Aoraki Mt Cook.
Thirty metres will be slashed off the official height of
New Zealand's tallest peak, following new measurements by Otago
While Aoraki/Mt Cook is officially listed as 3754 metres
above sea level, analysis of high accuracy GPS data obtained
during an Otago-led climbing expedition in November has
revealed that it is actually only 3724m tall at its highest
The readings confirm new aerial photography based
calculations performed by Otago National School of Surveying
researcher Dr Pascal Sirguey and masters student Sebastian
Dr Sirguey, the project leader for the research, said the
discrepancy between the old height - estimated from aerial
photography immediately following a massive rock-ice collapse
in December 1991 - and the new height can be explained by a
two-decade reshaping process affecting the remnant of the
originally thick ice cap.
"By carefully studying photos taken after the collapse, it
appears that there was still a relatively thick ice cap,
which was most likely out of balance with the new shape of
the summit ridge," he said.
"As a result the ice cap has been subject to erosion over the
past 20 years. While the effects of climate change may spring
to mind as an explanation, it is probably a case of a simple
change in the geomorphology of the mountain."
Despite being taken down a peg or two, Aoraki/Mt Cook still
towers above its close neighbour Rarakiroa/Mount Tasman,
which with its current official height of 3497m, remains the
second highest mountain in New Zealand.
The new GPS measurement is only the sixth non-aerial accurate
survey of the mountain's height to be taken, with the
previous trigonometric measurements made in 1851, 1879, 1881,
1883 and 1889, said Dr Sirguey.
The four-person Otago expedition that obtained the GPS data
was led by Dr Nicolas Cullen, a senior lecturer in the
Department of Geography at Otago.
Jim Anderson, a recent graduate from the National School of
Surveying, and Dr Cullen were responsible for taking the GPS
To observe Aoraki's tapu status, and as agreed with Ngai Tahu
and the three Papatipu Runanga who have a shared mana whenua
interest in Aoraki, the climbers did not step on the summit,
but instead took measurements with recently acquired
state-of-the art receivers while at the top of the ice cap a
few metres away and below the true summit.
An additional GPS point was measured at the top of the Summit
Rocks for further validation of Dr Sirguey's photogrammetric
"It was very exciting to see that the team's GPS data closely
matched our photogrammetric calculations from a 2008 aerial
survey," he said.
"From early on in this work we suspected that Aoraki was tens
of metres lower that the official height, so it is very
satisfying to have our estimates validated by GPS."
Graeme Blick, chief geodesist of Land Information New
Zealand, among several organisations that provided financial
and scientific support for the project, said the expedition
had resulted in a "significant change".
"This means LINZ online data will use this new height and it
will be incorporated when we next print hard copy topographic
maps for the Aoraki/Mt Cook region."