Coverage of ice velocities in the central part of the Southern Alps, New
Zealand, is obtained from feature tracking using repeat optical imagery
in 2002 and 2006. Precise orthorectification, co-registration and
correlation is carried out using the freely available software
COSI-Corr. This analysis, combined with short times between image
acquisitions, has enabled velocities to be captured even in the
accumulation areas, where velocities are lowest and surface features
ephemeral. The results indicate large velocities for mountain glaciers
(i.e. up to similar to 5 m d(-1)) as well as dynamic changes in some
glaciers that have occurred between 2002 and 2006. For the steep and
more responsive Fox and Franz Josef Glaciers the speed increased at the
glacier snout during the advance period, while the low-angled and
debris-covered Tasman Glacier showed no measurable velocity change.
Velocity increases on the steeper glaciers are the result of an observed
thickening and steepening of the glacier tongues as they moved from a
retreat phase in 2002 to an advance phase in 2006. This contrasting
behaviour is consistent with historic terminus position changes. The
steeper glaciers have undergone several advance/retreat cycles during
the observation period (1894 to present), while the low-angled glacier
showed little terminus response until retreat resulting from the
accelerating growth of a proglacial lake commenced in 1983.