The Swiss-designed,
Italian-built, United States
Navy bathyscaphe Trieste reached
the bottom at 1:06 p.m. on January
23, 1960, with U.S. Navy Lieutenant
Don Walsh and Jacques Piccard
on board. Iron shot was used
for ballast, with gasoline for
buoyancy. The onboard systems
indicated a depth of 11,521
meters (37,799 ft), but this
was later revised to 10,924
meters(35,813 ft) . At the bottom,
Walsh and Piccard were surprised
to discover soles or flounder
about 30 cm (1 ft) long, as
well as shrimp. According to
Piccard, "The bottom appeared
light and clear, a waste of
firm diatomaceous ooze".[2]
The
bathyscaphe Trieste as it
appeared just before the record
dive to the floor of the Marianas
Trench.
Image: Courtesy of the U.S.
Navy
The Woods Hole Oceanographic
Institution sent its Nereus hybrid
remotely operated vehicle (HROV)
to explore the trench on May 31,
2009.[2]
The Mariana Trench (or
Marianas Trench) is the deepest part
of the world's oceans, and the deepest
location on the surface of the Earth's
crust. It is located in the western
Pacific Ocean, to the east of the
Mariana Islands. The trench is about
1580 miles (2550 km) long but has
a mean width of only 43 miles (69
km). It reaches a maximum depth of
about 10,924 meters at the Challenger
Deep, a small slot-shaped valley in
its floor, at its southern end. (35,840
feet; 6.78 miles).
Part of the Izu-Bonin-Mariana
Arc system, the trench forms the boundary
between two tectonic plates, where
the western edge of the Pacific Plate
is subducted beneath the small Mariana
Plate. Because the Pacific plate is
the largest of all the tectonic plates
on Earth, crustal material at its
western edge has had a long time since
formation (up to 170 million years)
to compact and become very dense;
hence its great height-difference
(which translates to water depth)
relative to the higher-riding Mariana
Plate, at the point where the Pacific
Plate crust is subducted (is forced
down beneath the other). This deep
area, is the Mariana trench proper.
The movement of these plates is also
responsible for the formation of the
Mariana Islands.
At the bottom of the
trench, where the plates meet, the
water column above exerts a pressure
of 108.6 MPa, over one thousand times
the standard atmospheric pressure
at sea level. Some creatures of the
type normally encountered that could
live at these depths are few, but
some fish species, like the angler
fish or other deep-sea fishes, have
been spotted in these waters.[citation
needed] If Mount Everest, the tallest
point on Earth at 8,848 meters (29,029
feet), were set in the Mariana Trench,
there would be 2,076 meters (6,811
feet) of water left above it.[2]
The trench was first
sounded during the Challenger expedition
(December 1872 – May 1876),
which recorded a depth of 9,636 m
(31,614 feet).
Challenger II surveyed
the trench using echo sounding, a
much more precise and vastly easier
way to measure depth than the sounding
equipment and drag lines used in the
original expedition. During this survey,
the deepest part of the trench was
recorded when the Challenger II measured
a depth of 5,960 fathoms (10,900 metres,
35,760 ft) at 11°19'N 142°15'E?
/ ?11.317°N 142.25°E? / 11.317;
142.25,[3] known as the Challenger
Deep.[2]
In 1957, the Soviet
vessel Vityaz reported a depth of
11,034 meters (36,200 ft), dubbed
the Mariana Hollow. (Although this
claim was made by the Soviets in 1957,
the finding has not been repeated
by subsequent mapping expeditions
using more accurate and modern equipment.)[citation
needed]
In 1962, the surface
ship M.V. Spencer F. Baird recorded
a maximum depth of 10,915 meters (35,840
ft), using precision depth gauges.
In 1984, the Japanese
sent the Takuyo , a highly specialized
survey vessel, to the Mariana Trench
and collected data using a narrow,
multi-beam echo sounder; they reported
a maximum depth of 10,924 meters,
also reported as 10,920 meters ±
10 meters.
The most accurate measurement
on record was taken by a Japanese
probe, Kaiko , which descended unmanned
to the bottom of the trench on March
24, 1995 and recorded a depth of 10,911
meters (35,798 ft).[2]
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