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What is a Mud Volcano?

Institute for Exploration / Ocean Exploration Trust

My name is Noelle Turner, aboard Nautilus as an Educator at Sea from Knoxville, TN. I am a biology teacher, so if geology is going to impress me, it has to be really fascinating.  On this leg of the expedition, Hercules and Argus have been exploring the Amsterdam, Kula, and Thessaloniki mud volcanoes.  These mud volcanoes are located off the coast of Turkey and are a part of the Anaximander underwater mountains.  I will have to say, their geology is very.... well, cool.  Granted, part of my interest comes from all the living things that I have seen associated with the mud volcanoes, but I am giving credit where credit is due.  The geology is very interesting.  After seeing these features, I wanted to know what a mud volcano is and how one compares  to "real" volcanoes.

When most people think about volcanoes, they think of hot lava and heat coming together in a dynamic firework of eruption.  This is not what a mud volcano is.  In fact, typically the water around a mud volcano is no more than 1 or 2 ◦C higher than the surrounding water.  Mud volcanoes are caused by the build up and release of methane gas from the sediments.  The reason that methane gas is released is due either to faults and fractures created by plate tectonics or to the slow release of gases in shallow areas.  In this area, tectonic pressure comes from the collision of the African and Eurasian plates.  This interaction can push the methane hydrates through the mud which exposes them to lower pressures and causes them to turn into gas.  When this occurs, there can be a quick release of methane gas which brings mud and rocks up with the methane in an explosion which mimics the lava volcano, but it is not thought to be quite as powerful.  At other times, the gas just seeps out slowly from the sediments in bubbles.

Here is where the biology comes in. On land and in the shallower parts of the ocean, food chains start with plants or algae (producers.)  The producers use the sun to make sugars that can feed other organisms in a process known as photosynthesis.  At over 2000 meters below the ocean surface, there is no sunlight, and, therefore, there are no plants. So, one would think that there would be very little life.  What happens around these mud volcanoes is that some special bacteria use the methane (a chemical rather than sunlight) to make food in a process known as chemosynthesis. The bacteria either become food for other organisms or live in a close relationship with other organisms to provide food for their community. An example of this close symbiotic relationship is one found with tube worms.  Tube worms have bacteria living inside them. The bacteria provide the food to feed the tube worms, while in exchange, the tube worms provide a place for the bacteria to live.  The bacteria are the producers, and the food chain builds up from there.

During our dives, I have seen many areas of activity, as indicated by the methane bubbles.  Some of these places have lots of sea life.   We are still learning how these communities form and how long they last.  It is basically a new frontier.  Both the biology and the geology are very impressive.   I will have to admit, geology is growing on me.