Introduction
Mud volcanoes are eruptive landforms produced by the ascent and surface discharge of mud slurries, water and associated gases; smaller, localized seepage features of the same process are often called mud‑pots. Individual edifices span a broad morphological spectrum, from shallow seeps under a metre high and a few metres across to extensive mud‑dome complexes that may attain heights on the order of 700 m and lateral extents approaching 10 km. Active examples commonly exhibit relatively constant temperatures markedly lower than those of igneous volcanism, with measured values ranging from near 100 °C down to a few degrees above freezing; some thermally warm sites are exploited for commercial or recreational “mud baths.”
Formation reflects a coupled hydrodynamic and tectonic system: hot fluids rising from depth interact with mineral assemblages to produce a fine‑grained slurry that is forced upward through faults, fissures or permeable conduits by pressure differentials in the subsurface. Gas release is dominated by methane (approximately 86% of emitted gas), with lesser amounts of carbon dioxide and nitrogen; the solid and liquid ejecta are chiefly suspended fines in water often bearing salts, acids and hydrocarbons. Mud‑volcanic activity is frequently linked to hydrate‑bearing sediments, connecting these features to subsurface gas‑hydrate stability and release (e.g., USGS, 1996).
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Globally, mud volcanoes are most commonly associated with compressional and convergent tectonic settings, including subduction zones, and some 1,100 features have been catalogued on or near land. Well‑documented terrestrial occurrences include the clustered mud volcanoes of Gobustan (Azerbaijan), individual vents such as Htee Pwint Kan, and sites like Umbrella Pond (Myanmar) noted in relation to hydrate‑bearing strata. Comparable morphologies interpreted as mud‑volcanic in origin have also been reported on Mars, implying that analogous fluid‑driven processes may operate beyond Earth.
Mud volcanoes develop when pressurized mud diapirs ascend and pierce the seafloor or terrestrial surface, producing characteristic piercement structures and seafloor features such as those observed in the Gulf of Mexico. The expelled material can be unusually cold when venting is linked to the stability and dissociation of hydrocarbon clathrate hydrates on the seabed. Mud volcanism is closely tied to petroleum systems: these structures commonly form in settings of hydrocarbon generation and accumulation and characteristically emit hydrocarbon gases during episodic venting. Tectonic regime exerts a primary control on their distribution; regions affected by subduction, mountain‑building and related sediment overpressure and deformation favor diapirism and piercement. Gas composition varies with geological context: mud volcanoes spatially associated with magmatic volcanism tend to release incombustible gases such as helium, whereas isolated mud volcanoes more typically vent methane. Known occurrences are unevenly sampled—roughly 1,100 sites have been documented on land and in shallow water, but estimates indicate an order‑of‑magnitude greater population (well over 10,000) on continental slopes and abyssal plains. In basins like the Gulf of Mexico, seabed mud volcanism therefore reflects the interplay of sedimentary overpressure, hydrocarbon processes, cold‑temperature hydrate stability, and regional tectonics, producing localized sources of gas and fluid discharge along continental margins and deep‑water settings.
Mud‑volcanic fields display a spectrum of discrete morphologies that record variations in discharge volume, fluid composition, and thermal‑mechanical processes. These landforms range from small, steep vents to extensive effusive constructs and include features that directly indicate subsurface gas and fluid flux.
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At the smallest scale are gryphons: steep, conical vents typically less than about 3 m in height. Their sharply inclined flanks and limited stature reflect localized, low‑volume extrusion of viscous mud that accumulates as slope‑forming deposits; gryphons commonly act as individual vents within a larger mud‑volcanic assemblage. Larger conical edifices, here termed mud cones (generally under ~10 m high), form where discharge is more energetic and carries coarse lithic fragments. The inclusion of clastic material and gas‑driven fragmentation produces steeper slopes, stratified ejecta of mud and rock, and a more pronounced geomorphic expression than that of gryphons.
Thermally altered cones (sometimes described as scoria‑like cones) derive not from magmatic eruption but from high‑temperature alteration of organic‑rich muds. Combustion or intense heating causes thermal decomposition and sintering of sediments, producing a fragmented, vesicular residue that mimics volcanic scoria in appearance but is genetic ally distinct. These cones therefore record episodes of post‑depositional heating within mud‑dominated terrains and must be distinguished from true magmatic scoria cones.
Hydrologic and gas‑dominated manifestations include salses and small springs. Salses are shallow, water‑filled depressions where persistent gas seepage (commonly methane, CO2, and/or H2S) produces continuous bubbling and altered water chemistry; they mark focused pathways of subsurface gas migration and are surface indicators of gas‑charged hydrocarbon or geothermal systems. Small springs, defined here by outlet apertures <0.5 m, are point sources of groundwater or hydrothermal fluids; as concentrated loci of upwelling they commonly control local wetland development and microtopographic variation rather than forming broad seepage zones.
At the other end of the morphological range are mud shields: broad, low‑angle bodies emplaced by voluminous, effusive outpourings of low‑viscosity mud. Analogous in planform to lava shields but constructed of mudflow deposits, these features bury and smooth preexisting topography, create gentle regional slopes, and exert significant influence on drainage patterns through the deposition of extensive thin mud mantles. Together, these features document the interplay of fluid dynamics, gas expansion, and thermal processes in shaping mud‑volcanic terrains.
Mud volcanoes are important natural pathways that transport methane and other gases and fluids from subsurface sedimentary reservoirs into the overlying water column and, in some cases, the atmosphere. Their activity is governed by subsurface physical and thermodynamic conditions: high pressures and low temperatures near the seafloor favor methane supersaturation and trap ascending fluids and gas, permitting accumulation at depth and either episodic or continuous release at the seabed or surface.
Quantifying global emissions from mud volcanism remains highly uncertain. Deep-water (offshore) sources have been estimated to emit on the order of 27 Tg yr−1 of methane (1 Tg = 1 million metric tonnes), but this benchmark is sensitive to incomplete knowledge of the total number of seep systems and of how much methane is oxidized or retained in the water column versus reaching the atmosphere. Onshore and shallow systems tend to expel most solids and liquids during eruptive episodes while sustaining low-rate gas seepage in quiescent intervals; isotopic and occurrence evidence implicates deeply derived hydrocarbons, with gas generation depths commonly inferred to exceed ~5,000 m.
Regional and compositional variability is pronounced: emitted gas mixtures and chemical signatures reflect local geology and hydrocarbon maturity. For example, mud volcanoes in NW China have been reported to yield gas that is relatively enriched in methane with lower proportions of propane and ethane than some other provinces. Analyses of erupted solids reveal diverse mineralogy—field examples include the Gekpatlawuk mud volcano (Western Turkmenistan) and chemical data from Kampun Meritam, Limbang, where mud samples contained ~59.5 wt.% SiO2, 0.055 wt.% MnO and 1.84 wt.% MgO and were noted to be salt‑rich; overall solid chemistry can resemble, in broad respects, magmatic element patterns.
Published emission inventories illustrate the wide range of estimates and methodological differences. Early assessments reported broad ranges: Dimitrov (2002) estimated 10.2–12.6 Tg yr−1 from onshore and shallow offshore mud volcanoes, while Etiope and Klusman (2002) suggested at least 1–2 Tg yr−1 and possibly as much as 10–20 Tg yr−1 for onshore sources. Etiope (2003), using an inventory of about 120 mud volcanoes, proposed a conservative onshore/shallow range of 5–9 Tg yr−1 (roughly 3–6% of contemporary natural methane sources) and argued that the total geologic methane contribution (including seepage and geothermal fluxes) might reach 35–45 Tg yr−1. Milkov and colleagues (2003) presented a higher synthesis, proposing a possible global gas flux up to ~33 Tg yr−1 (partitioned as ~15.9 Tg yr−1 during background seepage plus ~17.1 Tg yr−1 during eruptions), with roughly 6 Tg yr−1 attributed to onshore/shallow systems and ~27 Tg yr−1 to deep‑water sources; they further noted that mud‑volcano fluxes could account for a nontrivial fraction of discrepancies in fossil methane budgets. Related work by A. Milkov (2003) produced a comparable total of ~30.5 Tg yr−1 of gases (mainly CH4 and CO2) escaping from mud volcanoes to ocean and atmosphere.
More extreme upper‑bound estimates emphasize the sensitivity of totals to assumptions about gas volume, partitioning, and oxidation. Kopf (2003) converted volumetric ranges (1.97×10^11 to 1.23×10^14 m^3 yr−1 for all mud volcanoes, of which 4.66×10^7 to 3.28×10^11 m^3 yr−1 were attributed to surface systems) into mass fluxes that spanned roughly 141 to 88,000 Tg yr−1 overall, with surface contributions from ~0.033 to 235 Tg yr−1—illustrating that varying assumptions produce orders‑of‑magnitude differences in inferred emissions.
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In sum, mud volcanoes are significant but variably quantified sources of methane and other gases. Estimates of their global contribution diverge widely because of incomplete inventories, regional heterogeneity in gas composition and generation depth, and strong sensitivity to assumptions about subsurface retention, oxidation, and atmospheric delivery.
Across Europe, mud‑volcanic activity is concentrated in a few regional clusters that reflect underlying sedimentary basins and compressional or foreland tectonic regimes where overpressured sediments and migrating fluids reach the surface. Along the northeastern Black Sea margin dozens of mud volcanoes occur on and around the Taman Peninsula (near Taman Stanitsa, Russia), the Kerch Peninsula (Crimea/Ukraine) and the Rupite area of south‑western Bulgaria, forming a transboundary concentration of features. Romania’s Berca site, on the Carpathian foothills in Buzău County, is a well‑known example on the margins of an orogenic belt and has been legally protected as a natural monument since 1924. In Italy, mud volcanism is spatially scattered but regionally significant: notable occurrences include the Salse di Nirano and Salse di Regnano on the northern Apennine front (Emilia‑Romagna), the Bolle della Malvizza in the southern Apennines, and sites in Sicily. The appearance of a mud volcano within the via Coccia di Morto roundabout in Fiumicino, near Rome, on 24 August 2013 demonstrates that these phenomena can emerge within or adjacent to developed infrastructure, with implications for hazard management and conservation of geologic heritage.
In Central Asia and the Caucasus, particularly along the shores of the Black and Caspian seas, mud volcanoes form abundant surface manifestations of subsurface fluid and sediment discharge. Around the Caspian Sea, the coincidence of active tectonism and thick accumulations of unconsolidated sediments has produced extensive fields of these features, reflecting regional structural deformation and high rates of sediment supply. Many vents release gases—chiefly methane but also other hydrocarbons—either continuously or in episodes, signaling ongoing fluid migration from depth and a genetic connection to hydrocarbon-bearing strata. In Azerbaijan, individual mud-volcanic cones attain heights in excess of 200 m (≈656 ft), illustrating the capacity for substantial edifices to build up where seepage is persistent and vigorous. Episodic large eruptions can be sufficiently energetic to ignite escaping hydrocarbons, producing flames reported on scales comparable to the tallest cones; such events underscore both the geohazard potential of these systems and their value as surface indicators of subsurface hydrocarbon dynamics.
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Mud volcanoes — Georgia
Mud volcanoes occur in Georgia as distinctive geomorphic features produced by the eruption of fine-grained sediments, water, gases and entrained clasts rather than by igneous activity; a documented surface expression is located at Akhtala. Morphologically these constructs range from small conical or dome-shaped extrusive edifices to mud flows, pools or craters, and are commonly mantled by mud‑breccia deposits. Individual vents differ markedly in size, activity and longevity and typically exhibit intermittent venting of brackish fluids and gases (notably methane).
Genetically, mud volcanism in the Caucasus, including the Akhtala example, is driven by overpressure in fine‑grained sedimentary strata that forces pore fluids and entrained gases upward along structural weaknesses such as faults, fractures and diapiric pathways. Regional compressional tectonics, sediment loading and migration of deep hydrocarbons and fluids provide the driving forces that connect subsurface fluid systems to surface expression.
As point‑source landforms, mud volcanoes exert local control on surface processes and landscape properties: they alter drainage patterns, influence soil salinity and chemistry, modify slope stability, and create distinctive microtopography. Their surface manifestations therefore serve as visible indicators of deeper fluid flow and hydrocarbon migration within Georgia’s sedimentary basins; Akhtala exemplifies such a localized link between subsurface processes and surface geomorphology.
Mud‑volcanic activity also poses natural‑hazard and environmental concerns. Sudden venting or collapse can produce ground instability and subsidence; emitted methane and other gases present flammability and air‑quality risks; and saline or hydrocarbon‑bearing fluids discharged at the surface can contaminate soils and water bodies and damage infrastructure located near active vents.
From a scientific and economic perspective, mud volcanoes are valuable windows into the subsurface. Extruded mud breccia, pore fluids and emitted gases provide material for geochemical and isotopic analyses, paleofluid reconstruction and sedimentary‑basin studies, and can inform hydrocarbon exploration by indicating active fluid migration pathways.
To support hazard assessment and geological interpretation, systematic study of Georgian mud volcanoes (including Akhtala) should record precise geographic coordinates and elevations, vent morphology and dimensions, composition of extruded material, gas composition and fluxes, temperature, documented activity history with observation dates, and spatial relationships to regional faults and sedimentary units. Such standardized datasets will improve assessment of activity, environmental impact and subsurface processes.
Turkmenistan
Akpatlawuk is one documented mud volcano in western Turkmenistan, exemplifying the dense assemblage of mud-volcanic landforms concentrated along the country’s Caspian Sea margin. Western Turkmenistan—notably the Cheleken Peninsula—contains many such features, placing numerous mud volcanoes at or near the onshore edge of the Caspian Basin.
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These occurrences reflect processes typical of sedimentary basin margins: fine-grained, overpressured strata force upward-migrating fluids and gases, producing episodic surface extrusions of slurry and gas that accumulate as mounds, cones and mudflows. The spatial association with the western Turkmenistan–Caspian margin indicates a close genetic link between mud-volcanism and the basin’s sedimentary and hydrocarbon systems.
This coupling has practical consequences for regional geology and management. Mud-volcanic distribution informs geological mapping and hydrocarbon exploration, influences coastal geomorphology where features occur near the shoreline, and constitutes a local geohazard that warrants targeted assessment and monitoring.
The southern Makran mountain range, spanning the Iran–Pakistan border, contains a notable concentration of mud-volcanic landforms. These features episodically discharge mud, formation fluids and gases to the surface; their presence indicates the upward migration of overpressured sediments and fluids that build mud cones and extrusive deposits across the transnational range.
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A prominent example in Pakistan’s Balochistan is the large mud-volcanic edifice known locally as Baba Chandrakup (“Father Moonwell”). Situated on the route to the Hindu shrine of Hinglaj, it functions both as a geomorphological landmark and as part of a religious landscape visited by pilgrims. The co-location of active mud-volcanism, mountainous terrain and a pilgrimage corridor in the southern Makran thus exemplifies the intersection of physical and cultural geography in this borderland region.
Mud volcanism in Azerbaijan
Azerbaijan’s Caspian littoral hosts an exceptional concentration of mud-volcanic activity: nearly 400 mud volcanoes along the coast and adjacent shelf, representing well over half of the mud volcanoes known on continental landmasses. These occur in clustered fields such as Gobustan onshore and in offshore localities including Dashli Island. Most of these features are presently active; because eruptions and gas releases can pose hazards to people and infrastructure, the Azerbaijan Ministry of Ecology and Natural Resources has placed several sites under protection and restricts public access.
The mud-volcanic system in Azerbaijan is fed from a deep, hydraulically connected subsurface mud reservoir. This connection persists through apparent dormancy, as shown by continuous seepage whose source is demonstrably deep and by seep temperatures that are typically about 2–3 °C above ambient ground temperature. The region’s mud-volcanic behavior can be sudden and dramatic: a 2001 eruption about 15 km from Baku produced flames roughly 15 m high and attracted international attention. A striking offshore example occurred on 4 July 2021 when an eruption at Dashli Island—near an oil-production platform—generated a large explosion and fireball reportedly visible from Baku, 74 km away; observers described flames rising to c. 500 m, and no injuries or platform damage were reported. Individual mud-volcano edifices may remain quiescent for decades between such events (Dashli Island has recorded eruptions in 1920, 1945 and 2021), underscoring the episodic nature of activity even within a region of frequent occurrence.
Although Azerbaijan contains the dominant share of continental mud volcanoes, analogous features are found in other coastal and island settings worldwide (for example, Gobustan within Azerbaijan and the Diglipur mud volcano on North Andaman Island, India), reflecting common tectono-sedimentary controls on mud-volcanic processes.
India — Andaman accretionary prism
The Andaman accretionary prism, a large, deformationally thickened wedge of marine sediments adjacent to the Andaman Islands, hosts widespread mud‑volcanic activity rather than isolated vents. This structural domain—created at a convergent plate margin by the progressive scraping, shortening and uplift of sediments off a subducting plate—provides mechanically weak, overpressured strata that favor upward migration and eruption of mud and fluids.
Mud volcanism in the prism involves extrusion of fine-grained sediment, formation waters and volatiles (notably methane) onto the seabed and, locally, the land surface. Surface and near‑surface expressions include mud cones, flows, diapirs and seep‑related morphologies that modify bathymetry and geomorphology. The principal driving force is fluid overpressure generated by rapid sediment loading and tectonic compression—processes such as compaction disequilibrium, dewatering and fault‑controlled fluid pathways concentrate pressure and force mud and pore fluids upward along faults, fractures and diapiric conduits.
The spatially extensive distribution of these features implies active, region‑scale fluid migration and ongoing deformation, with attendant effects such as subaqueous mud flows, alteration of seabed topography and development of seep habitats. Because mud‑volcanic sites mark deep fluid pathways and overpressure regimes and may overlie hydrocarbon‑bearing sediments, they are important targets for sedimentological, tectonic and geochemical investigation as well as for seismic and geohazard assessment in the Andaman region.
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Mud volcanism in Indonesia
Mud volcanism is widespread across the Indonesian archipelago, with numerous onshore and offshore mud‑volcanic structures reflecting the country’s active tectonics and thick, gas‑charged sedimentary sequences that facilitate upward escape of fluids and gases. These systems range from periodically eruptive vents to long‑lived, landscape‑transforming flows and commonly couple sedimentary hydrocarbons with heat and volatiles in tectonically active basins.
The Lusi (Lumpur Sidoarjo) eruption in East Java exemplifies a hybrid mud volcano in which pressurized sedimentary gas and fluids interact with steam and volcanic gases derived from a nearby igneous system. Geochemical, petrographic and geophysical evidence links the deep source region of the Lusi fluids to the Arjuno–Welirang volcanic complex. The Lusi event began on 29 May 2006 in Porong (Sidoarjo Regency); attribution remains contested, with proponents of both a drilling‑related perturbation by PT Lapindo Brantas and seismic triggering from the 27 May 2006 M6.4 Yogyakarta earthquake. The eruption inundated roughly 440 ha (4.40 km2), submerging villages, infrastructure and agricultural land, displacing about 24,000 people and causing 14 reported fatalities.
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Long‑term monitoring and modelling of Lusi reveal progressive ground instability and persistent fluid discharge. Forecasts have indicated the potential for substantial subsidence (models suggested local sagging up to ~150 m within a decade under some scenarios), while observations document episodic rapid drops—up to ~3 m recorded during a single night in March 2008—and an average long‑term subsidence on the order of 1 mm per day. Indonesian geoscientists, including assessments led by Bambang Istadi, delineated areas at risk over decadal timescales; subsequent studies (circa 2011) projected continued mud output for at least two decades, implying protracted geomorphic and socio‑environmental consequences. The name Lusi derives from Lumpur Sidoarjo (lumpur = “mud” in Indonesian) and the system is treated in the literature as a sediment‑hosted hydrothermal‑mud‑volcanic complex.
Other Indonesian occurrences illustrate the diversity of mud‑volcanic behaviour. The Suwoh depression in Lampung (Sumatra) contains dozens of mud cones and pots with variable temperatures, indicating localized heat and fluid flux within a tectono‑sedimentary basin. In Central Java’s Grobogan Regency, the Bledug Kuwu vent displays short‑interval, periodic discharge of mud and gas (roughly every 2–3 minutes), demonstrating the range of temporal regimes—from quasi‑steady to highly pulsed—found among Indonesian mud‑volcanic systems.
Iran
Mud‑volcanism is a widespread and noteworthy geomorphological process in Iran, with concentrations of occurrences in Golestan, Hormozgan and Sistan and Baluchestan provinces. These extrusive features form part of the nation’s catalogue of surface fluid‑discharge phenomena and attest to ongoing or recent fluid‑ and gas‑driven activity in multiple regions.
A mud‑volcanic site in Hormozgan Province documents such activity along the southern coastal margin, while the Pirgel locality in Sistan and Baluchestan represents a documented southeastern example. Together these localities illustrate the geographic distribution and regional significance of mud volcanoes within Iran.
Mariana Forearc
Within the Izu–Bonin–Mariana arc system ten active mud volcanoes are clustered in the forearc between the Mariana Trench and the volcanic arc, forming a pronounced linear belt that trends north–south parallel to the trench axis. This spatial alignment reflects strong tectonic control by the subduction geometry and the forearc structural fabric, with emplacement and venting organized along the regional trend created by plate convergence and associated deformation.
The erupted material is dominated by blue to green serpentinite mud that contains both fresh and serpentinized peridotite fragments. This lithologic assemblage records upward transport of mantle-derived ultramafic material from the subduction channel. Fluids liberated by dehydration and alteration of descending Pacific Plate lithologies and sediments play a central role: they mobilize mafic and ultramafic components and drive serpentinization reactions as they migrate and interact with susceptible rocks in both the downgoing slab and the overriding Philippine Plate, producing the serpentinite-rich mud erupted at the seafloor.
Structural permeability exerts primary control on fluid and mud migration; each volcano is spatially associated with faults that act as focused conduits transmitting serpentinite-rich fluids and entrained clasts from depth through the forearc to surface vents. The edifices are geomorphically significant at basin scales: individual mud-volcanic constructions can be enormous, with the largest documented edifice approaching 50 km in diameter and rising more than 2 km above the surrounding seafloor, demonstrating that mud-volcanic processes can build bathymetrically prominent forearc relief.
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Balochistan province in Pakistan hosts a very high concentration of mud volcanism, with more than 155 active vents clustered in roughly ten primary localities and additional scattered occurrences across several districts. This density places the province among the world’s more active regions for mud‑volcanic activity and reflects extensive subsurface fluid and sediment dynamics in the region.
Spatially, mud‑volcanic activity is organized into a western coastal cluster and an inland corridor. The western cluster, principally in Gwadar District, comprises relatively small volcanoes concentrated south of Koh‑e‑Mehdi and trending toward Sur Bandar, with a separate concentration northeast of Ormara along the Arabian Sea coast. The principal inland concentration runs through Lasbela District and the Hangol Valley corridor, extending from south of Gorangatti on Koh Hinglaj northward to Koh Kuk at the northern margin of Miani Hor. In this corridor, individual edifices commonly rise between about 300 and 2,600 feet (91–793 m).
Notable individual features illustrate the range of morphology and scale. Chandragup (also identified in satellite studies as Changradup) is the best‑known site in the region. The V15 volcano hosts the largest recorded crater locally, approximately 450 ft (137.2 m) in diameter, located at 25°33’13.63″N, 65°44’09.66″E. The tallest named edifice is the Khatkandi mud volcano, which attains roughly 7,500 ft (2,286 m). Mount Mehdi, near Miani Hor, is distinguished by a large mud glacier encircling its caldera; this feature indicates sustained venting and the mobilization of large volumes of mud and fluidized material.
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Fieldwork is often constrained by steep valleys, coastal cliffs, and generally remote terrain; consequently, many formerly active cones now exist as columnar, dormant mud edifices that preserve the morphology of past eruptions but are difficult to sample directly. Beyond the coastal and Lasbela/Gwadar concentrations, discrete occurrences near Qila Saifullah and in the Zhob region demonstrate a wider regional distribution of mud volcanism across Balochistan.
Given access limitations, remote sensing has been instrumental in documenting these systems. Satellite imagery provides essential spatial context, records crater dimensions, maps relationships between vents and surrounding landscapes, and has specifically documented the Chandragup/Changradup group and the Mount Mehdi mud glacier, thereby supporting geomorphological and distributional analyses of otherwise inaccessible sites.
Philippines — Turtle Islands
The Turtle Islands, situated at the southwestern extremity of the Philippine province of Tawi-Tawi adjacent to the maritime boundary with Malaysia in the Sulu Sea, host a localized cluster of mud-volcanic activity. Within this small archipelago, active mud extrusion has been recorded on three islands — Lihiman, Great Bakkungan and Boan — indicating concentrated surficial sedimentary volcanism rather than a broadly distributed regional field.
Morphologically, the most vigorous activity is concentrated on the hilly northeastern sector of Lihiman Island. There, higher-energy extrusions have entrained and ejected sizeable rock fragments and have excavated a roughly 20 m-diameter crater on the elevated terrain, demonstrating the capacity for substantial substrate disruption even in this confined island setting.
Field observations provide evidence of the eruptive dynamics: the more violent extrusive episodes are temporally associated with mild local earthquakes, and ballistic ejecta have been deposited into surrounding vegetation, with expelled material found lodged high in nearby trees. These deposits record both the intensity of individual events and the mechanisms of near-source dispersal.
Mud volcanism in the Turtle Islands also manifests offshore. Local witnesses report submarine mud extrusions in adjacent waters, showing that extrusion processes extend to the shallow seafloor and implying a connected sedimentary-volcanic system that operates across the subaerial–submarine interface.
Mud-volcanism in Asia exhibits a wide geographic and socioenvironmental range, appearing across continental interiors, coastal lowlands, offshore settings and islands. In northwestern China, mud volcanoes in Xinjiang extend the Eurasian record of such features within continental basins. Southeast Asia records both natural and culturally embedded occurrences: Minbu Township (Magway Region, Myanmar) hosts mud volcanoes that are integrated into local belief systems as refuges of the mythological Nāga, while Pulau Tiga off Sabah (Malaysia) and sites in northern Borneo (e.g., the Meritam “lumpur bebuak” near Limbang, Sarawak) demonstrate that mud-volcanic landforms occur on nearshore islands and may acquire economic functions, including tourism. Southern Taiwan contains clustered examples with variable activity—the Wushan mud volcanoes in Yanchao (Kaohsiung) and active cones in Wandan (Pingtung) alongside several inactive edifices—illustrating spatial heterogeneity in activity within coastal lowlands. Timor-Leste preserves both contemporary and historical activity, with active vents at Oesilo (Oecusse) and documented eruptions of the Bibiluto mud volcano in Viqueque during the mid–late 19th century. The region also evidences significant anthropogenic interactions: a 1979 offshore drilling accident in Brunei generated a large mud-volcano event whose remediation required drilling some 20 relief wells and nearly three decades to control, underscoring the potential for prolonged, large-scale hazards when hydrocarbon operations intersect pressurized subsurface mud and fluids. Collectively, these cases highlight the heterogeneous activity status, cultural meanings, economic uses and hazard potentials of Asian mud-volcanic systems.
North America
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Mud-volcanic phenomena in North America occur across a broad latitudinal range from California through Alaska into British Columbia and manifest in both onshore and submarine settings. Sizes vary markedly: onshore mud pots commonly measure less than a few metres in height, whereas submarine edifices can protrude up to ~30 m above the seafloor with summit diameters approaching 100 m. Documented water depths of offshore features span roughly 43–1,000 m. Gas emissions are frequently dominated by carbon dioxide and, locally, nitrogen; genetic controls include shallow, fault-controlled cold seeps as well as associations with deeper magmatic activity. These systems attract scientific interest for insights into sedimentary and magmatic fluid flow and have local economic relevance for clay extraction and potential hydrocarbon prospectivity.
Representative occurrences illustrate this variety. Small, fault-associated cold mud pots on the Mendocino Coast near Glenblair and Fort Bragg are typically under 2 m high and supply fine-grained clays used by nearby potters. On the Nahlin Plateau in northwestern British Columbia, aerial imagery reveals clusters of small, roughly 20 m‑diameter mud edifices on a plateau setting. In the Copper River basin adjacent to the Wrangell Mountains, the Shrub and Klawasi mud volcanoes emit CO2- and N2‑rich gases and are interpreted to reflect magmatic influence rather than purely shallow sedimentary degassing.
Offshore examples include a submarine edifice located about 24 km seaward of Redondo Beach, California, which rises ~30 m from the seafloor and possesses a summit near 100 m across at ~800 m water depth, and the Smooth Ridge feature near Monterey Canyon, occurring at ~1,000 m depth and representing deep‑water mud‑volcanic expression along the central California margin. Within the Salton Sea geothermal field near Niland, numerous small mud volcanoes (generally <3 m high) emit CO2‑rich gases; the Niland Geyser is notable for persistent, erratic surface migration. In the northern margin, the Kaglulik feature beneath the Beaufort Sea lies in shallow water (~43 m) near the Alaska–Canada boundary and is of interest for regional hydrocarbon potential. The Maquinna mud volcano, located 16–18 km west of Vancouver Island, constitutes a prominent submarine center on the northeastern Pacific margin.
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Yellowstone’s “Mud Volcano”
The landform commonly referred to as “Mud Volcano” in Yellowstone National Park is not a single, classical mud volcano but rather a compact assemblage of hydrothermal features—hot springs, mud pots and fumaroles—whose behaviour and appearance reflect shallow geothermal processes. Heat supplied from a relatively near-surface magma reservoir, together with volatiles released from depth, drives vigorous near‑surface hydrothermal circulation; boiling and bubbling mud, intermittent steam vents and chemical alteration of sediments (both acidic and alkaline) are all expressions of this circulation. Although the intensity of activity recorded today is lower than in the earliest written accounts, the site remains highly dynamic: variations in subsurface heat flux, fluid pathways and gas discharge continually modify vent morphology and activity. Steam, carbon dioxide and hydrogen sulfide are the dominant gases emitted, and their fluxes exert primary control on vent mechanics, surface water chemistry and the local hazard environment. In addition to the named Mud Volcano complex, Yellowstone hosts other mud volcanoes and mud geysers—some eruptive features can behave cyclically and vigorously, with a notable example that periodically expels mud columns to heights on the order of 30 feet. The present fragmented mound morphology of the Mud Volcano area records past hydrothermal explosions—a major thermal blast in the 1800s ruptured a former continuous mound—illustrating how explosive hydrothermal events can rapidly and dramatically reshape geothermal terrains.
Mud volcanism in this part of the Caribbean is concentrated in southern Trinidad but extends offshore into the Barbados accretionary prism. On Trinidad numerous named onshore vents occur in coastal and lowland settings (Devil’s Woodyard near New Grant, Moruga/Moruga Bouffle, Digity at Barrackpore, Piparo, Erin Bouffe by Los Iros Beach, and L’eau Michel in Bunsee Trace, Penal). The spatial clustering of these features in southern Trinidad corresponds with known subsurface hydrocarbon-bearing sediments, reflecting a common genetic link between mud-volcanic conduits and deeply sourced fluids and gases.
Documentary and observational records indicate ongoing activity: a c.1967 photograph shows mid-20th-century activity at Devil’s Woodyard, and the Moruga vent was observed emitting methane on 15 August 2007, demonstrating episodic gas discharge as a visible indicator of vent activity. Offshore, the Chatham submarine mud volcano in the Columbus Channel has episodically built a short-lived emergent island, illustrating that submarine vents in the region can produce transient landforms. Geologic surveys off Barbados further document large mud volcanoes within the accretionary complex, underscoring that mud-volcanic processes here operate both onshore and within the adjacent offshore prism. These occurrences are significant for regional geomorphology, fluid migration pathways, and their links to hydrocarbon systems.
Yagrumito mud volcano (Monagas, Venezuela)
The Yagrumito mud volcano, located in Monagas state approximately 6 km southeast of Maturín, appears at the surface as a mud dome set within the regional savanna. Mud domes of this part of eastern Venezuela occur in association with the region’s petroleum-bearing basins and are best understood as surface manifestations of subsurface hydrocarbon systems in which fluids, gases and fine-grained sediments are mobilized and expelled. Material emitted at Yagrumito comprises a mixture of water, hydrocarbons, significant salt content and biogenic gas, indicating co-migration of aqueous fluids, oil-phase components and salt-rich sediments from depth. The presence of biogenic gas points to microbial gas generation in near-surface or shallow subsurface strata; such gas contributes buoyancy that aids the upward transport of mud and hydrocarbons. The salt-enriched dried mud also produces a notable ecological effect: local cattle routinely lick the deposits for their mineral content, illustrating a direct socio-environmental interaction between the mud volcano and surrounding pastoral land use.
Volcán El Totumo (Colombia)
Volcán El Totumo is a small mud-volcanic cone located on the administrative boundary between the Departamento de Bolívar and the Departamento del Atlántico, where it also functions as a territorial marker. The cone attains a height of roughly 15 m (≈50 ft) and hosts a shallow crater, filled with mud and large enough to accommodate about 10–15 bathers simultaneously. The mud-filled crater is a well‑known recreational and therapeutic site; locals and tourists regularly bathe there owing to locally attributed medicinal properties of the mud. Positioned immediately adjacent to a ciénaga (lake or wetland), the feature lies in close association with local surface water bodies, which contributes to its landscape context and accessibility. The site’s economic importance as a tourist attraction has precipitated an ongoing legal dispute between Bolívar and Atlántico over administrative jurisdiction and the distribution of visitation‑derived benefits.
New Zealand
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The Runaruna Mud Volcano serves as a documented exemplar of mud-volcanic morphology within New Zealand’s geothermal terrain and provides a comparative reference for the numerous small conical mud accumulations found in the country. New Zealand’s geothermal fields host many mud pools or mudpots whose peripheral splatter-cone deposits—built by repeated ejection and accretion of hot mud and entrained material around a vent—can attain shapes and dimensions that, under some classificatory schemes, are indistinguishable from small mud volcanoes.
Whether such splatter cones are classified as true mud volcanoes depends chiefly on interpretive criteria. Key distinctions include eruption mechanism (shallow hydrothermal boiling and vent splash versus deeper fluid- and gas-driven overpressure), material provenance and alteration (near-surface hydrothermal sediments versus deeper-seated mud and fluids), and morphological attributes (cone size, stability and the presence of a vent network). Because identical outward forms may derive from different processes, classification is contingent on which of these attributes is privileged by researchers.
For geographic and geomorphological inventories, therefore, features like Runaruna and the mudpot-associated splatter cones should be recorded with explicit notes on origin (hydrothermal versus deep-seated), dimensions, eruption behaviour and their relationship to local geothermal systems. Such documentation is important not only for consistent scientific interpretation but also for accurate hazard appraisal and informed conservation management.
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Possible mud volcanoes on Mars
High-resolution HiRISE imagery acquired through the HiWish program documents an extensive field of candidate mud volcanoes at multiple spatial scales, providing both broad overviews of crater- and plain-scale distributions and close-up views that resolve small-scale morphology. Near-range HiRISE scenes (down to centimeter- to meter-scale resolution across areas on the order of ~1 km) reveal discrete conical edifices, subtle relief contrasts on dome flanks, and accumulations of cobble- to boulder-sized clasts adjacent to or atop the constructs. The presence of these coarse fragments suggests either excavation of deeper lithologies during mud eruption or later transport and emplacement onto volcanic surfaces.
The surrounding low-lying terrain commonly contains transverse aeolian ridges (TARs), indicating that wind-driven reworking has modified inter‑volcanic depressions and that aeolian processes interact closely with the volcaniclastic substrate. Interpretation of compositional variability from HiRISE color data is complicated by the instrument’s partial color coverage (a single color strip typically runs along an image centerline), which produces lateral discontinuities in color information and limits continuous color-based mapping in some scenes. Nonetheless, at least one edifice exhibits a distinct color contrast with its surroundings, consistent with uplifted subsurface material and exposing strata or fluids otherwise buried beneath the martian surface.
Because mud volcanoes are capable of transporting deeper sedimentary and volatile-bearing layers to the surface, these features constitute high-priority exploration targets. Their erupted deposits may preserve materials shielded from the harsh surface radiation environment, offering accessible samples for reconstructing subsurface sedimentary history and for astrobiological investigations seeking evidence of past life.