Application of optical televiewing (OPTV) to ice-mass boreholes: NEEM Deep Ice Borehole, Greenland

CfG staff: Bryn Hubbard

Figure 1Key collaborators: Université Libre de Brussels; Alfred Wegener Institut; Robertson Geologging Ltd

Overview:
‌We have worked with Robertson Geologging Ltd to adapt and apply optical televiewing (OPTV) to boreholes drilled through ice masses (Figure 1). OPTV holds several advantages over traditional directional video, most importantly in providing a complete, geometrically undistorted image of any logged borehole wall. The technique therefore has great potential to reveal the internal structure of ice masses. 

Since 2008, we have deployed OPTV in boreholes in ice masses in the European Alps, Svalbard, Greenland and Antarctica, initially testing and refining the hardware and more recently addressing some key glaciological research issues. These include using OPTV to (i) reconstruct ice structural generations within a polythermal valley glacier, (ii) identify and discriminate between the ice types present within an Antarctic ice shelf, (iii) reconstruct from annual layer identification an age-depth scale for the near-surface zone of the Greenland ice sheet, and (iv) reconstruct snow, firn and ice density from OPTV logs from Greenland and Antarctica.

Having logged a shallow borehole at NEEM, Greenland, in 2010 (Figure 2), more recent research has focused on the application of OPTV to the 2.5 km long NEEM deep ice borehole, with particular emphasis on (i) identifying annual layers at depth, (ii) identifying and dating internal ash layers, and (iii) reconstructing the dip and dip direction of steeply-dipping internal layers, particularly debris-rich basal layers.

‌Current research is also focusing on reconstructing vertical strain from annual layer change in Antarctica.

Key publications: 

Hubbard, B., Tison, J.-L., Philippe, M., Heene, B., Pattyn, F., Malone, T., Freitag, J. In review. Ice-shelf density reconstructed from optical-televiewer borehole logging. Geophysical Research Letters

Malone, T., Hubbard, B., Merton-Lyn, D., Worthington, P. and Zwiggelaar, R. 2013. Borehole and Feature Annotation Tool (BIFAT): A program for the automatic and manual annotation of glacier borehole images. Computers and Geosciences 51, 381-389. doi: 10.1016/j.cageo.2012.09.002 

Hubbard, B., Tison, J.-L., Pattyn, F., Dierckx, M., Boereboom, T. and Samyn, D. 2012. Optical televiewer-based identification and characterization of material facies associated with an Antarctic ice-shelf rift.  Annals of Glaciology 53 (60), 137-146. doi: 10.3189/2012AoG60A045 

Roberson, S. and Hubbard, B. 2010. Application of borehole optical televiewing to investigating the 3-D structure of glaciers: implications for the formation of longitudinal debris ridges, Midre Lovénbreen, Svalbard. Journal of Glaciology 56 (195), 143-156. doi: 10.3189/002214310791190802 

Hubbard, B., Roberson, S., Samyn, D. and Merton-Lyn, D. 2008. Digital optical televiewing of ice boreholes. Journal of Glaciology 54 (188), 823-830. doi: 10.3189/002214308787779988