link between major flank slip and 2002 2003 eruption at mt etna italy 1 the 2002 2003 etna eruption is studied through earthquake distributions and surface fracturing in september 2002 earthquake induced surface rupture sinistral offset 0 48 m occurred along the e w striking pernicana fault pf on the ne flank in late october a flank eruption accompanied further 0 77 m surface rupturing reaching a total sinistral offset of 1 25 m the deformation then propagated for 18 km eastwards to the coastline sinistral offset 0 03 m and southwards along the nw se striking timpe dextral offset 0 04 m and later trecastagni faults dextral offset 0 035 m seismicity 4 km bsl on the e flank accompanied surface fracturing fault plane solutions indicate an overall ese wnw extension direction consistent with ese slip of the e flank also revealed by ground fractures a three stage model of flank slip is proposed inception september earthquake climax accelerated slip and eruption and propagation e and s migration of the deformation

the role of viscous magma mush spreading in volcanic flank motion at kīlauea volcano hawai i 1 multiple mechanisms have been suggested to explain seaward motion of the south flank of k lauea volcano hawai i the consistency of flank motion during both waxing and waning magmatic activity at k lauea suggests that a continuously acting force like gravity body force plays a substantial role using finite element models we test whether gravity is the principal driver of long term motion of k lauea s flank we compare our model results to geodetic data from global positioning system and interferometric synthetic aperture radar during a time period with few magmatic and tectonic events 2000 2003 when deformation of k lauea was dominated by summit subsidence and seaward motion of the south flank we find that gravity only models can reproduce the horizontal surface velocities if we incorporate a regional decollement fault and a deep low viscosity magma mush zone to obtain quasi steady state horizontal surface velocities that explain the long term seaward motion of the flank we find that an additional weak zone is needed which is an extensional rift zone above the magma mush the spreading rate in our model is mainly controlled by the magma mush viscosity while its density plays a less significant role we find that a viscosity of 2 5 1017 2 5 1019 pa s for the magma mush provides an acceptable fit to the observed horizontal surface deformation using high magma mush viscosities such as 2 5 1019 pa s the deformation rates remain more steady state over longer time scales these models explain a significant amount of the observed subsidence at k lauea s summit some of the remaining subsidence is probably a result of magma withdrawal from subsurface reservoirs

sediment pumping by tidal asymmetry in a partially mixed estuary 1 observations collected at two laterally adjacent locations are used to examine the processes driving sediment transport in the partially mixed york river estuary estimates of sediment flux are decomposed into advective and pumping components to evaluate the importance of tidal asymmetries in turbulent mixing at the instrumented location in the estuarine channel a strong asymmetry in internal mixing due to tidal straining is documented with higher values of eddy viscosity occurring during the less stratified flood tide as a result of this asymmetry more sediment is resuspended during the flood phase of the tide resulting in up estuary pumping of sediment despite a net down estuary advective flux at the instrumented location on the adjacent shoal where no pronounced tidal asymmetry in internal mixing was found both the pumping flux and advective flux were directed down estuary the down estuary pumping of sediment on the shoal appears to be driven by asymmetries in bed stress the impact of tidal asymmetries in bed stress at the channel location was negated because the amount of sediment available for resuspension was limited as a result the pumping flux was dominated by the overlying asymmetries in internal mixing the asymmetries in stratification appear to exert an important control on the vertical distribution of sediment by both impacting the eddy diffusivity as well as the fall velocity during the more turbulent flood tide the fall velocities are smaller suggesting the kolmogorov microscale is setting the upper bound on floc diameter

late quaternary slip rates on the acireale piedimonte normal faults and tectonic origin of mt etna sicily abstract mt etna is located along the east coast of sicily near the boundary between the continental crust of the hyblean plateau and the mesozoic oceanic crust of the ionian basin the main active faults near mt etna cut the base of its eastern flank forming a 30 km long system of nne and nnw trending ene chelon fault segments the acireale piedimonte system showing dip slip and oblique right lateral motion most segments are associated with shallow depth seismicity and all have late pleistocene to holocene vertical slip rates ranging between 1 and 2 mm yr typical of major active normal faults worldwide eruptive fissures arranged in nne to ne trending zones cut the highest slopes of the volcano on the footwall of the normal fault system structural analysis suggests that current motions along both the active faults and eruptive fissures are kinematically compatible and simply linked with ongoing wnw ese directed regional extension such extension characterizes at a greater scale the active tectonics of southern italy where all large shallow historical earthquakes have remained confined within a narrow normal fault belt or rift zone stretching from the northern calabrian arc to southeastern sicily the southernmost west dipping faults of that rift zone in calabria aspromonte cut across the calabro peloritan thrust belt to join the mostly east dipping acireale piedimonte faults along the western boundary of ionian oceanic lithosphere which continues southwards as the malta escarpment we thus relate magmatism at etna to dilational strain on the footwall of an east facing crustal scale normal fault at the bend where the siculo calabrian rift zone veers 60 eastwards as it begins to cross the calabrian arc leaving the east facing margin of the ionian sea to catch up with the west facing margin of the tyrrhenian sea farther north

extensional and strike slip tectonics across the monte amiata monte cetona transect northern apennines italy and seismotectonic implications abstract this paper deals with the structural evolution along a transect across the inner northern apennines monte amiata volcano geothermal area monte cetona mainly focussing on the post orogenic middle miocene quaternary structures the tectonic setting of the study area derives from the superimposition of three main faulting events the first and second events developed during the middle late miocene and early middle pliocene respectively and took place in response to extensional tectonics the third faulting event developed in a transcurrent transtensional setting during the quaternary quaternary faults mainly strike ne sw and show left lateral kinematics with a minor dip slip normal component they caused the monte amiata volcanic eruptions 300 190 ka and controlled the widespread pleistocene and present hydrothermal fluids circulation quaternary strike slip faults have been documented in the monte amiata monte cetona area for the first time in this paper correlation with the adjoining areas e g vulsini region identifies the quaternary strike slip faulting recognised in the study area as a feasible source for the seismic activity in the monte amiata region where the origin of diffuse low magnitude seismicity is still under debate and poorly understood

correlation between seismic reflectivity and rheology in extended lithosphere southern tuscany inner northern apennines italy abstract in southern tuscany inner zone of the northern apennines the lithosphere has been affected by extensional deformation since the middle miocene and is characterized by high heat flow 120 mw m 2 both local shallow and regional deep seismic reflection profiles clearly show the occurrence of a sharp reflector k horizon within the upper crust which is probably located at the top of a shear zone acting as the decollement horizon for the latest pliocene quaternary normal faults its depth varies between 3 and 6 km in geothermal areas and 9 and 12 km elsewhere borehole control in the geothermal areas shows that it occurs at a temperature of approximately 450 c the hypothesis that the k horizon represents the top of the brittle ductile transition agrees with two lines of evidence a it approximately follows the same isotherm over the whole region and b its depth coincides with rheological predictions of the brittle ductile transition for the range of high pore fluid pressures and strain rates estimated for southern tuscany it appears therefore that at least under specific conditions very high pore fluid pressures strain concentration the brittle ductile transition may have a seismic signature

the volcano tectonic evolution of concepcion nicaragua we describe the evolution of concepcion volcano by integrating regional geology eruptive activity morphology stratigraphy petrology structure and active deformation data this nicaraguan volcano is set close to the back limb of the northwest trending tertiary rivas anticline a regional structure that bounds the southwest side of lake nicaragua concepcion rises 1 600 m above a 1 km thick sequence of quaternary lacustrine mud stones there is no record of volcanism in the lake prior to concepcion in addition the only nearby volcano maderas volcano has not deposited material on concepcion because of the trade winds thus concepcion and made ras too can be considered as pristine volcanic environments unaffected by other centres a topographic rise forms an annulus 20 km in diameter around the cone the rise is created by thrust related folds at the western base where the trade winds have accumulated a thick sequence of tephra and by mud diapirs at the eastern base where only lake mudstones are present four magmatic eruptive episodes exist in the stratigraphic record the first begins with primitive low alumina basalt and subsequently evolves to dacitic compositions the following three episodes begin with high alumina basalts and evolve only to silicic andesites the occurrence of the high alumina basalt after the first episode is indicative of crystal fractionation at lower crustal depths the first episode may be associated with a compressive phase of volcano evolution in this phase the edifice load compresses substrata allowing a longer magma residence time and differentiation in a shallow reservoir possibly located at the density contrast between the lake sediments and the tertiary flysch during the next three episodes the weak sediments below the volcano started to rupture and yield under its increasing load beginning a thrusting diapiring phase of volcano evolution because of outward thrusting vertical and horizontal stresses above the chamber were reduced allowing magma to erupt more easily and to reach a lesser degree of evolution if we consider the future evolution of concepcion the differentiation in the shallow reservoir has probably generated a cumulitic complex which eventually will start to deform and spread beginning another this time plutonic spreading phase this phase which may be beginning now could allow less evolved magmas to be erupted again four components influence the phases of volcano evolution 1 the regional geology that is the boundary condition of the environment 2 the substrata rheology that controls deformation 3 the load of the volcanic edifice and 4 the magma which provides the input of mass and energy our model of volcanic evolution suggests that concepcion is a complex geologic environment the volcanic activity tectonics and hazards can only be constrained through a complete knowledge of the many components of this environment

effects of mangroves and tidal flats on suspended sediment dynamics observational and numerical study of darwin harbour australia the suspended sediment dynamics in darwin harbour australia were investigated using field measurements and numerical modeling the model suspended sediment concentration ssc agreed well with observation the root mean square error was less than 0 02 kg m 3 and the anomaly correlation coefficient greater than 0 6 model results indicate that the tide is the dominant forcing for suspended sediment transport total sediment transport was seaward in the channel and landward at the east and middle arm entrances dominated by the eulerian residual current further numerical experiments indicate that mangroves and tidal flats play key roles in redistributing suspended sediment and affecting total sediment transport by modulating the tides and the tidal asymmetry in darwin harbour if these areas were reclaimed there would be a significant transport of sediment into the inner harbor however the water in east arm would be less turbid with about 70 lower bottom ssc during spring tides the landward sediment flux at its entrance would decrease by 99 because of reduced currents in the arm due to a weakened tidal choking effect tidal pumping would then dominate sediment transport in the channel and at the entrances of east and middle arms dredging for the east arm wharf affected the ssc upstream in east arm according to the model material from dredging disposed of at a location outside the harbor will be transported back into the outer harbor generating higher ssc values there although this study is site specific the findings may be applicable to suspended sediment dynamics in other harbors and estuaries with extensive tidal flats and mangroves

propagation of strike slip faults across holocene volcano sedimentary deposits pasto colombia this study contributes to the understanding of shear failure development on the basis of macroscopic field data collected in latest pleistocene holocene pyroclastic and fluvio lacustrine deposits in the pasto valley sw colombia here there is a pervasive system of microfaults and joints right lateral strike slip microfaults strike n0658 whereas left lateral strike slip microfaults strike n1208 three main joint sets strike n n0658 and n0208 in decreasing order of frequency stress computation gives a horizontal s1 trending wn0608 and a horizontal s3 trending wn1508 consistent with earthquake focal mechanisms and stress inversion of main faults synthetic shears dominate resulting from nucleation of older cracks in the basement cropping out northeast of pasto the ne to ene striking buesaco aranda and pasto faults show evidence of latest pleistocene holocene right lateral strike slip motions the structures in the pasto valley can be interpreted as a mode iii damage zone representing the up dip propagation of the main faults across the young volcano sedimentary deposits q 2005 elsevier ltd all rights reserved

precadomian relicts in the armorican massif their age and role in the evolution of the western and central european cadomian hercynian belt abstract well dated precambrian is mostly developed in the north of the armorican massif in which area voluminous cadomian magmatism is dated at between 650 and 550 ma much older relicts occur at cap de la hague in guernsey and in the tregor and are also found in the northern continental margin of the iberian peninsula in all these occurrences whole rock systems have been opened so that the true ages cannot be determined by the rb sr whole rock isochron method four u pb zircon ages are between 1 8 and 2 ga in guernsey icart orthogneisses in tregor port beni trebeurden morguignen orthogneisses there is no evidence from strontium isotopes that these isolated and scattered relicts have a wide extension or that such ancient continental crust played an important role in magma genesis from 650 ma to 270 ma ago on the contrary the evolution of initial 87sr 86sr ratios with time shows that the observed mid and west european continental crust is probably not older than 700 ma the increase of the initial 87sr 86sr ratios of the magmas with time suggests that after its formation in cadomian times this segment of continental crust evolved virtually as a closed system and hercynian magmatism arose principally from re melting of relatively young sialic components

experimental modelling of thin skinned shortening around magmatic intrusions magmatic intrusions can trigger thin skinned compression of the adjacent sedimentary cover by three processes a gravity gliding away from the topographic dome resulting from the ascending magma b fluid push from the rear resulting from forceful intrusion then lateral spreading of the magma and c increased loading by volcanic accumulation the applicability of the first two mechanisms gravity gliding and fluid push was tested using dynamically scaled experiments model results help to elucidate the kinematics and structural evolution of thrusts and folds formed by such processes and determine which geological parameters control the deformation style the results show that the presence of a weak layer within the sedimentary overburden is essential to form thrust and fold belts around the intrusion experiments suggest that although gravity gliding can dominate the early stages of deformation most of the deformation is caused by lateral spreading of the fluid magma pushing the adjacent sedimentary rocks models also suggest that true laccoliths can form only if the sedimentary section comprises a basal low viscosity stratum comparison with natural examples allows the evaluation of the applicability of experimental results

toughness and failure of volcanic edifices abstract major volcanic edifices are of two main types stratovolcanoes composite edifices and basaltic edifices shield volcanoes these types of edifices show several remarkable differences for example while some basaltic edifices erupt very frequently many stratovolcanoes erupt very infrequently also most basaltic edifices have gentle slopes commonly 2 12 whereas stratovolcanoes have steeper slopes particularly in their uppermost parts where the slopes may reach 35 42 there have been various attempts to explain these differences but here the focus is on edifice strength or rather toughness toughness of a material is a measure of its resistance to fracture alternatively for a tough material large amounts of energy are needed to cause failure most quoted material toughness critical energy release rate values for rocks are 20 400 j m 2 for extension fractures such as dykes and 0 01 0 03 mj m 2 for shear fractures such as dip slip faults the related property of critical stress intensity or fracture toughness is for most rocks 0 5 3 mpa m 1 2 these values for material and fracture toughness refer to small essentially homogeneous laboratory rock samples here i present equations for calculating the material toughness in volcanic edifices based on the measured or estimated dimensions of associated large structures such as dykes and faults for typical dykes the calculated material toughness is 1 3 47 mj m 2 with a corresponding stress intensity of 114 690 mpa m 1 2 similarly for a 3 8 km long dip slip fault in an edifice the calculated material toughness is 2 3 mj m 2 and the corresponding stress intensity 150 mpa m 1 2 these results compare well with previous material toughness estimates for large strike slip faults and stress intensity estimates for large dykes generalising these results and using field data as well as materials science results i conclude that stratovolcanoes normally have a much higher material toughness than basaltic edifices this is primarily because of different internal structures a basaltic edifice is made of layers and contacts all of which have essentially similar mechanical properties whereas a stratovolcano is made of layers and contacts many of which have widely different properties accordingly it requires much more energy is more difficult for a fracture to propagate through a stratovolcano than through a basaltic edifice thus contrasting toughnesses may be one principal reason why these edifices differ in slope and in failure frequencies including the number of dyke fed eruptions caldera collapses and landslides

volcanic spreading forcing and feedback in geothermal reservoir development amiata volcano italia abstract we made a stratigraphic structural and morphologic study of the amiata volcano in italy we find that the edifice is dissected by intersecting grabens that accommodate the collapse of the higher sectors of the volcano in turn a number of compressive structures and diapirs exist around the margin of the volcano these structures create an angular drainage pattern with stream damming and captures and a set of lakes within and around the volcano we interpret these structures as the result of volcanic spreading of amiata on its weak substratum formed by the late triassic evaporites burano anhydrites and the middle jurassic to early cretaceous clayey chaotic complexes ligurian complex regional doming created a slope in the basement facilitating the outward flow and spreading of the ductile layers forced by the volcanic load we model the dynamics of spreading with a scaled lubrication approximation of the navier stokes equations and numerically study a set of solutions in the model we include simple functions for volcanic deposition and surface erosion that change the topography over time scaling indicates that spreading at amiata could still be active the numerical solution shows that as the central part of the edifice sinks into the weak basement diapiric structures of the underlying formations form around the base of the volcano deposition of volcanic rocks within the volcano and surface erosion away from it both enhance spreading in addition a sloping basement may constitute a trigger for spreading and formation of trains of adjacent diapirs as a feedback the hot hydrothermal fluids decrease the shear strength of the anhydrites facilitating the spreading process finally we observe that volcanic spreading has created ideal heat traps that constitute todays exploited geothermal fields at amiata normal faults generated by volcanic spreading volcanic conduits and direct contact between volcanic rocks which host an extensive fresh water aquifer and the rocks of the geothermal field constitute ideal pathways for water recharge during vapour extraction for geothermal energy production we think that volcanic spreading could maintain faults in a critically stressed state facilitating the occurrence of induced and triggered seismicity

field and modelling investigations of fresh water plume behaviour in response to infrequent high precipitation events sydney estuary australia abstract runoff from the urban environment is a major contributor of non point source contamination for many estuaries yet the ultimate fate of this stormwater within the estuary is frequently unknown in detail the relationship between catchment rainfall and estuarine response within the sydney estuary australia was investigated in the present study a verified hydrodynamic model environmental fluid dynamics computer code was utilised in concert with measured salinity data and rainfall measurements to determine the relationship between rainfall and discharge to the estuary with particular attention being paid to a significant high precipitation event a simplified rational method for calculating runoff based upon daily rainfall subcatchment area and runoff coefficients was found to replicate discharge into the estuary associated with the monitored event determining fresh water supply based upon estuary conditions is a novel technique which may assist those researching systems where field measured runoff data are not available and where minor field measured information on catchment characteristics are obtainable the study concluded that since the monitored fresh water plume broke down within the estuary contaminants associated with stormwater runoff due to high precipitation events daily rainfall 50 mm were retained within the system for a longer period than was previously recognised

mapping capable faulting hazard in a moderate seismicity high heat flow environment the tuscia province southern tuscany northern latium italy abstract this study is focused on potential evidence of capable faulting affecting southern tuscany northern latium a region of high heat flow and moderate to low seismicity here we refer to this region as tuscia the latin name for the land of the etruscans the review of the evidence for active tectonics in this area has allowed us to identify several potentially active capable faults mapped using a combination of analysis of digital terrain models with remote sensing and local geological information derived from bibliographic data and different scale maps active and capable faulting is certainly more evident in the eastern sector of tuscia chianti cetona ridge pienza amiata and bolsena caldera however even in the western tuscia e g colline metallifere and tyrrhenian coast capable faulting may be hypothesized along numerous structural elements the characterization of active faulting potential in terms of geometry slip types and rates in such a high heat flow environment beyond its usefulness in improving the assessment of fault displacement and earthquake hazard also helps to improve knowledge of the stress field and structural setting of the many geothermal fields in the area this allows new useful insights into geothermal exploitation and hazard e g induced triggered seismicity moreover this new knowledge of active tectonics and capable faults of the hinterland sector of the northern apennines may also provide useful insights into the siting processes of highly hazardous and strategic structures and more generally in land use planning and management of infrastructures especially during emergencies

the structure of composite volcanoes unravelled by analogue modelling a review abstract volcanic edifices are unstable accumulations of eruptive and intrusive products with complex internal structures a documentation of these structures facilitates the assessing of the various hazards associated with volcanoes e g flanks instabilities and eruptive events however structures are not easily assessed in the field as volcanoes are regularly covered by eruptive products and are rapidly eroded in the case of recent and active volcanoes internal structures are generally extrapolated from the external morphology of the edifice which can be documented using digital elevation models dem and geodetic data interpretation of such data greatly benefits from analogue models which are idealised representations of reality used to test the impact that various processes may have on the shape of a volcanic edifice this short review focuses on the contribution of analogue models to our comprehension of the internal structure of composite volcanic cones the other volcanic morphologies e g caldera are excluded from this review as they have distinct structure and evolution that have already been thoroughly reviewed the reviewed models were used to investigate the impact that regional faults magma injections and ductile substratum among other processes have on the internal structure and surface morphology of many volcanic edifices these models were also used to locate unstable flanks and eruption sites

crustal models of the geothermal areas of southern tuscany italy abstract geological and geophysical data gathered in the geothermal areas of southern tuscany located in the inner part of the northern apennines indicate the presence of granite intrusions the most relevant data are 1 regional asthenospheric ascent to a depth of 40 50 km 2 granitic dykes as old as 3 8 2 9 ma and a widespread contact aureole found in several deep geothermal wells 3 very high heat flow values interpreted as the result of convective circulation of hot fluids above shallow magmatic bodies 4 the presence of low density bodies inferred from low gravity values often correlated with positive heat flow anomalies 5 the occurrence of a highly reflective horizon named k in a depth range of 3 12 km in the geothermal areas as shown by seismic reflection data 6 a 30 40 km wide low velocity body below the k horizon whose existence is supported by local earthquake tomography and teleseismic studies 7 the presence of a conductive body which correlates well with the anomalous tomographic and teleseismic body as revealed by magnetotelluric surveys the goal of the paper is to test different alternative crustal models by using these data the models are 1 granite intrusion 2 geopressurized fluids below impervious layers 3 contact metamorphic aureole 4 mylonite layers at the upper lower crust transition and 5 some combination of the four the occurrence of shallow intrusive bodies still partially molten and associated with saline brines is considered the most tenable model

the influence of edifice slope and substrata on volcano spreading gravitational volcano spreading is caused by flow of weak substrata due to volcanic loading and is now a process known to affect many edifices the process produces extension in the upper edifice evidenced by graben and normal faults and compression at the base seen in strike slip faults and thrusts where spreading is identified host volcanoes have a range of fault densities variable rift and graben shapes and different degrees of structural asymmetry previous studies have suggested a link between edifice shape and structure and the proportion of brittle to ductile material in the substrata or lower edifice we study this link using refined sand cone analogue models standing on a brittle ductile sand silicone substrata two scenarios have been investigated the first mainly represents oceanic volcanoes with a ductile layer within the edifice type i where there is an outer ductile free surface the second represents most continental volcanoes that have ductile substrata type ii we apply the model results to natural examples and develop quantitative relationships between slope brittle ductile ratio fault density spreading rate and structural style displacement fields calculated from stereophotogrammetry show significant differences between different slope models we find that more faults are produced when the cone is initially steeper or when the brittle substratum is thinner however the effect of the brittle layer dominates over that of slope the strike slip movements are found to be an essential feature in the spreading mechanism and the graben are in fact transtensional features strike slip and graben faults make a conjugate flower pattern the structures produced are well organised for type ii edifices but they are poorly organised for type i models type i models represent good analogues for oceanic volcanoes that are commonly affected by large slumps bounded by an extensional zone and lack of well formed sector graben the well observed connection between oceanic volcano rifts and large landslide slumps is confirmed to be a consequence of spreading

fault propagation folds induced by gravitational failure and slumping of the central costa rica volcanic range implications for large terrestrial and martian volcanic edifices long sublinear ridges and related scarps located at the base of large volcanic structures are frequently interpreted as normal faults associated with extensional regional stress in contrast the ridges bordering the central costa rica volcanic range ccrvr are the topographic expression of hanging wall asymmetric angular anticlines overlying low angle thrust faults at the base of the range these faults formed by gravitational failure and slumping of the flanks of the range due to the weight of the volcanic edifices and were perhaps triggered by the intrusion of magma over the past 20 000 years the thrust fault underlying alajuela ridge rises from a depth of 700 m at a dip of 15 over a distance of a few kilometers it ramps up at 600 m depth on a 40 slope and terminates in the axis of the forward syncline 400 m below the surface the hanging wall of this fault has been thrusted about 200 m away from the volcanic range axis thrusting on the lower flanks of the ccrvr is compensated by extension on the range axis with formation of summit grabens shallow seismicity in the volcanic range suggests that thrusting is still active we postulate that at kilauea volcano hawaii the gravity and magma induced slumping of the southern flank on low angle thrust faults generates hanging wall anticlines similar to those observed in costa rica these anticlines are hypothesized to occur along the base of the volcano where the thrust faults ramp up toward the sea bottom ridges and scarps between 2000 and 5000 m below sea level are interpreted as the topographic expression of these folds we further suggest that the scarps of the ccrvr and kilauea are valid scaled terrestrial analogs of the perimeter scarp of the martian volcano olympus mons we suggest that the crust below olympus mons has failed under the load of the volcano triggering the radial slumping of the flanks of the volcano on basal thrusts the thrusting would have in turn formed the anticlinal ridges and scarps that surround the edifice the thrusting seems to be preferential toward the northwest and southeast and a northeast southwest rift zone seems to have developed perpendicular to the regional topographic gradient the thrust faults may extend all the way to the base of the martian crust about 40 km and they may have been active until almost the end of the volcanic activity we suggest that gravitational failure and slumping of the flanks of volcanoes is a process common to most large volcanic edifices in the ccrvr and at kilauea this slumping of the flanks is a slow intermittent process but it could evolve to rapid massive avalanching leading to catastrophic eruptions thus monitoring of uplift and displacement of the folds related to the slump tectonics could become an additional effective method for mitigating volcanic hazards

relation of thin skinned thrusting of colorado plateau strata in southwestern utah to cenozoic magmatism structural studies in upper cretaceous and eocene sedimentary rocks in the high plateaus of southwestern utah attempted to establish the cause of layer parallel shortening expressed in a regional scale arcuate pattern of thin skinned thrusts and related structures the thrusts sole into jurassic evaporites of the carmel formation tectonic transport direction verges radially from 125 to 215 stress analysis reveals a fan like pattern of the principal compressional stress sweeping southeastward to south south westward through 90 along an arc extending 35 km across the paunsaugunt plateau regional compressional structures of sevier and laramide origin are older than the thin skinned deformation and regional extensional structures of basin and range origin are younger the thrusting postdates deposition of the claron formation eocene and probably took place in the interval 30 ma to 20 ma that is coeval with the formation of the marysvale volcanic center located 40 to 60 km northwest of the thrust belt the forces that created the thrusts could have formed through a combination of processes related to the dynamics of formation of the marysvale volcanic center including gravity gliding and or compressional push related to the emplacement of batholithic intrusions and gravitational spreading and or end loading related to vertical loading of the column and the underlying evaporite decollement by the weight of the thick marysvale volcanic pile

volcano core collapse triggered by regional faulting it has been proposed recently that large scale caldera like structures may result from the viscous lateral spreading of a hydrothermal system located in the central part of volcanic edifices for this to occur an unbutressed boundary resulting in reduced lateral stresses must exist or be created not far from the hydrothermal system different ways to achieve such a weak lateral confinement may be proposed in this paper we show that regional tectonics may provide an unconfined boundary if a normal fault lowers part of the volcanic edifice a natural example is the island of nuku hiva in the marquesas archipelago french polynesia for which geological data strongly suggest that a regional fault oriented n75 e is responsible for the present day shape of the island i e an ellipse cut in the middle by a straight side along which two nested calderas are breached analogue modelling shows the mechanical consistency of the model and reveals that very low velocity faulting is needed for the formation of a caldera like structure

transtensional shear zones controlling volcanic eruptions the middle pleistocene mt amiata volcano inner northern apennines italy terra nova 00 1 10 2010 abstract the mt amiata volcano is characterized by the sw ne alignment of the eruption centres as well as other italian pleistocene volcanoes we carried out a structural and kinematic analysis in a broad stripe comprehending the eruption centres and the substratum towards ne and sw the results point out that a transtensional left lateral brittle shear zone affects the pre neogene substratum the middle pleistocene volcanic rocks and the late pleistocene travertines this transtensional structure is active since the early pliocene it controlled the location of the eruption centres through pull apart structures thus providing the deep structural channels for the uprising of magma to the surface the mt amiata volcano represents a key study area to investigate the pleistocene to present relationships between tectonics and magmatism in the tyrrhenian area

faults strengthening and seismicity induced by geothermal exploitation on a spreading volcano mt amiata italia abstract seismogenic structures such as faults play a primary role in geothermal system generation recharge and output they are also the most susceptible to release seismic energy over fluid injection extraction operations during anthropic exploitation we describe the microseismic activity recorded in 2000 2001 in the piancastagnaio geothermal field on the se flank of mt amiata volcano southern tuscany italy from our field observations we find that a relatively high percentage i e about 5 of the recorded events are of hydro fracturing origin and have a distinct waveform seismic signature when compared to the recorded events of tectonic shear fracturing origin while hydrofracturing events are mostly concentrated around the geothermal fields the spatial distribution of hypocenters shows a deepening and a density increase of the micro seismic activity from the volcanic axis toward the exploited geothermal reservoir suggesting that volcanic spreading at amiata is still active the study of different data sets from different time periods together with the knowledge from terzaghi s law that production of large quantity of pore fluid with the associated fluid pressure reduction could augment the stress normal to faults surfaces and thus their resistance to slip make us argue that the process of volcanic spreading affecting the edifice of amiata may allow augmented accumulation of stresses on faults eventually leading to the release of higher stress drops once ruptures occur the gutenberg richter magnitude frequency distribution shows that the strongest events on record have a local magnitude in the 5 5 5 m l range for 100 year recurrence time in conclusions we infer that geothermal exploitation at mt amiata should be closely monitored in order to understand how fluid injection production is responsible for the hydrofracturing seismic activity and affects stress accumulation on and rupture of faults within and in the neighborhood of the geothermal fields this understanding may allow a geothermal field management that will hopefully reduce the risk for inducing larger seismic events in the area

importance of gravitational spreading in the tectonic and volcanic evolution of mount etna the interaction between gravity and thermal effects largely determines the structural and magmatic evolution of volcanic constructs at scales spanning several orders of magnitude from small cones to the oceanic crust1 3 although gravitational spreading is a direct consequence of this interaction and a fundamental process in volcano growth it is rarely recognized as such here we describe a striking example of this process at etna volcano in italy the volcano and its clay rich substratum are slowly spreading towards the east and south driven by gravity spreading produces extensional structures in the summit region and contpressional structures at the base of the volcano eastward movement of the volcanic edifice over a stationary magma supply may be the cause of an apparent westward migration of volcanic activity as gravitational spreading seems to control the location and magnitude of shallow seismicity and flank eruptions an appreciation of its effects could become an essential element of future volcanic hazard evaluation our model proposed here for etna may also be relevant to a reinterpretation of the geological history of a number of other volcanoes

scaled experiments of volcanic spreading experiments were conducted to study the spreading of volcanic constructs volcanoes are simulated by a sand cone and the volcanic substratum is simulated by a sand layer brittle substratum overlying a silicone layer ductile substratum similarity conditions between natural volcanoes and experimental prototypes led to the definition of dimensionless numbers experiments determine values which predict whether or not spreading takes place of particular importance are the ratio between the thickness of the brittle substratum and the height of the volcano 2 and the brittle ductile ratio of the substratum 3 2 indicates that the volcano must be large enough to break the substratum before spreading occurs whereas 3 controls the style of deformation during spreading these dimensionless numbers change with time reaching values that tend toward those observed for stable configurations experimental values are compared with those from well constrained natural examples it is found that an essential requirement for volcanic spreading is the presence of a low viscosity layer within the substratum flow of the weak layer away from the excess load is responsible for the spreading the overlying edifice displays radial intersecting grabens due to concentric stretching dissected summit areas concentric zones of thrusts and folds form in the substratum around the edifice and diapirs of the ductile substratum rise within the fault zones

tertiary extensional tectonics in tuscany northern apennines italy abstract two extensional events have been recognized in the tertiary evolution of tuscany the first event occurred in the period between the late oligocene and late tortonian and caused a stretching of 120 or greater the second event occurred between the late tortonian and quaternary periods and caused a stretching not greater than 10 the first event is characterized by the exhumation of middle crust rocks and therefore by the development of core complexes the most significant structures of the first event are low angle normal faults which characterize the upper plate of the core complexes and ductile shear zones which characterize the lower plate the low angle normal faults tend to die out in the late triassic evaporite level which constitutes the main detachment of the core complexes the main structures of the second extensional event are high angle normal faults which dissect all the previous tectonic features these faults border tectonic depressions which were the site of clastic sedimentation from late tortonian to quaternary time these normal faults may tend to flatten in a seismic lozenge shaped band explained as an active extensional shear zone which is located at the brittle ductile boundary a similar explanation is given for the detachment located in the late triassic evaporite level during the first extensional event while the first extensional event is in the framework of the northern apennine post collisional evolution the second extensional event because it affects an already stretched crust could be attributed to the southern tyrrhenian opening which began during late tortonian

the managua graben and las sierras masaya volcanic complex nicaragua pull apart localization by an intrusive complex results from analogue modeling abstract there is a well documented association between pull apart basins in strike slip zones and large volcanic caldera complexes las sierras masaya volcanic complex nicaragua is a large basaltic lava and ignimbrite shield with nested calderas the widest caldera is partly underlain by a large and dense intrusive complex evidenced by a positive gravity anomaly the las sierras caldera relating to this cumulate complex is less than 30 000 years old and is probably still hot and ductile the inner masaya caldera hosts an active magmatic system the volcanic complex is in a dextral transtensional tectonic context of the nicaraguan depression the highly active managua graben is on the northern part of the volcano we speculate that the graben and volcano are linked tectonically with the graben initiating in response of a regional stress field modified around the dense ductile intrusive complex previous field work and reappraisal of structures with digital elevation model morphological analysis show that the volcano is surrounded by a rhombic fault pattern that may form a nascent pull apart basin we have done scaled analogue models to test the effect of intrusion density and rheology anomalies on strike slip fault geometries the models show that intrusion density variations alone do not significantly change fault patterns in contrast ductile rocks silicone in the models as analogue for hot mafic intrusive rocks markedly alter strike slip fault patterns in transtension the presence of a ductile intrusion causes the formation of a pull apart while in pure strike slip or transpression uplift and thrusting is generated pull apart and uplift structures are rhomb shaped even when the ductile inclusion is circular we conclude that a pull apart is developing at las sierras masaya volcanic complex in response to the transtensive regional deformation regime and the dense ductile intrusive complex we suggest that the volcano and graben are one dynamic system and should be monitored as one entity

quantifying the contributions of tidal straining and gravitational circulation to residual circulation in periodically stratified tidal estuaries abstract this numerical modeling study quantifies for the first time the contribution of various processes to estuarine circulation in periodically stratified tidal flow under the impact of a constant horizontal buoyancy gradient the one dimensional water column equations with periodic forcing are first cast into nondimensional form resulting in a multidimensional parameter space spanned by the modified inverse strouhal number and the modified horizontal richardson number as well as relative wind speed and wind direction and the residual runoff the along tide momentum equation is then solved for the tidal mean velocity profile in such a way that it is equated to the sum of the contributions of tidal straining resulting from the temporal correlation between eddy viscosity and vertical shear gravitational circulation resulting from the depth varying forcing by a constant horizontal buoyancy gradient wind straining and depth mean residual flow resulting from net freshwater runoff this definitio

extension and compression in the northern apennines italy hinterland evidence from the late miocene pliocene siena radicofani basin and relations with basement structures 1 the northern apennines na hinterland area is characterized by a complex neogene quaternary tectonics where both crustal extension associated with the tyrrhenian basin opening and crustal shortening in the onshore area took part in the deformation analysis of synorogenic deposits preserved in the nnw trending siena radicofani basin srb extending along a large part of the na hinterland documents the evolution of deformation of this sector during the last 9 ma information from subsurface geology deep seismic lines commercial seismic lines and deep wells surface geology mapping and structural analysis and from analogue modeling was integrated and used to infer the tectono sedimentary history of the srb and its relation with structures in the substratum as well as the possible implications for the evolution of the na hinterland the results we obtain indicate that the srb and the adjoining hinterland basins were bounded by thrust anticlines controlling basin development and deformation seismic lines across the srb display various examples of compressional structures affecting the basin fill and the substratum such as thrust anticlines and reverse faults notably these basin scale structures exhibit a good correlation with those observed in the field and are consistent with the kinematics of the outcrop scale compressional structures the thrust anticlines bounding the basins are often cored by triassic evaporites burano formation suggesting that this weak layer decoupling the sedimentary cover from the underlying crystalline basement controlled their evolution in this circumstance three series of scaled brittle ductile physical models have been used to investigate the development of a basement cover system with a decollement ductile layer at the base of the sedimentary cover these models simulate the evolution of the northern apennines hinterland where the basement is involved in the thrusting and the sedimentary cover is shortened above a basal ductile layer given by the burano formation longitudinal models cross sections display similar deformation patterns to those observed in the na hinterland such as characteristic wavelength of both basement and cover structures as well as detachment and fault propagation folding in the cover extensional tectonics is instead found to control sedimentation in the southern part of the srb at 8 ma or representing recent deformation the older extensional event is here related to the forelandward propagation of tyrrhenian related extension that could reactivate suitably oriented basement thrusts transfer zones produced a differential propagation of extension such that along strike sectors of the hinterland were eventually deformed by different stress fields analysis of the srb and of other adjoining basins reveals that the na hinterland experienced alternated periods of forward and backward migration of the compression extension transition in our interpretation the competition between extension and compression in the hinterland is related to the nnw directed africa pelagian indentation responsible for the lateral extrusion of the na and the contemporaneous opening of the tyrrhenian basin in the inner zone increased marginal loading at the foreland promoting reactivation of hinterland thrusts may have influenced this process as well

volcanic spreading and lateral variations in the structure of olympus mons mars the olympus mons volcano on mars is notable not only for its immense height and width but also for substantial asymmetries in its structure the gently sloped northwest flank extends to a much greater distance from the central caldera complex than the more steeply sloped southeast flank furthermore the northwest flank exhibits lower flank extensional faults whereas the southeast shows upper flank compressional terraces and lower flank upthrust blocks however both the northwest and southeast flanks exhibit characteristic concave upward profiles and steep bounding scarps in contrast to other sectors the nw se asymmetries are aligned with the regional slope from the tharsis rise but an understanding of the underlying causes has remained elusive we use particle dynamics models of growing spreading volcanoes to demonstrate that these flank structures could reflect the properties of the basement materials underlying olympus mons we find that basal slopes alone are insufficient to produce the observed concave upward slopes and asymmetries in flank extent and deformation style that are observed at olympus mons instead lateral variations in basal friction are required these variations are most likely related to the presence of sediments transported and preferentially accumulated downslope from the tharsis rise such sediments likely correspond to ancient phyllosilicates clays recently discovered by the mars express mission

regional stress influence on the opening direction of crater amphitheaters in southeast asian volcanoes abstract holocene volcanoes in the philippines and indonesia were studied to determine the possible relationship between the regional maximum horizontal stress hmax and the opening direction of volcanic amphitheatre craters the study was conducted using publicly available shuttle radar topographic mission srtm images and the world stress map wsm the results corroborate findings in similar research on japanese and indonesian volcanoes indicating that opening of craters occur at an acute angle relative to the hmax direction further investigation of volcanoes in southwest and southeast luzon philippines regions where fault structures and their kinematics are better constrained reveal a promising tectonic stress related rationale for crater opening direction several volcanoes in these regions of the philippines appear to have amphitheatre craters open in the direction related to the fault underlying the volcano these observations are consistent with those derived from analogue models of volcanic cones deformed by basal strike slip faulting these findings can be useful in advancing our understanding of volcanic flank failure and for hazards preparedness against such catastrophic events

tide induced sediment resuspension and the bottom boundary layer in an idealized estuary with a muddy bed abstract sediment transport and bottom boundary layer bbl in an idealized estuary with a muddy bed were studied by numerical simulations the focus was placed on description and prediction of the dynamics of nepheloid layer a fluid mud layer developed in the estuary because of the coupling effect of the seawater and resuspended sediment concentration the princeton ocean model was coupled to a sediment transport model to conduct the numerical experiments a semidiurnal tide with a spring neap cycle was used to force the model at the estuary entrance a stability function was introduced to the bottom drag coefficient cd for a slip bottom boundary condition in order to consider the effects of sediment induced stratification when the seawater density is not affected by the resuspended sediments spring tides resuspend sediments to the sea surface near the estuary entrance where the bottom stress is larger than the critical stress value the sediment distribution in the bbl near the entrance is dominantl

dynamic basis of volcanic spreading the established models of the structure and dynamics of a typical hawaiian volcano lead inevitably to a paradox finite element viscoelastic calculations using tecton melosh and raefsky 1980 1981 predict that a compressional stress field should characterize their upper flanks instead extension is observed the paradox is solved by postulating that volcanic evolution is determined by feedback processes related to growth and spreading of the volcanic edifice many examples of the process of spreading are documented in the geologic literature on volcanoes of a very broad size range and very different geologic settings the process is similar across many orders of magnitude in size the deformation of the substratum related to magma intrusion during lava dome building events is at the lower end of the scale the spreading of seafloor at oceanic ridges is at the higher end of the scale volcanoes may evolve from small constructs into huge shield volcanoes and perhaps into ocean plates key elements for volcanic spreading are 1 the existence of a weak basal layer and 2 a sufficiently high mass and magma influx to drive the process as the mass of a volcano grows it passes through five phases which may overlap repeat or be omitted building compressing thrusting intruding and spreading during the building phase the mass of a volcano does not significantly affect the stress field of the substratum primitive magmas are likely to be erupted as the mass increases the volcano subsides and becomes characterized by a compressional stress field which inhibits any further intrusion of magma into the volcanic edifice magma may differentiate in the crust allowing for large caldera forming eruptions to occur in the next phase thrusting begins on a decollement usually located at the foot of the edifice while the stress field on the upper slopes of the volcano remains compressional the stress at the base close to the center becomes extensional allowing the magma to intrude and differentiate at the base of the edifice a basal intrusive complex begins to grow explosive eruptions may be expected finally spreading of this complex creates an extensional stress field on the upper flanks of the volcano confining compression to the lower slopes of the edifice the extension allows primitive magma to erupt again at the summit the process of spreading seems to have a fundamental influence on the structural and magmatic evolution of volcanoes at every scale this process results from coupling and feedback between the gravitational and thermal fields thus studying this process may improve our understanding of the relation between structural dynamics and magma evolution and of the origin and evolution of volcanic seismicity and eruptions

the effect of volcanic constructs on rift fault patterns volcanoes in rift situations often show distinctive hour glass fault patterns with increased fault throw as the volcano is approached we present analogue models that show that this is caused by an interaction of the regional stress field with that set up by the volcano mass for faults to be reorientated there must be a ductile layer below the volcano this can be hot crust at mid ocean ridges continental rifts or weak sedimentary strata increased volcano size or mass and lower brittle ductile ratios lead to increased fault curvature whereas an increased regional extension rate decreases the effect volcanoes on one side of a rift may capture it forming the axis of a new rift with curved or en echelon zones on either side by concentrating extension magma is more easily erupted so volcanoes may erupt more magma of less evolved composition a positive feedback between increased extension and magma eruption rate will lead to rift narrowing which can favor the formation of oceanic crust

shale diapirism in the quaternary tectonic evolution of the northern apennine bologna italy 1 we use morphologic stratigraphic and structural data to identify a set of diapirs just southward uphill of the northern margin of the northern apennine range the diapirs consist mainly of ligurid chaotic shaley units that reach a maximum thickness of over 3 km we also reconstruct marine sedimentation abrasion surfaces that record a 1 cm a differential uplift induced by diapirism on the basis of this data we use the lubrication approximation of the navier stokes equations and analogue experiments to show that thrusting of the epiligurid units can be generated by diapirism of the underlying ligurid units in addition to regional compression owing to a gravity component parallel to the strata the structures formed by diapirism are similar to those generated by compressive tectonics differing in that thrusting is lubricated by diapiric rise using the analogue experiments we show that deformation begins with folding eventually evolving to thrusting and we derive an empirical relation to infer the time remaining to the end of deformation in our area diapiric deformation is still in the folding regime but it should eventually evolve to the thrusting regime and terminate in about 105 a we suggest that the whole northeastern slope of the northern apennine is controlled by diapiric tectonics our interpretation contrasts with the more traditional one which views regional tectonic compression as the only responsible for the structures observed in the field since our model is based on first principles it could be applied to other areas with similar geology and topography

hybrid character and pre eruptive events of mt amiata volcano italy inferred from geochronological petro geochemical and isotopic data abstract a new geochronological and geochemical study was carried out to better constrain the petrogenesis and eruptive history of monte amiata a large pleistocene trachydacitic volcano of southern tuscany previous studies suggested a magma mixing origin between calc alkaline silicic melts from the tuscan magmatic province tmp and potassic mafic melts like those found in the roman magmatic province rmp two eruptive episodes the first at ca 300 kyr the second at ca 200 kyr were distinguished from the few available ages however both the involvement of a rmp like melt as mafic end member and the timing of volcanic activity remained to be ascertained the k ar ages obtained on plagioclase sanidine and glass separated from mt amiata volcanic rocks demonstrate the sanidine is the most suitable phase for k ar dating sanidine yields ages of 304 293 kyr for the basal trachydacitic unit btc 298 280 kyr in the domes unit dlc and unexpected older ages of 312 308 kyr for the more mafic summit lava unit oll a careful re examination of the literature ages together with those obtained in this study shows that they tend to a common age of ca 300 kyr whatever the volcanic unit we interpret this as a reset of the k ar chronometer in response to a consequent recharge of the silicic magma reservoir by hot mafic melts this recharge most probably triggered the first volcanic eruption of mt amiata magmas in our model we suppose an initially chemically stratified magma chamber the input of deep hot mafic melts reset the crystals clock and probably allowed the eruption of the huge amount of trachydacitic crystal mush we propose that the controversial btc unit could have emplaced during a non explosive eruption if we consider either pre eruption passive degassing or extrusion of the trachydacites as magmatic foam first pb isotopic data of mafic enclaves from the trachydacitic units together with major and trace elements and new sr and nd data support the magma mixing as the dominant process at the origin of the mt amiata volcanic rocks the similar lile hfse ratios evidenced in this contribution between the magmatic enclaves of mt amiata and rmp volcanic rocks together with their comparable sr nd and pb isotopic compositions definitively argue for the involvement of a rmp like melt in the mixing the mt amiata is thus indisputably a hybrid volcano between tmp and rmp in terms of petrogenesis and ages

lateral variability of sediment transport in the delaware estuary lateral processes contribute significantly to circulation and material transport in estuaries the mechanisms controlling transport may vary spatially such that shallow and deep regions of an estuary contribute differently to the total transport an observational study was conducted to explore the importance of lateral variability in sediment transport mechanisms in the delaware estuary seven moorings were deployed across the channel in the region of the estuarine turbidity maximum etm zone from april to august 2011 time series of along channel sediment transport reveal a consistent pattern of sediment export across the entire estuary during periods of high river discharge followed by a transition to import within the channel and export on the flanks during low river flow there is a persistent divergence of across channel sediment fluxes on the delaware side where sediment from the flank is transported toward both the channel and wetland coast decomposition of the fluxes highlight that across channel sediment transport is driven by mean lateral circulation whereas along channel transport is driven primarily by mean advection with tidal pumping contributing to about 30 of total transport the spatial and temporal variability of mean advection and tidal pumping were generally complementary with both contributing to the observed sediment transport pathways tidal pumping linked to tidal asymmetries in stratification and sediment resuspension was shown to drive both ebb driven export and flood driven import depending on the tidal variability of stratification the spatiotemporal patterns of sediment transport highlight the three dimensional structure of the etm and shed light on the variability of sediment transport mechanisms

suspended sediment transport in the deepwater navigation channel yangtze river estuary china in the dry season 2009 2 numerical simulations 1 a three dimensional wave current sediment coupled numerical model with wetting and drying process is developed to understand hydrodynamics and sediment transport dynamics in the deepwater navigation channel dnc the north passage of the yangtze river estuary yre china the model results are in good agreement with observed data and statistics show good model skill scores and correlation coefficients the model well reproduces the spring neap variation between a well mixed estuary and a highly stratified estuary model results indicate that the estuarine gravitational circulation plays the most important role in the estuarine turbidity maximum etm formation in the dnc the upstream nonlocal sediment intrusion through the spillover mechanism is a major source of sediment trapping in the north passage after the morphological changes numerical studies are conducted to show scenarios in the yre under the effects of different forcings river discharges waves and winds between these study cases surface wave breaking relieves the sediment trapping and bottom wave current interaction aggravates the bed erosion and elevates the ssc in the etm the former and the latter have the least and largest influence on the suspended sediment transport in the dnc the wind effects have a greater influence on sediment trapping than the river discharges and the steady northwesterly wind condition favors the siltation in the dnc most the significance of density driven turbidity current is also assessed which can enhance the saline water intrusion and suppress the turbulent mixing in the bottom boundary layer

styles of volcano induced deformation numerical models of substratum flexure spreading and extrusion the gravitational deformation of volcanoes is largely controlled by ductile layers of substrata using numerical finite element modelling we investigate the role of ductile layer thickness and viscosity on such deformation to characterise the deformation we introduce two dimensionless ratios a volcano radius ductile layer thickness and b viscosity of ductile substratum failure strength of volcano we find that the volcanic edifice spreads laterally when underlain by thin ductile layers a 1 while thicker ductile layers lead to inward flexure a 1 the deformation style is related to the switch from predominantly horizontal to vertical flow in the ductile layer with increasing thickness increasing a structures produced by lateral spreading include concentric thrust belts around the volcano base and radial normal faulting in the cone itself in contrast flexure on thick ductile substrata leads to concentric normal faults around the base and compression in the cone in addition we show that lower viscosities in the ductile layer low b lead to faster rates of movement and also affect the deformation style considering a thin ductile layer if viscosity is high compared to the failure strength of the volcano high b then deformation is coupled and spreading is produced however if the viscosity is low low b substratum is effectively decoupled from the volcano and extrudes from underneath it in this latter case evidence is likely to be found for basement compression but corresponding spreading features in the volcano will be absent as the cone is subject to a compressive stress regime similar to that produced by flexure at volcanoes where basement extrusion is operating high volcano stresses and outward substratum movement may combine to produce catastrophic sector collapse an analysis of deformation features at a volcano can provide information about the type of basement below it a useful tool for remote sensing and planetary geology also knowledge of substratum geology can be used to predict styles of deformation operating at volcanoes where features have not yet become well developed or are obscured

the structure of the monte amiata volcano geothermal area northern apennines italy neogene quaternary compression versus extension the tectonic evolution of the mt amiata volcano geothermal area is under discussion some authors state that this region as well as the hinterland of the northern apennines were affected by compression from the cretaceous to the quaternary in contrast most authors believe that extension drove the tectonic evolution of the northern apennines from the early miocene to the quaternary field data seismic analyses and borehole logs have been integrated in order to better define the structural features of the continental crust in the mt amiata geothermal area in this paper i propose the hypothesis that the structure of the crust in the mt amiata volcano geothermal area derives from two main geological processes 1 contractional tectonics related to the stacking of the northern apennines cretaceous early miocene 2 subsequent extensional collapse of the hinterland of the mountain chain and related opening of the northern tyrrhenian sea early miocene quaternary compressional and extensional structures characterise the mt amiata region although extensional structures dominate its geological framework in particular the extension produced a middle late miocene boudinage of the previously stacked tectonic units b pliocene quaternary normal faulting which favoured the emplacement of a magmatic body in the middle upper crust and c the eruption of the mt amiata volcano which gave rise to an acid and intermediate volcanic complex 0 3 0 19 ma the extension produced the space necessary to accommodate the middle late miocene marine and continental sediments pliocene and quaternary normal and transtensional faults dissected the previous structures and influenced the early middle pliocene marine sedimentation within the structural depressions neighbouring the mt amiata volcano the magmatic body was emplaced at depth about 6 7 km during the pliocene extension and produced the eruption of the mt amiata volcano during the late pleistocene this gave rise to local uplift presently reaching about 3 000 m as well as a negative bouguer anomaly 16 mgal both centred on the mt amiata area the crustal dome shows a good correspondence with the convex shape of the regional seismic marker known as the k horizon which corresponds to the 450 c isotherm and the areas with greatest heat flow this is probably a consequence of the above cited magmatic body presently in the process of solidification a late pleistocene eruption occurred along a crustal fissure striking n50 mt amiata fault which crosscuts the crustal dome hydrothermal circulation proven by the occurrence of thermal springs and gas vents mainly co2 and h2s mainly occurs along the mt amiata fault both in the northeastern ans southwestern sides of the volcano

comment on borgia a mazzoldi a brunori c a allocca c delcroix c micheli l vercellino a grieco g 2014 volcanic spreading forcing and feedback in geothermal reservoir development amiata volcano italia j volc geoth res 284 16 31 abstract borgia et al 2014 illustrated an active volcanic spreading model for the amiata volcanic area southern tuscany italy although at first glance the model may appear appealing this is not fully supported by the available data and the paper does not take into account their discussion accordingly the supposed negative consequences of the borgia et al 2014 model on both contamination of shallow water and geothermal exploitation can likely be regarded as speculative

a numerical study of residual circulation induced by asymmetric tidal mixing in tidally dominated estuaries 1 residual currents induced by asymmetric tidal mixing atm were examined using a series of idealized numerical experiments for weakly stratified partially mixed and highly stratified narrow estuaries that neglected lateral variations of bathymetry and the effects of earth s rotation the eulerian residual currents were decomposed into four components i e river induced density driven nonlinearities induced and atm induced flows such that the longitudinal distribution and strength of each component can be depicted and evaluated in weakly stratified estuaries atm induced flow has a two layer structure similar to that of density driven flow it reinforces the estuarine exchange flow in partially mixed and highly stratified estuaries the atm induced flow tends to have a three layer structure with landward flows near the surface and the bottom and seaward flow in the middle of the water column it appears to act against the estuarine exchange flow in parts of the water column the relative importance of atm induced flow to estuarine residual currents varies in different types of estuaries compared to the density driven flow the relative importance of atm induced flow decreases as stratification increases in the central regime of the estuary the strength of the atm induced flow is greater than that of density driven flow under weak stratification and tends to be smaller under strong stratification

large scale rheomorphic shear deformation in miocene peralkaline ignimbrite e gran canaria the single ignimbrite cooling unit e average thickness 28 m volume ca 30 km3 forms the uppermost member of the miocene upper mogan formation on gran canaria it is strongly chemically zoned from basal first erupted comendite peralkaline rhyolite to late erupted trachyte and apart from an upper trachytic zone it is densely welded e was emplaced onto a surface inclined ca 2 5 from the source caldera detailed mapping of key sections up to 300 m long exposed in barranco walls ca 10 km from the caldera margin reveals structures that are interpreted to have been produced by rheomorphic deformation of the ignimbrite along shear zones the shear zones formed within the lower viscosity comenditic tuff extensional structures include mega boudinage and decapitated sequences and compression resulted in sequence repitition by overthrusting mechanisms traditionally thought to be important during rheomorphic deformation of welded tuffs compaction lateral creep folding vertical density driven diapirism cannot account for these features which reflect lateral post compactional rheomorphic movement locally in excess of 800 m we suggest the following sequence of events emplacement of the several flow units compaction with little lateral movement rheomorphic deformation during and after compaction layers of secondary porosity developed within the comenditic tuff possibly where upward escape of gas was prevented by overlying relatively impermeable layers of densely compacted ignimbrite these structurally weak layers of high porosity subsequently acted as shear zones

deformed symmetrical volcanoes analog modeling of volcanic cones traversed by strike slip faulting was conducted and the cones were analyzed for deformation characteristics the study shows that symmetrical volcanoes that have undergone basal strike slip offset may be deformed internally without manifesting any change in their conical shape volcanoes deformed by strike slip faulting may already have well developed fractures in their interior yet still appear as a symmetrical cone exhibiting concentric contours when viewed on a topographic map moreover slight changes in the basal shape of the cone induced by strike slip movement can be restored by the relatively faster resurfacing and reshaping processes from the deposition of younger eruptive products these findings pose a subtle but significant point in the assessment of volcanic landslide hazards not all perfect cones are undisturbed the detection of concealed deformation is important because fractures induce further instability in volcanoes and act as slip planes during volcano collapse events there are many examples of symmetrical volcanoes in nature the faultless appearance of such perfect cones can be misleading which requires careful attention in hazards assessment

extension induced by volcanic loading in regional strike slip zones volcanoes and strike slip pull apart structures are commonly found together we use theoretical predictions and analogue modeling to evaluate the effect of volcanic loading in strike slip zones and the converse effect of regional strike slip faults on volcano structure theoretical predictions indicate that regional stress is reoriented by volcano loading to cause extension analogue models indicate that volcanoes in strike slip zones develop extensional pull apart structures a graben typically forms normal to the minimum regional stress axis 3 at a cone cones emplaced onto preexisting faults increase that fault9s tensional component if the substratum is weak enough to permit volcano spreading thrusts form normal to the maximum stress axis 1 a feedback situation can arise i e loading related extension allows more magma influx more eruption and thus increased loading this process can create large volcano tectonic depressions volcano structures may also be used as indicators of regional strike slip movements

the role of the pernicana fault system in the spreading of mt etna italy during the 2002 2003 eruption flank instability and collapse are observed at many volcanoes among these mt etna is characterized by the spreading of its eastern and southern flanks the eastern spreading area is bordered to the north by the e w trending pernicana fault system pfs during the 2002 2003 etna eruption ground fracturing along the pfs migrated eastward from the ne rift to as far as the 18 km distant coastline the deformation consisted of dextral en echelon segments with sinistral and normal kinematics both of these components of displacement were one order of magnitude larger 1 m in the western previously known portion of the pfs with respect to the newly surveyed 9 km long eastern section 0 1 m this eastern section is located along a pre existing but previously unknown fault where displaced man made structures give overall slip rates 1 1 9 cm year only slightly lower than those calculated for the western portion 1 4 2 3 cm year after an initial rapid motion during the first days of the 2002 2003 eruption movement of the western portion of the pfs decreased dramatically while parts of the eastern portion continued to move these data suggest a model of spreading of the eastern flank of etna along the pfs characterized by eruptions along the ne rift instantaneous short lived meter scale displacements along the western pfs and more long lived centimeter scale displacements along the eastern pfs the surface deformation then migrated southwards reactivating one after the other the nnw sse trending timpe and trecastagni faults with displacements of 0 1 and 0 04 m respectively these structures along with the pfs mark the boundaries of two adjacent blocks moving at different times and rates the new extent of the pfs and previous activity over its full length indicate that the sliding eastern flank extends well below the ionian sea the clustering of seismic activity above 4 km b s l during the eruption suggests a deep decollement for the moving mass the collected data thus suggests a significant movement volume 1 100 km3 of the eastern flank of etna both on shore and off shore

edifice and substrata deformation induced by intrusive complexes and gravitational loading in the mull volcano scotland it is likely that the structure of a volcanic edifice can be significantly modified by deformation caused by large shallow intrusions such deformation may interact with that caused by volcano loading we explore such intrusion related and loading related deformation with field evidence and analogue models to do this we have chosen the eroded palaeogene mull volcano scotland that had a major edifice has well exposed intrusions and significant deformation there are thin mesozoic sedimentary rocks forming ductile layers below the volcano but their thickness is insufficient to allow the gravitational spreading of the volcanic edifice especially when considering that a thick lava pile covers them thus intrusive push may have been the driving force for deformation the mull activity migrated toward the northwest forming three successive intrusive complexes centres 1 2 and 3 our detailed fieldwork reveals that deformation due to these was accommodated on three levels along thrust planes in lava sequences along a decollement located in a thin clay rich sediment succession and in basement schists a relative chronology has been established between different groups of structures using dyke and sill cross cutting relationships centre 1 is surrounded by a fold and thrust belt leading to radial expansion in contrast centre 2 and 3 are connected to thrusts located to the south and east bounded by strike slip faults leading to expansion to the southeast the migration of centres and the directed sliding of the edifice may be related to the presence to the southeast of low resistance dalradian basement that failed significantly during growth of centres 2 and 3 to study the observed relationships we have carried out scaled analogue models models are made with fine powder intruded by a viscous magma analogue the models show an intimate relationship between intrusion growth uplift of the volcano and subsequent flank sliding the structures produced can be compared with mull and suggest that the centre 1 thrust belt probably formed following edifice gravitational sliding as a consequence of the uplift associated with centre 1 formation centre 2 and 3 are responsible for the sector sliding of the edifice flank toward the southeast as the magmatic complex became more asymmetric the features observed at mull and in the models are similar to those seen on active volcanoes such as etna providing a structural framework for their deformation and evolution

actively growing anticlines beneath catania from the distal motion of mount etna s decollement measured by sar interferometry and gps we used sar interferometry and gps to measure the rise of an anticline beneath the urban area of catania italy which originates from outward thrusting above the basal decollement of etna volcano the anticline grows at a rate of over 0 015 m a 1 of se thrusting and about 0 007 m a 1 of relative uplift by relating this growth to the simultaneous extension measured at the summit of the volcano we demonstrate the occurrence of active volcanic spreading this process may exert a control on eruptions earthquakes sector collapses and landslides

analogue models of caldera collapse in strike slip tectonic regimes regional scale faulting particularly in strike slip tectonic regimes is a relatively poorly constrained factor in the formation of caldera volcanoes to examine interactions between structures associated with regional tectonic strike slip deformation and volcano tectonic caldera subsidence we made scaled analogue models tabular sill like inclusions of creamed honey in a sand gypsum mix replicated shallow level granitic magma chambers in the brittle upper crust lateral motion of a base plate sited below half the sand gypsum pack allowed simulation of regional strike slip deformation our experiments modelled 1 strike slip deformation of a homogeneous brittle medium 2 strike slip deformation of a brittle medium containing a passive magma reservoir 3 caldera collapse into sill like magma reservoirs without regional strike slip deformation and 4 caldera collapse into sill like magma reservoirs after regional strike slip deformation our results show that whilst the magma chamber shape principally influences the development and geometry of volcano tectonic collapse structures regional tectonic strike slip faults riedel shears and y shears may affect a caldera s structural evolution in two main ways firstly regional strike slip faults above the magma chamber may form a pre collapse structural grain that is exploited and reactivated during subsidence our experiments show that such faults may preferentially reactivate where tangential to the collapse area and coincident with the chamber margins in this case volcano tectonic extension in the caldera periphery tends to localise on regional tectonic faults that lie just outside the chamber margins in addition volcano tectonic reverse faults may link with and reactivate pre collapse regional tectonic faults that lie just inside the chamber margins secondly where regional tectonic strike slip faults define corners in the magma chamber margin they may halt the propagation of volcano tectonic reverse faults the experiments also highlight the potential difficulties in assessing the relative contributions of volcano tectonic and regional tectonic subsidence processes to the final caldera structure seen in the field disruption of the pre collapse surface by regional tectonic faulting was preserved during coherent volcano tectonic subsidence to produce a caldera floor of differentially subsided fault blocks without definitive evidence for syn eruptive growth faulting thickness changes in caldera fill across such regional tectonic fault blocks in nature could be mistaken as evidence for piecemeal volcano tectonic collapse

anatomy of an unstable volcano from insar multiple processes affecting flank instability at mt etna 1994 2008 1 volcano deformation may occur under different conditions to understand how a volcano deforms as well as relations with magmatic activity we studied mt etna in detail using interferometric synthetic aperture radar insar data from 1994 to 2008 from 1994 to 2000 the volcano inflated with a linear behavior the inflation was accompanied by eastward and westward slip on the eastern and western flanks respectively the portions proximal to the summit showed higher inflation rates whereas the distal portions showed several sectors bounded by faults in some cases behaving as rigid blocks from 2000 to 2003 the deformation became nonlinear especially on the proximal eastern and western flanks showing marked eastward and westward displacements respectively this behavior resulted from the deformation induced by the emplacement of feeder dikes during the 2001 and 2002 2003 eruptions from 2003 to 2008 the deformation approached linearity again even though the overall pattern continued to be influenced by the emplacement of the dikes from 2001 to 2002 the eastward velocity on the eastern flank showed a marked asymmetry between the faster sectors to the north and those largely inactive to the south in addition from 1994 to 2008 part of the volcano base south west and north lower slopes experienced a consistent trend of uplift on the order of 0 5 cm yr this study reveals that the flanks of etna have undergone a complex instability resulting from three main processes in the long term 103 104 years the load of the volcano is responsible for the development of a peripheral bulge in the intermediate term 101 years observed from 1994 to 2000 inflation due to the accumulation of magma induces a moderate and linear uplift and outward slip of the flanks in the short term 1 year observed from 2001 to 2002 the emplacement of feeder dikes along the ne and south rifts results in a nonlinear focused and asymmetric deformation on the eastern and western flanks deformation due to flank instability is widespread at mt etna regardless of volcanic activity and remains by far the predominant type of deformation on the volcano

numerical modelling of suspended sediment transport in a geographically complex microtidal estuary sydney harbour estuary nsw abstract a numerical study was conducted to investigate the sediment dynamics in a geographically complex estuary the sydney harbour estuary she the she is a good example of a microtidal estuary with irregular shorelines and a complex bathymetry characterized by many headlands and islands forming a meandering main channel horizontal sediment transport showed a local estuarine turbidity maximum etm as a result of complex topography independent of salinity fields and river flows during dry weather the along estuary advection of sediment was mainly driven by the mean advection with a minor contribution by tidal pumping mean advection associated with barotropic forcing drives sediment flux seaward in the upper estuary and landward in the middle estuary leading to a longitudinal convergence of sediment transport without upstream or downstream migration of etm during high river flows the interactions between tidal currents complex topography and asymmetric vertical mixing led to spring neap and flood ebb variations in sediment distribution the singular spectrum analysis ssa method was used to calculate the relative contributions of the identified environmental forcing frequencies tidal range tidal frequency river discharges wind stress to the variability in suspended sediment concentration tidal frequency and river discharges were the major contributors to this variability tidal range made the highest contribution in the middle estuary where the etm was located driving the spring neap cycle of the etm

space accommodation by roof lifting during pluton emplacement at amiata italy the amiata area is characterized by an uplift attributed to pluton emplacement during the pliocene epoch the shape of the buried pluton is constrained by gravity data fieldwork was carried out to identify possible deformations within the overburden in order to evaluate the mechanism of emplacement the attitudes of lower pliocene marine sediments deposited immediately before the uplift were measured also the overall pattern of the deposits defines a dome approximately 2 5 km high and 35 50 km wide consistency between these field data and the existing geophysical data suggests that the dome results from the emplacement of a laccolith like intrusion which was responsible for lifting and flexuring the overburden the amiata case shows that roof lifting is a viable process by which space in the upper crust to a depth of 7 km can be accommodated during pluton emplacement

volcano spreading controlled by dipping substrata most volcanoes grow on slopes and some tend to fail catastrophically on the downslope side many volcanoes also deform by volcano spreading which may lead to failure we look at the effect of dipping substrata on the potential for spreading and collapse with analogue models the dip is found to strongly control the spreading style rate and direction a distinct change from purely radial spreading occurs even with small 1 substrata tilt structures on the cone and surrounding area are modified according to the underlying dip direction spreading becomes concentrated on downslope sectors where movement is predominantly in the dip direction the degree of structural realignment is a function of the slope angle our models are applied to previously known and new examples of volcano spreading the effect of dipping substrata in confining spreading to sectors increases the potential for deep seated sector collapses this finding provides a mechanism for failure on the downslope side the incorporation of substrata can create very large volume collapses