Seismometers and station life

Seismometers in ice

Geology is generally a tricky topic, as any prospector will tell you, but geology hidden under hundreds of metres of ice is even more challenging.

So why care?

Well, it turns out that how the Antarctic ice sheet responds to warming oceans to some extent depends on the nature of the rocks and sediment beneath.

Imagine rolling down a steep hill on a pushbike. Gravity pulls you down the hill just as gravity pulls the bulging ice sheet towards the ocean. Now, it would be nice to slow down a bit before you and your bike reach that busy junction (or the ice sheet reaches the ocean, where it forms icebergs or melts)! You hit the brakes.

What is the road like? Consider those three options:

1. Dry asphalt, with good tread on your tyres.

2. Rounded gravel and sand, with worn tread.

3. A wet road with a thin sheet of water and no tread.

You can almost feel it; the bike would roll on the gravel or aquaplane, no matter how tight your grip on the brakes is. However, with good tread on dry asphalt, you can actually slow down and keep control.

Just as your breaking wheels make a connection with the road, the Antarctic ice sheet is also connected to the earth beneath. The warmer the ocean, the quicker it melts, and the steeper the slope that pushes the ice sheet towards the coast. In areas where the ice sheet is frozen to rugged hard rocks at its base, it takes a much steeper gradient for it to flow quickly. However, on soft sediments or, worse, on a layer of water, there is not much holding the ice sheet back from speeding up towards the ocean, pushed by its own weight.

This is why we are keen on understanding the properties at the ice sheet's base. Is there any water? Are there soft sediments beneath? Is the sediment water-saturated? Without this knowledge, it is difficult to predict the rate that Antarctic ice contributes to global sea level rise.

Geophysical data collected using methods from satellites or aeroplanes are a great way to understand some aspects of the subsurface, such as bedrock topography, particularly in Antarctica, where it can be tricky to get around (ask anyone at AAD). However, ground-based seismic data is particularly well suited to look for changes in hardness and density and the existence of water or soft sediments.

Conducting seismic surveys with dynamite is great fun, but far more complicated in Antarctica than elsewhere. Is there another way? Yes, we think so. By studying the seismic signal from background noise, that is, noise from storms, waves, and even distant human activities, we can learn about the material the seismic waves travelled through. Some seismic waves are essentially the same thing as sound waves, and most of us can tell with closed eyes if the sound of a radio comes from the room we are in or from the neighbour. The sound that goes through a wall will be different if the wall is of concrete or thin boards. Seismic signals work the same way but at lower frequencies, and the walls we detect might be kilometres thick ice or rocks. Using seismic signals collected over long time, we can also detect changes, gradual, seasonal, or abrupt.

This season we are deploying seismometers near Casey station in defined configurations to optimise how we understand the rock, sediments and water under the ice. Our experiences will apply to upcoming campaigns when we look in detail at Denman Glacier and further inland, and other Antarctic programs could also adopt the improved methods in the future.

So far, the data collected looks very promising. Thanks to great support and a bit of luck, we are ahead of schedule; however, the infamous A-factor can strike anytime.

- Tobias Stål and Anya Reading,

University of Tasmania (Physics)

Bringing the Antarctic experience to you

After a few weeks in this place, I’m still struggling to incorporate my thoughts into some form of coherent, natural progression for the purposes of storytelling. As such, I’ve instead assembled a haphazard assortment of sentences with some observations and reflections.

In no particular order:

The people here are kind. They laugh often. They come from all walks of life, each with their own specialisations and expertise, but they find a common purpose in this place. They care. They miss their loved ones back home. They grow quite a lot of hair. They find comfort in small things.

Until a month ago I had never seen an iceberg. I now find myself unable to count the number of icebergs outside.

There are two large tubs with magical properties that always seem to be full of chocolate. Help yourself.

Bottleneck (adj.): A hundred people using a single ADSL internet connection simultaneously.

Things change rapidly. There is this continuous shifting and adjusting of priorities for the station (and the crew) as adjustments are made for changes in weather, the condition of equipment, staff availability, flight schedules and a thousand other factors. Antarctica will cast a lazy eye over your plans and scoff.

Penguins are more inquisitive than you might think. And noisier. And more…aerodynamic.

I haven’t witnessed a sunset since arriving, and I won’t for at least another month.

The food is plentiful, hearty and warming to both the body and the soul. The birthday cakes, when they happen, are impressive as hell. It’s not hard to find yourself eating five or six meals a day, if you aren’t careful. But, an extra layer of ‘insulation’ doesn’t hurt.

Spong (v.): To suffer a misfortune through accident or injury.

There are moments of stillness and silence, and times when the weather turns the world outside to chaos. The world can be bright and clear, or it can be white oblivion – sky and land become indistinguishable and it’s hard to know which way is up.

It…is wild here. The air is clear, crisp and clean. The enormity and scale of this place is impossible to fathom.

It is beautiful and rugged and vast.

- Tim Ward