paleomagnetic determination of emplacement temperatures of pyroclastic deposits an under utilized tool paleomagnetic data from lithic clasts collected from mt st helens usa volcan lascar chile volcan de colima mexico and vesuvius italy have been used to determine the emplacement temperature of pyroclastic deposits at these localities and to highlight the usefulness of the paleomagnetic method for determining emplacement temperatures at mt st helens the temperature of the deposits tdep at three sites from the june 12 1980 eruption was found to be 532 c 509 c and 510 570 c respectively one site emplaced on july 22 1980 was emplaced at 577 c these new paleomagnetic temperatures are in good agreement with previously published direct temperature measurements and paleomagnetic estimates lithic clasts from pyroclastic deposits from the 1993 eruption of lascar were fully remagnetized above the respective curie temperatures which yielded a minimum tdep of 397 c samples were also collected from deposits thought to be pyroclastics from the 1913 2004 and 2005 eruptions of colima at colima the sampled clasts were emplaced cold this is consistent with the sampled clasts being from lahar deposits which are common in the area and illustrates the usefulness of the paleomagnetic method for distinguishing different types of deposit tdep of the lower section of the lithic rich pyroclastic flow lrpf from the 472 a d deposits of vesuvius was 280 340 c this is in agreement with other recently published paleomagnetic measurements in contrast the upper section of the lrpf was emplaced at higher temperatures with tdep 520 c this temperature difference is inferred to be the result of different sources of lithic clasts between the upper and lower sections with the upper section containing a greater proportion of vent derived material that was initially hot our studies of four historical pyroclastic deposits demonstrates the usefulness of paleomagnetism for emplacement temperature estimation

active faulting induced by slip partitioning in montserrat and link with volcanic activity new insights from the 2009 gwadaseis marine cruise data 1 new high resolution marine data acquired aboard r v le suroit was used to map active normal faults offshore montserrat in greater detail the main faults of the montserrat havers fault zone have cumulative scarps up to 200 m high and offset sedimentary layers by hundreds of meters they are arranged in a right stepping en echelon trans tensional array which confirms that they accommodate the left lateral component of motion resulting from slip partitioning of oblique convergence along the volcanic arc they cut across montserrat s recent volcanic complex faulting and fissuring exerted control on the position of andesitic domes which are aligned along the n110 e average fault trend the 10 km long fault segments that cross the island could produce damaging m 6 events comparable to the shallow 16 march 1985 mw 6 3 earthquake that ruptured a submarine n140 e striking left lateral fault near redonda

vesicle distribution in basalt lava flow units in the mesozoic rift basins of northeast china and its application in gas reservoir prediction the mesozoic rift basins of northeast china are characterized by a significant proportion of basalt due to the progressive emplacement of basalt lava flows the objective of this study was to construct vesicle distribution models of the basalt lava flow units including conceptual geological models and thickness models to understand the architecture of the basalt and the gas reservoir distribution the conceptual geological models were constructed based on the characteristics of outcropping basalt lava flows with supplemental seismic data used to extrapolate the lateral extents of large scale basalt lava flows the thickness models were constructed using data on the thicknesses of basalt lava flow units and vesicle zones these data were obtained from 27 units in outcrop and 204 units interpreted from well logs in the basin the conceptual geological models revealed that the shapes of the basalt lava flow units change from braided to tabular with increasing thickness and that their inner structures can

volcanic evolution of central basse terre island revisited on the basis of new geochronology and geomorphology data twenty six new and seven previous k ar ages obtained on groundmass separates for samples from the axial chain massif guadeloupe f w i associated with geomorphological investigations allow us to propose a new model of the volcanic evolution of the central part of basse terre island the axial chain is composed of four edifices moustique mateliane capesterre and icaque mounts showing coeval activity from 681 12 to 509 10 ka which contradicts a previous hypothesis that flank collapse affected them successively our geomorphological reconstruction shows that the axial chain can be considered as a single large volcano named the southern axial chain volcano sca rather than a succession of several smaller volcanoes it raises questions regarding the formation of a large depression within the sca volcano prior to the construction of the sans toucher volcano between 451 13 and 412 8 ka given presently available evidence a slump affecting the western part of the sca volcano is the most probable scenario to reconcile the complete age dataset and the present day morphology of central basse terre finally our study shows that the sca volcano had a post activity volume of 90 km3 implying a construction rate of 0 5 km3 kyr this value strongly constrains interpretations of magma generation processes throughout the lesser antilles arc

current block motions and strain accumulation on active faults in the caribbean the caribbean plate and its boundaries with north and south america marked by subduction and large intra arc strike slip faults are a natural laboratory for the study of strain partitioning and interseismic plate coupling in relation to large earthquakes here we use most of the available campaign and continuous gps measurements in the caribbean to derive a regional velocity field expressed in a consistent reference frame we use this velocity field as input to a kinematic model where surface velocities results from the rotation of rigid blocks bounded by locked faults accumulating interseismic strain while allowing for partial locking along the lesser antilles puerto rico and hispaniola subduction we test various block geometries guided by previous regional kinematic models and geological information on active faults our findings refine a number of previously established results in particular slip rates on the strike slip faults systems bounding the caribbean plate to the north and south and the kinematics of the gonave microplate our much improved gps velocity field in the lesser antilles compared to previous studies does not require the existence of a distinct northern lesser antilles block and excludes more than 3 mm yr of strain accumulation on the lesser antilles puerto rico subduction plate interface which appears essentially uncoupled the transition from a coupled to an uncoupled subduction coincides with a transition in the long term geological behavior of the caribbean plate margin from compressional hispaniola to extensional puerto rico and lesser antilles a characteristics shared with several other subduction systems

factors influencing the capability of lava to erode its substrate application to venus there is evidence that a uniquely venusian type of channel may be at least partly erosional in origin a number of published models discuss the erosion process on various planetary bodies however these relate to lavas of specifically different compositions here a numerical model is derived to investigate the sensitivity of the erosion process to various physical parameters of the lava and substrate placing constraints on the physical characteristics required to obtain a suitably rapid erosion rate the model allows for the effects of latent heat and also considers the presence of a liquid substrate boundary layer between the lava and solid substrate the results indicate that the thermal erosion process is particularly sensitive to the melting temperature when the melting temperature is doubled from 700 to 1400 k the erosion rate decreases by approximately an order of magnitude also the erosion rate associated with a venusian initial substrate temperature is approximately 1 5 times greater than the equivalent terrestrial one mechanical erosion is considered by altering the percentage of latent heat required to melt the substrate as this percentage is varied from 0 to 100 the erosion rate decreases by about a factor of 2

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

numerical modeling of lava flow cooling applied to the 1997 okmok eruption approach and analysis 1 throughout february and march of 1997 okmok volcano in the eastern aleutian islands of alaska erupted a 6 km long lava flow of basaltic a a within its caldera a numerical model for lava flow cooling was developed and applied to the flow to better understand the nature of its cooling radiation and convection from the surface as well as conduction to the ground were used to transport the flow s heat to its surroundings in the model internally a conduction only approach moved heat from the interior outward vesiculation latent heat generation and thermal conductivity changes with temperature are among the other factors that were dynamically accounted for results indicate that ambient temperature fluctuations on the scale of days to weeks must be taken into account to create an accurate short term prediction of lava surface temperature daily data of rainfall and ambient temperature as opposed to yearly averages greatly increased the accuracy of the model furthermore convective cooling of the lava surface was observed to be a dominant heat loss process during the first 200 days indicating the convective heat transfer coefficient is a prime determinant of the accuracy of the model for predicting surface temperatures over a longer cooling period 2 years thermal conductivity and porosity proved to be among the dominating factors for heat loss because of the limiting role of conductive heat flow in the interior the model s flexibility allows application to flows other than the 1997 okmok eruption

the influence of topographic roughness on lava flow emplacement a quantitative understanding of the factors controlling lava flow emplacement is critical for both hazard assessment and mitigation and for the interpretation of past flow emplacement conditions the influence of topography with a vertical amplitude smaller than flow thickness i e substrate roughness is currently not accounted for in most flow emplacement models and hazard estimates here we measure the effect of substrate roughness on flow emplacement through experiments using analog fluids and molten basalt complementing recent work on the interaction of lava flows with obstacles taller than flow thickness we present results from three sets of analog experiments in which corn syrup polyethylene glycol and molten basalt were each extruded onto a sloping plane covered with a series of beds of varying grain sizes we find that flow front advance rates are impacted by bed roughness for all materials with decreases in average velocities by up to 50 with increases of substrate grain sizes by 5 100 times ranges analogous with topographic variations found in nature these decreases in flow front advance velocities are equivalent to up to an order of magnitude increase in fluid viscosity we interpret this velocity decrease to be caused by the movement of material into void spaces between substrate grains and by enhanced cooling through heat conduction to the substrate due to increased surface contact area the difference in advance velocity with increasing grain size diminishes with time after initial emplacement as a basal boundary layer is established additionally the experimental flow geometry measured by the complexity of the flow external perimeter became increasingly complex with increasing substrate grain size this effect will act to both slow the forward advance of lava flows and to create irregular emplacement paths of flows moving over rough surfaces we propose that flow emplacement models should be modified possibly through a calibrated effective viscosity term to account for bed roughness to increase accuracy in flow prediction and hazard estimation models

thermal erosion of felsic ground by the laminar flow of a basaltic lava with application to the cave basalt mount st helens washington 1 the thermal erosion of cold felsic ground by the steady laminar flow of a hot basaltic lava is examined theoretically and experimentally initially a chill layer is grown and then remelted at the base of the lava flow a steady thermal erosion velocity is then established which is limited by the buoyant instability of the melted ground or by the effective freezing temperature of the basaltic lava when the theoretical analysis is applied to the longest lava tube system of the cave basalt on mount st helens it is found that about 100 days of flow is sufficient to produce the observed ground erosion in little red river ape and lake caves

temperature profile around a basaltic sill intruded into wet sediments abstract the transfer of heat into wet sediments from magmatic intrusions or lava flows is not well constrained from field data such field constraints on numerical models of heat transfer could significantly improve our understanding of water lava interactions we use experimentally calibrated pollen darkening to measure the temperature profile around a basaltic sill emplaced into wet lakebed sediments it is well known that upon heating initially transparent palynomorphs darken progressively through golden brown and black shades before being destroyed however this approach to measuring temperature has not been applied to volcanological questions we collected sediment samples from established miocene fossil localities at clarkia idaho fossils in the sediments include pollen from numerous tree and shrub species we experimentally calibrated changes in the color of clarkia sediment pollen and used this calibration to determine sediment temperatures around a miocene basaltic sill emplaced in the sediments results indicated a flat temperature profile above and below the sill with t 325 c within 1 cm of the basalt sediment contact near 300 c at 1 2 cm from the contact and 250 c at 1 m from the sill contact this profile suggests that heat transport in the sediments was hydrothermally rather than conductively controlled this information will be used to test numerical models of heat transfer in wet sediments on earth and mars

petrophysical properties of volcanic rocks and impacts of hydrothermal alteration in the guadeloupe archipelago west indies abstract the results of the geotref project presented here aim to develop high enthalpy geothermal energy in fractured reservoirs they focus on active volcanic islands especially the basse terre island guadeloupe archipelago as part of this project we measured several petrophysical properties to better understand how fluids flow in the hydrothermal system provide a set of parameters to modelers and build datasets for future interpretation of well logs the thermo physical rock properties of bulk and grain density porosity permeability compressional wave velocity thermal conductivity and diffusivity specific heat capacity of outcropping volcanic rocks from the guadeloupe archipelago lesser antilles were measured and a dataset was built according to field observations samples were grouped into three lithological classes and then separated by their degree of alteration according to macroscopic aspects and optical microscopy results geochemical data were obtained and magnetic minerals identified by combining anisotropy of magnetic susceptibility and variation of magnetic susceptibility with temperature the lithotypes investigated were lava flows debris flows and pyroclastics gathering ash pumice and scoria deposits for lavas and debris flows three degrees of alteration were defined fresh slightly to moderately altered and highly hydrothermalized only fresh pyroclastics were studied because the altered state was not outcropping typically samples are composed of andesite and belong to tholeiitic and calc alkaline series lava porosity consists of high density cooling joints and vesicles of different shapes whereas pores in debris flows and pyroclastics are located both between and within particles median porosities and permeabilities are clearly distinct for lavas 4 and 6 10 18 m2 debris flows 33 and 4 10 14 m2 and pyroclastics 34 and 8 10 13 m2 the porosity difference implies a thermal conductivity twice to three times higher for lavas 1 68 w m 1 k 1 specific heat capacity of all lithothypes is similar 0 75 0 97 kj kg 1 k 1 advancing hydrothermal alteration removes magnetic minerals and transforms initial rocks the original plagioclases and pyroxenes in neoformed chlorite white micas quartz epidote and clay minerals are replaced this modifies the shape of the pore network furthermore hydrothermal alteration results in a reduction of pore throat diameter it tends to decrease petrophysical differences between lavas and debris flows increasing the porosity and permeability of effusive rocks while the opposite effects are observed for debris flows

the chengwatana volcanics wisconsin and minnesota petrogenesis of the southernmost volcanic rocks exposed in the midcontinent rift the southernmost exposed rocks of the north american midcontinent rift system 1100 ma consist of 3000 m of mafic volcanic flows and minor interflow sediment exposed along the st croix river in minnesota and wisconsin the flows are mostly high fe tholeiitic basalt with plagioclase phenocrysts and ophitic to subophitic clinopyroxene abundant secondary chlorite epidote and actinolite indicate the group was metamorphosed to greenschist facies 350 c low sodium m4 site and tetrahedral aluminum aliv contents of actinolite indicate low pressure metamorphism 0 25 gpa and imply a geothermal gradient of 45 50 c km low magnesium mg 0 37 0 58 and ni contents 36 185 ppm indicate the basalts have undergone significant fractionation and are not primary mantle melts incompatible element abundances are inversely correlated with mg and most samples plot within either high or low trace element groups e g ti p zr the basalts are enriched in the light rare earth elements and th and are v

fracture and compaction of andesite in a volcanic edifice the failure mode of lava dilatant or compactant depends on the physical attributes of the lava primarily the porosity and pore size and the conditions under which it deforms the failure mode for edifice host rock has attendant implications for the structural stability of the edifice and the efficiency of the sidewall outgassing of the volcanic conduit in this contribution we present a systematic experimental study on the failure mode of edifice forming andesitic rocks porosity from 7 to 25 from volcan de colima mexico the experiments show that at shallow depths 1 km while low porosity 10 lava remains dilatant the failure of high porosity lava is compactant and driven by cataclastic pore collapse although inelastic compaction is typically characterised by the absence of strain localisation we observe compactive localisation features in our porous andesite lavas manifest as subplanar surfaces of collapsed pores in terms of volcano stability faulting in the upper edifice could destabilise the volcano leading to an increased risk of flank or large scale dome collapse while compactant deformation deeper in the edifice may emerge as a viable mechanism driving volcano subsidence spreading and destabilisation the failure mode influences the evolution of rock physical properties permeability measurements demonstrate that a throughgoing tensile fracture increases sample permeability i e equivalent permeability by about a factor of two and that inelastic compaction to an axial strain of 4 5 reduces sample permeability by an order of magnitude the implication of these data is that sidewall outgassing may therefore be efficient in the shallow edifice where rock can fracture but may be impeded deeper in the edifice due to compaction the explosive potential of a volcano may therefore be subject to increase over time if the progressive compaction and permeability reduction in the lower edifice cannot be offset by the formation of permeable fracture pathways in the upper edifice the mode of failure of the edifice host rock is therefore likely to be an important factor controlling lateral outgassing and thus eruption style effusive versus explosive at stratovolcanoes

imaging the deep source of the rotorua and waimangu geothermal fields taupo volcanic zone new zealand abstract magnetotelluric data were recorded in a 45 10 km band crossing the rotorua and waimangu geothermal fields in the northern part of the taupo volcanic zone in the central north island of new zealand 3 d inverse modelling of these data show that beneath the low resistivity areas marking the near surface geothermal fields localised electrically conductive zones are present in the crust below about 2 5 and 3 5 km depth at rotorua and waimangu respectively at increasing depth these conductive zones broaden and appear to merge with a larger conductive zone at 8 km depth situated between the geothermal systems at rotorua the top of the conductive zone is situated directly beneath the area of greatest surface heat and gas discharge at waimangu the uppermost part of the deeper conductive zone is situated beneath the western part of lake rotomahana also an area of intense surface thermal activity and high heat flux the localised conductive zones are interpreted to be high temperature quasi magmatic fluids rising from a broader zone of partial melt at deeper levels

the heating of substrates beneath basaltic lava flows as populations around volcanoes grow the potential for society to be impacted by lava flows is increasing while lava flows are known to ignite bulldoze and or bury structures little is known about potential impacts to buried infrastructure we measure temperature profiles below molten rock to constrain a heat transfer model thermomagnetic and palaeomagnetic measurements on soil samples from beneath a 2014 hawaiian lava flow are then used to verify the model finally we illustrate the model s utility in lava flow hazard assessments by modelling a hypothetical lava flow active for 4 weeks in auckland new zealand the modelling predicts the upper 1 7 m of dry soil would exceed 100 c after 1 week and the upper 3 8 m of soil would exceed 100 c after 4 weeks determining the depth profile of substrate heating has important implications for planning and preparedness e g siting buried infrastructure volcanic impact and risk assessments and decision making before and during lava flow crises e g mitigation measures to be employed

erosion by flowing lava field evidence erosion of substrate materials by melting or mechanical means has been suggested in active lava flows on earth and other planets although there are many references to lava erosion on earth unambiguous evidence is rare geological relationships commonly cited as evidence of downcutting by lava can be explained without recourse to erosion in order to assess possible erosion by flowing lava we carried out field studies of tube fed basalt flows sheet flows of the columbia river basalt province crb and precambrian komatiites unequivocal evidence for thermal erosion melted dacite substrate was found at the cave basalt lava tube mount st helens for which fluid dynamic analysis indicates laminar flow although erosion was enhanced in areas of locally steep slopes possibly as a result of localized turbulence other lava tubes in our study display strong but inconclusive evidence for erosion komatiite flows display good evidence for erosion of their substrate possibly in a turbulent regime but assessment of the extent of erosion is hampered by limited and disrupted exposures no evidence for thermal erosion was found in the crb our findings suggest that an erosional origin for planetary sinuous rilles and canali would be favored by high reynolds number flows high mass flux low viscosity lava steep slopes and substrates having a lower melting temperature than the lava or low mechanical strength e g regolith

joint inversion of p wave velocity and density application to la soufriere of guadeloupe hydrothermal system we present the result of a 3 d gravity and p wave traveltime joint inversion applied to the hydrothermal system of la soufri ere of guadeloupe the joint inversion process is used here to overcome the different resolution limitations attached to the two data sets p wave traveltimes were obtained from three active seismic surveys that were conducted from 2001 to 2007 gravity data collected during a microgravity campaign is described in a companion paper we use a joint inversion process based on a bayesian formulation and a deterministic iterative approach the coupling between slowness and density is introduced through a supplementary constraint in the misfit function that tries to minimize the distance between parameter values and a theoretical relationship this relationship is derived from measurements on samples representative of mt pel ee of martinique and la soufri ere volcanoes we chose a grid discretization that leads to an under determined problem that we regularize using spatial exponential covariance between the nodes parameters our results are compared to geophysical electromagnetic results obtained using resistivity and vlf surveys they confirm the presence of highly contrasted dense fast and light slow zones in la soufri ere dome and crater basement our images suggest however that some non conductive zones may be massive andesite bodies rather than argilized zones and that these bodies may have deeper roots than hypothesized

on the role of thermal conductivity on thermal erosion by lava lava channels are abundant on the surface of both the moon and venus there is evidence that erosion may have played a part in their formation here a study of the relationship between thermal conductivity and erosion rate is presented a numerical model is used to investigate the sensitivity of the erosion rate to the relative value of the thermal conductivity of the lava solid substrate and liquid substrate boundary layer results show that the highest rates for thermal erosion are achieved by a high liquid substrate and low solid substrate thermal conductivity and that the thermal erosion process is most sensitive to the liquid substrate s thermal conductivity

influence of rainfalls on heat and steam fluxes of fumarolic zones six months records along the ty fault soufriere of guadeloupe lesser antilles fumarolic zones are permeable areas where both steam and heat are expelled to the atmosphere surface fluxes and flows which are representative of the intensity of the hydrothermal circulation in depth can be monitored by thermometers thermal infrared cameras spectrometers or condensers however the superficial activity of fumarolic zones can be modified by the meteorological conditions in particular the rainfalls which might result in erroneous estimations from this perspective we developed a set of physical equations to quantify the effects of rainfalls on the thermal behavior of fumarolic zones results were faced to continuous measurements achieved at the ty fault fumarolic zone la soufriere volcano guadeloupe lesser antilles during six months in 2010 using six vertical series of thermometers measuring the heat transfer in the ground and one condenser measuring the rising steam flux results demonstrate that in the absence of rainfalls heat and steam flux reach an equilibrium that is representa tive of the geothermal flux in depth conversely after the rainfalls the cooling of the ground provokes a deepening of the condensation level the related soil temperature drop can be estimated by computing the heat required to warm the infiltrated water up to boiling temperature while the recovery rate is directly linked to the geothermal flux our observations allow defining in which conditions flux are at steady state but also to build a first order numer ical model allowing estimating both the physical parameters of the ground thermal conductivity precipitation efficiency coefficient and surface flux constant and the long term thermal behavior of the hydrothermal system in particular our results predict that the hydrothermal activity must vanish on the zones where the geothermal flux drops under a certain threshold 60 w m 2 at la soufriere the existence of this limit may have strong implications for the precipitation rate of minerals and the possible reactivation of the fumarolic zones during volcanic crises

paleomagnetic directions and k ar dating of 0 to 1 ma lava flows from la guadeloupe island french west indies implications for time averaged field models twenty six lava flows spanning the last million years were sampled in la guadeloupe french west indies because of the lack of continuous volcano stratigraphic sections in la guadeloupe dating is necessary in order to describe the temporal evolution of the geomagnetic field in this time interval new k ar ages ranging from 50 ka to 1 ma have been obtained on andesites using the cassignol gillot technique at the universite paris sud institut de physique du globe de paris orsay laboratory additional flows with k ar ages obtained using the same dating technique were also sampled for paleomagnetic investigations more than 200 samples were analyzed using both alternating field af and thermal stepwise demagnetization techniques duplicate samplings of two flows at three different sites demonstrate that within flow dispersion is negligible for the andesitic lava flows sampled in this study direct comparison with an earlier paleomagnetic study performed on the island indicates that for the three investigated flows modern demagnetization techniques yield much better defined paleomagnetic directions the matuyama brunhes transition was recorded in a three flow section and is dated at 781 18 ka in good agreement with other recent radiometric age determinations the mean paleomagnetic pole calculated from the 23 normal polarity flows is indistinguishable from geographic north which implies that no significant persistent axial quadrupole term can be identified at this site for the last million years this result contradicts earlier results and has important implications for models of the time averaged field taf an occam algorithm was used to construct a taf model from the global volcanic database from the last 5 ma substitution of the mean direction calculated from the earlier study for the lesser antilles by our new mean value reduces the quadrupole term by more than 30 this effect which was produced by changing data from a single site demonstrates that older paleomagnetic sites may need to be reinvestigated furthermore it also highlights the limitations of taf models that can be inferred from paleomagnetic databases in their present state

reaction induced fracturing during replacement processes replacement processes are common transformation mechanisms in minerals and rocks at a variety of conditions and scales the underlying mechanisms are in general poorly understood but both mechanical and chemical processes are thought to be important replacement of leucite kalsi2o6 by analcime naalsi2o6 h2o is common in silica poor igneous rocks a 10 increase in volume is associated with the replacement process and this generates stresses that eventually cause fracturing of the reacting leucite experimentally reacted leucite samples display characteristic fracturing patterns that include both spalling of concentric onion skin like layers near the reacting interface and the formation of cross cutting often hierarchically arranged sets of fractures that divide the remaining leucite into progressively smaller domains these structures may explain the patchy alteration patterns observed in natural leucite samples and similar so called mesh textures associated with the serpentinization of olivine grains during hydration of mafic or ultramafic rocks they are also strikingly similar to larger scale patterns formed during spheroidal weathering processes a simple discrete element model illustrates the mechanics that control the formation of such systems and shows how these replacement processes may be accelerated due to the generation of new reactive surface area by hierarchical fracturing processes

reaction enhanced permeability during retrogressive metamorphism abstract retrogressive metamorphism is in most cases associated with influx of external fluids into igneous or metamorphic rocks with low to negligible initial permeabilities thus fluid migration is associated with some process that creates the necessary channels for migration one such mechanism is associated with the volume changes resulting from volatilization reactions petrographic studies of a partly serpentinized troctolite from the duluth complex in minnesota reveal how the increase in solid volume associated with hydration of olivine phenocrystals generates an extensive network of microfractures in the surrounding plagioclase dominated matrix this microfracture network allows hydrous fluids to penetrate further into the rock a 2 d spring network model illustrates how expanding polygons or non spherical grains in an elastically deforming matrix cause dilatant microfracturing and porosity generation even if the overall stresses are compressive the model emphasises how fluid infiltration may be promoted by stress heterogeneities set up by metamorphic reactions

factors influencing lava substrate heat transfer and implications for thermomechanical erosion we develop numerical simulations of basaltic lava flowing laminarly over a basalt substrate in order to examine the details of the lava dynamics and thermal boundary layers and to understand the implications for substrate heating as the initial stage of a larger study of thermomechanical erosion in different planetary environments we aim to understand why erosion occurs on earth why erosion features are not ubiquitous given the high temperatures involved and whether it is a plausible mechanism for the formation of planetary channels such as lunar sinuous rilles and venusian canali here we confine our attention to terrestrial lavas with well known properties and eruption parameters with relatively simple computational fluid dynamic simulations most closely representing tube fed hawaiian basalts for which erosion has been documented we demonstrate the importance of incorporating several key factors in models of lava flow substrate heat transfer which have commonly been neglected in previous treatments by addressing the interaction of the flow dynamics and heat transfer in the lava our work suggests that the development of a temperature gradient in the base of the lava even for undeveloped flow has a significant influence on substrate temperature the sensitivity of the lava substrate interface temperature to the thermophysical properties of the lava and substrate suggests that a delicate balance is required for partial melting to occur thus it might take weeks of continuous flow to initiate partial melting of the substrate at distances of several kilometers from the vent these durations exceed the periods of stability typical of lava flowing in tubes pauses blockages surges and breakouts frequently disrupt the flow however natural irregularities in the flow dynamics or substrate topography might help to initiate and maintain substrate melting on shorter timescales by disturbing the intimately coupled dynamic and thermal boundary layers although a purely thermal mechanism cannot be ruled out our findings support the premise that mechanical erosion may play a key role in reports of erosion based on field evidence

cooling and crystallization in sheet like magma bodies revisited abstract in order to characterize the interaction of convection and crystallization during the solidification of magmatic sills a one dimensional model for the solidification of magmatic sills cooling from above has been used the model is based on a stefan type solution for a mushy zone and takes into account the inward moving solidification front whose speed is exclusively controlled by crystal growth below the solidification front the magma cools by convection it may eventually cool below its liquidus and start to partially crystallize a kinetic model has been implemented to account for this crystallization the model calculations lead to three main conclusions 1 crystal growth is not the only factor controlling the advance of magmatic solidification fronts the advance appears to be mainly controlled by nucleation processes and only to a small extent by crystal growth 2 the longevity and vigor of convection inside a magma chamber is strongly dependent on the kinetics of crystallization of magma inside the chamber 3 immediately after the initiation of cooling the melt becomes laced with nuclei

comparative field study of shallow rhyolite intrusions in iceland emplacement mechanisms and impact on country rocks abstract shallow silicic intrusions are known to exist in many active volcanoes and can fuel both eruptions and hydrothermal fields however our knowledge of magma intrusions remains far from complete and processes occurring at intrusion margins are poorly understood in this field based study we characterise four shallows dissected rhyolitic intrusions at three sites in iceland njar vik dyrfjoll krafla and husafell central volcanoes we focus on the relationship between intrusion emplacement mechanisms and country rock response employing scanline mapping of fractures and in situ rock property measurements hardness and permeability along transects from the intrusion margins to damaged and undamaged country rocks we identify various scenarios of shallow intrusion emplacement style based upon their diverse geometry and lithofacies architecture additional information from rock properties and characteristics of fractures and vesicles indicates that initial country rock properties strongly influence the emplacement style we identify two discrete types of country rock response to magma injection the matrix permeability of weak porous and permeable lithologies conglomerate and hyaloclastite is reduced by 1 order of magnitude adjacent to intrusions due to pore occlusion stronger and denser low permeability lithologies basalt and welded ignimbrite undergo a decrease in hardness by a factor 2 related to an up to fivefold increase in fracture density with no significant change in matrix permeability our observations highlight the importance of robust characterisation of the mechanical properties of caldera filling or geothermal reservoir formations for appropriate forecasting of magma mobility geophysical data interpretation and geothermal resources characterisation

volcanic settings and their reservoir potential an outcrop analog study on the miocene tepoztlan formation central mexico abstract the reservoir potential of volcanic and associated sedimentary rocks is less documented in regard to groundwater resources and oil and gas storage compared to siliciclastic and carbonate systems outcrop analog studies within a volcanic setting enable to identify spatio temporal architectural elements and geometric features of different rock units and their petrophysical properties such as porosity and permeability which are important information for reservoir characterization despite the wide distribution of volcanic rocks in mexico their reservoir potential has been little studied in the past in the valley of mexico situated 4000 m above the neogene volcanic rocks groundwater is a matter of major importance as more than 20 million people and 42 of the industrial capacity of the mexican nation depend on it for most of their water supply here we present porosity and permeability data of 108 rock samples representing five different lithofacies types of the miocene tepoztlan formation this 800 m thick formation mainly consists of pyroclastic rocks mass flow and fluvial deposits and is part of the southern transmexican volcanic belt cropping out south of the valley of mexico and within the two states of morelos and mexico state porosities range from 1 4 to 56 7 average porosity is 24 8 generally permeabilities are low to median 0 2 933 3 md with an average permeability of 88 5 md the lavas are characterized by the highest porosity values followed by tuffs conglomerates sandstones and tuffaceous breccias on the contrary the highest permeabilities can be found in the conglomerates followed by tuffs tuffaceous breccias sandstones and lavas the knowledge of these petrophysical rock properties provides important information on the reservoir potential of volcanic settings to be integrated to 3d subsurface models

thermal mapping of a pāhoehoe lava flow kīlauea volcano abstract p hoehoe lava flows are a major component of hawaiian eruptive activity and an important part of basaltic volcanism worldwide in recent years p hoehoe lava has destroyed homes and threatened parts of hawai i with inundation and disruption in this study we use oblique helicopter borne thermal images to create high spatial resolution 1 m georeferenced thermal maps of the active p hoehoe flow on k lauea volcano s east rift zone thermal maps were created on 27 days during 2014 2016 in the course of operational monitoring encompassing a phase of activity that threatened the town of p hoa our results illustrate and reinforce how p hoehoe flows are multicomponent systems consisting of the vent master tube distributary tubes and surface breakouts the thermal maps accurately depict the distribution and character of p hoehoe breakouts through time and also delineate the subsurface lava tube surface breakouts were distributed widely across the p hoehoe flow with significant portions concurrently active well upslope of the flow front often concentrated in clusters of activity that evolved through time gradual changes to surface breakout distribution and migration relate to intrinsic processes in the flow including the slow evolution of the distributary tube system abrupt disruptions to this system and the creation of new breakouts and associated hazards were triggered by extrinsic forcing namely fluctuations in lava supply rate at the vent which disrupted the master lava tube although the total area of a p hoehoe flow has been suggested to relate to effusion rate our results show that changes in the proportion of expansion vs overplating can complicate this relationship by modifying existing techniques we estimate time averaged discharge rates for the flow during 2014 2016 generally in the range of 1 2 m 3 s 1 mean 1 3 0 4 m 3 s 1 less than half of k lauea s typical eruption rate on the east rift zone and suggestive of a weak eruptive regime during 2014 2016 we caution however that this discharge rate approach requires further independent corroboration the thermal maps provide the first synoptic characterization of p hoehoe flow activity at high spatial resolution essential both for operational hazard assessment and fundamental understanding of p hoehoe behavior

numerical modeling of lava regolith heat transfer on the moon and implications for the preservation of implanted volatiles 1 we have performed a series of numerical simulations of heat transfer between lunar lava flows and the underlying regolith with the goal of determining the depths in the substrate beneath which implanted extralunar volatiles would survive outgassing by the downward propagating heat pulse exogenous materials of interest include solar wind and solar flare particles and the cosmogenic products of galactic cosmic ray gcr particles emplaced in the lunar regolith early in solar system history extraction and analysis during future lunar missions would yield information about the evolution of the sun and inner solar system environment particles implanted in regolith deposits may be protected from gardening and saturation if buried by a lava flow but must be sufficiently deep in the regolith to survive the consequent heating our simulations include detailed treatments of lava and regolith thermophysical properties thermal conductivity specific heat capacity which vary widely over the temperature range relevant to lava flows in the lunar environment 200 to 1500 k simulations adopting temperature dependent properties together with a treatment of latent heat of lava crystallization indicate that implanted volatiles would be fully preserved at depths greater than 20 cm beneath 1 m thick lava flows 60 deeper than predicted by simulations employing constant properties these results highlight the necessity of appropriate prescription of material properties consideration of the range of lunar lava flow thicknesses allows us to determine the range of depths from which pristine samples may be recovered

investigating lava flow rheology using video analysis and numerical flow models abstract lava rheology is a major control on lava flow behavior and a critical parameter in flow simulations but is very difficult to measure at field conditions or correctly extrapolate from the lab scale we present a new methodology for investigating lava rheology through a combination of controlled experiments image analysis and numerical forward modeling our experimental setup part of the syracuse university lava project http lavaproject syr edu includes a large furnace capable of melting up to 450 kg of basalt at temperatures well above the basalt liquidus the lava is poured onto either a tilted bed of sand or a steel channel to produce meter long flows this experimental setup is probably the only facility that allows such large scale controlled lava flows made of natural basaltic material we document the motion of the lava using a high resolution video camera placed directly above the flows and the temperature using infrared probes and cameras after collecting the footage we analyze the images for lava deformation and compare with numerical forward models to constrain the rheological parameters and laws which best describe the flowing lava for the video analysis we employ the technique of differential optical flow which uses the time variations of the spatial gradients of the image intensity to estimate velocity between consecutive frames an important benefit for using optical flow compared with other velocimetry methods is that it outputs a spatially coherent flow field rather than point measurements we demonstrate that the optical flow results agree with other measures of the flow velocity and estimate the error due to noise and time variability to be under 30 of the measured velocity our forward models are calculated by solving the stokes flow equations on an unstructured finite element mesh defined using the geometry of the observed flow itself we explore a range of rheological parameters including the lava s apparent viscosity the power law exponent m and the thermal activation energy our measurements of apparent viscosity agree well with predictions of the composition based shaw 1972 and grd model giordano russell and dingwell 2008 we find that for the high temperature portion of the flow a weakly shear thinning or newtonian rheology m 0 7 with an effective activation energy of b 5500 j gives the best fit to the data our methodology is the first time that high resolution optical flow analysis of flowing lava is combined with numerical flow models to constrain rheology the methodology we present here can be used in field conditions to obtain in situ information on lava rheology without physical interaction with the flow and without being limited to point wise low strain rate local measurements currently available through the use of rotational viscometers in the field

measurements of the cooling at the base of pahoehoe flows temperature measurements were made in august and october of 1994 at the base of small active pahoehoe flow lobes on kilauea volcano hawai i surprisingly after about 2 minutes of initial rapid cooling the basal temperatures increased significantly before resuming a slower cooling trend the recorded temperatures are also warmer than those predicted by simple conductive cooling models preliminary calculations suggest that these observations can be explained by the insulating effect of microfractures in the underlying flow and the kinetics of crystallization the initial cooling may be rapid enough to super cool the lava such that the onset of crystallization is delayed when crystallization does begin it is initially rapid releasing sufficient latent heat to re heat the lava as the system equilibrates the flow resumes a slow cooling

cretaceous volcanic reservoirs and their exploration in the songliao basin northeast china major reservoirs in the songliao basin sb are composed of volcanic rocks below 3000 m 9843 ft of buried depth gas accumulations are mostly found in the buried volcanic highs which in general correspond to paleovolcanic centers porosity in the volcanic rocks depends on both primary and secondary processes the best porosity is preferentially developed in a proximal facies near the central part of each volcanic edifice porosity and permeability decrease with depth of burial for both volcanic and nonvolcanic sections but their porosity depth trends differ lava and welded ignimbrite slowly lose porosity with burial depth because they solidified by cooling and their groundmasses are poor in quartz and calcite precipitation thus preserving porous space in contrast the associated sandstone conglomerate tuff and tuffite are more sensitive to overburden pressure suffering more intense compaction and cementation as a result porosity and permeability of lava and ignimbrite exceed that of the other rocks and thus they are the best reservoir rocks below burial depths of ca 3000 m 9843 ft in the sb the paleovolcanic domes are rich in both lava rocks and fractures of diverse origin and the topographic highs provide favorable locations for gas migration and accumulation

palaeomagnetic determination of emplacement temperature of vesuvius ad 79 pyroclastic deposits the city of herculaneum was hurried under 20 m of pyroclastic deposits during the ad 79 eruption of vesuvius whose crater is only 7 km to the east these deposits have been interpreted as the deposits of mudflows1 or hot pyroclastic flows2 5 maury s studies6 of incinerated wood in herculaneum demonstrate heating to at least 400 c we have studied the variation of remanent magnetism with temperature for specimens taken from the deposits including specimens of the matrix material and of embedded lithic fragments we conclude that the temperature of the deposit at emplacement is unlikely to have been greater than 400 c which further supports the interpretation of the pyroclastic deposits at herculaneum as largely ignimbrites hot pyroclastic flow deposits

the initial cooling of pahoehoe flow lobes in this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows the accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation this model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data we find that the only significant processes are a heat loss by thermal radiation b heat loss by atmospheric convection c heat transport within the flow by conduction with temperature and porosity dependent thermal properties and d the release of latent heat during crystallization the numerical model is better able to reproduce field measurements made in hawai i between 1989 and 1993 than other published thermal models by adjusting one parameter at a time the effect of each of the input parameters on the cooling rate was determined we show that a the surfaces of porous flows cool more quickly than the surfaces of dense flows b the surface cooling is very sensitive to the efficiency of atmospheric convective cooling and c changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures these model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes jones 1992 1993 the predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification and the model provides a tool to begin studies of the dynamic crystallization of real lavas future versions of the model can also be made applicable to extraterrestrial submarine silicic and pyroclastic flows

thermal history of volcanic debris flow deposits on the eastern flanks of mt taranaki new zealand implications for future hazards abstract we use palaeomagnetic methods to decipher the thermal histories of a succession of massive to weakly stratified debris flow deposits ngatoro and te popo formations of late holocene age located on the eastern lower flanks of mt taranaki egmont volcano western north island new zealand results from two sites vickers quarry and surrey road quarry both c 9 6 km from the present day summit enable us to distinguish between clast incorporation temperatures of about 400 c and emplacement temperatures between 150 and 200 c consistent with observation of superficial charring and desiccation of outer podocarp hardwood tree trunks at vickers quarry analysis of palaeomagnetic directions and lithofacies architecture suggest that these deposits were likely initiated as a closely spaced succession of block and ash flows bafs that rapidly cooled as they descended the volcano flanks radiocarbon chronology and the widespread occurrence of a palaeosol between the products of the preceding inglewood eruptive phase c 3 4 cal ka b p and the overlying ngatoro formation suggest that these two events are temporally unrelated certainly there is no field evidence of contemporaneous explosive volcanic activity that might be related to the emplacement of ngatoro formation however we suggest that these low temperature deposits might either relate to collapse of a small emergent lava dome or a cooling dome remnant possibly emplaced in the aftermath of the inglewood eruption how collapse was initiated remains uncertain the remnant dome may have been rendered unstable by volcano tectonic or tectonic seismic events and or by adverse meteorological events nevertheless this study demonstrates that edifice collapse events generating potentially hazardous debris flows can occur independent of specific eruptive activity

observations on basaltic lava streams in tubes from kilauea volcano island of hawai i from 1986 to 1997 the pu u o o kupaianaha eruption of kilauea produced a vast pahoehoe flow field fed by lava tubes that extended 10 12 km from vents on the volcano s east rift zone to the ocean within a kilometer of the vent tubes were as much as 20 m high and 10 25 m wide on steep slopes 4 10 a little farther away from the vent some tubes formed by roofing over of lava channels lava streams were typically 1 2 m deep flowing within a tube that here was typically 5 m high and 3 m wide on the coastal plain 1 tubes within inflated sheet flows were completely filled typically 1 2 m high and several tens of meters wide tubes develop as a flow s crust grows on the top bottom and sides of the tubes restricting the size of the fluid core the tubes start out with nearly elliptical cross sectional shapes many times wider than high broad flat sheet flows evolve into elongate tumuli with an axial crack as the flanks of the original flow were progressively buried by breakouts temperature measurements and the presence of stalactites in active tubes confirmed that the tube walls were above the solidus and subject to melting sometimes the tubes began downcutting progressive downcutting was frequently observed through skylights a rate of 10 cm d was measured at one skylight for nearly 2 months

insights on lava ice snow interactions from large scale basaltic melt experiments quantitative measurements of interactions between lava and ice snow are critical for improving our knowledge of glaciovolcanic hazards and our ability to use glaciovolcanic deposits for paleoclimate reconstructions however such measurements are rare because the eruptions tend to be dangerous and not easily accessible to address these difficulties we conducted a series of pilot experiments designed to allow close observation measurements and textural documentation of interactions between basaltic melt and ice here we report the results of the first experiments which comprised controlled pours of as much as 300 kg of basaltic melt on top of ice our experiments provide new insights on 1 estimates for rates of heat transfer through boundary layers and for ice melting 2 controls on rates of lava advance over ice snow 3 formation of lava bubbles i e limu o pele by steam from vaporization of underlying ice or water and 4 the role of within ice discontinuities to facilitate lava migration beneath and within ice the results of our experiments confirm field observations about the rates at which lava can melt snow ice the efficacy with which a boundary layer can slow melting rates and morphologies and textures indicative of direct lava ice interaction they also demonstrate that ingestion of external water by lava can create surface bubbles i e limu and large gas cavities we propose that boundary layer steam can slow heat transfer from lava to ice and present evidence for rapid isotopic exchange between water vapor and melt we also suggest new criteria for identifying ice contact features in terrestrial and martian lava flows

thermally altered palagonitic tephra a spectral and process analog to the soil and dust of mars we studied six palagonitic soil samples ph 1 through ph 6 which were collected at 30 cm intervals from a lava slab on mauna kea hawaii the samples represent an alteration sequence caused by heating during emplacement of molten lava over a preexisting tephra cone they are both spectral and weathering alteration process analogs to the martian surface techniques employed included visible and near ir spectroscopy mossbauer spectroscopy and magnetic analysis the two samples collected from beyond 90 cm from the slab ph 5 and ph 6 did not see the transient heating event and are composed of coarse grained glassy basaltic hawaiitic particles some of which have been moderately palagonitized since formation of the cone in the late pleistocene the four samples closest to the slab ph 1 through ph 4 have been strongly altered in response to heating during its emplacement their iron oxide mineralogy is dominated by nanophase ferric oxide the sample adjacent to the slab ph 1 which would have seen the highest temperatures has a factor of 3 less h2o and contains crystalline hematite and magnetite in addition to nanophase ferric oxide lesser amounts of magnetite but not hematite are present in samples 30 cm ph 2 and 60 cm ph 3 from the slab the reflectivity spectra of samples ph 2 through ph 4 are similar to spectra of palagonites reported by other workers to be good mars visible to near ir spectral analogs the reflectivity spectrum of ph 1 is an even better spectral analog to mars in that it exhibits absorption features indicative of both nanophase and crystalline ferric oxides similar to several new martian telescopic data sets our sampling site may also be a process analog for mars in that heating episodes by volcanism and or impact cratering could produce crystalline ferric oxides from poorly crystalline palagonitic material thus localized thermal alteration events may provide a volumetrically important mechanism for the palagonitization of basaltic glass and the production of crystalline ferric oxides on mars

a new scenario for the last magmatic eruption of la soufriere of guadeloupe lesser antilles in 1530 a d evidence from stratigraphy radiocarbon dating and magmatic evolution of erupted products la soufriere of guadeloupe is a dangerous volcano characterized over the last decade by moderate seismic and fumarolic unrest in the last 15 000 years it has experienced phreatic and magmatic eruptions and unusually numerous flank collapse events sometimes associated with a magmatic eruption we propose a new age of 1530 a d and a new eruptive scenario for the last magmatic eruption on the basis of a novel statistical analysis of radiocarbon age dates and new field and geochemical data this eruption is the only magmatic eruption likely to have occurred in guadeloupe during the last 1400 years the eruption mainly involved an andesitic magma which in the first phase of the eruption partially mixed with a slightly more differentiated magma stored in a small and shallow magma chamber ascent of magma to the surface generated a partial collapse of the hydrothermally altered edifice that increased the magma discharge and led to a sub plinian phase with scoria fallout and column collapse pyroclastic flows followed by near vent pyroclastic scoria fountains the eruption ended with growth of a lava dome our revised interpretation of the last magmatic eruption of la soufriere constitutes the most likely key to a future magmatic eruption scenario for this volcano which displays strong evidence of unrest since 1992

observations of the effect of wind on the cooling of active lava flows 1 we present the first direct observations of the cooling of active lava flows by the wind we confirm that atmospheric convective cooling processes i e the wind dominate heat loss over the lifetime of a typical pahoehoe lava flow in fact the heat extracted by convection is greater than predicted especially at wind speeds less than 5 m s and surface temperatures less than 400 c we currently estimate that the atmospheric heat transfer coefficient is about 45 50 w m 2 k 1 for a 10 m s wind and a surface temperature 500 c further field experiments and theoretical studies should expand these results to a broader range of surface temperatures and wind speeds

arc parallel extension and localization of volcanic complexes in guadeloupe lesser antilles 1 subduction of atlantic seafloor under the caribbean plate causes shallow earthquakes within the lesser antilles volcanic arc such earthquakes above the subduction interface show strike slip or normal fault plane solutions the latter with e w striking nodal planes to better assess seismic hazard and the coupling between volcanism and tectonics we investigated faulting related to overriding plate deformation in the guadeloupe archipelago using aerial photographs satellite spot images and topographic maps 1 25000 scale we mapped active and middle to late pleistocene fissures and normal fault systems that cut the uplifted coral platforms grande terre and marie galante and the volcanic rocks of basse terre the available marine geophysical data show that the faults extend offshore to bound submarine rifts the e w striking 1500 m deep v shaped marie galante rift separates the two islands of marie galante and grande terre normal faults in the north of grande terre appear to mark the similarly v shaped western termination of the 5000 m deep n 50e to n130 e striking desirade graben three shallow m 5 5 earthquakes 6 may 1851 29 april 1897 3 august 1992 appear to have ruptured segments of the marie galante rift boundary faults the young la grande decouverte volcanic complex of basse terre including the 1440 a d soufriere dome lies within the western termination of the marie galante rift the ancient volcanic shoulders of the rift buttress the active dome to the north and south which may explain why major prehistoric sector collapses and pyroclastic avalanches have been directed southwestward into the caribbean sea or southeastward into the atlantic ocean the marie galante rift is typical of other troughs transverse to the northeastern edge of the caribbean plate we interpret such troughs which are roughly orthogonal to the arc to result from slip partitioning and extension perpendicular to plate convergence that they disappear southward implies that they result from interaction between the caribbean and north american plates

growth strategies of the tabulate coral favosites bohemicus on unstable soft substrates an example from the hamar laghdad lower devonian anti atlas morocco abstract coralla of the tabulate coral favosites bohemicus coming from the famous kess kess mud mound locality of the hamar laghdad se morocco area have been studied with respect to their growth patterns and colony development the emsian kess kess mounds developed in a relatively deep water low energy environment below fair weather wave base after the mound growth ceased the slopes of the mounds were covered by soft muddy sediment and colonised by tabulate corals the morphological characteristics of f bohemicus coralla analysed in the present study document various responses of the coral colonies to sediment creeping on the steeply inclined slopes the coralla are massive and display a strong variability in shape and size most of the specimens are however of spherical and sub spherical shape the striking feature of the majority of the colonies is that they are either deflected and tilted in one direction or display indications of being continuously overturned both features reflecting changes in growth direction of the corals the tilted and curved direction of growth was likely caused by the slow creeping of the sediment along with which the colonies were being slowly moved down the slope the most important factor that controlled the intensity of the mass movements was presumably the slope inclination which varied among both different mounds and different slopes of individual mounds since corals affected differently by mass movements of variable strength attained various sizes and shapes morphological analyses of f bohemicus provide clues on the sediment characteristics as well as type and frequency of mass movements in the cover of the kess kess mud mounds enabling valuable insights into the initial stages of their burial