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Macquarie Island History [pg1,
pg2]
Origins and Formation.
From the time the Australian
National Antarctic Research Expedition (ANARE) set up a permanent
station on Macquarie in 1948, there have been a considerable
number of geologists keen to carry out detailed research into
the origins of this tiny speck of land in the Southern Ocean.
Macquarie
Island is geologically unique in a number of ways. Among subantarctic
islands, it is the only one to be totally oceanic in origin
and is a rare example of uplifted oceanic crust. It does not
have large scale sedimentation and has not been built up from
actual volcanic activity. It is also now thought that the
island has been subjected to little or no glaciation during
its development.
It all
started some 12 million years ago. Basalt magma from deep
inside the earth flowed from a fissure on the seabed at the
abutting edges of two large tectonic plates, the Indian/Australian
Plate, to which Macquarie Island belongs, and the Pacific
Plate. A third tectonic plate, Antarctic, abuts the other
two plates some 650 kilometres south of the island. Geologists
now indicate that the Pacific Plate is being pushed, in an
anticlockwise direction, under the Indian/Australian Plate
at 2-3 centimetres a year. Consequently, the Indian/Australian
Plate is riding up vertically over the Pacific Plate at 1
- 2 millimetres a year.
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Macquarie Island,
looking accross the Isthmus towards north
(photographer unknown)
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Macquarie
Island ANARE station on the Isthmus, looking south
(photographer unknown) |
As a
result of these complicated movements and pressures, the Macquarie
Ridge complex has been growing upwards. Trending NNE in its
northern part and curved towards the SE at its southern end,
it runs from the New Zealand coastal shelf off the west coast
of South Island to the triple plate junction at about 61ºS,
162ºE.
When
the Macquarie Ridge had risen more than 2.5 kilometres from
the sea floor, it broke through the ocean surface where it
has since been subjected to the effects of the very strong
winds and huge waves that are generated in the vast Southern
Ocean. In spite of these eroding forces the island is now
some 200 - 400 metres high. The date at which Macquarie Island
broke through the sea surface is currently being debated by
geologists. Some suggest 700,000 years ago while others think
that it could be from 80,000 to 300,000 years ago.
(More to come..)
Information
from: http://www.parks.tas.gov.au/fahan_mi_shipwrecks/infohut/geology.htm
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