late pliocene and quaternary glaciations of new zealand abstract evidence of late pliocene glaciations is fragmentary the ross glaciation in northwest south island is correlated with the first marine faunal evidence of marked cooling in the wanganui basin in southern north island it is inferred to be in the 2 6 2 4 ma age range the porika glaciation in a separate area of northwest south island is younger judged by palynology and is correlated with a cooling 2 2 2 1 ma bp inferred from stratigraphic evidence of lowered sea level in the wanganui basin a gap of 1 5 ma in the record of glaciations is largely filled by wanganui basin marine sediments although an unconformity cuts out the record between ca 1 45 and 1 0 ma bp since then the many sedimentary cycles caused by sea level changes are presumed to be glacio eustatic in origin uplifted interglacial marine terraces back to marine oxygen isotope stage 17 and river terraces formed by cold climate aggradation are linked into the cyclic sequence through loess and tephra in their cover beds east of the south island cores from the dsdp site 594 in the southwest pacific record the earliest glaciation and higher in the core nine periods of south island glaciation in the last 0 7 ma onshore because of uplift and erosion only the last four glaciations assigned to oxygen isotope stages 10 8 6 and 4 2 are identified being named nemona waimaunga waimea and otira glaciations they are best known in north westland northwest south island where the relations of glacial outwash and interglacial shoreline deposits are displayed the late otira glaciation stage 2 is radiocarbon dated as beginning somewhat before 22 3 ka bp culminating ca 18 ka bp and ending at ca 14 ka bp when rapid deglaciation began a relatively small advance at ca 12 ka bp may have been followed by little change until after 8 6 ka bp recession was then followed by a period of advance from ca 5 ka bp until recent centuries and a subsequent recession that still continues

processes of forearc and accretionary complex formation during arc continent collision in the southern ural mountains the southern ural mountains of russia contain a well preserved well exposed paleozoic accretionary wedge and forearc that can be readily compared to those in active arc continent collision zones the early convergent history in the southern ural mountains is marked by the generation of boninite bearing arc tholeiites in the magnitogorsk forearc followed by arc tholeiite to calc alkaline volcanism with the entry of the east european craton continental crust in the subduction zone volcanism waned and stopped and high pressure metamorphism of its leading edge took place the arrival of the full thickness of the continental crust at the subduction zone is marked by increased sedimentation in the forearc basin and deposition of arc derived volcaniclastic turbidites across the subducting slab these together with offscraped continental material the exhumed high pressure rocks and a lherzolite massif formed an accretionary wedge a broad melange zone containing ultramafic fragments separates the forearc basement from the accretionary wedge and marks the damage zone that developed along the backstop region shallow water carbonates deposited unconformably on top of the mildly deformed arc record the end of the collision and the collapse of the arc

paraglacial rock slope stability glaciation and deglaciation along with their associated climatic and non climatic processes modify slope stresses and influence slope stability paraglacial slope failures are those that are a part of or influenced by the transition from glacial conditions to non glacial conditions gravitational failure of rock slopes is a primary and dominant process of slope evolution in mountainous terrain and is the subject of this paper which 1 reviews the approaches taken for researching paraglacial rock slope failure patterns and processes 2 summarises the spatial and temporal patterns of post glacial failures 3 assesses the factors influencing slope stability during glaciation and deglaciation 4 explores some of the applications of paraglacial research and 5 highlights some of the outstanding issues to be resolved and provides recommendations for terminology relating to paraglacial slope processes

erosional feedbacks and the oscillation of ice masses 1 an analytical solution to the development of a glacier or ice sheet in a region where the underlying rock rises steadily shows that the ice mass oscillates in size independefntly of changes in the climate in response to a feedback in which ice thickness is linked to topography by ice induced erosion the rate of vertical movement of the underlying rock uplift and the parameters governing ice erosion ablation and precipitation determine the period of oscillation two dimensional numerical simulations show that the tectonic uplift rate is the most important control on the period of oscillation and that the feedback period is likely to be between 10 and 100 kyr an examination of sediment data from the deep sea drilling project shows evidence of ice mass oscillations in the chugach st elias mountains and in the himalayas with periods consistent with those produced by the proposed mechanism localized changes in glacial extent may not therefore always be the consequence of climate change and care must be taken in interpreting evidence of glacial advance and retreat

wide angle seismic constraints on the internal structure of tenerife canary islands abstract we have used wide angle seismic data to constrain the internal structure of tenerife canary islands the experiment was designed as a seismic fan profile to detect azimuthal variations in the seismic structure of the volcanic edifice and its flanks seismic energy was generated using a 75 l airgun array on board the rrs charles darwin fired every 40 s along a quasi circular profile around the island of tenerife centered on teide volcano we present the results obtained from the data recorded by five portable land stations distributed on the island the travel times indicate that the averaged p wave velocity within the volcanic edifice is greater than 6 km s the observed travel times were reduced to residual travel times by removing the effects of variations in the bathymetry along the profile variations in the shot receiver distance and from local heterogeneities negative residual travel times up to 0 8 s in amplitude indicate that the southwestern part of tenerife is characterized by a high p wave velocity zone coincident with a gravity maximum that was previously modeled as a high density body forming the core of an old large mafic volcano we estimate velocities greater than 7 3 km s within the anomalous body suggesting that it represents an intrusive plutonic complex this high velocity high density body may have played an important role in the evolution of tenerife buttressing las canadas edifice and preventing the occurrence of landslides in the southern and western areas of tenerife the bathymetric high between tenerife and la gomera is associated with travel time delays up to 0 4 s suggesting that it may be composed of large deposits of lava flows and volcaniclastic materials probably erupted from the shield massifs of teno roque del conde and la gomera the post shield volcanic zones of santiago and dorsal rifts also seem to be characterized by moderate high p wave velocities

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

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

valley formation by fluvial and glacial erosion cross valley profiles from the west slope of the olympic peninsula washington are used to investigate the relative effects of fluvial and glacial erosion on valley formation unlike most ranges where glaciers and rivers sequentially occupied the same valleys neighboring valleys in the olympic mountains developed in similar lithologies but were subject to different degrees of glaciation allowing comparison of the net effect of glacial and fluvial processes integrated over many glacial cycles upslope drainage area was used to normalize comparisons of valley width ridge crest to valley bottom relief and valley cross sectional area as measures of net differences in the mass of rock excavated from below ridgelines for 131 valley spanning transects valley width relief and cross sectional areas are similar for glaciated partly glaciated and unglaciated fluvial valleys with drainage areas of 10 km 2 but diverge downslope glaciated valleys draining 50 km 2 reach two to four times the cross sectional area and have to 500 m greater relief than comparable fluvial valleys partly glaciated valleys have intermediate dimensions at distances of 5 km from valley heads the cumulative upstream volume of rock removed to form valleys is two to four times greater in glacially incised valleys than in fluvial valleys the finding of strong differences in the net result of valley excavation by fluvial and glacial erosion supports the interpretation that alpine glaciers are more effective erosional agents than are rivers and implies that large alpine valleys deepened and enlarged in response to pleistocene glaciation

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

convection and crystallization in magma cooled from above calculations are presented for the cooling from above of melts in the di an system in which the kinetics of crystallization are incorporated and play a dominant role the results indicate that even with no initial superheat whatsoever convection plays an important role in the cooling of magma chambers and allows substantial internal cooling crystallization and differentiation the calculations show in agreement with observations that in magma bodies hundreds of meters thick crystallization occurs predominantly in the interior or at the floor even though heat is lost only from the roof the ratio of the final thickness of the layer formed at the floor to that formed at the roof increases as the overall size of the chamber increases owing to the effects of convection

a new sulphur isotopic study of some iberian pyrite belt deposits evidence of a textural control on sulphur isotope composition the sulphide deposits of the iberian pyrite belt ipb represent an ore province of global importance our study presents 113 new sulphur isotope analyses from deposits selected to represent the textural spectrum of ores measured 34s values range from 26 to 10 mostly for massive and stockwork ores in agreement with data previously published in situ laser 34s analyses reveals a close correlation of 34s with texture primary diagenetic textures are dominated by relatively low 34s 8 to 2 whereas stockwork feeder textures are dominated by higher 34s 3 to 5 intermediate textures mainly coarse textures in stratiform zones have intermediate 34s although they are mostly dominated by the high 34s component rare barite has a homogeneous 34s around 18 which is consistent with direct derivation from lower carboniferous seawater sulphate a dual source of sulphide sulphur in the ipb deposits has been considered a hydrothermal source derived from reduction of coeval seawater sulphate in the convective systems is represented by sulphide in the feeder zones here variations in 34s are caused by variations in the extent of the sulphate reduction which governs the so4 h2s ratio the second end member was derived from the bacterial reduction of coeval seawater sulphate at or near the surface as reflected in the primary textures a distinct geographical variation in 34s and texture from sw more bacteriogenic and primary textures to ne more hydrothermal textures and 34s which reflects a variation in the relative input of each source was likely controlled by local geological environments given that the sulphur isotope characteristics of the ipb deposits are unlike most vms and kuroko deposits and noting the dominance of a mixed reduced sedimentary and volcanic environment we suggest that the ipb could represent an ore style which is intermediate between volcanic and sedimentary hosted massive sulphide types

vertical and lateral collapses on tenerife canary islands and other volcanic ocean islands recent studies demonstrate that tenerife has undergone large lateral collapses this has led to the suggestion that the las canadas caldera one of the best exposed calderas in the world is the result of lateral collapse we have tested this idea using the available structural stratigraphic volcanological and geochronological data we conclude that the las canadas caldera is the result of a complex sequence of vertical collapse events associated with a long history of phonolitic explosive activity in the central part of tenerife our results indicate however that vertical collapses may have played a major role in triggering lateral collapses we propose that the association of vertical and lateral collapse events such as inferred for tenerife can also explain similar sequences of events interpreted to have affected other large volcanic ocean islands

a quantification of the glacial imprint on relief development in the french western alps abstract the morphology of the western alps has been strongly influenced by quaternary glaciations on the basis of observations of glacial morphology in the belledonne grandes rousses taillefer and pelvoux ecrins massifs south eastern france we reconstitute the glacial trimline and equilibrium line altitude ela during the most extensive glaciation meg our best estimate of the meg ela is 1800 100m using digital elevation models we compare our glacial reconstruction with the relief structure of nine major catchments draining the massifs modal elevations of the largest catchments occur at 2000 2500m and coincide with minima in plots of mean slope angles as a function of elevation modal elevations and slope minima occur between the modern and meg elas confirming a strong glacial imprint on relief in order to quantify glacial valley carving in the massifs we isolated high elevation low relief surfaces that form rock shoulders adjacent to the glacial valleys from a digital elevation model and constructed an interpolated surface passing through these subtracting the present day topography from this surface allows us to quantify the maximum glacial valley depths maximum valley depths determined in this manner are typically 1000m with spatial maxima occurring around the location of the meg ela in most valleys these numbers do not take into account glacial valley widening and local glacial overdeepenings the also neglect however potential pre glacial fluvial valley incision which could account for 20 50 of the measured valley depths in spite of these problems inferred valley depths are reasonably well correlated with the mean reconstructed ice thickness and constitute about half of the sub ridgeline relief of the studied catchments these results lead us to propose a significant quaternary increase in the relief of the french western alps controlled by climate and associated with the initiation of alpine glaciations for reasonable values of the effective elastic thickness of the lithosphere the isostatic response to glacial valley carving reaches values of 300m across the massifs this number is insufficient to substantially offset topographic lowering due to regional denudation and we conclude that the isostatic response to glacial valley carving has not increased peak elevations significantly

oxygen isotope composition as a tracer for the origins of rubies and sapphires oxygen isotopic compositions of rubies and sapphires from 106 deposits worldwide as well as heated natural corundum have been measured in this study artificially heated corundums have the same oxygen isotopic composition as unheated material the 18o 16o ratio of natural corundum is a good indicator of its geological environment of formation the consistently restricted 18o range found for each type of deposit is explained by host rock buffering during fluid rock interaction the 18o constrains the geological source of the major type of gem quality rubies sold on the market and brings new insight to gems found in placers high quality blue sapphires from kashmir andranondambo and sri lanka have specific oxygen isotopic ranges but they overlap those of mogok in myanmar combined with traditional gemology techniques oxygen isotope analysis will contribute toward defining the origin of some commercial high value blue sapphires especially from kashmir

geodynamic setting of the mineral deposits of the urals the first order geodynamic domains of the uralide orogen constitute a relatively simple pattern across the orogenic belt continental rifting along the western margin is expressed by a system of vendian early palaeozoic structures with shale hosted siderite and magnesite and basalt hosted base metals it is superimposed on a middle riphean rift system with layered mafic ultramafic complexes with chromite and ilmenite titano magnetite and subordinate ophiolite massifs with gold and magnetite an oceanic spreading domain immediately east of the main uralian fault is associated with chromite titano magnetite and massive sulphide deposits dombarovsky or cyprus type further east bimodal volcanic associations in island arcs with oceanic crust have formed copper zinc massive volcanic sulphide deposits uralian type subsequently complex volcanic sulphide deposits are associated with belts of andesite dacite and co magmatic diorite baymak or kuroko type the eastern destructive margin of the orogen is characterized by magnetite and copper magnetite skarns and porphyry systems relatively small plagiogranite to granodiorite complexes related to oceanic crust carry scheelite and gold calc alkaline granitic massifs have formed associations of tungsten tantalum and beryllium this pattern was dissected by major thrusts and transcurrent shear zones increased fluid activity in the course of deformation inferred to have been involved in complex multi phase gold mineralization was most probably controlled by deep reaching faults and shears although the recognition of the first order domains represents a guideline for exploration detailed structural geological studies of the kinematics of the major faults and shear zones are required in conjunction with radiometric dating of suitable fault and ore associated minerals in association with on going deep reaching geophysical investigations

seismic heterogeneity of mt etna structure and activity a dense seismic array maintained temporarily for 7 weeks provides an approach to deducing the 3 d heterogeneity of the structure of the upper crust beneath mt etna volcano from the inversion of p and s wave arrivals of local earthquakes independent data from a different source array geometry using waves generated by distant shots at sea confirm a main lateral variation a high velocity body underlies part of the volcano its contrast with the surrounding thick sedimentary pile and its location extending from the present summit to the southeast suggests that it may have been built by the development and migration of past eruptive centres followed by caldera collapse local low velocity anomalies near its sharp western edge may be associated with presently active features

distribution and inferred age of exfoliation joints in the aar granite of the central swiss alps and relationship to quaternary landscape evolution abstract exfoliation joints are well known natural fractures limited to near the ground surface relatively few details however are known about their distribution and age in the swiss alps exfoliation joints follow the landscape surface at the time of their formation the age of the associated landscape feature then provides a maximum age of exfoliation joints while landscape forms can change through time exfoliation joints preserve elements of former landscape morphologies by their undisturbed orientations the grimsel region of the central alps is well suited for analyzing the impact of erosional episodes and accompanying stress changes on exfoliation joint formation in granitic rocks mapping above and below ground revealed that exfoliation joints are widespread and occur between valley bottoms and mountain crests within glacial inner and hanging u shaped trough valleys glacial cirques and steep mountain crests and predominantly fluvial landforms gently inclined linear slopes above the inner trough valleys narrow inner valley gorges and steep v shaped side gullies based primarily on their geometric properties at the ground surface three exfoliation joint types were distinguished in our study area 1 closely spaced

microgravimetric model of the las canadas caldera tenerife abstract an approximative method to obtain inner mass distributions starting only from gravimetric data and topographic chart digitalization is described roughly the sensitive subsoil volume is divided into a suitable cell partition of equally determinable regular blocks then the gravimetric effect for unit density for each cell on each surface point is determined a global least squares adjustment for every cell and every regular gravimetric point is carried out in order to derive the anomalous density values for each block and finally by using local polynomial approximation a continuous structural model from the discrete cubist solution is performed a volcanic caldera structure the known caldera of las canadas has been gravimetrically observed in this paper we present the methodology we have developed to analyze the measured gravimetric data and show the results corresponding to the inner mass density distribution for this volcanic structure

glacial steady state topography controlled by the coupled influence of tectonics and climate glaciers and rivers are the main agents of mountain erosion while in the fluvial realm empirical relationships and their mathematical description such as the stream power law improved the understanding of fundamental controls on landscape evolution simple constraints on glacial topography and governing scaling relations are widely lacking we present a steady state solution for longitudinal profiles along eroding glaciers in a coupled system that includes tectonics and climate we combined the shallow ice approximation and a glacial erosion rule to calculate ice surface and bed topography from prescribed glacier mass balance gradient and rock uplift rate our approach is inspired by the classic application of the stream power law for describing a fluvial steady state but with the striking difference that in the glacial realm glacier mass balance is added as an altitude dependent variable from our analyses we find that ice surface slope and glacial relief scale with uplift rate with scaling exponents indicating that glacial relief is less sensitive to uplift rate than relief in most fluvial landscapes basic scaling relations controlled by either basal sliding or internal deformation follow a power law with the exponent depending on the exponents for the glacial erosion rule and glen s flow law in a mixed scenario of sliding and deformation complicated scaling relations with variable exponents emerge furthermore a cutoff in glacier mass balance or cold ice in high elevations can lead to substantially larger scaling exponents which may provide an explanation for high relief in high latitudes

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

the role of fluvial and glacial erosion in landscape evolution the ben ohau range new zealand a morphometric comparison of valleys has been made for the ben ohau range in the central southern alps of new zealand the range is undergoing rapid tectonic transport and uplift the humid north of the range is a glacial trough and arete landscape with a temperate glacial climate the dry south has rounded divides and plateau remnants dissected by fluvial valleys assuming that space time substitution allows today s spatial valley form transition to represent evolutionary stages in valley development the tectonic history allows time constraints to be placed on the rate of transition to an alpine glacial landscape morphometric change has been quantified using hypsometric curves and distance elevation plots of cirque and valley floor altitudes ancestral fluvial valleys have less concave long profiles but are stepped at altitude owing to the presence of high level cirques and remnant plateau surfaces and possess a low proportion of land area at low elevation increasing glacial influence is manifest as smoother more deeply concave long profiles and u shaped cross profiles associated with a higher proportion of the land area at lower elevation the full morphological transition has involved up to 2 4 km of vertical denudation over the 4 ma lifetime of the mountain range of which 80 per cent would have occurred by preglacial fluvial erosion combining the trajectory of tectonic transport with reconstructed glaciation limits and climatic history it is indicated that about 200 ka of temperate glacial erosion produces recognizable trough and areete topography mean and modal relief increase where glacial activity is confined to cirques but decrease when trough incision by ice becomes established as a dominant process in the landscape 1997 by john wiley sons ltd

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

tectonics climate and mountain topography 1 by regressing simple independent variables that describe climate and tectonic processes against measures of topography and relief of 69 mountain ranges worldwide we quantify the relative importance of these processes in shaping observed landscapes climate variables include latitude as a surrogate for mean annual temperature and insolation but most importantly for the likelihood of glaciation and mean annual precipitation to quantify tectonics we use shortening rates across each range as a measure of topography we use mean and maximum elevations and relief calculated over different length scales we show that the combination of climate negative correlation and tectonics positive correlation explain substantial fractions 25 but 50 of mean and maximum elevations of mountain ranges but that shortening rates account for smaller portions 25 of the variance in most measures of topography and relief i e with low correlations and large scatter relief is insensitive to mean annual precipitation but does depend on latitude especially for relief calculated over small 1 km length scales which we infer to reflect the importance of glacial erosion larger scale averaged over length scales of 10 km relief however correlates positively with tectonic shortening rate moreover the ratio between small scale and large scale relief as well as the relative relief the relief normalized by the mean elevation of the region varies most strongly with latitude strong positive correlation therefore the location of a mountain range on earth with its corresponding climatic conditions not just tectonic forcing appears to be a key factor in determining its shape and size in any case the combination of tectonics and climate as quantified here can account for approximately half of the variance in these measures of topography the failure of present day shortening rates to account for more than 25 of most measures of relief raises the question is active tectonics overrated in attempts to account for present day relief and exhumation rates of high terrain

bismuth and cobalt minerals as indicators of stringer zones to massive sulphide deposits iberian pyrite belt the stringer zones and commonly the interaction zone at the base of the massive sulphide mounds in the iberian pyrite belt contain bismuth and cobalt minerals that are not found in the overlying massive sulphides these are fairly rare cobalt sulphoarsenides cobaltite alloclasite galucodot that were formed at the beginning of the massive sulphide genesis and fairly common bismuth sulphides bismuthinite hammarite wittichenite cosalite kobellite joseite etc including species rare at world scale nuffieldite giessenite jaskolskiite that were deposited from last stage high temperature 300 c copper bearing fluids containing bi te se the last stage fluids precipitated chalcopyrite containing cu bi te se sulphosalts at the base of the sulphide mound to form a high cupriferous zone their interaction with the massive sulphides is reflected by the formation of an exchange zone a few metres thick showing chalcopyrite disease textures at the base of the mound this zone forms the upper limit of potentially economic copper enrichment and of bismuth minerals gold is undoubtedly in part if not totally related to this last phase the bismuth concentrations being equivalent in the massive sulphides and the stringers the presence of bismuth minerals in the stringer zones results from high temperature conditions combined with a rarity of galena which impedes absorption of available bi the distribution of these bismuth minerals provides a basic mineralogical zoning in the stringer zone with a deep low as2 zone containing native bismuth and tellurides and a shallow higher as2 zone in contact with the massive ore sensu stricto and containing complex bismuth sulphides these results make it possible to distinguish between sulphide veinlets belonging to stockwork zones of massive orebodies and veinlets of an ambiguous nature and provide mineralogical criteria for the proximity of copper rich zones they enrich the very complex mineralogy of the iberian pyrite belt

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

k ar chronology of the volcanic eruptions in the canarian archipelago island of la gomera a geochronological study of the island of la gomera canaries has been carried out by the k ar method the 26 new ages obtained together with the 17 previous determinations show that above the main unconformity of the island separating the basal complex from the later volcanic series there is a unit of lower old basalts more than 10 m y old polymictic volcanic breccias were emplaced between 10 and 9 m y ago the upper old basalts above them were formed between 9 and 6 m y ago with a peak of activity around 7 m y after a period of erosion 6 5 m y a thick series of young basalts associated with trachytic and phonolitic domes and flows were rapidly emplaced between 4 5 4 m y ago finally local basaltic activity took place 2 8 m y ago the age of the basal complex is not well known although three ages 14 6 15 5 and 19 3 m y have been obtained for some alkaline intrusives which seem to represent the youngest events in the complex

gravity constraints on the structure and volcanic evolution of tenerife canary islands a detailed gravity study of tenerife constrains the internal structure of the island and its active magma system the maximum bouguer anomaly 2636 gu 1 gu 10 6 m s 2 0 1 mgal occurs over the sw part of the postshield las canadas edifice lce while smaller highs occur over the eroded shield volcanoes the main high extends ne and nw over the adjacent dorsal and santiago rift zones a deep low occurs over the northern lce and teide volcano the power spectrum of the anomalies suggests shallow causative structures 3 km inferred to belong to the island s dense core a model computed from the anomalies uses core and carapace densities of 2900 and 2360 kg m 3 respectively except beneath the main high where the core requires a higher density 3210 kg m 3 this part of the body is interpreted as a buried mafic volcano of substantial size the boca tauce volcano containing an old mafic plutonic complex the enigmatic las canadas caldera that truncates the lce shows strong asymmetry dense materials occupy the southern part whereas low density materials occupy the northern part to 2 3 km depth consistent with a vertical collapse origin high density materials in the south are related to the intracaldera extension of the dorsal rift zone the boundary between subcaldera domains is interpreted as the buried head of the giant icod landslide valley the icod landslide appears to have modified the caldera truncating its northern side and to have subsequently controlled the location of the active pico teide pico viejo vent systems voluminous chaotic deposits lying off northern tenerife previously associated with the formation of the caldera and icod valley are better interpreted as being derived from older mass wasting events the southern lce has been buttressed against lateral failure by the buried boca tauce volcano

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

assessing the potential for future explosive activity from teide pico viejo stratovolcanoes tenerife canary islands abstract since the onset of their eruptive activity within the canadas caldera about 180 ka ago teide pico viejo stratovolcanoes have mainly produced lava flow eruptions of basaltic to phonoltic magmas the products from these eruptions partially fill the caldera and the adjacent icod and la orotava valleys to the north although less frequent explosive eruptions have also occurred at these composite volcanoes in order to assess the possible evolution teide pico viejo stratovolcanoes and their potential for future explosive activity we have analysed their recent volcanic history assuming that similar episodes have the highest probability of occurrence in the near future explosive activity during the last 35000 years has been associated with the eruption of both mafic basalts tephro phonolites and felsic phono tephrites and phonolites magmas and has included strombolian violent strombolian and sub plinian magmatic eruptions as well as phreatomagmatic eruptions of mafic magmas explosive eruptions have occurred both from central and flank vents ranging in size from 0 001 to 0 1 km3 for the mafic eruptions and from 0 01 to 20 km3 dre eruptions of phonolitic magmas while teide pico viejo is dominated by effusive eruptions these differences can be explained in terms of the different degree of evolution of teide pico viejo compared to the preceding cycles and consequently in the different pre eruptive conditions of the corresponding phonolitic magmas a clear interaction between the basaltic and phonolitic systems is observed from the products of phonolitic eruptions indicating that basaltic magmatism is the driving force of the phonolitic eruptive activity the magmatic evolution of teide pico viejo stratovolcanoes will continue in the future with a probably tendency to produce a major volume of phonolitic magmas with an increasing explosive potential therefore the explosive potential of teide pico viejo cannot be neglected and should be considered in hazard assessment on tenerife

ice ages and nuclear waste isolation abstract the greatest natural threats to the integrity of the geological barriers to nuclear wastes isolated in cavities mined at depths between 400 and 800 m are likely during rapid retreats of future ice sheets the next major glacial retreat is expected at ca 70 ka well within the lifetime of high grade nuclear waste but it is not yet clear how long man s greenhouse effect may delay it this contribution discusses the potential problems posed to european waste isolation sites during erosion by ice and over pressurizing of meltwater and gasses in a lithosphere flexed by major ice sheets these depend on the target rocks and the location of the site with respect to the ice streams and margins of future ice sheets of particular size no sites are planned under the centres of future ice sheets in europe where end glacial earthquakes can be expected to reactivate major faults nor where ice can be expected to deepen and lengthen fjords along the atlantic coast sites in the alps may be vulnerable to radical changes in the patterns of glacial troughs the stability and geohydrology of sites in coastal areas beyond future ice margins are threatened by river gorges when sea level falls ca 125 m or in enclosed basins like the mediterranean ever lower the greatest problems are likely in lowland regions exposed by the rapid retreat of thick ice fronts where large lakes on or under thick warm based ice are dammed by more distal cold based ice groundwater in subhorizontal fractures dilated by glacial unloading may reach over pressures capable of hydraulically lifting megablocks of bedrock with fracture permeability and or the ice damming them so that less permeable substrates are susceptible to incisions eroded to depths of ca 360 at locations controlled mainly by ice topography kinematics and history

mineralogical and microtextural parameters in metals ores traceability studies abstract the demand in mineral resources is increasing rapidly but there is a lack of transparency in the trade of concentrated raw mineral materials because of speculation and involvement in the finance of armed conflicts because of the distance between primary extraction and the final production sites it is difficult to check the origin of these products an identity card is required for mineral commodities so that trading in the industry can be verified and the traceability of concentrates ensured this problem may be considered as an inversion process studying the products sold to identify the original ore the discriminant parameters are mineralogical composition identification of textural microfacies of the target minerals pseudo paragenetic sequence and the contents and distribution of minor elements of target minerals for base metal the selected target minerals are pyrite for its ubiquity sphalerite for its ability to host numerous discriminant and potentially valuable minor elements in its lattice and chalcopyrite for its proximity with the two other minerals the kolmogorov smirnov distance and the colin white test are used to compare the chemical composition of the three target minerals the application to volcanic massive sulfide ore deposits shows that it is possible to distinguish pyrite sphalerite and chalcopyrite between two ore deposits in the iberian pyrite belt province and seven ore deposits from the urals province using the selected characteristics ore deposits from different provinces may be discriminated using the identity cards as well as different deposits in the same province

hypsometric analysis to identify spatially variable glacial erosion 1 relatively little research has been undertaken on the use of digital elevation models to recognize the spatially variable glacial imprint of a landscape using theoretical topographies and a landscape evolution model we investigate to what extent the hypsometric analysis of digital elevation models may be used to recognize the glacial signature of mountain ranges a new morphometric parameter which we term the hypsokyrtome from the greek ipsos elevation kyrtoma curvature is derived from the gradient of the hypsometric curve the efficacy of the hypsometric integral and hypsokyrtome is tested through the study of the ben ohau range new zealand whose glacial imprint has been described previously with a numerical model we further test the geomorphic parameters in describing the morphologies of regions subject to diverse climatic and tectonic conditions the hypsokyrtome is highly sensitive to glacial erosion and the maps produced provide insights into the spatial distribution of glacial erosion we use srtm data and focus on two alternative geomorphic settings the european alps and the apennines the former has been affected by both fluvial and glacial erosion while the latter mainly exhibits a fluvially dominated morphology the correlation between elevations with increased glacial erosion and last glacial maximum lgm equilibrium line altitudes elas suggests the prevalence of a glacial buzz saw in the alps indicating that climate may put a limit on alpine topography

three dimensional p wave velocity structure of mt etna italy the three dimensional p wave velocity structure of mt etna is determined to depths of 15 km by tomographic inversion of first arrival times from local earthquakes recorded by a network of 29 permanent and temporary seismographs results show a near vertical low velocity zone that extends from beneath the central craters to a depth of 10 km this low velocity region is coincident with a band of steeply dipping seismicity suggesting a magmatic conduit that feeds the summit eruptions the most prominent structure is an approximately 8 km diameter high velocity body located between 2 and 12 km depth below the southeast flank of the volcano this high velocity body is interpreted as a remnant mafic intrusion that is an important structural feature influencing both volcanism and east flank slope stability and faulting

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

the influence of sub glacial bed evolution on ice extent a model based evaluation of the last glacial maximum pukaki glacier new zealand abstract a potential complication in using glacier extent to estimate paleoclimatic conditions is the influence of glacier bed evolution on changes in ice extent over time here we examine this issue through model based reconstructions of the last glacial maximum lgm pukaki glacier southern alps new zealand whose lgm extents are exceptionally well defined by lateral and terminal moraines using the well dated moraine limits as an empirical constraint on maximum ice extents we employ a one dimensional glacier flowline model driven by a mass balance model in order to evaluate the influence of climate and glacier bed profile on the extent of the lgm pukaki glacier the lgm glacier bed is buried by lateglacial and post glacial sediment so we calculate bed profiles using a modified version of the one dimensional model and available geologic constraints a best fit to the moraine record occurs with a lgm temperature of 7 8 c cooler than present with precipitation ranging from 80 to 100 of present levels modeling of the bed profile evolution indicates that bed changes alone could account for kilometer scale changes in glacier width and length

dykes and structures of the ne rift of tenerife canary islands a record of stabilisation and destabilisation of ocean island rift zones many oceanic island rift zones are associated with lateral sector collapses and several models have been proposed to explain this link the north east rift zone nerz of tenerife island spain offers an opportunity to explore this relationship as three successive collapses are located on both sides of the rift we have carried out a systematic and detailed mapping campaign on the rift zone including analysis of about 400 dykes we recorded dyke morphology thickness composition internal textural features and orientation to provide a catalogue of the characteristics of rift zone dykes dykes were intruded along the rift but also radiate from several nodes along the rift and form en echelon sets along the walls of collapse scars a striking characteristic of the dykes along the collapse scars is that they dip away from rift or embayment axes and are oblique to the collapse walls this dyke pattern is consistent with the lateral spreading of the sectors long before the collapse events the slump sides would create the necessary strike slip movement to promote en echelon dyke patterns the spreading flank would probably involve a basal decollement lateral flank spreading could have been generated by the intense intrusive activity along the rift but sectorial spreading in turn focused intrusive activity and allowed the development of deep intra volcanic intrusive complexes with continued magma supply spreading caused temporary stabilisation of the rift by reducing slopes and relaxing stress however as magmatic intrusion persisted a critical point was reached beyond which further intrusion led to large scale flank failure and sector collapse during the early stages of growth the rift could have been influenced by regional stress strain fields and by pre existing oceanic structures but its later and mature development probably depended largely on the local volcanic and magmatic stress strain fields that are effectively controlled by the rift zone growth the intrusive complex development the flank creep the speed of flank deformation and the associated changes in topography using different approaches a similar rift evolution has been proposed in volcanic oceanic islands elsewhere showing that this model likely reflects a general and widespread process this study however shows that the idea that dykes orient simply parallel to the rift or to the collapse scar walls is too simple instead a dynamic interplay between external factors e g collapse erosion and internal forces e g intrusions is envisaged this model thus provides a geological framework to understand the evolution of the nerz and may help to predict developments in similar oceanic volcanoes elsewhere

evaluation of tectonic activity using morphometric indices case study of the tatra mts western carpathians poland the tatra mountains tatra mts are the highest and most glacially reshaped mountain massif in the carpathians previous studies suggested the tectonic uplift of this massif along the large sub tatric fault during quaternary the main goal of this paper is to characterise the tectonic activity in the tatra mts using 6 geomorphic indices for 78 drainage basins the stream gradient index sl asymmetry factor af basin shape ratio bs hypsometric integral hi valley floor width valley height ratio vf as well as mountain front sinuosity smf these parameters were combined in order to obtain the relative tectonic activity index iat using gis the average of the six computed geomorphic indices was used to evaluate the distribution of relative tectonic activity in the study area according to iat values four classes of different tectonic activity can be distinguished in the tatra mts class 1 of very high tectonic activity 0 7 of tatra mts class 2 of high activity 24 3 class 3 of moderate activity 68 4 and class 4 of low activity 6 6 our study confirmed previous suggestions about unequal uplift of different parts of the massif iat values show high tectonic activity along the sub tatric fault as well as in the northern part of the belianskie tatra distribution of vf and hi values correlate with extend of glaciers during last glacial maximum it seems that values of some geomorphic indices such as vf and hi are strongly associated with glacial reshaping of the tatra mts during the pleistocene

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

roots of etna volcano in faults of great earthquakes abstract results from several seismic methods allow us to sketch the deep structure of etna and its ionian margin under etna a volume of high velocity material is found in a structurally high position the emplacement of this suggests spreading of the surrounding medium just offshore down to the east normal faults penetrate through the upper crust the deeper crustal structure beneath appears upwarped from the basin towards etna juxtaposed with the crust of sicily a thinner crust reaches from the ionian basin under etna and the mantle is upwarped in such a structure magma can then be viewed as a melted lens capping a mantle upwarp at shallow depth rather than in an intracrustal chamber this reduces the conflict between estimates of its volume from excess output of volatiles and short residence times a link in time is indicated between volcanic and seismic activity at a large scale over the millennium the reported ends of episodes of high output rates of magma are followed by the reported occurrences of magnitude 7 earthquakes which caused destruction in southeastern sicily several steep active normal fault have been imaged to a depth of 10 km the crust up to 30 km offshore of the cities of catania and augusta which may be fault planes for such large earthquakes they expand and prolongate the system of the timpe faults on the eastern flank of etna thus linking large scale tectonics offshore with the volcano etna developed together with normal faulting upwarp and spreading during the recent evolution of the former ionian subduction activation of the material at depth at the lateral edge of the slab by vertical motion with extension above could produce the peculiar type of etna magmatism

hotspot volcanism in the southern south atlantic geophysical constraints on the evolution of the southern walvis ridge and the discovery seamounts abstract the southern atlantic hosts a variety of magmatic structures namely the walvis ridge the discovery seamounts and the shona ridge which are believed to be related to the evolution movement of hotspots although the basement of the walvis ridge has been sampled at different locations geophysical data are too sparse to provide sufficient information about its deeper structure to compare it with other hotspot tracks the discovery seamounts represent a completely different type feature in a way that it cannot be connected to any onshore volcanic feature however geological sampling of the volcanic basement indicates that the petrology of the discovery track is very similar to gough island and the southern branch of walvis ridge both structures erupted into already existing seafloor and so have been seismically investigated to document how if an associated thermal anomaly might have modified the underlying and surrounding oceanic crust seismic lines for both structures indicate rather normal seismic velocity distributions for oceanic crust both the walvis ridge and the largest volcano of the discovery seamounts have a maximum thickness in our research area of 13 km an interesting difference between these structures is a high velocity cone 6 km s at 2 4 km depth in the central part of discovery seamount this might indicate a primarily intrusional type of seamount such as has been reported for several similar structures in contrast the walvis ridge velocity structure does not show evidences for a shallow intrusional cone but seismic velocities typical for oceanic layer 3 at a more or less constant depth level along the entire profile this might indicate that the ridge s present day topography is built mainly by extrusive material

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

cirque development in a steadily uplifting range rates of erosion and long term morphometric change in alpine cirques in the ben ohau range new zealand the intractable obstacle to understanding cirque evolution has been the lack of an independent timescale against which to measure morphometric change by using known rates of transport and uplift of the southern alps combined with the oxygen isotope record contained in marine sediments it is possible to estimate the duration of glacial occupancy of cirques in the ben ohau range the pattern is one of very limited glaciation of the southern range with glacial occupancy increasing northwards map based measurement of 18 morphometric properties in each of 92 cirques reveals systematic northward trends in cirque size form and altitude which are explained as reflections of increasing cirque age i e length of glacial occupancy thus the validity of space time substitution is demonstrated rather than assumed and morphometric trends define evolutionary stages of cirque development for cirques with up to c 750 ka occupancy rates of downcutting average 0 29 mma 1 and headwall retreat 0 44 mm a 1 there is no indication of attainment of an equilibrium form within this time both cirque size and form continue to evolve throughout with few parameters showing a convergence of value with cirque age some morphometric parameters perform much better than others the k coefficient of the long profile descriptor is the most powerful predictor of cirque age and simple measures correlate better than derived measures e g ratios of dimensions the trends identified concur with some previously published ideas but for the first time provide empirically quantified rates of change at an appropriate timescale copyright 2006 john wiley sons ltd

seismic tomography of etna volcano abstract a 3 d velocity model beneath etna volcano has been obtained through inversion of p wave arrivals of local earthquakes about 300 seismic events distributed around this volcano from surface up to a depth of 20 km have been used to infer the p wave velocity structure high p wave velocity bodies have been found in the upper portion of the volcanic edifice in a region where positive values of bouguer anomalies have previously been found low velocity bodies are identified at depths lower than 10 km and may be related to magmatic reservoirs the spatial pattern of these deeper velocity anomalies appears to be correlated at surface with the distribution of spatter cones in the nw quadrant a high velocity anomaly is correlated to the presence of a deeper seismicity the distribution of relocated hypocenters is not homogeneous but shows some features apparently related to the presence of magmatic bodies

microtremor analyses at teide volcano canary islands spain assessment of natural frequencies of vibration using time dependent horizontal to vertical spectral ratios we use time dependent horizontal to vertical spectral ratios hvsr of microtremors to determine the dominant frequencies of vibration of the geological structures beneath several recording sites in the vicinity of teide volcano canary islands spain in the microtremors the time dependent hvsrs ratiograms are a useful tool to discriminate between the presence of real dominant frequencies linked to resonances of the subsurface structure and the spurious appearance of peaks due to local transients we verified that the results are repeatable in the sense that microtremors recorded at the same site but at different times yield a very similar hvsr function two types of results are found 1 sites where there is no resonance of the propagating microtremors and therefore no value of a dominant frequency can be assessed and 2 sites where a stationary peak in the hvsr is found and a dominant frequency related to resonance of the shallow structure can be estimated these resonant frequencies show substantial spatial variations even for nearby sites which reflects the complexity of the shallow velocity structure in the las canadas area large dominant frequencies occur near the caldera walls and also at a few locations that coincide with the intersections of the inferred rims of the three calderas forming las canadas small dominant frequencies also occur near the caldera rim and may be due to discontinuities in the caldera wall and or to local velocity anomalies intermediate frequencies are mostly found in the eastern part of the caldera where a tentative profile of the basement depth has been obtained intermediate frequencies have also been measured south of ucanca and south of montana blanca in view of the present results we conclude that the use of ratiograms constitutes an improvement of the hvsr method and provides an appropriate tool to investigate the shallow velocity structure of a volcanic region

quantifying periglacial erosion insights on a glacial sediment budget matanuska glacier alaska glacial erosion rates are estimated to be among the highest in the world few studies have attempted however to quantify the flux of sediment from the periglacial landscape to a glacier here erosion rates from the nonglacial landscape above the matanuska glacier alaska are presented and compare with an 8 yr record of proglacial suspended sediment yield non glacial lowering rates range from 1 8 0 5 mm yr 1 to 8 5 3 4 mm yr 1 from estimates of rock fall and debris flow fan volumes an average erosion rate of 0 08 0 04 mm yr 1 from eight convex up ridge crests was determined using in situ produced cosmogenic 10be extrapolating these rates based on landscape morphometry to the matanuska basin 58 ice cover it was found that nonglacial processes account for an annual sediment flux of 2 3 1 0 106 t suspended sediment data for 8 years and an assumed bedload to estimate the annual sediment yield at the matanuska terminus to be 2 9 1 0 106 t corresponding to an erosion rate of 1 8 0 6 mm yr 1 nonglacial sources therefore account for 80 45 of the proglacial yield a similar set of analyses were used for a small tributary sub basin 32 ice cover to determine an erosion rate of 12 1 6 9 mm yr 1 based on proglacial sediment yield with the nonglacial sediment flux equal to 10 7 of the proglacial yield it is suggested that erosion rates by nonglacial processes are similar to inferred subglacial rates such that the ice free regions of a glaciated landscape contribute significantly to the glacial sediment budget the similar magnitude of nonglacial and glacial rates implies that partially glaciated landscapes will respond rapidly to changes in climate and base level through a rapid nonglacial response to glacially driven incision copyright 2009 john wiley sons ltd

a mass movement origin for cirques the glacial process of cirque initiation whereby small initial hillslope hollows grow by nivation until snow can form glacier ice and ice motion then enlarges the hollow to a fully developed cirque appears to have difficulty explaining the creation of large cirques in the time available during quaternary glaciations at the rates at which glaciers are reported to erode rock and in rapidly uplifting mountain ranges it also has difficulty explaining the striking proliferation of cirques in fiordland south island new zealand an area of harder rock and less glaciation than the nearby cirque poor area of south westland here we show that cirques can be initiated as large deep seated often coseismic rock slope failure source area depressions in which snow may accumulate to form cirque glaciers which can then remove detritus from smooth and enlarge the cirque we present an example of a classically shaped cirque that has never held a glacier we show that many similarities between the locations sizes and shapes of rock slope failure source area depressions and cirques are understandable on this basis as is the occurrence of cirques in presently aseismic intraplate locations and their relative paucity in actively uplifting ranges the extent to which cirques may be of mass movement origin has implications for their value as palaeoclimatic indicators copyright 2006 john wiley sons ltd

hypsometry of glaciated landscapes hypsometry frequency distribution of elevations is often used to characterize landscape morphology traditionally in the context of the degree of uvial dissection recently the hypsometry of glaciated regions has been used to infer how rates of glacial erosion compare with tectonic uplift rates however many factors other than tectonics can also exert a major in uence on the hypsometry of a glaciated landscape resulting in a wide variety of hypsometries using examples from the eastern sierra nevada california the western sangre de cristo range colorado and the ben ohau range new zealand we demonstrate that all else being equal the hypsometries of neighbouring basins can indicate the relative degree of glacial modi cation in each a selection of drainage basins from the rocky mountains shows that the position of the equilibrium line altitude ela within the drainage basin relief is a dominant variable in determining the hypsometry of a glaciated basin this is a non linear effect once the ela falls to some critical level the glaciers scour deeply below the ela causing a noticeably different hypsometry the hypsometry of an arbitrary region encompassing many drainage basins can disguise the variation present in the hypsometries and thus landforms of the individual basins unique local circumstances such as the presence of a mountain ice eld waiho basin southern alps substantial hanging valleys avalanche creek glacier national park a narrow outlet canyon sawmill creek sierra nevada and isolated geologic structures baker creek sierra nevada can have a major impact on the hypsometry of an individual basin copyright 2004 john wiley sons ltd

jasper seamount structure seafloor seismic refraction tomography the velocity structure of jasper seamount was modeled using one and three dimensional inversions of p wave travel times the results represent the first detailed seismic images of a submerged intraplate volcano two seismic refraction experiments were completed on jasper seamount incorporating ocean bottom seismometers and navigated seafloor shots the p wave travel times were first used to compute a one dimensional velocity profile which served as a starting model for a three dimensional tomographic inversion the seamount p velocities are significantly slower than those observed in typical oceanic crust at equivalent subbasement depths this suggests that jasper seamount is constructed predominantly of extrusive lavas with high average porosity the velocity models confirm morphological predictions jasper seamount is a shield volcano with rift zone development high seismic velocities were detected beneath the large radial ridges while low velocities characterize the shallow summit and flanks comparisons between p velocity models of jasper seamount and the island of hawaii reveal that these two shield volcanoes are not structurally proportional jasper seamount is far smaller than hawaii yet both volcanoes exhibit an outer extrusive layer of similar thickness this suggests that seamount size influences the intrusive extrusive proportions density equilibrium between melt and country rock may explain this behavior

quantified time scale for glacial valley cross profile evolution in alpine mountains space is used as a proxy for time in determining the role of glaciation in shaping valley cross profiles in the two thumb range southern alps new zealand the range is undergoing rapid tectonic transport and uplift as it is advected toward the alpine fault repeated cycles of glacial erosion during the quaternary have fashioned u shaped valleys in the north of the range close to the main divide while valleys in the less glaciated south of the range have rounded divides and convex fluvial cross profiles tectonic transport and uplift rates coupled with an offshore oxygen isotope 18o record and glacial geological reconstructions allow time constraints to be applied to valley development along the range valley width and depth measurements and power law equations were used to quantify the shape of cross profile transects in 37 valleys valleys evolved into a characteristic u shaped cross profile formed over 400 k y of glacial occupancy this regardless of other models of glacial flattening of valley long profiles suggests that alpine glaciation excavates greater volumes of rock indicating that glaciers are a more effective erosional agent than fluvial activity in alpine mountain belts

controls on slope to channel fine sediment connectivity in a largely ice free valley hoophorn stream southern alps new zealand there has been little work to date into the controls on slope to channel fine sediment connectivity in alpine environments largely ice free for most of the holocene characterization of these controls can be expected to result in better understanding of how landscapes relax from such perturbations as climate shock we monitored fine sediment mobilization on a slope segment hydrologically connected to a stream in the largely ice free 8 3 km2 hoophorn valley new zealand gerlach traps were installed in ephemeral slope channels to trap surficial material mobilized during rainfall events channel sediment flux was measured using turbidimeters above and below the connected slope and hysteresis patterns in discharge suspended sediment concentrations were used to determine sediment sources over the 96 day measurement period sediment mobilization from the slope segment was limited to rainfall events with increasingly larger particles trapped as event magnitude increased less than 1 of the mass of particles collected during these events was fine sediment during this period 714 t of suspended sediment was transported through the lower gauging station 60 of it during rainfall events channel sediment transfer patterns during these events were dominated by clockwise hysteresis interpreted as remobilization of nearby in channel sources further suggesting limited input of fine sediment from slopes in the lower valley strong counterclockwise hysteresis representing input of fine sediment from slope segments was restricted to the largest storm event jd2 2009 when surfaces in the upper basin were activated the results indicate that the slopes of the lower hoophorn catchment are no longer functioning as sources of fine sediment but rather as sources of coarse material with flux rates controlled by the intensity and duration of rainfall events although speculative these findings suggest a shift to a coarse sediment dominated slope to channel transfer system as the influence of pre holocene glacial erosion declines copyright 2011 john wiley sons ltd

accretionary complex structure and kinematics during paleozoic arc continent collision in the southern urals abstract the southern urals contain a well preserved accretionary complex that has overthrust the continental margin during arc continent collision between the east european craton eec and the magnitogorsk island arc in the late devonian within the accretionary complex we study three tectonic units that differ in deformation style and each provides a unique geodynamic implication the zilair nappe the largest and best exposed unit consists of 5 6 km of syncollisional arc derived upper devonian to lower carboniferous polymictic and graywacke turbidites that were deposited across the continental margin and incorporated by frontal accretion into the accretionary complex the zilair nappe is a bivergent thrust imbricate where the west vergent thrusts dominate and have associated kilometer scale ramp anticlines with well developed east dipping axial planar cleavage along its eastern contact however the cleavage fans until it dips moderately westward and the folds are east vergent following its emplacement west vergent basement involved thrusting that breached the whole accretionary complex imbricated the zilair nappe the timirovo duplex is structurally beneath the zilair nappe and outcrops for several tens of kilometers along its northwestern margin the duplex forms a west vergent thrust stack composed of a highly deformed and sheared lower and middle devonian reef carbonates of the former eec margin platform these rocks were shallowly underplated at the base of the accretionary complex during emplacement over the margin the suvanyak complex outcrops along the eastern contact of the zilair nappe and consists of polydeformed greenschist facies metasediments of the former eec slope that were offscraped underplated and incorporated at the rear of the accretionary complex

microgravimetric survey in the caldera of teide tenerife canary islands abstract in this study the first results obtained in a gravimetric exploration in the caldera of teide tenerife canary islands are presented the gravimetric anomalies observed permit us to deduce the existence of a double vault with an important mass deficit centered in the southeast base of the volcano teide that seems to support the hypothesis of a caldera collapse at least for an important part of the present depression

high resolution 3d p wave velocity structure beneath tenerife island canary islands spain based on tomographic inversion of active source data 1 we present a high resolution 3 dimensional 3d p wave velocity model for tenerife island canaries covering the top of teide volcano 3 718 m a s l down to around 8 km below sea level b s l the tomographic inversion is based on a large data set of travel times obtained from a 3d active seismic experiment using offshore shots air guns recorded at more than 100 onshore seismic stations the obtained seismic velocity structure is strongly heterogeneous with significant up to 40 lateral variations the main volcanic structure of the las canadas teide pico viejo complex ctpvc is characterized by a high p wave velocity body similar to many other stratovolcanoes the presence of different high p wave velocity regions inside the ctpvc may be related to the geological and volcanological evolution of the system the presence of high p wave velocities at the center of the island is interpreted as evidence for a single central volcanic source for the formation of tenerife furthermore reduced p wave velocities are found in a small confined region in ctpvc and are more likely related to hydrothermal alteration as indicated by the existence of fumaroles than to the presence of a magma chamber beneath the system in the external regions surrounding ctpvc a few lower p wave velocity regions can be interpreted as fractured zones hydrothermal alterations porous materials and thick volcaniclastic deposits

imaging the crustal magma sources beneath mauna loa and kilauea volcanoes hawaii three dimensional seismic p wave traveltime tomography is used to image the magma sources beneath mauna loa and kilauea volcanoes hawaii high velocity bodies 6 4 km s in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro ultramafic cumulates from which the surface volcanism is derived the proximity of these high velocity features to the rift zones is consistent with a ridge spreading model of the volcanic flank southeast of the hilina fault zone along the south flank of kilauea low velocity material

scattering images from autocorrelation functions of p wave seismic velocity images the case of tenerife island canary islands spain we present a p wave scattering image of the volcanic structures under tenerife island using the autocorrelation functions of p wave vertical velocity fluctuations we have applied a cluster analysis to total quality factor attenuation q t 1 and scattering quality factor attenuation q psc 1 images to interpret the structures in terms of intrinsic and scattering attenuation variations on a 2d plane corresponding to a depth of 2000 m and check the robustness of the scattering imaging the results show that scattering patterns are similar to total attenuation patterns in the south of the island there are two main areas where patterns differ at canadas teide pico viejo complex high total attenuation and average to low scattering values are observed we interpret the difference as induced by intrinsic attenuation in the santiago ridge zone srz region high scattering values correspond to average total attenuation in our interpretation the anomaly is induced by an extended scatterer geometrically related to the surficial traces of garachico and el chinyero historical eruptions and the area of highest seismic activity during the 2004 2008 seismic crises

gravimetric study of the shallow basaltic plumbing system of tenerife canary islands abstract recent studies on intraplate volcanic islands reveal that magma ascends sub vertically through these volcanic edifices following well defined zones in the lithospheric mantle and oceanic crust and occasionally suffering lateral propagation along rift zones when it reaches very shallow depths visualizing the internal structure of the shallowest part of such magma plumbing systems is crucial to understanding magma transport and the location of basaltic volcanism in these volcanic environments tenerife canary islands is a very good example of an intraplate volcanic island in which the distribution of basaltic volcanism includes well defined rift systems and wider monogenetic fields where cinder cones form clusters along different tectonic alignments in order to characterize the structure of the uppermost part of the basaltic plumbing system of tenerife we conducted a detailed gravimetric study of the north western central and southern sectors of the island we developed a 3d density contrast model of the subsoil based on the application of a genetic algorithm for the inversion of gravity data the results of our inverse modelling suggest that the observed gravimetric anomalies below the northwestern rift zone are shallow and aligned parallel to this structure this is consistent with a shallow character for the rift system and a lateral migration of magma along it that comes from a deeper zone located towards the east of this rift zone conversely the anomalies located in the south are also shallow but are distributed along more than one alignment and are connected to much deeper sub vertical similar density anomalies these results support the existence of several main channels at the north and south of the island that allow the ascent of deep basaltic magma to shallower zones of tenerife there magma may be either caught by the rifts systems being distributed laterally and occasionally erupting or may continue its ascent to the surface using a secondary system of shallow fractures that dominates the southern part of tenerife the results of our inverse model also offer new insights on others aspects of the internal structure of tenerife such as the distribution of the basaltic shield or that of las canadas caldera

modification of peripheral mountain ranges by former ice sheets the brecon beacons southern uk abstract the brecon beacons in southern wales is a large upland area 900 km 2 close to the periphery of the former british irish ice sheet the geomorphology of the brecon beacons highlands and surrounding areas was mapped using satellite imagery and a digital elevation model dem a fragmentary pattern of glacial lineations is inferred to represent ice build up in the mountains a more coherent set of glacial lineations formed by southward ice flow across the area from the welsh ice cap represents recession from the last glacial maximum lgm during this phase the brecon beacons acted as an obstacle deflecting the ice around higher terrain most of the higher terrain in the brecon beacons therefore appears to have escaped significant glacial erosion during both phases of ice flow due to cold based ice or low basal ice velocities beneath a local ice cap landforms previously interpreted as cirques in fact have v shaped profiles and lack evidence of major over deepening they are interpreted to have been formed primarily by processes other than glacial erosion the overall impact of glaciation in the brecon beacons appears to be limited primarily to the time when the area was over run by the welsh ice cap and the influence of local glaciation has been minimal this study has two main implications for landscape evolution in mountain ranges that lie at the periphery of former ice sheets first due to the presence of cold based ice or low basal ice velocities beneath a local ice cap it may be possible to find fragmentary traces of pre lgm ice flow second the pattern of glacial lineations in and around the brecon beacons indicates that peripheral mountain ranges may have deflected ice flow at the lgm resulting in low basal ice flow velocities and possible frozen bed conditions over higher terrain which consequently resulted in ineffective glacial erosion within the mountains themselves

numerically simulating alpine landscapes the geomorphologic consequences of incorporating glacial erosion in surface process models abstract a numerical model that simulates the evolution of glaciated mountain landscapes is presented by employing a popular sliding based glacial erosion model many common glacial landforms are created the numerical model builds on earlier work as it is fully two dimensional and employs the first order forcing on mountain evolution these forcings include tectonic uplift isostasy hillslope processes fluvial processes and glacial processes a climate dependent model of ice dynamics is employed to determine ice coverage and ice flux two simulations are presented one with generic model parameters and a second with parameters that correspond to conditions in the southern alps of new zealand landforms that are produced by the model include climate climate dependent elevation lowering similar to what might be expected by a glacial buzz saw valley overdeepening terminal moraines and valley retreat the model also predicts that current rates of sedimentation are higher than the long term average and that several tens of thousands of years are required for the landscape to adjust to a change in the dominant erosional forcing therefore glaciated orogens are unlikely to achieve topographic steady state over milankovitch timescales

the influence of rock mass strength on glacial valley cross profile morphometry a case study from the southern alps new zealand the erosional morphology in the vicinity of the main divide of the southern alps and fiordland new zealand appears to be a product of the interaction between alpine fault induced tectonic processes rock mass strength of the uplifted and eroded bedrock and the processes acting to denude the developing mountain landscape the magnitude of the effects of glacial erosion on the landscape is directly controlled by the size and physical properties of the glaciers whilst the form of the trough is a direct consequence of the rock mass strength rms properties of the slope rock realistic models of development of the cross profile shape of glacial valleys must take into consideration the rms properties of the eroded substrate

quantitative relationships between uplift and relief parameters for the southern alps new zealand as determined by fission track analysis the southern alps mountain chain new zealand has formed as a consequence of late cenozoic collision of the continental parts of the pacific and australia plates fission track analysis has yielded estimates of the amount age of initiation and rate of late cenozoic rock uplift for 82 surface samples taken from transects across the southern alps the mean surface summit and valley elevations in the vicinity of each of the rock sample sites have also been measured regression of the geomorphic variables on the uplift variables has been used to establish quantitative relationships between uplift and geomorphology there are strong and consistent linear associations between uplift and the elevations of the mean surface summits and valleys the preferred regression models have uniform slope but varying elevation response between transects substitution of space for time has allowed the evolution of landforms to be studied to the east of the main divide elevation and relief are proportional to and closely related to the age of initiation of rock uplift uplift age and the amount of rock uplift r2 0 8 mean surface uplift was delayed for 2 ma after the start of rock uplift a result of the stripping of a soft cover rock succession that prior to rock uplift overlaid the harder greywacke basement inter transect variations in regression response and x intercept are inferred therefore to reflect the variable preuplift thickness of cover rocks however the regular regression slope for the transects reflects the consistent nature of the interaction between uplift and the erodibility of greywacke basement uplift of the mean surface proceeded at 0 4 km km and 0 4 km ma of rock uplift while the rock uplift rate was 0 8 km ma summit elevations have increased at a rate of 0 6 km ma and valley elevations have increased at 0 2 km ma regression lines relating mean surface summit and valley elevations to rock uplift and uplift age diverge from common intercepts it is concluded therefore that the mountains east of the main divide have continued to increase in elevation and relief and change in form over time since the start of mean surface uplift mountain elevation has little relationship with late cenozoic mean rock uplift rates of 0 8 1 0 km ma or inferred contemporary rock uplift rates r2 0 3 in contrast to the west of the main divide elevation is shown to be closely related to rock uplift rate r2 0 3 in contrast to the west of the main divide elevation is shown to be closely related to rock uplift rate r2 0 8 transects with higher rock uplift rates support higher topography landforms are therefore in a stable equilibrium with rock uplift rate and the landscape contains no residual evidence of the total amount of rock uplift or the age of uplift lithological variation appears to have no relationship with elevation

oxygen isotope systematics of emerald relevance for its origin and geological significance oxygen isotopic composition of emerald from 62 occurrences and deposits in the world reveals a wide range in 18o smow between 6 2 and 24 7 the 18o values for each deposit are restricted and can be used to determine the origin of emerald from the world s most important producers the 18o value of emerald appears to be a fingerprint of its origin especially for gems of exceptional quality from colombia eastern emerald zone 18o 16 8 0 1 western emerald zone 18o 21 2 0 5 afghanistan 18o 13 5 0 1 pakistan swat mingora districts 18o 15 7 0 1 brazil santa terezinha de goias 18o 12 2 0 1 quadrilatero ferrifero 18o 6 9 0 4 and zimbabwe sandawana 18o 7 5 0 5 furthermore the 18o composition of emerald appears to be a good marker of its geological environment because the data suggest that host rock buffering of fluid 18o is considerable during fluid rock interaction

geomorphic evolution of the southern alps new zealand the southern alps are the topographic expression of late cenozoic 8 ma ago uplift of the crust of the leading edge of the pacific plate in south island new zealand new fission track data on the basement exposed in the southern alps quantify the age amount and rate of rock uplift and in combination with geomorphic parameters permit the construction of a new model of the geomorphic evolution of the southern alps the model emphasizes the development over time and space of rock uplift mean surface elevation exhumation of crustal section and relief the earliest indications of mean surface uplift are between 4 and 5 ma ago at the alpine fault mean surface uplift which lagged the start of rock uplift propagated southeastward from the alpine fault at a rate of 30 km ma by about 4 ma ago exhumation had exposed greywacke basement adjacent to and east of the entire 300 km long central section of the alpine fault at 3 ma ago greenschist was exposed in the southern parts of the southern alps near lake wanaka and since then has become exhumed along a narrow strip east of the alpine fault the model infers that amphibolite grade schist has been exhumed adjacent to the alpine fault only in the last 0 3 ma the age of the start of rock uplift and the amount and rate of rock uplift all of which vary spatially are considered to be the dominant influences on the development of the landscape in the southern alps the southern alps have been studied in terms of domains of different rock uplift rate at present the rate of rock uplift varies from up to 8 10 mm a adjacent to the alpine fault to 0 8 1 0 mm a along the southeastern margin of the southern alps this spectrum can be divided into two domains one northwest of the main divide where the present rock uplift rates are very high up to 8 10 mm a and exceed the long term value of 0 8 1 0 mm a and another to the southeast of the main divide where the long term rate is 0 8 1 0 mm a a domain of no uplift lies immediately to the east of the southern alps and is separated from them by a 1 0 1 5 km step in the basement topography we argue that this spatial sequence of uplift rate domains represents a temporal one the existing models of the geomorphic development of the southern alps the dynamic cuesta model of j adams and the numerical model of p koons are compared with the new data and evolutionary model particular constraints unrealized by these two earlier models include the following the earlier timing of the start of rock uplift of the southern alps 8 ma ago the spatial variation in the timing of the start of rock uplift 8 ma ago to 3 ma ago the lower long term rock uplift rate 0 8 1 0 mm a of the southern alps for most of the late cenozoic the lag between the start of rock uplift and the start of mean surface uplift and the patterns of the amounts of late cenozoic rock uplift and erosion across the southern alps

the canary islands swell a coherence analysis of bathymetry and gravity summary the canary archipelago is an intraplate volcanic chain located near the west african continental margin emplaced on old oceanic lithosphere of jurassic age with an extended volcanic activity since middle miocene the adjacent seafloor does not show the broad oceanic swell usually observed in hotspot generated oceanic islands however the observation of a noticeable depth anomaly in the basement west of the canaries might indicate that the swell is masked by a thick sedimentary cover and the influence of the canarian volcanism we use a spectral approach based on coherence analysis to determine the swell and its compensation mechanism the coherence between gravity and topography indicates that the swell is caused by a subsurface load correlated with the surface volcanic load the residual gravity geoid anomaly indicates that the subsurface load extends 600 km ssw and 800 km n and nne of the islands we used computed depth anomalies from available deep seismic profiles to constrain the extent and amplitude of the basement uplift caused by a relatively low density anomaly within the lithospheric mantle and coherence analysis to constrain the elastic thickness of the lithosphere t e and the compensation depth of the swell depth anomalies and coherence are well simulated with t e 28 36 km compensation depth of 40 65 km and a negative density contrast within the lithosphere of 33 kg m 3 the density contrast corresponds to a temperature increment of 325 c which we interpret to be partially maintained by a low viscosity convective layer in the lowermost lithosphere and which probably involves the shallower parts of the asthenosphere this interpretation does not require a significant rejuvenation of the mechanical properties of the lithosphere

crustal intrusion beneath the louisville hotspot track we report here the first detailed 2d tomographic image of the crust and upper mantle structure of a cretaceous seamount that formed during the interaction of the pacific plate and the louisville hotspot results show that at 1 5 km beneath the seamount summit the core of the volcanic edifice appears to be dominantly intrusive with velocities faster than 6 5 km s the edifice overlies both high lower crustal 7 2 7 6 km s and upper mantle 8 3 km s velocities suggesting that ultramafic rocks have been intruded as sills rather than underplated beneath the crust the results suggest that the ratio between the volume of intra crustal magmatic intrusion and extrusive volcanism is as high as 4 5 in addition the inversion of moho reflections shows that the pacific oceanic crust has been flexed downward by up to 2 5 km beneath the seamount the flexure can be explained by an elastic plate model in which the seamount emplaced upon oceanic lithosphere that was 10 myr at the time of loading intra crustal magmatic intrusion may be a feature of hotspot volcanism at young hot oceanic lithosphere whereas magmatic underplating below a pre existing moho may be more likely to occur where a hotspot interacts with oceanic lithosphere that is several tens of millions of years old

a numerical model of landform development by glacial erosion the jagged peaks knife edged ridges and steep sided valleys of alpine landscapes are well known products of glaciation yet little is known about how the dynamics of ice flow and glacial erosion give rise to such landforms by linking a finite element model for ice flow through a valley with a model for glacial erosion we have simulated the gradual evolution of one of the most striking of glacial landforms the u shaped valley incorporating realistic glacier sliding laws and spatial variations in rock resistance our simulations illustrate how ice flow erosion patterns and topography interact in the long term evolution of glacial landforms in addition our results indicate for the first time that the formation of a steady state u shaped valley takes approximately 105 years

shear wave velocity structure around teide volcano results using microtremors with the spac method and implications for interpretation of geodetic results deformation analysis and simulation of volcanic edifices require the construction of models of elastic properties of those structures in this paper we present an analysis of microtremor measurements recorded during the performance tests of two temporary seismic arrays installed in the eastern portion of the teide caldera in 1994 we take advantage of recent developments of the spac method and use spatial cross correlation computations to estimate phase velocity dispersion of rayleigh waves at the location of the arrays we show that the extension of the standard spac method is valid in the case of our data justifying its use and supporting the generalization of the spac method to single station pairs the phase velocity dispersion curve obtained was inverted to recover the shear wave profile at the site of the arrays our results indicate that the subsoil structure of the caldera is laterally homogeneous at the scale of a few km about the location of the arrays we obtained about 315 m of volcanic sediments overlying rocks with a shear wave velocity of 2 km s these results are robust and are a starting point to further modelling of deformation permanent or transient at this volcanic edifice which can be useful in the interpretation of different observed fields in fact the computation of deformations and gravity changes due to possible volcanic intrusions in two models one considering the volcanic sediments and the other without considering them provided different results in the near field

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

quantifying variable erosion rates to understand the coupling of surface processes in the teton range wyoming short term geomorphic processes fluvial glacial and hillslope erosion and long term exhumation control transient alpine landscapes long term measurements of exhumation are not sufficient to capture the processes driving transient responses associated with short term climatic oscillations because of high variability of individual processes across space and time this study compares the efficacy of different erosional agents to assess the importance of variability in tectonically active landscapes responding to fluctuations in quaternary climate we focus on the teton range where erosional mechanisms include hillslope glacial and fluvial processes erosion rates were quantified using sediment accumulation and cosmogenic dating bedrock and stream sediments results show that rates of erosion are highly variable with average short term rockfall rates 0 8 mm y occurring faster than either apparent basin averaged 0 2 mm y and long term ridge erosion rates 0 02 mm y examining erosion rates separately also demonstrates the coupling between glacial fluvial and hillslope processes apparent basin averaged erosion rates amalgamate valley wall and ridge erosion with stream and glacial rates climate oscillations drive the short term response of a single erosional process e g rockfalls or other mass wasting that may enhance or limit the erosional efficiency of other processes glacial or fluvial while the teton landscape may approach long term equilibrium stochastic processes and rapid response to short term climate change actively perpetuate the transient ruggedness of the topography

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

modelling landscape evolution under ice sheets we use an ice sheet model glimmer with an erosion component to examine the evolution of landscapes under ice sheets over long time scales in hypothetical situations glimmer is a fully coupled thermomechanical 3 dimensional ice sheet model with a sliding component the model thus has the ability to predict ice thickness the distribution of areas at pressure melting point and basal velocities the erosion rate is assumed to be a simple linear function of the basal velocity and therefore erosion only occurs where the bed is not frozen and basal sliding is possible in addition sliding velocities are assumed to be related to basal water production thus giving a mechanism for smooth temporal and spatial transitions between eroding and non eroding portions of the bed the eroding glacial landscape system is modelled for long term persistent glaciation assuming a variety of initial landscapes results indicate that without the inclusion of basal water production in the calculation of sliding velocities any thermal feedbacks are exaggerated because of steep horizontal basal temperature gradients additionally bed morphology exerts a greater influence under low basal slip conditions because ice cannot respond readily to thermal instabilities we suggest that erosion and valley overdeepening may aid stabilisation of the thermal regime of an ice sheet and that it is possible to generate glacial signals in previously fluvial systems after only 100 kyr of glaciation at conservative erosion rates

the three dimensional structure of kilauea volcano hawaii from travel time tomography a linear travel time tomography study of the most active shield volcano of the world kilauea volcano hawaii was undertaken to determine the lateral heterogeneities produced by its intricate magmatic and tectonic environment kilauea provides an ideal setting to do tomography because of its dense seismograph array and many local earthquakes that allow excellent ray coverage of complex subsurface features local p wave data from 12 295 events were inverted using a one dimensional layered velocity model inversions were done for two cell sizes 5 5 5 km and 1 1 1 km to resolve structural regions on different length scales this study provided a view of the average velocity variations relative to a one dimensional velocity model analysis and interpretation of the tomographic images allowed us to infer the following model the main shallow magma reservoir is delineated by a slow velocity region southeast of the summit from 0 to 2 km depth there is a distinct high velocity region centered northwest of the summit from 0 to 2 km depth that represents a cap of dense intrusive dikes surrounding the magma chamber we suggest that the shallow reservoir is a narrow compartmentalized region of sills and dikes centered just south southeast of halemaumau caldera below the main reservoir the summit is imaged as a slightly fast region from 5 to 10 km in the coarse model indicating that the main conduit is structurally defined by an intrusive dike complex until about 10 km the rift zones of kilauea are imaged as major high velocity entities widening to the south with depth until 6 km these fast anomalies are related to the sheeted dike complexes along the rifts on a finer scale slow anomalies suggest the presence of magma pockets centered at 0 2 km depth beneath mauna ulu makaopuhi and puu oo along the east rift zone erz two significant high velocity regions along the lower erz near kalalua and kaliu are inferred to represent intrusive barriers to magma injection along the shallow 0 4 km erz conduit the southwest rift zone may have an intrusive barrier related to a high velocity region just southwest of mauna iki the hilina and kaoiki fault zones are imaged as slow features at shallow depths 5 km related to the open fractures and scarps along the normal faults the koae fault system is imaged as a slightly fast shallow structure 6 km possibly related to intrusive diking from the adjacent rift zones that fill and may even induce the extensional structures associated with this complex fault zone continued inversions with the immense amount of seismic data collected for hawaiian events will allow the detailed development of a three dimensional structural model for kilauea such a model will be extremely useful to seismologists and petrologists alike for understanding the tectonic growth and magmatic evolution of this dynamic shield volcano

crustal structure and origin of the eggvin bank west of jan mayen ne atlantic the eggvin bank located between the jan mayen island and greenland is an unusually shallow area containing several submarine volcanic peaks confined by two transforms on the northern kolbeinsey ridge nkr we represent p and s wave velocity models for the eggvin bank based on an ocean bottom seismometer profile collected in 2011 showing igneous crustal thickness variations from 8 km to 13 km a 2 5 km increase is associated with two separate 20 30 km wide segments under the main seamounts the oceanic crust has three layers upper crust l2a 2 8 4 8 km s middle crust l2b 5 5 6 5 km s and lower crust l3 6 7 7 35 km s both the thick layer 2 a b and the high ratio of layer 2 a b thickness to total crustal thickness indicate that secondary intraplate magmatism built the seamounts of the eggvin bank the seamount in the north where the crust is thickest has a flat top indicating subaerial exposure but is deeper than those with rounded tops in the south and is therefore probably older comparing lower crustal seismic velocity with crustal thickness also indicates that the degree of mantle melting may be higher in the north than in the south an enriched mantle source presently feeds the nkr magmatism and probably influenced the eggvin bank development also at earlier times to what extent the eggvin bank has been influenced by the iceland plume is uncertain both an enriched mantle component and elevated mantle temperature may have played a role at different times and locations

perturbation to the lithosphere along the hotspot track of la reunion from an offshore onshore seismic transect a 250 km long ne sw lithospheric transect spanning the 40 km wide island of la reunion and its submarine edifice is derived from lines of air gun shots at sea on either side along the assumed hotspot trace seismic records were obtained from an array spanning the whole transect and including sea bottom and land receivers providing a system of reversed and overlapping observations low seismic velocity and hence density is found on average for the whole edifice above the oceanic plate we attribute high velocity anomalies within the edifice to an intrusive core confined under the central northern quarter of the island crossing segment unexpectedly the main seismic interfaces top and bottom of the prevolcanic crust do not show significant flexural downwarping under the island in addition clear multipathing in the recorded wave field requires the presence of a body with a seismic velocity intermediate between the prevolcanic crustal material and the normal mantle this lithospheric structure provides the first example where underplating occur s beneath an active volcanic island suggesting a genetic relationship the underplated body could represent residues of the evolution of primary picritic melts that yield erupted basalts evidence for reflectors deeper in the lithosphere may indicate further related heterogeneity in the plate hotspot model commonly assumed the structural variation along the transect could be interpreted as a variation with time of the amount and physical state of underplated material

vertical axis rotation of the upper portions of the north east rift of tenerife island inferred from paleomagnetic data abstract paleomagnetic sampling sites were established in 82 dykes along an 8 km long section of the north east rift zone nerz of tenerife canary islands spain of the 70 interpretable sites 16 are of normal polarity and 54 of reversed polarity four normal polarity sites and fifteen reverse polarity sites were excluded from the grand mean calculation for statistical reasons after inverting the reverse polarity sites through the origin the in situ grand mean yields a declination d 023 8 an inclination i 42 3 95 3 2 39 0 n 51 that is discordant to the expected late miocene to pleistocene field direction d 357 6 i 38 8 95 4 7 this discordance can be explained as either a 26 clockwise vertical axis rotation or a 28 wnw side down tilt about an average 009 horizontal tilt axis the sampled section is composed of numerous semi vertical dykes cutting mainly lava flow units that are sub horizontal and cross cut by steeply dipping faults 70 90 field evidence is therefore more compatible with a vertical axis rotation rather than a horizontal axis tilt of the drilled units we argue that this clockwise vertical axis rotation is likely related to strike slip movements that occurred along the edges of the collapse scars and accommodate the emplacement and growth of the underlying intrusive core and associated dykes six new 40ar 39ar age determinations constrain the main interval of dyke emplacement within the nerz between 0 99 ma and 0 56 ma the intrusive activity in the sampled section of the rift appears to have been almost continuous with several intrusion pulses that are probably related to flank destabilisation event s during the mid pleistocene our study thus demonstrates a long lived multi faceted history that shaped the nerz