BBC News –
Stretching for more than 2,500km (1,500 miles), the Mariana Trench is a very narrow, very deep crack in the ocean floor.
At its deepest, it reaches nearly 11km (seven miles) down – making it the lowest point in our oceans.
Once, its record-breaking depth was thought to be the only interesting thing about the trench, but now scientists are beginning to think otherwise.
Jim Gardner, from the US Centre for Coastal and Ocean Mapping (CCOM), says: “Trenches are becoming much more focused in the scientific community.”
The geologist has spent the past five years creating the most detailed survey of the Mariana Trench to date. And he says that finding out more about the inner workings of these deep-sea spots is vital.
There are more than 20 trenches like the Mariana around the world, but most are in the Pacific Ocean.
They are formed at the boundary of two tectonic plates, where very heavy oceanic crust (in the case of the Mariana Trench, the Pacific Plate) dives underneath lighter continental plate – a process called subduction.