Mud volcanoes are formed around subduction zones at tectonic plate boundaries and other areas which causes huge pressures, for example changes deep down in the Earth’s crust [click here to find out more about plate tectonics]. The fractures in the Earth’s crust allow gases such as methane and carbon dioxide, and fluids such as water and solids such as mud to erupt, which causes cones to form around the fissures. There are examples of mud volcanoes on land (like the one pictured on the right) but when they are found under the sea, they are difficult to get images of, so this is when scientists use the techniques at their disposal on a cruise like this.
Cross-section through the seafloor to show how fluids and gases move through the sub-seafloor to erupt at the seabed and form mud volcanoes.
(Image after Whelan et al. 2005)
Each mud volcano has its own individual ‘personality’ and it is only by taking measurements that the ‘personality’ can be described.
- One form of measuring is to sample using corers. This is a giant pipe which boars into the sediment and brings up a column of sediment that can be analysed to determine what it is made up of. There are 4 different types of corer for different jobs.
- The ROV Isis is also be used to make a detailed map of the volcano’s surface using a technique called bathymetry.
One of the clues that it may be a mud volcano is that gases are seen escaping from the crate or the side vents and these can be picked up on an ROV image at a resolution of 10cm. Sometimes the gas gets trapped and forms a solid called gas hydrates which only exist in this form because of the enormous pressures. The Isis can pick these up in its manipulator arms and bring them to the surface. So, after these techniques have been used and after a lot of laboratory analyses of the gases and sediment, we know what the mud volcano looks like and what its composition is.
Above left: Mud volcanoes on land can be explosive, like this one in Azerbaijhan.
The picture on the right shows gas bubbles escaping from the Håkon Mosby mud volcano at 950m water depth offshore Norway
The JC10 cruise is going to focus on at least 3 mud volcanoes at different depths in The Gulf of Cadiz: Mercator at 370m, Darwin at 1100m and Carlos Reberio at 2200m . They have been investigated before but not this precisely. There are now new techniques that will allow this to be done in detail.
Map showing the locations of our target areas: the Mercator, Darwin and Carlos Ribeiro mud volcanoes in the Gulf of Cadiz
As each mud volcano is different it supports different life forms. The idea is to see how they affect the ecosystems around them. The volcanoes are biological hotspots which means that they have specialised organisms that quite possibly will not be found anywhere else! This can be quite a hostile environment in human terms; not only huge pressures and cold temperatures but plenty of hydrogen sulphide and methane gas together with low oxygen environments. The teams of scientists will investigate these organisms from the smallest microrganisms such as bacteria to larger mesofauna like different types of worms and then the mussels and shrimps etc that live on them. The Isis will be able to film larger animals swimming in the sea in the vicinity of the volcanoes.
Some of the weird and wonderful creatures found living at cold seeps and mud volcanoes in the eastern Mediterranean (left) and Norwegian margin (right).
Images courtesy MARUM and Ifremer.
As the cruise progresses images like these will emerge from Isis and we will bring them to you. Clearer images of the shape of the volcano will emerge from micro bathymetry using Isis....Keep looking!