Flaming Eruptions and Ejections from Mud Volcanoes in Azerbaijan: Statistical Risk Assessment from the Historical Records

Abstract

Information from approximately 220 mud volcanoes in Azerbaijan over the last 183 years has been used to assess the likelihood of: (a) new mud volcano formation; (b) new gryphon or salse formation: (c) mud flow parameters; (d) flame production and flame height distribution. These computations have been undertaken to provide a risk assessment for offshore rig siting based on historical information, with the offshore Chirag area, of major interest to oil exploration corporations, being used as an example of probable hazard evaluation. The results show that: over the past 100 years only four new mud volcanoes have been observed onshore in Azerbaijan. Furthermore, newly-formed mud volcanoes are usually very small, and their eruptions do not present a serious hazard. The most probable waiting time for the formation of a new volcano in the Chirag area is about 1600 years. The probability that a new volcano will not form in this area over the next 100 years is greater than 90%. The formation of new gryphons and salses is probable. These gryphons usually lie within the area of the crater field and along faults. In the volcanoes studied the average diameter of the crater field is about 120 m. The most probable waiting time for a first eruption is about 95 years, and for a powerful or average-strength eruption is about 270 years. On land there is a 95% probability that the length of mud flow from an eruptive center is less than about 340 m, and that the mud width does not exceed 260 m; the average values of these parameters are 74 m and 56 m, respectively. For the marine environment establishing the corresponding values presents particular hydrodynamic problems. The gas volume distribution during eruptions can be described by an exponential distribution with an average value of about 590 × 106m3. Small volumes of gas are also given off by degassing of volcanic breccia, but the mean value is only about 560 m3, many orders of magnitude lower than the gas volume emitted during the eruptive phase. The gas composition is mostly methane (averaging 95%), with smaller amounts of carbon dioxide (3.5%), and minor quantities of nitrogen, ethane, heavy hydrocarbons, hydrogen and helium. The hydrogen sulfide content is extremely low, of order of 10−5%. Gas ignition depends both on volume and on the rate at which gas moves along exit channels and is emitted from such channels. The ignition coefficient, characterizing the probability that the gas will self-ignite during an eruption, is about 42% which is the average likelihood that gas will flame spontaneously. The flame height, which can reach hundreds of meters, averages 77 m, and there is a 95% probability that a flame will be in the range 60 m to 100 m, although in the majority of eruptions there is no flame recorded.