BENEATH THE SURFACE
Typically, during rifting of a continent, as one
section of land pulls away from another, large
wedges on landmass drop down to fill the
widening gap. This is actually happening in
the Great Rift Valley in Africa and the Red Sea
today. When the sea floods in to fill this lowered
landscape – a process that may take many
millions of years – new seafloor is created. In
the case of the Great Australian Bight that new
seafloor was extremely wide, and it has left
Australia with a southern continental shelf over
260km in width in the centre section of the
Bight and about 80km wide at each end.
This area has a very unique ecology as
a result of a long period of geographic
segregation, high energy turbulence from
the rough Southern Ocean and an isolation
resulting from the inflow of nutrient rich cold
waters around Bass Straight and warm waters
brought in by the Leeuwin Current flowing
down the WA coast and around into the Bight.
The life forms living there are extraordinarily
diverse, many of them unique to the Bight,
and many rated as endangered. Notable
among these are the southern right whales
which come there to breed and calve, and the
Australian sea-lion and a number of species of
albatross.The rich upwelling of nutrients, especially
summer and autumn, produce a healthy
ankton community that supports a rich crop
sardines and anchovies. These in turn attract
ge schools of juvenile blue fin tuna.
The seaweed beds of the Great Australian
ht are among the world’s richest, with over
0 species known.GH AND MIGHTY
geography of the Great Australian Bight
varies greatly across its shoreline. About 40
million years ago thick carbonate sediments
deposited along the relatively newly formed
southern continental margin were uplifted
to form the land which forms the current
Nullarbor Plain. The upper layers were a very
hard crystalline limestone, which provided a
hard capping, while the lower layers are a paler
chalky limestone which undercuts the rocks
above as it is eroded by the heavy seas rolling
in from the south.
This has resulted in the formation of a t
and dramatic cliff line that averages ove
80 metres for the 200km from the hea
the Bight to near the WA border. The Eyr
Highway passes close to the cliffs betwe
the head of the Bight and Eucla and ther
side tracks leading down to the cliff edge
Any travellers are recommended to mak
time for the side trip, but caution should
exercised along the unfenced and precip
drops into the ocean far below.
This is a great place for whale watchin
especially around the head of the Bight
during winter when the whales migrate
north from their summer feeding ground
off Antarctica. Their numbers were
greatly reduced by hunting but have bee
increasing in recent years despite theNT
12G
depredations of Japanese whaling fleets.
There are no rivers flowing across the
Nullarbor, preventing sediments from the land
from muddying the offshore and near-shore
waters, due to the low rainfall and the draining
of any surface water into the subterranean
caves and holes which are to be found right
across the landscape. Carbonic acid found in
rainfall gradually dissolves limestone and leads
to the formation of underground cave systems
and their enclosed features right across the
world.
As with most such rift zones, which were the
scene of active river systems – one believed to
have been greater than the Amazon of today -
and deep sediment deposition before oceanic
flooding, the Bight is believed to be rich in oil
and gas deposits. Some oil and gas drilling has
taken place along the Bight since the 1960s
and proposals for further exploratory drilling
has been the focus community opposition as
opponents argue that a worst case scen rio of
asteep
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pitous,dsenrsp wo va e the rTuna fleetThe NullarborThe Obelisk at Robe, South Australia on a
stormy day