pre drilling background groundwater quality in the deep river triassic basin of central north carolina usa abstract unconventional natural gas development via horizontal drilling and hydraulic fracturing has greatly increased the supply of natural gas in the united states however the practice presents concerns about the possibility for impacts on shallow groundwater aquifers the deep river triassic basin in central north carolina is likely to contain natural gas that could be extracted via hydraulic fracturing in the future unlike other states where hydraulic fracturing has been employed north carolina has no history of commercial oil and gas extraction in this study we measured water chemistry dissolved gases and volatile organic compounds in 51 private drinking water well samples over the deep river triassic basin our data document the background water quality of shallow aquifers in the deep river basin which could provide an important baseline dataset if hydraulic fracturing occurs here in the future we found only two of the 51 water wells sampled had dissolved ch 4 concentrations 0 1 mg l and no well had a methane concentration 0 5 mg l the 13 c ch 4 of the two highest ch 4 concentration water wells 69 5 and 61 suggest a biogenic ch 4 source and are distinct from the 13 c ch 4 of two test gas wells drilled in the area 54 41 and 45 11 unlike other basins overlying shale gas formations in the us we find no evidence for ch 4 migration into shallow groundwater in the triassic basin in addition we found only seven vocs in five water samples with all levels below the us epa s maximum contaminant levels ion and trace metal concentrations in most samples were also below us epa primary drinking water standards with the exception of two samples that exceed the standards for as we modeled the depth of the upper surface of the cumnock shale formation in the deep river basin using a kriging algorithm and found that its depth below the surface is shallow 0 1500 m relative to other shale formations that have been drilled commercially in the us including the marcellus in pennsylvania and the fayetteville in arkansas the relatively shallow shale combined with the presence of multiple faults and diabase intrusions that characterize the geology of the area may make the deep river triassic basin more vulnerable to deep fluid connectivity to shallow aquifers

the tectonically controlled emplacement of a vertically sheeted gabbro pyroxenite intrusion feeder zone of an ocean island volcano fuerteventura canary islands abstract the miocene px1 gabbro pyroxenite pluton fuerteventura canary islands is a 3 5 5 5 km shallow level intrusion 0 15 0 2 gpa and 1100 1120 c interpreted as the feeder zone to an ocean island volcano it displays a vertical magmatic banding expressed in five 50 to 100 metre wide nne ssw trending alkaline gabbro sequences alternating with pyroxenites this emplacement geometry was controlled by brittle to ductile shear zones generated by a regional e w extensional tectonic setting that affected fuerteventura during the miocene at a smaller scale the px1 gabbro and pyroxenite bands consist of metre thick differentiation units which suggest emplacement by periodic injection of magma pulses as vertical dykes that amalgamated similarly to a sub volcanic sheeted dyke complex individual dykes underwent internal differentiation following a solidification front parallel to the dyke edges this solidification front may have been favoured by a significant lateral horizontal thermal gradient expressed by the vertical banding in the gabbros the fractionation asymmetry within individual dykes and the migmatisation of the wall rocks pyroxenitic layers result from the fractionation and accumulation of clinopyroxene olivine plagioclase crystals from a mildly alkaline basaltic liquid they are interpreted as truncated differentiation sequences from which residual melts were extracted at various stages of their chemical evolution by subsequent dyke intrusions either next to or within the crystallising unit compaction and squeezing of the crystal mush is ascribed to the incoming and inflating magma pulses the expelled interstitial liquid was likely collected and erupted along with the magma flowing through the newly injected dykes clinopyroxene mineral orientation as evidenced by ebsd and micro x ray tomography investigations displays a marked pure shear component supporting the interpretation of the role of compaction in the generation of the pyroxenites conversely gabbro sequences underwent minor melt extraction and are believed to represent crystallised coalesced magma batches emplaced at lower rates at the end of eruptive cycles clinopyroxene orientations in gabbros record a simple shear component suggesting syn magmatic deformation parallel to observed nne ssw trending shear zones induced by the regional tensional stress field this emplacement model implies a crystallisation time of 1 to 5 years for individual dykes consistent with px1 emplacement over less than 0 5 my a minimum amount of approximately 150 km3 of magma is needed to generate the pluton part of it having been erupted through the central volcanic centre of fuerteventura if the regional extensional tectonic regime controls the px1 feeder zone initiation and overall geometry rates and volumes of magma depend on other source related factors high injection rates are likely to induce intrusion growth rates larger than could be accommodated by the regional extension in this case dyke intrusion by propagation of a weak tip combined with the inability of magma to circulate through previously emplaced and crystallised dykes could result in an increase of non lithostatic pressure on previously emplaced mushy dyke walls thus generating strong pure shear compaction within the pluton feeder zone and interstitial melt expulsion these compaction dominated processes are recorded by the cumulitic pyroxenite bands

geomagnetic paleosecular variation in the brunhes period from the island of el hierro canary islands we have sampled a sequence of 69 flows in the island of el hierro canary islands 46 of them belong to the el golfo formation and 23 to the most recent rift formation radiometric dating brackets this section between 442 ka and 134 ka with six intermediate datings all the samples were stepwise demagnetized partly with alternative field partly thermally with very similar results the large majority of the samples are characterized by a single stable component of magnetization chrm isolated after the first steps of demagnetization are all of normal polarity inclinations are on average shallower than expected from a geocentered dipole field but consistent with results from other areas at the same latitude mean declinations of the rift and el golfo sequences are both easterly deviated about 5 and 15 respectively and significantly different suggesting that the section has undergone a progressive clockwise rotation vgp scatter and directional scatter calculated for the rift sequence are consistent with available data from other geographical areas and also with recent models of paleosecular variation on the other hand a significantly smaller directional scatter is obtained for the lower el golfo sequence suggesting that a period of low secular variation occurred in the canary islands area between approximately 440 and 260 ka

analysis and modelling of the aeromagnetic anomalies of gran canaria canary islands abstract in this paper we present a crustal magnetic model of the volcanic island of gran canaria based on aeromagnetic data this magnetic study has made it possible to constrain the location and geometry of 1 the mafic core of gran canaria built as the result of the crystallization of magmas which rose from the mantle during the submarine and shield basaltic stages of its evolution the most intense magnetic high displayed over the nw part of the island likely shows the main feeding system of the shield volcano 2 the residual syenitic shallow magma chamber which fed the salic volcanic activity in the center of the island linked to the formation of the tejeda caldera and to the intrusion of felsic rocks which made up a cone sheet 3 a reversely magnetized linear intrusion located in the marine area to the nw of the island which could be related to the magmatic source of the submarine volcanism between gran canaria and tenerife most of these magnetic sources show a linear pattern with trends that are in close agreement with the orientations of previously identified fractures the magmatic intrusion to the nw of the island could be related with a wsw ene active fault between gran canaria and tenerife while the main trend and location of the mafic core agree with a nw se fault suggested by geological studies this means that these magnetic sources are the result of the ascent and intrusion of magma along regional fractures therefore this study provides fresh data which demonstrate the influence of regional tectonics on the growth of gran canaria during its entire evolution finally the spectral analysis of the magnetic anomaly map suggests that it is possible that rocks located at mantle like depths from the moho to about 23 km behave as magnetic sources a fact that can be related with the magmatic underplating detected by other geophysical techniques

giant quaternary landslides in the evolution of la palma and el hierro canary islands in the past large morphological escarpments in the canaries have been generally related to explosive and or erosive processes recent onshore and offshore investigations drastically changed this interpretation by providing evidence of the importance of giant lateral collapses in the evolution of the islands especially in their earlier stages of growth giant landslide scars and deposits are readily observed both onshore and offshore in the younger western canaries and seem to be a common feature of the development of the entire archipelago at least one catastrophic collapse is apparent on la palma the cumbre nueva giant landslide which occurred about 560 ka ago this collapse removed some 200 km3 of central western la palma forming a large embayment three successive giant landslides and evidence of an aborted attempt at another are seen in the island of el hierro the combined volume of those collapses estimated at about 400 500 km3 considerably exceeds the present subaerial volume of the island about 140 km3 giant landslides and erosion during the past million years have removed more than half of the total subaerial volume of la palma and el hierro

evolution of ocean island rifts the northeast rift zone of tenerife canary islands the northeast rift zone of tenerife presents a superb opportunity to study the entire cycle of activity of an oceanic rift zone field geology isotopic dating and magnetic stratigraphy provide a reliable temporal and spatial framework for the evolution of the ne rift zone which includes a period of very fast growth toward instability between ca 1 1 and 0 83 ma followed by three successive large landslides the micheque and guimar collapses which occurred approximately contemporaneously at ca 830 ka and on either side of the rift and the la orotava landslide between 690 10 and 566 13 ka our observations suggest that canarian rift zones show similar patterns of development which often includes overgrowth instability and lateral collapses collapses of the rift flanks disrupt established fissural feeding systems favoring magma ascent and shallow emplacement which in turn leads to magma differentiation and intermediate to felsic nested eruptions rifts and their collapses may therefore act as an important factor in providing architectural and petrological variability to oceanic volcanoes conversely the presence of substantial felsic volcanism in rift settings may indicate the presence of earlier landslide scars even if concealed by postcollapse volcanism comparative analysis of the main rifts in the canary islands outlines this general evolutionary pattern 1 growth of an increasingly high and steep ridge by concentrated basaltic fissure eruptions 2 flank collapse and catastrophic disruption of the established feeder system of the rift 3 postcollapse centralized nested volcanism commonly evolving from initially ultramafic mafic to terminal felsic compositions trachytes phonolites and 4 progressive decline of nested eruptive activity

spatial probability distribution of future volcanic eruptions at el hierro island canary islands spain abstract the 2011 submarine eruption that took place in the proximity of el hierro island canary islands spain has raised the need to identify the most likely future emission zones even on volcanoes characterized by low frequency activity here we propose a probabilistic method to build the susceptibility map of el hierro i e the spatial distribution of vent opening for future eruptions based on the probabilistic analysis of volcano structural data of the island collected through new fieldwork measurements bathymetric information as well as analysis of geological maps orthophotos and aerial photographs these data have been divided into different datasets and converted into separate and weighted probability density functions which were included in a non homogeneous poisson process to produce the volcanic susceptibility map the most likely area to host new eruptions in el hierro is in the south western part of the west rift high probability locations are also found in the northeast and south rifts and along the submarine parts of the rifts this map represents the first effort to deal with the volcanic hazard at el hierro and can be a support tool for decision makers in land planning emergency measures and civil defense actions

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

volcanic and morphological evolution of la gomera canary islands based on new k ar ages and magnetic stratigraphy implications for oceanic island evolution the spatial and chronological evolution of canary islands volcanism is due to eastward progression of the slow moving african plate over a mantle plume la gomera is located between the western shield stage islands 12 ma with 23 k ar ages and palaeomagnetic data we can constrain the timing of the main subaerial volcanic phases of la gomera the shield volcano c 9 4 8 0 ma the postshield peripheral lava flows c 7 4 5 0 ma the postshield horizontal lava flows c 5 4 4 3 ma and late intra canyon lava flows c 1 9 ma the horizontal lava flows fill a 10 km wide depression formed by a giant landslide garajonay the entire structure of la gomera is in relief inversion declining volcanic construction rates from the shield to the postshield stages are correlated with increasing erosion rates whereas the period of volcanic quiescence hiatus has low erosion rates the succession and duration of the hotspot volcanic stages in the canary islands are compared with those in the hawaiian islands thus underlining differences between slow moving and fast moving plate settings

low temperature shallow water hydrothermal vent mineralization following the recent submarine eruption of tagoro volcano el hierro canary islands abstract hydrothermal iron fe rich sediments were recovered from the tagoro underwater volcano central atlantic that formed during the 2011 2012 volcanic event cruises in 2012 and 2014 enabled the monitoring and sampling of the early stage establishment of a hydrothermal system degassing vents produced acoustic flares imaged on echo sounders in june 2012 four months after the eruption a novel hydrothermal vent system was discovered and sampled in 2014 during a rov dive the system is characterized by hornito like structures and chimneys showing active co2 degassing and anomalous temperatures at 120 89 m water depth and along the se flank at 215 185 m water depth associated with secondary cones iron and silica rich gelatinous deposits pooled over and between basanite in the hornitos brecciated lavas and lapilli the low temperature shallow water hydrothermal system was discovered by the venting of fe rich fluids that produced a seafloor draped by extensive fe flocculate deposits precipitated from the neutrally buoyant plumes located along the oxic photic zone at 50 70 m water depths the basanite is capped by mm to cm thick hydrothermally derived fe oxyhydroxide sediment and contains micro cracks and degasification vesicles filled by sulfides mostly pyrite mineralogically the fe oxyhydroxide sediment consists of proto ferrihydrite and ferrihydrite with scarce pyrite at their base the fe rich endmember contains low concentrations of most trace elements in comparison with hydrogenetic ferromanganese deposits and the sediments show some dilution of the fe oxyhydroxide by volcanic ash the fe oxyhydroxide phase with a mean particle size of 3 4 nm low average la fe ratios of the mineralized deposits from the various sampling sites and the positive eu anomalies indicate rapid deposition of the fe oxyhydroxide near the hydrothermal vents electron microprobe studies show the presence of various organomineral structures mainly twisted stalks and sheaths covered by iron silica deposits within the mineralized samples reflecting microbial iron oxidation from the hydrothermal fluids sequencing of 16 s rrna genes also reveals the presence of other microorganisms involved in sulfur and methane cycles samples collected from hornito chimneys contain silicified microorganisms coated by fe rich precipitates the rapid silicification may have been indirectly promoted by microorganisms acting as nucleation sites we suggest that this type of hydrothermal deposit might be more frequent than presently reported to occur in submarine volcanoes on a geological scale these volcanic eruptions and low temperature hydrothermal vents might contribute to increased dissolved metals in seawater and generate considerable fe oxyhydroxide deposits as identified in older hot spot seamounts

eruptive and structural history of teide volcano and rift zones of tenerife canary islands the teide and pico viejo stratocones and the northwest and northeast rifts are products of the latest eruptive phase of the island of tenerife initiated with the lateral collapse of its northern flank that formed the las canadas caldera and the icod la guancha valley ca 200 ka the eruptive and structural evolution of this volcanic complex has been reconstructed after detailed geological mapping and radioisotopic dating of the significant eruptive events a set of 54 new 14 c and k ar ages provides precise age control of the recent eruptive history of tenerife particularly teide volcano the third highest volcanic feature on earth 3718 m above sea level 7 km high and unique in terms of its intraplate setting the development of the teide pico viejo volcanoes may be related to the activity of the northwest and northeast rifts volcanic and intrusive activity along both rift zones may have played an important role in activating the gravitational landslide and in the subsequent growth nested within the collapse embayment of an increasingly higher central volcano with progressively differentiated magmas the coeval growth of the central volcano with sustained activity along the rifts led to a clear bimodal distribution in composition of eruptive products with the basaltic eruptions in the distal part of the rifts and phonolitic and more explosive eruptions in the central area where the differentiated stratocones developed current volcanic hazard in tenerife is considered to be moderate because eruptive frequency is low explosivity is modest and the eruptive activity of the teide stratocone seems to have declined over the past 30 k y with only one eruption in this period 1150 yr b p

estimating the magnetization direction of crustal structures by means of an equivalent source algorithm abstract the estimation of the direction of the total magnetization vector of a magnetic source is the first step of a reliable modelling of a magnetic anomaly when remanent magnetization is not negligible we present a new method to obtain the magnetization direction of a crustal body based on an iterative equivalent layer inversion of a magnetic anomaly the main advantage of the proposed approach is that no a priori information about the source is needed the method is suitable for the interpretation of isolated magnetic sources for which magnetization is expected to be uniform in direction but not necessarily in intensity we have verified the success of the technique with synthetic data and with the magnetic anomaly of el hierro volcanic island

multi event oceanic island landslides new onshore offshore insights from el hierro island canary archipelago abstract this paper presents a combined onshore offshore morpho structural characterization of the el golfo giant landslide island of el hierro canary archipelago spain offshore data from multibeam echosounders chirp sub bottom profiles and multichannel seismic reflection data and onshore data coming from water wells and galleries have been analyzed the geomorphology and the internal architecture of this giant flank collapse are defined in order to determine its multi event nature the subaerial headscarp shows a non continuous arcuate profile formed by two nested semi circular amphitheaters that extend offshore along a smooth chute suggesting the occurrence of at least two large retrogressive events channels gullies and escarpments developed along the submarine sector of the scar also indicate smaller scale events and predominance of sediment bypass in the lower slope two subunits of submarine mass transport deposits mtds debris avalanche are identified on multichannel seismic reflection profiles with a total estimated volume of 318 km3 84 km3 and 234 km3 for the younger and older mtds respectively data from wells and galleries show abrasion platforms with beach deposits at sea level 0 masl formed after the landslide scar and buried by the post collapse el golfo lavas infill suggesting an age at least older than 23 5 82 5 ka for the landslide

multistage collapse of eight western canary island landslides in the last 1 5 ma sedimentological and geochemical evidence from subunits in submarine flow deposits volcaniclastic turbidites in the madeira abyssal plain provide a record of major landslides from the western canary islands in the last 1 5 ma these volcaniclastic turbidites are composed of multiple fining upward turbidite sands known as subunits the subunits indicate that the landslides responsible for the sediment gravity flows occurred in multiple stages the subunits cannot result from flow reflection or splitting because the compositions of volcanic glasses from each individual subunit in an event bed are subtly different this indicates that each subunit represents a discrete failure as part of a multistage landslide this has significant implications for geohazard assessments as multistage failures reduce the magnitude of the associated tsunami the multistage failure mechanism reduces individual landslide volumes from up to 350 km3 to less than 100 km3 thus although multistage failure ultimately reduce the potential landslide and tsunami threat the landslide events may still generate significant tsunamis close to source

submarine landslides around the canary islands the morphology and structure of the submarine flanks of the canary islands were mapped using the gloria long range side scan sonar system bathymetric multibeam systems and sediment echosounders twelve young 2 ma giant landslides have been identified on the submarine flanks of the canary islands up to now older landslide events are long buried under a thick sediment cover due to high sedimentation rates around the canary islands most slides were found on the flanks of the youngest and most active islands of la palma el hierro and tenerife but young giant landslides were also identified on the flanks of the older 15 20 ma but still active eastern islands large scale mass wasting is an important process during all periods of major magmatic activity the long lived volcanic constructive history of the islands of the canary archipelago is balanced by a correspondingly long history of destruction resulting in a higher landslide frequency for the canary islands compared to the hawaiian islands where giant landslides only occur late in the period of active shield growth the lower stability of the flanks of the canaries is probably due to the much steeper slopes of the islands a result of the abundance of highly evolved intrusive and extrusive rocks another reason for the enhanced slope instability is the abundance of pyroclastic deposits on canary islands resulting from frequent explosive eruptions due to the elevated volatile contents in the highly alkalic magmas dike induced rifting is most likely the main trigger mechanism for destabilization of the flanks flank collapses are a major geological hazard for the canary islands due to the sector collapses themselves as well as triggering of tsunamis in at least one case a giant lateral blast occurred when an active magmatic or hydrothermal system became unroofed during flank collapse

40ar 39ar dating of the brunhes matuyama geomagnetic field reversal magnetostratigraphic studies are widely used in conjunction with the geomagnetic polarity time scale gpts to date events in the range 0 to 5 million years ago a critical tie point on the gpts is the potassium argon age of the most recent brunhes matuyama geomagnetic field reversal astronomical values for the forcing frequencies observed in the oxygen isotope record in ocean drilling project site 677 suggest that the age of this last reversal is 780 ka thousand years ago whereas the potassium argon based estimate is 730 ka results from 4039 ar incremental heating studies on a series of lavas from maui that straddle the brunhes matuyama reversal give an age of 783 11 ka in agreement with the astronomically derived value the astronomically based technique appears to be a viable tool for dating young sedimentary sequences

changes in the diffuse co2 emission and relation to seismic activity in and around el hierro canary islands significant changes in the diffuse emission of carbon dioxide were recorded in a geochemical station located at el hierro canary islands before the occurrence of several seismic events during 2004 two precursory co2 efflux increases started thirteen and nine days before two seismic events of magnitude 2 3 and 1 7 which took place near el hierro island canary islands on march 23 and april 15 reaching a maximun value of 51 1 and 46 2 g m 2 d 1 respectively five and eight days before the two seismic events other similar increases started thirteen and five days before the occurrence of two seismic events of magnitude 1 3 and 1 5 which took place on october 15 and 21 respectively reaching the maximum values four and one day before the earthquakes these changes were not related to variations in atmospheric or soil parameters the material failure forecast method ffm which analyzes the rate of precursory phenomena was successfully applied to forecast the first seismic event that took place in el hierro island in 2004

radiometric dating of three large volume flank collapses in the lesser antilles arc abstract it is now recognised that flank collapses are a recurrent process in the evolution of the lesser antilles arc volcanoes large magnitude debris avalanche deposits have been identified off the coast of dominica martinique and st lucia with associated volumes up to 20 km 3 deplus c le friant a boudon g komorowski j c villemant b harford c segoufin j cheminee j l 2001 submarine evidence for large scale debris avalanches in the lesser antilles arc earth planet sci lett 192 145 157 we present new radiometric dating of three major events using the k ar cassignol gillot technique in the qualibou depression of st lucia a collapse has been constrained by dome emplacement prior to 95 2 ka in dominica where repetitive flank collapse events have occurred le friant a boudon g komorowski j c deplus c 2002 l ile de la dominique a l origine des avalanches de debris les plus volumineuses de l arc des petites antilles c r geoscience 334 235 243 the plat pays event probably occurred after 96 2 ka inside the depression caused by this event scotts head which is interpreted as a proximal megabloc from the subsequent soufriere avalanche event has been dated at 14 1 ka providing an older bound for this event on martinique three different domes within the carbets structure dated at 337 5 ka constrain the age of this high magnitude event finally these results obtained from three of the most voluminous flank collapses provide constraints to estimate the recurrence of these events which represent one of the major hazards associated with volcanoes of the lesser antilles arc

mega tsunami conglomerates and flank collapses of ocean island volcanoes abstract marine conglomerates at high elevation on the flanks of ocean islands are usually interpreted as evidence of mega tsunamis generated by volcano flank collapses although their origin is sometimes debated elevated littorals vs tsunami in this review we introduce case studies of well documented examples of tsunami conglomerates in hawaii pacific ocean the canary and cape verde islands atlantic ocean and mauritius island indian ocean other less documented marine conglomerates are also presented as tsunami candidates then we build a comprehensive picture of the general characteristics of these conglomerates and the different methods that can be applied to date them different perspectives of research are proposed especially on the use of tsunami conglomerates as proxies for better constraining numerical models of ocean island flank collapses and associated tsunamis we also discuss the possible links between volcano growth flank instability and climate

geochronology and stratigraphy of the roque nublo cycle gran canaria canary islands the roque nublo cycle of pliocene age is the second main cycle of subaerial volcanic activity in gran canaria during this cycle a stratovolcano at least 2500 m high developed in the central part of the island its volcanic products covered an area of about 540 km 2 the detailed stratigraphy of the roque nublo cycle together with a magnetostratigraphic study and six new k ar dates which complement 22 previously published ones have led to the reconstruction of the volcanic history of this cycle in which six main stages have been distinguished the revised chronology of the roque nublo cycle implies an overlap in age with the earliest rocks of the third cycle of subaerial activity in gran canaria no volcanic hiatus occurred between the second and third cycles as was previously thought to be the case

the giant submarine alika debris slide mauna loa hawaii probably represent multiple subsidence events before during and after the debris avalanches lower slopes of the slide contain distinctive lobate terraced deposits that are interpreted as having been emplaced more slowly prior to the debris avalanches estimated thicknesses of 50 200 m suggest volumes of 200 600 km 3 for the two lobes the combined volume of the entire slide and slump terrane is probably 1500 2000 km 3 the slide deposits predate a 13 ka coral reef and probably postdate the block faulted ninole basalt roughly dated as a few hundred thousand years old the alika slide or a similar deposit recognized on gloria images further north along the hawaiian ridge probably triggered a giant wave that washed 325 m high on lanai at about 100 ka slumping on mauna loa has been most intense adjacent to the large arcuate bend in its southwest rift zone as the rift zone migrated westward away from the growing kilauea volcano slumping events were probably triggered by seismic activity accompanying dike injection along the rift zone such massive slumps landslides and distal submarine turbidity flows appear to be widespread on the flanks of hawaiian volcanoes

40ar 39ar age constraints for the jaramillo normal subchron and the matuyama brunhes geomagnetic boundary our mid pleistocene 4oar 39ar age recalibration of the geomagnetic polarity timescale is nearly in accord with the oxygen isotope climate record calibration of the astronomical timescale proposed by johnson 1982 and shackleton et al 1990 4oar 39ar ages of a normally magnetized rhyolite dome in the valles caldera northern mexico yielded a weighted mean age of 1 004 0 019 ma a k ar age of 0 909 0 019 ma for this rock by doell and dalrymple 1966 was the linchpin for the recognition and calibration of the jaramillo normal subchron jns other 4oar 39ar ages from the vailes caldera and 4oar 39ar ages of ivory coast tektites indicate that the jns began at about 1 11 ma and ended before 0 92 ma probably near 0 97 ma the matuyama brunhes boundary occurred between 0 79 ma and 0 76 ma on the basis of 4oar 39ar sanidine ages from 1 three reversely magnetized rhyolite domes of the valles caldera 0 793 0 018 ma 0 794 0 007 ma and 0 812 0 023 ma and pumice 0 789 0 006 ma from the reversely magnetized oldest toba tuff of sumatra and 2 pumice 0 764 0 005 ma and 0 757 0 009 ma from the lower and upper units of the normally magnetized bishop tuff the age of the boundary may be close to 0 77 ma as deduced from rates of sedimentation in ancient lake bonneville utah increasingly aware that the polarity of earth s magnetic field has changed repeatedly through geologic time and isotopic dating of these polarity reversals resulted in a geomagnetic polarity time scale gpts for the late cenozoic this combined paleomagnetic and isotopic research played a pivotal role in confirming plate tectonic theory glen 19821 which revolutionized the earth sciences continual refinement of isotopic ages which define the gpts has increased the usefulness of geomagnetic polarity reversals as marker hori zons in many types of geologic studies we present 4oar 39ar data and ages for some key volcanic units that support changes in the isotopic age chronology of the gpts using volcanic rocks erupted near the time of the geologically youngest two geomagnetic polarity reversals figure 1 the older of the two reversals originally called by doell and dalrymple 1966 the jaramillo event is now named the jaramillo normal subchron jns it is recorded in middle pleistocene rocks as a brief episode of normal polar ity within the late matuyama chron the younger of the two called the matuyama brunhes boundary mbb is regis tered in middle pleistocene rocks worldwide and consists of

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

global risk from extreme geophysical events threat identification and assessment in an increasingly interconnected world any single geophysical hazard is capable of having consequences far beyond the range of immediate physical effects most recently this was demonstrated by the 2004 asian tsunami which took the lives of citizens from 57 different nations and by hurricane katrina in august 2005 which raised fuel prices worldwide and contributed to a record uk trade deficit in the month following the devastation of new orleans on an altogether wider scale global geophysical events gges are natural phenomena capable of having wholesale deleterious consequences for the world s environment economy and society these may arise i due to a global physical effect such as an episode of severe planetary cooling in response to a volcanic super eruption or large comet or asteroid impact or ii as a result of subsidiary ramifications for the global economy and social fabric of a cataclysmic regional event such as an atlantic or pacific wide mega tsunami or a more spatially confined event at a strategically sensitive location for example the awaited major tokyo earthquake while very infrequent the wide ranging and potentially ruinous consequences of a gge for the well being of the international community make it essential that they are seriously considered within any comprehensive assessment of natural threats

revisions to the age of the brunhes matuyama boundary and the pleistocene geomagnetic polarity timescale the currently referenced age of 730 ka for the brunhes matuyama b m geomagnetic polarity boundary mankinen and dalrymple 1979 is based largely on k ar and paleomagnetic data from postcollapse rhyolites in the valles caldera new mexico doell and dalrymple 1966 doell et al 1968 dating of sanidine from valles rhyolites by the 40a 39ar laser fusion technique indicates that samples critical to defining the b m boundary are up to 90 ka older than previously thought the new data combined with earlier results yield an age for the b m boundary of 780 10 ka 40ar 39ar ages from other samples suggest the jaramillo normal polarity subchron extended from 1010 to 915 ka

detecting and locating precursory signals during the 2011 el hierro canary islands submarine eruption pilar sanchez pastor acknowledges funding from the spanish ministry of economy and competitiveness project misterios cgl2013 48601 c2 2 r

geochemical signals related to the 2011 2012 el hierro submarine eruption abstract on 10 october 2011 a submarine volcanic eruption began 2 km south of the island of el hierro canary islands spain it was the first eruption after 40 years of quiescence in the canarian archipelago since mid july 2011 a multiparametric network has been deployed by the instituto geografico nacional hereinafter ign to monitor volcanic processes the data recorded by five stations measuring the air and soil temperature co2 and radon concentration in the air inside four galleries and one well are the focus of the present paper two important anomalies were found that improve comprehension of the volcanic process first a clear increase in co2 concentration in one gallery from 825 19 to 2305 35 ppm which seems to be mainly controlled by ground deformation measured during the unrest period preceding the eruption second a relationship between radon concentration in air in a well located in the northern side of the island with seismic energy release several peaks with up to 115 increase and ground deformation 50 growth in background level also before the eruption onset lastly changes in radon concentration during eruptive period seem to be modulated by seismic activity increases up to 233 which in turn is likely related to variations in magma rheology

evolution of submarine eruptive activity during the 2011 2012 el hierro event as documented by hydroacoustic images and remotely operated vehicle observations submarine volcanic eruptions are frequent and important events yet they are rarely observed here we relate bathymetric and hydroacoustic images from the 2011 to 2012 el hierro eruption with surface observations and deposits imaged and sampled by rov as a result of the shallow submarine eruption a new volcano named tagoro grew from 375 to 89 m depth the eruption consisted of two main phases of edifice construction intercalated with collapse events hydroacoustic images show that the eruptions ranged from explosive to effusive with variable plume types and resulting deposits even over short time intervals at the base of the edifice rov observations show large accumulations of lava balloons changing in size and type downslope coinciding with the area where floating lava balloon fallout was observed peaks in eruption intensity during explosive phases generated vigorous bubbling at the surface extensive ash vesicular lapilli and formed high density currents which together with periods of edifice gravitational collapse produced extensive deep volcaniclastic aprons secondary cones developed in the last stages and show evidence for effusive activity with lava ponds and lava flows that cover deposits of stacked lava balloons chaotic masses of heterometric boulders around the summit of the principal cone are related to progressive sealing of the vent with decreasing or variable magma supply hornitos represent the final eruptive activity with hydrothermal alteration and bacterial mats at the summit our study documents the distinct evolution of a submarine volcano and highlights the range of deposit types that may form and be rapidly destroyed in such eruptions

evidence of a modern deep water magmatic hydrothermal system in the canary basin eastern central atlantic ocean new seismic profiles bathymetric data and sediment rock sampling document for the first time the discovery of hydrothermal vent complexes and volcanic cones at 4800 5200 m depth related to recent volcanic and intrusive activity in an unexplored area of the canary basin eastern atlantic ocean 500 km west of the canary islands a complex of sill intrusions is imaged on seismic profiles showing saucer shaped parallel or inclined geometries three main types of structures are related to these intrusions type i consists of cone shaped depressions developed above inclined sills interpreted as hydrothermal vents type ii is the most abundant and is represented by isolated or clustered hydrothermal domes bounded by faults rooted at the tips of saucer shaped sills domes are interpreted as seabed expressions of reservoirs of ch4 and co2 rich fluids formed by degassing and contact metamorphism of organic rich sediments around sill intrusions type iii are hydrothermal volcanic complexes originated above stratified or branched inclined sills connected by a chimney to the seabed volcanic edifice parallel sills sourced from the magmatic chimney formed also domes surrounding the volcanic cones core and dredges revealed that these volcanoes which must be among the deepest in the world are constituted by oib type basanites with an outer ring of blue green hydrothermal al rich smectite muds magmatic activity is dated based on lava samples at 0 78 0 05 and 1 61 0 09 ma k ar methods and on tephra layers within cores at 25 237 ky the subvent hydrothermal volcanic complex constitutes the first modern system reported in deep water oceanic basins related to intraplate hotspot activity

rapid intensification eyewall contraction and breakdown of hurricane charley 2004 near landfall 1 the rapid intensification and decay in hurricane charley 2004 was sampled by the wsr 88ds in key west and tampa charley s axisymmetric wind fields vertical vorticity perturbation pressure and reflectivity were derived from the ground based velocity track display gbvtd technique charley s rapid intensification was accompanied by a contracting eyewall the central pressure dropped 33 hpa in three hours the vortex was unstable possessed a ring vorticity profile during the eyewall contraction while the vortex became stable monopole vorticity profile after charley reached its peak intensity charley s eyewall broke down during the decaying stage after the land fall this study demonstrates the powerful combination of the gbvtd technique and coastal wsr 88d data in monitoring landfalling tropical cyclones

volcanic tremors good indicators of change in plumbing systems during volcanic eruptions abstract geophysical and geochemical signals recorded during episodes of unrest preceding volcanic eruptions provide information on movements of magma inside the lithosphere and on how magma prepares to reach the surface when the eruption ensues continuous volcanic monitoring can reveal the nature of changes occurring in the volcano s plumbing system which may be correlated with changes in both eruption behaviour and products during the 2011 2012 submarine eruption of el hierro canary islands the seismic signal surface deformation a broad stain on the sea surface of the eruption site and the occasional appearance of floating lava balloons and pyroclastic fragments were the main observable signs a strong continuous tremor in the vent accompanied the eruption and varied significantly in amplitude frequency and dynamical parameters we analysed these variations and correlated them with changes in the distribution of earthquakes and in the petrology of the erupting magma this enabled us to relate variations in tremors to changes in the i stress conditions of the plumbing system ii dimensions of the conduit and vent iii intensity of the explosive episodes and iv rheological changes in the erupting magma the results obtained show how the tremor signal was strongly influenced by stress changes in the host rock and in the rheological variations in the erupting magma we conclude that the tracking of real time syn eruptive tremor signals via the observation of variations in plumbing systems and magma physics is a potentially effective tool for interpreting eruption dynamics and suggest that similar variations observed in pre eruptive tremors will have a similar origin

the distribution of basaltic volcanism on tenerife canary islands implications on the origin and dynamics of the rift systems abstract one of the most characteristic features of volcanic islands is the existence of rift zones defined commonly as orientated eruptive fissures or parallel rows of elongate cinder cones and dyke swarms occasionally these rifts can appear at the birth of the volcanic island and persist until the last episodes of its constructions controlling the form and structure of the island e g azores islands in the case of tenerife canary islands it is possible to observe two rift zones santiago del teide and dorsal rifts running nw se and ene wsw marked by parallel rows of aligned cones and eruptive fissures additionally at the southern part of the island southern volcanic zone basaltic volcanism is characterized by scattered vents and apparently non coherently orientated eruptive fissures some authors relate the existence of the latter volcanism to a n s running rift zone that defines the third branch of a three armed rift system in the island in the present paper we first investigate the tectonic controls on the distribution of basaltic volcanism at the southern volcanic zone and their relation with the nw se and ene wsw rifts the numerical results obtained suggest that basaltic volcanism of the southern part of tenerife can be easily explained as the result of a extensional stress field derived from the combined effects of the nw se and ene wsw rifts as a second objective we have also investigated the origin of the santiago del teide and dorsal rift zones and their role on the formation of the original shield volcano and the subsequent evolution of the whole island our numerical results contrast with previously published explanations on the origin of the tenerife rifts that included fracturing due to volcano spreading or to deformation of the volcano due to magma intrusion we consider that volcanic activity in tenerife began throughout fissural volcanism along these structures that were already present in the oceanic basement progressively accumulating the basaltic series that gave rise to the construction of the composite shield volcano

causal link between quaternary paleoclimatic changes and volcanic islands evolution 1 giant landslides and resulting tsunamis represent the main geologic hazards linked to volcanic island evolution from offshore and onland studies flank failures have been identified around numerous islands in most geodynamic contexts however the triggering conditions are still poorly understood and several causes may act simultaneously to reach a critical threshold here we show that most large volume 10 km3 landslides occur at glacial stages termination and we propose that a causal relationship between flank collapse of volcanic islands and global climatic changes has existed at least since 900 kyr moreover ages reported here favour the hypothesis that major collapses occurred during the onset of glacial to interglacial transitions when sudden influx of melt water from polar ice caps causes rapid sea level rise we propose that rapid sea level rise induces enhanced coastal erosion and sudden changes of pore pressure conditions within basal layers which favour edifice failure

seismicity patterns prior to the 2011 el hierro eruption abstract the first fully monitored volcanic eruption in the canary islands started on 10 october 2011 2 km south of the island of el hierro this submarine eruption was preceded by various precursory signals the most evident of which were the seismic series that started in july 2011 consisting of almost 10 000 low magnitude earthquakes located by manual picking this seismicity revealed a 20 km horizontal migration from the north of the island to the south at depths of between 10 and 17 km the deeper events occurring further south we applied a relative location algorithm hypodd to improve hypocentral locations the resulting distribution is more compact slightly shallower and reveals a clearer difference in depths from north to south tests performed to check the reliability of the results gave maximum uncertainties of 400 m in the relocations furthermore new features were found including the origin of the seismicity in the center of the island and the presence of two alternating seismogenic zones in the north of the island during the first month of activity online material figures of waveforms from cross correlation data statistics stereogram of ray parameters ray tracing tests and table of hypodd relocations

evidence from acoustic imaging for submarine volcanic activity in 2012 off the west coast of el hierro canary islands spain we report precursory geophysical geodetic and geochemical signatures of a new submarine volcanic activity observed off the western coast of el hierro canary islands submarine manifestation of this activity has been revealed through acoustic imaging of submarine plumes detected on the 20 khz chirp parasound subbottom profiler topas ps18 mounted aboard the spanish rv hesperides on june 28 2012 five distinct filament shaped acoustic plumes emanating from the flanks of mounds have been recognized at water depth between 64 and 88 m on a submarine platform located nw el hierro these plumes were well imaged on topas profiles as flares of high acoustic contrast of impedance within the water column moreover visible plumes composed of white rafts floating on the sea surface and sourcing from the location of the submarine plumes were reported by aerial photographs on july 3 2012 5 days after acoustic plumes were recorded in addition several geophysical and geochemical data support the fact that these submarine vents were preceded by several precursory signatures i a sharp increase of the seismic energy release and the number of daily earthquakes of magnitude 2 5 on june 25 2012 ii significant vertical and horizontal displacements observed at the canary islands gps network nagoya university iter grafcan with uplifts up to 3 cm from june 25 to 26 2012 iii an anomalous increase of the soil gas radon activity from the end of april until the beginning of june reaching peak values of 2 7 kbq m3 on june 3 2012 and iv observed positive peak in the air corrected value of 3he 4he ratio monitored in ground waters 8 5 atmospheric 3he 4he ratio ra at the northwestern el hierro on june 16 2012 combining these submarine and subaerial information we suggest these plumes are the consequence of submarine vents exhaling volcanic gas mixed with fine ash as consequence of an event of rapid rise of volatile rich magma beneath the nw submarine ridge of el hierro these precursory signals have revealed important to improve and optimize the detection of early warning signals of volcanic unrest episodes at el hierro

effects of canary hotspot volcanism on structure of oceanic crust off morocco analysis of over 6400 km of multichannel seismics mcs and 50 sonobuoy reflection and refraction experiments reduced both in the domain of x t and tau p shows that a region within the jurassic quiet zone off morocco underwent dramatic changes as a result of the passage of the lithosphere over the canary hotspot commencing approximately 60 ma a seismic unit ucf interpreted as volcanic in origin is observed within the sediments in a region characterized by a broad bathymetric swell it shows diffractions from its upper surface and an internally chaotic seismic facies and pinches out between sedimentary units of continuous subparallel facies a velocity inversion is noted between the ucf 4 7km s and the underlying sediment 3 1 km s the ucf is time transgressive it lies near the cretaceous s tertiary boundary in the northern portion of the study area and is younger to the south kinematic studies of the movement of the canary hotspot relative to africa show that the hotspot first appeared off nw africa about 60 ma and was located beneath oceanic crust in the region where the ucf is observed depth to basement measurements in areas not effected by the hotspot show a consistent linear trend of increased depth with age in areas effected by the hotspot the thermal rejuvenation is evident as basement depths shoal with increased proximity to the present hotspot the reheating of the crust resets the thermal age of the lithosphere with many of the properties of crust of a younger age subsidence curves of the reheated crust off morocco show good correlation to subsidence curves of other reheated crust on a global basis a zone characterized by high crustal velocities 7 1 7 4 km s and greater crustal thicknesses by 1 2 km is observed in an area that corresponds to the bathymetric swell the region of the ucf and the reelevated basement the high velocities and increased crustal thickness are interpreted to be the result of underplating and assimilation of existing oceanic crust caused by the canary thermal anomaly the presence of high crustal velocities coupled with a thickened crustal section has been noted on various passive margins of the world they have generally been attributed to the thermal processes associated with continental rifting off morocco we believe that similar thermally induced phenomena have occurred but that here the heat anomaly was the midplate volcanism associated with the canary hotspot

the distribution of basaltic volcanism on tenerife canary islands implications on the origin and dynamics of the rift system reply to the comment by carracedo et al

exploring deformation scenarios in timanfaya volcanic area lanzarote canary islands from gnss and ground based geodetic observations abstract we report on a detailed geodetic continuous monitoring in timanfaya volcanic area tva where the most intense geothermal anomalies of lanzarote island are located we analyze about three years of gnss data collected on a small network of five permanent stations one of which at tva deployed on the island and nearly 20 years of tiltmeter and strainmeter records acquired at los camelleros site settled in the facilities of the geodynamics laboratory of lanzarote within tva this study is intended to contribute to understanding the active tectonics on lanzarote island and its origin mainly in tva after characterizing and filtering out the seasonal periodicities related to non tectonic sources from the geodetic records a tentative ground deformation field is reconstructed through the analysis of both tilt strain records and the time evolution of the baselines ranging the gnss stations the joint interpretation of the collected geodetic data show that the area of the strongest geothermal anomaly in tva is currently undergoing a se trending relative displacement at a rate of about 3 mm year this area even experiences a significant subsidence with a maximum rate of about 6 mm year moreover we examine the possible relation between the observed deformations and atmospheric effects by modelling the response functions of temperature and rain recorded in the laboratory finally from the retrieval of the deformation patterns and the joint analysis of geodetic and environmental observations we propose a qualitative model of the interplaying role between the hydrological systems and the geothermal anomalies namely we explain the detected time correlation between rainfall and ground deformation because of the enhancement of the thermal transfer from the underground heat source driven by the infiltration of meteoric water

magma emission rates from shallow submarine eruptions using airborne thermal imaging abstract the effusion rate is the most important parameter to gather when a volcanic eruption occurs because it controls the way in which a lava body grows extends and expands influencing its dimensional properties calculation of lava flow volume from thermal images collected by helicopter surveys has been largely used during the last decade for monitoring subaerial effusive eruptions however due to the depths where volcanic activity occurs monitoring submarine volcanic eruptions is a very difficult task the 2011 2012 submarine volcanic eruption at el hierro canary islands has provided a unique and excellent opportunity to monitor eruptive processes occurring on the seabed the use of a hand held thermal camera during daily helicopter flights allowed us to estimate for the first time the daily and total erupted magma volumes from a submarine eruption the volume of magma emitted during this eruption has been estimated at 300 mm3 giving an average effusion rate of 25 m3 s 1 thermal imagery by helicopter proved to be a fast inexpensive safe and reliable technique of monitoring volcanic eruptions when they occur on the shallow seabed

landslides and the evolution of el hierro in the canary islands seismic and sonar data have been used to evaluate the extent and characteristics of giant landslides on the flanks of el hierro in the canary islands as the youngest and most southwesterly of the canary islands el hierro has experienced rapid growth and destructive events in its 1 12 million year history at least four giant landslides el golfo el julan san andres and las playas have modified 450 km3 of el hierro during the last 200 300 thousand years with each landslide event removing around 3 of the total edifice volume the extent of landsliding indicates that it is the main process of decay we characterise flank morphology around el hierro and distinguish between rugged unfailed flank failed flank and steep gullied ridge flanks affected by landsliding have downslope long profiles with distinctive b coefficients and exponential forms the el golfo landslide is the most recent 15 ka best described and clearly defined landslide in the canary islands the el julan landslide sw flank has an estimated volume of 130 km3 an age of 200 ka and is characterised by gravitational slumping on the se flank two new landslide events are reported the younger landslide las playas occurred 145 176 ka has a narrow steep sided embayment and a corresponding blocky debris avalanche deposit the older landslide san andres is recognised on the basis of a highly chaotic seismic facies offshore and reduced upper flank gradients its lack of an upper flank embayment and offshore blocky debris avalanche lead us to interpret that the landslide involved gravitational slumping possibly a series of events which reduced upper flank gradients but did not catastrophically collapse to produce a debris avalanche

k ar ages and magnetic stratigraphy of a hotspot induced fast grown oceanic island el hierro canary islands abstract the combined use of accurate radiometric dating and magnetic stratigraphy can be applied to define the main stages of the building of oceanic volcanic islands this method has been successfully applied on the island of el hierro the westernmost island of the canaries archipelago for the emerged part of this island built in the last 1 2 ma magnetic stratigraphy and mapping show the presence of four consecutive subchrons k ar dating of eighteen samples in stratigraphic sequences using an unspiked technique produced ages consistent with the general volcanic stratigraphy the ages show that the magnetic polarity zones correlate to the upper part of the matuyama and to the brunhes chrons the jaramillo normal polarity subchron of the upper part of the matuyama reverse polarity chron is recorded in one of the lava sequences the lower limit of this event is constrained by two ages of 1 04 0 02 ma and one of 1 05 0 02 ma close to the value deduced from the astronomically tuned magnetic polarity time scale apts the volcanic history can be summarised by two consecutive main basaltic volcanic edifices the el tinor active during the upper part of the matuyama chron and the el golfo edifice constructed during the brunhes chron

paleomagnetic determinations on lanzarote from magnetic and gravity anomalies implications for the early history of the canary islands the bouguer and aeromagnetic anomaly maps of lanzarote show a gravity high and a dipolar magnetic anomaly over the central part of the island indicating one isolated source assuming that the structure responsible for both anomalies is the same a methodology has been designed to estimate the total magnetization vector of the source which is interpreted as a large intrusive body mafic core positioned as a result of magma rising to the surface during the early stages of growth of lanzarote considering its geometry to be known from a previous three dimensional 3 d gravity model the approach proposed in this paper is based on the delineation of magnetic contacts through analysis of the horizontal gradient of the reduced to the pole anomaly map comparison between the gravity and the pseudogravity anomalies and 3 d forward magnetic modeling the total magnetization vector obtained by this method is defined by a module of 4 5 a m 1 and a direction d 20 degrees and i 30 degrees comparing the paleomagnetic pole obtained from this direction with the apparent polar wander path of africa for the last 160 myr it is concluded that the main component of the total magnetization vector is probably a primary natural remanent magnetization nrm which could have been acquired between 60 and 100 ma this result suggests that the emplacement of magmas at shallow depths linked to the beginning of volcanism in lanzarote took place during the upper cretaceous thus providing the first evidence of a timeline for the early formative stages of this volcanic island

offshore continuation of volcanic rift zones el hierro canary islands el hierro is the youngest and most southwesterly of the seven canary islands the established view based on subaerial geology is that el hierro is a classic example of an oceanic island with 120 spaced volcanic rift arms vrzs forming a mercedes star however new offshore data do not support this simple interpretation instead of the discrete ridges of vrzs we observe to the nw and ne broad areas of irregular morphology which suggest that rifting activity might not be confined to narrow zones furthermore our data suggest that the anomalously long and steep flanked southern ridge could be part of an older eroded volcanic edifice that predates much of the other submarine flanks of el hierro the southern ridge has a distinctive gullied morphology which strongly contrasts with adjacent flanks there is also a 400 m deep saddle in its longitudinal profile 15 km from the coastline which we interpret as evidence that the southern ridge did not form by continuous dyke intrusion from the el hierro volcanic centre south of the saddle mean flank slopes are 10 steeper 30 with a sharp slope break at 3700 m between the ridge and smoothly sedimented seafloor these steeper slopes and lack of landslide scars to the south of the saddle indicate that the southern ridge is a stable edifice relative to the rest of el hierro surrounding sediments to the southeast appear to onlap the southern ridge a large landslide deposit el julan estimated age 200 ka occurs to the west of the ridge this landslide appears to have been constrained from spreading southeastwards by the southern ridge resulting in an elevation difference of 300 m for the seafloor on either side of the ridge

repeated magmatic intrusions at el hierro island following the 2011 2012 submarine eruption abstract after more than 200 years of quiescence in july 2011 an intense seismic swarm was detected beneath the center of el hierro island canary islands culminating on 10 october 2011 in a submarine eruption 2 km off the southern coast although the eruption officially ended on 5 march 2012 magmatic activity continued in the area from june 2012 to march 2014 six earthquake swarms indicative of magmatic intrusions were detected underneath the island we have studied these post eruption intrusive events using gps and insar techniques to characterize the ground surface deformation produced by each of these intrusions and to determine the optimal source parameters geometry location depth volume change source inversions provide insight into the depth of the intrusions 11 16 km and the volume change associated with each of them between 0 02 and 0 13 km 3 during this period 20 cm of uplift was detected in the central western part of the island corresponding to approximately 0 32 0 38 km 3 of magma intruded beneath the volcano we suggest that these intrusions result from deep magma migrating from the mantle trapped at the mantle lower crust discontinuity in the form of sill like bodies this study using joint inversion of gps and insar data in a post eruption period provides important insight into the characteristics of the magmatic plumbing system of el hierro an oceanic intraplate volcanic island

anomalously shallow palaeomagnetic inclinations and the question of the age of the canarian archipelago summary extensive geological geophysical and geochronological data available from the canary islands establish conclusively that formation of the oldest subaerial volcanic structure of the islands began during the miocene a mid cretaceous age for these volcanic formations has been postulated in previous works on the basis of palaeomagnetic determinations the results obtained in the present palaeomagnetic study of lanzarote include analysis of the record of variations of magnetic inclination in boreholes that penetrate the whole of the oldest volcanic series they show that the excessive age previously assigned to these formations is due to the utilization of volcanic units with abnormally low 15 magnetic inclinations lgis in lanzarote lavas exhibiting lgis appear interbedded in a volcanic series that overall shows a typical miocene inclination 45 the units stratigraphically beneath and above the lgi horizons give in fact directions consistent with the middle upper miocene field direction d 359 i 45 with k 29 a95 6 7 and a palaeopole of 87 n 178 e thereby confirming the miocene age of the oldest subaerial volcanics of lanzarote short excursions of the geomagnetic field seem likely to be the explanation for these lgis since other factors such as tectonic tilting post eruptive modification of the primary remanence or errors in sample orientation can be disregarded the detection in the canary archipelago of volcanic units with abnormally low magnetic inclinations seems to be related to the relatively continuous record of the geomagnetic field in rapidly growing volcanic edifices as seems to be indicated by the presence of a few usually one or two short polarity events in volcanic suites of several hundred metres thickness

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

the crustal structure of el hierro canary islands from 3 d gravity inversion el hierro is the youngest and westernmost island of the canarian archipelago due to its singular and interesting characteristics with extensive landsliding studying its crustal structure can provide very useful information about its origin and evolution with this aim we use the gravity inversion methodology obtaining a crustal model of mass distribution we performed a gravity survey of the entire island completing the gravity anomaly map of this area with marine data from the united states geological survey the calculated bouguer gravity anomaly map was studied using a covariance analysis and the least squares technique to obtain crustal information from these data we used a 3d gravity inversion based on genetic algorithms ga thus our inversion technique aims to determine the geometry of the sources of the observed gravity field upon a prismatic partition of the subsoil volume and adopting a priori density contrast values the results of this gravity study of el hierro island show the correlation of several volcanic structures with the distribution of the gravity field sources the characteristic triple rift system of the island is associated with low density areas and the older volcanic stages with high density structures we also found differences among the structures related to the several landslides which helped the island takes shape

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

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

prodigious submarine landslides on the hawaiian ridge the extensive area covered by major submarine mass wasting deposits on or near the hawaiian ridge has been delimited by systematic mapping of the hawaiian exclusive economic zone using the side looking sonar system gloria these surveys show that slumps and debris avalanche deposits are exposed over about 100 000 km2 of the ridge and adjacent seafloor from kauai to hawaii covering an area more than 5 times the land area of the islands some of the individual debris avalanches are more than 200 km long and about 5000 km3 in volume ranking them among the largest on earth the slope failures that produce these deposits begin early in the history of individual volcanoes when they are small submarine seamounts culminate near the end of subaerial shield building and apparently continue long after dormancy consequently landslide debris is an important element in the internal structure of the volcanoes the dynamic behavior of the volcanoes can be modulated by slope failure and the structural features of the landslides are related to elements of the volcanoes including rift zones and fault systems the landslides are of two general types slumps and debris avalanches the slumps are slow moving wide up to 110 km and thick about 10 km with transverse blocky ridges and steep toes the debris avalanches are fast moving long up to 230 km compared to width and thinner 0 05 2 km they commonly have a well defined amphitheater at their head and hummocky terrain in the lower part oceanic disturbance caused by rapid emplacement of debris avalanches may have produced high level wave deposits such as the 365 m elevation hulopoe gravel on lanai that are found on several islands most present day submarine canyons were originally carved subaerially in the upper parts of debris avalanches subaerial canyon cutting was apparently promoted by the recently steepened and stripped slopes of the landslide amphitheaters

soil gas radon emissions and volcanic activity at el hierro canary islands the 2011 2012 submarine eruption 1 soil gas radon 222rn and thoron 220rn activities have been continuously measured during the period of the recent volcanic unrest that occurred at el hierro canary islands at two different monitoring stations namely hie02 and hie03 significant increases in soil 222rn activity and 222rn 220rn ratio from the soil were observed at both stations prior to the 2011 2012 submarine eruption off the coast of el hierro showing the highest increases before the eruption onset and before the occurrence of the strongest seismic event m 4 6 statistical analysis showed that the long term temporal trend of filtered radon data matched closely that of seismic energy release during the volcanic unrest the observed increases of 222rn are related to the rock fracturing processes seismic activity and the magmatic co2 outflow increase as observed in hie03 station

coherent intrusion complexes in large basaltic volcanoes a new structural model abstract highly concentrated coherent intrusion complexes consisting of thousands of small mafic intrusions occur in probably all major basaltic volcanoes and play an important role in volcano development magma excursions from the high level chamber travel laterally along a surface of neutral buoyancy at the margin of a complex and cause the complex to grow the limited distance however that narrow intrusions can propagate before becoming blocked causes complexes to be wedge like intrusive dike complexes underlie rift zones and asymmetric growth of the dike wedge causes rift zones of shield volcanoes to become non collinear and may initiate a third rift zone in the obtuse angle downbowing of stress trajectories across complexes causes dikes to be non vertical and results in axial subsidence intrusive sheet complexes form instead of dike complexes in volcanic systems that have a restricted ability to expand laterally and accommodate intrusions by expanding vertically instead downbowing of stress trajectories causes sheets to be non horizontal and this combined with subsidence increasing toward the thicker part of the sheet wedge produces the inward and inwardly increasing dip that characterizes cone sheet complexes this mechanism for cone sheets differs considerably from previously proposed mechanisms successive injections of sheets at the top of a sheet complex probably offers the most efficient means of powering a high intensity geothermal field such as the 5000 mw grimsvotn system in iceland it is inferred that similar mechanisms to those in major basaltic edifices operate in spreading ridges study of basaltic edifices has the potential to contribute significantly to the understanding of spreading ridges

underwater records of submarine volcanic activity el hierro canary islands 2011 2012 eruption abstract we present the monitoring of a submarine volcanic eruption that took place near the southernmost emerged land of el hierro island canary islands spain from october 2011 to february 2012 right after the onset of the eruption in mid october 2011 we deployed an offshore geophone array for the purpose of monitoring the submarine eruptive activity signals it acquired continuous data from october 2011 to may 2012 sometime after the end of the eruption the array consisted of 8 high frequency 3 component geophones assembled into a cable string with 6 m of separation the geophone string was installed in la restinga harbor at a distance of less than 2 km from the volcanic edifice the dataset acquired with the array is a unique continuous acoustic record of the activity associated with this eruption we analyzed the continuous signal of the eruptive activity with special interest in those events reflecting the eruption dynamics our results show that the geophone array was recording acoustic waves from a back azimuth source corresponding to the position of the submarine vent traveling at a speed of 1510 m s compatible with the speed of sound in water acoustic data shows a good correlation with the seismic data recorded on land for the case of earthquake occurrence in addition it provides relevant information towards the understanding of the eruptive surface activity therefore this methodology can be successfully used in cases of submarine eruptions

33 000 yr k ar dating of the volcano tectonic horst of the isle of ischia gulf of naples the gulf of naples corresponds to a tectonic sink connected with recent volcanic activity in the south campanian area phlegrean fields ischia and vesuvius at its extreme northwest the isle of ischia was early recognized as a volcano tectonic horst by rittmann1 previous data2 concluded that its uplift ended around 300 000 yr and that the green tuff formation of which it is predominantly composed had an age of some 700 000 yr but tectonic and morphological studies together with original tephrostratigraphical observations on the slope of the horst led us to do some new k ar datings these revealed that the 780 m uplift of the horst from the sea level is younger than 33 000 yr the green tuff which was considered to be the oldest volcanic unit in the island is now dated at 56 000 yr its eruption following the dismantlement of a first volcanic complex now dated as not older than 130 000 yr

three armed rifts or masked radial pattern of eruptive fissures the intriguing case of el hierro volcano canary islands abstract using new surface structural data as well as subsurface structural data obtained from seventeen water galleries we provide a comprehensive model of the volcano tectonic evolution of el hierro canary islands we have identified measured and analysed more than 1700 volcano structural elements including vents eruptive fissures dykes and faults the new data provide important information on the main structural patterns of the island and on its stress and strain fields all of which are crucial for reliable hazard assessments we conducted temporal and spatial analyses of the main structural elements focusing on their relative age and association with the three main cycles in the construction of the island the tinor edifice the el golfo las playas edifice and the rift volcanism a radial strike distribution which can be related to constructive episodes is observed in the on land structures a similar strike distribution is seen in the submarine eruptive fissures which are radial with respect to the centre of the island however the volcano structural elements identified onshore and reflecting the entire volcano tectonic evolution of the island also show a predominant ne sw strike which coincides with the main regional trend of the canary archipelago as a whole two other dominant directions of structural elements n s and wnw ese are evident from the establishment of the el golfo las playas edifice during the second constructive cycle we suggest that the radial striking structures reflect comparatively uniform stress fields during the constructive episodes mainly conditioned by the combination of overburden pressure gravitational spreading and magma induced stresses in each of the volcanic edifices by contrast in the shallower parts of the edifice the ne sw n s and wnw ese striking structures reflect local stress fields related to the formation of mega landslides and masking the general and regional radial patterns