Jökull - 01.01.2005, Side 155

Society report
Survey of flow, topography and ablation on NW-Mýrdalsjökull,
S-Iceland
Þröstur Þorsteinsson1,2, E. D. Waddington1, Kenichi Matsuoka1,
Ian Howat3 and Slawek Tulaczyk3
1University of Washington, Seattle, WA 98195-1310, USA
2Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, 101 Reykjavík
3University of California, Santa Cruz, USA throsturt@raunvis.hi.is
Abstract— Ground Penetrating Radar, velocity (stake displacements measured by GPS), and ablation mea-
surements were carried out on an approximately 4 km by 4 km area on NW-Mýrdalsjökull in 2003. The ice
thickness ranges from 112–304 m within the study area, revealing significant bed topography, with a total relief
of 185 m. The surface conditions vary considerably during the ablation season, with surface lowering of 4–10
m from April 22 to September 18, 2003. The dependence (relevant length scale) of velocity on surface slope
and ice thickness was difficult to estimate due to sparse velocity data and large spatial variations.
INTRODUCTION
To investigate the relationship between bed topogra-
phy, basal lubrication, and surface velocity, an area on
NW-Mýrdalsjökull was chosen. The field site location
(Figure 1) had sparse radar coverage (Björnsson, Páls-
son and Guðmundsson, 2000) and no velocity mea-
surements were known to the authors prior to this sur-
vey. Furthermore, accumulation and ablation had not
been measured at the site; however, it is known that
accumulation, especially on the south side, is as high,
or higher, than on other glaciers in Iceland.
The initial phase of the measurements took place
in April 2003, during a 5-day field campaign from
a base-station at the nearby Sólheimahjáleiga farm
guesthouse. Bad weather during the summer dis-
turbed fieldwork schedules, but subsequent trips were
made in June and September.
Surface conditions at the field site during the ab-
lation season were difficult, with many crevasses and
dirt cones (Figures 2 and 10). Traveling to and from
the field site meant traversing several cauldrons asso-
ciated with the Katla volcanic system.
In April we traversed the glacier using jeeps and
for the initial setup had help from the local rescue
squad in Vík with hauling gear across the glacier. In
June and September we used snow scooters and had
guides from Arcanum adventure tours to navigate the
heavily crevassed glacier. Below is a short description
of the equipment setup, the survey measurements and
preliminary results.
THE SURVEY
GPS measurements
In April, 2003, we established a grid of 13 poles/wires
(Figure 2) which were steam-drilled to a depth of 8–
10 m with the aim of allowing determination of all
components of the surface strain-rate tensor and the
longitudinal component over 3 length scales (∼3–10
ice thickness’ assuming 300 m ice thickness). Sur-
veys were done using four Trimble GPS receivers,
two 5700’s and two 4000’s. Surveys between the 4
receivers were performed for approximately 25 min-
utes; then all four receivers were moved to new loca-
tions, which gave up to 5 closed loops to solve per sur-
vey. Antenna heights were recorded; however, most
antennae were placed on the snow surface with a pole
inserted into the steam-drilled hole. The repeat survey
JÖKULL No. 55, 2005 155