Deep within Earth’s mantle lie two enormous regions, often referred to as "islands," which are the size of continents.

The LLSVPs are found in what scientists refer to as "slab graveyards," where tectonic plates sink through a process called subduction.

Two hidden mountains, more than 100 times larger than Mount Everest have been discovered deep underground. The two ‘islands of rock’ each measure more than 620 miles / 998km tall, dwarfing anything found on Earth’s surface and making Mount Everest look like an anthill.