower Ridge, Erebus

Having spent most of my previous two seasons working at LEH and the summit area, Ice Tower Ridge is still fairly new to me. None of the three members of my team are familiar with the area either, so a large part of a day in the field can be spent driving to the site, trying to find cave entrances, and choosing a good place to position instruments.

It usually falls to our mountaineer, Lyra Pierotti, to make sure we can safely access a cave. She often goes ahead to check whether the ice beneath us is sturdy, and to decide how best to enter – whether we can simply crawl in, or whether crampons or ropes might be required. Having someone to get us to our sites makes it a lot easier for us to focus on getting our science equipment set up!

Heroin Tower: Lyra has set up an anchor above the entrance (the small hole into which the ropes disappear). She has already belayed Tobias into the tower, and I’m about to follow. We climb up to the edge and then in, wearing crampons and using ice axes.

Heroin Tower: Lyra has set up an anchor above the entrance (the small hole into which the ropes disappear). She has already belayed Tobias into the tower, and I’m about to follow. We climb up to the edge and then in, wearing crampons and using ice axes.

Once inside, we must find suitable places to set up our gas sampling equipment and measure carbon dioxide flux. This can involve some exploration – looking for soft ground or a vent to place soil probes for gas sampling, checking soil temperatures, and ensuring the site is safe to access.

Crawling around an ice cave in search of a good sampling location

Crawling around an ice cave in search of a good sampling location

One spot I found was a deep hole with warm air coming out at up to 6 m/s, warmer than the cave air by over ten degrees Celsius.

Anemometer in front of large gas vent

Anemometer in front of large gas vent

It is quite warm in the caves – often above freezing, compared to -20°C or lower outside. This can be nice to work in – except that it is also much more humid in the caves, and all the liquid water dripping on us freezes rapidly when we head back out. Not all of our work is done in the ice caves, either. We are also working outside to take gas measurements in areas of warm ground, where heat and gas move more diffusely through the soil.

The Erebus ice caves and geothermal areas are home to unique micro-organisms. This means we do not enter any caves that are pristine (have not been entered previously) or certain areas of warm ground. We also need to take precautions to reduce contamination that in some sites involve sterilising the instruments that come into contact with the ground, and in others require protective clothing.

Spot the scientist: Here, my supervisor Tobias is working on some warm ground just above Ice Tower Ridge. He is wearing a Tyvek suit and setting up a sampling system that he has sterilised using isopropyl alcohol.

Spot the scientist: Here, my supervisor Tobias is working on some warm ground just above Ice Tower Ridge. He is wearing a protective suit and setting up a sampling system that he has sterilised using isopropyl alcohol.

Some of our work doesn’t require so much preparation, however! One of the sites nearby, Hut Cave, is a good place to work during bad weather since it’s just a few minutes’ walk from camp. I made a couple of trips out to place and retrieve a soil probe, with some copper tubes and a pump attached to collect gas.

Skylight in Hut Cave

Skylight in Hut Cave

Carbon dioxide levels can be high inside some of the caves, so it’s good to have a handheld monitor and someone for backup when investigating the smaller passageways and crevices in search of gas vents.

Lyra keeps an eye on carbon dioxide levels in the cave

Lyra keeps an eye on carbon dioxide levels in the cave

We made it into about five cave systems this season, and set up multiple sampling sites in some of them. We also spent time above ground collecting gas in areas of warm ground and around the crater rim. Collecting the samples is just the first step, though – I’ll be writing more about what we’re actually looking for in the next post!

Searching for a gas vent...

Searching for a gas vent…

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