geomorphometric analysis of the 2014 2015 barðarbunga volcanic eruption iceland abstract topographical information is of fundamental interest for a wide range of disciplines including glaciology agriculture communication network planning or hazard management in volcanology elevation data are of particular importance when assessing material flows throughout a volcanic system to obtain accurate estimates of time varying topography in volcanic active regions high resolution digital elevation models dems are required to monitor and evaluate topographical changes and especially volumetric gains and losses during the 2014 2015 bar arbunga eruption iceland multi temporal tandem x dem sequences were evaluated the 2014 2015 volcanic eruption was associated with the rare event of a caldera collapse visible on the surface of the vatnajokull glacier as well as major lava effusion in the holuhraun plain before investigating topographical change at the two study areas the tandem x dems were analysed for absolute and relative height errors resulting from the radar system parameters the sar processing or the local environment the uncertainty investigation determined that acquisitions over the snow covered bar arbunga caldera were primarily affected by microwave penetration into snow and dems over the holuhraun lava field exhibited increased height errors due to active lava flows and dynamic outwash plain the topographical analysis of the 2014 2015 bar arbunga eruption revealed a maximum vertical displacement of approximately 65 m and 43 m at the study area of the bar arbunga caldera and holuhraun lava field respectively with a total subsidence volume of 1 40 0 13 km3 and a dense rock equivalent dre lava volume of 1 36 0 07 km3 known uncertainties in volume were decreased by approximately 35 and 77 accordingly taking into account the calculation of rates the temporal development of caldera collapse and lava effusion was found to exhibit a near exponential decrease the ratio between subsidence and dre lava volume moreover indicated the coupling between piston collapse and magma drainage

segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

seismicity of the reykjanes peninsula 1971 1976 abstract the reykjanes peninsula oblique rift a segment of the mid atlantic plate boundary connects the reykjanes ridge to the rift zones of iceland the axis of the deformation zone of the plate boundary can be traced as a rather narrow epicentral zone of earthquakes that is highly oblique to the spreading direction of the north america plate with respect to the eurasia plate the seismicity of the area is episodic active periods with a duration of about a decade are separated by more quiet periods of one to two decades our observation period spans a good part of an episode that began in 1967 and ended in 1975 nine earthquake swarms illuminate a 50 km long segment of the plate boundary the epicentral zone cuts obliquely across the fissure swarms of the volcanic systems of the peninsula geothermal areas are preferentially located at the intersection of the fissure swarms with the seismic zone outside the intersections with the seismic zone the fissure swarms show very low seismicity the tectonic characteristics gradually change along the plate boundary segment from being similar to those of a spreading segment in the western part to being more like a transform zone in the eastern part this is seen in the type of earthquake sequences maximum magnitude and type of faulting

thermal permeability structure and recharge conditions of the mutnovsky high temperature geothermal field kamchatka russia abstract the mutnovsky geothermal area is part of the eastern kamchatka active volcano belt mutnovsky 80 ky old and an aging strato volcano a complex of 4 composite volcanic cones acts as a magma and water injector into the 25 km long north mutnovsky extension zone magmatic injection events dykes are associated with plane oriented meq micro earth quakes clusters most of them occurring in the ne sector of the volcano 2 10 km2 at elevations from 4 to 2 km while some magmatic injections occur at elevations from 6 0 to 4 0 km below the mutnovsky production field water recharge of production reservoirs is from the mutnovsky volcano crater glacier 1500 to 1800 masl which was confirmed by water isotopic data d 18o of production wells at an earlier stage of development the mutnovsky dachny 260 310 c high temperature production geothermal reservoir with a volume of 16 km3 is at the junction of nne and ne striking normal faults which coincides with the current dominant dyke injection orientation tough2 modeling estimates of the reservoir properties are as follows the reservoir permeability is 90 600 e 15 m2 the deep upflow recharge is 80 kg s and the enthalpy is 1420 kj kg modeling was used to reproduce the history of the mutnovsky dachny reservoir exploitation since 1983 with an effective power of 48 mwe by 2016 modeling also showed that the reservoir is capable of yielding 65 83 mwe of sustainable production until 2055 if additional production drilling in the se part of the field is performed moreover this power value may increase to 87 105 mwe if binary technologies are applied modeling also shows that the predicted power is sensitive to local meteoric water influx during development conceptual itough2 eos1sc thermal hydrodynamic modeling of the mutnovsky magma hydrothermal system as a whole reasonably explains its evolution over the last 1500 5000 years in terms of heat recharge dyke injection from the mutnovsky 4 funnel and mass recharge water injection through the mutnovsky 2 and mutnovsky 3 funnels conditions as previously mentioned

intense seismicity during the 2014 2015 barðarbunga holuhraun rifting event iceland reveals the nature of dike induced earthquakes and caldera collapse mechanisms

the kinematic and hydrographic structure of the gulf of maine coastal current the gulf of maine coastal current gmcc which extends from southern nova scotia to cape cod massachusetts was investigated from 1998 to 2001 by means of extensive hydrographic surveys current meter moorings tracked drifters and satellite derived thermal imagery the study focused on two principal branches of the gmcc the eastern maine coastal current emcc that extends along the eastern coast of maine to penobscot bay and the western maine coastal current wmcc that extends westward from penobscot bay to massachusetts bay results confirm that gmcc is primarily a pressure gradient driven system with both principal branches increasing their transport in the spring and summer due to fresh water inflows and flowing southwestward against the mean wind forcing during this period in the spring and summer the subtidal surface currents in the emcc range from 0 15 to 0 30 ms 1 while subtidal wmcc currents range from 0 05 to 0 15 ms 1 the reduction of southwestward transport near penobscot bay is accomplished via an offshore veering of a variable portion of the emcc some of which recirculates cyclonically within the eastern gulf of maine the degree of summer offshore veering versus leakage into the wmcc varied strongly over the three study years from nearly complete disruption in 1998 to nearly continuous through flow in 2000 observations show strong seasonal and interannual variability in both the strength of the gmcc and the degree of connectivity of its principal branches r 2005 elsevier ltd all rights reserved

drainage of a deep magma reservoir near mayotte inferred from seismicity and deformation the dynamics of magma deep in the earth s crust are difficult to capture by geophysical monitoring since may 2018 a seismically quiet area offshore of mayotte in the western indian ocean has been affected by complex seismic activity including long duration very long period signals detected globally global navigation satellite system stations on mayotte have also recorded a large surface deflation offshore here we analyse regional and global seismic and deformation data to provide a one year long detailed picture of a deep rare magmatic process we identify about 7 000 volcano tectonic earthquakes and 407 very long period seismic signals early earthquakes migrated upward in response to a magmatic dyke propagating from moho depth to the surface whereas later events marked the progressive failure of the roof of a magma reservoir triggering its resonance an analysis of the very long period seismicity and deformation suggests that at least 1 3 km3 of magma drained from a reservoir of 10 to 15 km diameter at 25 to 35 km depth we demonstrate that such deep offshore magmatic activity can be captured without any on site monitoring recent seismicity near mayotte in the indian ocean is due to dyke propagation from and drainage of a 25 35 km deep magma reservoir according to an analysis of earthquake and deformation data

time dependent dike propagation from joint inversion of seismicity and deformation data dike intrusions both deform earth s surface and induce propagating earthquake swarms we develop methods to utilize both deformation and seismicity from brittle volcano tectonic earthquakes to image time dependent dike propagation dieterich s 1994 seismicity rate theory is used to relate dike induced stress changes to seismicity rate and is combined with elastic green s functions relating dike opening to deformation different space time patterns of seismicity develop if earthquakes occur at the same depth as the dike compared to above below the dike in the former seismicity initiates near the dike s leading edges but shuts off as the dike tips pass and seismogenic volumes fall into stress shadows in the latter seismicity continues at a decaying rate after the tips pass we focus on lateral propagation and develop a nonlinear inversion method that estimates dike length and pressure as a function of time the method is applied to the 2007 father s day intrusion in kilauea volcano seismicity is concentrated at 3 km depth comparable to geodetic estimates of dike depth and decays rapidly in time with lateral propagation only and a vertical dike tip line it is difficult to fit both gps data and the rapid down rift jump in seismicity suggesting significant vertical propagation for the events to have occurred below the dike requires a very short aftershock decay time hence unreasonably high background stressing rate the rapid decay is better explained if the dike extends somewhat below the seismicity we suggest that joint inversion is useful for studying the diking process and may allow for improved short term eruption forecasts

seismic amplitude ratio analysis of the 2014 2015 bar arbunga holuhraun dike propagation and eruption magma is transported in brittle rock through dikes and sills this movement may be accompanied by the release of seismic energy that can be tracked from the earth s surface locating dikes and deciphering their dynamics is therefore of prime importance in understanding and potentially forecasting volcanic eruptions the seismic amplitude ratio analysis sara method aims to track melt propagation using the amplitudes recorded across a seismic network without picking the arrival times of individual earthquake phases this study validates this methodology by comparing sara locations filtered between 2 and 16hz with the earthquake locations same frequency band recorded during the 2014 2015 bar arbunga holuhraun dike intrusion and eruption in iceland integrating both approaches also provides the opportunity to investigate the spatiotemporal characteristics of magma migration during the dike intrusion and ensuing eruption during the intrusion sara locations correspond remarkably well to the locations of earthquakes several exceptions are however observed 1 a low frequency signal was possibly associated with a subglacial eruption on 23 august 2 a systematic retreat of the seismicity was also observed to the back of each active segment during stalled phases and was associated with a larger spatial extent of the seismic energy source this behavior may be controlled by the dike s shape and or by dike inflation 3 during the eruption sara locations consistently focused at the eruptive site 4 tremor rich signal close to ice cauldrons occurred on 3 september this study demonstrates the power of the sara methodology provided robust site amplification quality factors and seismic velocities are available plain language summary locating earthquakes usually implies picking phase arrivals p and s waves another technique called seismic amplitude ratio analysis sara was recently introduced to locate them only by using the amplitude recorded at different pairs of seismic stations however this technique was never proven to be true this study shows that the earthquake locations derived by sara compares remarkably well with the locations of 30 000 seismic events triggered when magma migrated in the icelandic crust prior to the 2014 2015 holuhraun eruption but the results also provide new insight into the magma dynamics that led to the largest eruption of the last two centuries in europe we show that ground vibration was continuously triggered during the 2week period preceding the eruption when magma forced its way toward the eruption site but also during the eruption itself several intriguing features were observed including low frequency vibrations possibly associated with eruption below the ice or large patches of seismic activity when the magma stopped propagating toward the eruption site this methodology performs very well provided some parameters are available and allows to gain insights into the complex dynamics associated with magma movements

spatial and temporal variability of the velocity and hydrographic structure in a weakly stratified system broad sound casco bay maine the velocity and hydrographic structure across broad sound a north south orientated subsystem of casco bay me that lacks continuous coastal boundaries were characterized using velocity observations from two moorings in late summer fall of 2013 and velocity and density observations from a repeat transect ship survey conducted over a tidal cycle during the same period at tidal time scales the system is dominated by a barotropic semidiurnal standing wave with a west to east decrease in tidal amplitude and relatively minimal phase change across the majority of the transect the stratification vertical differences of 0 5 1 0 kg m 3 was generally laterally uniform and stronger during the flood phase which is hypothesized to result from stronger offshore stratification the mean circulation had strong lateral shear with inflow over the deepest point in the bathymetric cross section and eastern slope and outflow over the western slope there was also vertical shearing of the horizontal velocities with stronger northward or northward trending velocities at depth the depth averaged subtidal fluctuations were relatively small 2 3 cm s 1 and uncorrelated between mooring sites suggesting the vertically uniform current response associated with remote wind forcing is of limited importance on the other hand the depth dependent velocity fluctuations at the subtidal time scale were in large part 36 72 driven by wind forcing the net flux ratio a means of quantifying the relative importance of the vertical and lateral shear in the flow field was typically 0 44 indicating the structure of the local wind response favored vertically sheared flow

crustal deformation associated with the 1996 gjalp subglacial eruption iceland insar studies in affected areas adjacent to the vatnajokull ice cap abstract crustal deformation signals associated with the september 30 october 13 1996 gjalp subglacial eruption vatnajokull ice cap iceland have been identified using interferometric analysis of synthetic aperture radar images insar in areas outside the ice cap on september 29 1996 an mw 5 6 earthquake occurred at the nearby bardarbunga volcano and on september 30 seismicity propagated 20 km southwards where the gjalp eruption occurred analysis of interferograms spanning different times from 1992 to 2000 allows us to separate two distinct co eruptive deformation periods in areas outside the ice cap diking at the bardarbunga caldera rim appears to be responsible for deformation during the first week of eruption while significant deflation occurred at bardarbunga only after october 6 when most of the magma had already been erupted at gjalp a pressure connection between the bardarbunga volcano and the gjalp eruptive fissure is inferred fault slip in three areas up to 30 km from the center of the bardarbunga volcano was triggered by the deflation local deformation signals there are consistent with small fault movements

volume changes of vatnajokull ice cap iceland due to surface mass balance ice flow and subglacial melting at geothermal areas 1 we present observed changes in the geometry of western vatnajokull over a period of about ten years which are caused by the surface mass balance ice flow both during surges and quiescent periods and basal melting due to geothermal and volcanic activity comparison of two digital elevation models shows that from 1985 to 1998 the outlet glaciers have lost 14 5 km3 on the average 1 m yr 1 evenly distributed over the area of 1360 km2 however the marginal areas of four outlets have gained up to 80 m in elevation and the uppermost parts have subsided similarly during surges altogether 26 3 km3 were transported from the accumulation areas to the ablation areas of which 19 3 km3 are attributed to surges comparison of dem s from august 1997 and august 1998 revealed 10 ice cauldrons produced by subglacial geothermal activity of which some were previously unknown

magma influence on propagation of normal faults evidence from cumulative slip profiles along dabbahu manda hararo rift segment afar ethiopia abstract measuring displacement length profiles along normal faults provides crucial information on fault growth processes here based on satellite imagery and topography we analyze 357 normal faults distributed along the active rift of dabbahu manda hararo dmh afar which offers a unique opportunity to investigate the influence of magmatism on fault growth processes our measurements reveal a large variety of slip profiles that are not consistent with elastic deformation their analysis contributes towards a better understanding of the lateral propagation of faults especially when nucleation points and existence of barriers are included using the fault growth model of manighetti et al 2001 we determine the preferred direction of lateral propagation for each fault our results suggest that lateral propagation of faults is easier away from areas where magma has been stored for long time at crustal depth and has thus modified the thermo mechanical properties of the host rock however these areas correspond also to areas where the initiation of fault growth appears as easiest along the rift in combining these results with the analysis of rift width and the position of magma reservoirs along dmh rift we show that fault growth keeps track of the magma presence and or movement in the crust

mechanical models for dikes a third school of thought abstract geological and geophysical data from continental volcanic centers and giant radial swarms and from oceanic shield volcanoes and rift zones indicate that dikes propagate laterally for distances that can be 10 to over 100 times their height what traps dikes within the shallow lithosphere and promotes these highly eccentric shapes gravity induced stress gradients in the surrounding rock and pressure gradients in the magma are the primary loading mechanisms pressure gradients due to magma flow are secondary to insignificant because the flow direction is dominantly horizontal this configuration of vertical blade shaped dikes with horizontal dike propagation and magma flow is fundamentally different from the two dike model configurations described in a recent review paper as two schools of thought for mechanical models of dikes in school i a dike is disconnected from its source and ascends under the influence of buoyancy in school ii a dike is connected to a magma reservoir and is driven upward by magma flux from the source we review the geological and geophysical data supporting the vertical dike horizontal flow propagation configuration and suggest the abundance and veracity of these data in many different geological settings and the modeling results that address this physical process warrant adding this as a third school of thought a new analytical solution for the boundary value problem of a homogeneous isotropic and linear elastic solid with a vertical fluid filled crack is used to investigate the effects of gravitationally induced stress and pressure gradients on the aperture distribution dike tip stress intensity and stable height model results indicate that in a homogeneous crust dikes can achieve stable heights greater than a kilometer only if the host rock fracture toughness k ic 100 mpa m 1 2 however density stratification of the crust is an effective mechanism for trapping kilometer scale dikes even if the host rock is very weak k ic 0 this analysis may explain why vertical dikes propagate laterally for great distances but reside within a narrow range of depths in the crust

the 2008 may 29 earthquake doublet in sw iceland summary on 2008 may 29 an earthquake doublet shook the southwestern part of iceland the first main shock originated beneath mt ingolfsfjall located near the western margin of the south iceland seismic zone sisz approximately 40 km east of the capital reykjavik immediate aftershock activity was recorded by the sil seismic network operated by the icelandic meteorological office imo with both n s and e w structures illuminated over a broad area a continuous gps cgps network also operated by the imo recorded coseismic offsets with up to 200 mm of horizontal motion at the closest stations we estimate the coseismic surface deformation observed by campaign and continuous gps and satellite radar data insar we invert the geodetic data to find the optimal geometry location and slip on the main faults accounting for variation in the elastic parameters of the crust with depth our models indicate that most of the slip occurred on two n s structures spaced 5 km apart from a joint inversion of gps and insar data for variable slip models we find that most of the slip for the first ingolfsfjall event was concentrated at 2 4 km depth with a maximum of 1 9 m whereas the slip on the second kross fault was located deeper at 3 6 km depth with up to 1 4 m of motion the models give similar geodetic moments for the two main events equivalent to a moment magnitude of mw5 8 and mw5 9 for the first and second event respectively our estimated composite moment therefore equals a mw6 1 for the doublet smaller than the mw6 3 estimated from teleseismic data e g neic and harvard the geodetic data support rupture on two main faults and analysis of high rate 1 hz cgps data suggests that slip on the second fault initiated within 3 s of the first main shock static coulomb failure stress calculations indicate that the first event caused a stress increase in the area of the main asperity i e at the location of the largest slip patch on the second fault however we cannot rule out dynamic stress triggering due to the short time between the two main events the 2008 may 29 earthquake doublet appears to be a continuation of the earthquake sequence that started in 2000 june when two mw6 5 events struck the eastern and central part of the south iceland seismic zone in the span of 81 hr the 2000 june 2008 may sequence has released about half of the moment accumulated by plate motion since the previous earthquake sequence in 1896 1912 therefore continued earthquake activity with moderate size events rupturing n s faults in the sisz in the coming decades is likely

deep crustal melt plumbing of barðarbunga volcano iceland understanding magmatic plumbing within the earth s crust is important for understanding volcanic systems and improving eruption forecasting we discuss magma plumbing under bar arbunga volcano iceland over a 4 year period encompassing the largest icelandic eruption in 230 years microseismicity extends through the usually ductile region of the earth s crust from 7 to 22 km depth in a subvertical column moment tensor solutions for an example earthquake exhibits opening tensile crack behavior this is consistent with the deep 7 km seismicity being caused by the movement of melt in the normally aseismic crust the seismically inferred melt path from the mantle source is offset laterally from the center of the bar arbunga caldera by 12 km rather than lying directly beneath it it is likely that an aseismic melt feed also exists directly beneath the caldera and is aseismic due to elevated temperatures and pervasive partial melt under the caldera

altered regional sediment transport regime after a large typhoon southern taiwan analyses of river suspended sediment response to record breaking regional rainfall in southern taiwan during typhoon morakot 7 9 august 2009 reveal systematic changes in the regional sediment transport regime as characterized by rating curve parameters with decreasing b typically considered to be a constant for a given gauging station and increasing intercept k values in concentration discharge c q relations c kq b these changes result in much greater sediment concentration and thus sediment transport in subsequent low flow events after the typhoon an effect that amplifies and extends the influence of such extreme events through increased low flow sediment transport our finding that the exponent b is not constant contrasts with the conventional assumption that large events influence sediment yields through increased intercept k values thereby supporting the interpretation that basin sediment delivery influences both rating parameters and increases post event low flow sediment transport surveys of landslide density and riverbed grain sizes before and after typhoon morakot support the interpretation that the observed decrease in b values and the synchronous shift from an inverse correlation between k and mean catchment slope before the typhoon to a positive correlation afterward reflect an altered sediment transport regime and a change from channel migration and bank erosion to reworking of landslide debris and enhanced bed mobility as the dominant processes supplying fluvial sediment

volcanic plume elevation model and its velocity derived from landsat 8 abstract in this paper we present a method to restitute the volcanic gas ash plume elevation model pem from optical satellite imagery as the volcanic plume is moving rapidly conventional satellite based photogrammetric height restitution methods do not apply as the epipolar offset due to plume motion adds up to the one generated by the stereoscopic view this is because there are time lags of tens of seconds between conventional satellite stereoscopic acquisitions depending on the stereo acquisition mode our method is based on a single satellite pass we exploit the short time lag and resulting baseline that exist between the multispectral ms and the panchromatic pan bands to jointly measure the epipolar offsets and the perpendicular to the epipolar p2e offsets the first are proportional to plume height plus the offsets due to plume velocity in the epipolar direction the second are proportional to plume velocity in the p2e direction only the latter is used to compensate the effect of plume velocity in the stereoscopic offsets by projecting it on the epipolar direction assuming a known plume direction thus improving the height measurement precision we apply the method to landsat 8 data taking into account the specificities of the focal plane modules we focus on the holuhraun 2014 fissure eruption iceland we validate our measurements against ground based measurements the method has potential for detailed high resolution routine measurements of volcanic plume height velocity the method can be applied both to other multifocal plane modules push broom sensors such as the esa sentinel 2 and potentially to other push broom systems such as the cnes spot family and pleiades

major impact of volcanic gases on the chemical composition of precipitation in iceland during the 2014 2015 holuhraun eruption the holuhraun eruption in 2014 15 was the largest in iceland for more than 200 years it resulted in emissions of large quantities of volcanic gases into the atmosphere 11 mt so2 0 1 mt hcl and 0 05 mt hf during the eruption the volcanic gases had major effects on f so4 and to a lesser extent cl concentrations in precipitation throughout iceland effects not observed in recent decades the concentrations of f cl and so4 n 705 reached values of 444 m 12 270 m and 17 324 m during the eruption and were on average 20 times higher for f and so4 and much lower for cl compared to pre eruption times the concentrations of major cations si na k ca mg al and fe n 151 in the precipitation were taken as having originated from seawater spray and dissolution of rock dust and aerosol based on the mixing model developed here it is demonstrated that the source of the enrichment of f and so4 was indeed the volcanic gas emissions with 60 100 mol of so4 and f in the precipitation originated from volcanic gas whereas the cl originated mostly from seawater spray making the volcanic gas input of cl relatively less important than for f and so4 the results showed that large volcanic eruptions can have major effects on atmospheric chemistry and impact the composition of precipitation

fracture movements and graben subsidence during the 2014 barðarbunga dike intrusion in iceland abstract a dike propagated 48 km from the bar arbunga central volcano into one of its fissure swarms in august and early september 2014 the dike intrusion was accompanied by caldera subsidence in the ice covered bar arbunga central volcano as well as a propagating earthquake swarm graben subsidence and fissure eruptions in the fissure swarm most of the dike was emplaced in the glacier covered part of the fissure swarm but a 10 km long section at the distal northern end of the dike is ice free new ground fractures were observed in the ice free part during the dike propagation and prior to the outbreak of a major lava producing eruption the fractures delineate two graben structures in direct continuation of each other here we show the extent and depth of the grabens and maps of fractures and eruptive fissures that were formed or reactivated north of the vatnajokull glacier during the dike intrusion the active graben subsidence was identified 3 days after seismicity reached the ice free area then fractures delineated a 700 1000 m wide and 5 km long graben visible from the northern edge of the vatnajokull glacier farther north a narrower 250 450 m wide graben was seen a short lived minor eruption occurred between these grabens on the 29th of august 2014 2 days after the grabens were identified the northern graben was extended southwards during or before the eruption and included the eruptive fissure on the 31st of august 2014 a much larger eruption began on the same eruptive fissure the fissure quickly obtained its maximum length of 2 km this eruption lasted 6 months a minor eruption lasting 2 days or less occurred on the southern graben on the 5th of september 2014 the first two eruptions took place on the same eruptive fissure that formed the pre existing holuhraun lava presumably in the 18th century measurements in january 2015 show that the southern graben was 3 5 5 5 m deep but the northern graben had been covered by lava from the depth and the opening of the graben we estimate that the dip of the boundary faults of the graben is 75 the narrow grabens observed before the eruptions indicated that magma was at shallow depth likely much less than 300 m 2 days before it opened to the surface such observations can serve as a tool to estimate likelihood of eruptions during dike intrusions

sediment transport in a large impounded river the lower ebro ne iberian peninsula abstract the sediment transport of the highly regulated lower ebro river is estimated on the basis of a measuring programme carried out between 2002 and 2004 total sediment transport including both suspended load and bedload was measured upstream and downstream from the mequinenza and riba roja reservoirs with special attention to the transport during floods annual total load upstream from the dams is estimated at around 1 64 106 t of which at least 99 is transported in suspension annual total load downstream from the dams is estimated at around 0 45 106 t of which 60 is transported in suspension and the remaining 40 as bedload mean d50 bl in the range of 32 mm total load represents 3 of what was transported at the beginning of the 20th century in the delta plain sediment yield is three to four times lower below the dams a fact that is caused by the trapping of sediment within the reservoirs around 90 in the case of suspended sediment and 100 in the case of bedload as a consequence sediment that is transported downstream from the dams is all entrained from the riverbed and eroded from the banks the sediment deficit causes a mean riverbed incision of 30 mm per year as estimated from bedload measurements and by means of scour chains and painted pebbles located between the lowermost dam and the measuring section 28 km downstream since floods have been reduced on average by 25 but sediment supply from upstream has been reduced to almost nothing the river channel of the lower ebro river will continue exporting sediment both during floods 2000 m3 s mostly bedload and frequent high flows 1000 m3 s to 2000 m3 s making the incision progressive unless restoration steps are taken

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

the april 2007 eruption and the dolomieu crater collapse two major events at piton de la fournaise la reunion island indian ocean abstract after 10 years of high activity and 24 eruptions piton de la fournaise pdf produced on april 2 to may 1 2007 one of its most voluminous and intense eruption since at least one century the eruption focused at 590 m elevation in the grand brule on the south east flank of piton de la fournaise 7 km away from summit it was located close to the southern cliff of the grand brule volcano tectonic collapse the rempart du tremblet and to the nearby village called le tremblet and it highly rattled and incommoded the inhabitants there eleven hours after the beginning of the eruption the lava flows reached the sea and created 0 45 km 2 of new land until the end of eruption in the night of april 5 the rock column beneath dolomieu crater started to collapse with a piston like mechanism into the magma chamber forming within less than 24 h the most recent and well documented caldera we report in this paper the chronology of these two related major events in the recent activity of pdf seen by the scientific networks of the volcanological observatory ovpf ipgp and field observations which allowed to back up the scenario of the caldera formation and to quantify these two exceptional episodes

observations of low frequency variability in great south bay and relations to atmospheric forcing abstract sea level and current data collected around great south bay new york during december 1979 are examined in conjunction with atmospheric data for evidence of wind forced low frequency variability in the bay and on the adjacent shelf the subtidal sea level along the coast was found to be highly coherent from sandy hook to montauk point with a single empirical mode accounted for more than 97 of the total variance these coherent fluctuations were forced primarily by longshore winds along 250 070 t through the coastal ekman effect the sea level within the bay exhibited large and spatially coherent subtidal fluctuations as a result of a strong coupling with the adjacent shelf the characteristic volume exchange associated with this bay shelf coupling was an active simultaneous inflow or outflow through both ends of the bay with fluctuations in excess of 20 cm s 1 in response to the rise or fall of coastal sea level induced by longshore winds

surface deformation and strike slip faulting controlled by dyking and host rock lithology a compendium from the krafla rift iceland abstract in the present work we have obtained a detailed complete view of surface deformation at a volcano tectonic structure belonging to the krafla fissure swarm ne iceland through the integration of field mapping and the aerial structure from motion technique asfm as well as through orthomosaics and digital surface models dsms the documented 2 5 km long deformation zone is marked by a range of features such as topographic bulging parallel extension fractures and narrow grabens affected by local floor uplift which we have explained as the effect of the northward shallow propagation of a dyke from the krafla magma chamber our lithostratigraphic field survey of the area at a 1 5000 scale indicates that major changes in the pattern of surface deformation take place across the contacts between deposits with different rheological properties the transition from very stiff lavas to softer hyaloclastites produces changes from extensional fracturing to normal faulting though the width of the deformation zone does not change we have also documented a number of ne sw left lateral and nnw sse right lateral strike slip fault zones that are rotated in clockwise and anticlockwise sense to the main nne ssw graben trend and extend outwards as much as about 17 m the graben zone terminates to the north by splitting into two strike slip fault zones these were likely generated at the front of the dyke tip during its propagation and were later on bypassed by the advancement of the dyke as the dyke entered the soft hyaloclastites propagation was slowed down and the dyke became thicker

volcano geodesy recent developments and future challenges abstract ascent of magma through earth s crust is normally associated with among other effects ground deformation and gravity changes geodesy is thus a valuable tool for monitoring and hazards assessment during volcanic unrest and it provides valuable data for exploring the geometry and volume of magma plumbing systems recent decades have seen an explosion in the quality and quantity of volcano geodetic data new datasets some made possible by regional and global scientific initiatives as well as new analysis methods and modeling practices have resulted in important changes to our understanding of the geodetic characteristics of active volcanism and magmatic processes from the scale of individual eruptive vents to global compilations of volcano deformation here we describe some of the recent developments in volcano geodesy both in terms of data and interpretive tools and discuss the role of international initiatives in meeting future challenges for the field

a simple model of estuarine subtidal fluctuations forced by local and remote wind stress observations of estuarine low subtidal sea level and current fluctuations have often shown domination by the remote effects of the wind acting on the adjacent coastal ocean over the local surface stress acting on the estuary itself the remote effects are transmitted to the estuary by impressment on its mouth of sea level change indtlced by the onshore component of coastal ekman transport and become increasingly dominant as the frequency decreases a simple barotropic model is developed to investigate the joint action of these two wind forcing mechanisms the relative shortness of most estuaries relative to low subtidal estuarine wavelengths explains the dominance of the remote effect for both sea level and barotropic current fluctuations in the estuary for the same reason however surface slope is dominated by local wind setup for an estuary with axis nearly parallel to the coast the two effects will operate either in concert or in opposition depending on hemisphere and orientation of the estuary axis relative to the coast for the geometries of both chesapeake bay and the delawm e estuary the model predicts opposition with the remote effect dominant at lower frequencies consistent with recent observations

triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke the role of static versus dynamic stresses in earthquake clusters is unclear analysis of earthquakes triggered by a dyke intrusion at an icelandic volcano unambiguously demonstrates that static stresses are important for earthquake clustering large earthquakes can generate small changes in static stress increases that trigger aftershock swarms or reductions that create a region of reduced seismicity a stress shadow1 2 however seismic waves from large earthquakes also cause transient dynamic stresses that may trigger seismicity3 4 this makes it difficult to separate the relative influence of static and dynamic stress changes on aftershocks dyke intrusions do not generate dynamic stresses so provide an unambiguous test of the stress shadow hypothesis here we use gps and seismic data to reconstruct the intrusion of an igneous dyke that is 46 km long and 5 m wide beneath bar arbunga volcano central iceland in august 2014 we find that during dyke emplacement bursts of seismicity at a distance of 5 to 15 km were first triggered and then abruptly switched off as the dyke tip propagated away from the volcano we calculate the evolving static stress changes during dyke propagation and show that the stressing rate controls both the triggering and then suppression of earthquake rates in three separate areas adjacent to the dyke our results imply that static stress changes help control earthquake clustering similar small static stress changes may be important for triggering seismicity near geothermal areas regions being hydrofractured and deflating oil and gas fields

circulation and dispersion in a cancellate coast the rivers bays and estuaries of central maine the glacially carved central coast of maine is incised by river systems with interconnecting channels offshore trending submarine ridges and narrow passages between nearshore islands and headlands the tidal range exceeds 3 m leading to complex and vigorous circulation patterns with strong flows in narrow channels near river mouths and between islands the spongiform coastal morphology allows enhanced exchange between offshore waters estuaries and internecine bays resulting in rapid dispersal of nutrients larvae and contaminants throughout the region a fine grid numerical circulation model has been used to examine the influences of the tides river flows and winds on the dispersion of lobster larvae and pollutants in the nearshore and riverine environment this paper describes the model application presents a few salient features of the circulation patterns and examines some implications for the coastal environment for example under realistic tides and variable southwest summer winds about 80 of neutral near surface particles introduced near the offshore islands a proxy for stage iv lobster larvae from offshore sources remain within a few km of the islands over a two week period on the other hand a persistent periodic sea breeze can remove more than two thirds of the particles from the domain over the same period tidal mixing disperses pollutants entering the upper kennebec river to the offshore and through internecine passages in about one week

tidal and subtidal water volume exchange in an estuarine system abstract estuarine water movements occur over a broad range of time scales in this study moored current meter data were used to investigate water volume exchange in the tidal passes of lake pontchartrain louisiana on the tidal and subtidal time scales a calibration technique employing cross channel measurements of water velocity was used to calibrate the moored current meters thus allowing for calculation of volume flow over a 35 day period the local diurnal tide accounted for 50 of the total volume exchange the rest being due to subtidal events frontal passage this subtidal exchange occurs primarily as large scale events characterized by volume fluxes up to six times greater than the normal tidal prism neglecting this subtidal component in the determination of the volume fluxes for a system such as lake pontchartrain could result in substantial underestimation by as much as 50 of these volume and their corresponding material fluxes

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

examining suspended sediment sources and dynamics during flood events in a drained catchment using radiogenic strontium isotope ratios 87sr 86sr soil erosion is recognized as one of the main processes of land degradation in agricultural areas high suspended sediment loads often generated from eroding agricultural landscapes are known to degrade downstream environments accordingly there is a need to identify suspended sediment sources and to investigate their dynamics here soil and sediment strontium isotopic ratios were used to examine suspended sediment sources and dynamics in a lowland drained catchment in france suspended sediment n 14 was collected in stream and at tile drain n 4 outlets during three flood events between december 2013 and february 2014 potential source soils n 28 representative of the carbonate and silicate substrates found in the catchment were sampled and analyzed strontium isotopic ratios 87sr 86sr were measured in different particle size fractions 2 m 63 m and 2 mm soil 87sr 86sr ratios significantly discriminated between source samples classified as carbonate 0 712625 to 0 717815 and silicate 0 719287 to 0 724631 soils 87sr 86sr ratios measured in suspended sediment 0 713660 to 0 720571 reflect variations in source contributions during different hydrological conditions the 87sr 86sr ratios varied in the different fractions of soil samples i e 2 m 63 m and 2 mm and in suspended sediment samples suspended sediment was interpreted as a mixture of two end members with the dominant contribution of the 2 m fraction of soil samples occurring during small scale flood events and the 2 mm fraction during more intense flood events modelling results indicate that carbonate source soil contributions are variable with their highest contributions occurring during the two first flood events compared to the last flood event the results also show that the tile drainage system enhances the connectivity between cultivated hillslopes and the river network providing a preferential pathway for fine 2 m particles this study demonstrates the potential of using strontium isotopic ratios to examine the variations of suspended sediment sources in drained catchments with contrasting carbonate and silicate sources more importantly the results highlight the need to improve the management of sediment exported from tile drains in similar agricultural environments as they were demonstrated to transfer very fine material to the riverine environment

river basin sediment flux assessments sediment load estimations are often limited by the difficulty in finding an adequate calculation method adapted to infrequent sediment concentration data in this article classic calculation methods averaging estimators ratio estimators and rating curves are tested using 61 river basin datasets from the french river quality database infrequent but long term datasets the analyses and results show that averaging methods are inadequate in deriving sediment fluxes from datasets with daily discharge q data and infrequent sediment concentration c data considering classic power rating curves analyses of c q relations for the 61 datasets show significant differences between seasons flow variations and in function of the antecedent conditions of flows the subdivision of datasets is thus essential before performing any c q fitting moreover the c aqb relation only relates instantaneous c and q values disregarding the influence of temporal flow dynamics rating curve equations including the dynamic of discharge time series are established and tested one equation and approach is selected an improved rating curve approach irca which combines a fitting based on the description of sediment stock dynamics with the flow variation subdivision between rising limbs rl and falling limbs fl of the hydrograph this method was validated with daily datasets from the us geological survey usgs database this rating curve equation can be used to quantify sediment exports from infrequent data for numerous river basins in temperate areas copyright 2010 john wiley sons ltd

comparison of dike intrusions in an incipient seafloor spreading segment in afar ethiopia seismicity perspectives 1 oceanic crust is accreted through the emplacement of dikes at spreading ridges but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood between 2005 and 2009 the 70 km long dabbahu manda hararo rift segment in ethiopia has experienced 14 large volume dike intrusions 9 of which were recorded on temporary seismic arrays a detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems all of the migrating swarms of earthquakes started from a 80 of energy is released during the propagation phase with minimal seismic energy release after the dike propagation ceases we interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip coincident with the onset of low frequency earthquakes dike lengths show no systematic reduction in length with time suggesting that topographic loading and stress barriers influence dike length as well as changes in tectonic stress the propagation velocities of all the dikes follow a decaying exponential northward propagating dikes had faster average velocities than those that propagated southward suggesting preconditioning by the 2005 megadike or ongoing heating from a subcrustal magma source north of the midsegment

subtidal circulation patterns in a shallow highly stratified estuary mobile bay alabama mobile bay is a wide 25 50 km shallow 3 m highly stratified estuary on the gulf coast of the united states in may 1991 a series of instruments that measure near surface and near bed current temperature salinity and middepth pressure were deployed for a year long study of the bay a full set of measurements were obtained at one site in the lower bay all but current measurements were obtained at a midbay site these observations show that the subtidal currents in the lower bay are highly sheared despite the shallow depth of the estuary the sheared flow patterns are partly caused by differential forcing from wind stress and river discharge two wind driven flow patterns actually exist in lower mobile bay a barotropic response develops when the difference between near surface and near bottom salinity is less than 5 parts per thousand for stronger salinity gradients the wind driven currents are larger and the response resembles a baroclinic flow pattern currents driven by river flows are sheared and also have a nonlinear response pattern only near surface currents are driven seaward by discharges below 3000 m 3 s at higher discharge rates surface current variability uncouples from the river flow and the increased discharge rates drive near bed current seaward this change in the river forced flow pattern may be associated with a hydraulic jump in the mouth of the estuary

sediment yield in africa abstract several studies have compiled and analysed measured contemporary catchment sediment yield sy t km 2 y 1 values for various regions of the world although this has significantly contributed to our understanding of sy africa remains severely underrepresented in these studies the objective of this article is therefore 1 to review and compile available sy data for africa 2 to explore the spatial variability of these sy data and 3 to examine which environmental factors explain this spatial variability a literature review resulted in a dataset of sy measurements for 682 african catchments from 84 publications and reports representing more than 8340 catchment years of observations these catchments span eight orders of magnitude in size and are relatively well spread across the continent a description of this dataset and comparison with other sy datasets in terms of spatial and temporal distribution and measurement quality is provided sy values vary between 0 2 and 15 699 t km 2 y 1 median 160 t km 2 y 1 average 634 t km 2 y 1 the highest sy values occur in the atlas region with sy values frequently exceeding 1000 t km 2 y 1 also the rift region is generally characterised by relatively high sy values while rivers in western and central africa have generally low sy values spatial variation in sy at the continental scale is mainly explained by differences in seismic activity topography vegetation cover and annual runoff depth other factors such as lithology catchment area or reservoir impacts showed less clear correlations the results of these analyses are discussed and compared with findings from other studies based on our results we propose a simple regression model to simulate sy in africa although this model has a relatively low predictive accuracy 40 it simulates the overall patterns of the observed sy values well potential explanations for the unexplained variance are discussed and suggestions for further research that may contribute to a better understanding of sy in africa are made

river sediment discharge to the oceans present day controls and global budgets empirical relationships between river sediment yields and a large number of hydroclimatic biological and geomorphological parameters are investigated at the global scale for a set of 60 major world river basins the environmental characteristics were extracted from various global computer data sets and natural river sediment fluxes were taken from the literature it is found that sediment yields can be best correlated by forming the products of hydroclimatic and geomorphological factors that is runoff intensity basin slope an index characterizing rock hardness and an index characterizing rainfall variability over the year the best parameter combination varies to some extent when the rivers are grouped according to their average climatic situation but it is always a combination of the above mentioned parameters that yields the most significant models in arid climates however regression coefficients are greater than in humid climates indicating that erodibility is much greater than in arid climates when extrapolated to the total continental area on the basis of the corresponding data sets the empirical models result in a total sediment flux of about 16 gigatons discharged to the oceans every year which is in good agreement with previous estimates derived from compilations of world wide river data consequently two global maps are proposed showing the spatial distributions of river sediment yields on the continents as well as the inputs of these sediments to the oceans in a grid point scale by far most of the sediments originate from the young orogenic belts of the continents mainly due to a combination of steep morphologies and high runoff intensities

forecasting the path of a laterally propagating dike an important aspect of eruption forecasting is predicting the path of propagating dikes we show how lateral dike propagation can be forecast using the minimum potential energy principle we compare theory to observed propagation paths of dikes originating at the bar arbunga volcano iceland in 2014 and 1996 by developing a probability distribution for the most likely propagation path the observed propagation paths agree well with the model prediction we nd that topography is very important for the model and our preferred forecasting model considers its in uence on the potential energy change of the crust and magma we tested the in uence of topography by running the model assuming no topography and found that the path of the 2014 dike could not be hindcasted the results suggest that lateral dike propagation is governed not only by deviatoric stresses but also by pressure gradients and gravitational potential energy furthermore the model predicts the formation of curved dikes around cone shaped structures without the assumption of a local deviatoric stress eld we suggest that a likely eruption site for a laterally propagating dike is in topographic lows the method presented here is simple and computationally feasible our results indicate that this kind of a model can be applied to mitigate volcanic hazards in regions where the tectonic setting promotes formation of laterally propagating vertical intrusive sheets

insights into the 3d architecture of an active caldera ring fault at tendurek volcano through modeling of geodetic data abstract the three dimensional assessment of ring fault geometries and kinematics at active caldera volcanoes is typically limited by sparse field geodetic or seismological data or by only partial ring fault rupture or slip here we use a novel combination of spatially dense insar time series data numerical models and sand box experiments to determine the three dimensional geometry and kinematics of a sub surface ring fault at tendurek volcano in turkey the insar data reveal that the area within the ring fault not only subsides but also shows substantial westward directed lateral movement the models and experiments explain this as a consequence of a sliding trapdoor ring fault architecture that is mostly composed of outward inclined reverse segments most markedly so on the volcano s western flanks but includes inward inclined normal segments on its eastern flanks furthermore the model ring fault exhibits dextral and sinistral strike slip components that are roughly bilaterally distributed onto its northern and southern segments respectively our more complex numerical model describes the deformation at tendurek better than an analytical solution for a single rectangular dislocation in a half space comparison to ring faults defined at glen coe fernandina and bar arbunga calderas suggests that sliding trapdoor ring fault geometries may be common in nature and should therefore be considered in geological and geophysical interpretations of ring faults at different scales worldwide

importance of horizontal seafloor motion on tsunami height for the 2011 mw 9 0 tohoku oki earthquake abstract it is now clear that the 2011 tohoku oki earthquake ruptured the subduction interface all the way to the japan trench however there is significant disagreement about just how much slip occurred at the trench with most geodetic studies locating only a small fraction of the maximum slip there whereas broadband seismic studies put the majority of the slip near the trench measurements of seafloor displacement near the trench also imply more slip there than is estimated by the geodetic studies here by means of a joint inversion of displacement measurements and seafloor pressure data we show that it is possible to reconcile geodetic and seismic studies and that a considerable amount of slip indeed occurred at the trench with slip magnitudes reaching 57 74 of the maximum slip the seafloor displacement predicted by our model agrees very well with independent measurements made close to the trench we also find good agreement between our tsunami model and independent measurements of tsunami height in the ocean and on land re running of the inversion without the near field pressure gauge data however leads to underprediction of the flooding on land even when the seafloor geodetic data are still included thus even if the seafloor geodetic measurements had been available in real time they would still not have allowed reliable prediction of near field tsunami inundation close to the trench the dip of the plate interface is shallow which serves to decrease the vertical motion of the sea floor for any given slip however the horizontal motion is conversely larger because the ocean floor slopes steeply near the trench it acted like a giant wedge converting the horizontal motion of the ground into an uplift of the water column and causing the peak initial tsunami wave height to be twice as high as it would have been from vertical displacement alone

new insights into magma plumbing along rift systems from detailed observations of eruptive behavior at axial volcano the magma reservoir in geophysical volcano plumbing models is often modeled as a simple geometric volume filled with magma of uniform properties however the constraints on reservoir size and magma properties in volcano roots are typically indirect and poor axial seamount a volcano at a depth of about 1500 m on the juan de fuca mid oceanic ridge in the pacific ocean has both high resolution seismic images of its subsurface magma and detailed results from monitoring of its most recent eruption and associated seismicity and ground deformation the 2015 eruption at axial seamount is the best monitored submarine eruption so far because of observations made possible by the ocean observatories initiative and seismic imaging of magma at this volcano is better than in most other environments because of advanced analysis of extensive seismic reflection profiling at sea and the relatively simple volcano structure this allows new understanding compared to findings from earlier observations from monitored rifting episodes on land geophysical magma plumbing models in general may need to allow for more complexities namely spatial heterogeneities in magma composition melt content and location of major volume changes within a single magma dominated crustal volume during eruptions

what controls the along strike slopes of volcanic rift zones we investigate the dynamics of viscous pressure losses associated with lateral magma transport in volcanic rift zones by performing 1 coupled elastic hydrodynamic simulations of downrift magma flow in dikes and 2 analog experiments mimicking lateral dike propagation in the presence of an along rift topographic slope it is found that near source eruptions are likely to be favored by shallow slopes while distant downrift eruptions may be encouraged by steeper slopes provided that along rift variations in the tectonic stress are negligible or uncorrelated on the timescale of multiple dike intrusions this implies the existence of a critical slope to which a volcanic rift zone would naturally evolve such behavior is produced by three dimensional 3 d elastic effects and is controlled by the ratio of the driving pressure gradient due to the along strike topographic slope to the vertical gradient in the excess magma pressure in the dike this model may be viewed as complementary to commonly cited mechanisms that appeal to magma viscosity and the dynamics of freezing of lava flows at the surface to explain the low profiles of basaltic shield volcanoes our estimated values of the critical slopes are in general agreement with observations in hawaiian rift zones but further development of fully 3 d models is required for more accurate predictions

geothermal activity in the subglacial katla caldera iceland 1999 2005 studied with radar altimetry the katla caldera is located under the myrdalsjokull ice cap and is one of the most hazardous volcanoes in iceland due to major jokulhlaups that accompany eruptions subglacial geothermal activity is manifested in several 10 50 m deep depressions ice cauldrons within and at the caldera rim and the total geothermal heat output is of the order of a few hundred megawatts a short lived but powerful pulse in geothermal heat output took place in 1999 probably including a minor subglacial eruption when new ice cauldrons formed in three places and an unexpected jokulhlaup occurred following these events a comprehensive monitoring program was set up for katla including ice surface elevation profiling from aircraft to monitor variations in geothermal heat and detect signs of subglacial water accumulation a radar altimeter coupled with a kinematic gps is used achieving an absolute elevation accuracy of 3 m and internal consistency of 1 2 m profiles across the caldera are flown twice a year an annual accumulation ablation cycle in surface elevation with amplitude of 5 10 m is observed by removing this cycle from the data changes due to subglacial geothermal activity are obtained after the events in 1999 a decline in geothermal activity was observed in 2001 03 some ice cauldrons expanded and deepened by 10 15 m indicating renewed increase in geothermal activity this trend is also apparent for 2003 05 the increase in geothermal power amounts to a few tens of megawatts it is likely that the increased thermal output is related to increased seismicity and caused by magma inflow

countrywide observations of plate spreading and glacial isostatic adjustment in iceland inferred by sentinel 1 radar interferometry 2015 2018

absolute and relative locations of similar events with application to microearthquakes in southern iceland it is well known that similar earthquakes i e earthquakes having almost identical waveforms allow extremely accurate relative timing of the seismic arrivals this has traditionally been used for

infrastructure and mechanics of volcanic systems in iceland the divergent plate boundary in iceland consists of more than two dozen systems where most of the volcano tectonic activity takes place at the surface the volcanic systems are characterised by 5 20 km wide and 40 100 km long swarms of tension fractures 102 m long normal faults 103 m long and volcanic fissures the holocene fissure swarms are confined to less than 10 000 year old basaltic lava flows mostly pahoehoe occurring near the centre of the active rift zone in any particular swarm the number of tension fractures exceeds that of normal faults all tension fractures and normal faults are vertical at the surface indicating that the surface parts were generated by an absolute tension in addition to a fissure swarm many volcanic systems have a central volcano some of which have developed collapse calderas in the late tertiary and pleistocene lava pile of iceland extinct volcanic systems are represented by local sheet swarms and regional dyke swarms the sheet swarms are normally circular or slightly elliptical several kilometres in radius and are confined to the extinct central volcanoes many swarms are associated with large plutons exposed at 1 2 km depth beneath the initial top of the rift zone and presumably the uppermost parts of extinct crustal magma chambers and in short traverses up to 90 of the rock may consist of sheets the sheets have a very variable strike dip on average 45 65 mostly towards the centre of the associated volcano and have an average thickness of about 1 m the regional dykes occur outside central volcanoes in swarms that are commonly 50 km long and 5 10 km wide in several kilometre long traverses commonly 1 5 of the rock consist of dykes but occasionally as much as 15 28 most regional dykes are subparallel and subvertical the average dyke thickness in the pleistocene swarms is less than 2 m but 4 6 m in the tertiary swarms while active the volcanic systems in the rift zone are supplied with magma from reservoirs located at the depth of 8 12 km at the boundary between the crust and upper mantle the reservoirs are partially molten with totally molten top regions and of cross sectional areas similar to those of the volcanic systems that they feed some active volcanic systems especially those that develop central volcanoes high temperature areas and calderas have in addition to the deep seated magma reservoirs shallow crustal magma chambers located at 1 3 km depth which in turn are fed by the deeper magma reservoirs it is proposed that the regional dyke swarms are supplied with magma largely from the deep seated reservoirs whereas the local sheet swarms are mainly fed from the associated crustal magma chambers because the volume of a crustal chamber is less than that of its deeper source reservoir a single magma flow dyke intrusion from the reservoir may trigger tens of magma flows sheet intrusions from the chamber which is one explanation for the enormous number of sheets associated with many central volcanoes the sheets follow the stress trajectories of the local stress fields around the source chambers whereas the regional stress field associated with the divergent plate movements controls the emplacement of the regional dykes it is suggested that many dykes develop as self affine some as self similar structures when applied to the krafla volcanic system in northern iceland model calculations suggest that a magma flow from the krafla reservoir with regional dyke formation should occur on average once every several hundred years and that tens of sheets might be injected from the shallow krafla chamber and triggered by a single magma flow from the krafla reservoir these results are in broad agreement with the available data

strike slip faulting during the 2014 barðarbunga holuhraun dike intrusion central iceland over a 13 day period magma propagated laterally from the subglacial bar arbunga volcano in the northern rift zone iceland it created 30 000 earthquakes at 5 7 km depth along a 48 km path before erupting on 29 august 2014 the seismicity which tracked the dike propagation advanced in short bursts at 0 3 4 7 km h separated by pauses of up to 81 h during each surge forward seismicity behind the dike tip dropped moment tensor solutions from the leading edge show exclusively left lateral strike slip faulting subparallel to the advancing dike tip releasing accumulated strain deficit in the brittle layer of the rift zone behind the leading edge both left and right lateral strike slip earthquakes are observed the lack of non double couple earthquakes implies that the dike opening was aseismic

operational response and hazards assessment during the 2014 2015 volcanic crisis at barðarbunga volcano and associated eruption at holuhraun iceland abstract on august 16 2014 an intense seismic swarm started below the eastern part of bar arbunga caldera in the north western part of vatnajokull ice cap iceland marking the onset of a major rifting event the intense seismicity corroborated by a complicated deformation pattern migrated away from the bar arbunga caldera for 45 km until a small effusive eruption started in holuhraun outside of the ice cap on august 29 which lasted a few hours on august 31 a second more intense eruption started it lasted 180 days and is the largest effusive eruption in iceland since the laki event in 1783 1784 a lava field covered about 84 km2 in the middle of the highlands with a bulk volume of 1 44 km3 although the potential danger of ice melting and subsequent flooding coupled with tephra fallout was the main concern at the beginning of the crisis the main associated hazard turned out to be an abundant and constant release of volcanic gases that polluted the country threatening human health and the environment for several months very little or almost no ash was produced the impact of the holuhraun eruption outside of iceland was minor if compared with what happened in 2010 when eyjafjallajokull erupted however on three occasions the dense gas cloud released by the fissure eruption reached some european countries where unusually high so2 concentrations were measured at ground level managing and living with such a prolonged effusive event was a major effort for the icelandic scientific community and civil protection authorities and it significantly affected the local population in the northern and eastern parts of the country this paper retraces the main events that accompanied the volcanic crisis at bar arbunga and focuses on the scientific and operative response provided throughout its duration particular attention is given to the direct links between the observed phenomena monitoring effort hazard assessment and concrete actions taken by the authorities in charge of risk and mitigation assessment the different roles of the involved institutions are clarified and the wide and collaborative response on a national basis is explained a major finding of this post event analysis is that a strong internal collaboration between the scientific community and operative institutions is the basic element for proper crisis management iceland has established protocols that while imperfect ensured a well coordinated response to the holuhraun eruption and the preceding unrest and will continue to provide a prompt and effective response for future events important realizations including the need for a proper ground based alert level system have been raised and they will be a matter for further development

the chemical composition of rivers and snow affected by the 2014 2015 barðarbunga eruption iceland abstract the 2014 15 bar arbunga volcanic eruption was the largest in iceland for more than 200 years this eruption released into the atmosphere on average 60 000 tonnes day of so2 30 000 tonnes day of co2 and 500 tonnes day of hcl affecting the chemical composition of rain snow and surface water the interaction of these volcanic gases with natural waters decreases fluid ph and accelerates rock dissolution this leads to the enhanced release of elements including toxic metals such as aluminium to these waters river monitoring including spot and continuous osmotic sampling shows that although the water conductivity was relatively stable during the volcanic unrest the dissolution of volcanic gases increased the so4 f and cl concentrations of local surface waters by up to two orders of magnitude decreasing the carbon alkalinity in addition the concentration of sio2 ca mg na and trace metals rose considerably due to the water molten lava and hot solid lava interaction the presence of pristine lava and acidic gases increased the average chemical denudation rate calculated based on na flux within jokulsa a fjollum catchment by a factor of two compared to the background flux melted snow samples collected at the eruption site were characterised by a strong dependence of the ph on so4 f and cl and metal concentrations indicating that volcanic gases and aerosols acidified the snow protons balanced about half of the negatively charged anions the rest was balanced by water soluble salts and aerosols containing a variety of metals including al fe na ca and mg the concentrations of f al fe mn cd cu and pb in the snowmelt water surpassed drinking and surface water standards snowmelt river water mixing calculations indicate that low alkalinity surface waters such as numerous salmon rivers in east iceland will be more affected by polluted snowmelt waters than high alkalinity spring and glacier fed rivers

tidal exchange at the bay ocean boundary for bays and inlets with narrow entrances tidal exchange with the ocean is often characterized by an ebb flood asymmetry in which the ebb flow exits the bay as a jet while the flood flow is drawn in approximately as a radial sink a process often termed tidal pumping in this paper the importance of tidal pumping in controlling the exchange of water at the bay ocean boundary is examined based on observations at the mouth of san diego bay the observations are novel in combining the use of shipboard acoustic doppler current measurements with a unique bay water tracer technique to provide visualization of the exchange as well as exchange budgets visualization of the tidal evolution of flow and tracers suggests that in accordance with the classical tidal pumping model the horizontal dynamics at the mouth of san diego bay are governed by an asymmetry between the jet like nature of the ebb flow and the sink like nature of the flood flow this asymmetry results in strong tidal velocity and phase gradients similar to those observed in previous numerical modeling studies a one dimensional trajectory model based on the observations indicates that the combined influence of the residual circulation and offshore gradients in the tidal velocity and phase provides the mechanism by which water from the bay is exchanged with water from the ocean both bottom friction and thermal gradients affect the dynamics of the vertical exchange the resulting asymmetry in the offshore flow leads to a vertical mode of pumping similar to that observed in the horizontal view this horizontal and vertical pumping of the offshore flow is shown to produce a strong correlation between the sectionally averaged velocity and bay water concentration resulting in a significant net tidal exchange between the bay and ocean

increased capture of magma in the crust promoted by ice cap retreat in iceland retreating ice caps overlying volcanoes are thought to relieve surface pressure causing enhanced magma generation and volcanic activity analysis of crustal stress during a dyke intrusion event associated with retreat of iceland s largest ice cap indicates that ice retreat could instead promote storage of magma in the crust rather than eruption at the surface

ice volume changes bias estimation of mass balance measurements and changes in subglacial lakes derived by lidar mapping of the surface of icelandic glaciers icelandic glaciers cover 11 000 km2 in area and store 3600 km3 of ice starting in 2008 during the international polar year accurate digital elevation models dems of the glaciers are being produced with airborne lidar more than 90 of the glaciers have been surveyed in this effort including vatnajokull hofsjokull myrdalsjokull drangajokull eyjafjallajokull and several smaller glaciers the publicly available dems are useful for glaciological and geological research including studies of ice volume changes estimation of bias in mass balance measurements studies of jokulhlaups and subglacial lakes formed by subglacial geothermal areas and for mapping of crevasses the lidar mapping includes a 500 1000 m wide ice free buffer zone around the ice margins which contains many glacio geomorphological features and therefore the new dems have proved useful in geological investigations of proglacial areas comparison of the lidar dems with older maps confirms the rapid ongoing volume changes of the icelandic ice caps which have been shown by mass balance measurements since 1995 96 in some cases ice volume changes derived by comparing the lidar measurements with older dems are in good agreement with accumulated ice volume changes derived from traditional mass balance measurements but in other cases such a comparison indicates substantial biases in the traditional mass balance records

low frequency earthquakes beneath tullu moye volcano ethiopia reveal fluid pulses from shallow magma chamber abstract the active magmatic processes beneath volcanoes in continental rifts is poorly understood for example until recently in the east african rift ear the majority of the young volcanoes were thought to be inactive more recent studies have shown that numerous volcanoes in the ear are seismically active and deforming rapidly however an unambiguous sign of actively degassing magma hosted in shallow magma bodies has eluded most investigators here we present detailed analysis of the first low frequency lf earthquake swarms to be observed in the main ethiopian rift the earthquakes locate to beneath tullu moye volcano and are directly related to the presence of a shallow magma body with a high fluid content using spectral modelling we show that the lf earthquakes appear to have low stress drops 1 50 kpa which we interpret in terms of low rupture velocities and high pore fluid pressure careful relocation of the lf earthquakes place them approximately 4 km below the surface within one of two possible clusters however analysis of the correlation between earthquake waveforms show that each swarm contains a range of earthquake families and as such a diversity of earthquake source mechanisms to explain these observations we propose the seismicity is induced by h2o co2 fluid pulses from the shallow magma body into a highly fractured region fluid pulses cause high pore fluid pressures which also cause the low rupture velocities

constraints on magma chamber geometry at sierra negra volcano galapagos islands based on insar observations abstract we investigate the problem of estimating magma chamber geometry using insar observations of sierra negra volcano galapagos ascending and descending interferograms are combined to determine vertical and one horizontal component of displacement the ratio of maximum horizontal to vertical displacement suggests a sill like source spherical or stock like bodies are inconsistent with the data we estimate the geometry of the sill assuming a horizontal uniformly pressurized crack with unknown periphery and depth the sill is discretized into small elements that are either open and are subjected to the pressure boundary condition or remain closed we find the best fitting sill to be located beneath sierra negra s inner caldera at a depth of about 2 km using boundary element calculations we show that any magma chamber with a flat top coincident with the sill model fits the data equally well the data are insensitive to the sides and bottom of the magma chamber

radar interferogram filtering for geophysical applications the use of sar interferometry is often impeded by decorrelation from thermal noise temporal change and baseline geometry power spectra of interferograms are typically the sum of a narrow band component combined with broad band noise we describe a new adaptive filtering algorithm that dramatically lowers phase noise improving both measurement accuracy and phase unwrapping while demonstrating graceful degradation in regions of pure noise the performance of the filter is demonstrated with sar data from the ers satellites over the jakobshavns glacier of greenland

challenging dyke ascent models using novel laboratory experiments implications for reinterpreting evidence of magma ascent and volcanism volcanic eruptions are fed by plumbing systems that transport magma from its source to the surface mostly fed by dykes here we present laboratory experiments that model dyke ascent to eruption using a tank filled with a crust analogue gelatine which is transparent and elastic that is injected from below by a magma analogue dyed water this novel experimental setup allows for the first time the simultaneous measurement of fluid flow sub surface and surface deformation during dyke ascent during injection a penny shaped fluid filled crack is formed intrudes and traverses the gelatine slab vertically to then erupt at the surface polarised light shows the internal stress evolution as the dyke ascends and an overhead laser scanner measures the surface elevation change in the lead up to dyke eruption fluorescent passive tracer particles that are illuminated by a laser sheet are monitored and the intruding fluid s flow dynamics and gelatine s sub surface strain evolution is measured using particle image velocimetry and digital image correlation respectively we identify 4 previously undescribed stages of dyke ascent stage 1 early dyke growth the initial dyke grows from the source and two fluid jets circulate as the penny shaped crack is formed stage 2 pseudo steady dyke growth characterised by the development of a rapidly uprising central single pseudo steady fluid jet as the dyke grows equally in length and width and the fluid down wells at the dyke margin sub surface host strain is localised at the head region and the tail of the dyke is largely static stage 3 pre eruption unsteady dyke growth an instability in the fluid flow appears as the central fluid jet meanders the dyke tip accelerates towards the surface and the tail thins surface deformation is only detected in the immediate lead up to eruption and is characterised by an overall topographic increase with axis symmetric topographic highs developed above the dyke tip stage 4 is the onset of eruption when fluid flow is projected outwards and focused towards the erupting fissure as the dyke closes a simultaneous and abrupt decrease in sub surface strain occurs as the fluid pressure is released our results provide a comprehensive physical framework upon which to interpret evidence of dyke ascent in nature and suggest dyke ascent models need to be re evaluated to account for coupled intrusive and extrusive processes and improve the recognition of monitoring signals that lead to volcanic eruptions in nature

the fluid geochemistry of icelandic high temperature geothermal areas abstract icelandic high temperature geothermal systems are considered to number thirty three thereof three are submarine and seven subglacial all are briefly described but the chemistry of fluids from twenty four of them is considered the fluid in the three submarine areas and those four on land that are closest to the sea are relatively saline but to a differing extent mixed with groundwater the rest contain dilute fluids the fluids of the central highland systems are mostly locally derived but may in some instances be quite old whereas those in the northerly krafla area which is inland and the oxarfjor ur area which is close to the sea appear to be a mixture of local and central highland water but those in the inland hengill geysir namafjall and theistareykir areas appear to have travelled relatively long distances from the central highlands the gas observed is magmatic except in the northerly oxarfjordur area close to the sea where it is apparently derived from organic sediments

interaction between central volcanoes and regional tectonics along divergent plate boundaries askja iceland activity within magmatic divergent plate boundaries mdpb focuses along both regional fissure swarms and central volcanoes an ideal place to investigate their mutual relationship is the askja central volcano in iceland askja consists of three nested calderas namely kollur askja and oskjuvatn located within a hyaloclastite massif along the nne ssw trending icelandic mdpb we performed an extensive field based structural analysis supported by a remote sensing study of tectonic and volcanic features of askja s calderas and of the eastern flank of the hyaloclastite massif in the massif volcano tectonic structures trend n 10 e to n 40 e but they vary around the askja caldera being both parallel to the caldera rim and cross cutting on the western side structural trends around the oskjuvatn caldera are typically rim parallel volcanic vents and dikes are preferentially distributed along the caldera ring faults however they follow the nne ssw regional structures when located outside the calderas our results highlight that the askja volcano displays a balanced amount of regional fissure swarm related and local shallow magma chamber related tectonic structures along with a mutual interaction among these this is different from krafla volcano to the north of askja dominated by regional structures and grimsvotn to the south dominated by local structures therefore askja represents an intermediate tectono magmatic setting for volcanoes located in a slow divergent plate boundary this is also likely in accordance with a northward increase in the spreading rate along the icelandic mdpb

observations of exchange between eastern casco bay and the western gulf of maine abstract exchange of water between eastern casco bay and the adjacent gulf of maine shelf is examined to assess the circulation processes that impact the distribution and occurrence of a toxic dinoflagellate alexandrium fundyense in eastern casco bay over the inner shelf adjacent to the bay tidal variance is weak and the across shelf current is highly coherent and in phase with the along shelf wind stress although tidal current variance increases as one advances into the bay non tidal currents account for 30 40 of the across shelf current variance at the bay entrance between the shelf and the bay interior is a transition region where the circulation response to wind forcing changes as the wind adjusts to the changing orientation of the shoreline far from shore the overall large scale coastline orientation dominates the wind driven response but within a few internal rossby radii the local coastline clearly dominates the flow patterns and across shelf wind becomes locally shore parallel inside the bay within the bay interior the across shelf wind is highly coherent and in phase with the near surface subtidal across shelf current the kennebec river north of the study area supplies freshwater to eastern casco bay in all seasons a pool of low density relatively fresh water at the entrance to the bay sets up an across shelf density gradient that is reversed from a typical estuary and likely contributes to the mean surface on shelf transport in this region surface drifter trajectories observed over the course of the study suggest that both the across shelf wind and the across shelf density gradient are important in driving surface up bay transport and in the retention of surface dwelling organisms in eastern casco bay

kinematic models of plate boundary deformation in southwest iceland derived from gps observations 1 we use data from gps campaign and continuous measurements from 1992 to 2004 in sw iceland to map the surface velocity field from the reykjanes peninsula to the eastern volcanic zone we divide the time series into preseismic july 1992 to june 2000 and postseismic june 2000 to may 2004 time intervals and we estimate gps station velocities for each interval as well as coseismic offsets due to the june 2000 earthquake sequence in the south iceland seismic zone sisz in addition to the plate spreading the preseismic velocity field shows the effects of inflation at hengill and hekla volcanoes whereas the postseismic velocities show deformation following the june 2000 earthquakes we consider several kinematic models to explain the preseismic velocities our preferred model includes several dislocations and point sources in an elastic half space with left lateral slip along the plate boundary on the reykjanes peninsula and below the sisz opening across the reykjanes peninsula and the western and eastern rift zones the optimal model has a locking depth of about 8 km in the central and eastern part of the reykjanes peninsula with a deep slip rate of about 17 mm yr and an opening of about 9 mm yr this locking depth is in agreement with the thickness of the seismogenic crust on the reykjanes peninsula which appears to vary between 7 and 9 km for the sisz we obtain a deep slip rate of about 19 mm yr below 16 km depth which is considerably deeper than the earthquake hypocenter depths in the area

the subtidal circulation in delaware bay and adjacent shelf waters surface and seabed drifters were used to study the subtidal circulation in delaware bay and over the adjacent continental shelf of the middle atlantic bight over 7000 drifters were released in eight experiments during the year long study period velocity vector maps representing the study period mean fields for the surface and bottom confirmed the pattern of classical two layer estuarine flow with surface water moving seaward from the bay onto the shelf and bottom water landward over the shelf from at least as far as 40 km seaward of the bay mouth within the bay bottom water moved laterally toward the nearest shore diverging horizontally along a line roughly marking the deep channels the surface speeds were about an order of magnitude larger than the bottom significant variations from this mean pattern were seen between the eight experiments return percentages for surface and bottom drifters correlated inversely over the eight experiments correlations with wind stress were above the level of significance and winds explained about two thirds of the total variance the strong coupling found between the subtidal circulation in the estuary and over the shelf is consistent with recent observational and modelling studies

improving sediment load estimations the case of the yarlung zangbo river the upper brahmaputra tibet plateau abstract suspended sediment load of a river represents integrated results of soil erosion landform change and ecosystem variation occurring within the river basin accurate estimation of suspended sediment load is helpful for distinguishing the impact of natural and anthropogenic factors on earth system processes within river basin under global climate change suspended sediment load with long term in situ observation limited by harsh conditions can be estimated by sediment rating curves and various subdivision methods with suspended sediment concentration and discharge data of low frequency new sediment rating curve subdivision methods based on flood ranks and suspended sediment concentration stages were proposed in this study the flood ranks subdivision method which defined a flood to begin when discharge exceeded the critical discharge value rank1 or the previous peak flow rank2 and the later and end when fluctuating discharge reached the peak flow of current flood again which is the beginning of next flood or lowered to the critical discharge value the last rank was suitable for application in the basin where sediments were mainly transported and exhausted in early events the suspended sediment concentration stages subdivision method i e the rising and falling limbs of suspended sediment concentration separated by peak dates estimated based on accumulated precipitation was suitable for application in the basin where soil erosion was closely related to precipitation compared to the traditional sediment rating curve and seasonal discharge classes and discharge stages subdivision methods these newly proposed methods can improve suspended sediment concentration and subsequently suspended sediment load estimation in the middle reach of the yarlung zangbo river with higher coefficients of determination and nash sutcliffe efficiency coefficients and lower bias and root mean square errors moreover combination of the two separately developed methods presented further improved estimation the newly proposed sediment rating curve subdivision methods could be helpful for suspended sediment load estimation and therefore are useful for water resource management within river basins

volcanism and hydrothermalism on a hotspot influenced ridge comparing reykjanes peninsula and reykjanes ridge iceland abstract current estimates indicate that the number of high temperature vents one of the primary pathways for the heat extraction from the earth s mantle at least 1 per 100 km of axial length scales with spreading rate and should scale with crustal thickness but up to present shallow ridge axes underlain by thick crust show anomalously low incidences of high temperature activity here we compare the reykjanes ridge an abnormally shallow ridge with thick crust and only one high temperature vent known over 900 km axial length to the adjacent subaerial reykjanes peninsula rp which is characterized by high temperature geothermal sites confined to four volcanic systems transected by fissure swarms with young holocene volcanic activity multiple faults cracks and fissures and continuous seismic activity new high resolution bathymetry gridded at 60 m of the reykjanes ridge between 62 30 n and 63 30 n shows seven axial volcanic ridges avr that based on their morphology geometry and tectonic regime are analogues for the volcanic systems and fissure swarms on land we investigate in detail the volcano tectonic features of all mapped avrs and show that they do not fit with the previously suggested 4 stage evolution model for avr construction instead we suggest that avr morphology reflects the robust or weak melt supply to the system and two or more eruption mechanisms may co exist on one avr in contrast to 4 stage evolution model our interpretations indicate that unlike on the reykjanes peninsula faults on and around avrs do not cluster in orientation domains but all are subparallel to the overall strike of avrs orthogonal to spreading direction high abundance of seamounts shows that the region centered at 62 47 n and 25 04 w between avr 5 and 6 is volcanically robust while the highest fault density implies that avr 1 and southern part of avr 6 rather undergo period of melt starvation based on our observations and interpretations we expect all of the avrs on reykjanes ridge to be hydrothermally active but morphological and hydrographic settings of this ridge may cause hydrothermal plumes to be quickly dispersed and diluted due to exposure to strong bottom currents therefore combined ctd and autonomous vehicles surveys are probably the most efficient methods for hydrothermal exploration along the reykjanes ridge