Mariana Trench : Earth's deepest and darkest secret

Planet Earth, mankind's home for thousands of years, is a mysterious planet with many hidden secrets. Though human population have spread across the globe yet there are still places on Earth which are as unknown and inhospitable to us as deep space.

Hidden in the depths of the Pacific Ocean there is a place so deep, dark and alien, where human seldom dares to venture or survive. The deepest place of the planet Mariana Trench, also called Mariana's Trench is such a place, a deep sea trench in the floor of the western North Pacific Ocean, the deepest known such trench on Earth, located mostly east as well as south of the Mariana Islands.

It is part of the western Pacific system of oceanic trenches coinciding with subduction zone (points where two adjacent tectonic plates collide, one being forced below the other.) The Mariana Trench is located at a convergent plate boundary. Here two converging plates of oceanic lithosphere collide with one another. At this collision point, one of the plates descends into the mantle. At the line of contact between the two plates, the downward flexure forms a trough known as an ocean trench. Ocean trenches form some of the deepest locations in Earth's oceans.

 

As the Pacific Plate is pushed into the mantle and heated, water in the sediment is volatilized, and gases are liberated as the basalt of the plate melts. These gases migrate to the surface to form a number of volcanic vents on the ocean floor.

The Mariana Trench occurs along a plate boundary between the Philippine Plate and the Pacific Plate. The Pacific Plate is on the eastern and southern side of this boundary, and the Philippine Plate is on the western and northern side of this boundary.

Both of these plates are moving in a northwesterly direction, but the Pacific Plate is moving faster than the Philippine Plate. The motion of these plates produces a convergent plate boundary because the greater speed of the Pacific Plate is causing it to collide into the Philippine Plate. This collision produces a subduction zone at the Mariana Trench as the Pacific Plate descends into the mantle and under the Philippine Plate.

This collision occurs at variable speeds along the curving boundary of the plates, but the average relative motion is in the range of tens of millimeters per year. Recurrent earthquakes occur along this plate boundary because the Pacific Plate's descent into the mantle is not smooth and uniform. Instead, the plates are usually stuck with pressure accumulating, but with sudden slips as the plates move a few millimeters to a few meters at a time. When the plates slip, vibrations are produced, and those vibrations travel through Earth's crust as earthquake waves.

As the Pacific Plate descends into the mantle, it is heated by friction and the geothermal gradient. At a depth of approximately 100 miles, the rocks have been heated to a point where some minerals begin to melt. This melting produces magma that rises towards the surface because of its lower density. As the magma reaches the surface, volcanic eruptions are produced. These eruptions have formed the Mariana Island Arc.

An arcing depression, the Mariana Trench stretches for more than 1,580 miles (2,540 km) with a mean width of 43 miles (69 km). The greatest depths are reached in Challenger Deep, a smaller steep-walled valley on the floor of the main trench southwest of Guam. In addition to Challenger Deep, another deep hole Sirena Deep was discovered south of Guam and east of Challenger Deep. First found in 1997, its depth has been reported variously as 34,911 feet (10,641 metres) and 35,463 feet (10,809 metres).

 

Measuring the greatest depths in the Mariana Trench is an extremely difficult task, given the technical challenges of delivering instruments to such a depth and then obtaining readings with accuracy. The first attempt was made in 1875 during the Challenger Expedition (1872–76), when a sounding of 26,850 feet (8,184 metres) was obtained near the southern end of the trench. In 1899 Nero Deep 31,693 feet (9,660 metres) was discovered southeast of Guam. That measurement was not exceeded, until a new 32,197-foot (9,813 metre) deep hole was found in the vicinity 30 years later. In 1957, during the International Geophysical Year, the Soviet research ship Vityaz sounded a new world record depth of 36,056 feet (10,990 metres) in Challenger Deep. That value was later increased to 36,201 feet (11,034 metres). Since then several measurements of the Challenger Deep have been made, using increasingly sophisticated electronic equipment. Notable among these is the depth of 35,840 feet (10,924 metres) reported by a Japanese expedition in 1984 and one of 36,070 feet (10,994 metres) obtained by a U.S. research team in 2011.

The first descent to the bottom of the Mariana Trench took place on January 23, 1960. The French built U.S. Navy operated Bathyscaphe Trieste with Swiss ocean engineer Jacques Piccard and U.S. naval officer Don Walsh aboard made a record dive to 35,814 feet (10,916 metres) in Challenger Deep. The next person to descend into that location did so more than 50 years after Piccard and Walsh. On March 26, 2012, Canadian filmmaker James Cameron piloted the submersible Deepsea Challenger to 35,756 feet (10,898 metres), in the process establishing a new world record depth for a solo descent.

To put the depth of Marianas trench into perspective, If Mount Everest, the highest mountain on Earth, were placed at this location it would be covered by over one mile of water.