do transcurrent faults guide volcano growth the case of nw bicol volcanic arc luzon philippines this paper shows that although volcanoes can be aligned along transcurrent faults their growth can in reality be controlled by secondary structures that have a different orientation and kinematics assessing the relationships between local structures and volcano growth can be very useful for the evaluation of volcanic hazards and for economic purposes such as geothermal and hydrogeological exploration in the north western bicol volcanic arc luzon philippines the quaternary labo and caayunan volcanoes are aligned with the nw striking transcurrent philippine fault system they are exceptional examples of composite volcanoes mostly comprising lava domes where regional tectonic structures and hydraulic radial fracturing have alternated to control volcano growth field data and analogue modelling demonstrate that apical depressions affecting the domes reflect the geometry of magma feeding fractures these data together with alignments of domes and hot springs and other structural information suggest that magma rose at depth along the nw striking transcurrent faults but that in the uppermost crust magma rose along ne striking fractures parallel to the greatest principal stress

fault reactivation and rift localization northeastern gulf of aden margin 1 the gulf of aden and the sheba spreading ridge gulf of aden forms the southern boundary of the arabian plate its orientation 075 e and its kinematics about 030 e divergence are interpreted as the result of an oblique rifting in this contribution a field study in the northeastern gulf of aden allows us to confirm the oligo miocene synrift directions of extension and to precise the normal fault network geometry the synrift extensions are 020 e and 160 e possibly in this chronological order the normal faults strike 070 e 090 e and 110 e the results show that some characteristics are consistent with oblique rifting analogue models while some others are not especially fault reactivation of mesozoic structures is shown to have occurred significantly at the beginning and during rifting these data are therefore compared to analogue models of oblique reactivation and this comparison demonstrates that fault reactivation played a key role during the early stage of the gulf of aden rifting finally scenarios of the lithospheric evolution during the eastern gulf of aden opening preexisting weaknesses in the lithosphere or not are discussed to better constrain the deformation history of the northern margin especially we show that rift localization processes may imply stress rotations through time

how summit calderas collapse on basaltic volcanoes new insights from the april 2007 caldera collapse of piton de la fournaise volcano in april 2007 piton de la fournaise volcano experienced a caldera collapse during its largest historical eruption we present here a structural analysis both of the caldera and the surrounding area and precise gps data recorded with a dense gps network specifically dedicated to the analysis of deformation related to the summit collapse structures despite a collapse of more than 300 m in the central zone the geometry of the new caldera is similar in map view to that of the pre existing collapsed structure which was formed from the coalescence of several pit craters the caldera shows an asymmetric inner geometry with sub vertical walls in the nw quadrant and steep scarps composed of inward tilted blocks in the southern half the presence of preserved polished surfaces on the lower part of the sub vertical scarp indicates that it corresponds to the caldera north western ring fault the april 2007 caldera collapse led to the development and the reactivation of concentric fractures on the caldera rim mostly along the southern limit of the caldera gps data show that fractures result from radial extensional stresses that are restricted within the first tens of meters of the caldera edge gps data also reveal that the caldera collapse was coeval with a centripetal deflation whose magnitude is largest along the southern half of the caldera the displacements recorded by gps result from both a general deflation due to magma withdrawal from piton de la fournaise s summit magma chamber and additional local effects related to the caldera collapse comparison of the caldera collapses at piton de la fournaise miyakejima and fernandina reveals striking similarities with cyclic seismic signals accompanying small scale deflation inflation cycles this strongly suggests a common mode of collapse hence we propose a unifying model of caldera collapse in basaltic setting in which the inward deflation due to magma withdrawal from the magma chamber prevents the collapse of the caldera roof until the gravitational stress acting on the rock column above the magma chamber exceeds the shear strength along pre existing ring faults the downward displacement stops when the pressure increase into the magma chamber is able to again sustain the rock column the succession of 1 inward deflation that prevents the collapse 2 collapse due to gravitational stress and 3 stopping of the downward motion is repeated many times the frequency of the cycles is influenced by the rate of magma withdrawal and by the amount of intrusion of magma along the ring faults

experimental study on the stability and failure of individual step pool abstract step pools are one of the most common bedforms in mountain streams the stability and failure of which play a significant role for riverbed stability and fluvial processes given this importance flume experiments were performed with a manually constructed step pool model the experiments were carried out with a constant flow rate to study features of step pool stability as well as failure mechanisms the results demonstrate that motion of the keystone grain ks caused 90 of the total failure events the pool reached its maximum depth and either exhibited relative stability for a period before step failure which was called the stable phase or the pool collapsed before its full development the critical scour depth for the pool increased linearly with discharge until the trend was interrupted by step failure variability of the stable phase duration ranged by one order of magnitude whereas variability of pool scour depth was constrained within 50 step adjustment was detected in almost all of the runs with step pool failure and was one or two orders smaller than the diameter of the step stones two discharge regimes for step pool failure were revealed one regime captures threshold conditions and frames possible step pool failure whereas the second regime captures step pool failure conditions and is the discharge of an exceptional event in the transitional stage between the two discharge regimes pool and step adjustment magnitude displayed relatively large variabilities which resulted in feedbacks that extended the duration of step pool stability step adjustment which was a type of structural deformation increased significantly before step failure as a result we consider step deformation as the direct explanation to step pool failure rather than pool scour which displayed relative stability during step deformations in our experiments

an unusual syn eruptive bimodal eruption the holocene cuicuiltic member at los humeros caldera mexico abstract the cuicuiltic member cm at los humeros caldera eastern mexican volcanic belt is a holocene 6 4 ka b p succession of alternated fallout deposits of contrasting composition trachydacite pumice and basaltic andesite scoria the cm covers approximately 250 km 2 on its proximal facies and its thickness ranges from 1 5 m to 8 0 m it postdates two caldera forming ignimbrites xaltipan and zaragoza and numerous plinian successions it is subdivided in 9 units c1 to c9 according to its textural and chemical characteristics sub horizontal topography draping layers of trachydacite pumice lapilli andesitic pumice lapilli and basaltic andesite scoria lapilli with sporadic one meter blocks are common lithofacies the base is formed by coarse trachydacite pumice lapilli c1 and c2 overlain by a layer with banded pumice c3 thin layers of ash and ash tuff are intermittent on lower units whilst continuous at the base of c4 the middle units c4 and c6 are basaltic andesite pumice and scoria lapilli to blocks c5 is in between the two mafic units and it is represented by a layer of pale grey pumice lapilli units c7 and c8 are a mixture of white trachydacite pumice scoria lapilli and banded pumice the uppermost layer c9 is a brown to grey andesitic pumice lapilli extensive fieldwork allowed a close and reliable correlation of layers that helps to understand the complexity of stratigraphic relations and sources for those layers the distribution of these units is varied across the caldera with the trachydacite layers dispersal from the centre towards the nw whilst the andesitic units have maximum thicknesses over the se and ne sectors of the caldera isopach and isopleth maps combined with detailed mapping of near vent spatter facies orientation of local bomb sags and variation of mean clasts size for some layers were very useful to determine the vent location particularly for the andesitic basaltic layers the cm represents the last explosive event registered at los humeros caldera combining simultaneously both plinian and strombolian activities the eruption was fed from one central vent and at least two independent but simultaneously active vents up to 6 km apart the eruption began with a trachydacite explosive eruption depositing pristine white pumice in the centre of the caldera in two stages after a short repose period at least two andesitic to basaltic fissure vents erupted ejecting pumice and scoria over the southeast and northeast sector mainly along a weakness structural plane parallel to the potreros scarp these eruptions became less energetic with time until reaching classic strombolian style with sudden fluxes generating local and discrete pyroclastic currents trachydacite pumice kept falling intermittently accompanied by mingling at depth the end of the cuicuiltic eruption is marked by the well graded layer c9 which registers lapilli sized pumice fall clasts from a hybridized magma chamber the cm may represent a either a trachydacite magma chamber disturbed by a basaltic intrusion triggering the eruption of the evolved material first or b a heterogeneously zoned magma reservoir tapping the evolved magma first and due to contrasting density and viscosity conditions the basaltic and andesitic materials were extruded through adjacent weakness planes up to the surface

recent left oblique slip faulting in the central eastern trans mexican volcanic belt seismic hazard and geodynamic implications 1 detailed structural analysis was conducted on the e w trending tenango fault system tfs at the western end of the la pera fault system a major structure within the trans mexican volcanic belt tmvb field mapping which included trenching the fault trace revealed the displacement of recent volcanic deposits the study indicates that the tfs is an active subvertical fault with transtensive left lateral movement consistent with the contemporary stress regime in the region the estimated holocene slip rate is 0 3 0 5 mm yr the tfs activity constitutes an important seismic hazard in the intra arc lerma basin several towns are located within this basin and are particularly vulnerable to seismic risk because of its underlying strata consisting of lacustrine and volcaniclastic deposits estimated maximum mw 6 8 7 the tfs is an important structural element in the complex tectonic deformation history of central eastern tmvb and influenced the behavior of recent volcanism within the lerma basin

structural evolution of calderas insights from two dimensional discrete element simulations the manner in which calderas develop is a key question in volcanology and has important implications for associated volcanogenic risk and geothermal and ore exploitation to better understand the structural evolution of calderas i use a discrete element model of a frictional cover undergoing piston like subsidence at its base simulating magma chamber deflation and cover collapse these novel simulations capture not only the initiation of cal deras but also much of the complexity of faulting during their later development in all models both normal and reverse faults accommodate deeper subsidence at higher structural levels curved outward dipping reverse faults are consistently the first structures to develop subsequent caldera growth is mainly the result of movement on vertical or steeply inward dipping normal faults this may be followed by a later phase of lateral collapse on shallower normal faults the roof aspect ratio r cover thickness piston width is seen to be an important factor calderas with low aspect ratios r 1 exhibit a coherent central subsiding block while those with higher aspect ratios have a complexly faulted internal structure

understanding caldera structure and development an overview of analogue models compared to natural calderas abstract understanding the structure and development of calderas is crucial for predicting their behaviour during periods of unrest and to plan geothermal and ore exploitation geological data including that from analysis of deeply eroded examples allow the overall surface setting of calderas to be defined whereas deep drillings and geophysical investigations provide insights on their subsurface structure collation of this information from calderas worldwide has resulted in the recent literature in five main caldera types downsag piston funnel piecemeal trapdoor being viewed as end members despite its importance such a classification does not adequately examine a the structure of calderas particularly the nature of the caldera s bounding faults and b how this is achieved including the genetic relationships among the five caldera types various sets of analogue models specifically devoted to study caldera architecture and development have been recently performed under different conditions apparatus materials scaling parameters stress conditions the first part of this study reviews these experiments which induce collapse as a result of underpressure or overpressure within the chamber analogue the experiments simulating overpressure display consistent results but the experimental depressions require an exceptional amount of doming seldom observed in nature to form therefore these experiments are not appropriate to understand the structure and formation of most natural calderas the experiments simulating underpressure reveal a consistent scenario for caldera structure and development regardless of their different boundary conditions these show that complete collapse proceeds through four main stages proportional to the amount of subsidence progressively characterized by 1 downsag 2 reverse ring fault 3 peripheral downsag 4 peripheral normal ring fault the second part of this study verifies the possibility that these latter calderas constitute a suitable analogue to nature and consists of a comprehensive comparison of the underpressure experiments to natural calderas this shows that all the experimental structures as well as their progressive development are commonly observed at natural calderas highlighting a consistency between models and nature as the shallow structure of experimental calderas corresponds to a precise architecture at depth it provides a unique key to infer the deeper structure of natural calderas recognizing diagnostic surface features within a caldera will thus allow it to be categorized within a precise structural and evolutionary context the general relationship between the evolutionary stage of a caldera and its d s diameter subsidence ratio allows such a quantification with stage 1 calderas characterized by d s 40 stage 2 by 18 the four stages adequately explain the architecture and development of the established caldera end members along a continuum where one or more end members downsag piston funnel piecemeal trapdoor may correspond to a specific stage while such a continuum is controlled by progressive subsidence specific collapse geometries will result from secondary contributory factors roof aspect ratio collapse symmetry pre existing faults these considerations allow proposing an original classification of calderas incorporating their structural and genetic features

eruption rates and compositional trends at los humeros volcanic center puebla mexico the los humeros volcanic center located 180 km east of mexico city is one of several pleistocene silicic centers in the back arc portion of the mexican neovolcanic belt the eruptive history at los humeros suggests that average eruptive rates increased with time and exceeded rates of regeneration of differentiated magma silicic volcanism began 0 47 ma ago with extrusion of high silica rhyolite domes shortly thereafter at 0 46 ma ago 115 km3 of magma zoned from high silica rhyolite to rhyodacite were erupted resulting in formation of the xaltipan ignimbrite and collapse of the 21 15 km los humeros caldera high silica rhyolite domes then erupted along the northwestern ring fracture zone of the caldera they are covered by the faby tuff a dominantly rhyodacitic sequence of plinian fall deposits erupted from the southeast quadrant of the los humeros caldera dated at 0 24 ma a second major caldera forming event occurred 0 1 ma ago with the eruption of the zaragoza tuff a nonwelded ignimbrite zoned from rhyodacite to andesite eruption of these 12 km3 of magma led to collapse of the 10 km diameter los potreros caldera which is nested within the older los humeros caldera between 0 04 and 0 03 ma ago an arc of andesitic scoria cones concentrated along the southern ring fracture zone of the los humeros caldera fed lavas that flowed southward from the volcanic center and andesite lavas built two small shields between the eastern rims of the two calderas approximately 6 km of andesitic magma were extruded during this stage activity continued up to 0 02 ma ago with eruption of 10 km3 of rhyodacitic to andesitic lava flows from centers near the northern margin of the los potreros caldera in the area between the eastern rims of the two calderas and within a broad band where the southern segments of the inferred los humeros and los potreros ring fracture zones nearly coincide simultaneous venting of rhyodacitic and andesitic tephra within this band led to formation of the 1 7 km diameter el xalapazco caldera minor fault bounded uplift of the southeastern quadrant of the los potreros caldera followed the latest stage of volcanic activity is represented by the eruption of 0 25 km3 of olivine basalt lavas along the southern ring fracture zone of the los humeros caldera and on the floors of the los potreros and el xalapazco calderas erupted magmas show an overall trend with time toward more mafic compositions volumetric eruptive rates increased from 0 06 km3 per thousand years 0 25 ma ago to 0 2 km3 per thousand years in the last 0 1 ma the increase in eruptive rate may have been the result of a progressive decrease in the structural integrity of the roof zone of the system as successive caldera forming eruptions reactivated old zones of weakness and created new ones an increasingly disrupted roof allowed mafic and intermediate magmas to reach the surface relatively rapidly decreasing their residence time in a high level chamber and thus the time available for their differentiation

field measurements of three dimensional hydraulics in a step pool channel we investigated the effects of morphologic position and discharge on flow structure in a steep 0 10m m mountain channel by collecting three dimensional measurements of time averaged and turbulent velocity components with a sontek flowtracker handheld adv acoustic doppler velocimeter on a 30 m reach of a step pool channel in the colorado rockies velocity profiles were measured at morphologic positions characteristic of steep channels above steps step lips base of steps pools cascades runs and at five different discharges a marked three dimensionality of flow structure was documented in east st louis creek velocities in the streamwise component were the largest contributors to overall velocity vector magnitudes cross stream and vertical components contributed averages of 20 and 15 respectively to overall vector magnitudes turbulence intensities were especially multi dimensional however with large contributions to turbulent kinetic energy from the vertical component of velocity analysis of variance indicated that discharge and morphologic position significantly affected mean streamwise velocities with substantially higher velocities upstream from steps than in pools discharge and morphology effects on cross stream and vertical velocity components however were not significant discharge and morphologic position also significantly affected turbulence intensities for all flow components with the greatest turbulence intensities occurring in pools and at high discharges these results illustrate the strong discharge dependence of hydraulics in step pool channels where relative submergence of bedforms changes rapidly with discharge and the substantial spatial variation in hydraulics created by step pool sequences

tectonic evolution of the central eastern sector of trans mexican volcanic belt and its influence on the eruptive history of the nevado de toluca volcano mexico abstract the nevado de toluca is an andesitic to dacitic stratovolcano of late pliocene holocene age located within the central and eastern sectors of the trans mexican volcanic belt morphostructural analysis aerial photograph and satellite image interpretation structural analysis and geological fieldwork were methods used to investigate the relationship between the evolution of the volcano and the tectonic framework of its basement the study revealed that the area of nevado de toluca is affected by three main fault systems that intersect close to the volcanic edifice these are from oldest to youngest the taxco queretaro san antonio and tenango fault systems the nnw sse taxco queretaro fault system was active in the area since early miocene and is characterized by right lateral transtensive movement its reactivation during early to middle pleistocene was responsible for the emplacement of andesitic to dacitic lava flows and domes of la cieneguilla supersynthem the ne sw san antonio fault system was active during late pliocene before the reactivation of the taxco queretaro fault system and is characterized by extensional left lateral oblique slip kinematics the youngest is the e w tenango fault system that has been active since late pleistocene this fault system is characterized by transtensive left lateral strike slip movement and partly coeval with the youngest eruptive phase the nevado supersynthem which formed the present summit cone of the nevado de toluca volcano the stress re orientation from the taxco queretaro to the tenango fault system during late pleistocene is responsible for the 1 ma hiatus in the magmatic activity between 1 15 ma and 42 ka after this period of repose the eruptive style drastically changed from effusive to explosive with the emission of dacitic products the methodology presented here furnish new data that can be used to better assess the complex structural evolution of this sector of the trans mexican volcanic belt and to understand the influence of changes in the tectonic setting on the growth of volcanic edifices

local earthquake tomography at los humeros geothermal field mexico a passive seismic experiment using 25 broadband and 20 short period stations was conducted between september 2017 and september 2018 at los humeros geothermal field an important natural laboratory for superhot geothermal systems in mexico from the recorded local seismicity we derive a minimum 1 d velocity model and obtain 3 d vp and vp vs structures of los humeros we improved the classical local earthquake tomography by using a postprocessing statistical approach several inversions were computed and averaged to reduce artifacts introduced by the model parametrization and to increase the resolution of the investigated region finally the resulting vp and vp vs structures and associated seismicity were integrated with newly acquired geophysical and petrophysical data for comprehensive interpretation the recorded seismicity is mainly grouped in three clusters two of which seem directly related to exploitation activities by combining new laboratory measurements and existing well data with our vp model we estimate possible geological unit boundaries one large intrusion like body in the vp model together with neighboring high vp vs anomalies hints at a region of active resurgence or uplift due to the intrusion of new magma at the northern portion of the geothermal field we interpret high vp vs features as fluid bearing regions potentially favorable for further geothermal exploitation deep reaching permeable faults cutting the reservoir unit could explain fluid flow from a deeper local heat source in the area

simple shearing block resurgence in caldera depressions a model from pantelleria and ischia abstract similar resurgent blocks occur in caldera depressions at the islands of pantelleria and ischia the two blocks which are tilted show similar deformation patterns and similar distributions of volcanic vents related to resurgence the remaining parts of the floors of the two calderas are not deformed similarities between the two features are so striking that the resurgence mechanism must have been alike a dynamic model for resurgence is presented and called simple shearing block resurgence the triggering mechanism is an increase of the magmatic pressure in the upper part of a shallow magma chamber which results in a vertical direction of the maximum stress applied on the roof rocks the block is first defined by high angle inland dipping marginal detachments and then deformed through a simple shearing mechanism reverse faults on its mostly uplifted side determine an horizontal shortening of the block which is balanced on the opposite side by normal faults oblique movements take place along the other two sides due to this distribution of the stress around the block magmas can reach the surface only through the extensional faults on the less uplifted side

geochemical evidence for a lithospheric source for magmas from los humeros caldera puebla mexico abstract this study reports new geochemical and sr nd pb radiogenic isotope data on hy normative quaternary basaltic to rhyolitic volcanic rocks as well as two samples of mesozoic to palaeozoic intrusive igneous rocks from los humeros caldera lhc located in the eastern part of the mexican volcanic belt mvb the isotopic ratios of mafic basaltic rocks range as follows 87 sr 86 sr 0 703350 0 703387 143 nd 144 nd 0 512867 0 512888 206 pb 204 pb 18 849 18 866 207 pb 204 pb 15 593 15 598 and 208 pb 204 pb 38 490 38 491 these values are similar to the rift related mafic rocks from the volcanic front of the central mvb for comparison the entire suite from basalt b to rhyolite r in the lhc shows the following ranges 87 sr 86 sr 0 703350 0 704678 143 nd 144 nd 0 512702 0 512888 206 pb 204 pb 18 710 18 866 207 pb 204 pb 15 593 15 631 and 208 pb 204 pb 38 444 38 594 the basaltic rocks from los humeros do not show the characteristic negative nb anomaly with respect to ba and ce as is typical of such magmas in volcanic arcs the available geochemical and isotopic evidence does not support the generation of the lhc mafic magmas by direct slab melting nor by indirect fluid transport to the mantle participation of the subducted cocos plate instead they could be generated in the upper mantle from a lithospheric source the evolved andesitic to rhyolitic magmas could have been originated from such mafic magmas through assimilation coupled with extensive fractional crystallisation two different compositions representing lower lc and upper crusts uc as well as a hypothetical crust ha were tested as plausible assimilants for the assimilation coupled with fractional crystallisation process

the effects of discharge and slope on hyporheic flow in step pool morphologies this paper focuses on surface subsurface water exchange in a steep coarse bedded stream with a step pool morphology we use both flume experiments and numerical modelling to investigate the influence of stream discharge channel slope and sediment hydraulic conductivity on hyporheic exchange the model step pool reach whose topography is scaled from a natural river consists of three step pool units with 0 1 m step heights discharges ranging between base and over bankfull flows scaled values of 0 3 4 5 l s and slopes of 4 and 8 results indicate that the deepest hyporheic flow occurs with the steeper slope and at moderate discharges and that downwelling fluxes at the base of steps are highest at the largest stream discharges in contrast to findings in a pool riffle morphology those in this study show that steep slopes cause deeper surface subsurface exchanges than gentle slopes numerical simulation results show that the portion of the hyporheic zone influenced by surface water temperature increases with sediment hydraulic conductivity these experiments and numerical simulations emphasize the importance of topography sediment permeability and roughness elements along the channel surface in governing the locations and magnitude of downwelling fluxes and hyporheic exchange our results show that hyporheic zones in these steep streams are thicker than previously expected by extending the results from streams with pool riffle bed forms copyright 2014 john wiley sons ltd

calderas and caldera structures a review abstract calderas are important features in all volcanic environments and are commonly the sites of geothermal activity and mineralisation yet it is only in the last 25 years that a thorough three dimensional study of calderas has been carried out utilising studies of eroded calderas geophysical analysis of their structures and analogue modelling of caldera formation as more data has become available on calderas their individuality has become apparent a distinction between caldera caldera complex cauldron and ring structure is necessary and new definitions are given in this paper descriptions of calderas based on dominant composition of eruptives basaltic peralkaline andesitic dacitic rhyolitic can be used and characteristics of each broad group are given styles of eruption may be effusive or explosive with the former dominant in basaltic calderas and the latter dominant in andesitic dacitic rhyolitic and peralkaline calderas four end member collapse styles occur plate or piston piecemeal trapdoor and downsag but many calderas have multiple styles features of so called funnel and chaotic calderas proposed in the literature can be explained by other collapse styles and the terms are considered unnecessary ground deformation comprises subsidence or collapse essential characteristics of a caldera and uplifting doming and fracturing due to tumescence and or resurgence frequent but not essential collapse may occur on pre existing structures such as regional faults or on faults created during the caldera formation and the shape of the collapse area will be influenced by depth size and shape of the magma chamber the final morphology of a caldera will depend on how the caldera floor breaks up whether collapse takes place in one event or multiple events whether vertical movement is spasmodic or continuous throughout the eruptive sequence and whether blocks subside uniformly or chaotically at one or more collapse centres a meaningful description of any caldera should therefore include number of collapse events presence or absence of resurgence caldera floor coherency caldera floor collapse geometry and dominant composition of eruptives

subaqueous calderas in the archean abitibi greenstone belt an overview and new ideas abstract the 300 700 km abitibi greenstone belt in canada contains numerous world class archean volcanogenic massive sulfide vms deposits yet documentation of archean subaqueous calderas hosting such deposits is lacking the modern sunrise deposit in the myojin knoll caldera of the izu bonin arc shows that submarine calderas are first order sites for vms the hunter mine and normetal calderas as well as the blake river megacaldera complex are reviewed with respect to geometry regional geology physical volcanology dyke emplacement and hydrothermal carbonate alteration these subaqueous calderas are placed into the geodynamic context of the abitibi greenstone belt the abitibi belt displays a complex history of oceanic arc formation evolution collision and fragmentation with numerous types of volcanic edifices and sedimentary basins controlled by oblique subduction and mantle plumes analogue models yielding new insights into the sequence of caldera forming events and their synvolcanic fault patterns are applied to explain archean examples underpressure experiments develop a consistent sequence of fault patterns that compare favourably with natural caldera events during subsidence two sets of faults propagate from the magma chamber margin 1 early reverse outward dipping faults and 2 normal inward dipping faults the largest massive sulfide deposits form preferentially at the caldera margin based on experimental studies and detailed facies mapping the hunter mine caldera is of the segmented piecemeal variety and the normetal caldera is akin to a piston structure the blake river megacaldera contains 1 the e w trending misema 2 the nw trending new senator and 3 the ne trending noranda calderas with the latter two being nested graben type calderas consistent with oblique archean subduction the poorly documented hydrothermal carbonate alteration is discussed and a new exploration model for calderas is presented the alteration study was evaluated at three levels microprobe analysis geochemical staining of drill core and whole rock analyses there were two principal stages of alteration related to vms formation an early silicification phase developed either at depth and or at the seawater interface whereby silicification was bedding parallel in fine grained volcaniclastic deposits near the water surface a pervasive and extensive semi conformable carbonate alteration zone with a discordant focused root zone along faults evolved subsequently three distinct carbonate pairings were observed 1 proximal siderite sideroplesite fe ankerite next to the vms deposit 2 an intermediate ankerite fe dolomite zone and 3 a distal calcite dolomite zone the carbonate phase is associated with the mineralizing event transitions between carbonate species are subtle and changes are indicated by mineral assemblage overlap the silica carbonate hydrothermal alteration pattern is a replacement product and is far more widespread than has been documented this alteration can be easily confused with primary carbonates and chemical precipitation deposits e g banded iron formation if detailed volcano sedimentary facies mapping with alteration has not been conducted and if outcrop is insufficient

reappraisal of los humeros volcanic complex by new u th zircon and 40ar 39ar dating implications for greater geothermal potential

the dynamic history of the trans mexican volcanic belt and the mexico subduction zone abstract the trans mexican volcanic belt tmvb is a 1000 km long neogene continental arc showing a large variation in composition and volcanic style and an intra arc extensional tectonics it overlies the rivera and cocos slabs which display marked changes in geometry geophysical studies indicate that lithospheric mantle is very thin or absent beneath the forearc and arc the fluids from the slab are released in a 40 to 100 km wide belt beneath the frontal part of the arc and the lower crust beneath the arc is partially molten east of 101 w the tmvb is built on a precambrian to paleozoic crust with thickness of 50 55 km west of 101 w the tmvb is underlain by jurassic to cenozoic marine and continental arcs with a 35 40 km thick crust the evolution of the tmvb occurred in four stages 1 from 20 to 10 ma the initial andesitic arc moved inland showing progressively drier melting and eventually slab melting suggesting flattening of the subducted slab 2 since 11 ma a pulse of mafic volcanism migrated from west to east reaching the gulf of mexico by 7 ma this mafic lavas marks the lateral propagation of a slab tear triggered by cessation of subduction beneath baja california 3 thereafter the volcanic front started moving trenchward with a marked phase of silicic volcanism between 7 5 and 3 ma local emplacement of small volume intraplate like basalts since 5 ma and development of extensional faulting these features are related to slab rollback enhancing asthenophere flux into the mantle wedge and promoting partial melting of the crust 4 the modern arc consists of a frontal belt dominated by flux and slab melting and a rear belt characterized by more differentiated rocks or by mafic lavas with little or no evidence of subduction fluids but higher asthenosphere fingerprint

genetic links between ash flow calderas and associated ore deposits as revealed by large scale thermo mechanical modeling abstract in addition to a number of epithermal ore deposits some porphyry type ore deposits are also hosted by ash flow calderas spatial correlation between ash flow calderas and these deposits is observed in several parts of the world but temporal correlation between the mineralization and the episode of caldera formation remains unclear especially because geochronological data indicate that the mineralization may date to several million years before or after caldera formation because caldera collapse represents only a very short event in a long time scale evolution between a silicic magma chamber and its host rocks we have developed a thermo mechanical model of upper crustal and magmatic system behavior during the pre and post caldera formation stages major petrophysical properties of ash flow caldera related rocks are incorporated into the model which accounts for brittle elasto ductile rheology and heat transfer and reproduces fault initiation and various caldera collapse scenarios large scale mechanisms of initiation of thermal and structural traps for epithermal ore deposits are described in particular we found that the outer sides of caldera border faults are associated with both anomalous heat transfer and a high fracture density the finite size of the insulating intracaldera units forces the accumulated heat excess to be laterally transferred across the border faults in most cases the model predicts y shaped fault geometry which is surprisingly similar to that of mineralized faults in the field variations in lithostatic pressure on the magma chamber roof and in the vicinity of the border faults can reach 10 to 20 mpa with deep overpressured zones close to the inner edge of the chamber corners despite the fact that hydrothermal convection and fluid geochemistry are not included in the model these thermal and mechanical results are believed to constrain the conditions for mineralization processes our results show that in the presence of regional extension the development of caldera border faults may be suppressed to the advantage of deep seated fractures clustered above the central part of the magma chamber thus favoring conditions for the formation of porphyry type ore deposits finally we demonstrate that well before the eruption the gradual emplacement of a hot and large silicic magma chamber may create significant extensional stress in the brittle upper crust resulting in breakup and pre eruptive normal faulting and thus allowing for conditions of pre caldera mineralization

the structural architecture of the los humeros volcanic complex and geothermal field abstract the los humeros volcanic complex lhvc is a large silicic caldera complex in the trans mexican volcanic belt tmvb hosting a geothermal field currently in exploitation by the comision federal de electricidad cfe of mexico with an installed capacity of ca 95 mw of electric power understanding the structural architecture of lhvc is important to get insights into the interplay between the volcano tectonic setting and the characteristics of the geothermal resources in the area the analysis of volcanotectonic interplay in lhvc benefits from the availability of subsurface data obtained during the exploration of the geothermal reservoir that allows the achievement of a 3d structural view of the volcano system the lhvc thus represents an important natural laboratory for the development of general models of volcano tectonic interaction in calderas in this study we discuss a structural model of lhvc based on morphostructural and field analysis integrated with well logs focal mechanism solutions and magnetotelluric imaging the structural analysis suggests that inherited regional tectonic structures recognized in the basement played an important role in the evolution of the magma feeding system caldera collapses and post caldera deformations these inherited weak planes have been reactivated by resurgence faults and post caldera magma driven hydrofractures under a local radial stress field generated by the shallow lhvc magmatic hydrothermal system the local stress field induced caldera resurgence and volcanotectonic faulting the results of this study are important to better constrain the structural architecture of large caldera complexes also our study is useful to understand the structure of the los humeros geothermal field and support the exploration of deeper super hot geothermal systems shgss and engineering of enhanced geothermal systems egss for electric power production in the lhvc and other active resurgent calderas

hyporheic exchange in gravel bed rivers with pool riffle morphology laboratory experiments and three dimensional modeling received 7 june 2005 revised 30 june 2006 accepted 25 august 2006 published 31 january 2007 1 we report the first laboratory simulations of hyporheic exchange in gravel pool riffle channels which are characterized by coarse sediment steep slopes and three dimensional bed forms that strongly influence surface flow these channels are particularly important habitat for salmonids many of which are currently at risk worldwide and which incubate their offspring within the hyporheic zone here we perform a set of laboratory experiments examining the effects of discharge and bed form amplitude on hyporheic exchange with surface subsurface mixing measured directly from the concentration decay of a conservative tracer fluorescein injected into the surface flow near bed pressure measurements were also used to predict hyporheic exchange from a three dimensional pumping transport model comparison of the predicted and observed hyporheic exchange shows good agreement indicating that the major mechanism for exchange is bed form induced advection however the effect of bed forms is modulated by discharge and the degree of topographic submergence we also tested the performance of the hydrostatic pressure as a proxy for the observed near bed pressure in driving hyporheic exchange which would facilitate field measurement and analysis of hyporheic flow in natural rivers we found agreement with measured hyporheic exchange only for low bed form amplitudes and high flows

modeling volcanic deformation in a regional stress field implications for the formation of graben structures on alba patera mars abundant grabens transect the volcano alba patera their complex geometry and formation mechanisms are still poorly understood tectonic processes and magmatic intrusions are responsible for these long surface features cross cutting relationships of the grabens show radial fractures that were formed during early stages and were progressively overprinted by concentric fractures on the mid and upper flanks of the volcano two modeling methods are used to understand the formation of the observed structures and to evaluate their implications for hidden subvolcanic processes surface deformation and fault arrangements predicted in finite element models are compared to the graben systems observed in viking images the orientation and position of the concentric grabens are found to be best reproduced by local crustal subsidence superimposed on a regional nw se oriented extension with decreasing magnitude from south to north in analogue sandbox models we also simulate surface structures of arrangements that almost perfectly mimic the observed lineaments on alba patera formation of the grabens spans a period on the order of a billion years suggesting long term geodynamic processes to be responsible for the subsidence of the central alba patera area the progressive change toward higher concentricity is likely resultant from an increase in density in the crust by accumulation of intrusive material and cooling thus causing subsidence of the region above this volcanic root

caldera forming processes and the origin of submarine volcanogenic massive sulfide deposits certain volcanogenic massive sulfide vms ore deposits form in submarine calderas this association is well known but the link between caldera formation and the origins of the deposits remains poorly understood here we show that the size and location of a vms deposit within a submarine caldera may be determined by how and when the caldera formed these spatial temporal conditions control development of the hydrothermal system associated with the vms deposit we propose that caldera opening along outward dipping faults promotes magma degassing seawater influx and high temperature leaching resulting in a metal rich hydrothermal fluid these outward dipping faults are considered to provide critical pathways for ore forming fluids responsible for some caldera hosted vms deposits and may also be fundamentally important for the formation of many other caldera hosted ore deposit types

structural architecture of the colima volcanic complex 1 the colima volcanic complex cvc is currently the most active mexican volcano and is located in the western sector of the trans mexican volcanic belt inside the active colima rift a regional n s striking extensional structure the colima rift is filled by a 1 km thick sequence of quaternary lacustrine sediments alluvium and colluvium mostly underling the about 3000 m thick volcanic pile of the cvc in this work we present the results of a detailed morphostructural and field study of quaternary faults and fractures in the cvc and the surrounding area including the regional structures of the colima rift we also present a geometrical modeling of the faults inside the volcano and a numerical model of the gravity induced stress and strain fields of the cvc the study attempts to characterize the geometry kinematics and dynamics of the deformation features of the cvc and relate it with the volcano structure the geology of the substratum and the geodynamic setting of the region our model considers that the observed deformation of the cvc and the surroundings results from the interplay between the active n s trending regional extensional tectonics and the southward spreading of the volcano over its basement forming an e w oriented volcanotectonic graben the interaction between regional tectonics and previously unrecognized volcanic spreading can control magma migration and flank instability in an area where eruptions and sector failures represent a potential high risk for more than 500 000 people

experimental studies of collapse calderas we present experiments to investigate the formation of calderas using inflatable balloons in a medium of fused alumina powder this system provides a model of a magma chamber in an homogeneous elastic media which scales to volcanic systems in terms of geometry and strength of the media three kinds of experiment were performed i the balloon was inflated and then deflated simulating pre emption tumescence and caldera collapse ii the balloon was deflated without prior inflation simulating caldera formation without pre eruption tumescence iii three balloons were inflated and deflated in a line simulating multiple magma chambers the influence of magma chamber shape was investigated using different shaped balloons balloon inflation formed a dome with a surface pattern of shallow polygonal fractures centrally and radial fractures peripherally uplift occurs along deep inward dipping concentric reverse faults deflation generated depressions with an outer set of concentric ring fractures surrounding a central funnel formed by sagging along numerous minor faults some of which formed during doming during collapse the concentric reverse faults were converted to normal faults and the radial normally faulted fractures were converted to reverse faults without prior tumescence an outer set of near vertical ring faults surround a flat central depression due to collapse of a coherent block an inner set of outward dipping reverse ring faults also develop the experimental caldera area increased with balloon size and increased as the balloon depth decreased for a given balloon volume and depth collapse area is significantly smaller if doming had occurred prior to collapse arcuate fractures can provide the pathways for magma ascent during pre emption tumescence smith bailey 1968 but the shallow radial and polygonal fracture systems may also influence vent location changes in fault geometry and sense of movement extension to compression and vice versa occur when subsidence initiates and can account for changes in vent location that occur in many eruptions multiple overlapping collapse calderas are associated with magma chamber migration whereas nested calderas can result from the activity of a single magma chamber

activating and reactivating pairs of nested collapses during caldera forming eruptions campi flegrei italy 1 a structural model for campi flegrei caldera cfc italy one of earth s most hazardous calderas is provided data from the north outer rim show that this formed by downsag soon after the neapolitan yellow tuff emplacement 15 ka campanian ignimbrite s cfc s other major eruption 39 ka displacement at depth also suggests the activity of a buried caldera fault therefore during the campanian ignimbrite eruption the north rim was activated as caldera bounding fault and during the neapolitan yellow tuff eruption as downsag previously published data reveal an inner collapsed structure to the south formed during the campanian ignimbrite eruption and reactivated during the neapolitan yellow tuff eruption so cfc consists of 2 nested depressions both active during the campanian ignimbrite and neapolitan yellow tuff eruptions but with different amounts of collapse cfc is a major example of how 2 nested calderas may 1 form during the same collapse episode 2 be reactivated together during caldera forming eruptions

experiments on cauldron formation a polygonal cauldron and ring fractures abstract the sequence of formation of the motojuku type cauldron fujita et al 1970 is summarized as follows 1 doming due to ascent of a magma body 2 development of normal faults which produce a polygonal cauldron and 3 eruption of acidic to intermediate pyroclastic material model experiments on a scale of 1 200 000 reveal that ascent of the magma body which was imitated by a ball of hardened putty produced a polygonal cauldron composed of radial and concentrically arranged short fractures on the roof of a dome no ring fractures were formed this type of cauldron develops near the surface on the other hand emission of magma which was imitated by evaporation of a ball of dry ice in brittle powdered material caused ring faults dipping outward and a circular cauldron without up or downwarping this type of cauldron develops upward from the magma body the former model is equated to the motojuku type cauldron and the latter model to the other types of cauldrons with ring fractures

velocity characteristics along a small step pool channel this paper summarizes measurements of velocity along three reaches of a small mountain channel with step pool bedforms a one dimensional electromagnetic current meter was used to record velocity fluctuations at 37 fixed measurement points during five measurement intervals spanning the peak of the annual snowmelt hydrograph measurement cross sections were located upstream from a bed step at the step lip downstream from the step and in a uniform gradient run data analyses focused on characteristics of velocity profiles and on correlations between velocity characteristics and the potential control variables bedform type reach gradient and flow depth to test the hypothesis that velocity characteristics are related to channel bedform types anova and ancova tests were performed for the average velocity and coefficient of variation of point velocity data results indicate that high frequency velocity variations correlate to some degree with both channel characteristics and discharge velocity became more variable as stage increased particularly at low gradient reaches with less variable bed roughness velocity profiles suggest that locations immediately downstream from bed steps are dominated by wake turbulence from mid profile shear layers locations immediately upstream from steps at step lips and in runs are dominated by bed generated turbulence adverse pressure gradients upstream and downstream from steps may be enhancing turbulence generation whereas favourable pressure gradients at steps are suppressing turbulence the bed generated turbulence and skin friction of runs appear to be less effective energy dissipators than the wake generated turbulence and form drag of step pool bedforms copyright 2000 john wiley sons ltd

high resolution satellite and airborne thermal infrared imaging of precursory unrest and 2009 eruption at redoubt volcano alaska abstract a combination of satellite and airborne high resolution visible and thermal infrared tir image data detected and measured changes at redoubt volcano during the 2008 2009 unrest and eruption the tir sensors detected persistent elevated temperatures at summit ice melt holes as seismicity and gas emissions increased in late 2008 to march 2009 a phreatic explosion on 15 march was followed by more than 19 magmatic explosive events from 23 march to 4 april that produced high altitude ash clouds and large lahars two or three lava domes extruded and were destroyed between 23 march and 4 april after 4 april the eruption extruded a large lava dome that continued to grow until at least early july 2009

the geological and structural evolution of the cerro tuzgle quaternary stratovolcano in the back arc region of the central andes argentina abstract the aim of our paper is to contribute to a better knowledge of the volcanism in the back arc region of the central andes and its relationships with the basement geology the stress field and the tectonic evolution by studying in detail the stratigraphy and the structure of the quaternary cerro tuzgle stratovolcano in the puna plateau field mapping and remote sensing analysis reveal the stratigraphic architecture the geological evolution and the volcanotectonic interactions in the cerro tuzgle area for the first time in a volcano of the puna plateau synthemic units bounded by unconformity surfaces have been defined unrevealing the temporal and spatial relationships between constructive and destructive phases of the volcano history our study indicates that after the emplacement of a small ignimbrite deposit and of few scattered lava domes the central cerro tuzgle volcano built up throughout three distinct phases of edifice construction the first of these constructive phases ended with a previously unreported destructive event consisting of 0 5 km 3 catastrophic sector collapse of the volcanic edifice whose stratigraphic position and main characteristics have been identified the study suggests that the regional stress regime and the topography of the substrata are the main non magmatic factors controlling the constructive and destructive phases of the volcano including the directions of magmatic intrusions faulting and gravitational sector failure of the volcano the integration of synthemic stratigraphy and volcanotectonic analysis in the study of volcanic edifices showed to be an effective methodological approach for the understanding of the magmatic and tectonic evolution of the puna plateau

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

a field investigation of the influence of sediment supply on step pool morphology and stability abstract the effect of the sediment supply on step pool morphology and stability was studied through the investigation of 42 step pool reaches eight in the vosges and 34 in the alps france step pool geometry step wavelength l and height h was measured for each reach and the data set split into two distinct groups comprising 25 connected to a sediment source step pool reaches and 17 disconnected step pool reaches the geometry analysis showed differences between the two groups with the shape factors k l hr and the h hr ratios hr is the residual pool depth being lower for disconnected step pools this was interpreted to result from progressively changing geometry over time with disconnected step pool geometry defining the probable asymptotic characteristic associated with this long term process the measured step pool dimensions were in good agreement with equations based on maximum flow resistance abrahams et al 1995 energy of a falling jet comiti et al 2005 and channel spanning deposition chartrand et al 2011 however the average shape factor for the comiti et al equation was k 17 instead of 8 as the authors had proposed the data set was extended to 255 values with data from the literature which confirmed this average value for k field evidence moss cover and stone imbrication indicate that connected step pools are mobile whereas disconnected step pools are stable this was investigated by a hydraulic analysis of threshold motion conditions for the boulder steps comparison with discharges measured at nearby gauging stations indicates that remobilization return periods are 20 50 years for connected step pools and even less when considering scouring effects and greater than 50 years for disconnected step pools this difference in step mobility was ascribed to the fact that with sediment supply the channel can freely adjust its local slope allowing a relatively efficient transfer downstream of large boulders by scouring effects

step pool evolution in the rio cordon northeastern italy the principle that formative events punctuated by periods of evolution recovery or temporary periods of steady state conditions control the development of the step pool morphology has been applied to the evolution of the rio cordon stream bed the rio cordon is a small catchment 5 km2 within the dolomites wherein hydraulic parameters of floods and the coarse bedload are recorded detailed field surveys of the step pool structures carried out before and after the september 1994 and october 1998 floods have served to illustrate the control on step pool changes by these floods floods were grouped into two categories the first includes ordinary events which are characterized by peak discharges with a return time of one to five years 1 8 5 15 m3 s 1 and by an hourly bedload rate not exceeding 20 m3 h 1 the second refers to exceptional events with a return time of 30 50 years a flood of this latter type occurred on 14 september 1994 with a peak discharge of 10 4 m3 s 1 and average hourly bedload rate of 324 m3 h 1 step pool features were characterized primarily by a steepness parameter c h ls s the evolution of the steepness parameter was measured in the field from 1992 to 1998 the results indicate that maximum resistance conditions are gradually reached at the end of a series of ordinary flood events during this period bed armouring dominate the sediment transport response however following an extraordinary flood and unlimited sediment supply conditions the steepness factor can suddenly decrease as a result of sediment trapped in the pools and a lengthening of step spacing the analogy of step spacing with antidune wavelength and the main destruction and transformation mechanism of the steps are also discussed copyright 2001 john wiley sons ltd

caldera structure amount of collapse and erupted volumes the case of bolsena caldera italy calderas are common on volcanoes but their structure is seldom visible the 19 km wide bolsena caldera italy formed between 0 6 and 0 2 ma the largely preserved structural rim and subsurface data make bolsena ideal to investigate caldera structure in relation to the subsidence and erupted volume in this paper we use remote sensing field analysis and available subsurface data at the surface the caldera passes from a downsag south rim to a narrow and densely faulted area north rim with outer normal and inner reverse faults the caldera structure on the widely faulted east rim appears to be scale dependent with a staircase like fault zone larger scale horst and graben like structures intermediate scale and domino like structures smaller scale subsurface data indicate asymmetric collapse with a northward increase in subsidence ranging from diffuse to the south to focused to the north deformation at the surface the collapse rate constant between ca 490 and 175 ka was more than magma output between ca 330 and 130 ka highlighting significant 200 m and prolonged 200 ka posteruptive subsidence as the nearby latera caldera west rim of bolsena was mostly active between ca 265 and 160 ka much of the subsidence at bolsena may be related to this activity suggesting a common magmatic reservoir the subsidence related structural variations along the caldera rim and the significant posteruptive subsidence found at bolsena have not been found in other calderas

dykes cups saucers and sills analogue experiments on magma intrusion into brittle rocks magma is transported in the crust by blade like intrusions such as dykes sills saucers and also collects in thicker laccoliths lopoliths and plutons recently the importance and great number o

morphology of pyroclastic cones and tectonics the relationships between morphology and spatial distribution of 1315 quaternary pyroclastic cones and coeval faulting of the volcanic substrate are analyzed in the following regions with different structural settings tepic rift mexico ethiopian rift mexican volcanic belt canary archipelago and mount etna field data and analog experiments of tephra cone emplacement and collapse enable the definition of a number of parameters which can be used to infer the geometry of the fracture feeding the magma to a pyroclastic cone the strike of the feeding plane is directly related to 1 the elongation of cone base and crater 2 the location of depressions on the crater rim and 3 the alignment of pyroclastic cones in relation to a given vent spacing in addition the strike and dip of faults affect the direction of cone breaching these relationships are valid for volcanic substrate topographic surfaces with an inclination of less than 9 and are especially sensitive to fault escarpment and cone height lava and cone density and fault orientation with respect to the dip of the volcanic substrate topography relations 1 and 2 become more pronounced for regions undergoing extensional tectonics where edifices also have a larger dimension whereas breaching in the direction of the fault dip is more widespread in regions under extension breaching along the fault strike as well as the coincidence between fault strike and vent alignment are more frequent in regions with transcurrent or transtensional tectonics

channel morphology gradient profiles and bed stresses during flood in a step pool channel abstract the stability of a step pool channel is investigated on the basis of measurements during a median annual flood the study reaches range in gradient from 5 to 10 and the flow was 3 m3 s 1 in an 8 m wide channel the estimated shear stress based on the channel gradient was 102 pa which implies that the channel ought to move half meter class boulders calculations of the shear stress using flow resistance equations yield values of about 30 pa these figures imply that the largest boulders in the channel could be moved in fact the channel is stable the effective stress remains well below the threshold to move the large structure forming boulders the steps are stable structures that result from interlocking of the larger stones they are semi randomly located depending on the location of keystones that are deposited in the channel by debris flows or fall out of the banks the high variation in step pool wavelength step height residual pool depth and pool length is indicative of the random nature of step location and structure along a reach there is no convincing evidence that special conditions govern their formation

a wave induced transport process in marine sediments we show how surface wave action can increase the rate of transport of solutes into a sandy seabed by orders of magnitude via a mechanism known as mechanical dispersion it is most effective for large sediment permeability and thickness high surface wave amplitude and shallow water a method for setting up the appropriate transport equation valid when dispersion is well developed is given its dispersion term contains two mechanical dispersion parameters that can be estimated roughly from existing data when the sediments are well sorted the dispersion can be inhomogeneous and anisotropic in homogeneous isotropic sediments the effect of surface wave action on transport into sediments on the eastern u s shelf is shown to be significant under certain conditions the effect on thawing of subsea permafrost beneath prudhoe bay alaska seems negligible

magmatic volatiles to assess permeable volcano tectonic structures in the los humeros geothermal field mexico abstract magmatic volatiles can be considered as the surface fingerprint of active volcanic systems both during periods of quiescent and eruptive volcanic activity the spatial variability of gas emissions at earth s surface is a proxy for structural discontinuities in the subsurface of volcanic systems we conducted extensive and regular spaced soil gas surveys within the los humeros geothermal field to improve the understanding of the structural control on fluid flow surveys at different scales were performed with the aim to i identify areas of increased gas emissions reservoir scale ii their relation to un known volcano tectonic structures fault scale favoring fluid flow and iii determine the origin of gas emissions herein we show results from a co2 efflux scouting survey which was performed across the main geothermal production zone 6 km 4 km together with soil temperature measurements we identified five areas with increased co2 emissions where further sampling was performed with denser sampling grids to understand the fault zone architecture and local variations in gas emissions co2 efflux values range from below detection limit of the device to 1464 g m 2 d 1 with a total output of 87 t d 1 across an area of 13 7 km2 furthermore 13cco2 and 3he 4he analyses complemented the dataset in order to assess the origin of soil gases carbon isotopic data cover a broad spectrum from biogenous to endogenous sources determined 3he 4he ratios indicate a mantle component in the samples of up to 65 being most evident in the northwestern and southwestern part of the study area we show that a systematic sampling approach on reservoir scale is necessary for the identification and assessment of major permeable fault segments the combined processing of co2 efflux and 13cco2 facilitated the detection of permeable structural segments with a connection to the deep high temperature geothermal reservoir also in areas with low to intermediate co2 emissions the results of this study complement existing geophysical datasets and define further promising areas for future exploration activities in the north and southwestern sector of the production field

progressive assembly of a massive layer of ignimbrite with a normal to reverse compositional zoning the zaragoza ignimbrite of central mexico the zaragoza ignimbrite and two enclosing rhyodacite pumice fall layers were emplaced during the 15 km3 dre 0 1 ma zaragoza eruption from los humeros volcanic centre 180 km east of mexico city the ignimbrite comprises several massive flow units the largest of which locally exceeds 20 m in thickness and is regionally traceable it comprises massive lapilli ash with vertical elutriation pipes and has a fine grained inverse graded base and a pumice concentration zone at the top it also exhibits an unusual gradational double vertical compositional zonation that is widely traceable a basal rhyodacitic 67 6 69 wt sio2 zone grades up via a mixed zone into a central andesitic 58 62 wt sio2 zone which in turn grades up into an upper rhyodacitic 67 6 69 wt sio2 zone zoning is also defined by vertical variations in lithic clast populations we infer that pyroclastic fountaining fed initially rhyodacite pumice clasts to a sustained granular fluid based pyroclastic density current the composition of the pumice clasts supplied to the current then gradually changed first to andesite and then back to rhyodacite inverse grading at the base of the massive layer may reflect initial waxing flow competence the pumice concentration at the top of the massive layer is entirely rhyodacitic and was probably deposited during waning stages of the current when the supply of andesitic pumice clasts had ceased the return to rhyodacitic composition may have been the result of eruption conduit modification during collapse of los potreros caldera marked in the ignimbrite by a widespread influx of hydrothermally altered lithic blocks and or a decrease in draw up depth from a compositionally stratified magma chamber as the eruptive mass flux waned the massive layer of ignimbrite thins locally to less than 2 m yet it still shows the double zonation correlation of the zoning suggests that the thin massive layer is stratigraphically condensed and aggraded relatively slowly during the same time interval as did the much thicker 50 m massive layer

magma genesis and chamber processes at los humeros caldera mexico nd and sr isotope data the mexican volcanic belt mvb a roughly east west structure consists of many late tertiary and quaternary cindercones domes calderas and stratovolcanoes1 2 los humeros caldera approximately 19 40 n latitude 97 25 w longitude lies on the northeastern part of the mvb where the belt overlaps with another major volcanic province the eastern cordillera3 fig 1 a compilation6 of the bulk chemical analyses of the two major volcanic provinces indicates that the mvb is characterized largely by calc alkaline series whereas rocks of the alkaline series dominate the eastern cordiliera ec pleistocene to recent basaltic to rhyolitic volcanism in los humeros caldera one of the best known examples of a well developed caldera in mexico7 9 presumably associated with the subduction of cocos plate along the middle america trench shows that the initial 87sr 86sr ratios range from 0 7039 to 0 7048 and the initial 143nd 144nd ratios from 0 5126 to 0 5129 we show here that these isotope ratios are negatively correlated and lie on the mantle array defined by morb and oceanic island rocks implying that los humeros magmas were generated in the upper mantle with very little if any contribution from the subducted oceanic crust sediments or continental crust

the role of extensional structures on experimental calderas and resurgence the structure and shape of collapses and resurgences is often controlled by pre existing discontinuities such as normal faults in rift zones in order to study the role of extensional structures on collapse and resurgence we used analogue models dry sand simulated the brittle crust silicone located at the base of the sand pack simulated magma in the experiments regional extension pre dated collapse or resurgence forming normal faults in a graben like structure the graben was filled with additional sand simulating post rift deposits a piston then moved the silicone downward or upward inducing collapse or resurgence within the previously deformed sand the collapses showed an ellipticity length of minor axis length of major axis between 0 8 and 0 9 with the major axis parallel to the extension direction the partial reactivation of the pre existing normal faults was observed during the development of the caldera reverse faults which conversely to what was expected from experiments without pre existing extension became partly inward dipping resurgence showed an elongation of the uplifted part with the main axis perpendicular to the extension direction at depth pre existing normal faults were partly reactivated by the reverse faults formed during resurgence these locally became outward dipping normal faults a total reactivation of pre existing faults was also observed during resurgence the experiments suggest that the observed elongation of calderas and resurgences is the result of the reactivation of pre existing structures during differential uplift such a reactivation is mainly related to the loss in the coefficient of friction of the sand the results suggest that elliptic calderas and resurgences in nature may develop even from circular magma chambers

fissure ignimbrites fissure source origin for voluminous ignimbrites of the sierra madre occidental and its relationship with basin and range faulting the sierra madre occidental is mostly composed of middle tertiary large volume ignimbrites from the united states mexico border 318n the sierra madre occidental extends southward to its intersection with the mexican volcanic belt 218n ignimbrites of equivalent age extend into southern mexico as discontinuous outcrops considering the average thickness of 1000 m for these ignimbrites based on representative measured sections a conservative estimate of their total volume is 393 000 km 3 fewer than 15 calderas have been identified in this province and the source of most of these ignimbrites has been an unsolved problem we present geologic evidence indicating that fissures most of them with the regional trend of basin and range faults served as conduits for the ignimbrites these fissures can be several kilometers long and are represented by pyroclastic ignimbrite dikes rhyolitic lava dikes linearly aligned lava domes and elongated coignimbrite lithic lag breccias adjacent to basin and range faults considering that the basin and range extension overlapped in time and space with the ignimbrite flare up we propose a model in which batholith sized magma chambers reached shallow crustal levels and erupted their contents when they reached basin and range normal faults the faults acted as vents and caused fast decompression when the system was opened and large volumes of silicic magmas were explosively erupted finally devolatilized rhyolitic magmas were emplaced as domes or dikes we propose the term fissure ignimbrites for ignimbrites formed in this way

step pool formation models and associated step spacing step pool bedforms develop under conditions of high flow rates and high sediment influx and transport rates step setting events are capable of mobilizing and rearranging the large step forming grain sizes thus observations of the processes of step formation are limited to flume experiments the results of laboratory experiments involving active transport of widely sorted sediment including large grains whose deposition readily formed steps are presented over 350 step formations were observed and documented creating a large data set for detailing and evaluating step formation processes existing step formation models focus on step development from antidunes particle clusters transverse ribs or depositional berms or from a hydraulic regime that includes cascade flow and hydraulic jumps these models were developed using field measurements of artificial grade control structures or stable step pool systems during low flow conditions or degradational flume experiments where flows elucidated the step pool bedform in the channel profile but did not create equilibrium transport of the large step forming clasts this research evaluates the pre existing formation models and proposes three new models the rough bed exhumation and dune models the rough bed model was dominant throughout the experiments followed by the exhumation model and then the dune model a single model was not responsible for all step formations the rough bed exhumation and dune models all influenced step development and every step sequence was created through a mixture of formation processes this research generated a large data set where each step spacing is paired with the corresponding step formation model making it possible to identify a distinct exclusion zone length for each model thus given knowledge of the step formation model the minimum distance to the next step downstream can be predicted from the final spacing of a step sequence it may be possible to deduce the likely formation mechanisms active during a step resetting event copyright 2007 john wiley sons ltd

aster watches the world s volcanoes a new paradigm for volcanological observations from orbit onboard nasa terra spacecraft is one of the most sophisticated earth observing instruments ever flown the advanced spaceborne thermal emission and reflection radiometer aster created as part of a joint project between the japanese ministry of economy trade and industry and nasa this instrument consists of three independent bore sighted telescopes with 14 channels in the visible near infrared and thermal infrared regions capable of being pointed up to 22 5 off nadir in addition there is an additional backward looking visible channel telescope for stereo photogrammetric observations the spatial resolutions are 15 m pixel in the visible 30 m pixel in the near ir and 90 m pixel at thermal wavelengths and the swath width is 60 km aster instrument offers unprecedented opportunities for observing volcanoes and their activity from low earth orbit it is the purpose of this short paper to introduce aster to the volcanological community highlight its capabilities advantages and limitations and to show some examples of aster data and related analyses we will also explain how users can readily access aster data

the effect of collapse structures on ground deformations in calderas ground deformations related to unrest episodes in calderas are generally interpreted like in other volcanic environments in terms of increased pressure within a magma chamber embedded in a continuous elastic medium in this framework the depth of the pressure source is inferred from the size of the deformed area this scheme works quite well for individual volcanoes for instance hawaiian shields where a good correspondence between inflation events and eruptive episodes has been observed ground deformation in calderas however show unusual features that are difficult to interpret within such a scheme because considerable positive deformation in the order of several meters and microfracturing i e intense seismicity may occur without eruptions altough the estimated depth for the magma source is sometime very shallow less than 1 2 km it has been recently suggested that the contact zones at the border of collapsed calderas could act as stress strain discontinuity zones and thus bias modeling results obtained for continuous elastic media we use both observations and theoretical modeling based on 3 d finite element techniques to show that ground deformations in collapsed calderas are strongly influenced by the caldera structure giving a new perspective in related geological and geophysical observations in such areas

the effects of kinetic sorting on sediment mobility on steep slopes in poorly mobile static armour sorting is usually considered the result of hiding exposure effects we called this effect static sorting in opposition to very efficient grain to grain mechanisms produced by a mobile mixture called kinetic sorting we hypothesized that kinetic sorting can be an important contributor to the morphodynamics of mountain streams and attempted to demonstrate this with new flume experiments two long runs were produced with natural poorly sorted sediments and with transport stages of the coarse fraction defined by the ratio between the shear stress and the critical shear stress for transport smaller and higher than 1 respectively both runs produced an efficient transfer downstream of the injected material but with a major difference the first run no kinetic sorting produced permanent armour figuring clusters akin to what has already been observed in similar experiments the second run with kinetic sorting also produced bed armouring but this armour was periodically totally destroyed leading to substantial bed erosion this phenomenon was explained by kinetic sorting the effects of which are to produce an efficient downward migration of fine materials and bed surface armouring the consequence is that fine materials are hidden to the flow during aggradation allowing the slope to attain values much steeper than would have been expected at equilibrium for the mixture however whereas the surface armouring tends to stabilize the bed construction of a layer of fine sediments at the subsurface also contributes to making it very unstable these two contradictory effects explain the complex bed behaviours and the existence of very large bedload and slope fluctuations copyright 2014 john wiley sons ltd

elliptical calderas in active tectonic settings an experimental approach abstract caldera volcanoes form due to collapse of a magma chamber roof into the underlying magma chamber many field theoretical and experimental studies have postulated that calderas are delimited by reverse ring faults and are surrounded by peripheral concentric normal faults in the simplest theoretical scenario circular magma chambers produce circular calderas many calderas however are elliptical in shape particularly those in extensional and compressive tectonic settings several factors may explain elliptical calderas the first is the presence of an elliptical magma chamber established by for instance preferential intrusion along pre existing basement structures or differential spalling of the magma chamber walls the second is the overlap nesting of several discrete calderas to form a single larger elliptical structure the third is asymmetric subsidence the fourth is variable pre collapse topography a fifth possible factor is distortion of the caldera faults by the regional stress field during caldera formation a sixth factor is the post collapse distortion of the caldera structure due to continued regional deformation to better understand relationships between caldera surface expression reservoir geometry and regional tectonic stresses we conducted scaled analogue experiments these experiments examined the impact of regional stress and associated structures on calderas formed during evacuation of reservoirs circular rubber balloons of known dimensions and depths the results show that in principle calderas produced in compression extension experiments are elongated parallel to the direction of minimum horizontal compressive stress despite the chamber beneath being circular in plan view as a consequence model ring fault orientation varied from steeply dipping where striking perpendicular to the minimum horizontal regional compressive stress to shallower dips where striking parallel to the minimum horizontal regional compressive stress this leads us to suggest that the influence of a regional stress field on caldera fault orientation during and or after caldera formation may be significant in the development of elliptical calderas in addition such variation of caldera ring fault dip from steep to relatively shallow could influence location and behaviour of ring fissure eruptions

caldera subsidence in areas of variable topographic relief results from analogue modeling calderas form in volcanic areas commonly associated with topographic relief pre existing topography plays an important role in the style of the caldera subsidence topography increases the load and affects the principle stress trajectories located between the roof of the magma chamber and the surface the morphology internal structure and temporal evolution of calderas are therefore sensitive to the local topography we carried out scaled analogue experiments to investigate the effect of pre existing topographic relief on caldera subsidence by modeling the presence of stratocones and plateaus of variable mass diameter and positions prior to collapse we induced collapse in sandbox experiments by withdrawing water from a rubber bladder to simulate caldera collapse into a large shallow reservoir deformation was first manifested by sagging of the sand at the surface followed by the upward propagation of a set of subsidence controlling faults from the bladder in experiments with no topography these faults usually reached the surface near the centre of the cylinder as evacuation and incremental growth progressed a second outer set of subsidence controlling faults developed this outer set dominated the subsidence by increasing the topographic load by 6 the subsidence efficiency increased producing calderas up to approximately 20 deeper the inner set of subsidence controlling faults steepened and controlled most of the collapse by contrast to the experiments without topography adding load also reduced outward growth of peripheral sagging and development of extensional faults leading to a diameter of sagging 20 smaller than with no topography a comparative analysis of our results with mount mazama at crater lake oregon and glass mountain at long valley california supports the interpretation that the addition of topographic load modifies the evolution of the major caldera faults

the morphologic structure of step pools in mountain streams abstract step pool sequences in streams in the santa monica mountains of southern california impart a characteristic morphologic structure that varies with slope but despite the strong association with slope that suggests a direct process control analysis of 464 step pools in 13 study reaches reveals the relationship to reflect correlation but not necessarily causality the direct control on step height is particle size whereas discharge is the probable causal process determining step wavelength because both particle size and discharge generally change with channel slope downstream a slope variation with step wavelength and height is the apparent indirect geometric result a conceptual model of process form linkages is proposed based on these results whereby the step pool morphology is produced by positive relationships between wavelength and discharge and between height and particle size the model offers new insights for explaining the step pool morphology and it is potentially useful in channeling future efforts toward the appropriate scales and variables

structural analysis and thermal remote sensing of the los humeros volcanic complex implications for volcano structure and geothermal exploration abstract the los humeros volcanic complex lhvc is an important geothermal target in the trans mexican volcanic belt understanding the structure of the lhvc and its influence on the occurrence of thermal anomalies and hydrothermal fluids is important to get insights into the interplay between the volcano tectonic setting and the characteristics of the geothermal resources in the area in this study we present a structural analysis of the lhvc focused on quaternary tectonic and volcano tectonic features including the areal distribution of monogenetic volcanic centers morphostructural analysis and structural field mapping revealed the geometry kinematics and dynamics of the structural features in the study area also thermal infrared remote sensing analysis has been applied to the lhvc for the first time to map the main endogenous thermal anomalies these data are integrated with newly proposed unconformity bounded stratigraphic units to evaluate the implications for the structural behavior of the caldera complex and geothermal field the lhvc is characterized by a multistage formation with at least two major episodes of caldera collapse los humeros caldera 460 ka and los potreros caldera 100 ka the study suggests that the geometry of the first collapse recalls a trap door structure and impinges on a thick volcanic succession 10 5 1 55 ma now hosting the geothermal reservoir the main ring faults of the two calderas are buried and sealed by the widespread post calderas volcanic products and for this reason they probably do not have enough permeability to be the main conveyers of the hydrothermal fluid circulation an active previously unrecognized fault system of volcano tectonic origin has been identified inside the los potreros caldera this fault system is the main geothermal target probably originated by active resurgence of the caldera floor the active fault system defines three distinct structural sectors in the caldera floor where the occurrence of hydrothermal fluids is controlled by fault induced secondary permeability the resurgence of the caldera floor could be induced by an inferred magmatic intrusion representing the heat source of the geothermal system and feeding the simultaneous monogenetic volcanic activity around the deforming area the operation of the geothermal field and the plans for further exploration should focus on both the active resurgence fault system and the new endogenous thermal anomalies mapped outside the known boundaries of the geothermal field

geometric scaling of step pools in mountain streams observations and implications understanding the geometric structuring of alluvial step pools is an enduring problem in mountain stream geomorphology many previous studies propose that the key control parameter governing the step pool form is mean bed slope as explored through several examples however we find that slope control formulations are inconsistently demonstrated for broad data sets on this basis we reexamine the bed form architecture of step pools with a new descriptive parameter termed the aspect ratio active stream width divided by step drop height we test with data collected from three different mountain settings for step pools observed over mean bed slopes ranging from 2 to 22 we find that step wavelength and height are well described by when these dimensions are normalized by the step drop height furthermore we observe that varies inversely with mean bed slope context for our findings is provided by recent field and laboratory work which highlights that the cross stream component to the overall flow structure in step pools and scour pools is significant this is important because it expands upon and relates our work to formative models which are based on jet scour and the associated three dimensional flow structure of step pools our work has practical implications for the design of step pool channels because existing approaches are based in large part on structuring artificial systems according to a narrowly defined geometry we observe however that under certain conditions this approach may yield constructed step pools that are unstable as an alternative approach we propose that the geometric relationships developed here can be applied to identify artificial step pool geometries that will be more fully reflective of natural analogs and thus possibly more stable

experimental modelling of shallow magma emplacement application to saucer shaped intrusions abstract saucer shaped dolerite and sandstone intrusions are common in sedimentary basins world wide we have conducted a series of scaled experiments simulating the process of magma emplacement in sedimentary basins with particular attention on the formation of saucer shaped sills the model materials were 1 cohesive fine grained silica flour representing brittle crust and 2 molten low viscosity oil representing magma the experiments were performed in both homogeneous and layered models in all the experiments oil injection resulted in doming of the surface in the homogeneous models the injected oil formed cone sheets and sub vertical dykes cone sheets formed for shallow injection 1 3 cm and vertical dykes formed for deeper injection 4 5 cm in layered models the injected oil always formed saucer shaped intrusions our experimental results show that 1 sill intrusion results in the formation of a dome with melt erupting at the rim 2 layering controls the formation of sills and saucer shaped sills 3 saucer shaped sills are fed from the bottom and the fluid flows upward and outward and 4 the diameter of saucer shaped sills increase with increasing emplacement depth the systematic relation between domes and sills and the depth dependence of sill diameters show that saucer shaped intrusions result from the interaction between a growing flat lying shallow sill and doming of the free surface we conclude that saucer shaped intrusions represent fundamental geometries formed by shallow magma intrusion in stratified basins

the interaction between regional and local tectonics during resurgent doming the case of the island of ischia italy abstract the volcanic island of ischia is located on the tyrrhenian margin of central italy characterized by plio quaternary nw se and ne sw trending extensional fractures ischia displays a resurgent dome uplifted by at least 800 m in the last 33 ka remote sensing and field data have been collected to study the structural setting of the island the deformation pattern associated with resurgence and the superimposition of the regional and the resurgence induced stress fields nw se and ne sw extensional fracture systems predominate throughout the island and around the resurgent block suggesting a relationship with the regional extensional structures these systems were formed before resurgence and were partly reactivated during resurgence the reactivation of pre existing regional systems during resurgence confined the extent of the uplifted area n s and e w trending systems have been found exclusively at the borders of the dome and are interpreted as being induced by resurgence the topmost resurgent block shows an octagonal shape in map view and is tilted at an angle of 15 around a ne sw trending horizontal axis the block is partly bordered by high angle inward dipping regional faults more than 90 in volume of the volcanic products coeval with resurgence on ischia have been erupted outside the resurgent block area suggesting that the resurgence process locally replaced volcanic activity in the last 33 ka

caldera collapse during the 2000 eruption of miyakejima volcano japan a collapsed caldera 1 6 km in diameter and 450 m in depth was formed at the summit of miyakejima volcano during the 2000 eruption the collapsed caldera appeared on 8 july with a minor phreatic eruption 12 days after seismic activity and magma intrusion occurred northwest of the volcano growth of the caldera took from 8 july to the middle of august with seismic swarms associated with the continuous intrusion of magma northwest of the volcano the growth rate of the caldera was about 1 4 107 m3 day and the final volume of the collapsed caldera was about 6 108 m3 major phreatomagmatic eruptions produced a total of about 1 6 1010 kg 1 1 107 m3 of volcanic ash after caldera growth the caldera structure and the nature of the eruptive materials of the first collapse on 8 july suggest that the surface subsidence was caused by the upward migration of a steam filled cavity with stoping of the roof rock above the magma reservoir the diameter of the stoping column was estimated to be 600 700 m from circumferential faults that developed in the caldera floor and the collapse of the caldera wall enlarged the diameter of the caldera to 1 6 km the total volume of the caldera and the horizontal diameter of the stoping column gave a subsidence of the caldera floor of 1 6 2 1 km

experimental investigations of the evolution of step pools in rills with heterogeneous soils in yuanmou dry hot valley sw china abstract as a common type of microtopography in rill channels the formation and dynamics of step pools are prerequisites for the occurrence of rills however the evolution of step pools in a rill sprs is still unclear scouring experiments in field plots were conducted to explore the dynamic evolution of sprs and the effect of steps on pools under conditions of strong runoff and soil like materials aggregated with gravels in yuanmou dry hot valley sw china using three dimensional laser scanning spatial analysis of a gis geographic information system and statistical analysis 11 parameters were used to characterize step pool morphology the results showed that sprs formed after several scourings at particular locations and some of them disappeared in the late stage a diverse range of sprs formed with geometrical parameters initially increasing then stabilizing and finally decreasing during scouring pool shape transformed from a deep v shape to a shallow v shape and then to a u shape the evolution of a typical pool included initial active stable and fading stages there were 59 oval shaped pools 88 06 of the total number of pools in plane form and 37 deep pools 55 22 in cross section and significant differences in the plane form and profile morphology of a pool presented themselves during its evolution sprs developed more easily in dry red soil like materials compared with vertisol like materials the geometrical parameters of pools correlated with step size and pools became deeper with increasing step height and longer with increasing step height and decreasing step slope the spatial heterogeneity of soil like materials as well as hydraulic conditions led to complex and nonlinear spr evolution it is helpful to further understand the mechanism of rill incision and evolution

thermal infrared remote sensing detection of thermal information associated with faults a case study in western sichuan basin china abstract using enhanced land surface temperatures lsts image retrieved from landsat etm this article shows that thermal information associated with faults have been detected these anomalies may be provided by geothermal natural convection through faults and partially influence the ground surface thermal environment the study area in southern segment of longmen mountains thrust belt of western sichuan basin contains complex faults and folds with recent earthquake activity in order to study the faults for future oil exploration we use lst data retrieved from landsat thermal infrared band to detect the thermal information associated with faults the lsts are enhanced by filtering out anthropogenic activity and influence land cover classes and interpolating to contour map the spatial patterns of the enhanced images revealed the spatial correspondence between the thermal information and the dip planes of faults when compared with the explanation profiles and geologic features obtained from the 3d seismic geophysical data the thermal affected ranges calculated and the statistically significant of regression model also indicate the result that the thermal information located near the faults are consistent with the faults dip planes

the impact of exceptional events on erosion bedload transport and channel stability in a step pool channel sediment transport in the erlenbach a small stream with step pool morphology in the canton of schwyz switzerland has been monitored for more than 20 years during this time three exceptional events events with high sediment yield and long return times that have a large effect on channel morphology have impacted the stream and partly or completely rearranged the existing step pool morphology in the aftermath of the events sediment transport rates at a given discharge and total sediment yield remained elevated for about a year or longer for the last event dated on the 20 june 2007 observations of boulder mobility and step destruction were used to interpret channel stability boulders with median diameters of up to 135 cm and estimated weights of more than 2 5 tons have moved during the 2007 event using hydraulic observations and shear stress calculations boulders up to 65 cm in diameter were predicted to have been fully mobile in peak conditions even if form resistance and increased critical stresses needed for the initiation of motion in steep streams were taken into account for two of the events estimated peak shear stresses at the bed exceeded 1000 pa calculated both from observations of the flow hydraulics and from boulder mobility this suggests that highly energetic flows occur relatively frequently in small steep streams and that large boulders can be transported by fluvial processes in such streams the observations have potential significance for hazard risk mitigation stream engineering and restoration copyright 2009 john wiley sons ltd

flow regimes bed morphology and flow resistance in self formed step pool channels received 3 july 2008 revised 28 december 2008 accepted 13 january 2009 published 25 april 2009 1 we used a mobile bed flume with scaled grain size distribution channel geometry and flow to examine morphology and hydraulics of stepped channels we hypothesized that 1 step geometry and flow resistance differs significantly as a function of the range of grain sizes present 2 a transition from nappe to skimming flow occurs in stepped channels with mobile beds for conditions similar to stepped spillways and 3 the partitioning of flow resistance changes significantly when flow passes from nappe to skimming conditions results support each of these hypotheses and help to illuminate the complexity of v q relationships in stepped channels in which a dramatic decrease in flow resistance and increase in velocity accompany the transition from nappe to skimming flow near step forming events therefore a single flow resistance equation applicable to both ordinary and large floods may not be ideal in stepped channels nonetheless models based on dimensionless velocity and unit discharge appear more robust compared to those based on the darcy weisbach friction factor

alluvial architecture in headwater streams with special emphasis on step pool topography alluvial mountain streams exhibit a range of channel forms pool riffle plane bed step pool and cascades previous work suggested that these forms exist within discrete and progressively steeper slope classes measurements conducted at over 100 sites in west central and central idaho confirm that slope steepens progressively as one moves from pool riffle to plane bed to step pool and finally to cascades median slope for pool riffle topography is 0 0060 for plane beds 0 013 for step pools 0 044 and for cascades 0 068 there is substantial overlap in the slopes associated with these channel forms pool riffle topography was found at slopes between 0 0010 and 0 015 plane beds between 0 0010 and 0 035 step pools between 0 015 and 0 134 and cascades between 0 050 and 0 12 step pools are particularly striking features in headwater streams they are characterized by alternating steep and gentle channel segments the steep segments step risers are transverse accumulations of boulder and cobbles while the gentle segments pools contain finer material step wavelength is best correlated to step height which is in turn best correlated to the median particle size found on step risers this result differs from past studies that have reported channel slope to be the dominant control on step wavelength the presumed geometry and froude number associated with the features under formative conditions are consistent with the existence field for antidunes and by extension with the hypothesis that step pools are formed by antidunes copyright 2000 john wiley sons ltd

from outcrop scanlines to discrete fracture networks an integrative workflow abstract understanding fractures and fracture networks is essential for the investigation and use of subsurface reservoirs the aim is to predict the fractures and the fracture network when there is no direct access to subsurface images available this article presents a universal workflow to numerically compute a discrete fracture network by combining the 1d scanline survey method processed with the newly written skapy script together with the multiple point statistic method mps this workflow is applied to a potential geothermal site in mexico called acoculco we use las minas outcrops and quarries as surface analogues for the acoculco reservoir as las minas and acoculco are both formed by the influence of a plutonic intrusion into the jurassic cretaceous carbonate sequence of the sierra madre oriental in the trans mexican volcanic belt tmvb the intrusion is associated with contact metamorphism and metasomatic phenomena providing the basis for the mining activities at las minas the results obtained using this workflow demonstrate the feasibility of the approach which presents a solution combining the efficiency of data processing and an interpretation driven approach to build realistic discrete fracture networks this workflow can be used in the process of estimating the permeability of a fracture controlled reservoir with using only scanline surveys data as input this is essential in the process of evaluating the feasibility to develop an enhanced geothermal system

stream bed stabilization using boulder check dams that mimic step pool morphology features in northern italy during the last 10 years the check dams made of boulders have been fully employed for torrent management particularly for high gradient stream stabilization the analysis of this typology is shown in relation to three aspects building features field of use and design according to geomorphologic principles the maso di spinelle torrent located in the province of trento italy north italian alps is an example where a sequence of low check dams made of boulders have been used for bed stabilization the design criteria are taken from the step pool morphology features and the results are encouraging for further applications the artificial step pool grade control structures in the maso di spinelle torrent have been successfully tested by floods events with return periods of about 7 10 and 20 25 years

an updated conceptual model of the los humeros geothermal reservoir mexico an analysis of production and reservoir engineering data of 42 wells from the los humeros geothermal field mexico allowed obtaining the pressure and temperature profiles for the unperturbed reservoir fluids and developing 1 d and 2 d models for the reservoir results showed the existence of at least two reservoirs in the system a relatively shallow liquid dominant reservoir located between 1025 and 1600 m above sea level a s l the pressure profile of which corresponds to a 300 330 c boiling water column and a deeper low liquid saturation reservoir located between 850 and 100 m a s l with temperatures between 300 and 400 c both reservoirs seem to be separated by a vitreous tuff lithological unit but hydraulic connectivity occurs through faults and fractures of the system allowing deep steam to ascend while condensate flows down porous heat pipe the geochemical and isotopic n 18 o nd composition of the produced fluids can be explained as the result of a boiling process with reservoir steam separation and partial condensation a fact that agrees with the proposed reservoir engineering model 2003 elsevier science b v all rights reserved

the role of laboratory experiments in volcanology experiment is central to scienti c methodology within science in general experiments are used for four primary purposes i e as a tool to explore novel phenomena and to provide systematic observations of processes to determine the values of key parameters to test hypotheses and theoretical models and to validate computational models which themselves can be considered as numerical experiments the study of volcanic eruptions and magmatic processes is becoming increasingly systematic quantitative and rigorous the drive is towards providing detailed quantitative descriptions and models of the ow phenomena in terms of fundamental physico chemical processes this is motivated in no small way by an increasing need for reliable and quantitative predictions of volcanic eruptions on which to base rational hazard and risk management decisions during volcanic crises a natural consequence of this development of the scienti c study of volcanic ow phenomena is that rigorous laboratory experimentation is becoming an increasingly important feature within volcanic research the contribution of experimental research to our understanding of volcanic processes is di cult to overstate the determination of the values of key parameters has traditionally taken place in the laboratory however more recently experiments have become much more widely applied to the problem of understanding complex dynamical processes and their underlying mechanisms without models experimental theoretical numerical we are limited to qualitative interpretations of eld observations and remote sensing field data are of course essential and provide the measure against which ultimately the applicability of observations from other sources must be assessed however there are several reasons why the scienti c study of volcanic phenomena cannot rely solely on eld data direct observations of eruption processes in the eld are limited to those parts of an eruption that are accessible this restricts detailed observations to a limited range of above surface processes moreover logistical constraints mean that the systematic collection of data will usually only be possible for volcanic eruptions near an established observatory and for activity for which there has been some forewarning as a result of these constraints direct eld based observations of natural volcanic eruption processes are generally incomplete and uncertain another source of natural data derives from observations made on volcanic deposits in principle processes can be inferred from the features

controls on large boulder mobility in an auto naturalized constructed step pool river san clemente reroute and dam removal project carmel river california usa

aster observations of thermal anomalies preceding the april 2003 eruption of chikurachki volcano kurile islands russia abstract chikurachki volcano northern kurile islands chain paramushir island 50 20 n 155 27 e elevation 1816 m stratovolcano has been in a state of unrest for over twenty years its most recent eruption that began in april 2003 was preceded by an eruption between january and may 2002 thermal infrared images from the japanese united states advanced spaceborne thermal emission and reflection radiometer aster 5 tir channels 8 12 m 90 m pixel noise equivalent delta temperature ne t 0 1 0 3 k onboard the u s national aeronautics and space administration s terra polar orbiting spacecraft of a snow covered chikurachki volcano taken in january 2003 show muted evidence of thermal activity aster thermal infrared tir images from february 2003 however indicate warmer areas within the summit crater average whole pixel temperatures of adjacent summit slopes are in the range of 250 252 k while many summit crater whole pixel temperatures are 2 6 k greater a two component planck solution for the warmer pixels yields a solution of 275 277 k for 10 15 of the chikurachki summit crater and 285 295 k for 25 35 of a prominent hotspot on its flank an interpretation of this enhanced pre eruption heat flow is the presence of surface melt water the detection in aster data of such subtle precursory heat flow enhancement even retrospectively raises important issues for remote monitoring of dormant snow capped volcanoes especially those that threaten nearby populations like mt rainier

local scouring and morphological adjustments in steep channels with check dam sequences this paper describes bed profile and grain size distribution adjustments in a mountain river maso di spinelle river italian alps stabilized by a sequence of boulder check dams the control works were originally designed to simulate the geometry of natural step pool channels where tumbling flow is the dominant hydraulic regime local scouring downstream of 29 drop structures is analysed through the use of nondimensional parameters where maximum scour depth and scour length are normalised to the drop height prior laboratory data reveal a pattern similar to field scours where complex interactions occur between drop height critical flow depth and step spacing the linkage between scour length and depth is also discussed there seems to be a maximum step height for impinging jets that is approximately twice the drop height this maximum may explain the upper limit of the steepness factor found in high gradient step pool streams if such a maximum upper limit is confirmed by further studies this may aid designs of foundation heights for transverse control works in steep channels

morphological effects of local scouring in step pool streams step pool morphology characterizes many high gradient streams in a variety of natural settings but formative processes and evolutionary dynamics are still poorly understood in this paper natural step pool geometry is compared with steep alluvial channels where grade control structures such as check dams and bed sills make the stream profile resemble a natural stepped stream along these channels local scouring due to falling jets forms plunge pools under each structure analogous to natural steps determining the formation of pools in order to test the hypothesis that natural pools are analogous to pools formed below grade control works with respect to their dimensions shape and formative dynamics 37 natural pools and 73 artificial pools were surveyed in 10 mountain streams of the eastern italian alps pools below grade control works featured a transitional zone between the scour hole and the downstream sloping bed marked by a depositional berm when geometric parameters such as maximum pool depth length and step berm distances are normalized to the jet virtual energy no statistically significant differences were detected between natural and artificial systems these results lend support to an upstream forced cascade model for step pool formation where the energy of falling jets controls the geometry of the pools and is therefore regarded as the most important scaling independent variable copyright 2005 john wiley sons ltd

anatomy of the xaltipan ignimbrite at los humeros volcanic complex the largest eruption of the trans mexican volcanic belt abstract the xaltipan ignimbrite ca 290 km3 dre represents the major explosive event from los humeros volcanic complex lhvc that can be ranked as the largest caldera forming eruption of the trans mexican volcanic belt tmvb this eruption marked the onset of an explosive period of lhvc producing the collapse of the main los humeros caldera at 164 4 2 ka this paper provides a detailed characterization of the xaltipan ignimbrite anatomy and eruptive chronology that records a multi phase single eruption this eruption resulted in more complex architecture and lithofacies variations of the ignimbrite than previously reported to support these findings we present two representative composite xaltipan stratigraphic columns based on two regional reference sections together with a welding lithofacies map digital mapping energy line projections geologic sections and high resolution petrophysical characterization micro ct he pycnometry additionally we have reevaluated the magnitude dre volume and the total erupted mass of the deposit by taking into account critical primary and post emplacement processes such as lithic concentration welding grade and bulk loss due to erosion the internal architecture of the xaltipan ignimbrite is composed of two flow units and two pumice fallout deposits a basal one and an intercalated layer which formed as a result of a voluminous and sequential eruption that can be resumed in four eruptive phases the initial stage of the eruption produced a basal pumice fallout bpf phase 1 derived from a buoyant plume that eventually collapsed generating pyroclastic density current pdc deposits with intra ignimbrite pumice fallout beds this event was followed by the climactic caldera forming boiling over type eruptive phase phase 2 that generated voluminous pdcs of the lower flow unit lfu as the eruption waned a brief eruptive hiatus occurred immediately followed by a second explosive event in the western rim of the caldera with a boiling over type eruptive column depositing a discrete pumice fallout layer ipf phase 3 which later collapsed depositing less voluminous pdc fu2 in the western flank of the los humeros caldera phase 4 the anatomy of the deposits shows that the xaltipan ignimbrite was emplaced in different behaviors radially in the proximal parts and channelized and confined in the distal parts showing significant welding variations that range from non to highly welded conditions welding ranks i vi controlled mainly by the paleotopography the size calculations indicate that the deposits have an aerial extent of ca 4600 km2 an ejected bulk volume of ca 330 km3 with a dre volume of ca 290 km3 and an ejected mass of 1 1 1012 kg which points out to a paroxysmal eruption vei 6 7