stratigraphy and k ar ages across the west flank of the northeast iceland axial rift zone in relation to the 7 ma volcano tectonic reorganization of iceland lithostratigraphy magnetostratigraphy and new k ar ages from the region between eyjafjordur and skjalfandi north central iceland reflect tectonic reorganization of crustal accretion zone activity 7 ma two flood basalt piles are in unconformable contact along this western flank of the northeast iceland axial rift zone neiarz the older ranges in age from 9 5 to 13 ma and is largely composed of tholeiite flows in eastern dalsmynni the upper to middle portions of this older basaltic pile define a 15 35 se dipping monoclinal flexure developed 6 7 ma during early development of the present neiarz lavas of a flood basalt group younger than about 6 5 ma were deposited unconformably on the older flexured basalt pile these postflexure age flows mostly consist of compound doleritic basalts and olivine tholeiites possible tillites are found in the upper portion of this sequence the unconformity between the older and younger basalt piles represents a major structural temporal and lithological boundary in north central iceland zeolite zones appear subhorizontal through the dalsmynni flexure zone and have been largely reset subsequent to flexuring by westward onlap of the younger basalt sequence onto the older subsided and flexured flows radiometrie ages regional isochron patterns and timing constraints for tjornes fracture zone related shear deformation indicate the model of a singular 130 km eastward jump of the axial rift zone in north iceland 6 7 ma is too simple crustal accretion older than 12 ma along a proto neiarz is apparently required indicating that northern iceland has had multiple branched crustal accretion zones up until about 7 ma at which time a single spreading zone along the present neiarz developed an eastward shift of axial rift zone activity 6 7 ma in southwestern iceland is time correlative with reorganization of spreading activity in northern iceland our proposed 6 7 ma reorganization of axial rift zone activity on land is time correlative with an independently proposed increase in discharge from the iceland mantle plume

change in climate ocean and ice sheet conditions in the ross embayment antarctica at 6 ka evidence from the ross embayment antarctica suggests an abrupt cooling and a concomitant increase in sea ice cover at about 6000 sp 6 ka stable isotope delta d concentrations in the taylor dome ice core at the western edge of the ross embayment decline rapidly after 6 ka and continue to decline through the late holocene methanesulfonic acid concentrations at taylor dome show opposite trends to delta d sediment cores from the western ross sea show a percentage minimum for the sea ice diatom fragilariopsis curta between 9 and 6 ka when taylor dome delta d values are highest followed by an increase through the late holocene radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the ross embayment ceased atabout 6 ka coincident with the environmental changes inferred from the sediment and ice core records the similarity in timing suggests an important role for climate in controlling the evolution of ice shelf margins following the end of the last 9 glaciation

longitudinal strike slip faults in oceanic rifting a mesostructural study from western to southeastern iceland abstract mesostructural analysis carried out in several localities of western southern central and southeastern iceland shows an unexpectedly frequent occurrence of strike slip faults parallel to or lying at relatively small angles with the axis of rifting some faults can be interpreted in terms of shear parallel to the rifts whereas others form conjugate systems referable to rift parallel compression axial shear can be explained by the accommodation of differences in the directions of tectonic extension between different segments of the axial rift system and subordinately by lateral rift parallel displacements between the major lithospheric plates axial compression may be attributable to rift oblique transform shear or to mantle transport parallel to the spreading axis compensating local deficiencies in mantle upwelling the data regard 1974 fault surfaces mainly small scale

deducing the thermal structure in the tongue of gornergletscher switzerland from radar surveys and borehole measurements we present the thermal distribution in the confluence area of gorner and grenzgletscher valais switzerland the area was mapped by ice penetrating radar at 1 5 and 40 mhz the higher frequency data reveal a thick surface layer of low backscatter in the center of the grenzgletscher branch based on datasets of borehole temperature measurements and flow velocity we interpret this as a thick layer of cold ice advected from the accumulation region of grenzgletscher along seven profiles the base of the low backscatter zone can be found at a maximum depths between approxi mately 100 and 200 m laterally the layer extends some 400 m 1 3 of the width of the grenz gletscher branch the lower boundary of the low backscatter zone is systematically higher than the cold temperate transition surface found in the boreholes this discrepancy is attributed to the direct sensitivity of radar backscatter to liquid water inclusions rather than to the temperature distributions as observed in boreholes we present the current state of the cold layer and discuss its influence on other glacier characteristics

a relative intercomparison between variable wave shoaling breaking and transition zone formulations the description of nearshore structural and sedimentary dynamics is highly dependant on a quantification of the nearshore wave regime which is subject to bathymetry induced transformation effects assuming straight and parallel bottom contours computed wave heights and water levels using variable wave shoaling incipient breaking wave decay and transition zone formulations are compared with measurements

major features and forcing of high latitude northern hemisphere atmospheric circulation using a 110 000 year long glaciochemical series the greenland ice sheet project 2 glaciochemical series sodium potassium ammonium calcium magnesium sulfate nitrate and chloride provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over both the high latitudes and mid low latitudes of the northern hemisphere interpretation of this record reveals a diverse array of environmental signatures that include the documentation of anthropogenically derived pollutants volcanic and biomass burning events storminess over marine surfaces continental aridity and biogenic source strength plus information related to the controls on both high and low frequency climate events of the last 110 000 years climate forcings investigated include changes in insolation of the order of the major orbital cycles that control the long term behavior of atmospheric circulation patterns through changes in ice volume sea level events such as the heinrich events massive discharges of icebergs first identified in the marine record that are found to operate on a 6100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics and rapid climate change events massive reorganizations of atmospheric circulation that are demonstrated to operate on 1450 year cycles changes in insolation and associated positive feedbacks related to ice sheets may assist in explaining favorable time periods and controls on the amplitude of massive rapid climate change events explanation for the exact timing and global synchroneity of these events is however more complicated preliminary evidence points to possible solar variability climate associations for these events and perhaps others that are embedded in our ice core derived atmospheric circulation records

seismological evidence of active faulting in the tendaho rift afar triangle ethiopia a temporary network has been used to study the seismic activity in the central northern part of the tendaho rift afar triangle ethiopia small size earthquakes m 2 5 characterize the seismicity during the time interval 1993 1994 when the seismic array was operating shocks are mainly located in the central part of the tendaho rift and their epicentral distribution highlights a remarkable coincidence with nw se trending tectonically active structures focal depths are confined in the range of 3 8 km the few acceptable fault plane solutions suggest the occurrence of both strike slip and dip slip rupture mechanisms which are often characterized by a nodal plane oriented approximately nw se a detailed study of earthquake waveforms using polarization analysis showed the occurrence of splitting phenomena for the s waves despite the differences in focal mechanisms the similarity of the faster s wave directions nw se to nnw sse suggests that the direction of geological structures and or the systems of fractures adjacent to the faults could bias shear wave propagation the splitting time between fast and slow shear waves shows no systematic relationship with either hypocentral distance or focal depth suggesting that the anisotropic volume is constrained to depths shallower than 3 km

chemical composition of fresh snow from glaciar marinelli tierra del fuego chile a fresh snow sampling campaign was conducted during the late austral summer of 2006 in the accumulation zone of glaciar marinelli located in the cordillera darwin tierra del fuego chile snow samples were analyzed for stable isotopes d 18 o major soluble ions na k ca 2 mg 2 cl no3 so4 2 ms and major and trace elements na mg al fe ca sr cd cs ba la ce pr dy ho er bi u as ti v cr mn the dominance of marine chemistry resembles that in studies from patagonian glaciers snow chemistry was dominantly loaded by marine species cl na and ssso4 2 while contributions of crustal species e g al and fe were very low empirical orthogonal function analysis suggests two possible dust sources one represented by al and fe and the other by la ce and pr enrichment factor calculations suggest the majority of elements are within average upper crustal ratios but major enrichments of bi and cd hundreds of times suggest possible anthropogenic sources linear correlation ofd 18 o and barometric pressure r 0 60 p 0 007 suggests a potential amount effect relationship between depletedd 18 o ratios and stronger storm conditions e g greater precipitation the snow chemistry records from glaciar marinelli are the first measured in tierra del fuego the southernmost glaciated region outside antarctica

tectonic deformation by rotating parallel faults the bookshelf mechanism abstract in various tectonic environments extension of crustal parts and shear distortion has been accommodated by the rotation of an array of parallel faults because of its kinematic resemblance to the tilting of a row of books on a shelf the tectonic process may be referred to as a bookshelf mechanism its most important manifestions are cross faulting between normal faults or parallel wrench faults the extension of deltaic slope deposits and all forms of tilted block tectonics kinematically there are two basic modes of the mechanism a the dilational mode where rotating faults tend to open up and possibly become paths for fluid migration and b the domino style where reclining faults remain closed in both cases formation and rotation of the faults may take place in one tectonic event fault displacements may therefore often remain small and difficult to detect from the mechanical point of view bookshelf operations that accommodate shearing between parallel and predominantly parallel moving rock boundaries bookshelf mechanisms proper have to be differentiated from those operations responding to an imposed crustal extension or shortening after a review of geological evidence the process is addressed from a geomechanical point of view in order to determine the geological operating conditions and controlling parameters the crucial mechanical factor in the bookshelf mechanism is the component of normal stress that acts in the direction of the imposed displacement component parallel to the driving boundary plates in contrast to the usual assumption the driving shear stress on the boundary plates not only depends on the normal stress on the plates but it also varies with the value of the normal stress that acts inside the sheared material in the direction of the plate parallel displacement component it is the relationship between the two normal stresses that also determines the type of rotating parallel faults large scale rotation of parallel normal faults in domino style tilted block tectonics is primarily associated with the extension of ductile substrata from mechanical arguments and sand box experiments it has been inferred how the process and in particular the dip direction of the parallel faults is controlled by the way substratal extension progresses by means of the direction of a substratal squeeze flow the presence of a surface slope the strength anisotropy associated with fore set beds and by the configuration of competent boundaries of the extending overburden

strike slip faults in a rift area a transect in the afar triangle east africa abstract the afar triangle a diffuse triple junction where the red sea ethiopian and gulf of aden rifts converge is examined along an e w cross section in order to recognize traces of strike slip faulting summarily known from earlier studies both field evidences from slickensides and airphotograph or satellite image data indicate that strike slip faults although less numerous than normal ones occur throughout this area these faults mainly strike parallel or at small angles relative to rifting axes rather than transversal to them as would be expected if they were transforms strike slip subparallel to rifts is explained through lateral displacement between the major lithospheric plates around the junction or subordinately by a domino fault mechanism in zones of diffuse transform deformation faults at small angles with the rift axes often constitute conjugate systems suggesting along axis compression which is considered to be frequently induced by the lateral intraplate shift mentioned above in other cases this compression may develop in intervals between mantle plumes wedging up along a rift or at the head of a propagating rift the main lateral displacements among the boundary lithospheric plates during the last million of years are supposed to have been sinistral this does not challenge the notion of mainly divergent plate movements but adds to this divergence an anticlockwise shift of the plates around the junction

electrical conductivity measurements from the gisp2 and grip greenland ice cores the direct current electrical conductivity of glacial ice depends on its acidity1 3 and can also indicate changes in climate as ice formed in cold dusty periods has a high concentration of alkaline dust1 4 5 which significantly reduces the conductivity6 7 compared to warmer less dusty periods here we present electrical conductivity records for the greenland ice sheet project 2 gisp2 and greenland ice core project grip ice cores drilled 28 km apart to enable direct comparison of the results the upper parts of both records are consistent with previous evidence from other greenland cores4 8 12 for a stable greenland climate during the holocene and a series of warm events punctuating the last glacial period however there is a significant discrepancy between the two records in the bottom 10 of the cores calling into question recent reports of climate variability in the last interglacial4 8 and the penultimate glaciation8 at this stage it is too early to say what exactly is causing the discrepancy although ice flow may have introduced some discontinuities into the records further work will be necessary to establish how much climatic information it will eventually be possible to extract from the lower parts of the two cores

deformation in the vicinity of ice divides calculs numeriques aux elements finis de la variation de la vitesse horizontale avec la profondeur au voisinage d une difference de la glace symetrique isotherme et ou glissement sur un lit plat

west antarctica s sensitivity to natural and human forced climate change over the holocene the location and intensity of the austral westerlies strongly influence southern hemisphere precipitation and heat transport with consequences for human society and ecosystems with future warming global climate models project increased aridity in southern mid latitudes related to continued poleward contraction of the austral westerlies we utilize antarctic ice cores to investigate past and to set the stage for the prediction of future behaviour of the westerlies we show that holocene west antarctic ice core reconstructions of atmospheric circulation sensitively record naturally forced progressive as well as abrupt changes we also show that recent poleward migration of the westerlies coincident with increased emission of greenhouse gases and the antarctic ozone hole has led to unprecedented penetration compared with 100 000 years ago of air masses bringing warmth extra antarctic source dust and anthropogenic pollutants into west antarctica copyright 2012 john wiley sons ltd

possible icelandic tephra found in european colle gnifetti glacier volcanic ash tephra provides unique time markers isochrons that are often used as an independent age control tool for stratigraphic correlations of paleoclimate archives from ice cores however little credence has been given to the notion of finding tephra in ice cores collected in the european alps because of the relatively large distance from volcanic sources and the presumed nature of regional atmospheric circulation patterns we filtered particles from melted ice core drilling chips gathered roughly every meter during a 2013 drilling operation at colle gnifetti glacier in the swiss italian alps 45 55 74 n 7 52 58 e 4450 m asl one filter preliminarily dated to the nineteenth century by annual layer counting contained a group of six visually similar tephra particles analyzing their chemistry using a scanning electron microscope equipped with an energy dispersive x ray spectrometer established that the six particles were volcanic in origin and are very similar in composition a distinctive geochemical signature pointing to a single volcanic eruption source we proposed that one of several massive nineteenth century eastern icelandic eruptions is a potential source given eruption timing size tephra dispersion area and similarities in chemical composition this first finding of tephra in an alpine ice core contributes to a regional tephrochronological framework that can be adapted for future correlation among different paleoclimate sequences

strike slip faults parallel to crustal spreading axes data from iceland and the afar depression slickenside studies in regions of crustal spreading such as iceland and the afar depression east africa reveal that a significant number of faults parallel and close to rift axes are strike slip rather than normal therefore the pattern of brittle deformation in these regions does not conform to the classic two dimensional schemes of oceanic tectonics and pre oceanic rifting dip slip and strike slip faulting presumably alternated along or in the vicinity of spreading axes indicate a varying stress field and a combination of transverse and longitudinal movements in iceland strike slip faults parallel to rifts are observed both west and east of the rift system as well as in a median area between overlapping rifts the mechanisms proposed for their origin include accommodation of oblique convergence or divergence of crustal sections due to variations of spreading directions along axis and the interaction of overlapping rifts in the afar depression this kind of fault is recorded west of the rift of asal and can be imputed to reflect an interaction among rifts in the vicinity of the afar triple junction rift parallel strike slip faults cannot however be assumed to be a feature of all crustal spreading axes due to the peculiarity of the examined regions both of them are hot spot areas and the afar depression lies at a triple junction

dynamics of the ice cap on king george island antarctica field measurements and numerical simulations king george island is located at the northern tip of the antarctic peninsula which is influenced by maritime climate conditions the observed mean annual air temperature at sea level is 2 4 c thus the ice cap is regarded as sensitive to changing climatic conditions ground penetrating radar surveys indicate a partly temperate ice cap with an extended water layer at the firn ice transition of the up to 700 m high ice cap measured firn temperatures are close to 0 c at the higher elevations and they differ considerably from the measured mean annual air temperature the aim of this paper is to present ice flow dynamics by means of observations and simulations of the flow velocities during several field campaigns from 1997 98 to 2008 09 ice surface velocities were derived with repeated differential gps measurements ice velocities vary from 0 7 m a 1 at the dome to 112 1 m a 1 along steep slopes for the western part of the ice cap a three dimensional diagnostic full stokes model was applied to calculate ice flow parameters of the numerical model were identified with respect to measured ice surface velocities the simulations indicate cold ice at higher elevations while temperate ice at lower elevations is consistent with the observations

potential for southern hemisphere climate surprises climate model results suggest that future climate change in antarctica will be accompanied by continued strengthening and poleward contraction of the southern ocean westerly wind belt paleoclimate records suggest past changes in the westerly winds can be abrupt and that healing of the antarctic ozone hole could lead to poleward contraction of the westerlies and increased meridional atmospheric transport of warm air regionally into antarctica an abrupt shift to more meridional circulation could lead to notable changes in moisture availability for extra antarctic regions increased antarctic ice sheet disintegration and more rapid sea level rise copyright 2015 the authors journal of quaternary science published by john wiley sons ltd

surface velocity and ice discharge of the ice cap on king george island antarctica glaciers on king george island antarctica have shown retreat and surface lowering in recent decades concurrent with increasing air temperatures a large portion of the glacier perimeter is ocean terminating suggesting possible large mass losses due to calving and submarine melting here we estimate the ice discharge into the ocean for the king george island ice cap l band synthetic aperture radar images covering the time span january 2008 to january 2011 over king george island are processed using an intensity tracking algorithm to obtain surface velocity measurements pixel offsets from 40 pairs of radar images are analysed and inverted to estimate a weighted average surface velocity field ice thicknesses are derived from simple principles of ice flow mechanics using the computed surface velocity fields and in situ thickness data the maximum ice surface speeds reach 225 m a 1 and the total ice discharge for the analysed flux gates of king george island is estimated to be 0 720 0 428 gt a 1 corresponding to a specific mass loss of 0 64 0 38 m w e a 1 over the area of the entire ice cap 1127 km 2

visual stratigraphic dating of the gisp2 ice core basis reproducibility and application annual layers are visible in the greenland ice sheet project 2 ice core from central greenland allowing rapid dating of the core changes in bubble and grain structure caused by near surface primarily summertime formation of hoar complexes provide the main visible annual marker in the holocene and changes in cloudiness of the ice correlated with dustiness mark wisconsinan annual cycles both markers are evident and have been intercalibrated in early holocene ice layer counts are reproducible between different workers and for one worker at different times with 1 error over century length times in the holocene reproducibility is typically 5 in wisconsinan ice age ice and decreases with increasing age and depth cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50 000 years visible observations are not greatly degraded by brittle ice or many other core quality problems allowing construction of long consistently sampled time series high accuracy requires careful study of the core by dedicated observers

the marine record of deglaciation of the south shetland islands antarctica since the last glacial maximum abstract the marine geological record of the glacial retreat history of the south shetland islands is derived from the integration of seismic data core lithofacies radiocarbon ages and geomorphological data from two study areas on the northern shelf we present one of the first published multibeam bathymetric images of the seafloor this new image combined with descriptions of new and existing short sediment cores and high resolution seismic data from the continental shelf north of king george island are used to map a grounding zone wedge that marks the minimum seaward extent of the south shetland ice cap during the last glacial maximum seismic data multibeam bathymetry and sediment cores from maxwell bay on the opposite side of king george island are used to provide further spatial constrains on the history of grounding and retreat of the ice cap along the southern margin of the south shetland islands during the last glacial maximum the south shetland ice cap extended onto the outer continental shelf some 50 km north of its present location the ice grounded on the shelf in troughs in present water depths of almost 400 m it had a minimum thickness of 570 m and was also grounded in the deepest part of fjords and straits between the islands to the south the ice cap extended seaward of the mouths of fjords and straits to the steep northern boundary of the bransfield strait sediment eroded from the fjords and straits was deposited in prominent fans that extend into the bransfield strait and show evidence for an ice shelf that covered the bransfield strait during the last glacial maximum a long drill core shaldril in maxwell bay and several jumbo piston cores yielded carbonate material used to constrain the timing and spatial extent of glacial retreat within maxwell bay the oldest glacimarine sediments in the fjord date back to 14 1 to 14 8 ka and suggest an initial deglaciation earlier than most previous studies of the south shetland islands upper maxwell bay was ice free by 9 1 ka and most of maxwell bay proper was ice free by 5 9 ka except for the smaller tributary fjords of maxwell bay these smaller tributary fjords were ice free by 1 7 ka but may have been ice free earlier but reoccupied by a neoglacial advance that ended approximately 1 7 ka

transition zone width and implications for modeling surfzone hydrodynamics the surfzone associated with a wave breaking on a plane slope may be subdivided into three regions the transition zone the inner zone and the swash zone the transition zone is the region just shoreward of the point of wave breaking and is characterised by rapid wave decay and also by constant wave setdown and thus constant radiation stress in this paper an empirical expression for the width of this zone is developed from monochromatic wave data two techniques are proposed for the consideration of this phenomenon in the numerical modelling of surfzone hydrodynamics for random waves the implications of a zone of nearly constant radiation stress inside the breakpoint are examined with respect to wave induced current generation both cross shore and longshore and sediment transport prediction comparisons are made to both field and laboratory data from plane and undulating profiles

past volcanism and climate revealed by greenland ice cores abstract a new method is outlined for estimating the annual injection of volcanic acids mainly sulphuric into the upper troposphere and the stratosphere the potentiality of the method is demonstrated by data on a number of historically well known eruptions analyses of annual layers in a mid greenland ice core reveal a continuous year by year record of the volcanic activity north of 20 s back to a d 553 comparison with various climatic records suggests that periods of frequent and violent eruptions usually coincide with cold climatic conditions for example the highest volcanic activities since a d 553 occurred in a d 1250 1500 and a d 1550 1700 i e in the initial and the culminating phases of the little ice age

the afar depression transition between continental rifting and sea floor spreading abstract detailed geophysical and geological studies were undertaken in the 1970 s in the afar depression ethiopia in order to study the processes of continental break up occurring in this unique setting the afar is located between the ethiopian and somali plateaus and the red sea we have re evaluated the available seismic refraction and gravity data using modern interpretation techniques and incorporated new information derived from magnetic gravity seismicity and seismic refraction data the results of the re evaluation indicate that the afar depression is a transition zone between the continental rifts of kenya and the present ongoing sea floor spreading of the red sea and the gulf of aden in the depression itself the crust is greatly attenuated and is underlain by a low velocity 7 4 7 5 km s high temperature upper mantle material however it is still a continental crust which thins to the northeast and east towards the red sea and the gulf of aden it is not a newly formed oceanic crust as has been suggested in the past the trends of the areas of crustal thinning are indicated by the gravity anomalies the trend of the ethiopian rift reaches south afar where the trend of crustal thinning changes and becomes parallel to the red sea trend it is offset en echelon from the spreading area of the red sea which is marked by an alignment of gravity maxima the gulf of aden trend continues west towards the ethiopian rift the gravity trends coincide with areas of maximum crustal thinning and may thus suggest a possible triple junction in development

the manda inakir rift republic of djibouti a comparison with the asal rift and its geodynamic interpretation abstract asal ghoubbet and manda inakir two axial zones and the mak arrassou n s strike slip zone are located between the afar depression where significant crustal thinning is shown by geophysical data and the relatively thicker continental crust of the danakil horst these three active structures were formed in response to the counterclockwise motion of the danakil horst the two modes of response rift and strike slip faults are related to the orientation of the horst boundaries the boundaries perpendicular to the opening direction lead to extensional zones and rifts asal and manda lnakir the parallel boundaries give strike slip faults mak arrassou the two narrow subsided axial structures rift in rift located on the crustal discontinuity seem to represent a stage where after crustal thinning between 4 and 1 ma when the stratoid series was erupted the breaking point was reached these two axes though not genuine oceanic crust the older continental series are found under the axial series represent a proto oceanic stage and foreshadow the future ridges they also indicate the southwest border of the arabian plate including the danakil horst

new la icp ms cryocell and calibration technique for sub millimeter analysis of ice cores ice cores provide a robust reconstruction of past climate however development of timescales by annual layer counting essential to detailed climate reconstruction and interpretation on ice cores collected at low accumulation sites or in regions of compressed ice is problematic due to closely spaced layers ice core analysis by laser ablation inductively coupled plasma mass spectrometry la icp ms provides sub millimeter scale sampling resolution on the order of 100 m in this study and the low detection limits ng l 1 necessary to measure the chemical constituents preserved in ice cores we present a newly developed cryocell that can hold a 1m long section of ice core and an alternative strategy for calibration using ice core samples from central greenland we demonstrate the repeatability of multiple ablation passes highlight the improved sampling resolution verify the calibration technique and identify annual layers in the chemical profile in a deep section of an ice core where annual layers have not previously been identified using chemistry in addition using sections of cores from the swiss italian alps we illustrate the relationship between ca na and fe and particle concentration and conductivity and validate the la icp ms ca profile through a direct comparison with continuous flow analysis results

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

holocene oceanographic and glacial changes recorded in maxwell bay west antarctica abstract three holocene core sections from maxwell bay south shetland islands west antarctica are investigated using ms grain size toc foraminifera 18o and 13c 14c and 210pb in order to examine holocene oceanographic glacial and climatic changes in the region they come from 190 221 and 333 m water depths and the bay margin proximal locations complementing earlier studies from the deep central part the three records vary between locations and reflect combined marine and terrigenous influence from the open ocean and surrounding islands respectively the longest and best dated composite section comes from the inner part of the bay core jtc jpc 17 and extends back to 6 3 cal kyr bp close to the termination of the holocene climatic optimum a combination of dating problems and mixed foraminiferal assemblages prevented reliable interpretation of core jpc 15 from the outer part of the bay core jpc 16 collected from the inner bay near the inlet between king george and nelson islands revealed repeated highs in planktonic neogloboquadrina pachyderma occurrence during last 3000 yr these highs are interpreted as indicating periods of decreased meltwater flow into the bay and thus greater influence of open marine surface waters core jtc jpc 17 located closest to king george island and the collins ice cap records increased glacial conditions at 2000 cal yr bp this event is recorded by turbidite deposition at core site jpc 16 major components of the benthic foraminiferal assemblage indicate decreasing tolerance to near glacier or near shore conditions however local climate variability appears to have overall little impact on benthic foraminiferal biota thus it is unlikely that in similar settings recent warming would be strongly manifest as changes in benthic foraminiferal communities stable isotopic analysis is based on cassidulinoides parkerianus and globocassidulina biora subtle decrease in 18o at 3500 cal yr bp followed by episodic increases at 1000 cal yr bp and in the youngest part of the record appear to correlate with the period prior to the beginning of the neoglacial with medieval warm period and with post little ice age warming respectively the latest event is also marked by a significant increase in sediment accumulation rate in the second half of the 20th century

climate variability in west antarctica derived from annual accumulation rate records from itase firn ice cores thirteen annually resolved accumulation rate records covering the last 200 years from the pine island thwaites and ross drainage systems and the south pole are used to examine climate variability over west antarctica accumulation is controlled spatially by the topography of the ice sheet and temporally by changes in moisture transport and cyclonic activity a comparison of mean accumulation since 1970 at each site to the long term mean indicates an increase in accumulation for sites located in the western sector of the pine island thwaites drainage system accumulation is negatively associated with the southern oscillation index soi for sites near the ice divide and periods of sustained negative soi 1940 42 1991 95 correspond to above mean accumulation at most sites correlations of the accumulation rate records with sea level pressure slp and the soi suggest that accumulation near the ice divide and in the ross drainage system may be associated with the mid latitudes the post 1970 increase in accumulation coupled with strong slp accumulation rate correlations near the coast suggests recent intensification of cyclonic activity in the pine island thwaites drainage system

geometry and thermal regime of the king george island ice cap antarctica from gpr and gps king george island is the largest of the south shetland islands close to the tip of the antarctic peninsula the annual mean temperature on the island has increased by 1 c during the past three decades and the ice cap that covers the majority of the island is sensitive to climatic change we present data from two field campaigns 1997 and 2007 700 km of global positioning system gps and ground penetrating radar gpr profiles were collected on arctowski icefield and on the adjacent central part the data were analysed to determine the surface and bed topography and the thermal regime of the ice average ice thickness is 250 m and maximum thickness is 420 m the gpr profiles show isochrones throughout the ice cap which depict the uparching of raymond bumps beneath or close to the ice divides a water table from percolation of meltwater in the snowpack shows the firn ice boundary at 35 m depth the firn layer may be temperate due to the release of latent heat in the area below 400 m a s l backscatter by water inclusions is abundant for ice depths below the water table we interpret this as evidence for temperate ice scatter decreases significantly above 400 m ice temperatures below the water table in this part of the ice cap are subject to further field and modelling investigations

antarctic ice rises and rumples their properties and significance for ice sheet dynamics and evolution locally grounded features in ice shelves called ice rises and rumples play a key role buttressing discharge from the antarctic ice sheet and regulating its contribution to sea level ice rises typically rise several hundreds of meters above the surrounding ice shelf shelf flow is diverted around them on the other hand shelf ice flows across ice rumples which typically rise only a few tens of meters above the ice shelf ice rises contain rich histories of deglaciation and climate that extend back over timescales ranging from a few millennia to beyond the last glacial maximum numerical model results have shown that the buttressing effects of ice rises and rumples are significant but details of processes and how they evolve remain poorly understood fundamental information about the conditions and processes that cause transitions between floating ice shelves ice rises and ice rumples is needed in order to assess their impact on ice sheet behavior targeted high resolution observational data are needed to evaluate and improve prognostic numerical models and parameterizations of the effects of small scale pinning points on grounding zone dynamics

the greenland ice sheet project 2 depth age scale methods and results the greenland ice sheet project 2 gisp2 depth age scale is presented based on a multiparameter continuous count approach to a depth of 2800 m using a systematic combination of parameters that have never been used to this extent before the ice at 2800 m is dated at 110 000 years b p with an estimated error ranging from 1 to 10 in the top 2500 m of the core and averaging 20 between 2500 and 2800 m parameters used to date the core include visual stratigraphy oxygen isotopic ratios of the ice electrical conductivity measurements laser light scattering from dust volcanic signals and major ion chemistry gisp2 ages for major climatic events agree with independent ages based on varve chronologies calibrated radiocarbon dates and other techniques within the combined uncertainties good agreement also is obtained with greenland ice core project ice core dates and with the specmap marine timescale after correlation through the 18 o of o 2 although the core is deformed below 2800 m and the continuity of the record is unclear we attempted to date this section of the core on the basis of the laser light scattering of dust in the ice

ultra high resolution snapshots of three multi decadal periods in an antarctic ice core we offer the first sub seasonal view of glacial age archives from the siple dome a sdma ice core using the ultra high resolution capabilities of a newly developed laser ablation inductively coupled plasma mass spectrometry la icp ms 121 m sampling resolution system capable of conducting multi element glaciochemical analysis our ultra high resolution data demonstrates that 1 the sdma ice core record can be annually dated based on seasonality in chemical inputs at a depth not previously possible using previous glaciochemical sampling methods 2 winter accumulation at the sd site was greater than summer accumulation during the three late glacial periods selected 15 3 17 3 21 4 ka ago in this study and 3 resulting annual layer thicknesses results show greater variability than the current sd ice core depth age model brook and others 2005 possibly due to depositional effects such as wind scouring and or decadal variability in snow accumulation that is not captured by the resolution of the current depth age model

low frequency radar sounding of temperate ice masses in southern alaska we present the warm ice sounding explorer wise a low frequency 2 5 mhz radar for the sounding of temperate ice wise deployment in southern alaska in 2008 and 2012 provides comprehensive measurements of glacier thickness reveals deep valleys beneath glaciers and the full extent of zones grounded below sea level the east branch of columbia glacier is deeper that its main branch and remains below sea level 20 km farther inland ice is 1000 m deep on tazlina glacier on bering glacier two sills separate three deep bed depressions 1200 m that coincide with the dynamic balance lines during surges the piedmont lobe of malaspina glacier and the lower reaches of hubbard glacier are entirely grounded below sea level 40 and 10 km respectively from their termini knowledge of ice thickness in these regions helps better understand their glacier dynamics mass balance and impact on sea level key points low frequency radar sounding works extremely well in alaska ice is much thicker than suggested by limited surveys data reveals full extent of areas grounded below sea level 2013 american geophysical union all rights reserved

extension direction re orientation in the oceanic rift of iceland and comparison with continental rifts abstract in this study we report the results of a structural analysis carried out on fault systems that form the active rift segments of two areas of iceland namely 1 the northern part of the eastern rift segment northern volcanic zone nvz and 2 the western rift segment that include the western volcanic zone thingvellir area and the reykjanes peninsula in the n s trending nvz mainly krafla volcanic area the obtained extension directions trend around ese at thingvellir the extension directions trend ca nw se and are perpendicular to the main ne sw trending faults in the ene wsw trending tectono magmatic segments of the reykjanes peninsula our data show a marked difference with the gps data and spreading directions the extension directions trend roughly orthogonal to the strike of the boundary faults in all the investigated sectors extension shows an overall southward increase in divergence from the regional directions indicated by gps vectors this behavior has been compared with the continental main ethiopian rift of east africa where structural studies show a re orientation of the extension direction between the rift margins and the internal sectors resulting in a divergence between local and regional extension directions aimed at investigating the causes of these differences we performed a new series of analogue models by varying different parameters such as rift obliquity and width our findings suggest that rift width exerts a primary control on the boundary axis variation of the extension direction in particular significant differences in fault orientation and local direction of extension between the margins and the rift axis are observed in wider rift valleys e g continental rift of ethiopia conversely fault orientation and local extension direction are much more homogeneous in narrower rift valleys e g rifts of iceland where a variations in the direction of extension from the margins to the rift axis are not observed

bar generating cross shore flow mechanisms on a beach random waves normally incident on a dissipative beach induce a variety of cross shore flows such as asymmetric oscillatory flow wave grouping induced long wave flow breaking induced turbulent flow and momentum decay induced undertow these flows are identified analyzed and hindcasted in a set of laboratory experiments with the aim of revealing the role of each of the flow mechanisms in the two dimensional case of bar generation on a beach

electrical measurements on the greenland ice sheet project 2 core the greenland ice sheet project 2 gisp2 electrical conductivity measurement ecm record is an indication of the concentration of h in the core the ecm detected seasonal variations in the nitrate concentration of the core which were used to assist in dating the core by annual layer counting volcanic eruptions that produce acidic aerosols are recorded in the ecm record evidence of biomass burning is detected by the ecm because fire related ammonium emissions neutralize the acids in the core rapid climate transitions associated with the younger dryas and dansgaard oeschger interstadial events alter the concentration of alkaline dust and are detected by the ecm the ecm has been used to develop stratigraphic ties between the gisp2 and the greenland ice core project cores users of the data should be aware of some instrument related artifacts in the ecm record

latitudinal variation in glacial erosion rates from patagonia and the antarctic peninsula 46 s 65 s we use extensive sedimentary and marine geophysical data to derive sediment volume based millennial time scale glacial erosion rates from glacially influenced fjords and bays across a broad latitudinal transect from central patagonia 46 s to the antarctic peninsula 65 s and to determine how glacial erosion rates change with increasing latitude and decreasing atmospheric temperatures we also calculate million year time scale erosion rates for the western antarctic peninsula cordillera and inner continental shelf from seismic stratigraphic analysis of the continental margin these results are complemented by erosion rates derived from existing thermochronology data sets apatite fission track and apatite u th he for both patagonia and the antarctic peninsula regions despite considerable regional variability our results show a clear trend of decreasing with increasing latitude millennial values span two orders of magnitude from 0 02 mm yr for illiad glacier on anvers island antarctica 64 5 s to 0 83 mm yr for san rafael glacier in northern patagonia 46 5 s regional averages are three times higher for the patagonian areas than the antarctic peninsula areas this trend is interpreted to result from a general decrease in temperature and water availability at the ice bedrock interface for the antarctic peninsula study sites erosion rates are highly clustered around 0 1 mm yr with the exception of maxwell bay for which the value is 0 36 mm yr in patagonia erosion rates are more variable than in the antarctic peninsula with ranging between 0 14 mm yr europa glacier area and 0 83 mm yr san rafael glacier area this regional variability in is interpreted as due to differences in hypsometry and bedrock resistance to erosion million year time scale values derived from thermochronology ages also decrease with latitude with maximum values decreasing from 0 9 1 1 mm yr north of 46 s to 0 1 0 2 mm yr south of 48 s in patagonia and reaching 0 2 0 3 mm yr in the antarctic peninsula the sediment based million year time scale estimates for the western antarctic peninsula cordillera indicate that glacial erosion rates increased by 25 30 after 5 3 ma from 0 09 mm yr 5 3 9 5 ma to 0 11 0 12 mm yr 5 3 ma for patagonia the decrease in long term erosion rates south of 46 s is interpreted to result from relatively long periods of slow glacial erosion associated with the ice masses having been colder subpolar on the southern patagonian cordillera and having eroded at rates comparable to those we obtained for the antarctic peninsula these long term erosion rates are 1 2 orders of magnitude lower than estimates based on recent sediment yields highlighting the transient nature of high sediment flux events however our sediment volume derived millennial time scale closely approximates the maximum values of tectonic time scale values derived from thermochronology ages our combined millennial and million year time scale glacial erosion data quantify the significant decrease in rates of glacially driven denudation at geological tectonic and millennial time scales with increasing latitude from patagonia to the antarctic peninsula highlighting the influence of climate on mountain denudation

timing of the most recent neoglacial advance and retreat in the south shetland islands antarctic peninsula insights from raised beaches and holocene uplift rates abstract the timing of the most recent neoglacial advance in the antarctic peninsula is important for establishing global climate teleconnections and providing important post glacial rebound corrections to gravity based satellite measurements of ice loss however obtaining accurate ages from terrestrial geomorphic and sedimentary indicators of the most recent neoglacial advance in antarctica has been hampered by the lack of historical records and the difficulty of dating materials in antarctica here we use a new approach to dating flights of raised beaches in the south shetland islands of the northern antarctic peninsula to bracket the age of a neoglacial advance that occurred between 1500 and 1700 ad broadly synchronous with compilations for the timing of the little ice age in the northern hemisphere our approach is based on optically stimulated luminescence of the underside of buried cobbles to obtain the age of beaches previously shown to have been deposited immediately inside and outside the moraines of the most recent neoglacial advance in addition these beaches mark the timing of an apparent change in the rate of isostatic rebound thought to be in response to the same glacial advance within the south shetland islands we use a maxwell viscoelastic model of glacial isostatic adjustment gia to determine whether the rates of uplift calculated from the raised beaches are realistic given the limited constraints on the ice advance during this most recent neoglacial advance our rebound model suggests that the subsequent melting of an additional 16 22 increase in the volume of ice within the south shetland islands would result in a subsequent uplift rate of 12 5 mm yr that lasted until 1840 ad resulting in a cumulative uplift of 2 5 m this uplift rate and magnitude are in close agreement with observed rates and magnitudes calculated from the raised beaches since the most recent neoglacial advance along the south shetland islands and falls within the range of uplift rates from similar settings such as alaska

dynamic source parameters of the march may 1969 serdo earthquake sequence in central afar ethiopia deduced from teleseismic body waves long period teleseismic p and s waveforms for the largest four earthquakes in the serdo sequence are compared with synthetic seismograms to infer mechanisms focal depths source time functions and dynamic energy release for all four events studied the mechanisms are predominantly strike slip depth estimates obtained for the four earthquakes by matching synthetic seismograms to the observations are found to lie between 5 and 8 km the azimuthal variation of observed body wave duration for the main event indicates that the rupture propagated from ne to sw average seismic moments obtained from body wave synthetics vary from 4 6 1017 to 2 5 1018 n m average final displacements stress drops and lengths of the fault are found to lie between 0 16 and 0 56 m 0 45 and 1 56 mpa and 10 and 16 km respectively the low stress drop value obtained may indicate the presence of softer materials near the source the energy release shows that the mode of energy release during the sequence took place in two steps mainly by the two largest shocks

polar ice stratigraphy from laser light scattering scattering from ice we demonstrate that laser light scattering lls off glacial pre holocene polar ice can be used to measure variations in dust concentration along sections of bubble free ice core we have used this technique with considerable success on the gisp2 ice core that was retrieved from central greenland down to bedrock the technique is fast non destructive and has a very high resolution 1 mm or less

strain accumulation across the asal ghoubbet rift djibouti east africa the asal ghoubbet rift in the republic of djibouti is a subaerial continuation of the gulf of aden ridge system many geological and tectonic arguments indicate that it represents one of the most typical spreading segments of the world rift system geodetic measurements regularly conducted from 1979 to 1983 across this area show an accumulation of extension in the inner floor of the rift valley with a rate of about 60 mm yr perpendicular to the normal faults that bound the rift periodic leveling surveys across major faults in the rift show vertical creep movements of about 5 to 10 mm yr although the observed deformations could be contamined by postseismic relaxation after a rifting episode in november 1978 the regularity and the magnitude of these movements during the last two years argue for a steady state mechanism of deformation of the rift valley the deformation is uniformly distributed in time and in space inside the inner floor of the rift the necking of the lithosphere in the central part of the rift and the high temperature gradient imply a ductile rheology in the inner floor which is stretched in a steady state process

methanesulfonic acid in a svalbard ice core as an indicator of ocean climate methanesulfonic acid msa is an atmospheric oxidation product of dimethyl sulfide produced by marine biota msa preserved in a svalbard glacier between 1920 and 1996 is compared with the sea surface temperature sst and sea ice extent of the surrounding ocean over the same period on decadal timescales high msa concentrations are found to be associated with warm sst and reduced sea ice extent msa appears to be influenced by climatic changes related to variations in the import of warm atlantic water to the barents sea atlantic water plays an important role in the arctic climate system therefore msa concentrations may indirectly reflect larger scale changes in the region and may be useful as a proxy for past climate

wave transformation in the nearshore zone a review this paper reviews works related to nearshore wave propagation with an emphasis on several aspects related to coastal morphodynamic modelling including randomness and directionality of waves energy transfer and dissipation in the surf zone shallow water non linearities and long period motions the first part briefly reviews four main issues in laboratory experiments and field campaigns the second part is devoted to spectral and probabilistic approaches then recent developments of advanced numerical models based on boussinesq equations are reviewed the last part is devoted to low frequency waves and vortical motions

seismotectonics of the central part of the south iceland seismic zone abstract the largest earthquakes in iceland are associated with strike slip faults in the south iceland seismic zone sisz major destructive earthquake sequences occur in this zone at an average interval of 80 years the last two sequences being in 1784 and 1896 the last major single earthquake in the zone was an earthquake of magnitude 7 m in 1912 the seismicity is mostly associated with a conjugate system of nne trending mainly right lateral faults and ene trending mainly left lateral faults but in addition there are many nw trending faults in the sisz particular attention is paid to the comparison between present day fault activity earthquake mechanisms and quaternary faulting fault slip data this comparison reveals a general similarity despite the temporal difference between these subsets independently collected the fault populations are well exposed in the hyaloclastite mountain vordufell near the central part of the south iceland seismic zone where considerable fault slip occurred during the earthquake sequences of 1784 and 1896 the cumulative displacement on most of these faults is 1 6 m in addition to the large scale faults we measured 79 minor faults displacements of the order of centimetres in the vordufell mountain most of the minor faults are left lateral analysis of these minor faults recording palaeostresses in rocks ranging in age from 3 1 to 0 7 ma as well as 50 focal mechanisms from a swarm of present day microearthquakes occurring beneath the vordufell mountain gave consistent results in terms of seismotectonic stress orientations of stress axes and ratios of principal stress differences this shows that the tectonic regime remained unchanged through recent times the results indicate however that there are two contrasting stress regimes in this part of the sisz the primary subset indicates nw se tension and ne sw compression whereas the secondary subset indicates nw se compression and ne sw tension we propose that the primary subset is consistent with the dominating time averaged regional stress field in the sisz this dominating stress field can be largely explained as a consequence of simple plate pull parallel with the spreading vector in south iceland the secondary subset and the associated stress field however may be partly related to stress release and rebound and partly to dike injections in the nearby segments of the rift zone in south iceland

initial reconnaissance for a south georgia ice core we present the first snow ice chemistry and ice radar results ever collected from south georgia as part of an initial reconnaissance with the ultimate goal of assessing the feasibility of a south georgia ice core to reconstruct past climate in the south atlantic south georgia is well situated to capture a record of past atmospheric chemical composition over the south atlantic and of past variability in the position and intensity of the austral westerlies the question is how well preserved an ice core record can be recovered from a region experiencing accelerated melting the results presented in this paper offer only a preliminary step in determining the feasibility of future deep ice coring on south georgia however this initial reconnaissance does provide some basic information including the chemistry of the atmosphere over south georgia relative to other southern hemisphere ice coring sites the potential for preservation of annual layers in old ice on the island a possible age for deep ice in the region and an estimate of glacier health in the lower elevation regions of the island

primary aerosol sea salt and soil dust deposited in greenland ice during the last climatic cycle comparison with east antarctic records ion chromatography data of ca mg cl and ca and coulter counter particle measurements are used to study the cycle of marine and continental primary aerosol reaching greenland in relation to climatic changes over the last 150 kyr a detailed comparison between greenland dome summit and antarctic vostok records provides new insight on a potential link between northern and southern patterns ca is a good indicator of continental input and is mainly emitted as caco3 an attempt is made to estimate the contribution of aluminosilicates using the concentration of insoluble particles greater than 0 5 m in diameter the relative abundance of non sea salt mg and ca and of aluminosilicate shows that the calcium content of continental background aerosol over greenland was much higher during the glacial age the neutralization capacity of carbonaceous aerosol is estimated the inverse relationship between 18o and continental input as well as the response of this input to the rapid climatic variations that have occurred during the second part of the glacial age are discussed in terms of source and transport modification in relation to the presence and the extent of the great laurentide ice cap the corresponding vostok profiles strongly suggest that some of the phenomena observed at high northern latitudes are of global concern the marine component of na nam is a good tracer of sea salt aerosol similarly to continental input it shows an inverse but more linear relationship with 18o the sensitivity of greenland and antarctic marine input to climate variations of small and large amplitude is compared and a corresponding estimation is made for the aeolian contribution the respective influence of atmospheric circulation and the water vapor cycle is discussed the chlorine to marine sodium weight ratio increases with temperature from values very close to the bulk seawater ratio during the last glacial maximum 18 20 kyr b p to values significantly higher during the holocene and warm eemian the corresponding excess of chloride hcl is discussed in terms of atmospheric transport taking into account the role of atmospheric acidity on sea salt fractionation processes owing to postdepositional phenomena similar vostok data must be considered cautiously nevertheless aerosol fractionation seems to have been much more important over the vostok site except during glacial extrema

historically unprecedented global glacier decline in the early 21st century observations show that glaciers around the world are in retreat and losing mass internationally coordinated for over a century glacier monitoring activities provide an unprecedented dataset of glacier observations from ground air and space glacier studies generally select specific parts of these datasets to obtain optimal assessments of the mass balance data relating to the impact that glaciers exercise on global sea level fluctuations or on regional runoff in this study we provide an overview and analysis of the main observational datasets compiled by the world glacier monitoring service wgms the dataset on glacier front variations 42000 since 1600 delivers clear evidence that centennial glacier retreat is a global phenomenon intermittent readvance periods at regional and decadal scale are normally restricted to a subsample of glaciers and have not come close to achieving the maximum positions of the little ice age or holocene glaciological and geodetic observations 5200since 1850 show that the rates of early 21st century mass loss are without precedent on a global scale at least for the time period observed and probably also for recorded history as indicated also in reconstructions from written and illustrated documents this strong imbalance implies that glaciers in many regions will very likely suffer further ice loss even if climate remains stable

geometry formation and development of tectonic fractures on the reykjanes peninsula southwest iceland abstract a study was made of 903 fractures most of which are of postglacial age on the reykjanes peninsula some 120 fractures belonging to the vogar fissure swarm he completely within the same postglacial lava flow and were studied in great detail for the vogar fractures 75 are pure tension fractures and 25 are normal faults the average length of the vogar fractures is 611 m the average width is 0 6 m the average spacing measured perpendicular to the average strike n54e of fractures is 456 m the estimated average depth is of the order of several hundreds of meters and the average throw of the faults is 2 3 m all major fractures on the peninsula appear to have formed by coalescence of smaller fractures as a result of absolute tensile stress the fractures group into four fissure swarms each being a part of a volcanic system which it is proposed is fed by an elongated partially molten magma reservoir located at a depth of about 8 km beneath the peninsula it is suggested that a slight magmatic pressure increase in these reservoirs and resulting uplift and tensile stress at the surface is the main cause of postglacial fracture formation

hengill triple junction sw iceland 1 tectonic structure and the spatial and temporal distribution of local earthquakes the hengill area is an unstable ridge ridge transform triple junction in sw iceland it contains the active central volcano hengill associated with the present accretionary zone and the extinct grensdalur central volcano associated with an accretionary zone that became inactive at about 0 7 m y when the locus of spreading migrated about 5 km w to the hengill zone the dominant tectonic trend of the area is n25 e parallel to the accretionary zones but transverse tectonic topographic features have also developed in the neighborhood of the two central volcanoes these result from local modification of the regional stress field associated with the spreading by radially symmetric stress fields associated with the volcanoes and the migration of volcanism a double high temperature geothermal system mirrors the double volcanic system the transform branch of the triple junction is represented by an ew striking zone of historic destructive earthquakes in the s of the area a seismological study was conducted with the aims of studying the tectonic structure and evaluating the passive seismic method as a geothermal prospecting tool the seismicity may be broadly divided into two groups first infrequent intense episodes of crustal movement occur that are associated with the release of tectonic stress along the plate boundary second continuous small magnitude activity occurs on a day to day basis this activity is mostly associated with the extinct grensdalur central volcano not the present plate boundary statistically significant temporal variations in b accompanied a swarm in the transform zone the continuous small magnitude activity may be geothermal in origin releasing thermal stress and not associated with plate boundary tectonics