Mud Volcano and Its Evolution
Bambang P. Istadi1,*, Handoko T. Wibowo2, Edy Sunardi3,
Soffian Hadi4 and Nurrochmat Sawolo1
1 Energi Mega Persada
2 Independent geologist
3 Universitas Padjajaran
4 Sidoarjo Mudflow Mitigation Agency Indonesia
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Mud Volcano and Its Evolution. Bambang P. Istadi1,*, Handoko T. Wibowo2, Edy Sunardi3,. Soffian Hadi4 and Nurrochmat Sawolo1. 1Energi Mega Persada.
Mud Volcano and Its Evolution | InTechOpen
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Mud Volcano and Its Evolution | InTechOpen, Published on: 2012-02-03. Authors: Bambang P. Istadi, Handoko T. Wibowo, Edy Sunardi, et.
1. Introduction
The term mud volcano refers to topographical expressions of naturally occurring volcano shaped cone formations created by geologically excreted liquefied sediments and clay-sized fragments, liquids and gases.
Ejected materials often are a mud slurry of fine solids suspended in liquids which may include water and hydrocarbon fluids.
The bulk of released gases are methane, with some carbon dioxide and nitrogen. Mud volcanoes may be formed by a pressurized mud diapir which breaches the Earth's surface or ocean bottom.
Flowing temperatures at the ocean bottom may be as low as freezing point and are associated with the formation of hydrocarbon hydrate deposits. Flowing temperatures can also be hot if associated with volcanic gases and heat escaping from deep magma which can turn groundwater into a hot acidic mixture that chemically changes rock into mud and clay-sized fragments.
These mud volcanoes are built by a mixture of hot water and fine sediment that either pours gently from a vent in the ground like a fluid lava flow; or is violently ejected into the air as a lava fountain of escaping mud, volcanic gas, stream and boiling water.
Mud volcanoes are most abundant in areas with rapid sedimentation rates, active compressional tectonics, and the generation of hydrocarbons at depth.
Typically they are also found in tectonic subduction zones, accretionary wedges, passive margins within deltaic systems and in active hydrothermal areas, collisional tectonic areas, convergent orogenic belts and active fault systems, fault-related folds, and anticline axes.
These structures act as preferential pathways for deep formation fluids to reach the surface. (see Pitt and Hutchinson, 1982, Higgins and Saunders, 1974; Guliyiev and Feizullayev, 1998; Milkov, 2000; Dimitrov, 2002; Kopf, 2002, Mazzini, 2009).
The existence of mud volcanoes are controlled by tectonic activity where fluid escapes from areas undergoing complex crustal deformation as a result of transpressional and transtensional tectonics. C
ollisional plate interactions create abnormal pressure condition and consequently overpressured buildup of deep sedimentary sediment which in turn result in formation of diapirs. Over pressured zones typically are under-compacted sedimentary layers which have lower density than the overlying rock units, and hence have an ability to flow.
They are the product of rapid deposition where the connate water is trapped, unable to escape as the surrounding rock compacts under the lithostatic pressure caused by overlying sedimentary layers.
In thick, rapidly deposited shale dominant sedimentary sequence, the low and reduced porosity and permeability due to compaction inhibit the expulsion of water out of the shale.
As burial continues, fluid pressure increases in response to the increasing weight of the overburden. This Non-equilibrium compaction is believed to be the dominant mechanism in formation of overpressured sediments.
Over pressure however can also result from maturing organic rich predominantly clay sediments which are generating methane and other heavier gases that are still trapped within the sedimentary sequences.
The above geological elements that result in diapirsm and mud volcano is often known as “elisional” basin mainly characterized by rapid deposition of thick young sediments, presence of abnormally high formation pressure or overpressures fluids, under-compacted sediments, petroleum generation, compressional setting, high seismicity and occurrence of faults (see Milkov, 2000, and Kholodov, 1983).
Fig. 1. Basic structure and anatomy of a conical mud volcano. The mud volcano is formed by the escaping natural gas that rises to the surface when it finds a conduit (strike slip fault) and carries mud which has a lower density (and typically found as low velocity interval) than the surrounding sedimentary succession. Fluid, gas, and surface water are ejected in a cone shape like a mountain and forms craters, mud pools (salses) and cones (gryphons).
Tectonic movement is very influential, as well as rapidly deposited sediments and burial of organic rich sediments. Strike-slip faults in active tectonic regions are the most ideal place for the formation of mud volcanoes.
Overpressure buildup mechanisms contribute to the brecciation of the deep sedimentary units include for example the dewatering of thick clay-rich sedimentary units, and geochemical reactions in sedimentary units with high temperature gradients are the mechanism for the eruption (Mazzini, 2009).
He further suggest that when the subsurface overpressure reaches a threshold depth where the overburden weight is exceeded, fracturing and breaching of the uppermost units occur, sometimes facilitated by external factors such as earthquakes. The upward movement of the mud to surface is due to buoyancy and differential pressure.
Geological structures like faults and anticlines where mud volcanoes are commonly found are easily perturbed by earthquakes as they represent weak regions for the seismic wave’s propagation.
This mechanism is well described by Miller et al. (2004) where earthquakes initiating local fluid movements cause fractures that propagate to the surface manifesting with a time delay from the main earthquake. Miller et al. (2004) propose a link between earthquakes, aftershocks, crust/mantle degassing and earthquake-triggered large-scale fluid flow where trapped, high-pressure fluids are released through propagation of coseismic events in the damaged zones created by the mainshock.
The resulting disturbance of the gravitational instability triggers the beginning of flow, while the pressure drops and the lower cohesion media is easily fluidized and ultimately vacuumed to the surface through piercement structures which provide the conduits for high pressure mud/fluid and gas release.
The geometry of mud volcanoes is variable. They can be up to a few kilometers in diameter and several hundred meters in height. The main morphological elements of a mud volcano are the crater(s), hummocky periphery mud flows, irregularly shaped terrains, gryphons, and mud lakes or salses.
A classification of mud volcanic edifices morphology was proposed by Kholodov, 2002 (in Akhmanov and Mazzini, 2007), these are:
(1) “classic” conic volcanic edifice with main crater and mud flow stratification reflecting periodical eruption;
(2) Stiff mud neck protrusion, typically due to its high viscosity and hence able to form steep hills;
(3) swamp-like area; contrary to no (2), due to its low viscosity the mud spreads over a large area;
(4) “collapsed synclinal” depression; and
(5) crater muddy lake, is the most abundant type in various mud volcanic areas.
It is often that mud volcano morphology shows a combination of the common types described above depending on the viscosity of the mud and the stage of its development. Mud volcanoes show different cyclic phases of activity, including catastrophic events and periods of relative quiescence characterized by moderate activity.
It appears that each eruptive mud volcano has its own period of catastrophic activity, and this period is variable from one volcano to another. The frequency of the eruptions seems essentially controlled by local pressure regime within the sedimentary sequences, while the eruptive mechanism and evolution seem strongly dependent on the state of consolidation and gas content of the fine-grained sediments. This is shown in the compilation of historical data onshore Trinidad as described by Deville and Guerlais (2009).
Approximately 1,100 mud volcanoes have been identified on land, in shallow as well asdeep waters. It has been estimated that well over 10,000 may exist on continental slopes and abyssal plains. The largest known structures are 10 km in diameter and reach 700 m in height.
Occurrences of mud volcanoes on the seafloor have been documented more frequently since the intensive use of side scan sonar began in the late 1960's. Mud volcanoes have been found in many parts of the world, and have been documented in Rumania, Italy, Iran, Iraq, New Zealand, India, the Myanmar, Malaysia, Gulf of Mexico, Trinidad,
Venezuela, Colombia and the USSR. The largest number of mud volcanoes is found in the Azerbaijan trend which continues into the Southern Caspian area.
In the Indonesian region, mud volcanoes are found on the Islands of Sumatera, Nias, Pagai, Sipora, East Java, East Kalimantan ‘(Borneo), Rote, Barbar, Aru, Timor, Tanimbar, Yamdena and Papua. They are found in high rate subsidence basins such as Madura-East Java Basin, Kutai Basin, in high seismicity areas such as islands in the Banda Sea and in tectonically complex areas such as Timor and Papua (Sukarna, 2007).
In Papua, Indonesia, mud volcanoes are found along a zone of disruption 400 km long and nearly 100 km wide, occupying hilly terrain with low relief scarred by landslip. T
hey are aligned along structural trends of up to 50 km long and 25 km wide. Individual mud volcanoes range from 3 m to 2.5 km in diameter and reach a maximum height of about 110 m. The ejected mud consist of mud stone containing various shapes and sizes of clasts of older rock assumed as exotic block, which is believed as part of mélange diapirsm (Sukarna, 2007).
Information on mud volcanoes can be used to study the subsurface condition and used as pathfinders of the conditions indicative of subsurface hydrocarbon accumulations in unexplored areas.
Gas geochemical data from mud volcanoes can be examined for possible presence of source rocks and their maturity levels. Mud volcanoes are often related to active petroleum systems, especially if the released gas shows a deep thermogenic character.
A global data-set of more than 140 onshore mud volcanoes from 12 countries shows that in 76% of cases the gas is thermogenic, with 20% mixed and only 4% purely microbial (Etiope et al., 2009).
The thermogenic nature of most of mud volcanoes is related to the relatively high thermal maturity of gas-generating organic-rich rocks. On the other hand, mud volcanoes which release large amounts of CO2, such as those related to magmatic activity, may not indicate the presence of significant hydrocarbon reservoirs (e.g., Milkov, 2005).
Many large onshore hydrocarbon fields were discovered after drilling around mud volcanoes in Europe, the Caspian Basin, Asia and the Caribbean (see Etiope et al, 2009, Link, 1952; Guliyev and Feyzullayev, 1997).
Gas origin, composition and secondary post-genetic processes such as secondary methanogenesis which follows anaerobic biodegradation of petroleum or heavy hydrocarbons however, are fundamental factors for determining depth and quality of the related petroleum system, especially in frontier or unexplored areas (see Etiope et al., 2009).
Apart from providing information and evidence of hydrocarbon potential and a working petroleum system, mud volcanoes also provide useful data about the sedimentary section which can be determined by examination of ejected rock fragments incorporated in mud volcano sediments (breccia).
Mud volcanoes, depending on their size and activity, can pose ecological hazards and disaster to the environment as well as to the population of the surrounding area.
Mud volcanoes typically ejected breccia and/or mud flows and/or flame in temporal association with earthquakes. Active mud volcanoes can vent a large amount of carbon dioxide and flammable methane, and may influence global climate.
Large eruptions are known to have occurred in the Black Sea and in areas around the Caspian Sea where gas exploded in a flame several hundred meters high that burns vegetation within the vicinity of the mud volcano.
Mud volcanoes may also pose a geohazard for drilling and platform constructions due to the potentially violent release of large amounts of hydrocarbons and mud breccia.
When the viscosity of the mud breccias is low, it may flood large area and inundate villages, homes, roads, rice fields, and factories and displace people from their homes.