The Origins of Mud Volcanoes

Even though they are scientifically known as mud volcanoes, these elements of the landscape are, in fact, visible manifestations of natural gas reserves found at depths of more than 3000 metres that, on their way to the surface, push through layers of clay and groundwater. In Romania, they can be found inside two nature reserves – Pâclele Mari and Pâclele Mici, in Buzău County, between Berca and Arbănași (Picture no.1).


From a geomorphological perspective, mud volcanoes are a component of the Berca Depression, created as a part of the Berca – Arbănași anticline axis, two relief inversions and a weal typical for an anticline. The anticline fold measures 18 kilometres in length and its general orientation is NNE-SSW.

If we look more closely at the landscape features of these mud volcanoes, without being carried away by the wild and, maybe, unique view, which seems to be a copy of our natural satellite, the Moon, we will be able to notice many geomorphological particularities. The volcanic area is surrounded by hills which are often connected with the surrounding areas through steep slopes. Although the transverse cross-section is convex, this will not mislead us, since the so-called volcanoes are just a local manifestation generated by its particular geology as a relief inversion. For example, the base of the anticline, with a W-E direction, is formed  by the greatest elevations that can be found on this direction, which borders the volcanoes, whereas the slopes  of surrounding heights make up the two lines of cuesta, facing each other (Picture no. 2)


The name of these volcanic complexes comes from the colour of the mud they produce, which is similar to that of thick fog (pacla in Romanian). Also, geological arguments can be found in order to explain the flora of this area, which is a perfect illustration of the steppe, although because of the altitude and even longitude of this place, we should encounter a forested steppe type of vegetation. The explanation comes from the red fields that can be found at the entrance of the complex, coloured this way by Nitraria schoberi, a plant species that comes from Central Asia and has adapted to a life in places with high salinity. Furthermore, this is the westernmost location one can find this species anywhere in the world,

Mud volcanoes have been studied for over a century and have long captured the interest of scientists due to their connexion with oilfields located nearby. These volcanoes are radically different from normal ones, with whom they only share a passing resemblance in terms of morphology. To be more precise, whereas normal volcanoes are a consequence of magmatic activity occurring at depths of tens or hundreds of kilometres, (with mountains reaching heights of hundreds or thousands of metres) and generate totally different volcanic products, mud volcanoes have a tectonic origin, appearing as a result of much smaller gas eruptions, from deposits contained in rocks at various depths, that never exceed a few thousand metres.

On its way to the surface, the gas takes with it fresh or salted water, which softens nearby rocks and turns them to mud, along tectonic lines of minimum resistance. The resulting mud surfaces and solidifies in contact with the air, forming conic structures that look like volcanoes. The mud that reaches surface is cold, because it is made from clay. Another major difference between mud volcanoes and normal volcanoes is the temperature of volcanic products, because whereas the former are found at normal temperatures, similar to those of the surrounding environment, the latter are formed by the cooling and solidification of lava, which has a temperature of hundreds or even thousands of degrees Celsius.

The two areas containing mud volcanoes are not that similar though. The ones at Paclele Mici (Photo no. 3) have a more rounded shape, with a few separate cones featuring gentle slopes, and overall, they are younger and less spectacular.


At Paclele Mari (Pictures no. 4 and 5), we can find a much more visible volcanic micro-landscape, with a single central volcano and several secondary cones on its flanks, and a large plateau at the base. On the slope, we encounter a torrential landscape, with barrancos (deep ravines cut by erosional processes in the flanks of the volcano, by means of divergent flow) and planezes (sloped interfluves that are wider than the barrancos and border them).


Such interactions between tectonics, the energy of natural gases and water, inversions of relief and salt reserves can also be found in the Gorj Subcarpathians, the Transylvania Depression and the Moldavian Plateau. The mud volcanoes of Buzau are remarkable due to their size and formation, because they are found in a very seismically active area. Outside Romania, there are other areas with mud volcanoes, such as Azerbaijan, Italy, Iran, Iraq, India and Russia, and in some instances, their appearance is strongly related to an intense volcanic activity.P1010563

We wish you good luck and an awesome trip to the mud volcanoes!

P.S.: From now on, don’t forget that you can see them through the eyes of a geomorphologist!


Article written by Gabriela Moroșanu and translated by Mihail Mitoșeriu.

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