A mud volcano or mud dome is a landform created by the eruption of mud or slurries, water and gases. Several geological processes may cause the formation of mud volcanoes. Mud volcanoes are not true igneous volcanoes as they do not produce lava and are not necessarily driven by magmatic activity. Mud volcanoes may range in size from less than a meter high and 1 or 2 meters across, to 700 meters tall and 10 kilometers wide. Smaller mud exudations are sometimes referred to as mud-pots. The mud produced by mud volcanoes is mostly formed as hot water, which has been heated deep below the Earth's surface, begins to mix and blend with subterranean mineral deposits, thus creating the mud slurry exudate. This material is then forced upwards through a geological fault or fissure due to local subterranean pressure imbalances. Mud volcanoes are associated with subduction zones and about 1100 have been identified on or near land. Scientists believe that there are more than 10,000 in the world. The temperature of any given active mud volcano generally remains fairly steady and is much lower than the typical temperatures found in igneous volcanoes. Mud volcano temperatures can range from near 100 °C (212 °F) to occasionally 2 °C (36 °F), some being used as popular "mud baths". About 86% of the gas released from these structures is methane, with much less carbon dioxide and nitrogen emitted. Ejected materials are most often a slurry of fine solids suspended in water that may contain a mixture of salts, acids and various hydrocarbons. Possible mud volcanoes have been identified on Mars.
Details
A mud volcano may be the result of a piercement structure created by a pressurized mud diapir that breaches the Earth's surface or ocean bottom. Their temperatures may be as low as the freezing point of the ejected materials, particularly when venting is associated with the creation of hydrocarbon clathrate hydrate deposits. Mud volcanoes are often associated with petroleum deposits and tectonic subduction zones and orogenic belts; hydrocarbon gases are often erupted. They are also often associated with lava volcanoes; in the case of such close proximity, mud volcanoes emit incombustible gases including helium, whereas lone mud volcanoes are more likely to emit methane. Approximately 1,100 mud volcanoes have been identified on land and in shallow water. It has been estimated that well over 10,000 may exist on continental slopes and abyssal plains.
Features Gryphon: steep-sided cone shorter than 3 meters that extrudes mud Mud cone: high cone shorter than 10 meters that extrudes mud and rock fragments Scoria cone: cone formed by heating of mud deposits during fires Salse: water-dominated pools with gas seeps Spring: water-dominated outlets smaller than 0.5 metres Mud shield
Emissions Deep Sea Mud Volcanoes Mud volcanoes are regularly found along the subsurface seafloor, they are primarily responsible for releasing methane into the water column along with other gases and fluids. The high pressure and low temperature associated with the bottom of the seafloor can be the predominant cause of why gases and fluids get trapped that are rising upward; this is a result of methane oversaturation. The total methane emission of offshore mud volcanoes is about 27 Tg per year. This estimate does come with uncertainties, such as the total number of mud volcanoes and their release of methane into the atmosphere/water column is unknown. Surface Mud Volcanoes
Most liquid and solid material is released during eruptions, but seeps occur during dormant periods. The chemical composition of mud volcanoes is almost entirely methane and hydrocarbons found within the mud and the shale from the mud volcanoes. The emissions from mud volcanoes can be entirely dependent on its location, mud volcanoes from NW China are more enriched with methane and have lower concentrations of propane and ethane. The origin of the gas is most likely from below 5000m in the Earth's crust. The mud is rich in halite (rock salt). The overall chemical composition of mud volcanoes is similar to normal magma concentrations. The content of the mud volcano from Kampun Meritam, Limbang are 59.51 weight percent (wt. %) SiO2, 0.055 wt.% MnO, and 1.84 wt.% MgO. First-order estimates of mud volcano emissions have been made (1 Tg = 1 million metric tonnes).
2002: L. I. Dimitrov estimated that 10.2–12.6 Tg/yr of methane is released from onshore and shallow offshore mud volcanoes. 2002: Etiope and Klusman estimated at least 1–2 and as much as 10–20 Tg/yr of methane may be emitted from onshore mud volcanoes. 2003: Etiope, in an estimate based on 120 mud volcanoes: "The emission results to be conservatively between 5 and 9 Tg/yr: that is 3–6% of the natural methane sources officially considered in the atmospheric methane budget. The total geologic source, including MVs (this work), seepage from seafloor (Kvenvolden et al., 2001), microseepage in hydrocarbon-prone areas and geothermal sources (Etiope and Klusman, 2002), would amount to 35–45 Tg/yr." 2003: analysis by Milkov et al. suggests that the global gas flux may be as high as 33 Tg/yr (15.9 Tg/yr during quiescent periods plus 17.1 Tg/yr during eruptions). Six teragrams per year of greenhouse gases are from onshore and shallow offshore mud volcanoes. Deep-water sources may emit 27 Tg/yr. Total may be 9% of fossil CH4 missing in the modern atmospheric CH4 budget, and 12% in the preindustrial budget. 2003: Alexei Milkov estimated approximately 30.5 Tg/yr of gases (mainly methane and CO2) may escape from mud volcanoes to the atmosphere and the ocean. 2003: Achim J. Kopf estimated 1.97×1011 to 1.23×1014 m³ of methane is released by all mud volcanoes per year, of which 4.66×107 to 3.28×1011 m³ is from surface volcanoes. That converts to 141–88,000 Tg/yr from all mud volcanoes, of which 0.033–235 Tg is from surface volcanoes.
Locations
Europe
… excerpt ends here. Continue reading the full article.
