sea cliffs their processes profiles and classification general concavity or convexity of sea cliff profiles is controlled by relative rates of erosion by marine and subaerial processes as well as by positions of more resistant strata in the cliffs profiles supplemented by on site examination can establish the activity and dominance of erosional processes and indicate changes in regimen a sharp angle at the sea cliff base generally indicates active marine erosion whereas a smooth curve at the base means that subaerial erosion may dominate talus shows absence of marine erosion studies of profiles can be useful for estimating stability for residences railroads and highways at the top face and base of sea cliffs generally increased erosion and retreat of sea cliffs are in prospect because of projected regionally wetter and stormier climate rising sea level and increased human activities

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

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

late pleistocene holocene ruptures of the lima reservoir fault sw montana abstract active tectonics within the northern basin and range province provide a natural laboratory for the study of normal fault growth linkage and interaction here we present new geologic mapping and morphologic fault scarp modeling within the centennial valley montana to characterize pleistocene holocene ruptures of the young and active lima reservoir fault geologic relationships and rupture ages indicate middle pleistocene activity on the henry gulch 50 ka and 23 10 ka trail creek 43 ka and 13 ka and reservoir 23 ka segments offset quaternary deposits also record holocene rupture of the reservoir segment 8 ka but unfaulted modern streams show that no segments of the lima reservoir fault have experienced a large earthquake in at least several millennia the clustered pattern of rupture ages on the lima reservoir fault segments suggests a seismogenic linkage though segment length and spacing make a physical connection at depth unlikely trail creek and reservoir segment slip rates were non steady and appear to be increasing the fault helps accommodate differential horizontal surface velocity measured by gps geodesy across the boundary between the northern basin and range province and the snake river plain

seismotectonics of the 20 august 1999 red rock valley montana earthquake on 20 august 1999 a magnitude 5 3 earthquake occurred in southwestern montana ending a 25 year hiatus for magnitude 5 seismicity in montana this earthquake occurred in the central part of the red rock valley a northwest trending graben bounded by late pleistocene and holocene faults a focal depth of 12 4 km and a normal faulting focal mechanism suggest that this earthquake resulted from continued graben development although not along graben bounding faults mapped at the surface the 1999 red rock valley earthquake occurred near the northern end and within the footwall block of the northeast dipping red rock fault we deployed a temporary network close to the mainshock epicenter and located 65 aftershocks over 3 days including a magnitude 4 0 aftershock on 26 august that allowed determination of p wave travel time delays for regional seismograph stations using these station delays to improve relative hypocenter locations we recomputed hypocenter locations for 1000 red rock valley area earthquakes that occurred since 1989 relocated hypocenters avoid the holocene portion of the red rock fault but do surround it the mainshock epicenter location is close to that of a magnitude 5 0 earthquake in 1965

coda q distribution in the canary islands abstract the canary archipelago near the african plate between 27 and 30 n and 13 and 19 w is included in the oldest region 135 m y of the eastern atlantic ocean the tectonic seismicity is moderate with low magnitudes and it is almost totally related to an active fault located between the islands of tenerife and gran canaria the purpose of this paper is to provide a clear idea of the anelasticity of coda waves in the region in order to compute master dispersion curves as a function of the quality factor q we have applied inversion methods to obtain analytical magnification curves for all the seismographic stations used fp t data corresponding to the coda wave dispersion of 52 local and regional seismic events recorded at 6 seismographic stations have been obtained the fit of the data to the master curves determined yields estimates of coda q values and their frequency dependence most of the q0 values determined at 1 hz vary between 100 and 300 showing a strong frequency dependence in the range 0 2 2 hz the characteristic v value degree of frequency dependence of q in the region given by the law q q0 fv is v 0 9 by applying regionalization techniques an iso q0 map for a reference frequency of 1 hz has been obtained for the canary archipelago this map shows important lateral variations in q0 reflecting the tectonics and the volcanism of the region the lowest q0 values are found along the trend of the fault and beneath the islands

a field based classification scheme for gravel beaches a tripartite classification of gravel beaches based upon morphodynamic properties is proposed and demonstrated for 42 new zealand beaches the main advantage of this scheme is that it is based on simple visual classification that can be applied globally in the field and is underpinned by morphodynamic differences between the beach types the three types identified from the results are 1 pure gravel beach 2 mixed sand and gravel beach 3 composite gravel beach pure gravel beaches have steep slopes tan 0 08 0 24 and gravels extending from the storm berm to below mean low water spring tide level mixed sand and gravel beaches have moderate slopes tan 0 04 0 13 with sand and gravel entirely mixed both cross shore and at depth composite gravel beaches have a steep gravel berm fronted by a low angle intertidal terrace with overall beach slopes of tan 0 05 0 14 on composite beaches there is distinct hydrodynamic cross shore sorting of the sand and gravel component these broad types are tested using discriminant analysis and the three classes are shown to be highly significant f 16 24 df 8 p 0 00005 the key discriminating variables are iribarren number beach width average grain size and storm berm height

seismicity of the eastern snake river plain region idaho prior to the borah peak idaho earthquake october 1972 october 1983 abstract in december 1971 the idaho national engineering laboratory deployed a network of short period high gain vertical seismographs to monitor earthquake activity within a designated study area 43 0 to 44 5 n 111 5 to 114 0 w centered on the eastern snake river plain in the 11 yr prior to the 28 october 1983 borah peak idaho earthquake there were 102 events located within the study area with a duration magnitude m range of 0 7 m 3 2 three microearthquakes m 1 were detected on the eastern snake river plain seventy five microearthquakes were located northwest of the eastern snake river plain primarily in the birch creek valley beaverhead mountains region during the 11 yr period that the idaho national engineering laboratory seismograph stations have been active there were only two events located inside the study area within 35 km of the epicenter of the borah peak idaho earthquake in the 2 6 yr prior to the borah peak idaho earthquake there were no foreshocks with magnitudes 1 observed within a 20 km radius of the epicenter future large earthquakes in the lost river range lemhi range and segments of the beaverhead mountains may also occur without significant foreshock activity

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

geological hazards in loess terrain with particular reference to the loess regions of china abstract the considerable morphodynamic energy provided by the continuing tectonic evolution of asia is expressed in high erosional potentials and very high rates of sediment production that make this continent unequalled as a terrestrial source of primary silt many of these environments are hazardous threatening human occupation health and livelihood especially in regions of dense population such as the loess lands of north china dry loess can sustain nearly vertical slopes being perennially under saturated however when locally saturated it disaggregates instantaneously such hydrocompaction is a key process in many slope failures made worse by an underlying mountainous terrain of low porosity rocks gully erosion of loess may yield very high sediment concentrations 60 by weight characteristic vertical jointing in loess influences the hydrology enlarged joints develop into natural sub surface piping systems which on collapse produce a loess karst terrain collapsible loess up to 20 m thick is common on the western loess plateau foundation collapse and cracked walls are common many rapid events following periods of unusually heavy monsoonal rain slope failure is a major engineering problem in thick loess terrain flow slide and spread types being common the results are often devastating in both urban and rural areas an associated hazard is the damming of streams by landslides the human population increases the landslide risk in china notably through imprudent land use practices including careless water management a number of environmentally related endemic diseases arise from the geochemistry of loess and its groundwaters including fluorosis cretinism kaschin beck disease keshan disease and goitre the chinese desert margins also have a major atmospheric dust problem the effect of such dust upon human health in these extensive regions including many large cities has yet to be evaluated but pneumoconiosis is thought to affect several million people in north and west china

dating of the upper pleistocene holocene volcanic activity of la palma using the unspiked k ar technique abstract combined unspiked k ar dating and detailed mapping have established the eruptive chronology of the cumbre vieja volcano in the canary islands the cv volcano is a large polygenetic volcano subaerial area 220 km2 subaerial volume 125 km3 elevation above sea level 2000 m which rests on the southern flank of the older taburiente cumbre nueva volcano we defined two stratigraphic units by their relationship to the development of coastal cliffs developed around the cumbre vieja volcano a cliff forming series and a scree forming series which is draped over the cliffs and forms the coastal platforms at their bases k ar ages were measured from 20 samples from the two series there are no discrepancies between k ar ages and the stratigraphy the k ar ages of one flow compare well with 14 c determinations 14 c 3 2 0 1 ka k ar 4 2 ka the ages of the scree forming series range from 3 2 ka to 21 2 ka the cliff forming series ages range from 20 2 ka to 123 3 ka but as the base of the sequence is not exposed the growth of the cumbre vieja volcano must have begun substantially earlier the boundary between the two coincides with the low sea level stand in the last glacial maximum which we infer to have been a period of intense coastal erosion dated samples from the upper part of the taburiente cumbre nueva volcano range in age from 853 10 ka to 566 8 ka the age of the youngest taburiente cumbre nueva volcano sample provides an upper bound on the age of the subsequent cumbre nueva giant lateral collapse

modelling gully erosion for a small catchment on the chinese loess plateau the rolling hills region of the chinese loess plateau is one of the areas with the highest erosion rates on earth a striking feature of this area is the occurrence of many large permanent gullies a 3 5 km2 catchment was selected to study the processes of erosion and to adapt the storm based limburg soil erosion model lisem to the conditions prevailing on the loess plateau part of this work consisted of mapping and measuring the largest gully headcuts the amount of loose soil material beneath the headcuts was also estimated observations suggest that gully headcuts are relatively stable i e do not migrate rapidly but that gullies can nevertheless produce significant amounts of sediment during overland flow events erosion of headcuts occurs mainly by soil falls in between storms the loose soil material produced by these soil falls accumulates on the gully bottom as the lisem simulates storm erosion the development of gullies over time can be ignored and only the amount of material produced by them during runoff events needs to be studied a digital elevation model dem was used to estimate the position of existing gully heads by applying an adapted form of the montgomery and dietrich science 255 1992 826 index using the assumption that headcuts are vertical it is possible to calculate headcut height from the slope angle map a simple stability model which assumes soil falls on gully headcuts to be a function of soil moisture content and headcut height was applied this daily based model can then be used to simulate the accumulation of loose soil material below the headcut the results show that while the dem is not accurate enough to allow the detection of individual headcuts this method can be used to produce a reasonable estimate of the amount of loose soil material available a map showing the amount of loose soil material accumulated can then serve as input for a storm based erosion model such as lisem

a physical model for the origin of volcanism of the tyrrhenian margin the case of neapolitan area abstract the onset of volcanism in the neapolitan area and the tensile tectonics of the tyrrhenian margin of the apennine chain have been related to the opening of the tyrrhenian basin which may have resulted in horizontal asthenosphere flows giving rise in turn to crustal distension local mantle upwellings and ensuing volcanism geological and structural data were taken into consideration the existence of a shallow crust mantle discontinuity in the neapolitan area the onset of volcanism in a graben type structure the distribution of volcanism along three main directions these facts are all consistent with processes of crustal deformation associated with hot masses as well as fracture systems along three branches often separated by a 120 angle such fracture mechanism was therefore analyzed in physical terms on the assumption of an elasto plastic behaviour of the crust and with reference to the limit analysis theorems

the off shore continuation of an active basaltic volcano piton de la fournaise reunion island indian ocean structural and geomorphological interpretation from sea beam mapping abstract in 1984 a sea beam survey of the submarine east flank of piton de la fournaise was performed with r v jean charcot three main types of volcanic or volcano tectonic features have been identified 1 1 the subaerial ne and se volcanic rift zones of piton de la fournaise do not extend more than about five kilometers offshore unlike typical hawaiian rift zones which form narrow 2 4 km ridges extending tens of kilometers from the summit the active rift zones of piton de la fournaise widen downslope attaining more than 10 km at their front 2 2 the submarine extension of the grand brule slide is larger than the subaerial portion the entire slide forms a 7 24 km scar bounded by two ramparts to the north and south the slumped material may have moved as a debris flow forming a large talus downslope of the slide however the submarine counterpart of the south area of the grand brule seems to be composed by a slumped block whose structure is apparently not disturbed 3 3 another prominent feature is a conspicuous topographic high that occupies nearly all the center of the surveyed zone this cast flank submarine plateau cannot be associated with any active structure of piton de la fournaise its surface generally dips gently 2 3 and its northern and southern flanks are extensively cut by landslides cones of variable dimensions are observed on the plateau and farther to the east three hypotheses are examined to account for the origin of this morphology a remnant flank of an ancestral fournaise volcano associated with a large buried intrusion found by drilling beneath the grand brule b distinct volcanic massif or c material of a huge and ancient landslide the geophysical data show that the western part of this submarine plateau is reversely magnetized and associated with a moderate positive gravity anomaly this confirms that as suggested by the bathymetric analysis this part of the plateau is relatively coherent conversely the eastern portion of the plateau appears to be poorly magnetized and composed of low density material probably chaotic materials derived from landslides the reversed magnetization of the western part shows that the whole structure is older than 0 7 ma these results show that the volcanic history of piton de la fournaise is more complex than previously thought

age of tilted reefs hawaii submerged carbonate reefs are preserved as a series of submarine terraces between molokai and hawaii along a 200 km span of the southeastern hawaiian ridge limestones from two of the terraces have been sampled from submersibles and dated radiometrically at 13 and 120 ka recognition that the terraces are tilted permits assignment of about a dozen terraces from 150 to 1300 m depth to eight general reef platforms these reefs were drowned by the combined effects of island subsidence and sea level rise at the end of successive glacial stages from 13 to 647 ka the platforms are tilted 5 m km southeast toward the locus of volcanic loading centered on the island of hawaii the end of the active period of volcanic shield building is represented on each nonactive volcano by a submerged change in slope dating of this slope change by reference to the dated reefs provides independent evidence that shield building ended at about the same time that the volcano changed from eruption of tholeiitic to alkalic basalt the variation in depth of the dated tilted reefs along the ridge indicates that the end of subsidence follows the end of shield building by about one half million years the present northwest margin of major subsidence probably crosses southeast maui during the last half million years the rate of southeast migration of the beginning of both subsidence and of tholeiitic volcanism does not appear to have increased however the rate of southeast migration of the end of both subsidence and of tholeiitic volcanism has apparently increased this shortening of the life history of the younger volcanoes implies an increase in eruption rates

volcanic complexes in the eastern ridge of the canary islands the miocene activity of the island of fuerteventura abstract fuerteventura has been since early stages of its growth the result of three different adjacent large volcanic complexes southern central and northern the definition of these volcanic complexes and their respective growing episodes is based on volcano stratigraphic morphological and structural criteria particularly radial dyke swarms each complex has its own prolonged history that might be longer than 10 m y during that time several periods of activity alternating with gaps accompanied by important erosion took place the evolution of each volcanic complex has been partially independent but all the three are affected by at least three miocene tectonic phases that controlled considerably their activity the volcanic complexes are deeply eroded and partially submerged in the core of the northern and the central volcanic complexes there is a set of submarine and plutonic rocks intensely traversed by a dyke swarm known as the basal complex the basal complex has been interpreted in different ways but all previous authors have considered it to be prior to the subaerial shield stage of the island here we advance the idea that the basal complex represent the submarine growing stage of the volcanic complexes and the hypabyssal roots plutons and dykes of their successive subaerial growing episodes two seamounts situated nearby southwest of the island might be interpreted as remains of two other major volcanoes these two volcanoes together with those forming the present emerged island of fuerteventura and finally those of famara and los ajaches situated further north on lanzarote constitute a chain of volcanoes located along a lineation which is subparallel to the northwestern african coastline and which may relate to early atlantic spreading trends in the area

geodiversity of high latitude landscapes in northern finland abstract geodiversity is a rather new emerging topic in earth science there is now increased awareness of our need to understand patterns of geodiversity in different landscapes facing global change in this study we systematically inventoried geodiversity and topographical parameters in an area of 285 km 2 in subarctic finland we quantified the spatial variation of geodiversity using four different measures and analysed the relationship between geodiversity and topography using a spatial grid system at a landscape scale the size of the analysis window was 500 500 m the number of different elements of geodiversity total geodiversity varied from 2 to 22 per grid cell the spatial pattern of the total geodiversity geomorphological process variability and geodiversity index were fairly similar whereas of the other geodiversity measures the measure of temporal diversity differed the most topographically the high diversity sites occurred in rather steep sided valleys areas of high geodiversity reflect heterogeneous abiotic conditions where both erosion and accumulation processes play a major role in landscape development the mapping of geodiversity may be indicative not only in the context of geomorphology but also provide a focus for conservation initiatives from a conservation point of view the lack of wider knowledge of the distribution of geodiversity and its relationship to biodiversity hinders the protection of ecologically and geomorphologically valuable regions thus we recommend that further studies focus on 1 quantifying spatial patterns of geodiversity in different regions 2 determining the key drivers that control the variability of geodiversity and 3 exploring the linkage between geodiversity and biodiversity

hotspot volcanism close to a passive continental margin the canary islands the canarian archipelago is a group of volcanic islands on a slow moving oceanic plate close to a continental margin the origins of the archipelago are controversial a hotspot or mantle plume a zone of lithospheric deformation a region of compressional block faulting or a rupture propagating westwards from the active atlas mountains fold belt have been proposed by different authors however comparison of the canarian archipelago with the prototypical hotspot related island group the hawaiian archipelago reveals that the differences between the two are not as great as had previously been supposed on the basis of older data quaternary igneous activity in the canaries is concentrated at the western end of the archipelago close to the present day location of the inferred hotspot this is the same relationship as seen in the hawaiian and cape verde islands the latter archipelago associated with a well defined but slow moving mantle plume shows anomalies in a plot of island age against distance which are comparable to those seen in the canary islands these anomalies cannot therefore be used to argue against a hotspot origin for the canaries individual islands in both archipelagoes are characterized by initial rapid growth the shield building stages of activity followed by a period of quiescence and deep erosion erosion gap which in turn is followed by a post erosional stage of activity the absence of post shield stage subsidence in the canaries is in marked contrast with the major subsidence experienced by the hawaiian islands but is comparable with the lack of subsidence evident in other island groups at slow moving hotspots such as the cape verdes comparison of the structure and structural evolution of the canary islands with other oceanic islands such as hawaii and reunion reveals many similarities these include the development of triple mercedes star rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones the apparent absence of these features in the post erosional islands may in part be a result of their greater age and deeper erosion which has removed much of the evidence for their early volcanic architecture we conclude that the many similarities between the canary islands and island groups whose hotspot origins are undisputed show that the canaries have been produced in the same way

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

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

role of olivine cumulates in destabilizing the flanks of hawaiian volcanoes the south flank of kilauea volcano is unstable and has the structure of a huge landslide it is one of at least 17 enormous catastrophic landslides shed from the hawaiian islands mechanisms previously proposed for movement of the south flank invoke slip of the volcanic pile over seafloor sediments slip on a low friction decollement alone cannot explain why the thickest and widest sector of the flank moves more rapidly than the rest or why this section contains a 300 km3 aseismic volume above the seismically defined decollement it is proposed that this aseismic volume adjacent to the caldera in the direction of flank slip consists of olivine cumulates that creep outward pushing the south flank seawards average primary kilauea tholeiitic magma contains about 16 5 wt mgo compared with an average 10 wt mgo for erupted subaerial and submarine basalts this difference requires fractionation of 17 wt 14 vol olivine phenocrysts that accumulate near the base of the magma reservoir where they form cumulates submarine erupted kilauea lavas contain abundant deformed olivine xenocrysts derived from these cumulates deformed dunite formed during the tholeiitic shield stage is also erupted as xenoliths in subsequent alkalic lavas the deformation structures in olivine xenocrysts suggest that the cumulus olivine was densely packed probably with as little as 5 10 vol intercumulus liquid before entrainment of the xenocrysts the olivine cumulates were at magmatic temperatures 1100 c when the xenocrysts were entrained olivine at 1100 c has a rheology similar to ice and the olivine cumulates should flow down and away from the summit of the volcano flow of the olivine cumulates places constant pressure on the unbuttressed seaward flank leading to an extensional region that localizes deep intrusions behind the flank these intrusions add to the seaward push this mechanism ties the source of gravitational instability to the caldera complex and deep rift systems and therefore limits catastrophic sector failure of hawaiian volcanoes to their active growth phase when the core of olivine cumulates is still hot enough to flow

the distribution of carbonate eolianite abstract carbonate eolianite forms distinctive coastal landforms on many mid latitude continents and islands numerous studies of extensive continental and smaller island deposits in both hemispheres have shown the eolianites are predominantly pleistocene in age the coorong coastal plain of south australia contains the world s longest record of eolianite deposition revealing that major phases of carbonate accumulation occurred during interglacial and some interstadial sea level highstands throughout the quaternary similarly the well studied eolianite islands of bermuda and the bahamas record a close match between dune accretion and sea level highstands since the middle pleistocene several other eolianite deposits appear to have formed at least partially during glacial periods the glacial age deposits are eolian reworked relict shelf or coastal sediments or remnants of former highly mobile coastal dunes sourced from low sea level shorelines the distribution and bioclastic composition of large scale eolianite deposits suggests carbonate production on shallow shelves and banks is the ultimate control on the formation of eolianite the bulk of the carbonate comprising those eolianites is heterozoan being produced where there is low terrigenous sediment input in dominantly temperate cool water and subtropical carbonate provinces quaternary cyclical movements of sea level have also controlled the form and rate of coastal carbonate deposition with repeated pulses of sedimentation during highstands forming laterally coalesced vertically stacked or composite dune successions major unconformities within the deposits are marked by paleosols which record hiatuses in coastal sedimentation in several regions major eolianite units overlie coastal deposits of terrigenous sediment those successions suggest that the trend towards aridity and reduction in the supply of terrigenous sediment to shelves during the quaternary has enhanced the production of carbonate and the deposition of eolianite

stress triggering of conjugate normal faulting late aftershocks of the 1983 ms 7 3 borah peak idaho earthquake the 1984 devil canyon sequence was a late aftershock sequence of the 28 october 1983 ms 7 3 borah peak idaho earthquake the sequence began on 22 august 1984 with the ml 5 8 devil canyon earthquake which nucleated at a depth of 12 8 0 7 km between the surface traces of two normal faults the challis segment of the lost river fault and the lone pine fault two hundred thirty seven aftershocks were recorded by a temporary array during a 3 week period their focal mechanisms and hypocenter distribution define a cross sectional v pattern whose base corresponds to the ml 5 8 event whose tips correspond to the exposed fault traces and whose sides define two planar fault zones oriented n25 w 75 sw challis fault segment and n39 w 58 ne lone pine fault this pattern describes a graben bounded by conjugate normal faults temporal aspects of the devil canyon sequence provide strong evidence that slip on conjugate normal faults occurs sequentially aftershocks occurred primarily along the challis segment until the occurrence of the 8 september 1984 ml 5 0 earthquake along the lone pine fault after which aftershocks primarily occurred along this fault these observations are consistent with worldwide seismologic and geologic observations and with physical andmore numerical models of conjugate normal faulting aftershocks of the devil canyon sequence occurred immediately northwest of the ml 5 8 devils canyon earthquake which itself was immediately northwest of the thousand springs segment of the lost river fault the fault that slipped in association with the ms 7 3 borah peak earthquake coulomb failure stress analysis indicates that stress increases resulting from both the borah peak mainshock and devil canyon ml 5 8 earthquake were sufficient to induce failure on the lone pine fault these space time patterns suggest that conjugate normal faults may transfer stress or accommodate stress changes at the terminations of major normal faults in the basin and range province less

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

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

the geological history of maio cape verde islands the oldest igneous rocks on maio are pillow lavas of mid ocean ridge pillow basalts character which have been tilted and uplifted about 4 km from the ocean floor to outcrop as a partial ring dipping steeply away from a central plutonic complex made up of pyroxenites essexites syenites and carbonatites the ocean floor volcanic rocks are overlain conformably by a stratigraphically continuous pelagic carbonate succession which demonstrates a shallowing depositional environment from the upper jurassic to upper cretaceous times when tuffaceous beds indicate renewed volcanism the tuffs are associated with rudites demonstrating the emergence of the island and amongst the clasts are plutonics indicating upper cretaceous magmatism and the unroofing of the volcano to a substantial depth deformation under compressive stress resulted in the folding and local repetition by thrusting of this sedimentary cover which together with the plutonic core had been intensively injected by major sills the mesozoic succession has been planed off and overlain with marked unconformity by a largely neogene sequence of volcanic and terrestrial sedimentary rocks there is a hiatus throughout the palaeogene and constructional activity appears to recommence with ankaramitic hyaloclastite and lava deltas and subaerial ankaramitic flows these are overlain by fluvial sediments and tuffs stratigraphically above these is an extensive plateau of silica undersaturated lavas olivine melilitites and nephelinites which rest on a planed and locally lateritized surface at topographically higher levels in the eastern part of the island there are thick ankaramitic lavas and pyroclasts which evidently flowed eastward through valleys cut down into the mesozoic strata and appear to be of pliocene age the subsequent history of the island appears to be non volcanic

characterization of the monument hill fault system and implications for the active tectonics of the red rock valley southwestern montana new geologic mapping morphologic fault scarp modeling and geomorphic metrics in the red rock valley southwestern montana help characterize the quaternary history of the virtually unstudied monument hill fault and tectonics of the youthful and seismically active red rock graben two generations of pleistocene surface ruptures are preserved along the monument hill fault similarity in rupture ages along multiple strands determined from offset alluvial surfaces and morphologic modeling suggest earthquake clusters at 22e32 ka and possibly 160 ka quaternary activity along the monument hill fault is also reflected in elongate drainage basins and channel profiles with anomalously steep reaches coincident with mapped faults an anticlinal accommodation zone at kidd accommodates a change in fault polarity between the en echelon monument hill and red rock faults and a northward decrease in extension within the red rock graben the unique rupture histories of the monument hill and red rock faults however suggest the systems are not seismogenically linked and that the accommodation zone serves as a rupture barrier the geometry interconnectivity and kinematics of faults in the red rock valley may represent a snapshot of the early stages of extension applicable to the evolution of other northern basin and range grabens 2007 elsevier ltd all rights reserved

geotechnical thresholds in the lanzhou loess of china abstract failure of cementation bonds leading to soil structure collapse and slope failure is a major problem encountered in loess slopes in the lanzhou region of china typical physical properties low plasticity indices short range bonds decrease in shear strength upon saturation show little variation throughout the loess strata however important variations in the modes of failure and collapse potential exist which are related to varying thresholds of cementation bond failure and packing transformations when geotechnical thresholds are exceeded metastable loess can rapidly transform from an open to close particle packing a phenomenon enhanced by leaching processes and degradation of cementation bonds geotechnical parameters from laboratory and in situ tests provide an insight into the variation of cementation bond condition which in turn provides enhanced understanding of processes underlying slope instability development and the triggering of catastrophic mass movements in loess

cyclic variability in microstructure and physio mechanical properties of the xiashu loess palaeosol sequence in nanjing china abstract for the xiashu loess palaeosol sequence in nanjing china further to our work on the cyclic variability in its chemical composition and swelling shrinkage properties xia j huang g l liu z t chen x m 2007 cyclic variability in chemical composition and swelling shrinkage properties of the xiashu loess stratum near nanjing china pedosphere 17 5 666 672 this paper studies the cyclic variability in its microstructure and physico mechanical properties and the corresponding influence on its engineering behaviour for geotechnical and geological practices in addition the cyclic variability in the soil s grain size distribution and geochemical characteristics is compared with that of the loess palaeosol sequences at two other sites in china indicating a geographical pattern of cyclic variation of the sequences

evidence for two shield volcanoes exposed on the island of kauai hawaii the island of kauai has always been interpreted as a single shield volcano but lavas of previously correlated reversed to normal magnetic polarity transitions on opposite sides of the island differ significantly in isotopic composition samples from west kauai have 87sr 86sr 18 25 samples from east kauai have 87sr 86sr 0 7037 nd 6 14 and 206pb 204pb 18 25 available data suggest that a younger eastern shield grew on the collapsed flank of an older western one

submarine geology of the hilina slump and morpho structural evolution of kilauea volcano hawaii abstract marine geophysical data including sea beam bathymetry hawaii mr1 sidescan and seismic reflection profiles along with recent robot submersible observations and samples were acquired over the offshore continuation of the mobile kilauea volcano south flank this slope comprises the three active hot spot volcanoes mauna loa kilauea and loihi seamount and is the locus of the hawaiian hot spot the south flank is the site of frequent low intensity seismicity as well as episodic large magnitude earthquakes its sub aerial portion creeps seaward at a rate of approximately 10 cm year the hilina slump is the only large submarine landslide in the hawaiian archipelago thought to be active and this study is one of the first to more highly resolve submarine slide features there the slump is classified into four distinct zones from nearshore to the island s base estimates of size based on these data indicate a slumped area of 2100 km 2 and a volume of 10 000 12 000 km 3 equivalent to about 10 of the entire island edifice the overall picture gained from these data sets is one of mass wasting of the neovolcanic terrain as it builds upward and seaward though reinforcement by young and pre hawaii seamounts adjacent to the pedestal is apparent extensive lava delta deposits are formed by hyaloclastites and detritus from recent lava flows into the sea these deposits dominate the upper submarine slope offshore of kilauea with pillow breccia revealed at mid depths along the lower flanks massive outcrops of volcanically derived sedimentary rocks were found underlying kilauea thus necessitating a rethinking of previous models of volcanic island development the morphologic and structural evolutionary model for kilauea volcano and the hilina slump proposed here attempts to incorporate this revelation a hazard assessment for the hilina slump is presented where it is suggested that displacement of the south flank to date has been restrained by a still developing northeast lateral submarine boundary when it does fully mature the south flank may be more subject to land slips triggered by large long duration earthquakes and thus kilauea may undergo more frequent episodes of failure with increased displacements

tectonic geomorphology of the red rock fault insights into segmentation and landscape evolution of a developing range front normal fault the red rock fault an active normal fault in southwest montana is reevaluated for fault segmentation using a multiproxy approach field characterization of soils coupled with radiocarbon ages in offset hanging wall fans and terraces constrain the rupture history at a number of locations along strike these data are coupled with morphometric analysis of dated alluvial fan deposits and adjacent 2nd and 3rd order footwall drainage basins to further constrain fault kinematics and segmentation morphometric analysis of the big sheep creek catchment which drains a large area of the footwall range provides a control on the spatial extent offault influence on footwall topography three fault segments are recognized by this study compared with the two segments recognized previously data from offset alluvial surfaces were synthesized with hanging wall fan and footwall drainage basin data to demonstrate a southward increase in displacement along the red rock fault since at least the latest pleistocene at a maximum rate of 1 5 mm yr red rock ruptures were mainly confined to segments suggesting a fault behaving as several discrete slip surfaces however simultaneous rupture of adjacent segments during one event indicates some fault zone coalescence a youthful red rock fault is supported by the absence of tectonic influences on footwall topography and is consistent with an eastward progression of normal fault development along the northern arm of the yellowstone hot spot q 2005 elsevier ltd all rights reserved

formation mechanism analysis of irrigation induced retrogressive loess landslides abstract the loess plateau covers about 6 6 of the total land area of china landslides are serious concerns in loess plateau of china and the south jingyang tableland on the loess plateau of china has received significant attention because of frequent occurrence of gradual retrogressive loess landslides grll there however the characteristics and mechanism of grll are largely unknown in this study three typical landslide groups namely miaodian zaitou landslide group jiangliu landslide group and dabuzi landslide group are chosen as examples to analyze the characteristics of grll by performing a field survey and undrained triaxial shear tests loess fissures are found to play a key role in controlling the evolution of landslides on the one hand the mechanical properties of loess surrounding fissures rapidly weaken due to water infiltration into loess fissures on the other hand the self weight of the overlying loess increases since water infiltrates into fissures the undrained triaxial shear tests results indicate that loess specimen shows either strain hardening or strain softening behavior depending on its initial moisture content furthermore reduction in the shear strength of loess samples is observed as moisture content increases three factors associated with the characteristics and mechanism of grll group including strata lithology slope shape irrigation and rainfall are discussed finally the formation mechanism and evolution of grll are summarized into three stages namely a creep tensional stage a localized liquefaction stage and a sliding stage this study provides important insights on gradual retrogressive characteristics of loess landslides and facilitates appropriate safeguards to reduce the risk of such landslide hazards

anomalous heat flow and geoid across the cape verde rise evidence for dynamic support from a thermal plume in the mantle summary we describe results from 200 heat flow measurements across the cape verde rise in the north atlantic they show that the heat flow through normal 125 myr old crust is 45 5 3 4mwm 2 close to the prediction for a lithospheric plate model heat flow increases towards the centre of the rise reaching a maximum of 16 4 mw m 2 above the normal oceanic value the concommitant geoid anomaly at the centre of the rise is 7 6 0 3 m and the depth anomaly is 1900 200 m the anomalous heat flow geoid and bathymetric values are used to constrain a variety of theoretical models of hot spot mechanisms lithospheric reheating models alone whether involving transient or sustained thinning of the lithosphere fail to model the broad heat flow anomaly and the long duration of uplift and volcanism observed on the cape verde rise axisymmetric convection models provide a better fit to the observed data and suggest that the swell is a consequence primarily of dynamic uplift generated by an ascending thermal plume in the underlying mantle uplift caused by expansion of the solid lithosphere is of smaller importance the observed geoid bathymetry and heat flow anomalies are reproduced well using convection models with upper mantle viscosities of 2 4 times 1020 pa s and a coefficient of thermal expansion in the range 2 0 2 5 times 10 5 k 1 the effect of melting in the ascending plume is to buffer the heat flow anomalies in the case of the cape verde rise partial melting is minimal but its effect on other hotspots will be to limit observed heat flow anomalies at the surface to less than 20 25 mw m 2

laboratory study on soil behavior in loess slope subjected to infiltration abstract in recent years heifangtai plateau in gansu province china has received significant attention as a loess region in which landslides frequently occur this study aims to examine the soil behavior and failure mechanism s of loess slopes subjected to water infiltration high quality samples were retrieved behind the failure plane of a landslide in heifangtai three sets of stress path tests were conducted to mimic the process of loess slope failures these tests include undrained compression on anisotropically consolidated saturated samples drained shear by decreasing mean effective stress at constant axial load on saturated samples and wetting by decreasing matric suction at constant axial load on unsaturated samples loess behavior was evaluated in terms of shear strength deformation upon shearing critical state state parameter and soil water characteristic curve three major observations were drawn from the test results first the anisotropically consolidated saturated loess exhibits a noticeable strain softening behavior upon undrained compression the peak shear strength is mobilized at less than 1 axial strain the ultimate shear strength is only 20 30 of the peak value second when subjected to shear by decreasing mean effective stress at constant axial load the saturated loess exhibits sudden failure when the confining stress is low at higher stresses the soil exhibits progressive failure third unsaturated loess deforms progressively when subjected to a reduction in matric suction i e wetting at constant axial load the failure mechanisms of the loess slopes are discussed based on the experimental findings

assessing regional geodiversity the iberian peninsula geodiversity is a landscape characteristic related to the heterogeneity of the physical properties of the earth surface in this work we quantify and compare geodiversity in several geodynamic zones of the iberian peninsula for this purpose we have developed a geographic information system gis procedure to carry out a regional terrain classification based on geodiversity factors a classification process helped to produce a morphometric map 10 classes a morphoclimatic map five classes and a geological map 15 classes these three maps were combined using an overlay operation union to obtain the final terrain classification 419 classes which was then applied to calculate diversity landscape indices the latter were calculated using common landscape diversity indices patch richness density shannon s diversity index shannon s evenness index simpson s diversity index and simpson s evenness index provided by fragstats free software these indices were calculated for the whole landscape of the main iberian geological regions thus revealing a close relationship between some index values and the geological and geomorphological characteristics the highest diversity values are associated with alpine collisional orogens and reactivated chains of the precambrian palaeozoic massif intraplate orogen with sedimentary cover characterized by extensive planation surfaces have lower values mesozoic areas with no significant tectonic deformation and cenozoic basins are characterized by the lowest diversity values amongst the latter the major diversity is associated with the most dissected basins which also present higher morphoclimatic variety though depending on the chosen scale and the landscape classification criteria these indices provide an objective assessment of the regional geodiversity of iberia copyright 2009 john wiley sons ltd

study of the 1920 haiyuan earthquake induced landslides in loess china many large scale landslides induced by earthquakes have been reported in loess soils they often cause catastrophes because they travel long distances at high velocity to clarify the mechanism of these landslides field survey was performed on the landslides triggered by the haiyuan earthquake china 1920 and a series of ring shear tests was conducted on the loess soils collected from a landslide the field surveys revealed that most of the loess landslides triggered by the haiyuan earthquake occurred on concave slopes gentler than 15 with long runout distance showing very small equivalent friction angle cyclic ring shear tests on saturated specimens in the undrained condition showed that when cyclic shear stress was applied to a loose loess specimen pore pressure was built up gradually before the failure and after that large pore pressure was quickly generated due to the failure of loess soil structure meanwhile to investigate the mechanism that produces the high mobility of loess landslides ring shear tests were conducted on loess specimens with large shear displacement of up to several meters under the undrained condition and it was found that the initial normal stress has no effects and overconsolidation ratio has little if any effects on the apparent friction angle in the steady state for loess soils results of tests on soils at different saturation degrees revealed that the reduction in shear strength results more likely from the generation of pore water pressure not of pore air pressure

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

distribution geomorphology and lithofacies of cliff top storm deposits examples from the high energy coasts of scotland and ireland abstract cliff top storm deposits ctsds occur on cliffs at elevations of up to 50 m above sea level at exposed sites on the deep water coasts of the british isles this study examines the distribution geomorphology and lithofacies of ctsds at sites from shetland orkney caithness and the outer hebrides in scotland and from the aran islands in galway bay in ireland ctsds are generated largely by the quarrying of blocks from the cliff top and transported by green water bores across cliff top platforms and ramps to be deposited in backing ridges or as debris spreads maximum boulder sizes reach 48 m 3 but it is likely that much larger blocks can be quarried prior to disintegration during transport eye witness accounts and field mapping demonstrate that formation and modification of ctsds has continued during major storms over recent decades recent ctsds bury a range of man made debris but older deposits lack this and instead show weathering effects that indicate a longer residence time in shetland osl dates on intercalated sands suggest that the oldest ctsds date from 800 ad radiocarbon dates on shell buried inside ctsd ridges relate to major storms between 1700 and 1900 ctsds represent an overlooked archive of storm sedimentation that has great potential for the elucidation of local storm chronologies ctsds also provide evidence of wave impacts on any part of the cliff face or top in fundamental contrast to the concentration of wave action at the cliff foot implicit in traditional models of the erosion of rock coasts

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

on dating the magmatism of maio cape verde islands conventional k ar and40ar 39ar studies of mesozoic ocean floor basalts and tertiary plutonic and volcanic rocks from maio cape verde islands have been determined to elucidate the magmatic evolution of this ocean island pillow lavas of the basement complex yield a minimum age of 113 8 ma though thermal overprinting of their formation age by the younger central intrusive complex cic and subsequent sheet intrusions is in some cases almost total activity in the cic began before 20 ma and plutons continued to develop until about 8 ma the youngest ages possibly indicating a cooling history of more than 2 ma for these bodies relative to their volcanic counterparts sheet intrusion occurred throughout the period 20 to 9 ma though the peak of this activity probably occurred 11 ma ago field relations allow the time of thrusting s on the monte branco thrust to be bracketed between 9 and 7 ma volcanic activity began in the tertiary probably before 12 ma and culminated in the development of a stratovolcano at 7 ma

analysis of the causes of large scale loess landslides in baoji china landslide hazards are common in western china understanding the mechanism of landslides in loess covered regions is particularly important for landslide risk assessment a detailed landslide survey including large scale slide drilling and geophysical exploration was carried out at the edge of the loess plateau on the north side of the wei river in china we reconstructed the geomorphological evolution model of the wei river and analyzed slope structures and lithology engineering geologic conditions and active fault properties in the landslide regions were investigated the results showed that paleogeomorphology of the north slope of the river gradually lowered from south to north ancient landforms showed a gradual transition to the south sanmen lake basin from the piedmont alluvial plain during the pliocene to early pleistocene the lake basin in the southern part of the study area gradually retreated and the wei river formed in the early pleistocene the main river flow shifted northward because of neotectonic movement and periodic climate changes until the holocene and then gradually moved southward to produce the current landforms the active wei river fault at the edge of the loess plateau acted as a route of water infiltration weakening the structural planes erosion and rise of the groundwater table caused old occurrence during the late pleistocene and ancient occurrence before the late pleistocene landslides to form on the edge of the plateau along active fractures and interfaces of pliocene sand gravel and clay these were multiple deep seated rotational slides and or multiple perched translational landslides slope stability analysis indicated that the complex landslides that occurred in the loess areas in recent years were closely related to the distribution of water and pliocene clay

growth structure instability and collapse of canarian volcanoes and comparisons with hawaiian volcanoes recent onshore and offshore investigations in the canarian archipelago especially in the western islands of la palma and el hierro have greatly improved the understanding of the genesis and evolution of these islands and allow interesting comparisons with other hotspot induced oceanic island volcanoes especially the hawaiian archipelago genesis induced by hotspot activity and consequently shield and post erosional stages of growth allow the definition of similar main stratigraphic units the canarian and hawaiian volcanoes show common constructional and structural features such as rift zones progressive volcano instability and multiple gravitational collapses however the canaries present some important geological differences from the prototypical hotspot volcanoes of the hawaiian islands particularly the absence of significant subsidence the canarian volcanoes remain emergent until completely mass wasted by gravitational collapses and erosion volcanic formations over 20 million years are observable in outcrop in the canaries including the seamount stages of growth in several of the islands

drowned reefs as indicators of the rate of subsidence of the island of hawaii a major submerged terrace whose seaward edge is at about 150 m depth was investigated in 1983 during 10 dives with the hawaii undersea research laboratory hurl submersible makali i off kealakekua bay hawaii the seaward termination of the terrace is a steep wall of reef limestone that extends from 150 to 250 m below sea level three samples of limestone collected from the reef face at depths of 204 219 m yield a weighted average 14 c age of 13 250 s d 380 years before present the 150 m terrace as well as two deeper terraces off northwestern hawaii at depths of 390 pm 50 m and 580 pm 40 m apparently were formed by the interaction of glacioeustatic sea level changes and island subsidence the best fit of depth age and subsidence data indicates that the northwestern coast of hawaii has subsided at an absolute rate of 1 8 to 3 mm yr and that the rate of subsidence has generally increased over the past 0 3 m y each reef terrace grew intermittently for nearly 0 1 m y the 150 m reef ter

interglacial sea levels abstract isotopic curves have been used as approximative estimators of global sea level calculations of the amplitude of sea level variations during interglacials especially for the last interglacial are based on the study of emerged coral terraces the application of different dating methods shows great uncertainty about the length of each interglacial and also about the number chronology and altitude of the different highstands that occur during each interglacial data of raised marine terraces from areas with different geodynamic behaviour bermudas bahamas peru chile italy and spain are summarized in order to analyze the relationships between sea level and interglacial stages two interglacials have been identified for the early pleistocene represented by two marine terraces with different highstands during the early middle pleistocene an interglacial with several highstands is recorded in uplifted areas during isotopic stage 11 at least one highstand with sea level equal or higher than present has been recorded similar sea level behaviour can be suggested for isotopic stage 9 all the analyzed areas record two highstands during isotopic stage 7 when warm equatorial fauna migrate into the mediterranean during isotopic substage 5e at least two highstands took place with evidence of lowstands between them and at least one highstand during substage 5c with similar sea level height above present msl except in barbados and bermuda during substage 5a at least one highstand has been recorded

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

emergent littoral deposits in the eastern canary islands abstract k ar ages a abdel monem p d watkins and p w gast 1971 american journal of science 271 490 521 this paper and revised paleontological determinations j meco 1977 los strombus neogenos y cuatenarios del atlantico euroafricano las palmas ediciones del excmo cabildo insular de gran canaria show that quaternary r crofts 1967 quaternaria 9 247 260 g lecointre k j tinkler and g richards 1967 academy of natural science of philadelphia proceedings 119 325 344 littoral deposits on lanzarote and fuerteventura are early pliocene and late pleistocene early and middle pleistocene strand lines are not represented early pliocene littoral and marine deposits contain a characteristic fossil assemblage strombus coronatus nerita emiliana gryphaea virleti patella cf intermedia and rothpletzia rudista differences in elevation record differential post pliocene uplift of the coastal platforms on which they lie late pleistocene beach deposits at low elevations belong to two groups an older with strombus bubonius and a younger without differences in elevation of early pliocene littoral deposits are reflected by differences in elevation of late pleistocene beach deposits nearby

instrumental seismicity of central idaho hypocenters of regionally recorded earthquakes that occurred in central idaho from 1944 through october 1985 have been recomputed with travel times calibrated by locally recorded aftershocks of the borah peak idaho earthquake of 1983 the effect of the relocation is to define more sharply the sizes and relative positions of seismic source zones in central idaho and to move epicenters systematically south often by more than 10 km from their previously cataloged positions the distribution of epicenters of the borah peak main shock and early aftershocks suggests that the fault segment that ruptured in the main shock was approximately a parallelogram with one pair of sides parallel to the zone of surface fault scarps associated with the earthquake and with the other pair of sides parallel to the slip vector of the earthquake such a rupture shape would be expected on geometrical grounds if the 1983 rupture zone were terminated on the north and south by intersection with adjacent segments of the lost river fault that have the same slip vector as the 1983 rupture epicenters of earthquakes occurring before 1983 define a seismic zone the white cloud peaks zone that is approximately parallel to the borah peak aftershock zone but situated from 30 to 40 km to the west the relocated epicenters may also be interpreted as defining a north northeast trending seismic zone near seafoam and a north northeast trending seismic zone that is situated north and west of challis here called the twin peaks myers cove zone the seafoam zone includes the epicenter of the largest instrumentally recorded central idaho earthquake prior to the borah peak earthquake the magnitude 6 1 shock of 12 july 1944 the region within 25 km of the epicenter of the borah peak main shock was quiescent for at least two decades before the main shock for magnitudes mb lg of 3 5 and greater

human impacts quantification on the coastal landforms of gran canaria island canary islands abstract the coastal areas of the canary islands are particularly sensitive to changes both from a natural perspective and for their potential socio economic implications in this paper the state of conservation of an insular coast is approached from a geomorphological point of view considering recent changes induced by urban and tourism development the analysis is applied to the coast of gran canaria a small atlantic island of volcanic origin subject to a high degree of human pressure on its coastal areas especially in recent decades currently much of the economic activity of gran canaria is linked to mass tourism associated with climatic and geomorphological features of the coast this work is addressed through detailed mapping of coastal landforms across the island 256 km perimeter corresponding to the period before the urban and tourism development late 19th century for the island s capital mid 20th century for the rest of the island and today the comparison between the coastal geomorphology before and after the urban and tourism development was established through four categories of human impacts related to their conservation state unaltered altered semi destroyed and extinct the results indicate that 43 of coastal landforms have been affected by human impacts while 57 remain unaltered the most affected are sedimentary landforms namely coastal dunes palaeo dunes beaches and wetlands geodiversity loss was also evaluated by applying two diversity indices the coastal geodiversity loss by total or partial destruction of landforms is estimated at 15 2 according to shannon index h while it increases to 32 1 according to an index proposed in this paper we conclude that the transformations of the coast of gran canaria induced by urban and tourism development have heavily affected the most singular coastal landforms dunes palaeo dunes and wetlands reducing significantly its geodiversity

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

irrigation induced loess flow failure in heifangtai platform north west china because the construction of dams and hydro electric power stations of liujiaxia and yanguoxia across the yellow river in west gansu province north west china inhabitants in the reservoir areas were resettled in heifangtai loess platform irrigation thus started in 1968 perched water table was significantly raised and resulted in many loess flow failures in the past 30 years this type of landslide was often featured by long runout distance high speed and recurrence laboratory tests along icu and csd stress paths were performed it is shown that the loess has a strong strain softening behavior and instability can occur in drained condition before undrained liquefaction the failure mechanism of loess flow can be interpreted as the following process with increasing perched water table collapse in loess was first triggered in drained condition and led to undrained loading to adjacent soil in the lower saturated part of the loess platform under gravity loading applied by upper dry loess undrained flow failure mobilized eventually

seismicity and late quaternary faulting of the northern basin and range province montana and idaho abstract examination of seismicity and late quaternary faults in montana and idaho north of the snake river plain shows a geographic correspondence between high seismicity and 24 faults that have experienced surface rupture during the late quaternary the lewis and clark zone delineates the northern boundary of this tectonically active extensional region earthquakes greater than magnitude 5 5 and all identified late quaternary faults are confined to the montana idaho portion of the basin and range province south of the lewis and clark zone furthermore all 12 holocene faults are confined to a seismologic zone centennial tectonic belt parallel to the northern flank of the snake river plain in extreme southwestern montana and adjacent idaho fault trends strain data and focal mechanisms suggest that both late quaternary faulting and seismicity in the region are primarily products of two distinct stress regimes 1 overall basin and range extension along a s45 w direction relative to the mid continent and 2 localized effects of the yellowstone hot spot which appears to have the least principle stress axis oriented horizontally at about s4 w the three largest historic earthquakes north of the snake river plain are indicative of three different stress provinces the 1983 borah peak earthquake occurred in the montana idaho basin and range the 1959 hebgen lake earthquake is associated with the yellowstone hot spot area and the 1925 clarkston valley event appears to be associated with the stress field of the united states mid continent

stratigraphic constraints on the timing and emplacement of the alika 2 giant hawaiian submarine landslide abstract previous work has found evidence for giant tsunami waves that impacted the coasts of lanai molokai and other southern hawaiian islands tentatively dated at 100 and 200 ka by u series methods on uplifted coral clasts seafloor imaging and related work off hawaii island has suggested the alika phase 2 debris avalanche as the source of the 100 ka giant wave deposits although its precise age has been elusive more recently a basaltic sand bed in odp site 842 300 km west of hawaii estimated at 100 20 ka has been suggested to correlate with this or another large hawaiian landslide our approach to the timing and linkage of giant submarine landslides and paleo tsunami deposits is a detailed stratigraphic survey of pelagic deposits proximal to the landslide feature beginning with a suite of seven piston gravity and box cores collected in the vicinity of the alika 2 slide we used u series dating techniques including excess 230 th and 210 pb profiling high resolution paleomagnetic stratigraphy including continuous u channel analysis 18 o stratigraphy visual and x ray sediment lithology and the petrology and geochemistry of the included turbidites and ash layers minimum ages for the alika phase 2a slide from detailed investigation of two of the cores are 112 15 ka and 125 24 ka 2 based on excess 230 th dating a less precise age for the alika phase 1 and or south kona slide is 242 80 ka 2 consistent with previous geological estimates oxygen isotope analyses of entrained planktonic foraminifera better constrain the alika phase 2a maximum age at 127 5 ka which corresponds to the beginning of the stage 5e interglacial period it is proposed that triggering of these giant landslides may be related to climate change when wetter periods increase the possibility of groundwater intrusion and consequent phreatomagmatic eruptions of shallow magma chambers our study indicates the contemporaneity of the alika giant submarine landslides and distal deposits from enormous turbidity currents as well as coral clasts reported to be tsunami deposits on lanai and molokai through direct dating and compositional analysis of the landslide deposits

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

glacial interglacial changes in dust deposition on the chinese loess plateau the chinese loess plateau clp contains an extensive record of aeolian deposition through multiple glacial interglacial cycles independent chronologies based on pedostratigraphy magnetic susceptibility radiocarbon and luminescence dating were developed for 79 sites and used to estimate aeolian mass accumulation rates mars for marine isotope stages 1 5 the regional median value of mar for stage 2 is 310 g m2 yr compared to an estimate of 65 g m2 yr for stage 5 estimated mars from individual sites for stage 2 are approximately 4 3 times greater than mars for stage 5 and 2 1 times greater than for stage 1 mar values at individual sites are consistently highest in the northwest and lowest in the southwest of the clp during all marine isotope stages mars estimated on sections through loess terraces are consistently higher than mar estimates at other sites indicating that local recycling of loess material from exposed river valley deposits has been significant throughout the last 130 kyr although the spatial and temporal patterns in mar are robust there are uncertainties about the magnitude of these changes due to a lack of bulk density measurements and uncertainties in the chronologies for individual sites b site and chronological biases in the sampling used to derive regional estimates and c the unquantified nature of human impact on accumulation rates during the late holocene nevertheless the records from the clp pose a number of challenges which could be addressed by numerical models of the palaeo dust cycle

complete gravity study of piton de la fournaise volcano reunion island abstract we present an interpretation of all available gravity data on piton de la fournaise volcano including a new set collected in the summit area using a linear programming inversion method we determine the extension of the grand brule ultramafic body drilled in 1985 and we propose to interpret it as a frozen magma chamber related to a disappeared volcano we also present evidence for superficial mass excess under the enclos fouque and plaine des sables calderas that we link to the present piton de la fournaise volcanism the detailed gravity survey of the summit area allows us to emphasize the great importance of dyke complexes associated with the ne and se rift zones and with the shallow magma chamber a negative anomaly in the summit area is interpreted as a relative minimum between the positive anomaly of grand brule and those of the western part of the enclos fouque and plaine des sables calderas

kinematic evidence for the effect of changing plate boundary conditions on the tectonics of the northern u s rockies we derive surface velocities from gps sites in the interior northwest u s relative to a fixed north american reference frame to investigate surface tectonic kinematics from the snake river plain srp to the canadian border the centennial tectonic belt ctb on the northern margin of the srp exhibits west directed extensional velocity gradients and strain distributions similar to the main basin and range province brp suggesting that the ctb is part of the brp north of the ctb however the vergence of velocities relative to north america switches from westward to eastward along with a concomitant rotation of the principal stress axes based on available seismic focal mechanisms revealing paired extension in the northern rockies and shortening across the rocky mountain front this change in orientation of surface velocities suggests that the change in the boundary conditions on the western margin of north america influences the direction of gravitational collapse of laramide thickened crust throughout the study region fault slip rate estimates calculated from the new geodetic velocity field are consistently larger than previously reported fault slip rates determined from limited geomorphic and paleoseismic studies

stress in western canada from regional moment tensor analysis more than 180 regional moment tensor rmt solutions for moderate sized earthquakes m 4 are used to examine the contemporary stress regime of western canada and provide valuable information relating to earthquake hazard analysis the overall regional stress pattern shows mainly ne sw oriented p axes for most of western canada with local variations in the northern cordillera the maximum compressive stress direction 1 varies from east west to north south to ne sw from south to north the stress direction 1 is consistent with the p axis direction for the largest earthquakes except in the central and northern mackenzie mountains where there is a 16 difference the yakutat collision zone shows a steady change in 1 from east west in the east to north south in the west in the canada united states border region rmt solutions suggest a north south compressional regime may extend through southern british columbia and northern washington to the eastern cordillera in the vancouver island puget sou

laboratory characterization of rainfall induced loess slope failure loess slopes are widely distributed throughout the northwestern region of china and are prone to slope failure in response to heavy rainfall we undertook three groups of flume experiments in the laboratory to study loess slope dynamics under artificial rainfall conditions additionally a laser scanner was used to observe loess landslide deformation characteristics and failure development a numerical analysis of unsaturated seepage in loess slopes because of rainfall infiltration was performed moisture content pore water pressure and slope deformation were monitored to quantify the relationship between rainfall infiltration and loess slope stability movement of the wetting front near the slope surface was triggered by rainfall and related to rainfall intensity and duration which is consistent with the numerical solution rainfall infiltration increased pore water pressure producing gravity driven landslides we observed that landslide development began with local failure in the toe slope that gradually retreated toward the crown forming a multi sliding displacement and eventually resulting in total slope failure

measuring geomorphological diversity on coastal environments a new approach to geodiversity abstract geodiversity can be defined as the spatial variability of geo elements its emergence as a research field is relatively recent with a wide range of approaches and methods of evaluation and quantification already in use the work described in this paper was carried out from a novel perspective firstly the emphasis is specifically centred on geomorphological diversity secondly mathematical ecology calculations are applied which tackle the problem on the basis of a larger number of diversity parameters in addition whereas most authors have focussed on mountainous and or continental areas for the first time a study of this type is applied to coastal landscapes the analysis covers the full 459 km of volcanic coastline of the islands of gran canaria and la palma canary islands these two oceanic islands were chosen for purposes of diversity comparison given their differing stages of geomorphic development in accordance with an ad hoc geomorphological taxonomy as developed in this study 14 geomorphic groups and 42 subgroups were identified and quantified according to their presence 1 or absence 0 along the coastline a cartographic analytical method coastline data storing or cds based on the computation of binary information in the cartographic vector of the coastline enabled calculation of the occurrence probability of these groups and subgroups both at local level analyses of coastal morphoassemblages and general level three components of geomorphological diversity richness evenness and dissimilarity were estimated through indices of richness r shannon s entropy h and rao s quadratic entropy q the data reveal that geomorphological coastal diversity is between 11 1 and 48 2 higher in gran canaria than in la palma the method was subjected to a fractal stress test through iterative mapping procedures to assess the effect of scale on the behaviour of the relative frequencies and indices the variability that was obtained allowed the extraction of corrected values in the indices for la palma h c 1 88 0 008 and qc 0 183 0 004 and gran canaria h c 2 11 0 019 and qc 0 232 0 003 a moving window test was also applied as a rarefaction method to confirm the contrast in diversity in coasts of different size the results enabled to advance hypotheses about the relation between coastal geomorphic diversity and geological age of islands

pore pressure generation and fluidization in a loess landslide triggered by the 1920 haiyuan earthquake china a case study abstract during the 1920 haiyuan earthquake numerous catastrophic landslides were triggered in the loess area in northwest china we investigated in detail a large example of these landslides referred to as dangjiacha landslide in this paper this landslide originated from a slope of about 20 and the displaced soil mass traveled about 3200 m damming a valley we performed a field survey and found that standing water existed in the landslide area and the loess had high porosity we infer that it was the liquefaction of the water saturated loess layer rather than the suspension of silt in the pore air in the loess that caused the great mobility of this landslide to test this inference we performed undrained triaxial compression and ring shear tests on loess samples to examine the shear behavior of loess saturated by either air or water the test results showed that the water saturated loess soil was highly susceptible to flow liquefaction failure fast shear tests on naturally air dried loess samples revealed that the generated pore air pressure was small under the undrained condition and no significant reduction in the shear resistance was observed implying that air entrapped in the loess was unlikely to be the main contributor to the high mobility of this large scale landslide