Geobrief 2 - kngmg

Ice deformation apparatus schematic (left) and in ‘real life’.
exists is a daunting task. It can take large
amounts of strain for a solid aggregate to
approach textural equilibrium and lab
strain rates for measurable GSS­flow in
ice are low. A direct approach of imitating
geology is therefore impractical. The solution
is to use a ‘bracketing’ technique, i.e.,
demonstrating that the direction of change
over a relatively small strain ( ­103°C and strain rates
between 10 −8 s −1 and 10 −4 s −1 were chosen.
Two types of starting material were
used. Fine­grained ice (~2 μm) and coarsegrained
ice (~250 μm). The deformation
apparatus was a 1.0 GPa gas deformation
apparatus which can be used for cryogenic
conditions. N2 gas is used as confining
medium. The ice samples in the gas vessel
are deformed axially by an upward moving
piston.
Where do we go?
Results of the extensive set of grain growth
experiments and the deformation experiments
on both coarse and fine­grained
ice are in now. Grain growth laws and
deformation mechanism maps are on their
way to be calibrated. However, ice appears
to behave in a more complex way than
anticipated. Nevertheless, grain size
clearly cannot be ignored as an important
parameter in the flow of planetary ice, and
this conclusion must probably be expanded
towards terrestrial ice. With the results
we can assess large­scale implications by
applying the obtained mechanism­based
description in building and calibrating
numerical models. This numerical modelling,
for which we will collaborate with
Bert Vermeersen from TU Delft, is, at the
moment, the only possible way to describe
tectonic and thermal processes on icy
moons.
Sabrina Diebold
This project is funded by NWO/NSO (The Netherlands Organisation
for Scientific Research and the Netherlands Space Office), as
part of the User Support Programme Space Research, subprogramme
Comparative planetology. Supervisors are Hans de Bresser
and Chris Spiers (Utrecht University) and William B. Durham
(MIT, US).