V13B-1341
Triggering and dynamic evolution of the LUSI mud volcano, Indonesia
Mud volcanoes are geologically important manifestations of vertical fluid flow and mud eruption in sedimentary basins worldwide. Their formation is predominantly ascribed to release of overpressure from clay- and organic- rich sediments, leading to impressive buildup of mud mountains in submarine and subaerial settings. Here we report data from two fieldworks on a newly born mud volcano named LUSI eruption in Eastern Java (Indonesia). The eruption site appears close to an active magmatic complex in a backarc sedimentary basin in Indonesia. Its specific location results in a high background temperature gradient that triggers mineralogical transformations and geochemical reactions at shallow depth. The eruption of 100 deg.C mud and gas that started the 29th of May 2006 flooded a large area within the Sidoarjo village in Northeast Java. Thousands of people have so far been evacuated and, since the initial eruption, the flow rate escalated from 5000 to 120,000 m3/d during the first eleven weeks. Then the erupted volume started to pulsate between almost zero and 120,000 m3/d in the period August-September, whereas it increased dramatically following swarms of earthquakes in September, before reaching almost 180,000 m3/d in December 2006. Fifteen months after the initial burst, LUSI is still vigorously erupting up to 111,000 m3/d, the average subsidence of the area reached 11 m. Seismic images show that a pre-existing structure was present before the eruption. Based on geochemical and field results, we propose a mechanism where the eruptions started following the 27th of May earthquake due to fracturing and accompanied depressurization of >100 deg.C pore fluids from > 1700 m depth released from a structure in already critical conditions. This resulted in the formation of a quasi-hydrothermal system with a geyser-like surface expression and with an activity influenced by the regional seismicity. http://folk.uio.no/adrianom/
V13B-1342
Heat Flow Distribution At A Mud Volcano In Kumano Basin, East Of Kii Peninsula, Central Japan
Mud volcano is a surface expression of mud diapir, where over-pressured unconsolidated sediment has been intruded into the overlying sediment column, and provides information on the process of material transport and physical and chemical conditions in a deeper part without a deep drilling. Kumano Knoll No.4 (KK4) is one of the mud volcanoes in the Kumano Basin, east of Kii Peninsula, central Japan. The diameter and height above the basin floor are 800 m and 100 m, respectively. The summit area has bumpy surface with pits whose diameter are several meters. There are living and dead clam colonies in the area. In order to survey thermal and hydrological characteristics of KK4, we deployed a long-term temperature monitoring system (LTMS), which has two probes including six thermistors, at the top of the mud volcano and monitored bottom-water and sub-bottom temperatures from August 2002 to May 2003. One probe (Probe-2) was penetrated into sediment within a pit with a dead clam colony that suggests the existence of cold seepage in the past. The other (Probe-1) was installed in the outside of the pit where there was no expression of cold seepage. Measured bottom-water temperature variation (BTV) shows large amplitude variation with various periods. Measured sub-bottom temperatures show similar variation to the bottom-water temperature variation but its amplitudes decay and the phases delay with increasing sub-bottom depth. By comparing amplitude and phase of BTV and sub-bottom temperature variation, we can identify whether there is vertical fluid migration in sediment. For sub-bottom temperatures measured outside of the pit, we could explain that the effects of BTV propagated into sediment by conduction only. By correcting the effects of BTV from the sub-bottom temperatures, we estimated heat flow value as 14 mW/m2. On the other hand, sub-bottom temperatures measured within the pit could be better explained by a model with upward water flow at a rate of 10-7 m/s order, than by conduction only. Heat flow combined conduction and this upward water flow was estimated as 60 mW/m2, about four times the heat flow values in the outside of the pit. Our results indicate that there was cold seepage activity at KK4. We conducted 11 heat flow measurements with small heat flow probes 60 cm in length along a survey line from west to east just before the recovery of LTMS. Using the BTV data obtained with LTMS, we removed the effects of BTV from temperature profiles measured with SAHF. The cross-section of corrected heat flow values indicates three characteristics: (1) high heat flow values higher than 70 mW/m2 was measured on the base of the mud volcano, (2) low heat flow values (20-30 mW/m2) were measured on the western slope, and (3) heat flow increases to 60 mW/m2 on the top of the mud volcano. Preliminary analysis by numerical computation indicates that to interpret this heat flow distribution, we need consider not only advective heat supply to KK4 but also topographic effects of KK4 on the subsurface thermal structure.
V13B-1343
High-Resolution Seismic Identification of the Caldera System and Dynamics of the Haakon Mosby Mud Volcano, Barents Sea Slope.
The Haakon Mosby Mud Volcano (HMMV) is an active 1 km wide cold seep structure located at 1250 m deep in the Bear Island Slide, southwestern Barents Sea. The HMMV is one of the few examples of mud volcanoes in non-compressional tectonic settings. Previous studies defined the deeper structure of the HMMV as an approximately 3 km deep seismic disturbance in Plio-Pleistocene deposits. Two-dimensional 3.5 kHz Sediment Echosounder Profiler data combined with Chirp seismic data collected during two cruises in 2005 and 2006 show the HMMV as an inverted-conical-shaped structure composed by five seismic units (U5-U1 from older to younger) and characterized by pull-down of reflections towards its geometrical centre as well as by a vertically oriented central area of poor seismic image quality. The lack of coherent reflectivity or "blanking" is likely due to the presence of gas in the section. Several studies have interpreted this lack of reflectivity as a "caldera" for mud volcanoes which constitutes the main pathway for fluid and gas in such structures. Isopach maps of the identified seismic units show that U5-U2 distribution is regional, but the youngest unit U1 is confined to the surroundings of the HMMV. The seismic signature of U5-U3 is mainly parallel or absent while unit U1 follows a hummocky trend, interpreted as mud flow deposits. Although the seismic unit U2 is mainly parallel, hummocky reflections as those in U1 have been identified westward of the geometrical centre of the volcano. Detailed analysis of the blanking effect over the seismic units reveals spatially overlapping calderas indicating different ages. Both size and position change, being circular and centrically located in U5-U3 units and oval and northeasterly displaced in both U2 and U1. The shallow structure of the HMMV can be described as a caldera complex in which five overlapping calderas have been identified. They record the migration dynamics of the HMMV over the time. Three years of in-situ sediment temperature measurements support the overlapping caldera as the main active centre of the HMMV. As no evidence of tectonic control has been observed, the deposition of mud flows seems to be controlled by the gravity gradient. The migration suggests a progressive restriction of the flux in the volcano which will affect the habitat distribution of the benthic communities in the HMMV.
V13B-1344
Simulation of Hydrothermal Vent Complexes
Vent-complexes are a common geological feature arising when fluid overpressure generation causes hydraulic fracturing reaching the surface. They are commonly associated with volcanic basins and basins with rapidly deposited clay sequences. We have developed models representing host rock as porous media with discrete and continous models, coupled with models for diffusive fluid flow. The results are compared with analytical solutions and experiments, as well as the geological analogues. Using these models we can determine parameters of vent formation, such as venting number and venting duration, dynamics of vent initialization, fracture velocity, granular velocity, ejecta and energy. We can also compare post-formation morphology (crater diameter, refill slope) and the dynamics as a result of periodic fluidization, secondary fluid migration and channel formation. We have also done statistical analysis on the distribution of vents-complexes in the field, and we have developed an analytical model for this. The simulation results have been compared with these, and and the critical parameters analysed.
V13B-1345
Ten Years of Monitoring the Eruption of Shrub Mud Volcano, Alaska
Shrub mud volcano, one of three in the Klawasi group on the eastern flank of Mount Drum volcano in the Wrangell volcanic field of eastern Alaska, has been erupting warm, saline mud and CO2-rich gas continuously since at least the summer of 1997, following 40 years of repose. The initial eruption in early summer of 1997, documented by Richter and others (1998), involved violent fountaining of mud, up to 6-8 m high, from nearly a dozen vents located near the summit, and quiet effusion from vents located about mid-way down the north flank of the 100-m-high cone. Guided by topography, early emissions of copious amounts of CO2 gas flowed in narrow streams through brushy foliage leaving behind stripes of brown, dead vegetation along the flow paths. The hazard posed by the CO2 emissions was evident from dead birds and mammals found near the vents. Initial surveys of the activity in 1997 recorded water temperatures up to 46°C. A survey in 1999 by Sorey and others (2000) found numerous active vents-many in different locations than those two years earlier-a maximum water temperature of 54°C, and an estimated total discharge of warm water of 50 l/s. Measured CO2 emissions were extrapolated to a discharge rate of 6-12 tonnes/day. The highest water temperature recorded was 57.3°C in 2000, with temperatures gradually declining since. From year to year, we found that eruptive activity migrated amongst clusters of vents, some new and some continuing from 1997. Between the summer of 2003 and the spring of 2004, the system changed dramatically when a large collapse pit formed a few tens of meters from the main summit vents and all previously active vents became inactive. This water-filled circular pit measured 28 m in diameter, up to 9 m deep, and encompassed an area that had previously been unaffected by the eruptive activity. In July 2004, water temperature and discharge at the outlet channel was 37.2°C and 9.4 l/s, respectively. The total CO2 discharge from the roiling pool was 140 l/s (about 20 tonnes/day), and the diffuse efflux (0.13 tonnes/day) was comparable to the 0.23 tonnes/day measured in 1999. Based on discharge and δ13C values of the gas and water phases (-4.6‰ and +1.35‰, respectively) carbon in the reservoir was calculated to be -3.1‰, supporting a mixed magmatic and limestone source for the CO2. Deep pits exposed during the current eruption have provided clues to the possible origin of Shrub, the largest, and highest mud volcano of the Klawasi group. Shrub stands about 100 m high and is an oblong cone in shape. Cross-sections of the material composing the cone reveal a chaotic pile of debris ranging from clay to boulders (angular to subrounded, up to 1.5 m across), the latter too large to have been rafted up by mud and gas venting. Pleistocene glaciers extending into the Copper River Valley from Mount Drum covered the area currently occupied by Shrub. We hypothesize that as the glaciers stagnated and began to retreat, subglacial melting caused by the rising warm mud formed an anomalous moulin that became the receptacle for rock and sediment debris washed in from supraglacier runoff. Thus the constructional form of Shrub is likely a moulin kame.
V13B-1346
CANDIDATE MUD VOLCANOES IN THE NORTHERN PLAINS OF MARS
Domes in the the `Borealis back-basin' (centre 76N 160W) on Mars resemble products of mud volcanism (MV) on Earth. Description of domes: Our mapping shows ~30 Early Amazonian domes in the back-basin (~50 x 40 km, height ~300 m). Many have marginal and central peaks (~7 x 5 km, height ~400 m), and moats ~2.5 km wide. Domes are rough at km-scale; some have central depressions; some have annular ridges. Mean rise/run is (0.93±0.22)%. Dome orientations, and alignments of multiple domes, run parallel to the continuation of grabens associated with Alba Patera diking [1]. Distributary channels are found in association with one dome. Aspect-frequency plots for the domes region show significant deviations from randomness. (Detrended) slopes facing S or N are more common than other aspects; local maxima are (S±5°) and (N±5°). N-facing slopes are more abundant than S-facing slopes, so mean S- facing slope must be steeper. A control region at the same latitude shows no comparable anomaly. Interpretation: Many worlds show igneous volcanism, but only Earth has confirmed MV. So, when assessing an extraterrestrial construct, one should assign a high prior probability to igneous volcanism. However, (1) Dome morphologies can be matched with MV in the Caspian Basin and Cadiz Gulf [2], though Martian domes have diameters ~5 times greater. (2) Moat morphometry excludes flexural origin and suggests a collapse origin. Collapse moats are often associated with MV on Earth. (3) Aspect anomalies suggest that near-surface dome material was subject to insolation-driven processing, requiring dome near-surface material to have been partially volatile [3]. (4) Volcanic constructs are rare closer to Alba Patera, inferred to have triggered dome construction. So there must be a major increase in the fusibility of materials in our basin. In the absence of Martian granites, volatile-rich deposits satisfy this requirement. (5) Mars' thick sediment piles permit MV. Crater fill studies suggest that the Scandia and Borealis back- basins contain the greatest thickness of cover in the Northern Plains, making these preferred MV locations [4]. We infer that domes may well result from MV. Outstanding puzzles: We currently lack a compelling mechanism for expulsion in the extensional tectonic setting required for dyking. One possibility is direct triggering of MV through intersection of dyke fluids with a volatile-rich sediment column. OMEGA spectra of domes show no significant differences between dome and non-dome terrain. Band depth methods and linear unmixing models [5] yield compositions uniformly dominated by ferric oxides and pyroxenes. This may be due to recent mantling, or MV may tap a source layer of similar composition to adjacent plains. Implications: Post-Hesperian cover in our study area is too thin for MV; older sediments are probably the source. These may record catastrophic flooding or oceans. Our results have implications for the ease of future drill-rig access to these ancient deposits. There is also a tempting geographic link with young evaporates [6]. [1] K.L.Tanaka (2006), 4th Mars Polar Sci., Abs. #8024. [2]L.Somoza et al. (2003), Mar. Geol. 195, doi:10.1016/S0025-3227(02)00686-2. [3] M.A.Kreslavsky and J.W.Head (2003),GRL 30, doi:10.1029/2003GL017795. [4] D.Buczkowski(2007),JGR-E, doi:10.1029/2006JE002836. [5] J.- P.Combe(2005),PhD thesis, U. Nantes. [6] K.E.Fishbaugh et al.(2007),JGR-E 112, doi:10.1029/2006JE00286. http://www.climatefutures.com/MVsEMSEC.pdf
V13B-1347
Seismic Evidence of a Gas Hydrate System on the Nile Deep-Sea Fan
The Nile Fan is a depocentre on a passive margin that hosts an active hydrocarbon province and a wide range of seabed cold seeps. A bottom simulating reflection (BSR) is identified, for the first time in the Mediterranean Sea, based on re-examination of two sets of academic multichannel seismic data: profiles acquired by OGS in 1973 (using explosive sources and a 2.4 km streamer), reprocessed for this study; and profiles acquired by Géosciences Azur from 1998-2002 (using airgun sources and 0.3 to 4 km streamers). On the central Nile Fan, a reflection of inverse polarity can be traced over a depth range of 2000-2500 m, deepening from c. 220-330 ms below seabed and in places cross-cutting (discontinuous) stratal reflections. Comparison with the modeled stability zone for methane hydrate in seawater (MHSZ) indicates the BSR to be consistent with free gas at the base of a hydrate occurrence zone up to 250 m thick. The MHSZ extends upslope beyond the observed BSR, to a limit at c. 1200 m depth. Modeling of hydrate stability for glacial-stage conditions in the Mediterranean Sea, when bottom waters were much cooler (at least - 4°C), shows that the MHSZ would have been at least 50% thicker and its upper limit at least 300 m shallower. Deglaciation thus corresponded to a dramatic reduction in hydrate stability, with consequences for slope stability along the upper limit of the HSZ as it migrated downslope (across water depths of c. 900-1200 m). The inferred deglacial release of gas and water also has implications for the functioning of cold seeps, which occur across the depth range of the BSR on the central Nile Fan and are linked to underlying hydrocarbon reservoirs. The episodic formation and dissociation of hydrates in response to large glacial-interglacial changes in bottom water temperatures may represent an important driving mechanism for shallow fluid flow, finding expression in the sedimentary records both of slope failure and of cold seep systems on the Nile Fan and elsewhere in the eastern Mediterranean Sea.
V13B-1348
A large-scale middle Miocene carbonate (?) mound structure in the Norwegian-Danish Basin: evidence for hydrocarbon migration?
A mounded structure has been observed in the Norwegian-Danish Basin about 10 km east of the Coffee Soil Fault outside the Central Graben and almost directly on top of the mid-Miocene unconformity. The mounded structure has been mapped using 3D seismic data; it consists of two culminations arranged in a triangular area; one is 1500 m long, 800 m wide and 70 m high while the other is 800 m long, 400 m wide and 30 m high. The composite mound comprises a volume of some 29 mio m3 and is characterised by a high positive reflection amplitude at the top, differential compaction as compared to the surrounding sediments and velocity pull up in underlying reflections. These observations indicate a high velocity fill with higher acoustic impedance and less compaction than that of the surrounding sediments, and the interior of the mounded structure has thus been interpreted as a relatively hard, coarse grained or well cemented sediment. The observed mound is an isolated feature and there have been no reports on any similar structures in the surrounding area. Several possible morphological mound-shaped features have been considered such as igneous and clastic intrusions and extrusions, mud volcanoes, contourites, turbidites and carbonate mounds. The succession below the mound shows no vertical disturbance such as seismic chimneys or deformation of layers, and this seems to exclude an extrusive origin, which most likely would have had some influence on the sedimentary succession. Investigation of the base reflection in the surrounding area shows no sign of any erosional features such as submarine channels and this appears to exclude an origin as a turbidite or contourite since these features often are associated with some kind of erosion. Large present day seismic chimneys have been found in close proximity to the mound along with numerous elongated pockmarks in the Miocene succession right above the mound. These observations indicate that the study area is highly influenced by gas escape both at middle Miocene time and at present, which is in accordance to the general maturation of the hydrocarbons in the area (the Central Graben). This seems to be an important factor in interpretation of the mound. Following the observations, explanation of the precise location, uniqueness and isolated position of the mound is most easily accomplished when applying a carbonate related model. This model relates the paleogeographic position of the mound to the extensive gas escape in the area by implying that carbonate precipitation and build up in e.g. a bioherm was accomplished by bacterial methano-genesis facilitated by excess nutrition in the water column resulting from a high middle Miocene gas flux from the mature source rocks in the nearby Central Graben.
V13B-1349
Stability of Gas Hydrates at Mud Volcanoes and Methane Seepage Sites in the Gulf of Cadiz: Correlation with Past Oceanographic Changes
The Gulf of Cadiz (GC) is a highly sensitive area to paleoceanographic changes, characterized by the occurrence of mud volcanoes, diapiric ridges, pockmarks and methane seepages, both active and inactive. The high methane content in shallow sediments and the presence of gas hydrates on the most active structures indicates that these are preferential areas for the escape of fluids enriched in hydrocarbons, especially methane. Extensive fields of methane-derived authigenic carbonates (MDAC) were found along the upper and mid-continental slope, where the Mediterranean Outflow (MO) water is in direct contact with the seafloor. The estimated ages of the MDAC indicate formation over discrete episodes that correspond to periods of rapid paleoceanographic changes (such as the onsets of glacial stages terminations). In this work, the gas hydrates stability zones (GHSZ) are investigated at 7 sites where MDAC occur. Calculations of the depths of the GHSZ were done considering gas compositions, as obtained from the gas compositional values of the active mud volcanoes in the GC, ranging from two end-members: from a pure biogenic origin, with 100% of methane, to the end-member with 20% of heavier hydrocarbons, considered a mixture of biogenic and thermogenic origins. The depths of the GHSZ were calculated for different paleoceanographic scenarios: present day conditions, with variable intensities of the MO, and estimated conditions for the Last Glacial Maximum. Results indicate that the transition from glacial to interglacial conditions reduces the depth of the GHSZ by more than 46%, for pure methane gas composition; and by more than 35%, for gas composition of 80% of methane and 20% of heavier hydrocarbons. At several sites the stability zone disappears entirely for both gas compositions. The temperature increase associated with the beginning of the MO influence can reduce the depth of the GHSZ by more than 23% and 17%, considering respectively pure methane composition or a mixed gas with 20% of heavier hydrocarbons. At two of the studied sites the stability zone can be entirely extinguished. Increases in the seafloor temperature associated with these two processes can efficiently trigger episodes of dissociation of potential gas hydrates that would result in intense flux of methane rich fluids to shallow sediments or even into the seabottom.
V13B-1350
Shallow plumbing systems in mud volcanoes (Azerbaijan)
Studies of mud volcano piercement structures intensified during the last decades in order to better understand both the eruptive and dormant stages and ongoing processes, from the source region to the surface. Our recent field studies and analyses in dormant Azeri mud volcanoes showed the presence of different seepage sites with an interconnected and intricate plumbing system in the near surface of the volcano craters. Gryphons and pools represent the two dominant seepage modes in the dormant mud volcanoes in Azerbaijan. Shallow water reservoirs appear to feed the water dominated pools. At these locations the water temperatures is controlled by external air temperature and the higher salinities (up to 42000 ppm) are ascribed to stronger evaporation processes. In contrast, evaporation is less effective in the mud dominated gryphons (salinities approx 900 ppm) that have deeper roots as also suggested from the lithology and isotopic analyses. Gryphons have stable temperatures during warm and cold season. Water isotopic analyses reveal little influence from meteoric fluids while the seeping gas has a general mixed thermogenic-biogenic signature. Reverse correlation between d13C in CH4 and CO2 supports the hypothesis of shallow chambers located at different depths where biogenic methane is produced. Deep reservoirs reveal the presence of thermogenic gas that rising mixes with shallow biogenic methane. http://folk.uio.no/adrianom
V13B-1351
3D Investigation of gas Hydrates and Free gas Saturation of a mud Volcano in the Black Sea With High Resolution Wide Angle Seismic Methods
Geoscientific investigations were performed as a part of the MARGASCH project with the aim to quantify the distribution of gas hydrates and relate them to fluid migration zones in sediments. The research area lies in the Sorokin Trough, Black Sea, south-east of the Crimea peninsula. It is affected by compressional tectonics, leading to diapiric compressional structures in the sediments where fluids and gas migrate to the seafloor. This study focuses on a 3D-grid, 7km x 2.5km, of high resolution seismic measurements. 14 Ocean Bottom Instruments (OBH/S) recorded the seismic signals generated by two 1.7l GI-guns at a shooting rate of 10s. A 2.5D Kirchhoff depth-migration applied to the OBH/S time sections (common receiver gathers) gives a spatial image of the subseafloor, where reflectors extend to a max. depth of 1000m and 400m distance to the receiver at the seafloor. Superimposing all OBH/S sections along one transect gives the depth image of the entire profile. The resulting image shows strong lateral variations in the reflection patterns: parallel layering to a max. depth of 1000m bsf occurs in the peripheral regions of this 3D-grid. The central part is characterized by blanking and fault zones dipping in the south-eastward direction. The traveltime inversion and its correlation with all seismic migrated sections results in a 3D-grid of seismic velocities and structures of the subseafloor. The two methods are complementary. The fluid-migration paths are indicated by reduced seismic velocities in the inversion models and extend to tens of meters. They are mainly found in the north-western part of the 3D-grid and originate from deeper sources, which are beyond the resolution of this seismic dataset. Lateral migration of gas is indicated by reduced velocities within certain sediment layers. This is especially found in the uppermost layer, with values of about 1.45km/s. A gas-hydrate bearing layer is imaged at a depth of about 300m bsf, implied by higher P-wave velocities than the ones in the layers above and below. The thickness of this layer is varying throughout the imaged research area at about 50-100m. http://www.ifm-geomar.de
V13B-1352
Mini 3D seismic surveys of mud volcanoes in the Kumano Basin
Kumano Basin is a forearc basin of the Nankai Trough subduction zone. Eight mud volcanoes have been found in the basin from previous diving and side-scan sonar surveys. Seismic sections clearly showed the BSR widely developed in the basin. The existence of the BSR near the mud volcanoes suggest that the methane gas dissociated from the hydrate excesses the activity of the mud volcanoes. To reveal the relation between activity of mud volcanoes and hydrate, we have conducted mini 3D seismic experiments. The experiments were separated to two phases; first experiment was conducted in 2004 covering Daigo and Dairoku Kumano Knolls (KK5 and KK6), and second was in 2006 covering Daisan Kumano Knoll (KK3). KK5 is located close to KK6 so they are called as twin mud volcanoes. Previous observation by diving and result from piston core sample analysis revealed following features; •KK5 is active now, or has been recently active. •KK6 is not active now. It stopped the activity at ~25,000 years ago. •KK3 is not active now, but it had been active more recent than KK6. We investigated the structure in and around the mud volcanoes in different phases of activity. All of three mud volcanoes studied have 'umbrella structure' beneath the seafloor. This structure is onlapped by the surrounding sedimentary sequence, which suggests that the 'umbrella structure' was formed by the ancient mud volcanism buried by the basin sediment. In KK3, accumulation of the umbrella (three or four times) is observed. This indicates the KK3 has been activated periodically in the last 500,000 years. BSR is continuously traceable beneath KK6, but it is vanished beneath the center of KK5. Beneath KK3, the BSR is also vanished just beneath its center, but the area without BSR is narrower then KK5. The observation on the BSR would suggest strong relationship between mud volcano activity and gas-hydrate.