transient hydrogeologic models for submarine flow in volcanic seamounts 2 comparison of the hawaiian canary and marquesas islands 1 large bathymetric gradients associated with volcanic seamounts can drive convective flow while thick sedimentary aprons that typically surround volcanic edifices host compaction driven flow in these submarine environments the interactions of compaction driven and buoyancy driven fluid flow lead to complex hydrogeologic regimes we apply transient numerical models of coupled fluid flow and heat transport to the hawaiian canary and marquesas islands to examine the role of volcanic architecture on the evolution of fluid flow and pore pressure during volcanic building lithospheric flexure sedimentation and compaction the islands differ in edifice size sedimentary apron structure amount of lithospheric flexure and sedimentation and volcanic growth rates by comparing these variations we examine how geometry and geologic history affect fluid flow and pore pressure patterns buoyancy driven flow is most influenced by edifice height and amount of lithospheric flexure compaction driven flow is altered primarily by thickness of prevolcanic sediment the sedimentation rate and the size of the volcanic edifice in hawaii the area with the highest edifice and most flexure flow velocities and excess pore pressures are greatest with darcy velocities of 30 mm yr and excess pressures of 7 mpa during the beginning of volcanic building high sedimentation rates in the marquesas sedimentary apron increase fluid velocities in the later portion of volcanic building with darcy velocities 12 mm yr in the canary islands compaction driven flow occurs for an extended time period because of long slower volcanic building resulting in darcy velocities 10 mm yr that endure over 5 myr

the role of partial melting in the 15 ma geochemical evolution of gran canaria a blob model for the canary hotspot the subaerial portion of gran canada canary islands was built by three cycles of volcanism a miocene cycle 8 5 15 ma a pliocene cycle 1 8 60 ma and a quaternary cycle 1 8 0 ma only the pliocene cycle is completely exposed on gran canaria the early stages of the miocene cycle are submarine and the quaternary cycle is still in its initial stages during the miocene sio2 saturation of the mafic volcanics decreased systematically from tholeiite to nephelinite for the pliocene cycle sio2 saturation increased and then decreased with decreasing age from nephelinite to tholeiite to nephelinite sio2 saturation increased from nephelinite to basanite and alkali basalt during the quaternary in each of these cycles increasing melt production rates sio2 saturation and concentrations of compatible elements and decreasing concentrations of some incompatible elements are consistent with increasing degrees of partial melting in the sequence melilite nephelinite to tholeiite the mafic volcanics from all three cycles were derived from co2 rich garnet lherzolite sources phlogopite ilmenite sulfide and a phase with high partition coefficients for the light rare earth elements lree u th pb nb and zr possibly zircon were residual during melting to form the miocene nephelinites through tholeiites phlogopite ilmenite and sulfide were residual in the source of the pliocene quaternary nephelinites through alkali basalts highly incompatible element ratios e g nb u pb ce k u nb pb ba rb zr hf la nb ba th rb nb k nb zr nb th nb th la and ba la exhibit extreme variations in many cases larger than those reported for all other ocean island basalts but these ratios correlate well with degree of melting survival of residual phases at higher degrees of melting during the miocene cycle and differences between major and trace element concentrations and melt production rates between the miocene and pliocene tholeiites suggest that the miocene source was more fertile than the pliocene quaternary source s we propose a blob model to explain the multi cycle evolution of canary volcanoes and the temporal variations in chemistry and melt production within cycles each cycle of volcanism represents decompression melting of a discrete blob of plume material small degree nephelinitic and basanitic melts are derived from the cooler margins of the blobs whereas the larger degree tholeiitic and alkali basaltic melts are derived from the hotter centers of the blobs the symmetrical sequence of mafic volcanism for a cycle from highly undersaturated to saturated to highly undersaturated compositions reflects melting of the blob during its ascent beneath an island in the sequence upper margin corelower margin volcanic hiatuses between cycles and within cycles represent periods when residual blob or cooler entrained shallow mantle material fill the melting zone beneath an island

modeling flow in phreatic and epiphreatic karst conduits in the holloch cave muotatal switzerland the holloch cave is a site where the hydrodynamic behavior of a karst conduit network can be observed with a high degree of precision observed heads discharge rates conduit sizes and conduit lengths have been compiled into a simple hydrodynamic model in order to check their consistency it was possible to calibrate and satisfactorily fit the observed data model results show the following 1 flow models which are able to simulate turbulent flow in variably saturated conduit networks can adequately model conduit flow dominated karst systems 2 karst systems may be strongly nonlinear especially because of the presence of epiphreatic conduits 3 under certain circumstances storage in the epiphreatic conduits and in the fissured limestone matrix can be neglected 4 the typical effective hydraulic conductivity of karst conduits ranges between 1 and 10 m s 1 and the louis formula is adequate to calculate head losses in those conduits 5 indirect measurements of flow velocity using scallop size indicate values of 30 40 of the maximal annual discharge and velocity derived from pebble size indicates values of 150 of the maximal annual discharge

a multichannel seismic study of lithospheric flexure across the hawaiian emperor seamount chain existing models assume that the thickened crust beneath seamounts is the result of a surface volcanic load flexing an elastic plate new results suggest that flexed oceanic crust beneath the hawaiian emperor seamount chain is underlain by a 4 km thick deep crustal body we intepret the body as a deep crustal sill complex associated with the tholeiitic stage of volcano building along the chain

water and air dynamics within a deep vadose zone of a karst massif observations from the lukina jama trojama cave system 1 431 m in dinaric karst croatia extreme heterogeneity of karst systems makes them very challenging to study variousprocesses within the system affect its global response usually measured at karstsprings research conducted in caves provides a unique opportunity for in situ analysisof separate processes in karst underground the aim of the present study was toresearch the water and air dynamics within a deep karst system air and water basicphysical parameters across the lukina jama trojama cave system 1 431 m werecontinuously monitored during a 1 year period recorded hydrograph of the siphonlake at the bottom of the cave was used to interpret the characteristics of an unex plored phreatic epiphreatic conduit network water origin in the siphon was deter mined based on temperature and electrical conductivity air temperature andhumidity monitoring revealed a strong inflow of air of sub zero temperature into theupper portion of the cave during winter cave passage morphology was interpretedas the main determinant of air dynamics which caused ice to accumulate extensivelyin the upper portions of the cave and caused the temperature on the top of thehomothermic zone to be significantly below the mean outside temperature air dynam ics also lowered the temperature of water flowing through the cave vadose zone andfeeding the phreatic zone of the massif the pronounced temperature differencebetween the phreatic zone and the top of the homothermic zone probably contributedto the thermal gradient observed in the cave which is steeper than in ice free caves inthe area our results enabled the development of a conceptual model that describescoupling between air and water dynamics in the cave system and its surroundings

the ocean study area tectonic history from magnetic anomaly data and seismic reflectivity the ocean experiment is a detailed geophysical study of a region of the cape verde basin a dense network of new magnetic and gravity profiles has enabled us to constrain the spreading rate history of the region and the location of fracture zones the main features on the gravity profiles are lineated perpendicular to the seafloor spreading magnetic anomaly lineations significant along axis variability in spreading history suggests that the mid atlantic ridge behaved as a series of loosely coupled segments within which spreading was fundamentally asymmetric such variability is associated with a minor jump in the ridge axis which changes the offset and expression of one of the fracture zones deep seismic reflection and refraction lines were oriented parallel and perpendicular to the magnetic lineations seismic reflections occur at all levels within the crust decreasing in amplitude and coherence below the level of the moho analysis of the subbasement reflectivity provides compelling evidence that at least two major sets of dipping structure are present and are imaged separately on the two perpendicular sets of seismic profiles dipping reflections on flow line dip profiles which are interpreted as faults due to their association with offsets in the basement surface appear to strike parallel to the paleoridge axis the majority of reflections that may be identified as faults dip toward the west and although basement topography suggests that east dipping faults are also present no reflections may be interpreted unambiguously as such east dipping reflections observed only in the middle to lower crust have a more obscure origin dipping reflections seen on isochron strike profiles show clear contrasts in strength lateral coherence depth and dip population a number of these strike parallel to flow lines comparing reflection and refraction data shows that both the layer 2 layer 3 boundary and the moho are marked by a change in the character of reflections and suggests that they may represent important structural as well as seismological boundaries within the oceanic lithosphere

seismic boundaries of the eastern central atlantic mesozoic crust from multichannel seismic data we report the results of a multichannel seismic study on eastern central atlantic oceanic crust unmigrated and migrated sections have been used to identify the main seismic boundaries within the crust the upper crust generally is seismically transparent except for a 20 km long continuous reflection which we interpret as associated with a long lived normal fault in the basement and with hydrothermal circulation short and discontinuous reflections in the upper crust have also been observed the lower crust is either transparent or variably reflective in form of subhorizontal layered reflection packages and or dipping reflections the reflectivity patterns are interpreted as magmatic in origin except for the dipping reflections that affect the whole crust which are interpreted as expressions of extensional faults the reflections dipping ridgeward are thought to have acted as detachment surfaces where plate separation took place the moho has been identified along most of the length of the seismic profiles either as the base of the reflective lower crust or as a sharp single reflection the igneous crust shows large variations in thickness sometimes associated with fracture zones in the cretaceous crust fracture zones in the jurassic crust do not show in general a crustal thinning this may be due to different accretionary processes during jurassic and cretaceous times

a seismic study of lithospheric flexure in the vicinity of tenerife canary islands seismic data have been used to determine the crustal and upper mantle structure of tenerife canary islands a volcanic island of tertiary age located on 140 ma oceanic crust reflection data show that oceanic basement dips gently towards the island forming a flexural moat which is infilled by 2 3 km of well stratified material the moat is characterised by a major angular unconformity which we attribute to volcanic loading of pre existing oceanic crust and overlying sediments and the subsequent infilling of the flexure by material that was derived at least in part from the islands refraction data show that the flexed oceanic crust has a mean thickness of 6 41 0 42 km and upper and lower crustal velocities of 4 8 5 4 km s 1 and 6 7 7 3 km s 1 respectively the flexure which has been verified by gravity modelling can be explained by a model in which tenerife and adjacent islands have loaded a lithosphere with a long term 106 yr elastic thickness of approximately 20 km seismic and gravity data suggest that up to 1 5 105 km3 of magmatic material has been added to the surface of the flexed oceanic crust which assuming an age of 6 16 ma for the shield building stage on tenerife implies a magma generation rate of about 0 006 to 0 02 km3 a 1 this rate is similar to estimates from other african oceanic islands e g reunion and cape verdes but is significantly less than that which has been calculated at hawaii there is no evidence in either the seismic or gravity data that any significant amount of magmatic material has underplated the flexed oceanic crust the crustal and upper mantle structure at tenerife therefore differs from other oceanic islands such as hawaii and marquesas where 4 km of underplated material have been reported

seismostratigraphy of the western flanks of el hierro and la palma canary islands a record of canary islands volcanism abstract a cruise carried out aboard the spanish r v hesperides using a 255 inch3 airgun allowed to identify three main seismostratigraphic units in the western submarine flanks of the islands of la palma and el hierro canary islands the time structure and thickness maps of each unit together with the interpretation of the seismic facies demonstrate that the evolution of the canary islands is recorded in the marine basin the structure maps show that the older reflectors dip to the nw in contrast to the present day sea floor which dips to the wnw the thickness maps also show that the depocentre moved from a position parallel to the northwest african margin to a position now occupied by the island of la palma despite the high sedimentation rates of hemipelagic background sedimentation in the study area the three seismic units can be interpreted in terms of their relation to the canarian volcanism unit i was deposited before the initiation of volcanism and the arrival of volcaniclastic flows and is thus mainly if not entirely composed of hemipelagic sediments unit ii seems to reflect the shield phases of the easternmost edifices and as such would be constituted by the distal products of erosion and mass wasting of these islands unit iii in contrast results mainly from the shield phase of the two westernmost islands la palma and el hierro and as such reflects more proximal conditions as demonstrated by the presence of lateral collapse deposits from these islands

long term versus short term deformation processes at tenerife canary islands 1 several geophysical investigations have identified that the tenerife volcanic complex is affected by crustal deformation processes occurring at timescales of millions of years recently space based geodetic observations have also detected a short term surface deformation characterized by a broad subsidence pattern with maximum ground velocities of about 4 mm yr 1 for the purpose of investigating the relationship between these long term and short term deformation processes we performed an advanced fluid dynamic analysis fda we first carried out a standard dimensionless fda to discriminate the deformation style of tenerife and found that at million year timescales basement flexure mainly controls its long term structural evolution secondly to highlight the driving forces of the short term deformation process we simulated a numerical fda based on finite element models that include topography as well as vertical and lateral material heterogeneities our results show that the recent surface deformation is mainly caused by a progressive sagging of the denser less viscous core of the island onto the weaker but more viscous lithosphere moreover over periods comparable to the hypothesized age of loading of the oceanic crust beneath tenerife this tendency would result in a total flexure of about 3 4 km which is in agreement with independent estimations based on geophysical analyses our study shows that a unitary physical model may explain both the deformation recorded in deep geological structures and the current active ground deformation processes occurring at the tenerife volcano

seismic evidence for crustal underplating beneath a large igneous province the sierra leone rise equatorial atlantic wide angle seismic profiles reveal anomalously thick crust with a high velocity 7 3 km s 1 zone under the sierra leone rise a major mid plate elevation in the atlantic lying between the cape verde platform and the cameroon volcanic line a profile recorded over the crest using an ocean bottom seismometer and surface sonobuoys shows that beneath a 3 km water layer and 1 km of sediments the basement extends to 16 20 km below sea level most velocity depth values fall outside the expected range for mesozoic early cenozoic ocean floor and stretched continental crust the detection of 7 3 7 5 km s 1 material beneath thick lower velocity volcanics suggests that magmatic underplating of the crust has occurred a prominent change in velocity gradient 10 12 km below sea level may mark the transition to underplated material emplaced during the late cretaceous early cenozoic a pronounced change in moho depth lies on the line of a long offset fracture zone extending from the african margin implying underplating was influenced by a pre existing discontinuity in the lithosphere other seismic lines show 7 0 7 2 km s 1 basement above the underplated zone extending into water depths of almost 5 km this is probably the intrusive foundation of early formed crust over a mantle hot spot it is suggested that the development of the sierra leone rise is distinct from other atlantic hot spot features to which it has been linked because of its setting in a region of intense lithospheric shear

volcanic evolution of the island of tenerife canary islands in the light of new k ar data new age determinations from tenerife together with those previously published 93 in all provide a fairly comprehensive picture of the volcanic evolution of the island the oldest volcanic series with ages starting in the late miocene are formed mainly by basalts with some trachytes and phonolites which appear in anaga teno and roque del conde massifs in anaga ne three volcanic cycles occurred one older than 6 5 ma a second one between 6 5 and 4 5 ma with a possible gap between 5 4 and 4 8 ma and a late cycle around 3 6 ma in teno nw after some undated units the activity took place between 6 7 and 4 5 ma with two main series separated by a possible pause between 6 2 and 5 6 ma in the zone of roque del conde s the ages are scattered between 11 6 and 3 5 ma between 3 3 and 1 9 ma the whole island underwent a period of volcanic quiescence and erosion the large canadas volcano made up of basalts trachytes and phonolites was built essentially between 1 9 and 0 2 ma to the ne of this central volcano linking it with anaga is a chain of basaltic emission centers with a peak of activity around 0 8 ma the canadas caldera had several collapse phases associated with large ignimbrite emissions there were at least an older phase more than 1 ma old on the western part of the volcano and a younger one less than 0 6 ma old in the eastern side the two large valleys of guimar and la orotava were formed by large landslides less than 0 8 ma ago and probably before 0 6 ma ago the present canadas caldera was formed by another landslide less than 0 2 ma ago this caldera was later filled by the huge teide volcano which has been active even in historic times during the same period a series of small volcanoes erupted at scattered locations throughout the island the average eruptive rate in tenerife was 0 3 km3 ka with relatively small variations for the different eruptive periods this island and la gomera represent a model of growth by discontinuous pulses of volcanic activity separated by gaps often coinciding with episodes of destruction of the edifices and sometimes extended for several million years the neighbouring gran canaria on the other hand had an initial rapid shield building phase during which more than 90 of the island was built and a series of smaller pulses at a much later period a comparison between these three central islands indicates that the previously postulated westward displacement in time of a gap in the volcanic activity is valid only as a first approximation several gaps are present on each island overlapping in time and not clearly supporting either of the models proposed to explain the evolution of the canaries

on the formation of collapse dolines a modelling perspective abstract collapse dolines are among the most striking surface features in karst areas although they can be the result of different formation mechanisms evidence suggests that large collapse dolines form due to chemical and mechanical removal of material at and below the level of groundwater we have applied a genetic model of a two dimensional fracture network to calculate the rate of dissolutional bedrock removal in the heavily fractured crushed zone intersecting a karst conduit in the phreatic zone to account for infilling and breakdown processes in the crushed zone two simple rules were added to the basic model 1 continuous infilling of dissolutionally created voids prevents fractures from growing beyond some limited aperture although the dissolution proceeds 2 discontinuous collapsing causes sudden closure of a fracture once some critical aperture has been reached both rules limit the transmissivity of the network and the related flow rates therefore the constant head difference between the input and the output points is sustained and the flow remains distributed over the entire crushed zone provided that restrictions posed by the two rules permit turbulent flow dissolution rates also remain high in the entire region high surface area of water rock contact and high dissolution rates result in high overall removal rates of rock from the crushed zone one of the necessary conditions for the formation of large closed depressions despite the fact that the model neglects some processes and dynamics that would increase the removal rate the results suggest that large closed depressions could form in the order of 1 million years

the channel between gran canaria and tenerife constructive processes and destructive events during the evolution of volcanic islands seismic sidescan sonar bathymetric multibeam and odp ocean drilling program data obtained in the submarine channel between the volcanic islands of gran canaria and tenerife allow to identify constructive features and destructive events during the evolution of both islands the most prominent constructive features are the submarine island flanks being the acoustic basement of the seismic images the build up of tenerife started following the submarine stage of gran canaria because the submarine island flank of tenerife onlaps the steeper flank of gran canaria the overlying sediments in the channel between gran canaria and tenerife are chaotic consisting of slumps debris flow deposits syn ignimbrite turbidites ash layers and other volcaniclastic rocks generated by eruptions erosion and flank collapse of the volcanoes volcanic cones on the submarine island flanks reflect ongoing submarine volcanic activity the construction of the islands is interrupted by large destructive events especially by flank collapses resulting in giant landslides several miocene flank collapses e g the formation of the horgazales basin were identified by combining seismic and drilling data whereas young giant landslides e g the guimar debris avalanche are documented by sidescan bathymetric and drilling data sediments are also transported through numerous submarine canyons from the islands into the volcaniclastic apron seismic profiles across the channel do not show a major offset of reflectors the existence of a repeatedly postulated major ne sw trending fault zone between gran canaria and tenerife is thus in doubt the sporadic earthquake activity in this area may be related to the regional stress field or the submarine volcanic activity in this area seismic reflectors cannot be correlated through the channel between the sedimentary basins north and south of gran canaria because the channel acts as sediment barrier the sedimentary basins to the north and south evolved differently following the submarine growth of gran canaria and tenerife in the miocene

gravity anomalies crustal structure and flexure of the lithosphere at the baltimore canyon trough seismic and gravity anomaly data have been used to examine the long term mechanical properties of the lithosphere beneath the baltimore canyon trough a 15 km deep sedimentary basin in the rifted u s atlantic margin seismic data constrain the crustal structure at the time of rifting as well as the amount of sedimentation and erosion that has occurred the gravity effect of the initial crustal structure sedimentary loading and erosional unloading have been computed and compared to the observed free air gravity anomaly the best fitting model is one in which the elastic thickness of the lithosphere te changes at the east coast magnetic anomaly landward of the anomaly te is significantly smaller than previously reported values for continental or oceanic lithosphere of the same thermal age seaward of the anomaly however te follows the depth to the 450 c oceanic isotherm which also describes the response of oceanic lithosphere to seamount and oceanic island loads these results are interpreted as indicating that the shelf part of the trough is underlain by continental lithosphere which following rifting did not acquire any significant long term strength

crustal structure of the tuamotu plateau 15 s and implications for its origin we investigate the sedimentary and volcanic structure of the tuamotu plateau with multichannel seismic seismic refraction and gravity data along a ship track crossing the plateau near 15 s the volcanic basement of the central portion of the plateau is capped with a 1 to 2 km thick sediment layer composed of two compositional sequences the uppermost sequence with semblance derived p wave velocities of 1 6 1 9 km s and thicknesses of 0 2 0 9 km is composed of pelagic sediments the underlying sequence with velocities 2 5 3 5 km s and thicknesses of 0 5 1 5 km is composed of limestone and volcaniclastic sediments sonobuoy refraction data show the upper 1 km of the volcanic basement to have velocities 4 5 5 5 km s the gravity data indicate that the platform is compensated by an elastic lithosphere with effective thickness 5 5 km and that the volcanic thickness is 9 10 km thicker than normal oceanic crust with a volume of 2 0 2 6 l06 km3 the inferred eruption rates of 0 1 0 13 km3 yr are comparable to those of the hawaiian and marquesas island chains but substantially less than those of many oceanic plateaus radiometric and paleontological ages for the plateau and geomagnetic dates of the surrounding seafloor indicate that the northwestern portion of the plateau formed 600 km off the axis of the paleo pacific farallon spreading center on lithosphere of age 10 20 ma linear volcanic ridges and scarps bounding deep sediment filled basins however are similar to features of oceanic plateaus which formed at or near accretionary plate boundaries we suggest that these volcanic ridges and the gross plateau like morphology were formed by magma that was channelled along the lithospheric discontinuities left behind by a southward propagating rift segment of the nearby spreading center we attribute the formation of the northwestern portion of the tuamotu plateau to the passage of two hotspots during times 50 30 ma as they migrated beneath the pacific plate but remained west of the tuamotu propagator

crustal structure of the madeira tore rise eastern north atlantic results of a dobs wide angle and normal incidence seismic experiment in the josephine seamount region summary during november december 1988 an extensive geophysical data set was collected over the josephine seamount which is located at the northeasterly end of the madeira tore rise in the eastern north atlantic the josephine seamount lies at the intersection of the madeira tore rise and azores gibraltar fracture zone the latter representing the africa eurasia plate boundary in this part of the eastern north atlantic from this data set a 275 km long explosive refraction line has been modelled together with wide angle airgun profiles seismic reflection and gravity data the velocity depth model shows that the crust either side of the seamount is typically oceanic in character however beneath the seamount there exists a region of anomalously high velocity and crustal thickening to a depth of about 17 18 km gravity modelling also suggests that the josephine seamount is compensated by a crustal root and that the josephine seamount madeira tore rise system is in local isostatic equilibrium calculations of the flexural rigidity and effective elastic thickness of the lithosphere in this region suggest that the madeira tore rise formed contemporaneously with the lithosphere on which it lies this age of crustal loading is consistent with the proposal that the madeira tore rise is an aseismic ridge which formed at or near the mid atlantic ridge

tilt observations in the normal mode frequency band at the geodynamic observatory cueva de los verdes lanzarote we have conducted observations with the aid of a seismo tiltmeter station which is based on the ostrovsky pendulum and installed at the geodynamic observatory cueva de los verdes at lanzarote island since 1995 in this station the signal is separated into two frequency bands tidal tilts from 0 to 5 mhz and ground oscillations in the frequency range of free earth s normal modes from 0 2 to 5 mhz the later band called accelerometer channel has additional amplification we analyzed the background records in the frequency range of earth s free oscillations from august 2000 to september 2001 as well as earth s normal modes after strong earthquakes we found several distinctive persistent peaks in the spectra of background oscillations both amplitudes of distinguished peaks and noises have seasonal variations we found that spectra of background oscillations are different in the frequency interval between 1 4 and 2 5 mhz for north south and east west components

seismic imaging of hotspot related crustal underplating beneath the marquesas islands volcanism in active continental rift zones1 2or on rifted continental margins3is frequently associated with unusually high lower crustal seismic velocities indicating the presence of large igneous intrusions at the base of the crust the only comprehensive investigation of crustal underplating at an oceanic hotspot beneath hawaii4 6 has yielded controversial results7 here we report the results of seismic refraction experiments across the marquesas islands hotspot trace which show that the island chain is underlain by crust 15 17 km thick and that a large lower crustal region 275 km wide and 2 8 km thick has seismic velocities 7 3 7 75 km s 1 indicative of crustal underplating wide angle reflections occur near the base of the normal lower crustal velocities and at the base of the underplating complex we interpret these reflectors as the relict pre hotspot moho and the current post hotspot moho respectively the high velocity material may be purely intrusive or may consist of a mixture of intrusive and preexisting rocks the volume of the high velocity body is impressive amounting to nearly twice the volume of volcanics erupted at the surface

seismic tomography model reveals mantle magma sources of recent volcanic activity at el hierro island canary islands spain summary we present a 3 d model of p and s velocities beneath el hierro island constructed using the traveltime data of more than 13 000 local earthquakes recorded by the instituto geogr afico nacional ign spain in the period from 2011 july to 2012 september the velocity models were performed using the lotos code for iterative passive source tomography the results of inversion were thoroughly verified using different resolution and robustness tests the results reveal that the majority of the onshore area of el hierro is associated with a high velocity anomaly observed down to 10 12 km depth this anomaly is interpreted as the accumulation of solid igneous rocks erupted during the last 1 myr and intrusive magmatic bodies below this high velocity pattern we observe a low velocity anomaly interpreted as a batch of magma coming from the mantle located beneath el hierro the boundary between the low and highvelocityanomaliesismarkedbyaprominentseismicitycluster thoughttorepresentanomalous stresses due to the interaction of the batch of magma with crust material the areas of recent eruptions orchilla and la restinga are associated with low velocity anomalies surrounding the main high velocity block these eruptions took place around the island where the crust is much weaker than the onshore area and where the melted material cannot penetrate these results put constraints on the geological model that could explain the origin of the volcanism in oceanic islands such as in the canaries which is not yet clearly understood

features of crustal structure under the canary islands abstract the data and interpretation of a seismic refraction project carried out in the canary islands in 1977 and 1979 are presented the moho is reached at about 15 km under fuerteventura gran canaria and tenerife whereas under lanzarote a value of 11 km has been found the velocity at the surface varies even within one island from 2 8 to 4 4 km s there are variations in the velocity of the main crustal layer under the volcanic deposits a continuous velocity depth function seems to be more appropriate for the island of tenerife contrary to fuerteventura lanzarote and gran canaria which seem to have a layered structure there is evidence for pronounced structural differences between lanzarote and fuerteventura the mantle velocity has a value of about 8 0 km s under the western islands whereas a very low value of 7 4 km s has been found under lanzarote and fuerteventura despite the clear structural differences between the islands our results leave little doubt about the oceanic character of all the islands the differences between the eastern and western group may be due to the islands being situated close to the african continental margin the seismic velocities under the volcanic deposits do not support the idea of a common basement for all the islands they rather suggest independent volcanic edifices finally a comparison of the structure of the crust under the canary islands with that under other volcanic islands reveals remarkable similarities

erosion of the submarine flanks of the canary islands surveying with multibeam echo sounders around old 1 ma volcanic ocean islands reveals that their submarine flanks contain a strong downslope oriented ridge and valley corrugation which modifies the original volcanic morphology of lava terraces and cones by analogy with canyons in other settings this corrugation was probably caused by channel incision by erosive sedimentary mass flows such as turbidity currents and debris flows we adapt a method first used in subaerial geomorphology to isolate the erosion depth exhumation and apply it to the eroded flanks of the 6 8 ma anaga massif of tenerife the channels formed around this massif divert around local topographic highs these highs which are probably original volcanic cones are therefore preferentially preserved during erosion so that their elevations can be used to construct an artificial reference surface terrain depth was calculated by subtracting this reference surface from measured bathymetry comparison of the terrain depth of the old eroded submarine flank of anaga with that of the young mostly unaltered submarine flank of el hierro allows us to infer the mean depth of anaga s submarine erosion which is 100 m volcanic terrains can be dated by radiometric methods so they also provide a way of quantifying long term denudation rates we infer that submarine denudation of anaga has occurred at comparable rates to that of subaerial lowlands and much slower than denudation of highlands illustrated locally by the more extensive erosion of the subaerial anaga edifice

modeling spatially and temporally varied hydraulic behavior of a folded karst system with dominant conduit drainage at catchment scale hochifen gottesacker alps summary karst aquifers are important for freshwater supply but difficult to manage due to highly variable water levels and spring discharge rates conduits are crucial for groundwater flow in karst aquifers but their location is often unknown thus limiting the applicability and validity of numerical models we have applied a conduit model swmm to simulate highly variable flow in a folded alpine karst aquifer system where the underground drainage pattern is comparatively well known from previous tracer studies the conduit model was coupled with a reservoir model representing recharge storage and transfer of water in the epikarst and unsaturated zone the global optimization approach ga was applied to achieve an efficient model calibration it was possible to simultaneously simulate the highly variable discharge characteristics of an estavelle and overflow spring and a permanent spring draining the conduit system the model allowed for the collection of spatially differentiated information on recharge rapid flow and slow flow in four individual sub catchments the formation of backwater upgradient from conduit restrictions turned out to be a key process in activating overflow springs the proposed modeling approach appears to be transferrable to other karst systems with predominant conduit drainage but requires previous knowledge of the configuration of the conduit system

identifying the characteristics of groundwater flow in the classical karst area slovenia italy by means of tracer tests tracer tests are a widely used research method in karst hydrology in the classical karst area on the border between slovenia and italy they have a long history and for the most part they have been used to research the underground flow in the main karst conduits between the ponors and the springs the results of the tracer test from 2013 presented in the article revealed new knowledge about the central part of the aquifer less well researched to date where the density of caves and the level of karstification are lower two tracers uranine and amidorhodamine g were used at two injection points a research borehole in the central part of the aquifer and the karst surface at a distance of 2 5 km from a drinking water pumping station and six springs a pumping station three boreholes and four karst caves were observed for tracer breakthrough for a full year after injection the results were compared with findings from three other selected older tracer tests in which uranine was likewise used as a tracer but where hydrological conditions varied very low low and medium water levels as did the methods of injecting tracer in a sinking stream in a fracture on the karst surface the comparison showed how different modes of aquifer recharge and the heterogeneity of aquifer structure affect the characteristics of water flow and solute transport in complex karst aquifers

vertical movements of ocean island volcanoes insights from a stationary plate the origin of hotspot swells is still controversial and their development is at present poorly constrained and strongly model dependent however since islands are built on top of these structures the role of swell development in island uplift subsidence should be assessed

a giant landslide on the north flank of tenerife canary islands the extent of mass wasting along the north flank of tenerife has been mapped using swath bathymetry gloria side scan sonar and 3 5 khz echo sounder data the marine surveys show that north of tenerife a giant landslide is exposed over an area of 5500 km2 of the seafloor more than twice the surface area of the island the landslide truncates an older ridge and valley topography that is associated with the shield building basalts on tenerife we interpret the ridge and valley topography as the result of subaerial erosion the landslide is estimated to have a length of 100 km a width of up to 80 km and a volume of about 1000 km3 it extends onshore into the orotava and icod valleys which have been interpreted as of landslide origin k ar dating of basaltic flows in the steep headwall of orotava suggests an age of formation for the valley is younger than 0 78 ma and may even be younger than 0 27 ma the icod valley is located immediately to the north of the most recent volcano on tenerife las canadas and has been associated with the collapse of its caldera between 1 2 and 0 2 ma a young age for the landslide is supported by the 3 5 khz echo sounder data which show that the landslide is draped by a thin 10 m layer of younger sediment the landslide did not form however during a single catastrophic event but represents the amalgamation of a number of separate landslides the occurrence of the ridge and valley topography in water depths of up to 2 5 km suggests that the shield building basalts have subsided by at least this amount since they formed 3 3 8 0 ma we speculate that this subsidence is caused by some form of stress relaxation that occurs in the underlying lithosphere the giant landslide imaged in our sonar data is associated with the late stages in the development of the most recent volcano on tenerife las canadas which only began at about 1 8 ma thus landsliding may be a particular feature of the time soon after emplacement when because of incomplete isostatic adjustment oceanic volcanoes have their greatest elevations above sea level and therefore are most susceptible to slope failure

crustal structure gravity anomalies and flexure of the lithosphere in the vicinity of the canary islands summary simple elastic plate models have been used to calculate the flexure of the lithosphere caused by volcanic loading at the canary islands and sediment loading at the moroccan continental margin by comparing the calculated flexure to observations based on seismic refraction and free air gravity anomaly data constraints have been placed on the long term 106 years elastic thickness of the lithosphere te the best fit between the calculated and observed flexure in the vicinity of the canary islands is for te 20 km this value of te also explains seismic reflection data in regions that flank the island provided that the lithosphere underlying the moroccan margin is sufficiently weak te 5 km for sediment loading to contribute little to the island flexure a backstripping study in which gravity data are used to constrain the value of te supports the suggestion that the lithosphere underlying the moroccan margin like its conjugate at the baltimore canyon trough is weak although sediment loading at the moroccan margin appears therefore to have exerted little influence on the structure of the canary islands there is evidence that island flexure may have influenced the stratigraphic development of the moroccan margin especially in the region of the slope anticline a te of 20 km is about 15 km lower than would be expected on the basis of the thermal age of the oceanic lithosphere that underlies the canary islands similar low values have been reported from oceanic islands in the pacific superswell region of french polynesia where they have been attributed to re heating of the lithosphere by one or more hotspots a general e w age progression of the volcanic rocks suggests that the canary islands were also generated by a hotspot they lack however the topographic swell and gravity geoid high which usually accompanies these features one possibility is that the low te values are the result of a pre existing weakness in the oceanic crust a te of 20 km is large enough however for a significant part of the mantle to still be involved in the support of the island loads a more likely explanation is thermal weakening by a hotspot which has been localized enough to reduce te but not to produce a swell or gravity geoid high irrespective of its cause the low te suggests that oceanic lithosphere does not necessarily progressively increase its strength with age so that even 140 ma old lithosphere is vulnerable and can in some regions be significantly weakened by later thermal and mechanical processes

variations in oceanic layer 2 elastic velocities near hawaii and their correlation to lithospheric flexure analysis of the travel times and amplitude range distributions of both compressional and shear wave arrivals on 15 closely spaced refraction profiles reveals a significant systematic and symmetric dependence of average layer 2 velocities on their distance to the north and south of the hawaiian ridge beyond the flexural arch surrounding the ridge the velocity depth solutions indicate a normal layer 2 within the arch approximately 155 km from the ridge the average elastic velocities in layer 2 are lowered by 0 8 0 9 0 2 km s within 75 km of the ridge the average velocities are again normal elastic and elastic plastic flexural models for the regional compensation of the hawaiian islands predict tensional stress drops of 0 8 kbar in the upper lithosphere for the region having lowered velocities in layer 2 which are similar in magnitude with laboratory measurements of the confining pressure drop necessary to reduce velocities in porous basalts by 0 5 km s a significant inverse relationship correlation coefficient of 0 818 exists between the average elastic velocities in the upper 1 0 km of the igneous crust and the strain in the upper crust calculated from these flexural models the correlation between lowered average velocities in layer 2 and increased tensional stresses and strains suggest that crack opening in the upper crust accompanies the flexure these observations are the first reported for a midplate load and corroborate previous suggestions from seismic and flexural data at subduction zones

looping caves versus water table caves the role of base level changes and recharge variations in cave development abstract the vertical organisation of karst conduit networks has been the focus of speleogenetic studies for more than a century the four state model of ford and ewers 1978 which still is considered as the most general relates the geometry of caves to the frequency of permeable fissures the model suggests that the water table caves are common in areas with high fissure frequency which is often the case in natural settings however in alpine karst systems water table caves are more the exception than the rule alpine speleogenesis is influenced by high uplift valley incision rates and irregular recharge to study the potential role of these processes for speleogenesis in the dimensions of length and depth we apply a simple mathematical model based on coupling of flow dissolution and transport we assume a master conduit draining the water to the spring at a base level incision of the valley triggers evolution of deeper flow pathways which are initially in a proto conduit state the master conduit evolves into a canyon following the valley incision while the deep pathways evolve towards maturity and tend to capture the water from the master conduits two outcomes are possible a deep pathways evolve fast enough to capture all the recharge leaving the master conduit dry or b the canyon reaches the level of deep pathways before these evolve to maturity we introduce the loop to canyon ratio lcr which predicts which of the two outcomes is more likely to occur in certain settings our model is extended to account for transient flow conditions in the case of an undulating master conduit floodwater is stored in troughs after the flood retreat this water seeps through sub vertical fractures soutirages connecting the master conduit with the deep pathways therefore the loops evolve also during the dry season and the lcr is considerably increased although the model is based on several approximations it leads to some important conclusions for vertical organisation of karst conduit networks and stresses the importance of base level changes and transient recharge conditions it therefore gives an explanation of speleogenesis that relies much more on the dynamic nature of water flow than on the static fracture density

crustal and upper mantle seismic structure and lithospheric flexure along the society island hotspot chain summary four wide angle and refraction lines have been shot along the society island hotspot track a 280 km long profile covers oceanic crust to the east of the islands the active hotspot region and the apron of tahiti the other profiles cover the region between moorea and huahine and the western archipelago of huahine raiatea bora bora and adjacent oceanic crust traveltime modelling provided lateral variations in crustal structure along the hotspot chain removal of the contribution of the uppermost low velocity layer which represents the volcanic edifices and debris suggests that the islands and atolls sit on normal oceanic crust and are surrounded by a large volcaniclastic apron seismic profiles running between raiatea and huahine and between raiatea and moorea cover a region where extreme down bending due to volcanic loading is expected a nearly flat crust mantle boundary indicates regional isostasy and clearly supports a stiff plate seismic structural models have been compared with calculated boundaries based on simple 3 d elastic plate models a good fit to the seismic crust mantle boundary was obtained for models with an effective elastic thickness of the lithosphere of 20 25 km these values are in accordance with a model in which the elastic thickness depends on the thermal age of the lithosphere and therefore contradict models that suggest that the region of french polynesia has been thermally rejuvenated amplitude modelling of crustal and upper mantle arrivals suggests that crust on the hotspot trail has been modified with respect to the pre hotspot crust to explain the observations we suggest that during the ongoing late stage volcanic activity the lower crust has been intruded by sills and some melts are trapped in the crust mantle boundary region if late stage volcanism and plutonism continue prolonged crustal growth may form a large underplate or subcrustal plutonic core complex along the hotspot chain

seismic structure of oceanic crust in the western north atlantic we examine the seismic structure of cretaceous aged ocean crust north of the blake spur fracture zone in the western north atlantic by using a combination of multichannel seismic and wide angle reflection refraction data although the oceanic crust in this area is characterized by a relatively uniform thickness and seismic velocity structure it displays large variations in crustal reflectivity on both ridge normal and ridge parallel profiles the upper crust is highly reflective and contains both subhorizontal or shallow dipping events and more steeply dipping reflectors subhorizontal reflectors are typically present between 1 5 and 2 km depth and are in some cases laterally continuous for distances of 15 to 20 km generally these events do not correlate with the depth of the seismic layer 2 layer 3 boundary determined from refraction data and their origin is still poorly understood the steeply dipping events are generally confined to the upper 2 5 km of the crust we interpret these reflectors as the subsurface expression of ridge parallel extensional faults commonly mapped at mid ocean ridges the lower crust in this area exhibits alternating regions of high and low reflectivity the highly reflective zones are made up of packages of linear or concave upward dipping reflectors that flatten out in a diffuse zone of high reflectivity near the base of the crust some of these dipping reflectors appear to cut through the whole crustal section although most fade out in the acoustically transparent midcrust on ridge normal profiles the majority of these events dip to the east toward the paleo spreading center whereas on ridge parallel profiles the events typically dip south toward the blake spur fracture zone the base of the crust is generally not associated with a strong discrete moho reflection but is a comparatively indistinct boundary usually associated with a 1 to 2 km thick band of diffuse high reflectivity we interpret the lower crustal and whole crustal dipping events as the subsurface expression of major fault systems that have ruptured the entire crustal section down to depths of 8 10 km with the available data we cannot unambiguously determine the geometrical relationship between the dipping lower crustal reflectors on the ridge normal and ridge parallel profiles we may be imaging a single major detachment surface that dips both toward the ridge axis and away from accommodation zones linking major boundary faults alternatively these events may represent two different classes of fault systems that form during different stages of the emplacement and aging of oceanic lithosphere

the pliocene seamount series of la palma canary islands a pliocene submarine series of alkali basaltic pillow lavas hyaloclastites and breccias a a sheeted dike swarm b and a basal suite of gabbro and ultramafic rocks c from la palma canary islands is interpreted as a cross section through an uplifted seamount this series has been tilted to its present orientation of 50 230 plunge and azimuth probably by upwarping due to intrusions in the central portion of the island the basal plutonic complex c also includes intrusives coeval with up to 2000 m of younger subaerial alkali basaltic lavas unconformably overlying the submarine series the plutonic suite c is overlain abruptly by more than 1800 m of sills b 0 4 1 m thick on average with minor screens of lavas and breccias extrusives a form a 1750 m thick sequence of pillow lavas breccias and hyaloclastites the clastic rocks increase in abundance upward and are of four main types 1 breccias consisting of partly broken pillows formed nearly in situ 2 heterolithologic pillow fragment breccias 3 hyaloclastites composed dominantly of highly vesicular lapilli and ash sized shards the latter thought to have formed by near surface explosive eruptions and been subsequently transported downslope by mass flows 2 and 3 being interpreted to have been resedimented and 4 pillow scoria breccias from the upper 700 m of the extrusive section consisting of amoeboidal highly vesicular pillows and lava stringers and local bombs probably formed by cracking and bleeding of gas rich expanding pillow lava and some shallow submarine subaerial lava fountaining the extrusive series is chemically and mineralogically crudely zoned with the most differentiated rocks metatrachytes and mugearites at the base and most picritic lavas occurring near the top of the series subsequent to emplacement the entire extrusive and intrusive series has been hydrothermally altered the lower part to greenschist and the upper part to smectite zeolite facies mineral assemblages the la palma succession combined with evidence from surface studies of seamounts suggests that seamounts are formed by intrusive and extrusive processes in approximately equal portions the nature of eruptive clastic and depositional mechanisms changes drastically during growth of a seamount if the critical depth for major magmatic degassing is surpassed and especially if magmatic explosive processes can occur at very shallow water depth the critical depth depending on magma and thus volatile composition changes in slopes of a seamount influence depositional processes based on these factors at least three major depositional sites develop as a seamount grows summit flank and apron facies nonexplosive extrusive processes prevail in the deep water stage dominantly producing pillow lavas 75 these consist of individual pillow volcanoes up to 200 m high with large pillows near the base and decreasing pillow size toward the top of a volcano pillow breccias and pillow fragment breccias comprise approximately 20 of this facies the deep water flank and apron facies are characterized by debris flow deposits with possibjy rather dense matrix material the shallow water shoaling stage is reached when the seamount top reaches the critical depth for drastic increase in exsolution of magmatic volatiles about 800 m for the alkali basaltic seamount of la palma resulting in formation of mainly clastic rocks 70 in situ pillow rind breccias and scoriaceous amoeboidal breccias and pillows are formed in the summit regions of the seamount by repeated expansion and leaking of frothy pillow lava possibly by lava fountaining resedimented heterolithologic pillow fragment breccias lapilli breccias and hyaloclastites are deposited on the flanks and aprons of the seamount pillow lavas comprise 30 of these deposits

crustal structure of mauna loa volcano hawaii from seismic refraction and gravity data abstract in october 1978 the u s geological survey established a 100 km long seismic refraction profile normal to the kona coast of hawaii island analysis of these data along with available gravity data suggest that the oceanic crust dips about 3 landward under the submerged flank of the island increasing to 8 5 under the kona coast maximum vertical deflection of the base of crust from beneath the deep ocean to a point beneath the summit of mauna loa is about 9 km high velocity high density rocks vp about 7 1 km sec density about 2 9 gm cm 3 comprise the bulk of the volcanic edifice and reach to within a few kilometers of the surface beneath the north flank of mauna loa the data also suggest that an elongate high velocity high density body lies parallel to the kona coast just below the surface this body probably represents an extinct buried rift zone

reflection seismic investigations in the volcaniclastic apron of gran canaria and implications for its volcanic evolution high resolution reflection seismic data obtained around gran canaria allow a detailed and consistent correlation of seismic reflectors of the northern and southern canary basins with the lithology drilled by dsdp leg 47a sse of gran canaria as well as with major phases of volcanic activity on gran canaria as mapped onshore two prominent reflectors were chosen as marker horizons and correlated with the drilled lithology the results indicate that reflector r7 above the miocene volcaniclastic debris flows v1 v3 reflects the shield building phase of gran canaria reflector r3 is interpreted as corresponding with the pliocene roque nublo formation the top of the massive island flank of gran canaria defined by seismically chaotic facies extends 44 to 72 km off the coast of gran canaria west of gran canaria the flank of tenerife onlaps the steeper and older flank of gran canaria which in turn is onlapping the older flank of fuerteventura to the east in a similar way erosional channels which can also be traced up to 50 km from the area between gran canaria and fuerteventura into the deeper northern basin have been identified in the bathymetry the data presented provide new detailed information for modelling the submarine and subaerial evolution of the central canary islands of gran canaria and tenerife i e the timing of their shield building phases and later stages of major volcanic activity as reflected by the position of prominent seismic reflectors in the seismic stratigraphy

buttressing and fractional spreading of tenerife an experimental approach on the formation of rift zones 1 the island of tenerife is composed of three miocene shields which are centered by the canadas volcano since the pliocene tenerife sits on more than 2 km thick oceanic sediments quaternary volcanism of the canadas series and giant landslides were principally confined to triaxial rift zones the mechanism of triaxial rifting however has remained unclear physical analog models show that these rift zones may have formed by gravity driven lateral escape of island segments induced by loading of the deformable substratum for experiments scaled to tenerife three adjacent sand cones were mounted onto viscous pdms substratum gravitational spreading caused circumferential expansion of each cone until a large edifice canadas was constructed in their center the older cones now acted each as a buttress radial fractures were overprinted by fractional spreading of the canadas edifice this resulted in formation of three main extensional zones resembling the triaxial rifting configuration of tenerife

on the relation between ground surface deformation and seismicity during the 2012 2014 successive magmatic intrusions at el hierro island abstract six different magmatic intrusions were detected around el hierro island in the two years that followed the end of the 2011 2012 submarine eruption each intrusion lasted between few days to three weeks and produced intense seismic swarms and rapid ground deformation we performed a hypodd relocation of 6000 earthquakes and inverted the gps data in order to obtain the location of the magma source of each intrusion each episode presents a spatial gap between seismicity and magma source of 3 8 km with the earthquakes located always deeper than the deformation sources we propose a magma plumbing system consisting on a deep structure injecting magma to a more ductile shallower location beneath el hierro crust while the seismicity is associated with the deeper structure the ascent and accumulation of magma at shallower level deforms the crust aseismically the mechanism of most of these episodes consists of an initial injection of magma producing most of the ground deformation and high b values of the seismicity indicating fluid fractures during the first days and finishes with high magnitude earthquakes and low b values indicating an overpressure of the injection process there is a correlation between the seismic and geodetic moment ratio and the direction of propagation of each intrusion towards one of the volcanic rifts of the island suggesting the possible existence of a deep structure beneath the island related with to the triaxial origin of the island this work presents important advances in the knowledge of monogenetic magmatic intrusions and specifically in those occurred in el hierro island between 2011 and 2014 with important implications for future volcano monitoring in the canary islands

transition from circular to stellate forms of submarine volcanoes large volcanic islands and guyots have stellate forms that reflect the relief of radiating volcanic rift zones multiple volcanic centers and embayments due to giant flank failures small mid ocean ridge volcanoes in contrast are commonly subcircular in plan view and show only embryonic rift zones in order to characterize the transition between these two end members the morphology of 141 seamounts and guyots was studied using the shape of the depth contour at half the height of each edifice irregularity was characterized by measuring perimeter distance elongation and moment of inertia of the contours assuming an ideal edifice is circular the analysis reveals a general transition over 2 4 km edifice height best transition estimate 3 km while some large edifices 4 5 km high show no major embayments or ridges suggesting considerable variation in the effectiveness of mechanisms that cause flank instability and growth of rift zones the various origins of the transition are discussed and the upper limit of magma chambers many of which lie above the basement of the larger edifices is proposed to affect the morphologic complexity via a number of mechanisms and is an important factor affecting the mode of growth the origins of the truncated cone shape of mid ocean ridge volcanoes are also discussed of the eruption mechanisms that have been proposed to explain their flat summits the most likely mechanisms involve eruption from small ephemeral magma bodies lying within the low density upper oceanic crust the discussion includes speculations on factors affecting the depths of magma chambers beneath oceanic volcanoes supporting table is available via web browser or via anonymous ftp from ftp kosmos agu org directory append username anonymous password guest subdirectories in the ftp site are arranged by paper number information on searching and submitting electronic supplements is found at http www agu org pubs csupp about html

a stagnation point flow model for melt extraction from a mantle plume we present a two dimensional dynamical model for melt extraction from a mantle plume mantle material rises at constant velocity wo until it reaches a depth at which melting begins the flow in the melt zone above this depth has the form of a stagnation point flow melt migrates through the unmelted matrix in response to the total nonhydrostatic pressure gradient which is the sum of contributions from the deformation of the matrix and the buoyancy of the melt melt extraction is modeled as a melt flux through the upper surface of the melt zone our main conclusions are as follows 1 the nonhydrostatic pressure gradient associated with the deformation of the matrix is small relative to the buoyancy of the melt everywhere within the melt zone and the melt migration within the plume obeys darcy s law the rate of melt extraction from a mantle plume is therefore controlled by the buoyancy and viscosity of the melt itself and not by the viscosity of the matrix 2 melt extraction from a plume occurs over an area comparable to that of the plume itself and about 60 80 of the melt generated within the plume is extracted both the geometry and rate of extraction predicted by the model are consistent with observations in the hawaiian islands 3 layers of segregated melt magma chambers are likely to form at the the base of the lithosphere under intraplate volcanoes

structural evolution of preexisting oceanic crust through intraplate igneous activities in the marcus wake seamount chain multichannel seismic reflection studies and seismic refraction surveys with ocean bottom seismographs in the marcus wake seamount chain in the northwestern pacific ocean reveal p wave velocity structures of hot spot origin seamounts and adjacent oceanic crust inside the seamounts are central high velocity 6 5 km s structures extending nearly to the top that may indicate intrusive cores thick sediment layers up to 4 km with p wave velocities of 4 5 km s have accumulated on seafloor that predates seamount formation downward crustal thickening of up to 2 km was documented beneath a large seamount cluster but thickening was not confirmed below a small seamount cluster volume ratios of an intrusive core to a seamount body are 15 20 indicating that most of the supplied magma was consumed in forming the thick sedimentary and volcaniclastic layer constituting the seamount flanks underplating and downward crustal thickening may tend to occur when second or later intrusive cores are formed in a seamount p wave velocities in the lowest crust and in the uppermost mantle below the seamount chain are 0 1 0 2 km s higher and 0 3 0 5 km s lower respectively than velocities below oceanic crust we explain this difference as a result of sill like intrusion of magma into the lower crust and uppermost mantle reflected waves observed at offsets 200 km are from mantle reflectors at depths of 30 45 km and 55 70 km the shallower reflectors may indicate structures formed by intraplate igneous activities and the deeper reflectors may correspond to the lithosphere asthenosphere boundary

metasedimentary xenoliths in the lavas of the timanfaya eruption 1730 1736 lanzarote canary islands metamorphism and contamination processes we report on the investigation of contact metamorphism provoked by the emplacement of a shallow magma chamber during the timanfaya eruption of lanzarote from 1730 to 1736 ad the study was carried out on metamorphic xenoliths from basaltic timanfaya lavas and shows how the primary basanitic magma was contaminated by sedimentary and metamorphic rocks mineralogical and chemical studies allowed the definition of several xenolith types silica xenoliths quartz tridymite cristobalite or a mixture of these constituting more than 50 of the xenolith and cale silicate xenoliths wollastonite sometimes the 2m type diopside forsterite or mixture of these constituting more than 50 of the xenolith are the most frequent other minerals recognized were calcite dolomite augite enstatite hypersthene spinel and scapolite the mineralogy and some textures of the metamorphic forsteritic xenoliths are identical to those found in ultrabasic xenoliths dunites and point to a possible metamorphic origin for some of them major and trace elements showed a diversity of composition controlled by the mineralogy the ree composition of the metamorphic xenoliths is high compared with the sedimentary xenoliths not affected by metamorphism the mineral assemblages define metamorphic facies of low medium and high grade depending on the distance of the sedimentary rocks from the magma chamber border the igpetwin mixing program was used to verify the contamination process taking the xenoliths as representative of the sedimentary metamorphic rocks that were melted the results indicated that sedimentary metamorphic rock contamination of a basanitic magma can produce tholeiitic compositions

a two dimensional seismic investigation of crustal structure under the hawaiian islands near oahu and kauai two expanding spread profiles esps were analyzed in detail to investigate the deep structure of the volcanoes and the underlying oceanic crust near oahu one esp was located on the southeastern submarine flank of kauai esp 10 and the other was located directly over the ridge axis between oahu and molokai esp 5 two dimensional models of the entire crust were obtained by iterative comparison of both travel times and relative amplitudes of arrivals on the ray theoretical synthetic seismograms with those in the data a 2 4 km vertical offset in the preexisting crust inferred to be a large fault zone was found near the midpoint of esp 10 this fault may form the southern wall of a graben or half graben in which kauai sits the layering and seismic velocities of the preexisting oceanic crust near kauai have remained unmodified by the load of the volcanic pile esp 5 is located over a shallow 4 km thick basin filled with volcaniclastics and possibly volcanic flows bordered by the islands of oahu and molokai penguin bank and two buried rift zones under this basin the main volcanic edifice is 4 to 5 km thick the top of the preexisting oceanic crust is 8 to 9 km below sea level and is 3 to 4 km lower than the crust away from the islands the underlying oceanic crust is 6 to 7 km thick excluding the moho transition zone which is of normal thickness and at a depth from 15 to 16 km the existence of a large subcrustal plutonic body is refuted

depth and geoid anomalies over oceanic hotspot swells a global survey the broad depth and geoid anomalies associated with 23 hotspot swells in oceanic areas have been analyzed maximum height and geographical extent of the topographic swell and of the geoid anomaly as well have been measured for each hotspot the results indicate a clear increase of the topographic swell height with age of the underlying lithosphere from values in the range 300 500 m at young ages to values in the range 1 500 2 000 m at ages larger than 100 ma the geoid anomaly amplitude also increases with plate age from nearly zero close to mid ocean ridges to 6 8 m over old plates on the other hand the geographical extent of the swell does not show any clear relationship with plate age the mean lateral extent of swells range from 1 000 to 1 500 km swells located close to spreading ridges show a significant non zero depth anomaly but are associated with negligible geoid signal these results complete those of a previous study where the apparent compensation depth of oceanic hotspot swells was showed to increase linearly with the square root of plate age and coincide roughly with the base of the thermal lithosphere this trend may either be interpreted in terms ofmore lithospheric thinning or dynamical support besides both seem necessary to explain the observed bathymetry in proportion evolving with aging of the lithosphere less

a detailed geophysical study in the canary basin eastern atlantic implications for the internal structure of 130 ma oceanic crust summary we report the results of a detailed geophysical survey sited on two previously imaged dipping reflectors one dipping towards and the other away from the present day mid atlantic ridge axis within mesozoic aged crust of the east atlantic the new data include gravity magnetic and seismic refraction and reflection profiles collected in a grid that constrain the crustal structure as well as the reflector geometry a second order axial discontinuity which is associated with anomalous crustal structure is located within the survey area the westward dipping reflector can be traced from the moho to the top of the igneous crust where it coincides with a step of 800 m in the basement this reflector is approximately planar with a dip of 28 2 w and occurs 8 km north of the axial discontinuity we interpret this reflector as being a whole crustal normal fault that was generated within the median valley the eastward dipping reflector cannot be traced across seismic layer 2 and does not correlate with any feature of the basement it penetrates 2 3 km into the upper mantle its reflection strength is about twice that of the moho reflection this reflector which is approximately planar strikes parallel to the isochrons has a length of 18 2 km and a dip of 28 2 e we speculate that this reflector is also a fault that was generated on the western wall of the median valley but was captured from the north american plate by a lateral shift in the axis of spreading possibly associated with a major change in plate motion

sea level controlled sediment transport to the eastern arabian sea over the past 600 kyr clay minerals and srnd isotopic evidence from iodp site u1457 abstract long marine sequences deposited in the arabian sea are suitable to study the orbital sensitivity of sediment dynamics from a source to sink perspective the clay mineralogy and sr nd isotopic compositions have been analyzed for the detrital fraction of sediments from iodp site u1457 located in the laxmi basin eastern arabian sea to constrain the sediment sources and reconstruct a high resolution record of sediment export to the indus deep sea fan over the past 600 kyr the 87sr 86sr ratio varying from 0 7154 to 0 7255 and end varying from 12 9 to 9 5 imply a mixing of sediments derived from not only the indus river but also the rivers draining the deccan traps the variations in the smectite illite chlorite ratio combined with sr nd isotopes permit the reconstruction of past changes in the relative proportions of sediments derived from the indus river mainly illite chlorite and kaolinite and the deccan traps smectite the wavelet and cross spectral analyses further reveal that sediment transport to the eastern arabian sea since 600 kyr is mainly dominated by sea level variations in the eccentricity 100 kyr band while the indian summer monsoon might contribute moderately to the precession 23 kyr band the end and turbidite frequency indicate that more turbidite events are associated with indus river sourced sediments at iodp site u1457 during sea level lowstands which might reflect a reconnection of deep sea channels to the indus river mouth and or reworking of previously deposited indus river sediments located northward

catastrophic collapse of the volcanic island of hierro 15 ka ago and the history of landslides in the canary islands landslides play an important role in the evolution of many volcanic islands producing huge fields of blocky volcanic debris on their submarine slopes sidescan sonar images presented in this paper provide evidence for a large debris avalanche el golfo on the northern flank of hierro island in the canary islands angular blocks as much as 1 2 km across and 200 m high cover the debris avalanche surface el golfo avalanche is related to both the canary debris flow and a volcaniclastic turbidite found in the madeira abyssal plain 600 km west of the canaries dating of the turbidite and the failure scarp onshore indicates that the failure probably occurred between 13 and 17 ka there appears to be a general correlation between volcaniclastic turbidites in the abyssal plain sequence and landslides in the canaries during the past 750 ka tentatively this correlation suggests that seven major landslides have affected the canaries in that time

hydraulics of epiphreatic flow of a karst aquifer abstract the nature of epiphreatic flow remains an important research challenge in karst hydrology this study focuses on the flood propagation along the epiphreatic system of reka timavo system kras carso plateau slovenia italy it is based on long term monitoring of basic physical parameters pressure level temperature specific electric conductivity of ground water in six active caves belonging to the flow system the system vigorously responds to flood events with stage rising 100 m in some of the caves besides presenting the response of the system to flood events of different scales the work focuses on the interpretation of recorded hydrographs in view of the known distribution and size of conduits and basic hydraulic relations furthermore the hydrographs were used to infer the unknown geometry between the observation points this way the main flow restrictors overflow passages and large epiphreatic storages were identified the assumptions were tested with a hydraulic model where the inversion procedure was used for an additional parameter optimisation time series of temperature and specific electric conductivity were used to assess the apparent velocities of flow between consecutive points

spatial distribution of hotspot material added to the lithosphere under la reunion from wide angle seismic data wide angle seismic lines recorded by ocean bottom and land seismometers provide a pseudo three dimensional investigation of the crust and upper mantle structure around the volcanically active hotspot island of la reunion the submarine part of the edifice has fairly low seismic velocities without evidence for intrusives an upper unit with a velocity depth gradient is interpreted as made of material erupted subaerially then transported and compacted downslope between this unit and the top of the oceanic plate imaged by normal incidence seismic reflection a more homogeneous unit indicated by shadow zones on several wide angle sections may correspond to lavas of a different nature extruded underwater in the earlier phase of volcanism coincident wide angle and normal incidence reflections document that the oceanic plate is not generally downwarping toward the island but doming instead toward its southeastern part with limited evidence for some intracrustal intrusion deeper in the lithosphere the presence of a layer of intermediate velocity between the crust and mantle is firmly established it is interpreted as resulting from the advection of hotspot magmatic products possibly partially molten and of a composition for which the crust is a density barrier the extensive wide angle coverage constrains the extent of this body it does not show the elongated shape expected from plate drift above a steady hotspot supply alternative propositions can hence be considered for example that la reunion is caused by a solitary wave of hotspot material or by a young hotspot the size of the underplate 140 km wide and up to 3 km thick corresponds to less than half the volume of the edifice on top of the plate

comment on the distribution of basaltic volcanism on tenerife canary islands implications on the origin and dynamics of the rift systems by a geyer and j marti tectonophysics 483 2010 310 326 in their article geyer and marti 2010 propose that the evolution and origin of the volcanic islands which constitute the canarian archipelago are strongly controlled by regional tectonic atlantic and african structures in their fig 1a they sketch the geometry of the iberian and moroccan microplates and the respective boundary zones with respect to africa nubia and eurasia mantovani et al 2007 dashed lines indicating presumed plate boundaries cross the canarian archipelago which will therefore be located along a lithospheric fracture the boundary between the moroccan and african nubia microplates this regional fracture extends from the atlas to the atlantis fracture zone coinciding in parts with the propagating fracture postulated by anguita and hernan 1975 in fig 1b of geyer and marti 2010 dashed lines indicate the orientation of the most evident tectonic structures visible on the ocean floor as we show in this comment all of these mapped faults are artifacts

modelling spring discharge and solute transport in conduits by coupling cfpv2 to an epikarst reservoir for a karst aquifer abstract karst aquifers differ from unconsolidated granular aquifers with respect to their groundwater flow behavior because of the dual permeability characteristics discrete conduit network coupled to a fissured matrix the duality of recharge point vs diffuse recharge as well as the duality of flow laminar vs turbulent state in many karst aquifers the epikarst frequently plays an important role in redistributing precipitation as diffuse recharge into the fissured matrix and as point recharge into the conduit network as well as for the temporal distribution of recharge input in this paper a coupled groundwater model ce cfpv2 erch is developed consisting of a combination of a simple reservoir model generating the recharge source function assuming the concept of an epikarst horizon erch with cfpv2 a discrete conduit continuum groundwater flow model of the phreatic karst aquifer the ce model is applied to simulate spring discharge and a tracer breakthrough in a karst aquifer near guilin city in southwest china in order to examine the effect of an added epikarst reservoir model simulations are carried out with cfpv2 but without including erch simulation results of both spring hydrograph and tracer breakthrough indicate that cfpv2 with erch performs much better a sensitivity analysis of the ce reveals the relative importance of parameters characterizing the epikarst reservoir point recharge is a main factor determining the large variation in spring discharge and its proportion to total recharge can reach 58 these simulation results highlight the importance of the temporal and spatial distribution of recharge to karst spring discharge response the coupled model provides an effective approach to include the effect of an epikarst zone in cfpv2 and it can easily be applied for the simulation of karst aquifers with similar characteristics as the study site

causes and mechanisms of the 2011 2012 el hierro canary islands submarine eruption 1 el hierro eruption started on 10 october 2011 after an unrest episode that initiated on 17 july 2011 this is the first eruption in the canary islands that has been tracked in real time although being submarine and not directly observable the data recorded allowed its reconstruction and to identify its causes and mechanisms seismicity surface deformation and petrological data indicate that a batch of basanitic magma coming from a reservoir located at a depth of about 25 km below the el hierro island was emplaced at shallower depth creating a new reservoir about 10 12 km above where magma evolved until the initiation of the eruption the characteristics of seismicity and surface deformation suggest that the necessary space to accumulate magma at this shallower position which coincides with the crust mantle boundary beneath el hierro was created in about 2 months by elastic deformation and magma driven fracturing of the crust after this first intrusion episode part of the magma started to migrate laterally toward the se for nearly 20 km always keeping the same depth and following a path apparently controlled by stress barriers created by tectonic and rheological contrasts in the upper lithosphere this lateral migration of magma ended with a submarine eruption at about 5 km offshore from the southern corner of el hierro island the total seismic energy released during the unrest episode was of 8 1 1011 j and the total uplift previous to the onset of the eruption was of 40 mm combining geological geophysical and petrological data and numerical modeling we propose a volcanological model of the causes and mechanisms of el hierro eruption that shows how the stress distribution in the crust beneath el hierro which was influenced by rheological contrasts tectonic stresses and gravitational loading controlled the movement and eruption of magma we also discuss the implications of this model in terms of eruption forecast in the canary islands

an estimation of the elastic thickness of the lithosphere in the canary archipelago using admittance function a recent compilation of shipborne gravity and bathymetry data has been used to determine the effective elastic thickness eet of the lithosphere beneath the canary islands volcanic complex by means of the admittance technique as a first approach we have computed the admittance which is interpreted in terms of isotropic elastic plate thickness with an eet of 23 km nevertheless the proximity of the west african continental margin wacm together with the lateral variability in lithosphere structure in part caused by the large volcanic history of the canaries require a slightly different approach to minimize the influence of the margin and to check whether or not any significant variation in eet occurs related to the known canary hotspot we have computed the admittance following the isochron lines the results show a higher eet 35 km than that obtained by the first approach but slightly smaller than that predicted by the cooling plate model

the marquesas archipelagic apron seismic stratigraphy and implications for volcano growth mass wasting and crustal underplating multichannel seismic lines sonobuoy and gravity data across the marquesas islands are used to study volcano growth island mass wasting and crustal underplating at island chains with overfilled moats the marquesas bathymetry reflects the changing thickness of the sedimentary infill rather than the basement topography the moat contains two major regions of differing seismic stratigraphy 1 the moat edges where a unit of continuous layered reflectors is present containing minor lenses of chaotic diffractors and 2 the central moat where the deep moat basins are overfilled by an acoustically opaque unit of discontinuous reflectors of up to 2 km thickness in places capped by a ponded unit plate flexure models require broad underplating of the crust by low density crustal material at the marquesas islands to explain the depth to volcanic basement and gravity observations the seismic velocities and seismic stratigraphy as well as the general structure of the islands and surrounding seafloor indicate the apron is mostly debris from island mass wasting reflectors of the outermost moat generally onlap the flexural arch in the lower section and offlap and overfill it in the upper section in the central moat reflectors change shape from concave up in the lower section to convex in the upper section three dimensional diffusion models of sedimentation which incorporate a time dependent seafloor deflection from progressive island loading and vary sediment influx as islands are formed and mass waste suggest that three main factors make the moat stratigraphy at the marquesas different from hawaii 1 the marquesas moat is overfilled while the hawaiian moat is underfilled 2 sediment diffusivities are lower at the marquesas and 3 the marquesas islands are separated by deep sedimentary basins in contrast to hawaii where islands are separated by a shallow ridge the lower sediment diffusivity at the marquesas may reflect a larger proportion of blocky massive material in the central marquesas moat or alternatively a change in the dominant process of sediment transport while there is similar sediment supply for a given along moat distance at both the marquesas and hawaii the underfilled moat at hawaii is apparently a consequence of greater moat volumes due to the larger size of the hawaiian volcanoes and possibly variations in underplating that load the plate the difference in sediment edifice ratios is likely related to the larger eruption rates at hawaii and different styles of volcano construction between hawaii and the marquesas

magmatic underplating in the canary archipelago abstract the location of the canary archipelago at the east edge of the north atlantic a few hundred kilometres from the west african coast has for years posed a serious difficulty in understanding the complex interaction between long lasting volcanic activity and one of the oldest seafloor basements 150 ma on earth many different hypotheses have been proposed in the last two decades to understand the genesis of the canary archipelago there is an increasing acceptance to explain the archipelago as the product of the slow passage of the african plate over a mantle hotspot in rival tectonic models stretching and thinning of the lithosphere would determine the islands as independent volcanic blocks we review recent geophysical and geological evidence supporting a mantle plume origin for the canary islands based on the recognition of crustal thickening by mafic intrusions produced by the interaction between the mantle plume and the old oceanic lithosphere beneath the canary archipelago

mechanisms of heat exchange between water and rock in karst conduits 1 previous studies motivated by understanding water quality have explored the mechanisms for heat transport and heat exchange in surface streams in karst aquifers temperature signals play an additional important role since they carry information about internal aquifer structures models for heat transport in karst conduits have previously been developed however these models make different sometimes contradictory assumptions additionally previous models of heat transport in karst conduits have not been validated using field data from conduits with known geometries here we use analytical solutions of heat transfer to examine the relative importance of heat exchange mechanisms and the validity of the assumptions made by previous models the relative importance of convection conduction and radiation is a function of time using a characteristic timescale we show that models neglecting rock conduction produce spurious results in realistic cases in contrast to the behavior of surface streams where conduction is often negligible conduction through the rock surrounding a conduit determines heat flux at timescales of weeks and longer in open channel conduits radiative heat flux can be significant in contrast convective heat exchange through the conduit air is often negligible using the rules derived from our analytical analysis we develop a numerical model for heat transport in a karst conduit our model compares favorably to thermal responses observed in two different karst settings a cave stream fed via autogenic recharge during a snowmelt event and an allogenically recharged cave stream that experiences continuous temperature fluctuations on many timescales

the crustal structure of the cocos ridge off costa rica 1 the submarine cocos ridge in the northwestern panama basin a bathymetric feature more than 1000 km long and 250 500 km broad is about 2 km shallower than the adjacent basin it is generally interpreted as the trace of the galapagos hot spot two 127 and 260 km long seismic wide angle sections were recorded along and across this ridge offshore the osa peninsula costa rica crustal thickening is seen everywhere along the sections on the northwestern outer ridge flank increased thickness is exclusively attributed to the upper crust and expressed by 2 km thick flow basalts the quepos plateau caps the upper crust in this area toward the center of the cocos ridge the moho deepens from 11 12 to 21 km depth and crustal thickening is almost entirely attributed to the lower crust which makes up 80 of the crust and is three times the thickness of normal oceanic lower crust it is homogeneously structured and the velocities which range from 6 5 km s at the top to 7 35 km s at the base are comparable to normal lower crust under these depth conditions and suggest no differences to a gabbroic rock composition similarities to the crustal velocity structure of iceland central kerguelen plateau and broken ridge are consistent with a formation of this 13 15 ma old cocos ridge segment by excessive magmatism in a near plate boundary setting

stratigraphy structure and geochronology of the las canadas caldera tenerife canary islands after a long period of subaerial fissure fed extrusions of basaltic magmas 12 to 3 ma volcanic activity was then concentrated in the central part of tenerife phonolitic magma chambers formed and a central volcanic complex was constructed the las canadas edifice the formation of a large depression the las canadas caldera truncated the top of the edifice the active twin strato cones teide pico viejo are sited in this depression the history of the las canadas caldera and edifice are established from stratigraphy geochronology k ar dates and volcanological studies two different groups are recognized separated by a major unconformity the lower group is dated at 2 to 3 ma and includes the products of several volcanic centres which together represent several cycles the upper group ranges from 1 56 to 0 17 ma and includes three different formations representing three long term 100 to 300 ka volcanic cycles the periods of dormancy between each formation were of 120 to 250 ka duration the las canadas caldera is a multicyclic caldera which formed over the period 1 18 0 17 ma each cycle of activity represented by a formation culminated in caldera collapse which affected different sectors of the las canadas edifice geological observation and geochronology support an origin by collapse into a magma chamber the minimum volume of pyroclastic ejecta is substantially greater than the present caldera depression volume 45 km3 but approaches the inferred volume of the original caldera depression 140 km3 after the formation of the caldera sector collapses could also occur at the northern flank of the volcano causing the disappearance of the northern side of the caldera wall

crustal structure of ascension island from wide angle seismic data implications for the formation of near ridge volcanic islands abstract the study of the internal structure of volcanic islands is important for understanding how such islands form and how the lithosphere deforms beneath them studies to date have focused on very large volcanic edifices e g hawaiian islands marquesas but less attention has been paid to smaller islands which are more common ascension island a 4 km high volcanic edifice with a basal diameter of 60 km is located in the equatorial atlantic 8 s 90 km west of the mid atlantic ridge on 7 ma oceanic lithosphere we present results of a wide angle seismic profile crossing the island revealing a crustal thickness of 12 13 km an overthickened layer 3 7 km thick and little evidence of lithospheric flexure together these results suggest ascension island may be older than previously assumed and may have begun forming at an on axis position around 6 7 ma this hypothesis is further supported by the presence of a young 1 4 km high edifice directly adjacent to the mid atlantic ridge with a volume about 1 7 that of ascension island possibly representing the earliest stages of seamount formation excess magmatism appears to be related to the tectonic setting at the ridge fracture zone intersection

understanding flooding in poljes a modelling perspective abstract poljes are large flat closed depressions that can be found in most karst areas around the world they are prone to regular flooding which occurs after abundant rainfall or snowmelt events the floods can form several meters deep intermittent lakes that can persist for months human settlements around poljes have been traditionally positioned above the level of the most severe floods however many neighbouring villages expanded during the last decades to areas that might be endangered by large flood events in addition a recent study has shown that several poljes encountered floods of more severe amplitude in mid holocene due to a prevailing humid climate as current knowledge of polje s hydrology appears to be still insufficient further research is needed this work aims to identify the factors controlling polje flooding and evaluates their impact on the flood amplitude and duration to do so a list of parameters potentially controlling flooding is established the relevance of each parameter is tested by using two idealized numerical models the first one considers exclusively the polje from the springs to the ponors whereas the second integrates the aquifer adjacent to the polje outflow side first results show the usefulness of simple numerical models to identify the effect of each parameter on the flood amplitude and duration the findings are combined to simulate a flood of medium intensity and long duration that occurred on a typical polje a comparison of the results with real data demonstrates that the aquifer draining the polje needs to be considered to understand properly the flooding dynamics the approach presented within this work has the potential to be used in other poljes encountering similar hydrological situations but also lays foundation for flooding modelling in other karst areas

modeling of storm responses in conduit flow aquifers with reservoirs abstract in aquifers containing large voids such as karst aquifers with caves or basaltic aquifers with lava tubes hydrographs at wells or springs are used to analyze the structure and response of the hydrogeological system numerical modeling of hydrograph response is commonly based on either inverse techniques or postulated flow geometries however the range of mechanisms for generating hydrograph responses have not been fully investigated physical modeling of these complex non darcian systems permits better understanding of the storm responses that conduit systems may generate using a numerical model of conduit flow systems which incorporates turbulent flow some of the mechanisms that can alter storm pulses were investigated by treating them as combinations of pipes that connect reservoirs the results indicate that the response of a conduit flow aquifer can range from what has been called diffuse or steady to conduit or flashy without employing a diffusive component a full range of behavior can be the result of changes from phreatic to epiphreatic conditions in a conduit changes in conduit geometry or multiple springs draining the same system the results provide a quantitative tool to assess spring and well hydrographs and illustrate mechanisms that can generate observed responses which have previously been qualitatively interpreted