Fieldwork Finale – Back in Bergen

Hi again, from Adam and the GIMMIC team, in the last of our field blog. I’m writing this entry from a spare desk in Anna’s office, back at Bergen University. After a successful nine-day trip at Finse Station, I’ve spent the last week collating and backing-up our GPR data, and I thought I’d also share with you some of our initial findings and observations. I should stress that although these are no longer hot-off-the-press, there’s still much more to do and the images I’m showing here still need more work – just consider them as promising introductions to our results!

The first image I’ll show is just a map of where we actually surveyed around the glacier, totalling around 43 km of line data! Many of our acquisitions are just single straight lines, and the data we get from them can just be interpreted as two-dimensional slices through the glacier (like the profile I showed in our Imaging the Ice entry). However, you’ll also notice that our coverage at the front of the glacier is much more dense, and we essentially have 3-D coverage across the whole of the margin. This is pretty exciting for Benny, as we’ll be able to interpret precisely the location of the transition from frozen to unfrozen ice, and also work out how thick Midtdalsbreen has to be before unfrozen conditions dominate at the bed. Zooming in to our coverage map shows just how dense our observations are: in places, we’ve sampled the front of the glacier every 30 cm! I’m not actually aware of too many GPR studies that have sampled a glacier margin at such high resolution.

Left: Locations of GPR surveys on Midtdalsbreen Glacier, between 20th-26th April 2014, with the 2004 glacier margin digitised from Google Earth.  Right: Enlarged window of dense surveys on the glacier margin (location shown by the red dashed box in the left-hand image).
Left: Locations of GPR surveys on Midtdalsbreen, between 20th-26th April 2014, with the 2004 glacier margin digitised from Google Earth. Right: Enlarged window of dense surveys on the glacier margin (location shown by the red dashed box in the left-hand image).

The image below shows our first estimates of ice thickness for the western margin of Midtdalsbreen, along with our best guess of where the current margin position is and where the ice becomes unfrozen at its bed. The position of the margin we identify (yellow/black line), compared to its 2004 position in the previous image, suggests that the glacier has retreated around 150 m in this area during the last decade. Note that the histogram shows the separation between successive radar acquisitions, and this is typically below 0.6 m; however, the distribution is bimodal, with one peak around 0.3 m separation and one around 0.5 m. I’d suggest that these correspond to data when the radar is being towed by either Benny or me, with the smaller interval resulting from the slower tow-speed (I think I’m the slower one!).

Estimates of Midtdalsbreen’s ice thickness on the western margin.  The yellow-black dashed line shows the interpreted 2014 ice margin, with the black hashed area showing where unfrozen water is detected at the glacier bed.  A corridor of 40-50 m of frozen basal ice is present at the ice margin.  The histogram (right) shows the distribution of distances between radar acquisitions; the two operators obviously walk with the GPR at slightly different speeds!
Estimates of Midtdalsbreen’s ice thickness on the western margin. The yellow-black dashed line shows the interpreted 2014 ice margin, with the black hashed area showing where unfrozen water is detected at the glacier bed. A corridor of 40-50 m of frozen basal ice is present at the ice margin. The histogram (right) shows the distribution of distances between radar acquisitions; the two operators obviously walk with the GPR at slightly different speeds!

Our data imply that this part of the margin has a corridor of frozen basal ice around 40 m wide, which becomes unfrozen (hashed area) when the thickness of the ice exceeds around 10 m. At this point, most of the ice column becomes unfrozen and only the upper few metres have no liquid water. To emphasise this point, the GPR data below show a slice through the glacier margin, showing frozen and unfrozen basal ice; remember it’s the ‘fuzzy’ GPR responses which show where liquid water is present. This position of this profile is highlighted with the white dashed white line in the previous map.

Representative profile from the dataset in the previous image.  Liquid water inclusions over the thickest areas of ice suggest that Midtdalsbreen is unfrozen at its bed, but frozen basal conditions are present where the ice is thinner.
Representative profile from the dataset in the previous image. Liquid water inclusions over the thickest areas of ice suggest that Midtdalsbreen is unfrozen at its bed, but frozen basal conditions are present where the ice is thinner.

All in all, it was a really successful stay at Finse, and undoubtedly we’ll be back on Midtdalsbreen before too long to develop the observations we made in the last few weeks. Furthermore, my time at Bergen University has been really productive, and I’ve been able to initialise a few collaborations with other researchers here. Meeting other researchers and sharing ideas really is one of the biggest benefits of overseas projects such as GIMMIC.

In closing this blog, I’d like to thank the INTERACT-TA board for electing to sponsor our GIMMIC project, and likewise the board of Imperial College’s Arthur Holmes Centenary Research Grant. Our stay at Finse Station was permitted by Erika Leslie and Torbjørn Ergon at Oslo University, and we acknowledge the logistical support of Kjell Magne Tangen for during the fieldwork. Permission for snowmobile use in the area was granted Lars Præstiin from Ulvik Kommune and Petter Braaten at SNO, and we are especially grateful for this. Finally, our radar equipment was provided by Jostein Bakke at Bergen University.

Just to close, I’ll leave you with our final view of the Finse valley on our last evening in the town. Looking forward to being back, and thanks for reading our blog!

A final view over Finse valley - see you soon!
A final view over Finse valley – see you soon!
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s