The last few blog posts have been out of this world, so I thought this week I would bring it down to Earth and tell you about the fieldwork I have been carrying out in Iceland for my PhD.
My last blog post was explaining the processes that create subglacial volcanoes and these are what I have been sampling while I’ve been in Iceland. Subglacial volcanoes (also known by their Icelandic names: tuyas and tindars) possess information about the ice sheet that once covered them, and so they can act as a land based record. These volcanoes therefore, can be used instead of ice cores or marine core sediments, which are other methods used to find evidence about past glacial cycles.
The main purpose of sampling these once active subglacial volcanoes is that no-one knows when the volcanoes were created and therefore into which glacial cycle they were formed. This is largely due to the lack of a suitable dating technique that works for relatively young (∼25000 years old – young in geological terms) volcanic rocks. These volcanoes do not possess enough organic material for radiocarbon dating and are not old enough to be dated via Ar-Ar dating (which works best on rocks over 100,000 years old). Instead, I’m using a method called U-Th/He dating, which works by calculating how many 4He atoms have built up from the decay of U and Th since the volcano’s formation. These 4He atoms (essentially alpha-particles) are held in the lava by a mineral called olivine, named so due to its olive green colour (see pic). It is these olive green crystals which I am setting out to collect and will eventually tell me the ages of these subglacial volcanoes.
So, while I’ve been in Iceland, my aim has been to reach as many of these subglacial volcanoes as possible and take a sample of well-shielded pillow lavas (again cleverly named so due to their round pillow shape – see pic). These pillows are found at the base of the volcanoes as they make the initial product of the volcano when it formed under the ice. The pillows get their shape as the magma enters melt-water, which is under a lot of pressure, from the overlying ice.
As well as collecting samples from these volcanoes formed under ice, we (myself and my three trustee supervisors) have collected from some post-glacial (erupted when no ice was present) shield volcanoes and interglacial lavas (erupted between two glacial periods). The reasoning for this is that some of the shield volcanoes have been dated using tephrachronology; a method using the layers of ash to find when they erupted. I can therefore use these shield volcanoes as validation for the dating method I am using to find the ages of the subglacial volcanoes. U-Th/He dating works better when the rock is relatively old, therefore sampling a few interglacial lavas is ideal as they will have a minimum age of 100,000 years old.
I am now in my third week out of five here in Iceland and I have currently acquired 84 samples. So far, so good. The longest part of analysing the samples will be preparing the olivines before analysis. This involves crushing the lava and picking out the olivine crystals by hand while looking through a microscope. These are then put into a noble gas mass spectrometer, which are crushed and the amount of helium released is recorded. This information can then be used further to calculate when the olivine was formed and consequently how old the volcano is.
There have been a lot of long days, but all have been filled with amazing sights. Along with the volcanoes, lakes, rivers and waterfalls, the land is filled with sheep, horses and even an arctic fox now and then. The scenery can change drastically from one area to another and can at times look very alien like. Iceland is an amazing place to visit whether you have an interest in what’s happening to the land itself or not. It’s no wonder that Iceland is chosen as a setting for many movie and TV filming locations. You never know, if you visit, you could even be lucky enough to see some filming take place…