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.
The
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
Waikato,
and the Te Arawa Lakes Trust Board.
Lake
Rotomahana, roughly 3km by 6km in size, enlarged in size
after the eruption of Mt Tarawera in 1886, which is thought
to have
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.
The
battery-powered AUVs will motor through the lake at about
walking pace on a pre-programmed grid pattern to produce a
highly
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.
GNS
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.
END