Mud Eruption Research Articles

Structural control on carbon emissions at the Nirano mud volcanoes – Italy

The Nirano Salse in Italy is a well-studied site where natural gas seepage (NGS) and other hydrocarbon fluids and gases are emitted at the earth's surface. A novel integrated approach is applied to define a comprehensive structural interpretation of the gas seepage and flow dynamic in the mud volcano system of the Nirano Salse Regional Nature Reserve (Modena, Northern Apennines). The paper investigates the relationship between gas emissions and local structures, particularly faults and fractures, in the shallow subsurface (down to 500–600 m depth) to understand the control that structures have on fluid ascent from deep leaky hydrocarbon traps. We performed continuous monitoring of mud levels within vents; carried out geological surveys to characterize the main stratigraphic and structural discontinuities; measured the carbon emissions (CH4 and CO2) seepage both from volcanoes and the surrounding soil by a portable gas fluxmeter; and integrated the results with available geophysical surveys. The authors argue that the transgressive Pleistocene-Pliocene Argille Azzurre Formation hides the complex and highly structured pre-Pliocene geology of the area, in which faults and fractures act as pathways for deep fluid ascent. The emissions are aligned along a NE-SW trend at the intersection of a NE-SW fracture system and NW-SE-oriented normal faults, which are both associated to the local tensional stress field of a likely left-lateral strike-slip transfer structure or in the extrados of a fold. By examining both natural gas macroseepage and diffuse flux, it is shown that local structures control the fluid ascent and contribute to the emission of hydrocarbon gases and fluids at the Earth's surface. Understanding the structural control of carbon emissions at the Nirano Salse is also important for evaluating the carbon budget at the site, particularly in areas where there are detectable surface emissions. The study has implications for geologic, environmental, and economic issues, including hydrocarbon exploration, hazard assessment, and impact on the atmospheric carbon budget. Furthermore, the outcomes have an important implication to evaluate the potential for dangerous abrupt mud eruptions, and the site safety in proximity to the mud volcanoes.

NEW FINDINGS OF MUD VOLCANISM IN NORTHWEST COAST OF LAKE BAIKAL BASED ON UNDERWATER VIDEO RECORDING

We present new data on manifestations of mud volcanism accompanied by gas emissions in Lake Baikal. Brittle deformations of the bottom with traces of erupted liquefied sediments were found in the Malaya Kosa Bay and the Goryachinskaya Bay in the North Baikal depression at depths of 105–163.6 m. The deposits outcropping in the extended scarps and mud craters are mainly represented by highly-porous clays. In places there are ledges of boulder-pebble sediments. The areas of the mud volcanism distribution are confined to the damage North Baikal fault zone, indicating its current activity. Disturbance of the clays and soft sediments covering them indicates the recent eruption of gas-saturated fluid and mud. At depths of 157–162 m in the Goryachinskaya Bay, cone-shaped structures ∼5 × 5 cm in size with a crater in the top part were found in them. Similar griffons were revealed in the Solontsovaya Bay along rectilinear faults opposite the paleoseismic rupture of the same name. It is necessary to continue studying the revealed shallow-water manifestations of mud volcanism and rupture deformations of the bottom by staging complex geological and geophysical studies.

Volumetric Changes of Mud on Mars: Evidence From Laboratory Simulations

AbstractSubtle mounds have been discovered in the source areas of Martian kilometer‐sized flows and on top of summit areas of domes. These features have been suggested to be related to subsurface sediment mobilization, opening questions regarding their formation mechanisms. Previous studies hypothesized that they mark the position of feeder vents through which mud was brought to the surface. Two theories have been proposed: (a) ascent of more viscous mud during the late stage of eruption and (b) expansion of mud within the conduit due to the instability of water under Martian conditions. Here, we present experiments performed inside a low‐pressure chamber designed to investigate whether the volume of mud changes when exposed to a Martian atmospheric pressure. Depending on the mud viscosity, we observe a volumetric increase of up to 30% at the Martian average pressure of ∼6 mbar. The reason is that the low pressure causes instability of the water within the mud, leading to the bubble formation that increases the volume of the mixture. This mechanism bears resemblance to the volumetric changes associated with the degassing of terrestrial lava or mud volcano eruptions caused by a rapid pressure drop. We conclude that the mounds associated with putative Martian sedimentary volcanoes might indeed be explained by volumetric changes in the mud. We also show that mud flows on Mars and elsewhere in the Solar System could behave differently to those found on Earth because mud dynamics are affected by the formation of bubbles in response to the different atmospheric pressures.

Large-scale igneous intrusion emplacement as a trigger for fluid seepage on the northern South China Sea margin

Widespread mud eruptions have been identified along the northern margin of the South China Sea. However, the ultimate driving force for initiation of the eruptions remains to be discussed. Here, we investigated the discovered hydrothermal vents and the presence of gas/fluid occurring above deep-seated igneous intrusions and volcanic edifices and consider them as a likely trigger. Using a one-dimensional (1D) numerical model, SILLi 1.0, we studied the thermal effect of a 100-m-thick dolerite sill complex emplaced at 1100 °C and 3.8 km depth within the organic-rich Triassic series (∼3.5 wt% total organic carbon). The modeled scenarios also account for variations in sill count and thickness and the effects of erosion. The calculated CH4 produced from contact metamorphism reaches a peak of ∼700 kg/m2/yr shortly after emplacement of the first sill in the complex. When scaled to a sill size of 100 m by 25 km2, i.e., a sill volume of 2500 km3, ∼42−550 Mt of CH4, depending on individual sill thickness, have been produced within 10,000 yr of sill emplacement from sedimentary organic matter in the aureole, with peak generation of ∼17.5 Mt CH4/yr just after emplacement. The newly discovered vents are suggested to have formed as a direct result of sill emplacement and by overpressure generated in the sediments around the sill by hydrothermal fluids and gases liberated during organic matter degradation. Combining data from seismic images with the likely production of carbon gas released from contact metamorphism with igneous intrusions, we suggest that volcanically induced gas release is common along the South China Sea margin. This study supports the important role of magmatism in driving regional-scale gas/fluid seepage. Our findings also suggest that the hydrothermal vents and intrusive magmatic bodies provide postemplacement fluid focusing pathways to shallower strata or the seafloor over long time scales.

Electric Discharge in Erupting Mud

AbstractSelf‐ignition during the explosive eruption of mud volcanoes can create flames that in some cases reach heights that exceed hundreds of meters. To study the controls on electrical discharge in natural mud, we performed laboratory experiments using a shock‐tube apparatus to simulate explosive eruptions of mud. We vary the water content of the mud and proportions of fine particles. We measure electric discharge within a Faraday cage and we use a high‐speed video camera to image the eruption of mud and some of the electric discharge events. We find that (a) decreasing the proportion of fine particles and (b) increasing water content each suppress the number and magnitude of electric discharge events. Experimentally observed mud volcano lightning occurs where particles exit from the vent and within the jet of erupting particles.

Advective structures of the bottom of lake Natron and its surroundings (Tanzania)

In this study we consider the features of the development of weakly lithified bottom sediments and the general structure of lake Natron against the background of its seasonal drying and watering. This study takes into account the laws of advection and the periodic placement of cellular zonal advective structures in space. The consedimentary structures in the lake sediments demonstrate the conditions for the formation of sodic ores and their positions. Provided space and aerial photographs depict unique genetic information about the evolution of geochemistry and the development of bottom morphology during sedimentation. This includes the presence of two sources that feed the lake - river and mud eruptions of the adjacent Oldoinyo-Lengai volcano, supposedly the only one on Earth that erupts carbonatite lavas. The combination of two sources and two processes leads to the development of an epimagmatic phreatic-hydrothermal recycling system. In it, the masses of the lake penetrate through fissure structures into the suprafocal space of the volcano, providing mud volcanism with solutions of soda masses containing organic matter of sediments. Volcanic soda eruptions are not carbonatite lavas. The morphological similarities and differences of structures are shown - small craters on the bottom of the lake, associated with the advection of thin layers of sedimentary material; large craters located nearby among volcanic strata along the shores of the lake; and both subsidence calderas and explosion calderas associated with magmatic and mud types of volcanism in the setting of strike-slip transtension.

Mud flow dynamics at gas seeps - Nirano Salse, Italy -

The Nirano Salse, known since the Roman Times, are one of the most beautiful and scenic mud volcanoes areas of Italy with thousands of visitors every year. In this work, we apply novel (for the context) hydrogeological techniques to characterize mud levels in the Salse by means of GPS-RTK positioning and continuous level logging within mud conduits. This is important to quantify the gas–liquid ratio in the conduits and evaluate the potential for dangerous abrupt mud eruptions. The results presented suggest that different mud levels in mud volcanoes clusters are due to the different gas–liquid ratio in the conduits and not necessarily exclude interconnection at depth, a hypothesis, on the other hand, that seems strengthened by mud level time series correlations. The presence of shallow aquifers at a depth of 5 to 30 m is also supported by our field data and allows us to delineate the boundaries of the shallow mud reservoir—pipes system and its overall shape. The shallow aquifers may provide a temporary storage for the ascending gas and when fluid pressure in these aquifers exceeds the tensional strength of the sedimentary rock, leakage of fluids to the surface would occur. In this case, if the gas–liquid ratio is high, mud volcanoes develop into tall gryphons and tend to have a discontinuous activity with sudden eruptions of mud after long periods of quiescence. This, together with the knowledge of shallow conduits localization has an important implication for site safety in proximity to the mud volcanoes. Our inferences based on mud level relationships to mud extrusion dynamics can be applied to lower risk in other mud volcanoes areas of the world with high geo-tourist visits, such as those of Trinidad, Azerbaijan, and Colombia.

Radon Monitoring in Artesian Wells at Mato-san Area of South Taiwan for Mud Eruption Studies

Abstract In the present study, radon monitoring in the artesian wells of Mato-san areas of south Taiwan were carried out to know the working of the mud eruption and the dependence of the eruption cycle with radon changes. Radon monitoring in water was carried out by using RAD7. Water samples were collected at different depths from different wells for the period of two weeks to one month. This study shows that anomalous radon value has been observed before and after to some eruptions during the study periods. The opposite radon behaviors at well No. 2 and well No. 3(B) were observed during the eruption. Noted behavior of these wells may be due to the movement of gas fluxes during the eruption period.

Multi-GPU based 3D numerical modeling of fluid migration and clay dehydration influence on Lusi hydrothermal activity (Java, Indonesia)

The Lusi mud eruption in East Java has been active since May 2006. Magma emplacement at depth, clay dehydration, and mud liquefaction during seismic wave propagation have been invoked as mechanisms fueling this eruption. However, the respective roles of these processes are still poorly constrained. In this focused study, we numerically investigate the influence of clay dehydration, mass and heat transport on fluid outflow at the Lusi site using a fully coupled 3D model for this active system. Using a multi-GPU parallel processing algorithm, we propose an estimate of the 3D time evolution of pressure, temperature, porosity, permeability and water liberation in a large-scale (9 km - 14 km - 5.5 km) deep hydrothermal system at high-resolution. Simulations indicate that high-pressure fluids generated by dehydration reactions are sufficient to induce hydro-fractures that would significantly influence the porosity and permeability structures. Dehydration is an essential component for understanding the Lusi system, because the fluids generated contribute to the outflow and may have a considerable impact for the maintenance of the infrastructure required to keep the Lusi site safe. High-Performance Computing (HPC) offers high-resolution simulations for studying time evolution of such natural systems, and potentially for geothermal resource development for the surrounding population.

Tectonic insight and 3-D modelling of the Lusi (Java, Indonesia) mud edifice through gravity analyses

SUMMARY Lusi is a sediment-hosted hydrothermal system located near Sidoarjo in Central Java, Indonesia, and has erupted continuously since May 2006. This mud eruption extends over a surface of ∼7 km2, and is framed by high containment dams. The present study investigates the geometry of the subsurface structures using a detailed gravimetric model to visualize in 3-D the Lusi system and surrounding lithologies. The obtained residual Bouguer anomaly map, simulated through geostatistical interpolation methods, supports the results of previous deformation studies. The negative gravity anomaly zones identified at Lusi are interpreted as fractured areas through which fluids can ascend towards the surface. A 3-D detailed geological model of the area was constructed with Geomodeller™ to highlight the main features. This model relies on the structures’ density contrasts, the interpreted residual Bouguer anomaly map, and geological data from previous authors. 3-D algorithms were used to calculate the gravity response of the model and validate it by inverse methods. The final output is a gravity constrained 3-D geological model of the Lusi mud edifice. These results provide essential details on the Lusi subsurface and may be useful for possible future geothermal resource exploitation and for the risk mitigation plans related to the maintenance of the man-made framing embankment.

Analisis Daya Tampung Lingkungan (Beban Pencemaran Air) di Kawasan Porong Kabupaten Sidoarjo ex Penambangan Lapindo

The Sidoarjo mudflow occurred in 2006 near the housing area that could cause physical and material environmental damage. Besides, secondary effects caused by it will increase the environmental capacity. If an area has detected exceeds the capacity of the environment it will impact permanent environmental damage. This study's objective was to evaluate the environmental capacity of the Porong District (Sidoarjo) as a result of Sidoarjo mud eruption ex. Lapindo Mining through the water pollution load-carrying capacity approach. Based on the research, it was found that in general, the parameters had exceeded the Class II quality standard according to PP No.82/2001, that are total dissolved solids (TDS) dan chemical oxygen demand (COD) (station 4), biological oxygen demand (BOD), chloride, and ammonia (all stations), Fe and nitrite (station 1), phosphate (station1, 3-4) and manganese (station 2). The parameters of TDS, BOD, COD (station 4), chloride, nitrite (station 1), ammonia, phosphate (station 1 and 3), and manganese (station 2) are known to have exceeded the environmental capacity. The recommendations include wastewater management, reducing pollutants into rivers, and implementing biotechnology to minimize water pollution.

The deep subsurface structure beneath Lusi and the adjacent volcanic chain inferred from local travel-time tomography

Since 2006, the Lusi mud eruption is ongoing in the northeast of Java Island, Indonesia. We perform a 3D seismic tomography of the area surrounding Lusi and the adjacent Arjuno-Welirang volcanic complex using P-wave arrivals of 797 local earthquakes recorded on 31 seismic stations for two years between 2015 and 2016. Resolution tests show that we can reasonably well constrain the subsurface velocity structure beneath Lusi down to a depth of 20 km. The results of our tomography reveal that Lusi has a shallow plumbing system that is interconnected with the neighboring Penanggungan volcano. Their joint system reaches down to a depth of 20 km. The Arjuno-Welirang volcanic complex has its own deep-rooted plumbing system that might be connected to Penanggungan volcano and Lusi along the Watukosek Fault zone. The connection of Lusi with this large reservoir volume elucidates the longevity of the Lusi eruption.

Characterization of Fresh Sidoarjo Mud as Material on Geopolymer System

Sidoarjo mud is the alternative cementitious material which derived from a volcano mud eruption in Porong, Sidoarjo, East Java, Indonesia. The calcination of fresh sidoarjo mud in high temperature was known rich in the content of Si and Al that has similar chemical content with the material of OPC. However, the calcination process had caused the consumption of energy, time duration and cost in the production. To solve the problem, this study was required to investigate the fresh sidoarjo mud without the calcination process. However, material of FSM was analyzed to understand its feasibility as a material in geopolymer referring to the material of fly ash. The results showed that the material of FA consisted of quartz (SiO2), mullite (3Al2O3 2SiO2 or 2Al2O3 SiO2) and hematite. While, the material of FSM consisted of quartz (SiO2), mullite (3Al2O3 2SiO2 or 2Al2O3 SiO2), magnetite (Fe3O4), hematite (Fe2O3), and rutile (TiO2). The particle of FA was amorphous and sphere with the misty surface that caused the absorption of alkaline solution and reduced the workability on fresh geopolymer mortar. While the particle of FSM was the agglomerate irregular shape with the rough surface that also caused the absorption of alkaline solution and reduced the workability on fresh geopolymer mortar. The analysis of FTIR identified that the material FA and FSM had the stretching in the gel of Si-O-Al and Si-O-Si. The compressive strength reached optimum at the replacement of 5% FSM.

Impacts of an Eruption on Cold-Seep Microbial and Faunal Dynamics at a Mud Volcano

Cold seeps are widespread in the deep sea and, like other chemosynthesis-based ecosystems, often host high faunal biomass. Temporal changes at seeps have been inferred by comparing communities at different successional stages; nonetheless, temporal studies in seep ecosystems are rare. Using data collected as part of a benthic observatory, we characterized intra-annual microbial and faunal dynamics in a microbial mat habitat on the Håkon Mosby mud volcano (1256 m depth; Barents Sea), and evaluated the effects of a mud eruption on the biota. Video sequences recorded twice daily for 4.5 months with an autonomous imaging module were analyzed to quantify changes in microbial mat cover and megafaunal density and behavior. In addition, time series data for pressure, bottom currents, and seabed temperature were analyzed to characterize environmental changes. Of the five taxa observed on the video footage, the zoarcid Lycodes squamiventer, the pycnogonid Nymphon macronyx, and the skate Amblyraja hyperborea were the most common. Zoarcids made frequent incursions on microbial mats, but were more often documented on the adjacent sediments. The cyclic behavior of common trends identified between microbial mat cover, zoarcid densities and abiotic variables using dynamic factor analysis (DFA) suggested that seep ecosystem dynamics at the Håkon Mosby mud volcano may be modulated by tides and the activity of the volcano. Moreover, the eruption that occurred about two months after the start of the study had a significant impact on faunal densities, microbial activity, and environmental variables. The eruption was preceded by a steady increase in seabed temperatures, density of small holes (indicative of gas emissions), and microbial mat cover. It was followed by 3- and 5-fold increase in zoarcid and pycnogonid densities, respectively. To our knowledge, this study is the first to analyze intra-annual temporal data in a cold-seep ecosystem and to present data on the effects of a mud eruption on seep microbial and faunal dynamics. Our results provide the first insight into ecosystem dynamics at a high-latitude cold seep and highlight the need to collect high-resolution temporal data to evaluate seep communities’ response to a warming Arctic and their potential role in mitigating methane emissions.

Recent magmatism drives hydrocarbon generation in north-east Java, Indonesia

Conventional studies of petroleum basins associate oil generation with the gradual burial of organic-rich sediments. These classical models rely on the interplay between pressure, temperature, and the time required for organic matter transformation to oil and gas. These processes usually occur over geological timescales, but may be accelerated by rapid reactions when carbon-rich sediments are exposed to migrating magmatic fluids. The spectacular Lusi eruption (north-east Java, Indonesia) is the surface expression of the present-day deep interaction between volcanic and sedimentary domains. Here we report the ongoing generation of large amounts of hydrocarbons induced by a recent magmatic intrusion from the neighbouring Arjuno-Welirang volcanic complex. We have investigated a unique suite of oil and clast samples, and developed a detailed conceptual model for the complex hydrocarbon migration history in this part of the basin by integrating multidisciplinary techniques. Our results show that palynology, organic petrology, and chlorite microthermometry are the most sensitive geothermometers for basins affected by recent magmatic activity. These findings further our understanding of the driving mechanisms fueling the world’s largest active mud eruption and provide a unique dataset to investigate modern hydrocarbon generation processes.

Integrated Subsurface Temperature Modeling beneath Mt. Lawu and Mt. Muriah in The Northeast Java Basin, Indonesia

Abstract The subsurface temperature has many impacts on geological phenomena such as hydrocarbon generation, geothermal energy, mineralization, and geological hazards. The Northeast Java Basin has various interesting phenomena, such as many oil fields, active faults, mud eruptions, and some active and dormant volcanoes. We measured temperature data from tens of wells along a 130 km survey line with an average spacing of 5 km. We also measured the thermal conductivity of rocks of various lithologies along the survey line to provide geothermal heat flow data. We propose integrated modeling for profiling the subsurface temperature beneath the survey line from Mt. Lawu to Mt. Muriah in the Northeast Java Basin. The modeling of subsurface temperature integrates various input data such as a thermal conductivity model, surface temperature, gradient temperature, a geological model, and geothermal heat flow. The thermal conductivity model considers the subsurface geological model. The temperature modeling uses the finite difference of Fourier’s law, with an input subsurface thermal conductivity model, geothermal heat flow, and surface temperature. The subsurface temperature profile along with survey line shows some interesting anomalies which correlate with either subsurface volcanic activity or the impact of fault activity.

Anatomy Of The ‘LuSi’ Mud Eruption, East Java

Early in the morning of the 29th of May 2006, hot mud started erupting from the ground in the densely populated Porong District of Sidoarjo, East Java. With initial flow rates of ~5000 cubic meters per day, the mud quickly inundated neighbouring villages. After almost four years, the ?Lusi? eruption has expelled over 73 million cubic meters of mud at an average rate of approximately 64000 cubic meters per day and at maximum rates of 170000m3/day. The mud flow has now covered over 700 hectares of land to depths of over 25 meters, engulfing a dozen villages and displacing approximately 40000 people. In addition to the inundated areas, other areas are also at risk from subsidence and distant eruptions of gas. However, efforts to stem the mud flow or monitor its evolution are hampered by an overall lack of knowledge and consensus on the subsurface anatomy of the Lusi mud volcanic system. In particular, the largest and most significant uncertainties are the source of the erupted water (shales versus deep carbonates), the fluid flow pathways (purely fractures versus mixed fracture and wellbore) and disputes over the subsurface geology (nature of deep carbonates, lithology of lithological unit between shales and carbonates). This study will present the first balanced overview of the anatomy of the Lusi mud volcanic system with particular emphasis on these critical uncertainties and their influence on the disaster.

Variations in CO2 emissions at a mud volcano at the southern base of Mt Etna: are they due to volcanic activity interference or a geyser-like mechanism?

Mud volcanoes are often associated with large areas of CO2 and CH4 emission that are potentially dangerous due to sudden paroxysmal gas and mud eruptions. Despite the interest in understanding such natural environments, they have not yet been thoroughly investigated and a single interpretative framework remains to be elaborated. This lack of knowledge may be due to the difficulty in measuring in-plume CO2 as there is very little contrast with atmospheric CO2, coupled with the complex organizational strategies required for long-term monitoring. This work features three different methods that were used to evaluate the CO2 flux at the Salinelle mud volcano in the foothills of Mt Etna (Italy), carried out periodically from December 2013 to April 2018. We computed in-plume CO2 flux indirectly using a tunable laser and a portable MultiGAS and, directly, measuring the gas volumetric flux from bubbling pools. The morphological variations of the mud field were recorded using unmanned aerial vehicle (UAV) imagery, which provided information on the migration of vents in relation to the observed variations in measured gas output. Our analysis shows that the three methods gave comparable values, indicating the feasibility of this approach. Our findings suggest a pseudo-cyclical pattern in the bulk CO2 emitted at Salinelle, introducing a new interpretation of the processes involved in mud volcano dynamics. We theorize that the periodic variation of the gas emitted at the Salinelle may be attributed to a “geyser-like” mechanism that may be subject to interruption or changes in magnitude by volcanic or seismic events.

In situ development of a methanotrophic microbiome in deep-sea sediments

Emission of the greenhouse gas methane from the seabed is globally controlled by marine aerobic and anaerobic methanotrophs gaining energy via methane oxidation. However, the processes involved in the assembly and dynamics of methanotrophic populations in complex natural microbial communities remain unclear. Here we investigated the development of a methanotrophic microbiome following subsurface mud eruptions at Håkon Mosby mud volcano (1250 m water depth). Freshly erupted muds hosted deep-subsurface communities that were dominated by Bathyarchaeota, Atribacteria and Chloroflexi. Methanotrophy was initially limited to a thin surface layer of Methylococcales populations consuming methane aerobically. With increasing distance to the eruptive center, anaerobic methanotrophic archaea, sulfate-reducing Desulfobacterales and thiotrophic Beggiatoaceae developed, and their respective metabolic capabilities dominated the biogeochemical functions of the community. Microbial richness, evenness, and cell numbers of the entire microbial community increased up to tenfold within a few years downstream of the mud flow from the eruptive center. The increasing diversity was accompanied by an up to fourfold increase in sequence abundance of relevant metabolic genes of the anaerobic methanotrophic and thiotrophic guilds. The communities fundamentally changed in their structure and functions as reflected in the metagenome turnover with distance from the eruptive center, and this was reflected in the biogeochemical zonation across the mud volcano caldera. The observed functional succession provides a framework for the response time and recovery of complex methanotrophic communities after disturbances of the deep-sea bed.

Deep hydrothermal activity driving the Lusi mud eruption

The Lusi mud eruption in East Java continues unabated after more than a decade of activity as a pulsating geyser system bursting mud, clasts, water, and gas. The origin of the fluids and their properties at depth are not well constrained, thus hampering our understanding and modelling of the system. Previous geochemical and geophysical studies show that Lusi is a sediment-hosted hydrothermal system with two sources of mud at depths between 0.3–2 km and another between 3.5–4.75 km. Here, we present results of mineral thermometry using Raman spectroscopy and chlorite composition on clasts erupted at Lusi. The results show that some of these specimens originate from the two main fluid sources, and at depths consistent with the geochemical and geophysical interpretation. Two main clast lithotypes erupt at Lusi. The first lithotype is a light grey shale returned to the surface from the Upper Kalibeng Formation (the primary mud source) and equilibrated at temperatures below 200 °C. The second lithotype is a black shale, whose source is the Ngimbang Formation at >3800 m depth. Two distinct temperature clusters are recorded in these black shales: one at 179±17 °C, consistent with the temperature estimate at 3800 m depth with the pre-eruption geothermal gradient, while younger minerals in the same specimen recorded substantial anomalous heating at ∼250 °C. These high temperatures indicate interaction with a heat source associated with the eruption through mixing with hydrothermal fluids. This temperature jump suggests rapid heating at ∼4000 m depth, consistent with a scenario of a magmatic intrusion and hydrothermal fluids circulation. This rapid and significant temperature increase would initiate devolatilisation reactions of hydrous minerals within the deep sedimentary package and generate substantial (highly overpressured) fluids at depths significantly below the main source of erupted mud. We infer that reactive and thermal pressurisation led to a deep and metastable system susceptible to e.g. seismic activity ultimately opening fluid pathways towards the surface along the Watukosek fault system. The two temperatures clusters recorded in the clasts show that conductive heat flow was the dominant heat transport prior to the eruption, while the system is now driven by large-scale convection and advective heat transport. The Lusi eruption occurred in a highly populated area forcing the evacuation of several tens of thousands of people. This system appears unstoppable and poses a real and present hazard for the settlements still surrounding the eruption site. Continuous research is necessary to understand this spectacular phenomenon, both for its important scientific relevance, and the societal impact of this natural disaster.