The Mariana Trench

Probably the most fascinating place underwater!

The Mariana Trench is found in the Western Pacific Ocean. This crescent-shaped trench is the deepest in the world, and lies east of the Mariana Islands, which are situated close to Guam. The environment is unique in many ways, both for its inhabitants and the underwater activity that it displays.

In the Trench, underwater vents are actively bubbling up liquid carbon dioxide and sulphur. Active mud volcanoes are to be found in depths that have a pressure 1,000 times that at sea level. The marine life, living in the depths of the Mariana Trench have adapted themselves to low light or complete darkness.

The Challenge Deep

Within the Mariana Trench, at the southern end, we can find ‘The Challenge Deep’. This is the deepest spot recorded in the ocean, and is sometimes referred to as Marianas Trench. The estimated depth, measured from the surface using modern day technology still varies, albeit with a small difference of 305 meters.

The estimated depth was recorded at 10,994 meters in 2010. The National Oceanic and Atmospheric Administration measured the Challenge Deep using sound impulses being sent the ocean and measured when they bounced back from the sea bed. The Challenge Deep is very difficult to measure and a very inhospitable place.

In 2012, an expedition was sent to try to explore the bottom of Challenge Deep. The maximum depth reached at 10,898 meters, although very briefly. In 2014 a high resolution seabed floor mapping survey was done by a University in New Hampshire, revealing that the Challenge Deep bottoms out at 10,984 m.

If we make a comparison to Mount Everest, which stands at 8,848 m above sea level, it means the Mariana Trench is 2,147 m deeper than Mount Everest is high.

Sirena Deep

We can find another deep trench, called the Sirena Deep, which lies 200 kilometers to the east of Challenge Deep. The Sirena Deep measures a whooping 10,809 m in depth, leaving it the second-deepest known trench to date. The Marina Trench is 2,542 km long, almost 5 times the length of the Grand Canyon. The narrow trench though is only 69 km wide.

In 2009, President G.W.Bush created a reserve approximately 506,000 square km of sea floor and waters surrounding the Mariana Trench. It is now a marine protected area and falls under the jurisdiction of Guam, United States of America.

How the Trench was formed:

Through the collision of two massive oceanic crusts, in the subduction zone. One large slab of crust is pushed upward and the other is driven downward into the Earth’s mantle. Where the two pieces of crust intersect, a deep trench forms above the bend in the sinking crust. In the case study of the Mariana Trench, the Pacific Ocean crust is bending below the Philippine crust. The Pacific crust, or tectonic plate is about 180 million years old, the Philippine plate is smaller and much younger in age.

Below the surface, the ever increasing water pressure becomes enormous. At floor level it records 703 kilograms per square inch, this is 1,000 times the pressure at sea level. There is a chain of active volcanoes that rise above sea level along the Mariana Trench. This chain of active, spewing volcanoes mirror the shape of the crescent of the Trench. Some volcanoes spew out liquid carbon dioxide, coming from thermal vents deep underwater. The liquid spewed out of active volcanoes is measured at 103 degrees Celsius. Other volcanoes, like the Daikoku submarine volcano sends out molten sulphur 410 m below the surface of the ocean. This phenomena has not been witnessed any where else in the world.

Life in the Deep

Life in the Mariana Trench is both harsh and unrelenting. The conditions for animals living here is darkness, cold and extreme pressures. Food resources are very limited due to the depth of the trench, and few organisms sink the thousands of meters down to the seabed. Some microbes rely on chemicals, like methane gas or sulphur, other animals survive on eating the lower life that exists down there. Small sea cucumber, 200 different microorganisms and Amphipods can be found in the deep, they have been brought back in containers full of mud, then analysed by researchers in Newcastle University.


Sadly researchers found that levels of contamination in the Amphipods, similar to that found in animals from an area called Suruga Bay. Suruga Bay is one of the most polluted industrial areas of the northwest Pacific Ocean. Plastic contamination was also found at high levels, which passes from species to species, as one animal eats the other to survive.

Pollution and plastic is in every corner of the globe and in all ocean waters. Due to the depth of the Mariana Trench, plastic and pollution becomes concentrated to such high levels within the marine species that live there.

Help to save our oceans. Do your bit too, join in doing beach clean-ups, underwater clean-ups and record these with ProjectAWARE.