evolution of the eastern volcanic ridge of the canary islands based on new kar data the results of 64 new k ar age determinations together with 32 previously published ages show that after a period of erosion of the basal complex miocene volcanic activity started around 20 ma in fuerteventura and 15 ma in lanzarote forming a tabular succession of basaltic lavas and pyroclastics with a few salic dykes and plugs this series includes five separate volcanic edifices each one with its own eruptive history in fuerteventura several miocene eruptive cycles have been identified in the central edifice one around 20 17 ma followed by two others centred around 15 and 13 ma in the southern edifice the maximum of activity took place around 16 14 ma whereas in the northern one the main activity occurred between 14 and 12 ma in lanzarote a first cycle of activity took place in the southern edifice between 15 5 and 14 1 ma followed by another between 13 6 and 12 3 ma in the northern edifice three pulses occurred 10 2 8 3 6 6 5 3 and 3 9 3 8 ma an important temporal gap greater in fuerteventura than in lanzarote separates series i from the plio quaternary series ii iii and iv formed by multi vent basaltic emissions in fuerteventura the following eruptive cycles have been identified 5 2 9 2 4 1 8 1 7 0 8 0 4 and 0 1 ma in lanzarote the activity was fairly continuous from 2 7 ma to historic times with a maximum in the lower pleistocene eruptive rates in the series i edifices were on the average 0 1 0 01 km3 ka comparable but slightly smaller than in similar edifices in tenerife and la gomera but much lower than in gran canaria average post miocene eruptive rates were about 0 013 0 027 km3 ka in lanzarote and 0 003 0 007 km3 ka in fuerteventura all these volcanic edifices show a similar general sequence fissural eruptions erosion multi vent volcanism repeated at different periods in different parts of the eastern islands of the canaries the model of growth of the series i edifices is comparable to those in tenerife and la gomera long periods of activity sometimes greater than 6 m y with pulses separated by gaps however salic and intermediate differentiates frequent in tenerife and la gomera are very scarce in these islands the fuerteventura lanzarote ridge shows a decrease in volcanic activity with time and also a certain ssw nne polarity in the temporal development of volcanism

deposit from a giant wave on the island of lanai hawaii limestone bearing gravel the newly named hulopoe gravel blankets the coastal slopes on lanai the deposit which reaches a maximum altitude of 326 meters formerly was believed to have been deposited along several different ancient marine strandlines but dated submerged coral reefs and tide gauge measurements indicate that the southeastern hawaiian islands sink so fast that former worldwide high stands of the sea now lie beneath local sea level evidence indicates that the hulopoe gravel and similar deposits on nearby islands were deposited during the pleistocene by a giant wave generated by a submarine landslide on a sea scarp south of lanai

variations of the east asian jet stream and asian pacific american winter climate anomalies in this study the authors apply the ncep ncar reanalysis and other observations to depict the association of the asian pacific american climate with the east asian jet stream eajs with an emphasis on boreal winter seasons and on interannual timescales they analyze the variations of the eajs and their relationships with el nino southern oscillation enso and extratropical north pacific sea surface temperature sst and assess the relative connections of the eajs and enso to the anomalies of atmospheric circulation surface temperature and precipitation in the asian pacific american region it is found that the eajs is coupled to a teleconnection pattern spanning the entire asian pacific american region with the strongest signals over east asia and the western pacific this pattern differs significantly from that associated with enso which influences the earth s climate extensively with a strongest impact on the climate over the central pacific and east a strong eajs is associated with an intensification of the weather and climate systems in asia and over the pacific such as deepening of the east asian trough and the aleutian low and strengthening of the east asian winter monsoon it is linked to colder and drier conditions in east asia and stronger convection over the tropical asia australia sector compared with enso the eajs seems to link to the climate signals of asia and the pacific more strongly an intensified eajs is also associated with anomalies of temperature and precipitation in north america due to the related changes in stationary wave patterns while the eajs does not strongly link to the tropical central eastern pacific sst it is significantly associated with the extratropical north pacific sst more specifically the second most dominant mode of the empirical orthogonal function analysis of the sst in addition a strong weak eajs seems to follow a large small meridional gradient of the western pacific sst associated with warming cooling in the tropics subtropics and cooling warming in the extratropics

growth and destruction of gran canaria deduced from seismic reflection and bathymetric data the morphology and structure of the submarine flanks of gran canaria have been mapped using hydrosweep swath bathymetry and high resolution reflection seismic data the growth and destruction of the island has been characterized previously by three major periods of volcanic activity 16 9 ma 4 5 3 5 ma younger than 3 ma separatedby erosional intervals two major sector collapses along the west coast inferred from the coastal morphology are believed to have formed at the end of the shield building phase one is characterized by a 19 km wide reentrant along the northwestern coast that may have formed synchronously with the formation of the 20 km diametermiocene tejeda caldera high sedimentation rates around gran canaria 50 m myr tend to cover and bury major landslide blocks ssw off the island several canyons continue seaward into a major sediment fan a 9 5 km wide volcaniclastic ridge in this fan is interpreted to represent deposits of the pliocene subaerial roque nublo debris avalanche we tentatively interpret the slope break at a depth of 600 800 m as the transition between subaerial and subaqueous chilled lavas at the end of the shield building phase the subsidence caused by the volcanic load 30 000 km3 on the lithosphere may thus amount to no more than 800 m several canyons on the island can be traced down the submarine flanks to a depth of 3 5 km indicating that at least deeper portions below the level of subsidence were eroded by mass flows continuing seaward from the subaerial canyons four submarine volcanoes were identified west and northeast of the island

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

cone sheet formation and intrusive growth of an oceanic island the miocene tejeda complex on gran canaria canary islands more than 500 trachytic to phonolitic cone sheet dikes hypabyssal syenite stocks and subordinate radial dikes form a 20 km diameter intrusive complex in the volcaniclastic fill of the miocene tejeda caldera 20 35 km on gran canaria canary islands the dikes intruded concentrically around a central axis of radial symmetry and dip uniformly an average of 41 toward the center single crystal 40ar 39ar ages of dikes and syenite stocks ranging from 12 3 0 1 to 7 32 0 05 ma suggest more or less continuous intrusive activity during both volcanically active and inactive phases intrusions were emplaced at average intervals of 5 10 k y while explosive eruptions took place at 50 k y intervals the estimated aggregate volume of evolved cone sheet magma added at shallow level 2000 m below sea level amounts to 250 km3 compared to 500 km3 of evolved extrusive volcanics erupted during the same period formation of the tejeda cone sheets most likely resulted from deformation processes due to resurgent doming initiated by the recurrent replenishment of a flat laccolith like shallow magma chamber magma supply exceeding the volume that could be compensated for by updoming of the overlying caldera fill resulted in the formation of cone shaped fractures

evolution of the canadas edifice and its implications for the origin of the canadas caldera tenerife canary islands the volcano stratigraphic and geochronologic data presented in this work show that the tenerife central zone has been occupied during the last 3 ma by shield or central composite volcanoes which reached more than 3000 m in height the last volcanic system the presently active teide pico viejo complex began to form approximately 150 ka ago the first canadas edifice ce volcanic activity took place between about 3 5 ma and 2 7 ma the ce i is formed mainly by basalts trachybasalts and trachytes the remains of this phase outcrop in the canadas wall cw sectors of la angostura 3 5 3 0 ma and 3 0 2 7 ma boca de tauce 3 0 ma and in the bottom of some external radial ravines 3 5 ma the position of its main emission center was located in the central part of the cc the volcano could have reached 3000 m in height this edifice underwent a partial destruction by failure and flank collapse forming debris avalanches during the 2 6 2 3 ma period the debris avalanche deposits can be seen in the most distal zones in the n flank of the ce i tigaiga breccia a new volcanic phase whose deposits overlie the remains of ce i and the former debris avalanche deposits constituted a new volcanic edifice the ce ii the dyke directions analysis and the morphological reconstruction suggest that the ce ii center was situated somewhat westward of the ce i reaching some 3200 m in height the ce ii formations are well exposed on the cw especially at the el cedro 2 3 2 00 ma sector they are also frequent in the s flank of the edifice 2 25 1 89 ma in tejina 2 5 1 87 ma as well as in the tigaiga massif to the n 2 23 ma during the last periods of activity of ce ii important explosive eruptions took place forming ignimbrites pyroclastic flows and fall deposits of trachytic composition their ages vary between 1 5 and 1 6 ma adeje ignimbrites to the w in the cw the upper ucanca phonolitic unit 1 4 ma could be the last main episode of the ce ii afterwards the can adas iii phase began it is well represented in the cw sectors of tigaiga 1 1 ma 0 27 ma las pilas 1 03 ma 0 78 ma diego hernandez 0 54 ma 0 17 ma and guajara 1 1 ma 0 7 ma the materials of this edifice are also found in the se flank these materials are trachybasaltic lava flows and abundant phonolitic lava and pyroclastic flows 0 6 ma 0 5 ma associated with abundant plinian falls the ce iii was essentially built between 0 9 and 0 2 ma a period when the volcanic activity was also intense in the dorsal edifice situated in the easterly wing of tenerife the so called valleys of la orotava and gu imar transversals to the ridge axis also formed during this period in the central part of tenerife the ce iii completed its evolution with an explosive deposit resting on the top of the ce for which ages from 0 173 to 0 13 ma have been obtained the cc age must be younger due to the fact that the present caldera scarp cuts these deposits on the controversial origin of the cc central vertical collapse vs repeated flank failure and lateral collapse of mature volcanic edifices the data discussed in this paper favor the second hypothesis clearly several debris avalanche type events exist in the history of the volcano but most of the deposits are now under the sea the caldera wall should represent the proximal scarps of the large slides whose intermediate scarps are covered by the more recent teide pico viejo volcanoes

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

the role of barents sea ice in the wintertime cyclone track and emergence of a warm arctic cold siberian anomaly abstractsea ice variability over the barents sea with its resultant atmospheric response has been considered one of the triggers of unexpected downstream climate change for example east asia has experienced several major cold events while the underlying temperature over the arctic has risen steadily to understand the influence of sea ice in the barents sea on atmospheric circulation during winter from a synoptic perspective this study evaluated the downstream response in cyclone activities with respect to the underlying sea ice variability the composite analysis including all cyclone events over the nordic seas revealed that an anticyclonic anomaly prevailed along the siberian coast during light ice years over the barents sea this likely caused anomalous warm advection over the barents sea and cold advection over eastern siberia the difference in cyclone paths between heavy and light ice years was expressed as a warm arctic cold siberian wacs anomaly the lower baroclinicity over the barents se

structure and emplacement of the pliocene roque nublo debris avalanche deposit gran canaria spain abstract collapse of the flanks of the pliocene roque nublo stratocone on gran canaria lead to large debris avalanches that traveled far beyond the coastline with velocities that may have exceeded 100 m s the deposits comprised at least 14 km 3 of debris and covered an area of about 180 km 2 in the southern half of the island the debris filled deep canyons are largely exhumed at present incomplete disintegration poor fluidization and a good preservation of megablocks are thought to be mainly due to the confinement of the debris avalanche within deep canyons the rheological behavior of lithologic domains varies with their size internal strength and relative position within the deposit the deformation structures indicate that distinct components flowed whereas others slid throughout the transport in a relatively dense mode the following factors are believed to have been important in generating the roque nublo debris avalanche deposit 1 unusual abundance of pyroclastic flow and other volcaniclastic deposits making up the upper roque nublo cone 2 highly asymmetric basement beneath the cone with a very high southern ridge and a steep erosional southern slope leading to major instabilities 3 intrusion of dikes and cryptodomes as well as hydrothermal alteration in the crater area further weakening the volcano

a neogene geomagnetic polarity transition record from lavas of the canary islands spain episodic volcanism and or metastable transitional fields summary we present results from a study of a partial magnetic polarity transition record from a 9 7 ma 40ar 39ar dated volcanic section on the island of gomera canary islands spain the record provides results that bear on the debate over whether long term persistent features of field behaviour exist during transitions the sampled section containing more than 20 flows begins after the onset of the transition the nine lowermost flows in the section which are all transitional yield virtually identical directions and similar low paleointensities following the recovery of virtual geomagnetic pole positions vgps to near the spin axis paleointensities progress to very high values transitional directions lay due west reflecting the presence of a non zonal intermediate field vgps for these flows cluster in the west atlantic which according to hoffman would correspond to a zone of fastest p wave propagation in the lower mantle and to a radial flux centre of the present day non dipole field hoffman had noted a similar occurrence at two other locations he found that in a select set of volcanic records vgps tended to group over two areas australia and south america which also corresponded to fast p wave and non dipole field anomalies given the discontinuous and irregular character typical of volcanic sequences it is natural to question whether these clusters are merely artefacts of episodic volcanism or actually reflect standstills of the reversing field we address this question for our record by comparing chemical and magnetomineralogic characteristics of the flows we find that all of the transitional flows have very similar chemical and rock magnetic properties furthermore these flows differ significantly from the overlying reverse flows which give distinctly different values and much greater flow to flow variation from this we conclude that the packet of transitional flows was derived from the same source and had erupted over a relatively short period of time as reflected by a magma source that presumably did not have time to evolve significantly while the vgp cluster in the gomera record is consistent with long term mantle control on transitional fields we cannot conclude that the cluster represents a standstill of the field these results highlight the difficulties of interpreting temporal changes in field behaviour from volcanic sequences in addition they provide a clear incentive for investigating physical characteristics of lavas to assess relative eruptive rates

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

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

contribution of asian dust and volcanic material to the western philippine sea over the last 220 kyr as inferred from grain size and sr nd isotopes asian dust and volcanogenic materials are two major components in the northwestern pacific quantitatively distinguishing them and estimating their mass accumulation rates mars are very important for understanding regional and global climate change here we present the grain size composition of detrital sediments and the radiogenic strontium sr and neodymium nd isotopic compositions of different grain size fractions of detrital sediments that were recovered from the western philippine sea these new records show that the different grain size distributions can be associated with 1 asian dust from the western and central chinese deserts and chinese loess and 2 volcanogenic materials that were derived from the luzon islands the mars of this asian dust and volcanic materials are obtained by using weibull function fitting the mars of asian dust and volcanic materials are coupled with the glacial interglacial cycle these values are found to have been higher and more variable during the glacial period than during the interglacial period we argue that the strengthening aridity of the asian continent which is connected to solar insolation and ice volume variations from orbital eccentricity constitutes an important mechanism that drives the high mars of glacial dust in the western philippine sea the internal positive feedback of dust may be another important mechanism the significant increase in volcanic material during the glacial period was caused by sea level changes which were driven by the ice volume and solar insolation at high latitudes and by strengthened precipitation from the el nino southern oscillation enso which is driven by orbital eccentricity and precession cycles on the luzon islands

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

a new chronostratigraphical and evolutionary model for la gomera implications for the overall evolution of the canarian archipelago a review of the general volcano stratigraphy and geochronology of la gomera one of the lesser known canary islands has led to the establishment of a new evolutionary model the oldest edifice corresponds to the submarine stage built up between 20 and 15 ma the construction of the submarine edifice was followed by an important break in the activity about 4 ma and deep erosion of the edifice about 10 5 ma ago the main present day edifice the old edifice 10 5 6 4 ma emerged which was also submarine in its initial phases two different main stages are distinguishable the first stage was represented by a large some 22 km wide basaltic shield volcano the lower old edifice several lateral collapse events tazo and san marcos avalanches occurred during this time and were responsible for the removal of an important part of its northern flank in the second growth stage the upper old edifice the activity migrated southwards a 25 km wide composite volcano arose covering part of the remaining earlier shield volcano the felsic trachytic to phonolitic activity occurring in two separate episodes formed a significant component of this composite volcano finally one more recent large edifice the young edifice built up from 5 7 to 4 ma the lava flows of this younger edifice covered completely the centre and the south of the island and filled deep ravines in the north more evolved magmas including significant felsic magmas the third and last felsic episode occurred in this phase of activity the growth of la gomera was long lasting separated by an important gap in the activity in the middle miocene with no quaternary activity at all at the same time on tenerife the nearest island east of la gomera three large edifices grew separately roque del conde anaga and teno initially three separated islands from the available data it is inferred that the subaerial activity started earlier in the roque del conde edifice then on la gomera and later in teno in the nw and anaga in ne of tenerife which is the youngest of all these edifices these facts together with the irregular general progress of the volcanic activity support more complex views of the genesis for the canary islands than the simple hotspot model

catastrophic debris avalanche from ancestral mount shasta volcano california a debris avalanche deposit extends 43 km northwestward from the base of mount shasta across the floor of shasta valley california where it covers an area of at least 450 km 2 the surface of the deposit is dotted with hundreds of mounds hills and ridges all formed of blocks of pyroxene andesite and unconsolidated volcaniclastic deposits derived from an ancestral mount shasta individual hills are separated by flat topped laharlike deposits that also form the matrix of the debris avalanche and slope northwestward about 5 m km radiometric ages of rocks in the deposit and of a postavalanche basalt flow indicate that the avalanche occurred between about 300 000 and 360 000 yr ago an inferred average thickness of the deposit plus a computed volume of about 4 km 3 for the hills and ridges indicate an estimated volume of about 26 km 3 making it the largest known quaternary landslide on earth

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

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

influence of wintertime large scale circulation on the explosively developing cyclones over the western north pacific and their downstream effects 1 the relationships between large scale wintertime circulation and extratropical cyclones that develop explosively the so called bomb cyclones over the western north pacific are investigated using japanese long term reanalysis project data on a monthly basis the east asian winter monsoon variability strongly modulates the bomb cyclone activity in terms of its geographical distribution when the monsoon is strong the bomb cyclone activity tends to concentrate in the vicinity of the kuroshio current and the kuroshio extension near japan while when the monsoon is weak it disperses over the broader areas the enhancement of the monsoon increases the heat and moisture supply from warm currents facilitating unstable conditions within the atmospheric boundary layer and intensifying baroclinicity in the lower troposphere these factors are believed to play a role in inducing bomb cyclones particularly along the warm currents on submonthly timescales the stationary rossby wave propagation along the south asian waveguide serves as a prominent trigger for the rapid reinforcement of synoptic scale disturbances around japan when a pronounced bomb cyclone comes to its mature stage northeast of japan it is capable of exciting stationary rossby waves downstream from the asian jet exit region as vorticity forcing the stationary wave packets developing southeastward across the north pacific ocean basin induce surface cyclogenesis in the vicinity of the hawaiian islands by leading to the equatorward advection of higher potential vorticity from the midlatitudes bringing about the occurrence of kona storms which cause weather hazards in hawaii

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

the contribution of landslides to landscape evolution in europe abstract after a review of some analytical and conceptual models of slope evolution with the intervention of mass movements a proposal is made of a series of indicators for the quantitative description of landscape evolution in relation to mass movements the ratio between landslide mobilisation rate and downwearing rate is proposed as a quantitative measure of the significance of mass movements in landscape evolution a subdivision of european regions with respect to their susceptibility to landsliding as a process of landscape evolution is proposed the role of landsliding for the evolution of landscape in some regions is described the data presented show that landsliding may in some cases be the main contributor to landscape change

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

enso impact on kelvin waves and associated tropical convection abstractthe impact of el nino southern oscillation enso on atmospheric kelvin waves and associated tropical convection is investigated using the ecmwf re analysis noaa outgoing longwave radiation olr and the analysis technique introduced in a previous study it is found that the phase of enso has a substantial impact on kelvin waves and associated convection over the equatorial central eastern pacific el nino la nina events enhance suppress variability of the upper tropospheric kelvin wave and the associated convection there in both extended boreal winter and summer the mechanism of the impact is through changes in the enso related thermal conditions and the ambient flow in el nino years because of sst increase in the equatorial central eastern pacific variability of eastward moving convection which is mainly associated with kelvin waves intensifies in the region in addition owing to the weakening of the equatorial eastern pacific westerly duct in the upper troposphere in el nino years

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

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

structure composition and age of the small islands of santa luzia branco and raso cape verde archipelago abstract the northern alignment of cape verde archipelago contains three small islands in its central sector santa luzia branco and raso on which there is very scarce geological petrological or geochronological information available the three islands along with the island of sao vicente arise on a continuous underwater relief less than 50 m deep and about 70 km long that formed from separate volcanic edifices the southernmost island raso is formed by accumulation of several tens of lava flows and some remaining strombolian cones an erosion surface covered by sediments allows the separation of two different episodes of growth the lower one older than 2 ma and the upper one between 0 9 and 1 2 ma the smaller island of branco is the remnant of a large stratovolcano about 6 km in radius 1000 m of altitude and between 5 and 6 ma in age santa luzia the northernmost and largest island of this particular group is essentially a remaining rift zone between 4 and 7 ma old at least 600 m high about 10 km long and 7 km wide the se extreme of the island is occupied by rocks of an older partially submarine stage of growth which also include gabbroic intrusions crossed by a dense network of dikes whose age may be estimated in 8 ma or more on the contrary the nw end shows the only remains of late post erosion activity that is of much less volumetric importance and it has been dated between 0 8 and 1 4 ma the three islands as a whole are formed by moderately or strongly alkaline basic and ultrabasic rocks similar to those found in the neighboring island of sao vicente ultraalkaline rocks only appear in raso and differentiate types as trachyandesites and phonolites are exclusively found in santa luzia the similar age found for the main stages of growth recorded in the mentioned four islands and even more in the other two islands santo antao and sao nicolau situated at the end of the barlovento alignment are not easily comprehensible with evolution models implying a simple spatial progression of the volcanic activity from east to west in this array of the archipelago on the other hand the temporal coincidence in periods of quiescence observed in the different islands seems to point to the existence of a cyclical activity for the ensemble

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

hydroclimate implications of thermocline variability in the southern south china sea over the past 180 000 yr abstract based on core top calibration the tex 86h derived temperature has been considered as representing subsurface sea temperature ssst and the difference between the u 37 k derived sea surface temperature sst and the tex 86h derived ssst can be used to reflect the depth of thermocline dot in the south china sea region jia et al 2012 we evaluated the dot dynamics in late quaternary records using this approach on paired analysis of samples from core md05 2896 7 in the southern south china sea the reconstructed dot over the last 180 000 yr 180 ka displays a shoaling trend in glacial periods which may be attributed to the strengthened cyclonic gyre by the enhanced east asian winter monsoon and walker circulation with prominent la nina like state and vice versa in interglacial periods corresponding to reduced winter monsoon with enhanced el nino like state these upper water thermal variations testify that enhanced winter monsoon was the direct cause of an uplifted local thermocline during glacial or la nina like states with strengthened cyclonic gyre due to positive wind stress curl in the southern south china sea our results provide insights into the relationship between monsoon and enso on both glacial and millennial time scales

constructive and destructive episodes in the building of a young oceanic island la palma canary islands and genesis of the caldera de taburiente the results of new field observations 23 new k ar determinations and sixteen previously published determinations provide the basis for the reconstruction of the subaerial volcanic history of the island of la palma after the seamount activity represented by the materials of the basal complex an eruptive phase between 2 0 and 1 3 ma formed a large shield a period of volcanic quiescence followed until around 1 ma during which a large lateral collapse partly destroyed the former edifice between 1 05 and 0 7 ma activity was renewed in the shield and a n s ridge was built in the southern part of the island around 0 7 ma two new large lateral collapses affected the western part of both edifices and they were followed by eruptions between 0 71 and 0 65 ma which built a new edifice that partly filled the depressions thus created the caldera de taburiente constitutes the eroded remnants of the depression formed in the northern shield from 0 65 ma to present activity has been restricted to the n s ridge which has continued to grow southwards there was a general n s migration of volcanic activity with time but in the shield the trend was northwest to southeast eruptive rates seem to have been fairly constant during the different eruptive phases considered between 0 15 and 0 37 km3 ka a very similar succession of constructive and destructive episodes has been obtained for the neighboring island of hierro but in this case the activity started around 0 8 ma and eruptive rates were about 0 5 km3 ka

water quality effects on clogging rates during reclaimed water asr in a carbonate aquifer summary well clogging remains a major operational issue particularly in light of the increased attention being given to the reuse of reclaimed water through the method of aquifer storage and recovery asr in seasonally arid regions at a reclaimed water asr trial site in a limestone aquifer at bolivar in south australia rates of clogging were related to the quality of the injectant over a 4 year study period during which time water quality generally improved due to advancements in pretreatment rates of clogging within a 4 m radius of the asr well defined by changes in the relative intrinsic permeability of the aquifer were enhanced at higher levels of turbidity total nitrogen ntot and ph due to their resultant effects on particle filtration microbial growth and calcite dissolution respectively water quality changes due to the movement of the injectant to an observation well at a radius of 4 m verified these processes at this site acceptably low rates of short and long term clogging were achieved for turbidity

field tests of pumping recharge technology for deep confined aquifers and its application to a deep excavation abstract the execution of deep excavation above confined aquifers asks for dewatering measurements to reduce the hydrostatic pressure so that the safety of the deep excavation can be assured dewatering will inevitably cause deformations in the surrounding strata to reduce the dewatering induced strata movement an innovative pumping recharge technology has been developed in which the dewatering is carried out in the excavation and the recharge is conducted near the protected facilities however the capacity and efficiency of this technology in deep confined aquifers need to be further investigated this paper presents two in situ pumping recharge tests in a deep confined aquifer under a deep foundation pit the feasibility of artificial recharge in the deep confined aquifer has been verified by conducting a single well pumping and multi well recharge test with different discharge and injection rates then a multi well pumping recharge test was carried out in accordance with the requirement and circumstance of construction to evaluate the capacity and efficiency of recharge in controlling the drawdown and ground settlement the results showed that multi well recharge could form a water curtain which has a water proof function to reduce the groundwater drawdown meanwhile by controlling the groundwater head of the confined aquifer during the recharge the pumping induced settlement of the surrounding area can be reduced or even eliminated the pumping effect in the pit would be affected by the recharge around the protected facilities so it is necessary to take in situ pumping recharge tests to determine the layout of wells and the discharge and injection rate finally the artificial recharge was applied to the construction of a deep excavation in shanghai and the drawdown and the ground settlement around the protected buildings were effectively controlled by recharge

later stages of volcanic evolution of la palma canary islands rift evolution giant landslides and the genesis of the caldera de taburiente the islands of la palma and el hierro form the western end of the hotspot induced canary islands chain both islands are at present in the earliest and fastest shield building stage of growth and show many similarities with the hawaiian islands la palma shows two very distinct phases of volcanic construction 1 a pliocene submarine volcanic and intrusive series interpreted as an uplifted seamount at least 1500 m above present sea level and 2 a subaerial volcanic series erupted in the past 2 m y taburiente volcano initially formed the northern part of the island and then extended to the south forming a ridge cumbre nueva ridge that was partially destroyed about 560 ka by a giant lateral collapse the cumbre nueva collapse possibly involving 180 200 km 3 of subaerial volcanic material the northwest boundary of the cumbre nueva collapse formed a vertical scarp that enlarged by headward erosion formed the spectacular depression of caldera de taburiente cumbre vieja volcano a north south elongated rift forms the southern half of la palma and constitutes its last stage of growth including all eruptive activity in the past 125 k y detailed field observations mapping and high precision radiometric dating have allowed reconstruction of the growth and structural changes of the cumbre vieja volcano interactions between eruption rates coastal erosion and glacio eustatic sea level change allow stratigraphic subdivision of the edifice the structure of the volcano has been controlled for most of its history by a rift system with a clearly dominant north south and less distinct north east and north west volcanic rift zones the rift reorganization of the volcano to a single north south rift since 7 ka and the opening of faults during the 1949 eruption probably reflect increasing instability of the west flank of the volcano

a large volcanic debris avalanche in the pliocene roque nublo stratovolcano gran canaria canary islands abstract during the second magmatic cycle of gran canaria between 5 and 3 ma the roque nublo stratovolcano rns achieved its almost total development reaching a height of 2500 2600 m and spreading about 100 km 3 of products over a surface area of at least 250 km 2 in the last growth stage of the rns and probably in connection with the paroxysmic genesis of the roque nublo explosive caldera a sector of the volcanic edifice suffered a gravitational collapse of significant importance the data reported here show that the collapse was accompanied by a great avalanche the roque nublo debris avalanche deposit rndad composed mainly of block facies the last explosive emissions of the rns were restricted to ignimbrites and some explosive breccias that locally overlap the avalanche deposits the features of the outcrops along the course of the avalanche make it possible to distinguish between the proximal intermediate and distal deposits the debris avalanche 3 4 km 3 moved sw then s and finally sse part of the deposit mainly formed by large megablocks remained very near the source area halfway along the course the avalanche was channelled by broad and steep paleovalleys in the most distal areas the rndad opens into a fan shape reaching a distance of 28 30 km a simplified kinematical physical model is used to understand the movement of the rndad the model is based on the speculative reconstruction of the rns edifice based in turn on its scarce peripheral remains an arbitrary avalanche path was selected with a total travel distance from the source area top of the stratovolcano of 28 km with these assumptions it is possible to calculate the speed at each point v m 90 m s and other parameters that show that the rndad is very similar to other well known volcanic avalanches

dike swarms key to the reconstruction of major volcanic edifices the basic dikes of la gomera canary islands the detailed study of the age and distribution of the basic dikes of la gomera canary islands has allowed us to reconstruct the evolution of its main volcanic edifice the dikes of the oldest unit the basal complex have a n70 80 dominant direction at regional scale on the other hand the dikes of the post basal complex subaerial units are the result of local stress fields the oldest swarm is composed of sills dated at 10 2 9 3 ma four younger radial dike swarms have been identified s1 s2 s3 and s4 with ages of 9 1 8 4 ma 8 2 6 7 ma 5 5 4 4 ma and 5 3 4 0 ma respectively the reconstruction of the magmatic focus location using these swarms shows a migration southwards with an average speed of 1 6 mm year this temporal sequence of parallel swarms sills and radial swarms is a pattern frequently repeated during the building of large insular volcanic edifices in the canary islands as well as in other archipelagos

the felsic complex of the vallehermoso caldera interior of an ancient volcanic system la gomera canary islands abstract a mid to upper miocene felsic cone sheet dike complex caldera collapse and dome intrusion located around the vallehermoso and tamargada areas north of la gomera island is described it constitutes one of the less known volcanic episodes in the canary archipelago and especially in la gomera island based on detailed field and structural evidence it is suggested that the cone sheet shows at the surface an almost circular geometry truncated to the nw sector after the cone sheet dike complex formed decompression of the interior of an assumed shallow magma chamber occurred due to the subsequent migration of felsic magma throughout the dikes of the cone sheet this last event caused the roof of the magma chamber to collapse leading to the formation of a 3 to 4 km wide caldera a breccia deposit formed during the collapse and filled a depressed central area which finally was affected by an episode of magmatic resurgence leading to a later almost circular dome intrusion the association of cone sheet breccia deposits and domes constitutes the so called trachytic phonolitic complex tpc and should be viewed as the root of an ancient intensely eroded volcanic edifice made of trachytes nepheline phonolites and minor hauyne phonolites as the dominant materials a description of the structural petrological and geochemical features of the trachytic phonolitic complex and a discussion about their origin are considered in this paper we also consider the correlation between another felsic intrusion of alkali gabbros and syenites called tamargada syenites that also crops out in the vallehermoso tamargada area with respect to the trachytic phonolitic complex our data suggest that this alkaline intrusion of alkali gabbros and syenites belongs to an earlier intrusive episode on the basis of petrological geochemical and detailed field studies both trachytes and nepheline phonolites included in the trachytic phonolitic complex most likely evolved from alkali mafic magmas from the upper old basalt formation through a dominant fractional crystallization process additionally hauyne phonolites could develop from local and later magmatic processes such as gas transfer that altered and changed a small part of the previously mentioned nepheline phonolites to hauyne phonolites

determination of sediment volumes accumulation rates and turbidite emplacement frequencies on the madeira abyssal plain ne atlantic a correlation between seismic and borehole data the sedimentary infill history of the madeira abyssal plain map is established from correlation of odp leg 157 drillsites sites 950 952 with an almost regular grid of 7000 km of intermediate resolution seismic reflection profiles covering the central part of the abyssal plain the most conspicuous seismic reflectors bounding the seismostratigraphic units have been identified and mapped correlation between seismic and borehole data using synthetic seismograms allows the lithological attribution and dating of the reflectors and seismostratigraphic units lateral mapping and correlation of seismic units also allows both the volumes and rates of accumulation of sediments within each seismostratigraphic unit and equivalent time periods of deposition to be determined these calculations have been corrected for the effect of compaction calculated at around 40 at the base of the drillholes three main turbidite types have been identified at the drillsites and their emplacement frequency has been calculated for each site and time period our results show that cretaceous oceanic crust was draped with red pelagic clays and the fracture zone valleys were completely infilled and levelled in a geologically rather short time probably during the latest oligocene and early miocene by organic rich turbidites derived from the nw african continental margin at 16 ma the topography was levelled enough to allow large turbidity current flows to cover the entire plain during the middle and late miocene 16 5 9 ma organic rich turbidites were emplaced on the abyssal plain at a low rate of accumulation 12 m my in the uppermost miocene early pliocene 5 9 3 6 ma turbidite emplacement increased markedly in both frequency and accumulation rate e g 26 m my for organic rich turbidites during this time period emplacement of volcanic rich turbidites also increased in volume and frequency a trend that continued into the pliocene increased volcanic rich turbidite emplacement correlates well with increased volcanic activity on the canary islands and increased organic rich turbidite emplacement may correlate with periods of erosion on the nw african continental margin these erosional periods may be related to global cooling and falling sea level intensification of bottom water currents and enhanced upwelling on the margin

deformation of the substratum of a large shield volcano triggering factor for past flank collapses in the old volcanic edifice of la gomera canary islands the basal complex of la gomera canary islands has been analyzed with the aim of deciphering its structural evolution spanning the middle to late miocene detailed structural maps and cross sections and the results of a systematic measurement of dike orientation and fault slip data are presented in this work the main structural features found in the basal complex of la gomera are four dike sets and two large normal faults guillama and montana de alcala faults several extensional episodes have been identified the main deformation phase corresponds to a nnw sse to nw se directed extension that generated first a dense swarm of mafic dikes and then a large scale collapse of the basal complex with displacement along the guillama and montana de alcala faults and associated rotation of large blocks of la gomera basement it is interpreted that the supposed staircase geometry of the guillama fault is responsible for the observed arrangement of rotated dikes due to development of kilometric scale fault bend folds with rounded hinges deformation of the basal complex shows a complete geometric kinematic and chronologic consistency with the large volcanic flank collapses that affected the units belonging to the early growth stages of la gomera subaerial shield volcano the results of this work support the models that invoke the importance of the large scale geodynamic setting on volcano destabilization more attention should be paid to the structural and geophysical characteristics of volcano basements in order to better evaluate the danger of large catastrophic volcanic landslide events

earlier history of the 70 ma old canary hotspot based on the temporal and geochemical evolution of the selvagen archipelago and neighboring seamounts in the eastern north atlantic major element trace element and sr nd pb isotope data combined with 40ar 39ar age determinations of volcanic rocks from the selvagen islands and neighboring seamounts in the eastern north atlantic reveal the earlier history of the 70 ma old canary hotspot a basanitic to phonolitic late shield stage intrusive complex 29 ma is exposed on selvagem pequena the evolution of selvagem grande can be divided into three magmatic phases a tephritic to phonolitic late shield stage intrusive complex 24 26 ma and two rejuvenated or post erosional stages 8 12 and 3 4 ma consisting of alkali basalt basanite and rare phonolite during the early to mid miocene volcanic hiatus 12 24 ma the top of the volcano was beneath sea level as evidenced by marine carbonate sediments 13 24 ma dated through correlation of 87sr 86sr with the seawater sr isotope curve the geochemistry of the shield stage lavas indicates that they derive from plume sources whereas the post erosional lavas are derived from metasomatized lithospheric sources five sampled seamounts to the east and northeast of the islands range in composition from alkali basalt and basanite to phonolite samples from dacia conception bank and lars were dated at 9 17 and 68 ma respectively geochemical data suggest that the dredged samples come from the post erosional stage of volcanism and therefore the dates represent minimum ages for the seamount volcanoes the elevation of erosional platforms formed at wave base decrease from selvagen grande 100 m above sea level to lars seamount 900 m below sea level suggesting a southwest to northwest age progression and that all of these seamounts are older than the selvagen islands trace element and sr nd pb isotopic composition of the selvagen islands and neighboring seamounts are consistent with their origin from the canary plume interaction of the weak canary mantle plume with a slow moving plate appears to be responsible for generating a 450 km wide irregular hotspot track extending 800 km from the youngest canary island of hierro in the southwest to lars seamount in the northeast

volcanic evolution of sao vicente cape verde islands the praia grande landslide abstract the island of sao vicente has undergone continuous volcanic activity from pliocene to pleistocene times the earliest evidence of activity corresponds to some 9 million years ago when a submarine edifice of alkaline basaltic affinity had already started to develop the island resulted from the growth of a single major edifice the sao vicente edifice built up in several distinguishable growth stages the early main stage occurred at 6 5 to 4 5 ma giving rise to an edifice of about 10 12 km in radius and more than 2500 m in height whose centre was located south of the present city of mindelo although the edifice in its earlier phase showed typical characteristics of a shield volcano the mindelo formation it adopted later on those of an ordinary composite volcano the madeiral monte cara formation a giant landslide event the praia grande landslide destroyed the ne sector of the edifice and left a 10 12 km large depression that was successively refilled by nephelinitic lava flows and some associated carbonatites the monte verde formation 4 5 3 1 ma the volcanic activity ceased about 3 2 ma ago when the edifice started to be deeply eroded until disappearing about 90 of its total volume only in recent times 0 3 ma very scarce and local strombolian activity has been developed aside the sao vicente edifice in the eastern sector of the island

low frequency variability in the northern hemisphere winter geographical distribution structure and time scale dependence abstract low frequency variability in wintertime 500 mb height is examined with emphasis on its structure geographical distribution and frequency dependence a 39 year record of 500 mb geopotential height fields from the nmc analyses is time filtered to partition the fluctuations into frequency bands corresponding to periods of 10 60 days 60 180 days and 180 days winter is defined as the six month period november through april variance teleconnectivity and anisotropy fields and selected loading vectors derived from orthogonal and oblique rotations of the eigenvectors of the temporal correlation matrix for each band are shown and discussed the variability in all frequency bands exhibits substantial anistropy with meridionally elongated features arranged as zonally oriented wave trains prevailing over the continents and zonally elongated features organized in the form of north south oriented dipole patterns prevailing over the oceanic sectors of the hemisphere the wave trains are most pronounc

sediment stability on the western flanks of the canary islands abstract sediment failures on the flanks of the canary islands are well documented but few geotechnical studies have been conducted in this study the sedimentological and geotechnical properties water content grain specific gravity bulk density grain size consolidation and triaxial test data of sediment recovered in cores from the submarine slopes of the island of la palma canary islands ne atlantic indicate that the sediment is heavily to lightly overconsolidated the overconsolidation is considered to be apparent in the absence of any evidence suggesting sediment erosion normalised strengths range from 0 53 0 77 for the carbonate rich sediment the sediment stability was semiquantitatively assessed the sediment off la palma is stable under drained and undrained static loading conditions at present however if affected by horizontal ground accelerations in excess of 15 of gravity the sediment will become unstable locally on sediment waves for instance slope angles may be greater thus enhancing the potential for sediment failure triggering can potentially be explained in terms of the likely magnitude and frequency of seismic accelerations although other trigger mechanisms may have enhanced the failure potential of these sediments in the past steady state analysis indicates that all the sediments tested are state ii type and are unlikely to result in disintegrative morphologies e g debris flows after initial failure the sediment in the source region of the canary debris flow must therefore have undergone transition from state ii to state i type sediment perhaps brought about by a progressive style of failure during or after initial failure this may be caused by a debris avalanche from the volcanic island flanks

recurrent large scale landsliding on the west flank of la palma canary islands a large area of debris avalanche deposits has been discovered on the western submarine flanks of the island of la palma multibeam bathymetry and its derivative backscatter data towed ocean bottom instrument tobi sidescan sonar images and 3 5 khz and airgun seismic reflection data have been used to identify at least two and possibly as many as four major landslide events the youngest of the events the cumbre nueva debris avalanche extends onshore into the valleys bounded by the caldera de taburiente and cumbre nueva ridge which mark the degraded collapse scars radiometric dating of the volcanic flows in the headwall indicate an age of between 536 and 125 ka for this landslide the debris avalanche covers an area of 780 km2 has a maximum thickness of 500 m and has an estimated volume of 95 km3 older deposits collectively referred to as the playa de la veta debris avalanche complex are probably as the name indicates an amalgamation of at least two or three events rather than the result of a single catastrophic failure the playa de la veta debris avalanche complex is associated onshore with an unconformity dated as late matuyama 1 ma to 800 ka it covers an area of 1200 km2 has a maximum thickness of 1300 m and may represent a total volume of up to 650 km3 the greater thicknesses and limited areas occupied by debris avalanches on the western flank of la palma compared to other landslides in the canary archipelago suggest that the la palma landslide masses have relatively low mobility the different debris avalanche lobes formed by each landslide event are separated by channels 2 2 5 km wide the clear relationship between channel position and the boundaries of each debris avalanche lobe indicates that debris avalanches control later channel formation and pathways the relief of the submarine flanks of the la palma volcanoes in the areas of island slope unaffected by landslides is mainly the result of constructional volcanic processes however the older submarine slopes such as in the northern taburiente volcano may also have been modified by smaller scale submarine mass wasting and sediment flows

global teleconnections in the 250 mb streamfunction field during the northern hemisphere winter abstract teleconnections of the streamfunction in the global domain based on ecmwf 250 mb winds for the 11 northern winters from 1978 79 through 1988 89 are documented in this study a zonal structure with a node near the equator indicating an out of phase relationship between the streamfunctions in the northern and southern hemisphere appears to mask the fluctuations of the asymmetric components of streamfunction after removing zonal means a global pattern emerges as the dominant structure in the low frequency band this pattern consists of several dipoles straddling either the exit region of midlatitude jets or the equator indicating the existence of teleconnections not only between the midlatitudes and the tropics but also between the northern and southern hemispheres teleconnection patterns in the intermediate frequency band are predominantly wavelike seven waveguides are identified based on the one point lag correlation maps for base points near the maximum teleconnectivity among them are thr

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

sixteen year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at shigaraki japan we analyzed the horizontal phase velocity of gravity waves and medium scale traveling ionospheric disturbances mstids by using the three dimensional fast fourier transform method developed by matsuda et al 2014 for 557 7 nm altitude 90 100 km and 630 0 nm altitude 200 300 km airglow images obtained at shigaraki mu observatory 34 8 n 136 1 e dip angle 49 over 16 years from 16 march 1999 to 20 february 2015 the analysis of 557 7 nm airglow images shows clear seasonal variation of the propagation direction of gravity waves in the mesopause region in spring summer fall and winter the peak directions are northeastward northeastward northwestward and southwestward respectively the difference in east west propagation direction between summer and winter is probably caused by the wind filtering effect due to the zonal mesospheric jet comparison with tropospheric re analysis data shows the difference in north south propagation direction between summer and winter is caused by differences in the latitudinal location of wave sources due to convective activity in the troposphere relative to shigaraki the analysis of 630 0 nm airglow images shows that the propagation direction of mstids is mainly southwestward with a minor northeastward component throughout the 16 years a clear negative correlation is seen between the yearly power spectral density of mstids and f10 7 solar flux this negative correlation with solar activity may be explained by the linear growth rate of the perkins instability and secondary wave generation of gravity waves in the thermosphere

impact of enso on east asian winter monsoon during interglacial periods effect of orbital forcing orbital forcing influences climate phenomena by changing incoming solar radiation in season and latitude here changes in the el nino southern oscillation enso s impact on the east asian winter monsoon eawm due to orbital forcing especially for three selected time periods in each of two interglacial periods the eemian 126 122 115 ka and holocene 9 6 0 ka are investigated there was a high negative correlation between enso and eawm when the obliquity was low the processional angle was large and especially when accompanied by large eccentricity which corresponds to a weaker monsoon period the correlation was also high when enso variability was high which interestingly corresponded to lower obliquity and higher degree precession periods therefore as both lower obliquity and higher degree precession such as during 115 ka and 0 ka cause the eawm to be weakened through higher winter insolation over northern hemisphere and the enso to be enhanced through an intensified zonal contrast of the equatorial sea surface temperature the relationship between the enso and eawm becomes tighter the opposite case i e during 126 and 9 ka is also true dynamically furthermore the sensitivity of boreal winter precipitation against sea surface temperature sst anomaly over the tropical pacific which depends on mean sst was positively correlated to the strength of the enso eawm correlation implying that the warmer mean ocean surface causes the strong response of atmosphere to change in the sst anomaly thereby enhancing the impact of enso on eawm warmer wintertime tropical sst is attributed to higher insolation over the tropics especially during 115 and 0 ka while cooler ssts occurred during 126 and 9 ka

repeated debris avalanches on tenerife and genesis of las canadas caldera wall canary islands geologic evidence on tenerife canary islands indicates six successive north directed debris avalanche events including the anaga and teno ca 6 ma events that affected the old basaltic series and the tigaiga 2 3 ma roques de garcia possibly 0 6 0 7 ma orotava ca 0 6 ma and icod 0 15 ma avalanche events that affected the canadas and dorsal volcanic edifices the approximate total volume 1000 km3 inferred for these events can account for the volume of previous estimates of offshore volcanic debris these repeated flank failures can also account for the present morphology of las canadas caldera wall which partly bounds a multiepisodic lateral collapse structure 25 km wide

mechanisms of intraseasonal amplification of the cold siberian high mechanisms of intraseasonal amplification of the siberian high are investigated on the basis of composite anomaly evolution for its strongest events at each of the grid points over siberia at each location the amplification of the surface high is associated with formation of a blocking ridge in the upper troposphere over central and western siberia what may be called wave train atlantic origin type is common where a blocking ridge forms as a component of a quasi stationary rossby wave train propagating across the eurasian continent a cold air outbreak follows once anomalous surface cold air reaches the northeastern slope of the tibetan plateau it is found through the potential vorticity pv inversion technique that interaction between the upperlevel stationary rossby wave train and preexisting surface cold anomalies is essential for the strong amplification of the surface high upper level pv anomalies associated with the wave train reinforce the cold anticyclonic anomalies at the surface by inducing anomalous cold advection that counteracts the tendency of the thermal anomalies themselves to migrate eastward as surface thermal rossby waves the surface cold anomalies thus intensified in turn act to induce anomalous vorticity advection aloft that reinforces the blocking ridge and cyclonic anomalies downstream of it that constitute the propagating wave train the baroclinic development of the anomalies through this vertical coupling is manifested as a significant upward flux of wave activity emanating from the surface cold anomalies which may be interpreted as dissipative destabilization of the incoming external rossby waves

las hijas seamounts the next canary island volcanic structures on the seafloor off the nw african coast between 25 n and 32 n were imaged by gloria side scan sonar and simrad em12 multibeam bathymetry the newly discovered las hijas seamounts located 70 km south east of hierro are interpreted as young volcanic edifices their location is consistent with the spacing and timing of propagation of volcanism of the canary archipelago and may represent future sites of volcanic islands

ancient oxide and sulphide mineralization in the islands of tenerife and la gomera canary archipelago spain the alkaline intrusive complexes of tenerife and la gomera canary archipelago spain are formed by nepheline syenites and alkali gabbroids and represent part of the oldest magmatic episodes in both islands this work presents new studies of the petrographic and geochemical features of these rocks and offers the first data about their respective ore minerals iron oxides and sulphides mineralization is represented in both complexes by iron rich patches and veins displaying a simple paragenesis of magnetite ilmenite pyrite and pyrrhotite in association with widespread chloritic alteration of the intrusive host rocks the comparative study of the mineralogical textural and chemical characteristics of the ore minerals allows a metallogenetic model to be proposed which comprises two stages magmatic and hydrothermal in la gomera and only one magmatic in tenerife the migration of the sulphide bearing hydrothermal fluids far from the intrusive complex in tenerife and or possible re melting process could explain the apparent absence of the later hydrothermal stage in tenerife

near collapse of the meridional sst gradient in the eastern equatorial pacific during heinrich stadial 1 1 sea surface temperatures sst and inorganic continental input over the last 25 000 years 25 ka are reconstructed in the far eastern equatorial pacific eep based on three cores stretching from the equatorial front 0 01 n me0005 24jc into the cold tongue region 3 6 s tr163 31p and v19 30 we revisit previously published alkenone derived sst records for these sites and present a revised chronology for v19 30 inorganic continental input is quantified at all three sites based on 230th normalized fluxes of the long lived continental isotope thorium 232 and interpreted to be largely dust our data show a very weak meridional cross equatorial sst gradient during heinrich stadial 1 hs1 18 15 ka b p and high dust input along with peak export production at and north of the equator these findings are corroborated by an earth system model experiment for hs1 that simulates intensified northeasterly trade winds in the eep stronger equatorial upwelling and surface cooling furthermore the related southward shift of the intertropical convergence zone itcz during hs1 is also indicative of drier conditions in the typical source regions for dust

correlation frequency of emplacement and source directions of megaturbidites on the madeira abyssal plain abstract this paper describes the sediments of the whole madeira abyssal plain including the madcap area to the south previous studies have centred on the central sub basin which occupies most of the plain and which has become one of the most studied areas of seafloor the plain is made up of a series of large turbidites separated by thin pelagic layers which can be used to provide a high resolution stratigraphy back to about 750 000 years many of the turbidites were deposited close to oxygen isotope stage boundaries suggesting a strong relationship to sea level climate change although the exact initiation mechanism for the flows is not known data from the northern and southern extensions of the plain shows the effects of different entry points for the four main turbidite groups volcanic rich turbidites enter from the ne and e calcareous turbidites from the w one group of organic rich turbidites enters from the se and one group from the ne and e different turbidite sources operate for limited periods before switching to one of the other source areas it is very rare for two sources to provide turbidites at the same isotope stage boundary

deformation structures associated with the tazo landslide la gomera canary islands deformation structures below the basal plane of gravitational slides can provide useful information about the state of stress undergone by rocks prior to the sliding process and about the triggering forces acting at each particular sliding event in the present work we conducted a structural analysis of the rocks below the surface of the gravitational slide of tazo la gomera canary islands and determined the epigenetic processes involved in the filling of the amphitheatre we also inferred the possible triggering phenomena related to the tazo landslide the rocks located below the surface of the gravitational slide of tazo i e the basaltic lava flows sills and dikes of the lower old edifice and the submarine volcanic rocks gabbros pyroxenites and dikes of the basal complex of la gomera are strongly deformed close to this sliding surface the lava flows and dikes of the lower old edifice are folded with fault breccias and gouges and locally foliated defining the sliding surface the dikes of the basal complex are also folded and the gabbros and pyroxenites are affected by a large number of small faults in the basal complex the sliding surface is defined by a foliated granular gouge in the damage zone the basal complex rocks show an incipient fracture cleavage the sliding amphitheatre has been filled by the debris avalanche or cohesive debris flow generated within the slide as well as by later debris flows hyperconcentrated flows sheet flows and by interspersed lava flows from the upper old edifice we suggest here that the collapse of the north western flank of the lower old edifice at tazo could in part have been triggered by continuous magma injection associated with the emplacement of dikes in a rift zone with an ene wsw direction enhanced by the mechanical weakness of the basal complex unit which was affected by hydrothermal metamorphism under greenschist facies conditions and by the displacement along the montana de alcala and guillama normal faults which are deeply entrenched in the altered rocks of the basal complex

sonar acoustic facies and sediment distribution on an area of the deep ocean floor abstract long range sidescan sonar can be used to map sediment distributions over wide expanses of deep ocean floor seven acoustic facies that arise from differing sediment or rock types have been mapped over the low relief saharan continental rise and madeira abyssal plain these have been calibrated with sampling profiling and camera studies and the facies can be traced confidently on a regional scale using the sidescan data the mapping of the sediment distribution shows that a complex interplay of turbidity current and debris flow processes can occur at a continental rise abysaal plain transition over 1000 km from the nearest continental slope

enso induced tropical convection variability over the indian and western pacific oceans during the northern winter as revealed by a self organizing map 1 the dominant low frequency patterns of outgoing longwave radiation over the tropical indian and western pacific oceans in response to el nino southern oscillation enso during the northern winter are investigated using the nonlinear classification method of the self organizing map som additionally aided by an empirical orthogonal function eof analysis there are at least two different air sea coupled phenomena in the tropical indian ocean i e the indian ocean dipole iod mode in late summer and fall and the wind evaporation sea surface temperature wes feedback driven mode in the winter and spring the som results exhibit that the phase of wes becomes positive negative at the el nino la nina phase which indicates a linear linkage of wes with enso in contrast few combined patterns of the negative iod and the la nina event can be extracted although the reversed pattern is prominent suggesting a nonlinear like relationship between iod and enso since the enso induced convective forcing over the tropical indian and western pacific oceans has strong asymmetric features with respect to the enso phase the remote response of the east asian winter monsoon to enso becomes complicated at the el nino event the monsoon circulation in the southern part of east asia tends to be attenuated in late winter through the dominance of the western north pacific anticyclone in the lower troposphere but at the la nina event the monsoon circulation over korea and japan is enhanced in early winter through the downstream development of stationary rossby wave packets along the south asian waveguide

mindanao dome variability over the last 160 kyr episodic glacial cooling of the west pacific warm pool we present sea surface upper thermocline and benthic delta 18 o data as well as temperature and paleoproductivity proxy data from the international marine global change study program images core md06 3067 6 degrees 31 n 126 degrees 30 e 1575 m water depth located in the western equatorial pacific ocean within the flow path of the mindanao current our records reveal considerable glacial interglacial and suborbital variability in the mindanao dome upwelling over the last 160 kyr dome activity generally intensified during glacial intervals resulting in cooler thermocline waters whereas it substantially declined during interglacials in particular in the early holocene and early marine oxygen isotope stage mis 5e when upwelling waters did not reach the thermocline during mis 3 and mis 2 enhanced surface productivity together with remarkably low sst and low upper ocean thermal contrast provide evidence for episodic glacial upwelling to the surface whereas transient surface warming marks periodic collapses of the mindanao dome upwelling during heinrich events we attribute the high variability during mis 3 and mis 2 to changes in the el nino southern oscillation state that affected boreal winter monsoonal winds and upper ocean circulation glacial upwelling intensified when a strong cyclonic gyre became established whereas el nino like conditions during heinrich events tended to suppress the cyclonic circulation reducing ekman transport thus our findings demonstrate that variations in the mindanao dome upwelling are closely linked to the position and intensity of the tropical convection and also reflect far field influences from the high latitudes

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

enso and east asian winter monsoon relationship modulation associated with the anomalous northwest pacific anticyclone using observational datasets and numerical model experiments the mechanism on the slowly varying change in the relationship between the el nino southern oscillation enso and the east asian winter monsoon eawm is investigated the decadal window 11 15 and 21 year moving correlations show a significant change in the boreal wintertime enso eawm relationship between two sub periods of 1976 1992 and 1997 2013 such recent change in enso eawm relationship is mainly attributed to the changes in the intensity and zonal location of the anomalous lower tropospheric northwest pacific anticyclone nwp ac nwp ac commonly develops near the region of the philippine sea during the enso s peak phase and plays an important role of bridging the tropical convection and mid latitude teleconnection on one hand the intensity of the nwp ac is influenced by the interdecadal variation in a linkage between enso and the indian ocean sea surface temperature sst variability referring that a strong connection between the pacific and indian oceans results in the strengthening of nwp ac response to enso on the other hand the zonal displacement of the nwp ac is associated with the pacific decadal oscillation pdo and the atlantic multidecadal oscillation amo that is the tropical pacific mean state i e zonal sst gradient between climatologically warm western pacific and cold eastern pacific strengthened by either the negative pdo phase or the positive amo phase drives the anomalous enso induced convection to be shifted to the west with this westward shift the zonal center of the nwp ac also migrates westward over the philippine islands and exerts stronger connection between enso and eawm in contrast the relaxed zonal sst contrast associated with either the positive pdo phase or the negative amo phase tends to exhibit weaker enso eawm relationship via both of eastward shifted zonal centers of the anomalous enso induced convection and the nwp ac finally a series of the numerical experiments conducted by an atmospheric general circulation model supports the observational findings

the felsic dikes of la gomera canary islands identification of cone sheet and radial dike swarms on the northern part of la gomera there exists a great abundance of trachytic phonolitic dikes showing a broad diversity in dip and strike several methods have been applied in order to separate these dikes in different sets localise the area from where they derive and reconstruct the geometry of the swarms the oldest dikes correspond to a radial swarm dated at 8 ma the felsic activity migrated then southwestwards and a second radial swarm and a cone sheet complex were developed between 7 5 and 6 4 ma ago the cone sheet complex is 10 km in diameter and shared its centre with that of the second radial structure the cone sheets exhibit an outward decrease of dip angle whilst every individual sheet maintains a constant inclination this geometry reflects the existence of an ancient single dome shaped shallow magma chamber situated some 1650 m below present sea level the eastern radial swarm represents a felsic episode that could mark the ending of the lower old basalts the earlier subaerial activity of la gomera the two other dike swarms represent a younger episode coeval with the upper old basalts

the winter concurrent meridional shift of the east asian jet streams and the associated thermal conditions abstractin this study the concurrent meridional shift of the east asian polar front jet eapj and the east asian subtropical jet easj and the associated thermal conditions have been investigate

geological evolution of the volcanic island la gomera canary islands from analysis of its geomorphology abstract erosion and landslide processes played an important role in shaping the geomorphology of the canary islands but for the heavily eroded la gomera island those processes have been unclear we conducted an integrated study of its offshore extension onshore geology and links between them in order to determine the geomorphological evolution of the island relative to the rest of the archipelago the characteristics of the island s barrancos and its interfluves have led us to differentiate four types of morphological areas whose fluvial networks are in different stages of evolution those barrancos offshore are interrupted by la gomera s shelf and its erosion has been much greater than for the rest of the canary islands such erosion is both a function of time and varied swell action la gomera s insular slope is carved by a system of submarine canyons and channels that have morphology indicative of turbidity current erosion many of the barrancos onshore and the canyons offshore have steps or knickpoints some are the result of varied resistance to erosion and others are explained by other mechanisms a ridge whose crest is covered by cone like shape structures is interpreted as of volcanic origin with the particularity that it lacks onshore continuation the opposite of what has been observed elsewhere in the canary islands also in contrast with the other islands of the archipelago la gomera s margin does not seem to have resulted from destructive mass wasting and the only offshore sign of catastrophic events are the presence of two embayments along la gomera s northern shelf edge and a lobe structure on the insular apron at 3000 m depth these features may be the remains of the catastrophic failures that took place on the island 9 4 8 7 ma ago alternatively they could be due to recent catastrophic failures on the upper slope due to sediment steeping since the conclusion of the main volcanic activity 4 0 ma ago la gomera has been intensively eroded by gradual fluvial denudation and secondary failures la gomera s insular margin reveals much regarding its evolution but more comprehensive studies including seismic and coring are needed to understand its whole geological history

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

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

remote response of the east asian winter monsoon to tropical forcing related to el nino southern oscillation 1 the mechanism of the east asian winter monsoon variability in response to el nino southern oscillation enso related tropical forcing is investigated using japanese long term reanalysis project data additionally aided by the japan meteorological agency climate data assimilation system there are at least two different responses zonally symmetric and asymmetric of the asian jet over south asia to the enso related tropical convective forcing during the northern hemisphere winter the zonally symmetric response induced by zonally extended anomalous convection from the philippine sea through southern india and sri lanka is pronounced at the mature phase of enso the zonally asymmetric response is intimately associated with anomalous convection localized in the vicinity of the philippine and south china seas accompanied by an anomalous walker circulation cell between the maritime continent and tropical indian ocean when this asymmetric response is prominent enso related anomalous convection can give rise to a change in the east asian winter monsoon system through stationary rossby wave propagation along the south asian waveguide the north atlantic oscillation nao related extratropical forcing is also a crucial factor and contributes not only to the downstream development of subpolar teleconnections across northern eurasia but also to the reinforcement of the zonally asymmetric pattern of the asian jet over south asia resulting in a significant effect on the east asian winter monsoon circulation a combination of the enso and nao related forcing plays a vital role in triggering the occurrence of extraordinary anomalous monsoon circulations such as extremely heavy snowfall in the 2005 2006 winter in japan

persistent severe drought in southern china during winter spring 2011 large scale circulation patterns and possible impacting factors 1 severe drought persisted in southern china from january to may in 2011 in this study a statistical analysis is carried out to discuss the multiple possible impacting factors including la nina the north atlantic oscillation nao and the thermal condition of the tibetan plateau tp the la nina event in 2010 11 excited a lower tropospheric anomalous cyclone over the northwestern pacific weakening the northwestern pacific subtropical high and caused an eastward shift of the high as a result transportation of wet and warm moisture from tropical oceans to southern china decreased the la nina event also strengthened the upper tropospheric east asian jet stream and deepened the east asian trough favoring a southward intrusion of dry northerly flow from the siberia the la nina condition in the previous two seasons also seemed to provide precursory signals for the drought moreover in january may 2011 the nao was in a positive phase and it tended to excite stationary rossby waves that were distributed along the sub polar and subtropical waveguides respectively the sub polar one induced an anomalous anticyclone over the siberia favoring a southward intrusion of high latitude northerly flow to southern china the subtropical one associated possibly with the enhanced convection over the broad region from the mediterranean to sahara was favorable for an influence of upper tropospheric flow on southern china the tp might also exert an influence on the drought by weakening the westerly flow to the southern flank of tp and reducing water vapor transport from the bay of bengal to southern china

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

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

numerical assessment of asr recharge using small diameter wells and surface basins summary aquifer storage and recovery asr methods are increasingly used to overcome the temporal imbalance between water demand and availability common asr recharge methods utilize large diameter injection wells or surface infiltration basins and trenches and can be costly to implement a new low cost asr recharge method is currently being developed this approach is based on recharge via gravity in small diameter wells installed with direct push dp technology numerical modeling is used here to assess the potential of this new approach under conditions commonly faced in field settings the primary objective is to investigate if a battery of small diameter dp wells can serve as a viable alternative to a surface basin under typical field conditions while the secondary objective is to assess which subsurface parameters have the greatest control on dp well performance simulation results indicate that gravity recharge via small diameter wells appears to have a distinct advantage over recharge via surface infiltration basins for example two 0 05 m shallow vadose zone wells with 9 m screens can recharge water at a greater rate than a 60 m 2 basin also results reveal that contrary to an infiltration basin the recharge rate in a dp well has a much stronger dependence on the horizontal component of hydraulic conductivity than on the vertical component moreover near surface layers of low hydraulic conductivity which can significantly reduce the recharge capacity of a surface basin have a relatively small impact on the recharge capacity of a well as long as a significant portion of the well screen is installed below those layers given that installation and operation costs can be low in comparison to common asr recharge methods this new approach appears to have great potential for recharging good quality water in shallow unconsolidated aquifers a field investigation has recently been initiated to follow up the findings of this simulation assessment