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Volcanoes

There she blows! Mud volcanoes in the Mediterranean

Article: Lopez-Rodriquez et al. Recent, deep-source methane/mud discharge at the most active mud volcano in the western Mediterranean. 2019. Marine Geology 408: 1-17. Link: https://www.sciencedirect.com/science/article/abs/pii/S0025322718302809

Mud volcanoes are a bit misleading. Mud volcanoes aren’t real volcanoes, like the volcano that erupted in Iceland several years ago and disrupted air travel, or the infamous Mt. Vesuvius that buried the ancient Roman town of Pompeii. Mud volcanoes usually don’t produce lava, aren’t very hot, and are often caused by different geological forces than their explosive volcano cousins. However, mud volcanoes are important on Earth, since they can release large amounts of greenhouse gases, like the powerful greenhouse gas methane. Mud volcanoes might even have formed on Mars! Because of this, it is important to study how and why mud volcanoes form.

Underwater mud volcanoes in the Flower Garden National Marine Sanctuary in the Gulf of Mexico. Escaping gas can be seen rising from the mud volcano. PC: Sea Research Foundation (SRF) and the Ocean Exploration Trust (OET).

 

Carmela López-Rodríguez and her colleagues set out to study mud volcano formation by examining the 1km in diameter Carmen mud volcano on the bottom of the Mediterranean Sea. They used a combination of seafloor mapping, sediment collection, chemical analyses, and mathematical modeling to determine where the mud volcano fluids are from and when the mud volcano could have formed.

Location (left panel) and bathymetric map (right panel) showing where the mud volcano studied by Lopez-Rodriguez and colleagues is located. In the bathymetric map, the warmer colors are the top of the mud volcano. Image from Lopez-Rodriguez et al (2019).

There are chemical indicators of where the mud volcano fluids are sourced. Two common elements, calcium and magnesium, were not present in high concentrations in the deepest mud volcano fluid the scientists examined. In contrast, two other elements which are usually dilute in seawater (trace elements), lithium and boron, were more concentrated. The scientists also measured variations of oxygen and hydrogen, called isotopes, to see where the mud volcano fluid came from. The amount of these oxygen and hydrogen isotopes showed the scientists that they probably came from chemically changing a common type of clay called smectite.

Taking all of these chemical measurements together, the scientists were able to calculate at what temperature this fluid was made, around ~140°C. That meant that the fluid was probably made around 5 kilometers (~ 3.1 miles) below the seafloor, and traveled upwards towards the top of the mud volcano.

The authors also looked at the methane being released from the mud volcano. Methane is a powerful greenhouse gas that can be made either by microorganisms or by geological processes. When it’s made through geological processes, the methane is called ‘abiotic’, meaning not made by life. When microorganisms make methane, it’s ‘biotic’ production. These have different chemical signatures when scientists measure the different isotopes in methane. When the scientists did that, they discovered the methane had a mostly biotic origin, and that when different places in the volcano were measured, the methane signatures were similar. The consistency led the scientists to conclude this means that the methane comes from deep beneath the mud volcano.

Images depicting the underwater mud volcano, with locations of sediment samples taken for chemical analyses marked on the panel to the right. From Lopez-Rodriguez et al. 2019.

 

Based on these results, plus many detailed observations of the types of mud found in and around the volcano, the scientists think that active geological movements in the Mediterranean caused a massive underwater expulsion of mud. This was accompanied by rapid release of gases, such as the deeply sourced methane. The scientists calculated that this even happened just 2,000 years ago!

Mud volcanoes known as mud pots in California (PC: Derek Hoyle, wikipedia.org)

While most of us will never see an underwater mud volcano with our own eyes, there are plenty of mud volcanoes and smaller mud pots dotted throughout the Earth’s surface. In the United States alone, you can see them (and smell them!) throughout California, including the Salton Sea, and in the famous Yellowstone National Park. Next time you see one on land, think about what you might observe, and how it might compare to the ones deep in the sea!

 

Discussion

One Response to “There she blows! Mud volcanoes in the Mediterranean”

  1. Very nice and well done summary of our paper.

    I’d like to remark the timing of the eruption we dated with geochemical modeling took place in the year 2000, thus only 19 years ago (taking an error of +- 5 years). This is the first time that so much recent mud-rich fluid emission is dated.

    Thanks to follow our investigations in West Mediterranean Mud Volcanoes

    Posted by Carmina Lopez Rodriguez | March 29, 2019, 3:13 pm

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