An avalanche this week which has altered the Hillary Ridge
on Mt Cook. Photos by Lucy Ibbotson
An Otago surveyor whose research knocked 30m of the
official height of Aoraki/Mt Cook last year says this week's
large rock avalanche on New Zealand's tallest peak does not
mean the mountain is continuing to shrink.
The avalanche from the south face of Mt Cook was reported by
a pilot on Tuesday.
It has altered the prominent Hillary Ridge and moved the
Department of Conservation's Gardiner Hut - which sits above
the Hooker Glacier - off its foundations.
Otago National School of Surveying senior lecturer Pascal
Sirguey said the slip was a ''normal process of formation of
mountains'' and another example of how ''dynamic'' the
Southern Alps were.
''They keep evolving ... they are rising by about 1cm per
year, but at the same time they experience very strong
erosion ... it's a constant process of creation and
The erosion could be triggered by factors including heavy
rain, earthquakes or ice expanding inside the rock and
Dr Sirguey was the leader of a research project which showed
Mt Cook was only 3724m above sea level, not 3754m as measured
in 1991 after a major rock and ice fall took 10m off the
The data was obtained during an Otago-led climbing expedition
last November using a high-accuracy GPS device.
The discrepancy between the old and new heights was because
of a 20-year erosion and reshaping process of the ice cap as
it adapted to the underlying rock summit.
It was ''hard to say'' whether Mt Cook would reduce in height
or go higher in the long term, Dr Sirguey said.
''I don't think we've got the data to say that it is
experiencing any trend, really. It could be in a relatively
stable position. It could be that in a long time it may
regain a lot of the height that we have lost in the recent
event. But it's still very small to the actual life of the
The damaged Gardiner Hut.
Doc media adviser Lizzy Sutcliffe said GNS Science was
trying to determine when the avalanche took place, although
people in the Mount Cook Village had reported hearing ''loud
rumblings'' around 10pm on Monday.
The topography of the Hillary Ridge would be ''quite
different'' as a result of the slip, Miss Sutcliffe said.
Doc had no records of visitors to the area in the mountain's
intention system at the time and aerial investigations
indicated no-one was caught in the incident.
The area affected was a remote location used only by
experienced alpine climbers.
Doc was working with GNS Science yesterday to assess the
stability of the area in order to carry out a more detailed
investigation of the rockfall and the damage.
''Until that assessment is complete, we are asking that
people keep out of the Noeline Glacier region of the upper
Hooker valley,'' services manager Mike Davies said. In 2011,
the South Ridge of Mt Cook was renamed Hillary Ridge in
honour of the late Sir Edmund Hillary. Sir Ed was a member of
the first party to climb the ridge in email@example.com