AUSTRALIA鈥橲 only active volcano has scientists puzzled. Unexplained volcanic
events have been occurring on or near Heard Island, an uninhabited Australian
possession in the southern Indian Ocean about 1600 kilometres from Antarctica.
鈥淧umice is being washed up on the beaches,鈥� says Pat Quilty, head of science
at the Antarctic Division in Hobart. 鈥淎nd by rights it shouldn鈥檛 be there. We
have no record of pumice on the island.鈥�
Big Ben, the 2750-metre high volcano in the centre of the island, is active.
But it produces basalt with a low silica content and low viscosity. Pumice 鈥� a
light kind of lava made porous by the escape of steam or gas during cooling 鈥�
is high in silicate.
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Quilty believes that the pumice is coming from a previously unknown fissure on
the seafloor or on the flank of the island. Samples were brought back to
Hobart last week by members of a scientific party that has been doing
biological research on the island. They returned aboard the supply ship,
Icebird. While at the island, the ship sucked pumice into its water intake
pipes. The samples have been sent for analysis to Wally Johnson of the
Australian Geological Survey Organisation in Canberra.
Heard Island is unusually active at the moment. The biologists reported
feeling an earthquake last December. And Rod Ledingham, a geologist who has
been lecturing on the Antarctic tourist ship, Kapitan Khlebnikov, says there
is evidence of a recent lava flow. But this lava did not reach the water 鈥� it
therefore was not the source of the pumice.
Australia had a research station on Heard Island from 1948 to 1954. Since then
visits have been sporadic. 鈥淟ots of interesting science is going on there and
we are missing it,鈥� says Quilty.
HEARD has also been of interest to the CSIRO Division of Oceanography. Working
with US scientists, Andrew Forbes from the division generated a low frequency
sound in waters near the Island. The sound, at a frequency of about 70 hertz,
was picked up by receivers across the world. The ultimate aim of the research
is to determine if the global water temperature is rising in response to
greenhouse. If the oceans are warming, the density of the water will decrease
and the sound will travel faster.
Earlier this month, at a conference in Hobart on southern ocean meteorology,
Forbes revealed that plans had changed. The signal from Heard lost strength
when it travelled across the so-called Antarctic conversion zone which divides
the cold southern waters from the warmer tropical waters. 鈥淲e have proved that
the experiment could be done,鈥� says Forbes, 鈥渂ut we now believe that up to six
low-powered transmitters, deeper in the water, are preferable to one
acoustic source off Heard.鈥�
Heard will no longer be the source of the sound for the experiment that is to
run for 10 years. Instead, beginning later this year or early next year,
transmitters will be moored at a depth of about 1000 metres in the Pacific,
Indian and Atlantic oceans. When the experiment is fully operational, about 40
receivers will be used including arrays in Australia and New Zealand.