Scientists To Probe Lake Rotomahana
MEDIA RELEASE from GNS Science, 15 NOVEMBER 2010
Scientists To Probe Lake Rotomahana’s Geothermal Vents
Scientists from the New Zealand and the United
States are planning to use two torpedo-like unmanned
underwater vehicles to map the
bottom of Lake Rotomahana, near Rotorua, and look for hydrothermal activity on the lake bed.
The project, scheduled to start in late
January, will be the first time in New Zealand that a lake
bed has been mapped by autonomous
underwater vehicles, or AUVs.
As well as producing a detailed
three-dimensional map of the lake bed, the sophisticated
sensors on the AUVs will enable the scientists
to locate hydrothermal vents at the bottom of the lake.
present-day chemistry of the lake indicates that geothermal
fluids are pouring into it from below Scientists are keen to
find out the
number of vents on the lake bed, their locations, and the intensity of venting.
The project is
a collaboration involving GNS Science, the Woods Hole
Oceanographic Institute (WHOI) in the US, the University of
and the Te Arawa Lakes Trust Board.
Rotomahana, roughly 3km by 6km in size, enlarged in size
after the eruption of Mt Tarawera in 1886, which is thought
destroyed and drowned the famed Pink and White Terraces. The Terraces, or their remnants, are believed to be buried at the bottom
of the lake.
battery-powered AUVs will motor through the lake at about
walking pace on a pre-programmed grid pattern to produce a
accurate three-dimensional view of the lake bed.
Other measurements they will take include temperature,
pH, conductivity, depth, optical clarity of the water, and
the electrical potential, or Eh,
of the lake water. The vehicles will also be able to map the magnetic signature of the volcanic rocks beneath the lake floor and are equipped
with side-scan sonar, which helps to distinguish different rock types.
Scientists will compile the data
into a layered map of the lake bed which will elucidate the
nature of the geology and hydrothermal
activity at Rotomahana.
Project leader, Cornel de Ronde of GNS
Science, said there were very few examples of hydrothermal
activity in freshwater lakes in the world,
and even fewer had been studied in detail.
“Our aim is to
determine what happened to the Pink and White Terraces
hydrothermal system when it was drowned in the enlarged
Lake Rotamahana soon after the 1886 eruption,” Dr de Ronde said.
“We also want to know what links there are
between the drowned geothermal systems of Lake Rotomahana
and the adjacent geothermal
system at Waimangu.
“This is a rare opportunity to document the death of a land-based geothermal system and its rebirth at the bottom of a lake.”
The accuracy of the mapping will enable the scientists to see features on the lake bed about the size of a suitcase.
When vents are located and given a GPS
coordinate, scientists will lower instruments from a boat to
determine temperature, flow rate,
and chemical composition of the vent fluids. This will help build a computer model of the hydrothermal and magma systems beneath the lake.
Prior to 1886, the Pink and White Terraces were
considered an international marvel and were sometimes
referred to the eighth natural
wonder of the world. They were the largest silica terraces in the world and represented an enormous outflow of geothermal fluid.
Scientists believe the Terraces, or their remnants, are
today covered by at least 50m of lake water plus an
additional unknown thickness
of sediment. Lake Rotomahana is 115m deep at its deepest point.
Science, with the support of the Royal Society, will be
offering activities to Rotorua primary and intermediate
schools in connection
with this project. Information on the activities will be sent teachers in the Rotorua area this week.