Home' Position : Position Jun Jul 2016 Contents The problem with both these methods
is that, in order to get the underwater
sonar to within a few hundred metres
of the bottom, one needs to know where
the bottom is. Prior to the crash, the
best sea floor mapping in the region was
Geoscience Australia's series of maps
of the ocean floor at 50 metre centres.
However, this coverage only extends
to 108 East (about 600 km from the
coastline). The Australian Bathymetry and
topography grid is a 2009 dataset with
250 metre centres that extends to 92 East.
Both fall short of the search area.
Very little was known about the sea
floor in the MH370 search area itself. The
best data of the sea floor morphology in
the search area were derived from satellite
gravity measurements and provided data
that might have a resolution of 1,500
metres per pixel at best. What was known
was that the dominant features in the
search area was Broken Ridge, an extensive
linear, mountainous sea floor structure
that once formed the margin between two
geological plates. Today, it is part of the
geologically quiescent Australian plate, but
between 20 and 100 million years ago, it
looked much like a divergent plate margin
such as the Mid-Atlantic Ridge.
This lack of information began to
matter when the Royal Australian Navy
deployed an unmanned underwater vehicle
from its support vessel, Ocean Shield, in
the immediate aftermath of the crash.
Without maps, operators had to guess how
far down to send the sub. Missions were
aborted and on at least one occasion, the
submarine went below its design depth.
As a result, the search was divided into
two phases: a bathymetric survey, followed
by a high definition search. Bathymetric
survey vessels—the Chinese survey ship
Zhu Kezhen supported by the Malaysian
ship Bunga Mas 6 and the Dutch vessel
Fugro Equator which was contracted by
Geoscience Australia—spent months at sea
in late 2014 and early 2015, scanning the
sea floor with multi-beam sonar to gather
detailed, high-resolution data.
The ships collected data over 200,000
square kilometres. Their data was
later processed into detailed maps
and three dimensional fly-throughs
at Geoscience Australia in Canberra.
Subsequent mapping was generated with
a definition of 40 to 110 metres per pixel,
sufficient for the guidance of deep diving
To the delight of oceanographers, the data
has revealed many seabed features for the
first time. They have found kilometre high
sea mounts, parallel ridges that stand 300
metres above the sea floor and depressions
1,400 metres below their surroundings. In
some places, the sea floor is 6 km deep.
The survey has also revealed regions of
harder and softer sea floor composition,
defining areas of sediment and rock. A
spokesperson for Geoscience Australia says
the region to the north of Broken Ridge
consists of much older seafloor that is
now covered with 300 metres of sediment.
“Mass wasting features such as rock slides
and debris flows are present throughout
the region, but mainly along the northern
flank of Broken Ridge and the Batavia and
Guldren Draak seamounts.”
For scientists, a greater knowledge
of deep ocean bathymetry is useful for
many reasons. It's obviously fundamental
to understanding plate tectonic history.
It's also essential for the creation of
hydrodynamic models that describe deep
ocean currents and connectivity. The
depth of oceans also play a major role
in defining the habitat of marine flora
and fauna. It is essential information for
people who wish to locate areas where
unique biological communities may exist.
On its website, Geoscience Australia
says: “The data acquired as part of the
bathymetric survey has been collected for
the sole purpose of finding the missing
plane and to bring closure to the families
of those on-board. However, as it is some
of the first high resolution data available
in these areas, it is of great interest to the
scientific community and will be released
to the public in due course”.
Jon Fairall is the founding editor of
Position magazine. He now operates as a
freelance journalist and author. ■
“A greater knowledge of deep ocean bathymetry is
fundamental to understanding plate tectonic history.”
Above: 3D view of volcano with
added icon showing location of
towfish. Source: ATSB.
Right: 3D model of the seafloor
terrain based on sparse pre-
existing data, some of which
has been derived from satellite
gravity measurements and some
from ocean passage soundings.
Source: Geoscience Australia.
26 position June/July 2016
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