Scientific expedition to the world's
deepest undersea volcanic rift

Geology

The forces pulling the plates apart at mid-ocean ridges are inexorable. So if a section of ridge is not supplied with enough magma to fill the gap, something else must happen. Instead of volcanoes erupting smoothly to create new seafloor, a block of existing seafloor may be pulled up out of the crust, creating a type of undersea mountain known as an Oceanic Core Complex.

Geologists have only been aware of Oceanic Core Complexes for a decade or so, and are still debating exactly how they form, because very few have been studied in any detail. Roughly halfway along the Mid-Cayman Spreading Centre is an undersea mountain called Mount Dent, which may be an Oceanic Core Complex. We will be looking for hallmarks that reveal how it was formed, such as any striations on its lower slopes, which would show it was pulled out of the crust.

Oceanic Core Complexes are also interesting to geologists because their lower slopes are formed of rocks from the Earth's upper mantle, laid bare as the seafloor is twisted up out of the crust. These mantle rocks can react with seawater to release hydrogen and heat, which can fuel a different kind of deep-sea vent.

We'll be examining Mount Dent very closely for such vents - only one set has been found so far elsewhere in the world, but largely because no-one has looked for them. If we find similar vents here, we should get a better idea of how widespread they may be globally - as well as seeing what lives at them in this particular corner of the ocean.

A few years ago, most scientists thought that ultraslow-spreading ridges were too cold to support 'normal' high-temperature deep-sea vents. We now know that they do, but very few have been investigated with underwater vehicles to find out how. By visiting the deep-sea vents in the Cayman Trough, we hope our work will help to plug that gap in our knowledge of how our planet works.

Page 1: Breaking new ground in the deep
Page 2: Moving mountains

Want to dive deeper?

Visit Venture Ocean for more about undersea volcanoes and mid-ocean ridges

Watch animations of the motion of the plates of the Earth's crust

Read more about ultraslow-spreading ridges

Download a feature about ultraslow-spreading ridges from the journal Oceanography