Gradual Sliding as a Common Growth Process in Caspian Mud Volcanoes

Many large-scale mud volcanoes (MVs) display kilometer-sized mud breccia flows that extend from the crater. These large-scale flows are assumed to be related to the intermittent episodic eruptive events that characterize MV activity. However, only a few sufficiently long-lasting and voluminous eruptions have been documented and considered to be able to generate such extensive flows. Therefore, the exact mechanisms promoting the formation of such long flows remain so far unclear.

In September 2022, shortly after the 11^th of August 2022 Lokbatan MV eruption in Azerbaijan, we carried out fieldwork measurements and observations. Although the eruption was short and produced only a volumetrically small amount of mud breccia circumscribed around the crater site, we observed a horizontal displacement of the whole >1km long pre-existing mud flow. This movement was highlighted by fractures indicating detachment and downslope sliding and was later confirmed by InSAR historical data. These findings suggest that this kilometer-sized mud flow may not result solely from massive eruptions, as previously thought, but instead from by a gradual sliding triggered by 1) the additional weight of freshly erupted material and b) by inflation/deflation of the whole MV. We speculate that this gravitative flow behaves similarly to warm-based glaciers.

To validate this model and assess whether this mechanism is unique to Lokbatan, we analyzed Google Earth™ satellite imagery of other large MVs in Azerbaijan. Here we present data that reveal that a similar behavior was observed for least 20 MVs in the Caspian region (e.g. Koturdag, Goturlug, and Pirsaat Burnu among others). These new observations highlight that this previously overlooked mechanism for the growth of kilometer-sized mudflows is more widespread than previously thought and is indeed common for many large MVs. Understanding this process is critical for better assessing their dynamics and the risks they pose to surrounding infrastructures and settlements. Further, this process is essential for understanding the dynamics of mud volcanoes on Earth and may provide insights into the formation of large-scale flow-like features on other bodies in the Solar System.