the evolution of oceanic and atmospheric anomalies in the northeast pacific during the el nino and la nina events of 1995 2001 abstract from late 1995 through early 2001 three major interannual climate events occurred in the tropical pacific the 1995 97 la nina ln 1997 98 el nino en and 1998 2001 ln we analyze atmospheric and upper oceanic anomalies in the northeast pacific nep during these events and compare them to anomalies both elsewhere in the north and tropical pacific and to typical en and ln anomaly patterns the atmospheric and oceanic anomalies varied strongly on intraseasonal and interannual scales during the 1995 97 ln and 1997 98 en the northeast pacific was dominated by negative slp and cyclonic wind anomalies and by upper ocean temperature and sea surface height ssh anomalies the latter were positive along the north american west coast and in the nep thermal anomaly pool between hawaii vancouver island and baja california and negative in the central north pacific this atmospheric oceanic anomaly pattern is typical of en an eastward shift in the atmospheric teleconnection from east asia created en like anomalies in the nep during the 1995 97 ln well before the 1997 98 en had begun the persistence of negative sea level pressure slp and cyclonic wind anomalies in the nep during the 1997 98 en intensified pre existing upper oceanic anomalies atmospheric anomalies were shifted eastward during late 1996 early 1998 leading to a similar onshore shift of oceanic anomalies this produced exceptionally strong positive upper ocean temperature and ssh anomalies along the west coast during the 1997 98 en and explains the unusual coastal occurrences of several species of large pelagic warm water fishes the growth and eastward shift of these pre existing anomalies does not appear to have been linked to tropical pacific en anomalies until late 1997 when a clear atmospheric teleconnection between the two regions developed prior to this remote atmospheric impacts on the nep were primarily from east asia as the 1998 2001 ln developed nep anomalies began reversing toward the typical ln pattern this led to predominantly negative slp and cyclonic wind anomalies in the nep and upper ocean temperature and ssh anomalies that were mainly negative along the west coast and positive in the central north pacific the persistence of these anomalies into mid 2001 and a number of concurrent biological changes in the nep suggest that a decadal climate shift may have occurred in late 1998 during 1995 2001 nep oceanic anomalies tracked the overlying atmospheric anomalies as indicated by the maintenance of a characteristic spatial relationship between these anomalies in particular wind stress curl and ssh anomalies in the nep maintained an inverse relationship that strengthened and shifted eastward toward the west coast during late 1996 early 1998 this consistent relationship indicates that anomalous ekman transport driven by regional atmospheric forcing was an important contributor to temperature and ssh anomalies in the nep and ccs during the 1997 98 en other studies have shown that coastal propagations originating from the tropical pacific also may have contributed to coastal nep anomalies during this en our results indicate that at least some of this coastal anomaly signal may have been generated by regional atmospheric forcing within the nep

the 1997 1998 oceanic el nino signal along the southeast and northeast pacific boundaries an altimetric view changes in the sea surface heights ssh and geostrophic currents along the eastern boundaries of the pacific north central and south america are examined during the 1997 1998 el nino using altimeter data and proxy winds these show that symmetric ssh signals left the equator and propagated into both hemispheres in two episodes with primary periods of high equatorial ssh during may july and october december 1997 these are the distant signals from the mid latitude perspective as the signals spread poleward in each hemisphere their loss of symmetry demonstrates the degree to which they were altered by topographic features local winds and or local currents the first four eofs are calculated for 2 d ssh fields in 10 wide strips along the eastern margins 60 n 60 s and extending out along the equator from the coast to 110 w these account for approximately 40 of the overall variability and represent the main features of the seasonal cycles and el nino interannual variability snapshots of the 2 d ssh fields depict the structure of the el nino signal at different phases of its evolution

coeval giant landslides in the canary islands implications for global regional and local triggers of giant flank collapses on oceanic volcanoes abstract giant landslides are an important part of the evolution of most intra plate volcanic islands they often proceed in catastrophic events likely to generate voluminous debris avalanches and eventually trigger destructive tsunamis although knowledge of the timing of their recurrence is a key factor regarding the hazard assessment in coastal environments only a few of them have been well dated in this contribution we focus on the la orotava event on tenerife which we date with the unspiked k ar technique between 534 and 523 ka such narrow temporal interval is compatible within uncertainties with the age of the cumbre nueva collapse on the neighboring island of la palma we thus examine here the possible common triggering mechanisms at the global regional and local scales both events occurred shortly after the climax of the oxygen isotopic stage 14 during the rapid transition towards the interglacial stage 13 reinforcing the hypothesis of a control from global paleoclimatic changes on the destabilization of oceanic islands intense volcanic pulses at the regional scale also lead to the synchronous overgrowth of several volcanic islands in the archipelago but coeval destabilization on tenerife and la palma appears significantly controlled by the intrinsic morphology of the edifices with contrasted instability thresholds for shield volcanoes and volcanic ridges respectively finally we propose that the two events may be genetically linked dynamic transfer of voluminous debris avalanches during a giant landslide episode can induce isostatic readjustments generate significant ground acceleration and finally produce a large tsunami three processes which can concur to trigger large scale flank collapse on a neighboring mature unstable volcanic island

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

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

satellite observations of the 1982 1983 el nino along the u s pacific coast satellite infrared temperature images illustrate several effects of the 1982 1983 el nino warm sea surface temperatures with the greatest anomalies near the coast weakened coastal upwelling and changes in surface circulation patterns phytoplankton pigment images from the coastal zone color scanner indicate reduced productivity during el nino apparently related to the weakened coastal upwelling the satellite images provide direct evidence of mesoscale changes associated with the oceanwide el nino event

characteristic patterns of the circulation in the santa barbara channel the subtidal near surface circulation in the santa barbara channel sbc and on the shelf north of point conception is described based on observations obtained during the 3 year period from 1993 to 1995 near surface currents in the channel are a superposition of a larger than sbc scale flow and a cyclonic circulation of variable intensity located inside the channel on seasonal timescales the larger than sbc scale flow near the surface is equatorward in spring and poleward from summer through winter the increase in equatorward flow in spring occurs concurrently with the increase in equatorward wind stress and the decrease in near surface temperatures and synthetic subsurface pressures ssps the flow reverses in late spring simultaneously with the increase in the along channel ssp difference and months before wind stress has reached its peak the period during which the cyclonic circulation within the sbc is strongest coincides with the period of strongest poleward flow through the eastern entrance a synoptic description of the circulation in the sbc is presented in terms of six characteristic patterns labeled upwelling relaxation cyclonic propagating cyclones flood east and flood west an analysis of the 5 and 45 m currents into empirical orthogonal functions eofs isolates 50 53 of the 5 m 45 m low frequency current variance into three two modes combining these modes with the mean current fields the modes have spatial patterns that correspond to the characteristic flow patterns subjectively deduced from inspection of daily averages of the near surface currents from late spring through fall the two largest 5 m current modes produce a repeating pattern of circulation in which the sequence of four states namely upwelling cyclonic relaxation and quiescent is traversed roughly every 16 days in addition to the large scale cyclonicity in the central sbc smaller cyclonic eddies form frequently in the eastern channel and travel toward the west with an average speed of 0 06 m s 1 the patterns described here develop in response to the wind stress and the along channel ssp gradient

a 40 50 day oscillation in sea surface temperature along the central california coast abstract previous studies of the tropical troposphere indicate the presence of a 40 50 day quasi periodic oscillation in zonal winds spectral analysis of extensive daily sea surface temperatures ssts reveals a significant increase in variance i e a quasi periodic oscillation between 40 and 50 days along the california coast as far south as santa barbara 34 3 n and at least as far north as port arena 39 n increases in the amplitude of this oscillation at granite canyon 36 n in some cases coincide with local el nino warming episodes the local surface winds which also contain a quasi periodic oscillation between 40 and 50 days are coherent with and lead sea surface temperature by approximately 10 days consistent with local wind forcing it is suggested that the 40 50 day oscillation in sea surface temperature off central california may be related to the 40 50 day oscillation in the tropical troposphere through atmospheric teleconnections between the tropics and mid latitudes

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

altimeter derived variability of surface velocities in the california current system 2 seasonal circulation and eddy statistics abstract satellite surface height and temperature fields are used to examine the seasonal surface circulation in the california current system in spring and summer an equatorward jet develops next to the coast with an initial latitudinal structure that responds to the latitudinal distribution of equatorward alongshore winds this jet moves offshore from spring to fall and develops meanders and closed eddies that contribute eddy kinetic energy and water mass properties to the nearby deep ocean higher eke appears first in spring near the coast and moves offshore with the seasonal jet along altimeter tracks parallel to the coastline 200 and 400 km offshore the greatest eke is found in summer and fall respectively with wavelengths of approximately 300 km these are the wavelengths of the largest meanders and the distance between the largest eddies visible in altimeter snapshots of the jet at 600 800 km offshore the wavelengths are generally smaller 100 150 km similar to eddy sizes reported by others for the quiescent northeast pacific some energy with longer wavelengths arrives at the track 600 km offshore in winter and 800 km offshore in spring which we interpret as the most offshore extension of the eke generated by the jet and eddy system closer to the coast in the previous spring and summer a sequence of snapshots from october 1992 to october 1993 shows details of the evolution of the jet and eddy system over one complete annual cycle

the california current system in the southern california bight and the santa barbara channel recent observations in the santa barbara channel and over the california cooperative oceanic fisheries investigations calcofi southern california grid are used to examine seasonal circulation patterns in and near the southern california bight defined as the region east of the santa rosa ridge and including the santa barbara channel poleward flow relative to 500 m is found throughout the bight in all seasons except for spring and all subregions except the western part of the santa barbara channel in spring there is equatorward flow throughout the bight at all depths to 500 m though it tends to be surface or midcolumn intensified equatorward flow offshore of the bight present in all seasons narrows and accelerates into a jet like feature and simultaneously moves close to the santa rosa ridge in summer current meter data from the eastern entrance to the santa barbara channel are consistent with the seasonal results from the calcofi data and further show an upward propagation of phase at annual period with a phase speed of 1 to 2 m d 1 comparison with the calcofi ship winds suggests that poleward flow in the bight may be the result of positive wind stress curl through a sverdrup balance though the observed transport is only about 75 of that expected from the curl amplitude equatorward flow in the bight may be the result of coastal upwelling though the transport is larger than expected from the relatively weak winds in the bight and the offshore extent of the equatorward flow is about 10 rossby radii farther than might be expected for linearized coastal upwelling equatorward flow outside the bight cannot be explained as a sverdrup flow because the wind stress curl is positive throughout most of the region upward propagation of phase and downward propagation of energy may be indicative of forcing by remote wind equatorward of the bight given the complexity of possible forcing mechanisms for circulation in and near the bight a model that includes effects of remote wind forcing ekman pumping and topography is needed to explain the observations in a satisfactory way

multiple related flank collapses on volcanic oceanic islands evidence from the debris avalanche deposits in the orotava valley water galleries tenerife canary islands abstract catastrophic flank collapses are common on oceanic islands of volcanic origin and often recognizable from the resulting morphology as large u shaped embayments however post collapse volcanic activity can infill such features thereby obscuring them this study takes advantage of a dense network of long sub horizontal galleries for groundwater extraction in the flank collapse structure of the orotava valley tenerife canary islands this impressive landform is located in the overlapping zone of the ne rift and the canadas edifice of this volcanic island three debris avalanche deposits dads have been identified inside the waterworks bored into the valley s western sector the deeper layer the lower dad l dad was previously described under the local name of mortalon this deposit lies unconformably over older volcanic rocks where a prominent shear zone is developed here interpreted as the detachment plane of a massive rockslide the l dad was therefore produced during the large failure event the orotava landslide ol which carved the depression two younger dads much smaller in volume and not previously described were also identified in the underground strata the intermediate i dad and upper dad u dad both correlate well with the thick breccia deposits cropping out at the base of the marine cliff along the western coast of the valley the i dad and u dad are conformably intercalated between the lava flows and other volcanics infilling the depression and their bases are erosive depositional features without structural deformation zones below them their stratigraphic setting and geometrical reconstruction indicate that both deposits were emplaced after the valley was formed by the ol event in two successive failures here called western orotava landslides wols the younger called wol 2 was dated at 494 22 ka using the 40ar 39ar method these two subaerial failures affected the upper eastern flank of the canadas iii edifice previously destabilized when the ol failure event carved a steep wall at its foot the western lateral escarpment of the orotava valley

long term 17 ma turbidite record of the timing and frequency of large flank collapses of the canary islands volcaniclastic turbidites on the madeira abyssal plain provide a record of large volume volcanic island flank collapses from the canary islands this long term record spans 17 ma and comprises 125 volcaniclastic beds determining the timing provenance and volumes of these turbidites provides key information about the occurrence of mass wasting from the canary islands especially the western islands of tenerife la palma and el hierro these turbidite records demonstrate that landslides often coincide with protracted periods of volcanic edifice growth suggesting that loading of the volcanic edifices may be a key preconditioning factor for landslide triggers furthermore the last large volume failures from tenerife coincide with explosive volcanism at the end of eruptive cycles many large volume canary island landslides also occurred during periods of warmer and wetter climates associated with sea level rise and subsequent highstand however these turbidites are not serially dependent and any association with climate or sea level change is not statistically significant

atmospheric forcing of interannual variability in the northeast pacific ocean connections with el nino the nature and causes of the observed interannual variability of oceanic conditions in the northeast pacific were investigated using a variety of meteorological and oceanographic data sets an examination of a long series of seasonal mean atmospheric sea level pressure slp charts showed that when the winter average slp pattern in the north pacific varies significantly from climatology it tends to do this in one of two characteristic ways in particular in some winters there is an anomalously strong circulation which differs from climatology mainly in having an intensified aleutian low in other winters there is an anomalously weak atmospheric circulation this is almost invariably associated with the westward displacement of the aleutian low and the production of a separate but much weaker low in the gulf of alaska the north pacific winter slp appears to have some relation to the southern oscillation so and oceanic temperatures in the tropics in particular el nino southern oscillation enso episodes are generally coincident with strong north pacific slp patterns and often follow winters with weak slp patterns however this relationship is far from being perfectly regular and predictable interannual variations in the intensity of the north pacific atmospheric surface circulation were found to be strongly correlated with the anomalies of both sea surface temperature sst and sea level height slh at stations along the british columbia coast an intense aleutian low is invariably associated with warm coastal waters and high coastal sea levels by comparing a large number of pacific slp and sst maps it was possible to verify that the relation between north pacific slp and oceanic surface temperature actually applies to the sst over much of the northeast pacific at least as far west as 150 w the relationship of north pacific slp with the so together with the relationship between north pacific slp and oceanic conditions in the northeast pacific can account for the observed general tendency for sst and slh along the west coast of north america to be anomalously high during tropical enso episodes on the other hand the lack of a truly predictable relation between the southern oscillation and north pacific slp explains the fact that not all enso events are associated with wanning of the northeast pacific

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

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

the growth collapse and quiescence of teno volcano tenerife new constraints from paleomagnetic data tenerife basically consists of three miocene shield volcanoes the anaga the teno and central shield as well as the pliocene canadas volcano the temporal evolution and structural significance of each volcano with respect to the history of tenerife is still a matter of debate we present paleomagnetic results in order to enhance the view of the volcanic history of the teno volcano by means of magnetostratigraphy it is found that the initial subaerial phase shows reverse magnetizations throughout after two major sector collapses dominantly normally magnetized lavas extruded comparisons of observed magnetic polarities with the geomagnetic polarity timescale show that these volcanic activities occurred within 0 4 myr between 6 3 and 5 9 ma significantly younger flows 5 3 myr old according to their radiometric age revealed again normal polarity throughout the absence of inversely magnetized lavas in between the two normal periods indicates a volcanic hiatus or erosional phase the evolutionary sequence and the estimated high production rates for the initial building phase are similar as would be expected for a hotspot volcano the average geomagnetic field for 6 0 0 2 ma is close to an axial dipole field showing a slight far sided right handed effect the field strength determined by thellier type intensity determinations corresponds to a virtual axial dipole moment of 4 9 1022 a m2 this value is approximately half of the present day field strength but similar to values obtained for the mid miocene it also corresponds to the proposed tertiary low field level of the geomagnetic dipole moment

40ar 39ar stratigraphy of pyroclastic units from the canadas volcanic edifice tenerife canary islands and their bearing on the structural evolution many felsic pyroclastic units of various types are exposed in different sectors of tenerife new 40ar 39ar determinations allow them to be placed more precisely in the general volcano stratigraphic succession according to geographic distribution stratigraphic position and isotopic ages four main pyroclastic phases may be identified the first san juan de la rambla phase 2 1 ma is only known in the north of tenerife in the tigaiga massif the second adeje phase 1 8 1 5 ma is most completely developed in the southwest of the island but occasionally occurs in the other sectors the third las americas phase 1 ma is only presently known in the southern region the fourth bandas del sur phase 0 7 0 15 ma is essentially exposed in the southeast sector the results of this work emphasise the complexity of the pre 1 ma eruptive history of tenerife and underline the fact that explosive volcanic activity has taken place for at least the last 2 ma vertical collapse structures have developed as a result of pyroclastic flow activity and these may be as old as 1 6 1 8 ma therefore much older than generally considered the precise location of calderas is difficult to ascertain as a result of the repeated lateral flank collapse during the construction of the canadas volcano

a view of the 1993 1994 california current based on surface drifters floats and remotely sensed data near surface drifters were deployed in the california current system during the period 1993 1994 in order to study mean and eddy currents the deployment scheme allowed a 2 year period where data density was high enough to make meaningful estimates of eddy statistics and of seasonal mean currents and variances on a 5 grid eddy variability which tended to be isotropic was higher near the coast standard deviations around 0 2 m s 1 and decreased offshore down to 0 1 m s 1 seasonal mean surface flow west of california was southward during all seasons if a davidson current existed during 1993 1995 it was probably either short lived or only found closer to the coast than our study area i e within 100 150 km of shore in some cases drifter populations within a discrete feature were high enough to allow some detailed resolution of its behavior we note a tendency for individual eddies which can last for up to 3 5 months to drift westward at rates of o 5 km day 1 not all eddies in the region are surface intensified there is clear evidence for at least the occasional presence of a thin meandering southward jet in the region that can be 1000 km or more long this jet can be identified with that found in the coastal transition zone program in association with cool filaments the jet appears to become broader and slower south of point conception we hypothesize on the basis of others results as well as ours that the eddies that are strongest at the surface result primarily from instabilities on a southward alongshore mean current and that eddies that are maximal at depth are spawned by the northward undercurrent

the large scale coastal wind field along the west coast of north america 1981 1982 we study the statistical properties of the coastal wind field along the west coast of north america for two summers 1981 and 1982 coastal ocean dynamics experiments 1 and 2 respectively and the intervening winter using measured winds and geostrophic winds calculated from fleet numerical oceanography center atmospheric pressure analyses summer wind fluctuations are driven primarily by the interaction between two relatively stationary pressure systems the north pacific subtropical high and southwest u s thermal low and by their interactions with propagating atmospheric systems to the north in particular propagating cyclones and associated fronts are often followed by a northeastward intensification of the high producing strong upwelling events along the california coast this summer event sequence occurs more frequently and is displaced farther to the south on average during summer 1981 winter wind fluctuations are primarily driven by propagating cyclones and anticyclones and they tend to have larger variance and space scales than in summer a preference for poleward equatorward propagation exists in summer winter and the largest time scales are observed in summer 1982 coastal atmospheric boundary layer processes substantially modify winds within 100 200 km of the coast consequently measured wind fluctuations are strongly polarized in the alongshore direction and have means and rms amplitudes that can vary considerably between nearby stations along the coast calculated wind fluctuations are less polarized in the alongshore direction and have alongshore correlation scales about 60 larger than those for measured winds they represent fluctuations with alongshore wavelengths of 900 km rather well but represent poorly those with smaller wavelengths and those due to coastal atmospheric boundary layer effects

satellite data empirical orthogonal functions and the 1997 1998 el nino off california abstract the features of the 1997 1998 el nino event were analyzed by empirical orthogonal functions eof statistical methods applied to the remotely sensed sea surface temperature anomalies ssta measured by avhrr radiometers anomalies of water circulation derived from sea surface height anomalies ssha measured by topex poseidon radar altimeter and meteorological information air temperature upwelling index and wind stress curl eof statistics demonstrated the features of an el nino event during the second half of 1997 and the first half of 1998 with sea level elevated along the coast and with ssha gradients indicating a retarding of both the equatorward california current and the alongshore poleward southern california countercurrent the positive sst anomaly developed first in the southern california bight and then in the zone of upwelling to the north of point conception the anomalies of upwelling index and the wind stress curl pattern also changed during the el nino event but these changes occurred later than hydrographic variations and were too weak to explain the observed changes in ssta and ssha we conclude that off central and southern california oceanic teleconnection i e the consequences of propagation northward of coastally trapped downwelling waves was responsible for the 1997 1998 el nino event

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

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

the evolution and depth structure of shelf and slope temperatures and velocities during the 1997 1998 el nino near point conception california abstract moored survey and drifter observations are used to describe the evolution of temperature sea level velocity and salinity from 1997 to 1998 over the california shelf between san luis obispo bay and the eastern entrance to the santa barbara channel the dominant event during this time was the 1997 1998 el nino its relation to background seasonal and interannual variability depended on which property is considered subsurface temperature and local sea level showed extreme anomalies between march 1997 and october 1998 three distinct peaks occurred the first two are associated with the regional response to el nino while the cause of the third remains unclear the first peaked in june 1997 and decayed until august the main el nino peak reached maximum amplitude between november 1997 and january 1998 after the collapse of the regional el nino anomaly in february 1998 a final peak occurred locally during the summer of 1998 the central result presented here concerns the spatial structure of temperature during these events the initial peak was surface intensified and was barely detectable at 45 m its amplitude varied with position along the coast decaying with distance north the main peak showed a strong signal down to at least 200 m the amplitude and timing of temperature anomalies during this event were depth dependent the largest absolute amplitudes relative to seasonal cycles were in excess of 4 c and occurred between 45 and 65 m depth the anomalies reached their maximum values at later time with increasing depth between october 1997 and january 1998 the amplitude of this main peak was comparable at all mooring sites the final peak in august 1998 had a comparable amplitude at all mooring sites to a depth of 100 m temperature increases during the three events were accompanied by a corresponding rise in sea level the el nino signals in currents and salinity are more difficult to distinguish from background variability than those in temperatures and sea level however stronger than average poleward flow was observed at the eastern entrance to the santa barbara channel between 5 and 100 m depth for most of 1997 and there are indications for greater than usual poleward flow over the santa maria basin in fall 1997 surface drifter evidence although qualitative also suggests greater than usual poleward displacement in november 1997 relative to other years along with increased temperature survey observations of salinity suggest changes to the regional temperature salinity relation during november 1997 with greater than usual salinity at temperatures below 12 c

slope failures on the flanks of the western canary islands abstract landslides have been a key process in the evolution of the western canary islands the younger and more volcanically active canary islands el hierro la palma and tenerife show the clearest evidence of recent landslide activity the evidence includes landslide scars on the island flanks debris deposits on the lower island slopes and volcaniclastic turbidites on the floor of the adjacent ocean basins at least 14 large landslides have occurred on the flanks of the el hierro la palma and tenerife the majority of these in the last 1 million years with the youngest on the northwest flank of el hierro as recent as 15 thousand years in age older landslides undoubtedly occurred but are difficult to quantify because the evidence is buried beneath younger volcanic rocks and sediments landslides on the canary island flanks can be categorised as debris avalanches slumps or debris flows debris avalanches are long runout catastrophic failures which typically affect only the superficial part of the island volcanic sequence up to a maximum thickness of 1 to 2 km they are the commonest type of landslide mapped in contrast slumps move short distances and are deep rooted landslides which may affect the entire thickness of the volcanic edifice debris flows are defined as landslides which primarily affect the sedimentary cover of the submarine island flanks some landslides are complex events involving more than one of the above end member processes individual debris avalanches have volumes in the range of 50 500 km3 cover several thousand km2 of seafloor and have runout distances of up to 130 km from source overall debris avalanche deposits account for about 10 of the total volcanic edifices of the small relatively young islands of el hierro and la palma some parameters such as deposit volumes and landslide ages are difficult to quantify the key characteristics of debris avalanches include a relatively narrow headwall and chute above 3000 m water depth on the island flanks broadening into a depositional lobe below 3000 m debris avalanche deposits have a typically blocky morphology with individual blocks up to a kilometre or more in diameter however considerable variation exists between different avalanche deposits at one extreme the el golfo debris avalanche on el hierro has few large blocks scattered randomly across the avalanche surface at the other icod on the north flank of tenerife has much more numerous but smaller blocks over most of its surface with a few very large blocks confined to the margins of the deposit icod also exhibits flow structures longitudinal shears and pressure ridges that are absent in el golfo the primary controls on the block structure and distribution are inferred to be related to the nature of the landslide material and to flow processes observations in experimental debris flows show that the differences between the el golfo and icod landslide deposits are probably controlled by the greater proportion of fine grained material in the icod landslide this in turn relates to the nature of the failed volcanic rocks which are almost entirely basalt on el hierro but include a much greater proportion of pyroclastic deposits on tenerife landslide occurrence appears to be primarily controlled by the locations of volcanic rift zones on the islands with landslides propagating perpendicular to the rift orientation however this does not explain the uneven distribution of landslides on some islands which seems to indicate that unstable flanks are a weakness that can be carried forward during island development this may occur because certain island flanks are steeper extend to greater water depths or are less buttressed by the surrounding topography and because volcanic production following a landslide my be concentrated in the landslide scar thus focussing subsequent landslide potential in this area landslides are primarily a result of volcanic construction to a point where the mass of volcanic products fails under its own weight although the actual triggering factors are poorly understood they may include or be influenced by dyke intrusion pore pressure changes related to intrusion seismicity or sealevel climate changes a possible relationship between caldera collapse and landsliding on tenerife is not in our interpretation supported by the available evidence

intraseasonal oscillations in sea level along the west coast of the americas abstract hourly observations of coastal sea level at stations from peru to british columbia are analyzed for low frequency content a space time contour plot of sea level from four years of data during the 1971 75 period shows the meridional structure of the seasonal cycle and interannual variability associated with the 1972 73 el nino oscillations with intraseasonal periods of 36 73 days are also evident coherent over alongshore distances of several thousand kilometers further investigation using spectral methods and empirical orthogonal function analysis in the frequency domain reveals in particular that intraseasonal sea level variability has a peak in spectral density along the coasts of south america central america and mexico with high coherence from near the equator tumaco 2 n north to central california 34 n and south to at least callao 12 s phase propagation north of the equator is poleward at 150 200 kilometers day atmospheric pressure alongshore wind stress and wind stress cu

subsidence history crustal structure and thermal evolution of the valencia trough a young extensional basin in the western mediterranean the valencia trough is an extensional basin that began rifting during the late oligoceneearly miocene yet it is located within a region of compression between the european and african plates seismic reflection seismic refraction well gravity and geoid data have been used to determine the relative importance of extensional and compressional processes in controlling the structure and evolution of the trough although the trough appears symmetric on bathymetric maps seismic and gravity and geoid data indicate a fundamental asymmetry in its deep crustal and upper mantle structure two dimensional flexural backstripping techniques have been used to estimate the total amount of crustal stretching along a transect of the trough between the catalan coastal ranges and mallorca there is good agreement between the predicted depth to the mono based on a stretching model and the seismically constrained depth beneath the catalan margin but poor agreement beneath mallorca the seismic moho beneath mallorca can be explained by a model in which the crust was modified by the flexural effects of thrust fold loading geoid data suggest that the differences in the crustal structure between the two margins extend into the upper mantle the catalan margin is characterized by a thermal and mechanical boundary which marks the transition between cold unstretched lithosphere and hot thin lithosphere while mallorca is located above a broad region of lithospheric thinning the subsidence history and amount of crustal thinning in the catalan margin resemble that of typical atlantic type nonvolcanic margin however a narrow transition zone 60 km the lack of any evidence for a conjugate margin and the absence of oceanic crust suggest fundamental differences in the way that extensional processes may occur in convergent plate settings

variability in the western equatorial pacific ocean during the 1986 87 el nino southern oscillation event abstract we describe variability in the western pacific ocean during the 1986 87 el nino southern oscillation enso event with emphasis on time series measurements of currents temperature sea level and winds near the equator at 165 e zonal winds were anomalously westerly from mid 1986 to late 1987 and were punctuated by 2 10 m s 1 episodes of westerlies lasting about 10 days to 2 months zonal current in the upper 100 m surface layer responded to these wind variations typically within a week in some cases with speeds exceeding 100 cm s 1 to the east zonal current variations in the thermocline below 100 m were generally less coherent with the local wires than currents near the surface they were also generally less variable although the equation undercurrent disappeared for 3 4 weeks in october november 1987 at a time when the normal eastward directed zonal pressure gradient force reversed along the equator periods of intense and prolonged eastward flow in the surface layer were associated with a

a medial to distal volcaniclastic record of an andesite stratovolcano detailed stratigraphy of the ring plain succession of south west taranaki new zealand the 25 ka volcaniclastic ring plain succession in south west taranaki has been remapped to establish a much more detailed understanding of the older stratigraphic record of mt taranaki coastal cliff exposures show a range of volcaniclastic lithofacies including debris avalanche and lahar deposits and allow a detailed chronological reconstruction of past volcanic and sedimentary events five new debris avalanche deposits were identified and their distribution in coastal cross sections mapped in addition four previously described units were renamed and their stratigraphic position and lateral extent redefined chronostratigraphic control of the younger 50 ka sequence was obtained by radiocarbon dating of wood found within or peat interbedded with the deposits emplacement ages of the older units were estimated from their stratigraphic position and underlying marine wave cut surfaces overall at least 14 widespread debris avalanche deposits occur within the 200 ka ring plain record of mt taranaki suggesting one major edifice failure on average every 14 000 years with an increase in frequency since 40 ka the stratigraphic reconstruction of the ring plain succession showed that the same pattern of deposition was repeatedly produced throughout the existence of mt taranaki depending on their sedimentological characteristics the different volcanic and sedimentary lithofacies can be related to phases of edifice construction or collapse events based on the identified cyclic sedimentation pattern we present a new episodic stratigraphy that integrates existing and new lithostratigraphic units into a coherent chronostratigraphic framework that can be applied to the entire volcanic and volcaniclastic succession at mt taranaki this model takes into account the complex geological processes that have taken place on the volcano and provides a more uniform stratigraphic terminology that could be applied to repeatedly collapsing stratovolcanoes elsewhere

circulation in the point conception santa barbara channel region during spring and early summer 1983 fifteen current moorings were deployed around the periphery of santa barbara channel and over the continental shelf to the west off point conception data from these moorings have been used to describe the regional circulation and to address problems of wind forcing and the spatial coherency scales for current fluctuations the mean circulation in santa barbara channel was dominated by a westward jet which occupied the northwestern portion of the channel current and temperature fluctuations were generally well correlated among all locations around the channel and time lags suggested cyclonic propagation of events around the channel the time fluctuations were dominated by a relatively few low frequency events it was impossible to determine exactly either the driving mechanisms for these events or their relationships to regional flow the flow regime was considerably different off point conception than in the channel locally wind driven upwelling was observed in both the mean and fluctuating flows and the time scales of current variability i e spectral shapes mimicked those of the local winds a dramatic change in the regime off point conception occurred in late may before the transition currents and sea levels had been well correlated in time with both local and remote winds after late may the relation to fluctuating winds was less clear and the alongshore structure of sea level variability had changed radically

el nino induced onshore transport in the california current during 1982 1983 persistent 9 month large scale positive temperature 3 4 c negative salinity 0 1 0 3 and positive dissolved oxygen 0 5 1 ml l subsurface anomalies characterize the el nino induced onshore transport in the california current during 1982 83 these anomalies characteristic diagrams and sign reversals in the salinity and oxygen anomalies are consistent only with enhanced onshore transport of subarctic water from the offshore california current onshore transport excludes poleward propagating kelvin waves as a generation mechanism for the 1982 83 californian el nino the data however support the conclusion simpson 1983 that an anomalous basinwide atmospheric circulation produced the californian el nino

eruptive response of oceanic islands to giant landslides new insights from the geomorphologic evolution of the teide pico viejo volcanic complex tenerife canary large sector collapses are a major component of oceanic islands evolution here we show that voluminous events such as the icod landslide on tenerife canary islands cause dramatic changes on the magma feeding system and control the subsequent volcanic and geomorphologic evolution of the eruptive complex over a period of more than 150 kyr instantaneous unloading by the icod landslide is marked by the development of a large phonolitic explosive eruption dated at 175 3 ka and interpreted as reflecting the immediate emptying of a shallow pre existing magma chamber geochronological geomorphological and geochemical analyses carried out on the post landslide volcanic succession sampled in a 4 4 km long underground water recovery gallery provide further evidence for an enhanced extrusion of primitive lavas starting in the 10 kyr time interval following the failure rapid construction 40 kyr of a thick basaltic volcano in the landslide scar at high eruptive rates up to 8 km3 kyr 1 increased the lithostatic pressure which then favored the intermittent storage of basic magma under the edifice this resulted in more episodic construction evidenced by a significant decrease in output rates and the increasing occurrence of lavas with intermediate composition from 117 7 to 52 7 ka an apparent volcanic gap is observed between 52 7 and 18 1 ka after which highly differentiated lavas have been dominantly erupted we propose that part of the gap can be explained by the individualization of a shallow magma reservoir a few kilometers below the base of the teide volcano during recent periods vertical and lateral extrusions of trachytic and phonolitic viscous bodies from this storage area contributed to increase the slope of the main edifice up to 35 overall favoring its present day instability

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

large scale structure of the spring transition in the coastal ocean off western north america past measurements off the coast of central oregon and washington have shown that the rapid change from northward monthly mean winter winds to southward summer winds forces a spring transition of the coastal ocean sea levels and temperatures drop and mean surface currents shift from northward to southward current and water temperature data from 35 n to 48 n from 1981 and 1982 and sea level and wind stress data from 1971 1975 and 1980 1983 show the transition to have a large alongshore scale typically 500 to 2000 km the large scale wind stress appears to be the forcing mechanism at latitudes north of approximately 37 n south of 37 n sea level usually falls more gradually before the northern transition event both wind and sea level events generally progress from south to north over a 3 to 10 day period but this is not always true several aspects of the spring transition reflect coastal trapped wave dynamics previous studies at 45 n found persistent vertical shear of the southward summer current associated with a cross shelf density gradient during 1982 the shear and the density front develop over the shelf break immediately after the transition at 43 n and to the south but they are much less persistent than at 48 n the stronger winds between 38 n and 42 n and the narrower shelf result in an offshore displacement of the density front and vertical shear past the shelf break leaving the water over the shelf less stratified and more subject to barotropic reversals of the current than that farther north where the front stays closer to the coast

morphological and geological aspects related to large slope failures on oceanic islands the huge la orotava landslides on tenerife canary islands huge volcanic landslides are one of the most hazardous geomorphological processes that can occur during the evolution of volcanic ocean islands the causes of these phenomena however are very complex and combine non volcanic and volcanic factors in the canary islands more than 20 events have been detected during the last decades a detailed analysis was carried out for la orotava amphitheatre on tenerife in order to understand the relationship between geomorphological and geological aspects and huge volcanic landslides the results indicated four major features that play a significant role in such mass movements deep erosive canyons high coastal cliffs widespread residual soils and structural axes high coastal cliffs and deep erosive canyons locally reduce the stability conditions and control both the seaward and the lateral boundary of the landslide weak residual soils formed above phonolitic pyroclastic deposits occur repeatedly in the stratigraphic column of la orotava and are characterised by their large extent thus one of these soils may have evolved into the slip surface of the failure part of the head scarp of the amphitheatre is defined by a volcanic rift zone as indicated by the measurement of dike orientation and a density map of eruptive vents the four features are not able to trigger a failure but to destabilise the volcano flank and determine the boundary of the slide therefore information on depth and orientation of canyons location and height of coastal cliffs stratigraphic repetition extension and thickness of residual soils and orientation and density of dikes and eruptive vents along structural axes should be incorporated into a hazard assessment on large landslides on volcanic islands

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

evolution of oceanographic conditions off baja california 1997 1999 abstract this paper examines the oceanic response off baja california mexico to the 1997 1998 el nino and the transition to la nina conditions the data presented were gathered during seven cruises over a grid based on the calcofi station plan from lines 100 130 out to station 80 t s diagrams with data obtained during the peak phase of el nino demonstrate that warmer and saltier spicier than normal conditions prevailed in the upper 600 m over this region temperature and salinity anomalies calculated for calcofi line 120 revealed waters near the coast at 50 m depth to be up to 8 7 c warmer and s 0 8 saltier than the climatology during october 1997 these large anomalies persisted through january 1998 with some slight diminution in the magnitudes near the surface this study suggests that anomalously warm and salty waters were fed from a source of spicy water to the southwest identified as subtropical surface water stsw and that low salinity tropical surface waters tsw were blocked to the southeast in the vicinity of the tip of the peninsula subsurface waters associated with the california undercurrent cu fed from the eastern tropical pacific etp were also warmer and saltier than normal and indicate a significant expansion in volume of the cu presumably a result of intensification of poleward flow at depth we postulate that the well defined near surface and deep poleward flows in the study area reflect anomalous large scale cyclonic circulation affecting the flow in the southeastern region of the north pacific subtropical gyre east of 125 w following the el nino event warm and salty upper waters retreated to latitudes south of punta eugenia with the return to normal and cooler conditions equatorward flow over the sampling grid predominated with an increased meandering and mesoscale activity transition to la nina conditions would have been associated with re establishment of normal anticyclonic flow in the southeastern quadrant of the pacific subtropical gyre

transport and emplacement mechanisms of channelised long runout debris avalanches ruapehu volcano new zealand the steep flanks of composite volcanoes are prone to collapse producing debris avalanches that completely reshape the landscape this study describes new insights into the runout of large debris avalanches enhanced by topography using the example of six debris avalanche deposits from mount ruapehu new zealand individual large flank collapses 1 km3 produced all of these units with four not previously recognised five major valleys within the highly dissected landscape surrounding mount ruapehu channelled the debris avalanches into deep gorges 15 m and resulted in extremely long debris avalanche runouts of up to 80 km from source classical sedimentary features of debris avalanche deposits preserved in these units include the following very poor sorting with a clay sand matrix hosting large subrounded boulders up to 5 m in diameter jigsaw fractured clasts deformed clasts and numerous rip up clasts of late pliocene marine sediments the unusually long runouts led to unique features in distal deposits including a pervasive and consolidated interclast matrix and common rip up clasts of tertiary mudstone as well as fluvial gravels and boulders the great travel distances can be explained by the debris avalanches entering deep confined channels 15 m where friction was minimised by a reduced basal contact area along with loading of water saturated substrates which formed a basal lubrication zone for the overlying flowing mass extremely long runout debris avalanches are most likely to occur in settings where initially partly saturated collapsing masses move down deep valleys and become thoroughly liquified at their base this happens when pore water is available within the base of the flowing mass or in the sediments immediately below it based on their h l ratio confined volcanic debris avalanches are two to three times longer than unconfined spreading flows of similar volume the hybrid qualities of the deposits which have some similarities to those of debris flows are important to recognise when evaluating mass flow hazards at stratovolcanoes

stratigraphy of the bandas del sur formation an extracaldera record of quaternary phonolitic explosive eruptions from the las canadas edifice tenerife canary islands explosive volcanism has dominated the large phonolitic shield volcano of tenerife the las canadas edifice for the last 1 5 m y pyroclastic deposits of the bandas del sur formation are exposed along the southern flanks and record the last two of at least three long term cycles of caldera forming explosive eruptions each cycle began with flank fissure eruptions of alkali basalt lava followed by minor eruptions of basanite to phonotephrite lavas minor phonotephritic to phonolitic lava effusions also occurred on the flanks of the edifice during the latter stages of the second explosive cycle non welded plinian fall deposits and ignimbrites are the dominant explosive products preserved on the southern flanks of these a significant volume has been dispersed offshore many pyroclastic units of the second explosive cycle exhibit compositional zonation banded pumice occurs in most units of the third youngest explosive cycle and ignimbrites typically contain mixed phenocryst assemblages indicating the role of magma mixing mingling prior to eruption at least four major eruptions of the third cycle began with phreatomagmatic activity producing lithic poor accretionary lapilli bearing fallout and or surge deposits the repeated brief phase of phreatomagmatism at the onset of these eruptions is interpreted as reflecting an exhaustive water supply probably a small caldera lake that was periodically established during the third cycle accidental syenite becomes an increasingly important lithic clast type in ignimbrites up sequence and is interpreted as recording the progressive development of a plutonic complex beneath the summit caldera successive eruptions during each explosive cycle increased in volume with the largest eruption occurring at the end of the cycle more than ten major explosive eruptions vented moderately large volumes 1 ges 10 km 3 of phonolitic magma during the last two cycles culminating each explosive cycle was the emplacement of relatively large volume 5 10 km 3 ignimbrites with coarse vent derived lithic breccias interpreted to record a major phase of caldera collapse in the extracaldera record explosive cycles are separated by 0 2 m y periods of non explosive activity repose periods were characterized by erosion remobilization of pyroclastic deposits by discharge events and pedogenesis the current period of non explosive activity is characterized by the construction of the teide pico viejo stratovolcanic complex within the summit caldera this suggests that eruptive hiatuses in the extracaldera record may reflect effusive activity and stratovolcano or shield building phases within the summit caldera alternating effusive and explosive cycles have thus been important in the volcanic evolution of the las canadas edifice

the quaternary pyroclastic succession of southeast tenerife canary islands explosive eruptions related caldera subsidence and sector collapse a much revised quaternary stratigraphy is presented for ignimbrites and pumice fall deposits of the bandas del sur in southern tenerife new ar 41 ar 39 data obtained for the arico granadilla fasnia poris la caleta and abrigo formations are presented allowing correlation with previously dated offshore marine ashfall layers and volcaniclastic sediments we also provide a minimum age of 287 7 ka for a major sector collapse event at the gaimar valley the bandas del sur succession includes more than seven widespread ignimbrite sheets that have similar characteristics including widespread basal plinian layers predominantly phonolite composition ignimbrites with similar extensive geographic distributions thin condensed veneers with abundant diffuse bedding and complex lateral and vertical grading patterns lateral gradations into localized massive facies within palaeo wadis and widespread lithic breccia layers that probably record caldera forming eruptions each ignimbrite sheet records substantial bypassing of pyroclastic material into the ocean the succession indicates that las canadas volcano underwent a series of major explosive eruptions each starting with a plinian phase followed by emplacement of ignimbrites and thin ash layers some of coignimbrite origin several of the ignimbrite sheets are compositionally zoned and contain subordinate mafic pumices and banded pumices indicative of magma mingling immediately prior to eruption because passage of each pyroclastic density current was characterized by phases of non deposition and erosion the entire course of each eruption is incompletely recorded at any one location accounting for some previously perceived differences between the units because each current passed into the ocean estimating eruption volumes is virtually impossible nevertheless the consistent widespread distributions and the presence of lithic breccias within most of the ignimbrite sheets suggest that at least seven caldera collapse eruptions are recorded in the bandas del sur succession and probably formed a complex nested collapse structure detailed field relationships show that extensive ignimbrite sheets e g the arico poris and la caleta formations relate to previously unrecognized caldera collapse events we envisage that the evolution of the nested las cahadas caldera is more complex than previously thought and involved a protracted history of successive ignimbrite related caldera collapse events and large sector collapse events interspersed with edifice building phases

39 ar 40 ar ages and geochemistry of the basaltic shield stage of tenerife canary islands spain abstract we report the first 39 ar 40 ar ages from the three early basic shield like massifs of tenerife canary islands and couple these with detailed major and trace element chemistry to constrain the nature and timing of the mantle melting processes the massifs have chemically different sources and independent evolutionary histories the teno and roque del conde massifs appear chemically to represent the products of single mantle melting cycles with progressive decrease in mean melt fraction and increase in mean melting depth in younger rocks the teno massif nw was erupted in a short time period around 6 0 6 4 ma while at least the lower half of the roque del conde massif sw is older than 11 ma in contrast the anaga massif ne is polygenetic with 39 ar 40 ar ages ranging from 8 0 4 2 ma and no simple stratigraphic chemical progression these ages run counter to published suggestions of progressive younging of canary shield stages to the southwest basic rocks in all three massifs are the result of much deeper melting and smaller melt fractions than equivalent units in gran canaria but nevertheless the melting column must have extended significantly into the spinel facies requiring substantial disruption of the local lithosphere the age and melting relationships broadly support the mantle blob model for canary magmatism proposed by hoernle and schmincke hoernle k schminke h u 1993 the role of partial melting in the 15 ma geochemical evolution of gran canaria a blob model for the canary hotspot j petrol 34 599 626 in all three massifs extensive fractional crystallisation has taken place at crustal levels so that mean mgo contents are only some 6 7 the fractionation sequence is olivine clinopyroxene magnetite in basaltic compositions with the involvement of plagioclase amphibole and apatite only to generate the infrequent more evolved hawaiites to benmoreites despite the abundance of basanitic magmas in the tenerife older massifs these follow a differentiation trend towards weakly undersaturated benmoreite rather than to phonolite this probably reflects early crystallisation of magnetite perhaps resulting from somewhat high oxygen fugacity the chemical evidence for replenished magma chambers in tenerife described by neumann et al neumann e r wulff oedersen e simonsen s l pearson n j marti j mitjavila j 1999 evidence for fractional crystallisation of periodically refilled magma chambers in tenerife canary islands j petrol 40 1089 1123 is a consequence of treating as a single cogenetic suite the products of several magmatic systems that differ in parental melt fraction

sector collapse forming at casita volcano nicaragua catastrophic sector collapse occurs when a volcano becomes structurally unable to support its own load one process particularly capable of weakening the edifice is hydrothermal activity it can produce high pore pressures and alter strong rock to clays alteration can extend progressively over long periods 100 yr allowing deformation to develop slowly before collapse an important finding is that structures produced by such deformation are recognizable and could permit collapse prediction we present the case of casita nicaragua where hydrothermal activity has been weakening the edifice core causing flank spreading altering original constructional shape and steepening flank slopes one side is slumping outward producing a crescentic scar with a basal bulge we identify this feature as the site of a potential sector collapse with conditions ripe for failure

a poleward jet and an equatorward undercurrent observed off oregon and northern california during the 1997 98 el nino abstract the timing and intensity of the effects of the 1997 98 el nino on sea surface temperature sst and coastal sea level along the us west coast are examined using in situ time series measurements and the effects on upper ocean currents on the continental shelf and slope off oregon and northern california are examined using repeated shipborne adcp transects a mid shelf mooring off newport oregon and an hf surface current radar an initial transient positive anomaly was observed in both adjusted sea level and sst during may june 1997 followed by anomalously high coastal sea levels generally strongest during september 1997 through february 1998 and abruptly returned to normal in late february 1998 and by positive temperatures anomalies over the mid shelf that persisted longer into april 1998 low frequency coastal sea level anomalies propagated poleward at 2 1 m s poleward flow over the shelf and slope was enhanced at most depths during the el nino compared with following years northward currents in the upper 12 m over the continental shelf off newport oregon averaged 13 7 cm s stronger during august 1997 through february 1998 than during the same period the following year enhanced poleward flow was present at all latitudes sampled during november 1997 and february 1998 particularly over the continental slope these transects also provided clear views of a fall winter equatorward undercurrent which was both strongest and had the most alongshore similarity of form during the enso finally subsurface intensified anticyclonic eddies originating in the poleward undercurrent appear to be a recurrent feature of the circulation off newport late in the upwelling season

the influence of palaeotopography on facies architecture and pyroclastic flow processes of a lithic rich ignimbrite in a high gradient setting the abrigo ignimbrite tenerife canary islands abstract the late pleistocene 188 19 ka abrigo ignimbrite represents the last major explosive caldera forming eruption on tenerife it consists almost entirely of a moderate volume 1 8 km 3 light grey phonolitic lithic rich ignimbrite deposit although a possible abrigo member thin fall deposit is locally preserved beneath the ignimbrite suggesting an initial short lived stable plinian eruption column the ignimbrite deposit is dispersed radially around the lower flanks of the las canadas edifice and correlates to a clast supported lithic breccia on the eastern and northern caldera wall much of the ignimbrite was probably deposited offshore or within the caldera now buried by more recent lavas two major depositional units separated by a co ignimbrite ash cloud deposit and which display dramatic variations in thickness pyroclastic flows were channelised along and deposited within the same valleys that exist today and were commonly continuous and sheet like across the interfluves the basal zones of pyroclastic flows are envisaged as a bed load of coarse lithic lapilli and blocks transported under their own momentum and with the support of the surrounding fine ash gas granular flow

stratigraphy structure and volcanic evolution of the pico teide pico viejo formation tenerife canary islands abstract the structure and volcanic stratigraphy of the pico teide pico viejo pt pv formation deriving from the basanite phonolite stratovolcanoes pt and pv and numerous flank vent systems are documented in detail based on new field and photogeologic mapping geomorphologic analysis borehole data and petrological and geochemical findings results provide insight into the structure and evolution of the pt pv magma system and the long term cyclic evolution of tenerife s post shield volcanic complex the pt pv formation comprises products of central volcanism mainly emplaced into the las canadas caldera lcc and contemporaneous products from adjacent rifts pt pv central volcanic products become more differentiated up section with felsic lavas dominating the recent output of the system this is attributed to the evolution of a shallow magma reservoir beneath pt that was emplaced early in the pt pv cycle on the intra caldera segment of tenerife s post shield rift system the rift axis has been the focus of pt pv intrusive and eruptive activity and has controlled the location of the stratocones the current geometry of the rifts reflects a major structural reorganisation defining the start of the pt pv cycle at 0 18 ma namely the truncation of the north side of the lcc lce by the giant icod landslide the internal stratigraphy of the pt pv formation suggests that pt developed early with pv developing as a satellite vent activity has since alternated between pt and pv due to episodes of vent blockage or chamber sealing these processes have allowed significant volumes of phonolitic magmas to develop and accumulate within the pt chamber which have vented through radial dike systems during tumescence episodes and from the rift system which has permitted lateral magma transport the pt pv magma system is a potentially hazardous source of future felsic eruptive activity on tenerife

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

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

volcanic and geochemical evolution of the teno massif tenerife canary islands some repercussions of giant landslides on ocean island magmatism large scale catastrophic mass wasting is a major process contributing to the dismantling of oceanic intraplate volcanoes recent studies however have highlighted a possible feedback relationship between flank collapse or incipient instability and subsequent episodes of structural rearrangement and or renewed volcano growth the teno massif located in northwestern tenerife canary islands is a deeply eroded miocene shield volcano that was built in four major eruptive phases punctuated by two lateral collapses each removing 20 25 km3 of the volcano s north flank in this paper we use detailed field observations and petrological and geochemical data to evaluate possible links between large scale landslides and subsequent volcanism magmatism during teno s evolution inspection of key stratigraphic sequences reveals that steep angular unconformities relics of paleolandslide scars are marked by polymict breccias near their base these deposits typically include abundant juvenile pyroclastic material otherwise scarce in the region while some of teno s most evolved low density magmas were produced just before flank collapses early postlandslide lava sequences are characterized by anomalously high proportions of dense ankaramite flows extremely rich in clinopyroxene and olivine crystals a detailed sampling profile shows transitions from low mg lavas relatively rich in sio2 to lavas with low silica content and comparatively high mg after both landslides long term variations in zr nb normative nepheline and la lu are coupled but do not show a systematic correlation with stratigraphic boundaries we propose that whereas loading of the growing precollapse volcano promoted magma stagnation and differentiation the successive giant landslides modified the shallow volcano tectonic stress field at teno resulting in widespread pyroclastic eruptions and shallow magma reservoir drainage this rapid unloading of several tens of km3 of near surface rocks appears to have upset magma differentiation processes while facilitating the remobilization and tapping of denser ankaramite magmas that were stored in the uppermost mantle degrees of mantle melting coincidently reached a maximum in the short time interval between the two landslides and declined shortly after probably reflecting intrinsic plume processes rather than a collapse induced influence on mantle melting our study of teno volcano bears implications for other oceanic volcanoes where short term compositional variations may also directly relate to major flank collapse events

seasonal cycles of currents temperatures winds and sea level over the northeast pacific continental shelf 35 n to 48 n seasonal cycles of coastal wind stress adjusted sea level asl shelf currents and water temperatures off the west coast of north america 35 n to 48 n are estimated by fitting annual and semiannual harmonics to data from 1981 1983 longer records 9 34 years of monthly asl indicate that these two harmonics adequately represent the long term monthly average seasonal cycle and that the current measurement period is long enough to estimate the seasonal cycles we characterize the differences between fall winter and spring summer as follows for fall winter monthly mean winds north of 35 n are northward for 3 6 months longer in the north than in the south south of 35 n the mean winds are near zero or weakly southward monthly mean alongshore currents are northward over midshelf and shelf break at all locations sampled at depths of 35 m and deeper and are associated with high coastal sea levels and relatively warm water temperatures for spring summer monthly mean wind stresses are southward at all latitudes for 3 6 months longer in the south than in the north sea levels are low and water temperatures are relatively cool monthly mean currents at 35 m depth over the shelf are southward for 1 6 months longer at the shelf break than over midshelf and longer in the north than in the south while the deeper currents are less southward or northward the magnitudes of the seasonal cycles of all variables are maximum between approximately 38 n and 43 n generally decreasing slightly to the north and greatly to the south at each location the seasonal cycle of the alongshore current from 35 m depth at midshelf leads the sea level slightly and both lead the wind stress and temperatures by 1 2 months the seasonal cycles of all variables show a south to north progression south leads north by 1 2 months at 48 n annual mean currents at 50 m depth over the shelf break oppose the annual mean wind northward wind and southward current similarly at 35 n annual mean currents at 35 m depth over both midshelf and shelf break are opposed to the annual mean wind southward wind and northward current from 35 n to 43 n both summer and winter regimes are dominated by strongly fluctuating currents

rifting recurrent landsliding and miocene structural reorganization on nw tenerife canary islands we studied mechanisms of structural destabilization of ocean island flanks by considering the linkage between volcano construction and volcano destruction exemplified by the composite teno shield volcano on tenerife canary islands during growth tenerife episodically experienced giant landslides genetically associated with rifting and preferentially located between two arms of a three armed rift system the deeply eroded late miocene teno massif allows insights into the rifting processes the failure mechanisms and related structures the semicircular geometry of palaeo scarps and fracture systems breccia deposits and the local dike swarm reconfigurations delineate two clear landslide scarp regions following an earlier collapse of the older los gigantes formation to the north the rocks around the scarp became fractured and intruded by dikes substantial lava infill and enduring dike emplacement increased the load on the weak scarp and forced the flank to creep again finally resulting in the collapse of the younger carrizales formation once more the changing stress field caused deformation of the nearby rocks a fracture belt formed around the scarp and dikes intruded into new concentric directions the outline size and direction of the second failed flank of teno very much resembles the first collapse we suggest structural clues concerning mechanisms of recurrent volcano flank failure verifying the concept that volcano flanks that have failed are prone to collapse again with similar dimensions

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

large scale thermal anomalies in the california current during the 1982 1983 el nino the large scale thermal structure of the california current during 1982 83 shows several anomalous conditions warm sea surface temperature anomalies 1 2 c depression of the thermocline by 50 m or more and pronounced subsurface warming 3 4 c relative to the 30 year mean the subsurface anomaly is much greater than the surface anomaly these persistent 6 months structures coupled with unusually high sea levels along the north american coast show that a major californian el nino occurred during 1982 83 the data support the conclusion that the expansion and intensification of the aleutian low and the decrease in strength of the pacific high produced an anomalous basin wide atmospheric circulation which coupled directly to the large scale oceanic wind driven circulation to produce the californian el nino the enhanced transport from the west offshore california and south baja california which such a circulation would produce is consistent with the observed water properties the equatorial 1982 83 el nino is probably related to the californian el nino through an atmospheric teleconnection between equatorial sea surface temperature and the atmospheric hadley circulations

the signature of el nino off oregon 1982 1983 national science foundation through grants oce 8026131 oce 8405232 oce 8014943 and oce 8315014

stratigraphy and k ar ages of the diego hernandez wall and their significance on the las canadas caldera formation tenerife canary islands the las canadas caldera corresponds to a volcanic caldera formed after a long period of explosive activity the structural and lithological variations which can be observed in the caldera wall make clear the complexity of the original las canadas edifice in which different eruptive centres existed the stratigraphic and structural reconstruction of the las canadas caldera indicates that the diego hernandez wall located at the eastern side of the caldera wall comprises the youngest pre caldera deposits determination of their k ar ages has provided the maximum age for the formation of the las canadas caldera the results are internally consistent with stratigraphic relationships and allow two pre caldera volcanic cycles in the diego hernandez wall to be differentiated in accordance with geological evidence the first cycle shows imprecise age limits the second cycle ranges from 0 35 to 0 17 ma this upper pre caldera age suggests that the las canadas caldera and the teide pico viejo were formed more recently than was previously assumed

seasonal variability of alongshore geostrophic velocity off central california seasonal variability of alongshore geostrophic velocity relative to 500 dbar is examined from 23 years of hydrographic data along two sections off central california one off point sur and the other off point conception the seasonal cycles are determined by least square fits of the gappy data records to harmonics with annual and semiannual periods attention is focused on variability over the outer continental slope geostrophic flow in the upper 100 m along both sections is coherent and predominantly annual with equatorward flow from february to september and poleward flow from october to january the flow deeper than 100 m is distinctly different along the two sections the nearshore deep flow is predominantly semiannual off point conception notably different from surface flow and poleward all year with maxima in december and june this semiannual variability at depth is a prevalent feature of the california current system the nearshore deep flow off point sur is unusual in that it is predominantly annual with maximum poleward flow in december and weak equatorward flow from march to may the seasonal variations over the continental slope compare favorably with existing models of eastern boundary current systems in two respects 1 the surface flow leads the predominantly annual wind forcing in this region by about one month and 2 the deep poleward counterflow is coherent with the local poleward barotropic pressure gradient at both locations with a phase lag of approximately 2 months however contrary to the results of existing dynamical models the semiannual poleward pressure gradient and undercurrent off point conception appear to be unrelated to the wind forcing which is predominantly annual in this region these semiannual variations are highly coupled to the semiannual flow throughout the water column inside the southern california bight suggesting that they may be topographically generated

evolution of the north flank of tenerife by recurrent giant landslides geomorphologic analysis of submarine and subaerial surface features using a combined topographic bathymetric digital elevation model coupled with onshore geological and geophysical data constrain the age and geometry of giant landslides affecting the north flank of tenerife shaded relief and contour maps and topographic profiles of the submarine north flank permit the identification of two generations of post shield landslides older landslide materials accumulated near the shore 40 km and comprise 700 km3 of debris thickening towards a prominent axis suggests one major landslide deposit younger landslide materials accumulated 40 70 km offshore and comprise the products of three major landslides the la orotava landslide complex the icod landslide and the east dorsal landslide complex each with an onshore scar a proximal submarine trough and a distal deposit lobe estimated lobe volumes are 80 80 and 100 km3 respectively the old post shield landslide scar is an amphitheatre 20 25 km wide partly submarine now completely filled with younger materials age width relationships for tenerife s coastal platform plus onshore geological constraints suggest an age of ca 3 ma for the old collapse young landslides are all less than 560 ka old the la orotava and icod slides involved failures of slabs of subaerial flank to form the subaerial la orotava and icod valleys offshore they excavated troughs by sudden loading and basal erosion of older slide debris the onshore east dorsal slide also triggered secondary failure of older debris offshore the slab like geometry of young failures was controlled by weak layers deep drainage channels and flank truncation by marine erosion the partly submarine geometry of the older amphitheatre reflects the absence of these features relatively low h l ratios for the young slides are attributed to filling of the slope break at the base of the submarine edifice by old landslide materials low aspect ratios of the failed slabs and channelling within troughs post shield landslides on tenerife correlate with major falls in sea level reflecting increased rates of volcanism and coastal erosion and reduced support for the flank landslide head zones have strongly influenced the pattern of volcanism on tenerife providing sites for major volcanic centres

sea level response to enso along the central california coast how the 1997 1998 event compares with the historic record abstract long term monthly sea level and sea surface temperature sst anomalies from central california show that during winter months positive anomalies are associated with el nino events and the negative ones with la nina events there is no significant impact on monthly mean anomalies associated with pacific decadal oscillations although there is a tendency for more extreme events and greater variance during positive decadal oscillations the very strong 1997 1998 el nino was analyzed with respect to the long term historic record to assess the forcing mechanisms for sea level and sst beginning in the spring of 1997 we observed several long period 30 days fluctuations in daily sea level with amplitudes of over 10 cm at san francisco california fluctuations of poleward long period alongshore wind stress anomalies awsa are coherent with the sea level anomalies however the wind stress cannot entirely account for the observed sea level signals the sea level fluctuations are also correlated with sea level fluctuations observed further south at los angeles and tumaco columbia which showed a poleward phase propagation of the sea level signal we suggest that the sea level fluctuations were to a greater degree forced by the passage of remotely generated and coastally trapped waves that were generated along the equator and propagated to the north along the west coast of north america however both local and remote awsa can significantly modulate the sea level signals the arrival of coastally trapped waves began in the spring of 1997 which is earlier than previous strong el nino events such as the 1982 1983 event

nutrient variability during el nino 1997 98 in the california current system off central california abstract nutrient conditions off central california during the 1997 98 el nino are described data were collected on 11 cruises from march 1997 to january 1999 along a hydrographic section off central california as well as every two weeks at a coastal station in monterey bay perturbations associated with el nino are shown as anomalies of thermohaline and nutrient distributions along this section the anomalies were obtained by subtracting seasonal averages for the period from april 1988 to april 1991 from the 1997 98 observations the first indications of el nino conditions high sea levels were observed at monterey between late may and early june 1997 but the coastal nutricline did not begin to deepen until august 1997 it reached maximum depth of 130 dbar in january 1998 at the time that maximum sea level anomalies were observed during this period 1 the highest subsurface temperature anomalies coincided with subsurface nutrient anomaly minima at the depth of the pycnocline 2 southern saline and nutrient poor waters occupied the upper 80 dbar of the water column along the entire section and 3 nitrate levels were close to zero in the euphotic zone collapsing the potential new primary production in the coastal domain at the end of february 1998 the nutricline shoaled to 40 dbar at the coast although it remained anomalously deep offshore higher temperatures and lower nutrient levels were observed for the entire section through august 1998 although in contrast with the previous winter there was a strong freshening mainly due to an onshore movement of subarctic waters

the late quaternary diego hernandez formation tenerife volcanology of a complex cycle of voluminous explosive phonolitic eruptions abstract the diego hernandez formation dhf 600 ca 180 ka represents the products of the most recent complete cycle of phonolitic explosive volcanism on tenerife canary islands spain we provide a revised and detailed stratigraphy new 40ar 39ar and u th he age determinations for major eruptive units a summary of new chemical data and an overview of the key characteristics of the cycle including volume estimates dispersal patterns eruption styles phreatomagmatic influences and caldera collapse episodes the complex stratigraphy of the dhf is divided into 20 named members each representing a major eruption as well as numerous unnamed members of limited present day exposure the major eruptions are represented by the fortaleza 370 ka roque 347 ka 3 km3 aldea 319 ka 3 km3 fasnia 309 ka 13 km3 poris 268 ka 3 5 km3 arafo 4 km3 caleta 223 ka 3 5 km3 and abrigo between 196 and 171 ka 20 km3 members the aldea fasnia and poris members consist of highly complex successions of plinian fall surge and flow deposits and several of the eruptions produced widespread and internally complex ignimbrite sheets phreatomagmatism occurred most frequently in the opening phase of the eruptions but also recurred repeatedly throughout many of the sequences inferred sources of water include a shallow caldera lake and groundwater and intermittent phreatomagmatic activity was an important influence on eruption style another important factor was conduit and vent instability which frequently loaded the eruption column with dense lithic debris and occasionally triggered column collapse and ignimbrite formation most of the major dhf eruptions were triggered by injection of mafic magma into existing phonolitic magma bodies two phonolitic magma types were available for eruption during the lifetime of the dhf but each was dominant at different times the results presented here support a caldera collapse rather than a landslide model for the origin of the las canadas caldera although the evolution of the caldera is evidently more complex and incremental than first thought

the coastal ocean off oregon and northern california during the 1997 8 el nino abstract the evolution and decay of el nino 1997 8 was observed in coastal waters off oregon in a sequence of cruises along 44 6 n from the coast to more than 150 km offshore hydrographic observations were made during eleven cruises between july 1997 and april 1999 at stations on the newport hydrographic line which had been occupied regularly from 1961 to 1971 the data from the earlier decade provide a basis for defining normal conditions and allow comparisons with the recent el nino in terms of t s spiciness and geostrophic velocity independent of el nino the ocean in july 1997 was already anomalously warm offshore of 50 km and above 100 m by september 1997 there were unambiguous indications of el nino isotherms and isohalines sloped down toward the coast indicating poleward flow over shelf and slope and anomalously spicy water was present at the shelf break in november 1997 and february 1998 shelf break waters were even warmer and there was strong poleward flow inshore of 100 km extending to depths greater than 200 m the april 1998 section closely resembled that of april 1983 another el nino year but by june 1998 the anomalies were mostly gone november 1998 was near normal and the sections from subsequent cruises resemble the mean sections from 1961 1971 four cruises between november 1997 and november 1998 included sampling at several latitudes between 38 and 45 n as expected these sections show significant alongshore gradients but also a surprising degree of homogeneity in the anomalous features associated with el nino in the temperature salinity spiciness and geostrophic velocity fields the anomalous signature of el nino was stronger at its winter peak in 1998 than in 1983 but the signature in the temperature and spiciness fields and in coastal sea level did not persist as long as in 1983 by april 1999 the coastal ocean from 38 n to 45 n was significantly colder than it had been in april 1984

geological and geomechanical models of the pre landslide volcanic edifice of guimar and la orotava mega landslides tenerife abstract the geological and geomechanical characterizations of the volcanic rock mass succession affected by the guimar and la orotava mega landslides tenerife canary island are presented here for the first time the estimated subaerial volume of rocks mobilized by each of these landslides is in the range of 30 50 km 3 one of the largest known in the world field data gallery surveys and borehole drilling have allowed the main types of materials and their structural arrangement to be identified based on these information a geological model of the pre landslide volcanic edifice is proposed a palaeo morphological reconstruction has been produced and possible slope angles and heights of the pre landslide volcanic edifice are presented five main lithological units have been identified in the emerged part of the edifice three of them forming the flanks and two forming the structural axis of the island on the flanks lava flows predominate with different degrees of alteration and proportion of dikes increasing near the structural axis the predominant materials on the structural axis are pyroclastic deposits lava flows and dikes in the submarine edifice four main lithological units have been distinguished formed by hyaloclastites pillow lavas dikes and gravitational deposits slope and basin facies the geomechanical characterization of these materials has been obtained from field data boreholes laboratory tests and literature review the geological and geomechanical models obtained provide the fundamental basis for the explanation of the instability processes that generated the guimar and la orotava mega landslides

the 1982 1983 el nino signal off northern california the major el nino event of 1982 1983 affected the entire california current system the anomalous conditions along the west coast of north america were related to the equatorial anomalies and also to the anomalous atmospheric circulation in the northeast pacific where the aleutian low was east of its usual position and the associated 700 mbar height reached its lowest value on record in february march 1983 positive temperature and negative salinity anomalies in the upper ocean extending from the coast to at least 200 km offshore were reported from san diego to vancouver island in data acquired in domains centered approximately 180 km off northern california by the ocean prediction through observation modeling and analysis program anomalies in both temperature and salinity were most pronounced subsurface spatially and monthly averaged temperatures were about 3 c warmer than normal at 80 to 100 m in april and again in december 1983 at 100 to 120 m salinity was about 0 4 parts per thousand lower than normal in july 1983 and july 1984 several months later than the temperature anomaly maxima the temperature anomalies may be related to the poleward propagation of the equatorial el nino perturbation by coastally trapped waves with offshore propagation by planetary rossby waves possibly playing some role in the relaxation of the perturbed eastern boundary current circulation anomalous onshore advection associated with the perturbed atmospheric circulation deeper than normal mixed layers or depression of the thermocline and halocline by the passage of rossby waves could each account for coincident positive temperature and negative salinity anomalies

the subarctic and northern subtropical fronts in the eastern north pacific ocean in spring abstract the subarctic and subtropical frontal zones of the eastern north pacific ocean were surveyed in june for five consecutive years starting in 1972 these surveys from the basis for a description of the complex frontal distributions and their year to year differences the fronts appear as surface outcroppings of haloclines the subarctic halocline where salinity increases with depth and the subtropical halocline where the opposite prevails between the fronts lies a transition zone where strong vertical gradients of salinity are generally absent an examination of the northern boundary of subtropical waters in this new dataset reveals the presence of two major fronts in the subtropical frontal zone in addition to the front commonly identified as the subtropical front 18 c and 34 8 is a northern subtropical front that forms the northern boundary of the subtropical halocline in the eastern north pacific it falls some 2 to 3 of latitude north of the subtropical front and is the same front observ

empirical orthogonal function analysis of cloud containing coastal zone color scanner images of northeastern north american coastal waters empirical orthogonal function eof analyses were performed on 36 coastal zone color scanner czcs images of the mid atlantic bight and gulf of maine taken from february 28 1979 through july 9 1979 the eof procedure was modified to allow images with significant portions of data missing because of clouds to be included in the analysis analyses performed both with the temporal and with the spatial means removed from the data produced similar results a strong gradient existed in the temporal mean from high pigment concentrations nearshore to much lower pigment concentrations offshore the first mode of the temporally averaged analysis explained 21 5 of the variance and showed a south to north pattern corresponding to an april mid atlantic bight bloom and a june bloom over nantucket shoals and platts bank the second temporally averaged mode explained 18 3 of the variance and corresponded to a shelf wide phytoplankton bloom that resulted in increased pigment concentrations through the spring the first mode of the spatially averaged analysis explained 59 1 of the variance and had a pattern similar to the temporal mean the second mode explained an additional 13 2 of the variance and was almost identical to the first mode in the temporally averaged analysis the inclusion of cloud containing images introduced some small scale spatial noise into the eof analyses however the inclusion of these images in the eof analysis allowed postanalysis image reconstruction that provided estimates of pigment concentrations beneath the clouds

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

spreading and potential instability of teide volcano tenerife canary islands 1 we analyze the role of low strength materials in the potential structural instability related to volcano spreading at the active teide stratovolcano tenerife canary islands to study the low strength materials we took advantage of a network of large tunnels within the volcano excavated for water supply which allows the in situ inspection and reconstruction of both volcano and substratum structure we identified two factors which are potentially important to teide s instability 1 a dipping low strength substratum breccia layer and 2 a hydrothermally altered weak core inside the volcano despite we do not find clear structural evidence for volcano substratum spreading both teide topographic shape and the summit faulting are features similar to those accepted as examples of volcano flank spreading over a weak core the detected asymmetric deformation of the edifice makes the north flank of teide a strong candidate for a potential failure

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

variability of the near surface eddy kinetic energy in the california current based on altimetric drifter and moored current data low pass filtered velocities obtained from world ocean circulation experiment woce surface drifters deployed in the california current off northern california during 1993 1995 have been compared with surface geostrophic velocity estimates made along subtracks of the topex poseidon altimeter and with moored acoustic doppler current profiler adcp data to obtain absolute geostrophic velocities a mean sea surface height ssh field was estimated using the mean drifter velocities and historical hydrographic data and was added to the altimetric ssh anomalies the correlation between collocated drifter and altimetric velocities is 0 73 significant at the 95 level the component of the drifter velocity which was uncorrelated with the altimetric velocity was correlated with the wind in the ekman transport sense monthly averages of eddy kinetic energy eke estimated using all drifter and altimeter data within the domain 124 132 w 33 40 5 n show energy levels for the drifters that are about 13 greater than those for the altimeter drifter altimeter and adcp measurements all exhibit similar seasonal cycles in eke with the altimeter data reaching maximum values of about 0 03 m 2 s 2 in late summer fall wavenumber spectra of the altimeter velocity indicate that the velocity fluctuations were dominated by features with wavelengths of 240 370 km while the adcp data suggest that the temporal scales of these fluctuations are at least several months between 36 and 40 5 n the region of monthly maximum eke migrates westward to about 128 w on a seasonal timescale this region of maximum eke coincides with the maximum zonal ssh gradient with increased eke associated with increased southward flow a simple model shows that much of the seasonal cycle of the ssh anomalies can be produced by linear processes forced by the curl of the wind stress although the model cannot explain the offshore movement of the front

poleward flow off central california during the spring and summer of 1981 and 1984 currents and winds measured over the continental shelf and upper continental slope during the first half of 1984 are analyzed to determine the character of the flow off central california point conception to san francisco the mean flow was poleward from point conception to point sur in opposition to the equatorward wind stress the mean flow was equatorward north of point sur fluctuations in alongshore currents over the shelf were highly correlated with local winds everywhere except off point conception where currents were not only uncorrelated with wind but also poorly correlated with currents farther north north of point buchon there is evidence for poleward propagation of shelf current variability at 175 200 cm s the correlation between currents and local wind forcing dropped considerably beyond the shelf break only 10 15 km offshore from the shelf moorings during extended periods of weak equatorward winds the poleward shelf flow south of point sur spreads farther offshore over the continental slope a three week period of calm winds in july 1984 resulted in a 100 km wide tongue of poleward flow extending 300 km along the california coast similar but somewhat weaker poleward surface flow occurred during the same period in 1981 a 2 to 3 week period of calm winds in late june and early july 1981 resulted in a 100 km wide tongue of poleward flow extending at least 150 km along the california coast in contrast to the poleward flow on the shelf which appears to be normal during spring and summer the poleward surface flow observed over the slope in july 1981 and 1984 is unusual based on historical hydrographic surveys off the central california coast poleward surface flow over the continental slope occurs seasonally in the winter but is not generally observed after february

characterization of debris avalanche deposits in japan abstract seventy one debris avalanche deposits are identified from 52 japanese quaternary volcanoes the structures of these volcanoes are mostly stratovolcanoes and lava domes no avalanche deposit is found in calderas pyroclastic cones or maar volcanoes debris avalanche deposits are found in 18 of all quaternary volcanoes or 25 of quaternary stratovolcanoes and lava domes the ratio rises to 49 when considering only active stratovolcanoes and lava domes at least five debris avalanche deposits have formed since 9th century the maximum height difference of sliding h for each debris avalanche ranges from 200 to 2400 meters and the maximum runout distance of sliding l ranges from 1 6 to 32 km the ratio h l ranges from 0 2 to 0 06 and becomes smaller in larger debris avalanches they are more mobile than landslides in non volcanic areas volume is within a range of 0 03 and 9 km 3 there is no relation between the direction of sliding and the regional horizontal compressional stress axis at the site of a volcano two dimensional computer simulations of avalanches using a simplified physical model are made the maximum velocity is mainly controlled by the length of steep slope

volcanic hazards from bezymianny and bandai type eruptions major slope failures are a significant degradational process at volcanoes slope failures and associated explosive eruptions have resulted in more than 20 000 fatalities in the past 400 years the historic record provides evidence for at least six of these events in the past century several historic debris avalanches exceed 1 km3 in volume holocene avalanches an order of magnitude larger have traveled 50 100 km from the source volcano and affected areas of 500 1500 km2 historic eruptions associated with major slope failures include those with a magmatic component bezymianny type and those solely phreatic bandai type the associated gravitational failures remove major segments of the volcanoes creating massive horseshoe shaped depressions commonly of caldera size the paroxysmal phase of a bezymianny type eruption may include powerful lateral explosions and pumiceous pyroclastic flows it is often followed by construction of lava dome or pyroclastic cone in the new crater bandai type eruptions begin and end with the paroxysmal phase during which slope failure removes a portion of the edifice massive volcanic landslides can also occur without related explosive eruptions as at the unzen volcano in 1792 the main potential hazards from these events derive from lateral blasts the debris avalanche itself and avalanche induced tsunamis lateral blasts produced by sudden decompression of hydrothermal and or magmatic systems can devastate areas in excess of 500km2 at velocities exceeding 100 m s 1 the ratio of area covered to distance traveled for the mount st helens and bezymianny lateral blasts exceeds that of many pyroclastic flows or surges of comparable volume the potential for large scale lateral blasts is likely related to the location of magma at the time of slope failure and appears highest when magma has intruded into the upper edifice as at mount st helens and bezymianny debris avalanches can move faster than 100 ms 1 and travel tens of kilometers when not confined by valley walls avalanches can affect wide areas beyond the volcano s flanks tsunamis from debris avalanches at coastal volcanoes have caused more fatalities than have the landslides themselves or associated eruptions the probable travel distance l of avalanches can be estimated by considering the potential vertical drop h data from a catalog of around 200 debris avalanches indicates that the h l rations for avalanches with volumes of 0 1 1 km3 average 0 13 and range 0 09 0 18 for avalanches exceeding 1 km3 h l ratios average 0 09 and range 0 5 0 13 large scale deformation of the volcanic edefice and intense local seismicity precede many slope failures and can indicate the likely failure direction and orientation of potential lateral blasts the nature and duration of precursory activity vary widely and the timing of slope faliure greatly affects the type of associated eruption bandai type eruptions are particularly difficult to anticipate because they typically climax suddenly without precursory eruptions and may be preceded by only short periods of seismicity

sea surface temperature variability in coastal areas of the northeastern pacific related to the el nino southern oscillation and the pacific decadal oscillation we examined monthly time series 1950 to 1999 of sea surface temperature sst anomalies in 47 quadrants 2 2 along the coast of north america and their relation to the el nino southern oscillation enso and the pacific decadal oscillation pdo we used the multivariate enso index mei and the pdo index pdoi and assumed a linear interaction of the mechanisms behind their interannual variations then we examined sst anomalies as functions of mei and pdoi using multiple linear regression mlr on average enso influence decreases poleward but is still dominant at 31 n northward the pdo signal dominates mlr was also applied to selected sea level height slh series enso effects on slh were clear up to 48 n while pdo showed a weak effect only in the gulf of alaska this suggests that poleward of southern california enso effects may be largely restricted to the inshore coastal environment