holocene history of fire vegetation and land use from the central pyrenees france located on a mountain pass in the west central pyrenees the col d ech peat bog provides a holocene fire and vegetation record based upon nine 14c ams dates we aim to compare climate driven versus human driven fire regimes in terms of frequency fire episodes distribution and impact on vegetation our results show the mid holocene 8500 5500 cal yr bp to be characterized by high fire frequency linked with drier and warmer conditions however fire occurrences appear to have been rather stochastic as underlined by a scattered chronological distribution wetter and colder conditions at the mid to late holocene transition 4000 3000 cal yr bp led to a decrease in fire frequency probably driven by both climate and a subsequent reduction in human land use on the contrary from 3000 cal yr bp fire frequency seems to be driven by agro pastoral activities with a very regular distribution of events during this period fire was used as a prominent agent of landscape management

failure of volcano slopes magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse their role is twofold involving both driving and resisting forces first flank stability is diminished by magmastatic and magma overpressures and steepened slopes that accompany intrusion second excess pore pressures in potential failure zones can be generated as a result of intrusion related mechanical or thermal straining of the rock fluid medium pressurized retrograde boiling in high level magma chambers or hydrothermal fluid circulation also earthquakes may aid collapse through inertial forces and shaking induced pore pressure generation these excess pore pressures reduce the sliding resistance as shown for wedge shaped slide blocks for selected cases the destabilizing influence of mechanically induced pore pressures is maximized as the intruded width or corresponding overpressure of the intrusion is increased the destabilizing influence of thermally induced pore pressures is conditioned by the seve

volcanic spreading at kilauea 1976 1996 the rift system traversing about 80 km of the subaerial surface of kilauea volcano has extended continuously since the m 7 2 flank earthquake of november 1975 widening across the summit has amounted to more than 250 cm decelerating after 1975 from about 25 to 4 cm yr 1 since 1983 concurrently the summit has subsided more than 200 cm even as the adjacent south flank has risen more than 50 cm the axes of the upper zones about 10 km from the summit subsided before 1983 at average rates of 9 and 4 cm yr 1 respectively and at rates of 4 and 3 cm yr 1 since the middle southwest rift zone is also subsiding and at the other end of kilauea s subaerial rift system subsidence along the lower east rift zone has averaged 1 2 cm yr 1 deformation of kilauea s south flank has been continuous although subject as well to displacements caused by major rift zone seismic swarms whereas horizontal strains across the subaerial south flank seem to have been generally compressive after 1975 they have been extensional since about 1980 or 1981 interrupted only by the east rift zone dike intrusion of 1983 because the magnitudes of these contractions and extensions are much less than the extension across the rift system the subaerial south flank is apparently sliding seaward on its basal decollement more than it is accumulating horizontal strains within the overlying volcanic pile kilauea suffers from gravitational spreading made even more unstable by accumulation of magma along the rift system at depths in excess of about 4 5 km in the presence hot rock incapable of withstanding deviatoric stresses this seismicly quiescent zone decouples the south flank from the rest of hawaii s volcanic edifice the rift zones at lesser depths exhibit a more brittle and therefore sporadic extensional behavior judging from the modern extension record of the summit which both predates the m 7 2 earthquake of 1975 and has outlived its 10 year period of aftershocks kilauea will continue to spread along its rift system as its south flank slips seaward to accommodate the accretion of magma and its relatively dense olivine rich differentiate

the selection of sites for paleovegetational studies the judicious selection of sites for paleovegetational and paleoclimatic studies permits paleoecologists to answer specific research questions that go beyond primary descriptions of past vegetation we present a model that describes the relationship between basin size and pollen source area and predicts the proportions of local extralocal and regional pollen sampled by lake basins of different size the distinctive sampling properties of lakes peats and small hollows can be exploited to provide details of pattern in paleovegetation so long as attention is given to the limitations and problems of these types of sites combinations of site types in a single study most fully exploit the information contained in sediments

linking changes in atmospheric dust deposition vegetation change and human activities in northwest spain during the last 5300 years a high resolution 5300 yr record of pollen and lithogenic elements k ca ti rb sr y zr from an ombrotrophic peat bog located in northwest spain reveals that the variations in the fluxes of lithogenic elements supplied to the bog by atmospheric deposition were coupled to the evolution of the vegetation of the area a strong negative correlation exists between the percentage of tree pollen and the concentration of lithogenic elements for example the correlation between total tree pollen and sr concentrations is 0 94 the main phases of decline of the deciduous forest occurred during known cultural periods late neolithic the metal ages the roman period the middle ages and the industrial period suggesting a close link between human activities fires and forest clearances changes in the vegetation and soil erosion the flux of lithogenic elements seems to have increased before a significant variation in pollen is detected which may indicate that changes in soil erosion are reflected earlie

environmental changes during the holocene climatic optimum in central europe human impact and natural causes abstract the priority programme changes of the geo biosphere aimed to reconstruct the environmental history of central europe with emphasis on the time interval from 9000 to 5500 cal bp time slice ii coinciding with the holocene climatic optimum during this period the onset of human activities such as settlement agriculture and animal husbandry caused environmental changes studies of different landscape units in germany were carried out to identify these anthropogenically induced changes and to distinguish them from natural effects on the environmental system the investigated archives included laminated lake sediments fluvial sediments colluvia and soils speleothems peat and coastal sediments the different archives were examined using refined research methods including a variety of sedimentary and geochemical analyses together with pollen analysis and dating methods for the establishment of a reliable chronology the results of the various research groups are summarised and critically discussed based on these results the climatic optimum can be subdivided into three periods 1 the early atlantic from 9000 to 7500 cal bp with negligible human impact and stable environmental conditions 2 the late atlantic during early and middle neolithic from 7500 to 6300 cal bp with pollen evidence for vegetation changes but only negligible changes detectable in other proxy records and 3 the late atlantic during the younger neolithic jungneolithikum after 6300 cal bp with human impact observed in many archives and proxy records especially in the pollen record but also in lacustrine and fluvial sediments during the whole climatic optimum natural causes such as minor shifts of temperature did not induce substantial environmental changes though some changes such as temporary droughts may have facilitated and amplified the observed human impact

seismostratigraphy of the western flanks of el hierro and la palma canary islands a record of canary islands volcanism abstract a cruise carried out aboard the spanish r v hesperides using a 255 inch3 airgun allowed to identify three main seismostratigraphic units in the western submarine flanks of the islands of la palma and el hierro canary islands the time structure and thickness maps of each unit together with the interpretation of the seismic facies demonstrate that the evolution of the canary islands is recorded in the marine basin the structure maps show that the older reflectors dip to the nw in contrast to the present day sea floor which dips to the wnw the thickness maps also show that the depocentre moved from a position parallel to the northwest african margin to a position now occupied by the island of la palma despite the high sedimentation rates of hemipelagic background sedimentation in the study area the three seismic units can be interpreted in terms of their relation to the canarian volcanism unit i was deposited before the initiation of volcanism and the arrival of volcaniclastic flows and is thus mainly if not entirely composed of hemipelagic sediments unit ii seems to reflect the shield phases of the easternmost edifices and as such would be constituted by the distal products of erosion and mass wasting of these islands unit iii in contrast results mainly from the shield phase of the two westernmost islands la palma and el hierro and as such reflects more proximal conditions as demonstrated by the presence of lateral collapse deposits from these islands

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

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

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

tripartite climate reversal in central europe 5600 5300 years ago abstract the history of variations in water level of lake constance as reconstructed from sediment and pollen analysis of a sediment sequence from the archaeological site of arbon bleiche 3 shows an abrupt rise in lake level dendrochronologically dated to 5375 yr ago 5320 yr relative to ad 1950 this event paralleled by the destruction of the neolithic village by fire provoked the abandonment of this prehistoric lake shore location established in the former shallow bay of arbon bleiche and was the last of a series of three episodes of successively higher lake level the first occurring at 5600 5500 cal yr b p the dendrochronologically dated rise event was synchronous with an abrupt increase in atmospheric 14 c this supports the hypothesis of an abrupt climate change forced by varying solar activity moreover the three successive episodes of higher lake level between 5600 and 5300 cal yr b p at arbon bleiche 3 coincided with climatic cooling and or changes in moisture conditions in various regions of both hemispheres this period corresponds to the mid holocene climate transition onset of the neoglaciation and suggests inter hemispheric linkages for the climate variations recorded at arbon bleiche 3 this mid holocene climate reversal may have resulted from complex interactions between changes in orbital forcing ocean circulation and solar activity finally despite different seasonal hydrological regimes the similarities between lake level records from lake constance and from jurassian lakes over the mid holocene period point to time scale as a crucial factor in considering the possible impact of climate change on environments

gravitational spreading controls rift zones and flank instability on el hierro canary islands ocean island volcanoes frequently develop local rift zones associated with flank movement and flank collapses the ocean island el hierro grew by coalescence and collapse of three volcanic edifices which are an elongated topographic ridge the southern ridge and two semi circular volcanic cones tinor volcano el golfo volcano during edifice growth and volcano coalescence eruption fissures nucleated into rift zones that developed a complex triangle pattern in scaled analogue experiments we could successfully reproduce the geometry of rift zones and unstable flanks as observed on el hierro the experimental results suggest that the rift configuration on el hierro is the result of gravitational volcano spreading over deformable basal substrata rather than of deep seated magma updoming as thought previously this paper elucidates the importance of the basal substratum and gravitational spreading and the relationship to rifting and flank instability on el hierro island and may help in understanding similar volcano architectures elsewhere

1500 years of soil use reconstructed from the chemical properties of a terraced soil sequence colluvial soils can store signals of the environmental conditions occurred during their formation including the anthropogenic activities they supported their study may provide important information for reconstructing and interpreting the evolution of cultural landscapes we studied the chemical properties of a terraced soil system located in the town of santiago de compostela nw spain aluminum fe and si fractionation was studied by selective dissolution techniques with high vertical resolution combined with elemental composition and other soil properties such as phosphate retention pret and naf ph aiming to identify modifications produced by land use changes and agricultural management practices since antiquity the buried epipedon of the paleosol which is considered to exemplify the pre terracing soil showed strong andic character we argue that its attenuation in the anthropogenic soil layers is firstly a consequence of the decreasing amounts of reactive components organic matter organo al complexes and low ordered aluminosilicates due to a dilution by mixing superficial and sub superficial horizons secondly the introduction of agricultural techniques led to modifications in the chemical stability of organo metal complexes influencing the accumulation of organic matter other signals such as variations in soil acidity and p and ca contents point to management practices as fertilization or liming the increasing amounts of fe inorganic compounds in the more recent layers indicate a strong weathering and degradation probably as a consequence of the intensification of the agricultural use our results indicated continued and progressively more intensive agricultural use during the last 15 centuries linked to the development of the town

the bronze age landscape of the bjare peninsula southern sweden and its relationship to burial mounds palaeoecological analyses from a small fen deposit combined with pollen analysis from buried soil profiles under prehistoric burial mounds have been used to investigate the timing and vegetation change associated with the holocene development of a cultural landscape in southern sweden traditional pollen analysis is complemented with plant macrofossil analysis and soil pollen analysis from within and in close proximity to the burial mounds in the coastal bjare peninsula well known for its high density of well preserved bronze age monuments the vegetation development is linked to the construction of the burial mounds a marked increase of cultural impact on the landscape is recorded during the neolithic bronze age transition and estimates of landscape openness suggest that by the onset of the bronze age forest cover was only 20 40 falling to 10 in the immediate vicinity of the burial mounds themselves the coastal strip appears to have been affected by human activity to a greater extent and at an earlier date than sites from further inland in southern sweden and the bronze age burial mounds were most likely designed to be visible in a largely deforested landscape

colluvium definition differentiation and possible suitability for reconstructing holocene climate data abstract this study examines whether colluvial soils store climatic data and if these data can be used as proxies colluvial soils as the correlated sediments of soil erosion represent a widespread geoarchive these soils store the morphology data of the eroded soils and contain clues as to the processes of the eroded soils formation as well as indications of the pedogenesis which took place after the deposition all of these processes are closely related to climatic factors especially rainfall this study discusses the genesis of young soils in colluvial sediments and shows that typical soil features may be related to climatic factors furthermore the study investigates the genesis of anthropogenic colluvial sediments which must be seen as a syngenetical product of relief field size time of usage pressure of population farming technique sediment erodibility deposition area and climatic factors to this end pedogenic features are separated from the sedimentological features the results show that the reconstruction of all factors which control the genesis of the formation of a colluvium is still not yet possible this is the necessary precondition for colluvial soils to yield proxy climate data or for the data to be correlated with already existing holocene climate archives as the results of our discussion are ambiguous in their interpretation we conclude that colluvial soils which clearly include climatic information cannot be used for the reconstruction of proxy climate data at present

prehistoric land use at an archaeological hot spot the rock art park of campo lameiro nw spain inferred from charcoal synanthropic pollen and non pollen palynomorph proxies pollen non pollen palynomorphs and charcoal from a colluvial soil surrounded by prehistoric petroglyphs campo lameiro nw spain were studied in order to assess the nature of human activities and their impact on holocene vegetation patterns several phases of anthropogenic impact were observed i between 7 6 and 6 5 ka cal bp synanthropic taxa urtica dioica type plantago lanceolata type and coprophilous fungi e g sporormiella type are indicative of early pre agricultural creation of small patches of pasture using fire possibly for incipient animal husbandry or as part of a deliberate strategy to improve game availability such activities only had a minor effect on the deciduous quercus dominated forest established earlier during the holocene thermal maximum ii between 5 9 and 4 8 ka cal bp a more intense signal indicative of pastoral activity was detected corresponding to the neolithic period iii between 4 8 and 3 4 ka cal bp which fits within the hypothetical timeframe of petroglyph creation the synanthropic and humidity e g cyperaceae mougeotia indicators diminished while charcoal concentration increased which can be explained by mid holocene cooling drying neoglaciation in combination with reduced human impact or by non pastoral activities in the area possibly in association with the development of the rock art culture converting pasture to protected open ground through anthropogenic fires iv during the late bronze age and early iron age 3 4 2 5 ka cal bp grazing pressure and fire regime intensity are high coinciding with evidence of regional forest regression despite an amelioration in climate v later phases not corresponding to prehistoric rock art contexts include a phase of heavy grazing and reduced fire frequency from ca 2 5 to 1 2 ka cal bp as well as the near complete elimination of the deciduous woodland the expansion of ericaceous shrubland and the evidence of local agriculture and afforestation these results are consistent with earlier studies in the area and highlight the spatial heterogeneity in the vegetation especially during periods of prehistoric anthropogenic interference

strike slip fault propagation cleavage in carbonate rocks the mattinata fault zone southern apennines italy disjunctive spaced solution cleavage in carbonate rocks is genetically associated with the propagation of the left lateral strike slip mattinata fault in the gargano promontory italy typical cleavage development is restricted within the 200 300 mwide fault zone which is bounded by virtually unfractured wall rocks the cleavage consists of sub parallel solution surfaces which are often reactivated as sheared solution planes geometrical and kinematic relationships exist between the fault and the associated cleavage planes thus 1 cleavage fault intersection lines lie parallel to the fault and the sheared cleavage rotational axes and 2 the cleavage fault angle is almost constantly equal to 408 a model for the development of the mattinata fault is proposed in which the cleavage surfaces are interpreted as fault propagation deformations cleavage nucleates as solution planes at the front of the advancing fault as the result of stress concentration in this region two distinct time sequential processes are shown to operate during the fault propagation 1 typical millimetre to centimetre spaced solution surfaces form in the distal tip zone of the advancing fault plane 2 as the tip advances the fault plane breaks through the cleavage as minor shear displacements reactivate some of these nascent surfaces these observations may prove useful in understanding mechanisms for fault controlled enhanced reduced permeability and fluid pathways 1999 elsevier science ltd all rights reserved

age and source of colluvial sediments at vaihingen enz germany abstract colluvial sediments accumulated on the lower slopes of a ridge as a result of past and present soil erosion were dated by optical 14 c and archaeological methods this allowed us to reconstruct the depositional history of the colluvium and also to identify temporary sedimentary sinks in its transportational pathway a cascade model of colluvium formation is developed colluvial sediments resulting from early soil erosion in the neolithic to iron age periods were mainly deposited on the upper slopes significant deposition on the lower slope occurred for the first time during the iron age and roman period since then deposition rates have increased because of more intensive land use

volcanic spreading on mauna loa volcano hawaii evidence from accretion alteration and exhumation of volcaniclastic sediments a transect of submersible dives across the submarine west flank of mauna loa volcano yields compelling evidence for volcanic spreading and associated hydrothermal circulation during volcano growth a frontal bench at the toe of the flank formerly thought to be a downdropped block of mauna loa contains a mix of volcaniclastic lithologies including distally derived siltstone mudstone and hyaloclastite the bench is overlain by bedded gravels and subaerially erupted pillow flows derived from local shoreline crossing lava flows the volcaniclastic strata in the bench were offscraped uplifted and accreted to the edge of the flank as it plowed seaward into the surrounding moat the accreted strata underwent significant diagenesis through deep burial and circulation of hydrothermal fluids expelled from porous sediments beneath the volcano timing constraints for bench growth and breakup suggest that catastrophic failure of the subaerial edifice ca 250 200 ka triggered volcanic spreading by reducing stresses resisting basal sliding and rift zone inflation increased eruptive activity and westward migration of mauna loa9s southwest rift zone gradually rebuilt the massive flank arresting slip prior to detachment of the alika 2 debris avalanche ca 120 ka

scaled experiments of volcanic spreading experiments were conducted to study the spreading of volcanic constructs volcanoes are simulated by a sand cone and the volcanic substratum is simulated by a sand layer brittle substratum overlying a silicone layer ductile substratum similarity conditions between natural volcanoes and experimental prototypes led to the definition of dimensionless numbers experiments determine values which predict whether or not spreading takes place of particular importance are the ratio between the thickness of the brittle substratum and the height of the volcano 2 and the brittle ductile ratio of the substratum 3 2 indicates that the volcano must be large enough to break the substratum before spreading occurs whereas 3 controls the style of deformation during spreading these dimensionless numbers change with time reaching values that tend toward those observed for stable configurations experimental values are compared with those from well constrained natural examples it is found that an essential requirement for volcanic spreading is the presence of a low viscosity layer within the substratum flow of the weak layer away from the excess load is responsible for the spreading the overlying edifice displays radial intersecting grabens due to concentric stretching dissected summit areas concentric zones of thrusts and folds form in the substratum around the edifice and diapirs of the ductile substratum rise within the fault zones

location and orientation of eruptive fissures and feederdykes at mount etna influence of gravitational and regional tectonic stress regimes abstract lava extrusion from fissures on the flanks of the etna volcano is a common feature of recent activity as evidenced by the eruptions of 1971 1981 1983 and 1985 and was of similar importance during prehistoric times we propose here a model within which the location and orientations of the large majority of historic eruptive fissures on etna s flanks together with their feeder dykes are explained within the framework of a gravitational stress regime stress orientations within this regime are controlled largely by the gross morphology of the volcano but are significantly modified by local topographic anomalies we propose that the gravitational stress regime largely supercedes an earlier developed regional tectonic stress regime which still operates in the sub volcanic basement and may remain the dominant control of eruptive fissure and feeder dyke disposition at lower altitudes on the flanks the proposed model is supported by 1 detailed examination of fissure locations and orientations and the relationship between fissure azimuths and topography 2 precise horizontal distance measurement and vertical ground deformation studies of a recent eruption and 3 qualitative physical modelling experiments in which coloured water is injected into solidified gelatine solutions representing variously shaped volcanic constructs a cautious approach is advocated when extrapolating trends of spatially limited fissure segments for the purpose of locating potential sites of magma ascent and implications of the model for hazard analysis are outlined

the mechanics of deep seated landslides results are presented of a sequence of laboratory tests undertaken to elucidate the behaviour of deep seated landslides in deep seated failures deformation has been reported at depths of up to 250 m in the movement zone owing to the weight of the overburden and the surrounding stress environment conventional soil mechanics cannot be used to explain effectively associations between the landslip activity and the deformation mechanisms operating within the moving mass a series of experiments has been undertaken on london clay using a high pressure servohydraulically controlled triaxial deformation system to replicate the stresses acting at the base of a large deep seated landslide a number of tests were undertaken the most significant focusing on the transition between ductile and brittle behaviour although sediments usually behave in a brittle manner at low effective stresses common to many geomorphological studies and in a ductile manner at high effective stresses the results presented here identify for the first time in mudrocks a transitional phase of behaviour in which creep like movement will manifest itself at the base of a deep seated landslide as the growth of microcracks the microcracks may eventually coalesce to form a shear surface a consequence of which is likely to be sudden failure the results thus have important implications in the understanding of movement mechanisms in large deep seated failures rates of displacement and how they may change through time 1997 by john wiley sons ltd

morphology of pyroclastic cones and tectonics the relationships between morphology and spatial distribution of 1315 quaternary pyroclastic cones and coeval faulting of the volcanic substrate are analyzed in the following regions with different structural settings tepic rift mexico ethiopian rift mexican volcanic belt canary archipelago and mount etna field data and analog experiments of tephra cone emplacement and collapse enable the definition of a number of parameters which can be used to infer the geometry of the fracture feeding the magma to a pyroclastic cone the strike of the feeding plane is directly related to 1 the elongation of cone base and crater 2 the location of depressions on the crater rim and 3 the alignment of pyroclastic cones in relation to a given vent spacing in addition the strike and dip of faults affect the direction of cone breaching these relationships are valid for volcanic substrate topographic surfaces with an inclination of less than 9 and are especially sensitive to fault escarpment and cone height lava and cone density and fault orientation with respect to the dip of the volcanic substrate topography relations 1 and 2 become more pronounced for regions undergoing extensional tectonics where edifices also have a larger dimension whereas breaching in the direction of the fault dip is more widespread in regions under extension breaching along the fault strike as well as the coincidence between fault strike and vent alignment are more frequent in regions with transcurrent or transtensional tectonics

dynamic basis of volcanic spreading the established models of the structure and dynamics of a typical hawaiian volcano lead inevitably to a paradox finite element viscoelastic calculations using tecton melosh and raefsky 1980 1981 predict that a compressional stress field should characterize their upper flanks instead extension is observed the paradox is solved by postulating that volcanic evolution is determined by feedback processes related to growth and spreading of the volcanic edifice many examples of the process of spreading are documented in the geologic literature on volcanoes of a very broad size range and very different geologic settings the process is similar across many orders of magnitude in size the deformation of the substratum related to magma intrusion during lava dome building events is at the lower end of the scale the spreading of seafloor at oceanic ridges is at the higher end of the scale volcanoes may evolve from small constructs into huge shield volcanoes and perhaps into ocean plates key elements for volcanic spreading are 1 the existence of a weak basal layer and 2 a sufficiently high mass and magma influx to drive the process as the mass of a volcano grows it passes through five phases which may overlap repeat or be omitted building compressing thrusting intruding and spreading during the building phase the mass of a volcano does not significantly affect the stress field of the substratum primitive magmas are likely to be erupted as the mass increases the volcano subsides and becomes characterized by a compressional stress field which inhibits any further intrusion of magma into the volcanic edifice magma may differentiate in the crust allowing for large caldera forming eruptions to occur in the next phase thrusting begins on a decollement usually located at the foot of the edifice while the stress field on the upper slopes of the volcano remains compressional the stress at the base close to the center becomes extensional allowing the magma to intrude and differentiate at the base of the edifice a basal intrusive complex begins to grow explosive eruptions may be expected finally spreading of this complex creates an extensional stress field on the upper flanks of the volcano confining compression to the lower slopes of the edifice the extension allows primitive magma to erupt again at the summit the process of spreading seems to have a fundamental influence on the structural and magmatic evolution of volcanoes at every scale this process results from coupling and feedback between the gravitational and thermal fields thus studying this process may improve our understanding of the relation between structural dynamics and magma evolution and of the origin and evolution of volcanic seismicity and eruptions

buttressing and fractional spreading of tenerife an experimental approach on the formation of rift zones 1 the island of tenerife is composed of three miocene shields which are centered by the canadas volcano since the pliocene tenerife sits on more than 2 km thick oceanic sediments quaternary volcanism of the canadas series and giant landslides were principally confined to triaxial rift zones the mechanism of triaxial rifting however has remained unclear physical analog models show that these rift zones may have formed by gravity driven lateral escape of island segments induced by loading of the deformable substratum for experiments scaled to tenerife three adjacent sand cones were mounted onto viscous pdms substratum gravitational spreading caused circumferential expansion of each cone until a large edifice canadas was constructed in their center the older cones now acted each as a buttress radial fractures were overprinted by fractional spreading of the canadas edifice this resulted in formation of three main extensional zones resembling the triaxial rifting configuration of tenerife

early agriculture and palaeoenvironmental history in the north of the iberian peninsula a multi proxy analysis of the monte areo mire asturias spain a multi proxy study pollen and npps geochemical composition and radiocarbon dating combined with principal components analysis was applied to a core sampled in the monte areo mire asturias n spain which covers the last 11 600 years cal bp both signals of holocene climate change and transformations by human activities were recorded the cooler stage of the early holocene the hypsithermal and the neoglaciation periods were indentified but later holocene abrupt climate changes seem not to have been recorded due to the particular evolution of the fen mire system and the impact of human activities on the local hydrology evidence for human activity included a first phase of pastoralism by 7300 cal bp and an extraordinary record of adoption and establishment of agriculture the first evidence of cereal pollen dated to approximately 6700 cal bp represents one of the earliest records of agriculture in northern spain contrary to previous studies which based on assumed biogeographical limitations proposed a late adoption of agriculture in the area our results indicate a rapid expansion of agriculture in northern spain from the eastern to the westernmost areas more in agreement with recent archaeobotanical investigations zapata et al 2004 zapata et al 2005 the research also indicates that climate and human activities interplayed to determine the evolution of the studied area and that a multi proxy approach applied to natural archives appropriately located in areas with evidence of past human occupation is a productive way to obtain circumstantial evidence of early human activity

overthrusting and sediment accretion along kilauea s mobile south flank hawaii evidence for volcanic spreading from marine seismic reflection data a large intermittently active submarine landslide known as the hilina slump has been interpreted along the south flank of kilauea volcano seaward dipping faults on land mark its headwall and an offshore bench may define its uplifted toe geodetic data show that the entire south flank is also moving seaward by a process referred to as volcanic spreading this provides an alternative explanation for the bench i e overthrusting along the edge of the sliding flank the latter interpretation is consistent with new seismic reflection data across the submarine flank a prominent reflection near the top of the oceanic plate suggests the decollement upon which the mobile flank slides landward dipping reflections rise from this horizon and bound packages of bedded strata faulted and imbricated within the bench the absence of correlative seaward dipping faults and rotated strata on the upper flank suggests that the bench is not coupled to a slump moreover kinematic reconstructions of the bench indicate that it has accommodated 15 24 km of displacement this value is consistent with estimates for rift zone extension but too high for shortening at the toe of a slump we interpret the bench to result from overthrusting and accretion of volcaniclastic sediments to the edge of the mobile flank and suggest that morphologic benches develop preferentially where landslide debris has accumulated near the base of the volcano and can be accreted to its sliding edifice

environmental change in nw iberia between 7000 and 500 cal bc abstract we review research done on environmental changes in northwest nw iberia spanning from the beginning to the late holocene 7000 500 cal bc the type of archives peat bogs lake sediments colluvium soils etc and proxies pollen element concentrations isotopes etc that were used to reconstruct changes on climate soils vegetation and atmospheric metal pollution are briefly described then we synthesize what the records suggest about the ecological history of nw iberia we identified four main phases 7000 5000 5000 3000 3000 1500 and 1500 500 cal bc each phase is determined by a set of environmental conditions a combination of changes in climate vegetation soils and human impact human activities seem to have been involved in landscape changes in nw iberia since at least 5000 cal bc with an increasing degree of anthropisation through time which accelerated by 1500 cal bc the interaction between human activities and natural changes expressed as modifications in the vegetation cover the elimination of the soil resources in many areas and its concentration in more localized control demanding sectors as well as a progressive acidification and pollution of continental ecosystems to a great extent the present landscape in nw iberia is the end product of these complex interactions a cultural landscape

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

palaeoenvironmental studies in nw iberia cantabrian range vegetation history and synthetic approach of the last deglaciation phases in the western mediterranean abstract at the north western limit of the mediterranean basin in the mediterranean oceanic transition zone the multidisciplinary study of two palaeolakes villaseca and la mata province of leon provides data on the last deglaciation the juxtaglacial lakes were formed during a deglaciation phase of the last cold stage weichselian wurm estimated from the regional and pyrenean chronological data between circa 48 ka and 32 ka ka 1000 years ago their drainage occurred circa 17 ka and 15 ka respectively during the definitive glacial retreat phases these results provide evidence for a glacial maximum extension preceding the global last glacial maximum lgm and an early deglaciation comparisons with the pyrenean data show that in the most important glacial basins of the pyrenean cantabrian range glaciers were still present at middle elevation circa 18 20 ka the final deglaciation did not happen until around 16 ka during the period 48 13 3 ka along the pyrenean cantabrian range three stages can be distinguished in the deglacial processes between circa 48 and 32 ka the deglacial retreats were contemporaneous with d o events 12 to 6 between circa 32 ka and 18 ka major sedimentary modifications were rare two of them are synchronous with d o 4 and 3 a glacial readvance also occurred during this period along the pyrenean cantabrian range between 18 and 17 ka major sedimentary changes and an increase in the 18o records of the ngrip ice core record are synchronous between 15 and 13 3 ka glacial retreats and sedimentary changes are synchronous with the climatic improvement observed from the end of the oldest dryas to the end of the bolling allerod period these correspondencies suggest relationships between the deglacial processes in the western mediterranean and the palaeoenvironmental events in the north atlantic region during the last glacial interglacial transition during the full glacial period the pollen data indicates dominant steppic environments the oldest dryas was not a constant cooling phase and from around 15 5 ka the pollen data indicates a slight warming during the holocene until circa 2040 cal bp mixed oak forests developed and pine was a prominent component of the cantabrian landscape then the forests were destroyed due to mining agriculture and fire and this favoured the extension of heathland

offshore continuation of volcanic rift zones el hierro canary islands el hierro is the youngest and most southwesterly of the seven canary islands the established view based on subaerial geology is that el hierro is a classic example of an oceanic island with 120 spaced volcanic rift arms vrzs forming a mercedes star however new offshore data do not support this simple interpretation instead of the discrete ridges of vrzs we observe to the nw and ne broad areas of irregular morphology which suggest that rifting activity might not be confined to narrow zones furthermore our data suggest that the anomalously long and steep flanked southern ridge could be part of an older eroded volcanic edifice that predates much of the other submarine flanks of el hierro the southern ridge has a distinctive gullied morphology which strongly contrasts with adjacent flanks there is also a 400 m deep saddle in its longitudinal profile 15 km from the coastline which we interpret as evidence that the southern ridge did not form by continuous dyke intrusion from the el hierro volcanic centre south of the saddle mean flank slopes are 10 steeper 30 with a sharp slope break at 3700 m between the ridge and smoothly sedimented seafloor these steeper slopes and lack of landslide scars to the south of the saddle indicate that the southern ridge is a stable edifice relative to the rest of el hierro surrounding sediments to the southeast appear to onlap the southern ridge a large landslide deposit el julan estimated age 200 ka occurs to the west of the ridge this landslide appears to have been constrained from spreading southeastwards by the southern ridge resulting in an elevation difference of 300 m for the seafloor on either side of the ridge

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

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

structure of the mobile south flank of kilauea volcano hawaii how do huge landslides occur in hawaii we can begin to address this question by examining an incipient landslide structure on the mobile south flank of kilauea volcano between 1970 and 1989 this part of the south flank moved in a southeast direction seaward by 4 m on its eastern end and by 10 m on its western end parallel to the western boundary of a large oifshore topographic bench we show that abrupt decreases in cumulative flank movement correspond to abrupt decreases in hypocenter concentration most of the earthquakes occur in a 7 to 10 km deep band beneath the south flank and relative relocation of a subset of these events shows that they are derived from a single horizontal plane which appears to be a decollement focal mechanisms for this deep seismicity are dominated by thrust fault mechanisms with the overlying block moving seaward a comparison of south flank bathymetry with decollement structures on other volcanoes suggests that the distal end of this decollement coincides with the distal end of the offshore topographic bench 30 50 km from shore and 5 km below sea level the fault system forming the hilina pali is connected with this decollement so that slip on the hilina pali s normal faults coincides with slip of the decollement and with reverse faulting of the distal end of the bench this interpretation is supported by studies of the events associated with the m7 2 kalapana earthquake in 1975 when the hilina pali is connected to the outer bench with a decollement inferred from seismicity a wedge 8 km thick adjacent to kilauea s magma system and 1 2 km thick along the edge of the outer bench an area over 3000 km2 is defined the thickness adjacent to the magma system decreases eastward along kilauea s east rift zone and southwestward from kilauea caldera whereas the thickness of the lip of the outer bench decreases only eastward geologic observations and geophysical studies of the subaerial flank reveal an extensive magma system beneath the koae fault system as well as beneath kilauea caldera and its east rift zone we infer that the boundary of the proximal end of the mobile flank is the southern boundary of this magma system and that this boundary coincides with the southern boundaries of both the koae fault system and kilauea s east rift zone

abrupt climatic changes and an unstable transition into a late holocene thermal decline a multiproxy lacustrine record from southern sweden the transition from a middle holocene relatively warm and stable climate to a cooler and unstable late holocene climate is reconstructed using sediments from lake igelsjon south central sweden this multiproxy study illustrates local regional and global scale responses to climatic change by focusing on a previously identified abrupt hydrological shift to cooler and or wetter conditions around 4000 cal yr bp the results suggest that between ca 4600 and ca 3400 cal yr bp the environment around and within the lake responded in two major well defined steps the first between 4450 and 4350 cal yr bp and the second between 4000 and 3800 cal yr bp a series of rapid fluctuations of short duration were superimposed on the general cooling trend with the most severe aquatic response peaking at ca 3800 cal yr bp pollen percentage and influx values show forest composition and pollen productivity changes and a distinct decline in total and corylus pollen influx in the period of 4000 3500 cal yr bp stomatal based reconstruction of atmospheric co2 concentration produced a tenuous decrease with a minimum between 3650 and 3500 cal yr bp copyright 2005 john wiley sons ltd

discrete element simulations of gravitational volcanic deformation 2 mechanical analysis 1 particle dynamics simulations of granular piles constructed upon planar substrates with different shear strengths model the gravitational deformation of natural volcanoes results reveal direct correlations among pile morphology layer stratigraphy deformation structures and stress field dependent upon the shear strength along the base of the pile piles constructed above a strong cohesive substrate that prevents basal slip develop outward dipping layers through particle avalanching down angle of repose slopes in the absence of basal cohesion slip occurs along a basal decollement if the topographically induced shear stresses exceed the basal shear strength for friction coefficients decreasing from 0 3 to 0 1 fault planes migrate progressively inward defining a transition in deformation mode from shallow slumping to deep seated landsliding and finally to full gravitational spreading the variations in deformation mode reflect the dependence of internal fault geometry on basal strength in accordance with critical coulomb wedge theory in order for slip to occur both internal and basal failure criteria must be met simultaneously topographically induced shear stresses increase outward along the base of the pile enabling decollement sliding once the basal failure criterion is met normal faults arise from the inside edge of the slipping decollement accommodating downward and outward displacements of the flanks surface slopes evolve to maintain equilibrium between gravitational driving and basal resisting stresses this simple mechanical understanding of gravitational deformation of granular piles provides insight into the controls on modes of volcanic deformation providing a predictive tool for understanding volcanic evolution and hazards in many settings

the environmental context of a prehistoric rock carving on the bjare peninsula scania southern sweden palaeoecological analysis of peat deposits from a small bog at lingarden southern sweden have been used to examine the nature and timing of vegetation changes and anthropogenic activity associated with a nearby rock carving located close to the edge of the wetland this study is the first of its type to investigate the environmental context of rock carvings in southern sweden debate has tended to focus on chronology and iconography with little consideration of the environmental relationships of rock carvings and how vegetation may help construct a site within its surrounding landscape the pollen evidence from lingarden demonstrates that the rock carving was located in an isolated semi wooded setting during the late bronze age this is in stark contrast to several other pollen studies from the bjare peninsula that record widespread woodland clearance and agricultural activity from the late neolithic bronze age transition the results of this study support hypotheses that suggest complex rock carvings such as lingarden were separated from settled areas this sense of separation and isolation is reinforced by the vegetation surrounding the rock carving this paper also discusses the relationship between charcoal in the pollen sequence and evidence that the decorated outcrop had been burnt

discrete alternating hotspot islands formed by interaction of magma transport and lithospheric flexure the large scale geometry and age progression of many hotspot island chains such as the hawaiian emperor chain are well explained by the steady movement of tectonic plates over stationary hotspots but on a smaller scale hotspot tracks are composed of discrete volcanic islands whose spacing correlates with lithospheric thickness1 moreover the volcanic shields themselves are often not positioned along single lines but in more complicated patterns such as the dual line known as the kea and loa trends of the hawaiian islands2 3 here we make use of the hypothesis that island spacing is controlled by lithospheric flexure1 to develop a simple nonlinear model coupling magma flow which feeds volcanic growth to the flexure caused by volcanic loads on the underlying plate for a steady source of melt underneath a moving lithospheric plate magma is found to reach the surface and build a chain of separate volcanic edifices with realistic spacing if a volcano is introduced away from the axis of the chain as might occur following a change in the direction of plate motion the model perpetuates the asymmetry for long distances and times thereby producing an alternating series of edifices similar to that observed in the kea and loa trends of the hawaiian island chain

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

a theoretical model of hotspot volcanism control on volcanic spacing and patterns via magma dynamics and lithospheric stresses many linear island chains are thought to be the result of the steady motion of the lithospheric plates over stationary hotspots the occurrence of discrete nearly regularly spaced volcanoes rather than continuous ridges are assumed to be caused by the interaction of flexural stresses due to the volcanic loads with magma percolation a parameter study is performed on a simple model that incorporates these effects in addition to dike wall erosion it is demonstrated that the strength of the erosional feedback determines whether the model generates discrete volcanoes or a continuous ridge the intervolcanic spacing depends not only on the elastic thickness of the lithosphere but also on the magma pressure at the base of the lithosphere the size of the eruptive region of the individual volcanoes is controlled by the elastic response of the lithosphere to magma overpressurization if an initial off axis edifice is introduced the model is able to preserve this asymmetry and produce an alternating series of volcanoes a small initial perturbation grows over time resulting in double lines or wider patterns depending on the width of the magma source region single lines of volcanoes therefore indicate very narrow magma source regions

holocene vegetation changes in nw iberia revealed by anthracological and palynological records from a colluvial soil macroscopic charcoal pollen and non pollen palynomorphs were isolated from a colluvial soil located on a small hill in campo lameiro nw spain in order to elucidate the vegetation history of the area and its relation to fire and human activities the presence of macroscopic charcoal throughout the 2 10 m thick soil 42 samples is evidence of frequent fires during the last c 6300 years the charcoal record was dominated by quercus probably q robur ericaceae probably arbutus unedo and erica arborea and fabaceae mainly genista type abrupt changes in the charcoal assemblage are less explicit in the pollen sequence probably as a result of pollen inflow from the downhill surroundings of the study site combined results indicated that the original oak woodland was gradually replaced by pyrophytic shrubs ericaceae and fabaceae as a result of fire recurrence non pollen palynomorphs strongly suggested that vegetation was deliberately ignited by past human societies to facilitate grazing no evidence of local agricultural practices was found episodes of accel erated shrubland expansion occurred c 6000 5500 cal bp c 4000 3500 cal bp and c 1700 cal bp the latter of which caused the definitive settlement of shrublands dominated by ericaceae and fabaceae which are nowadays widespread in nw iberia

discrete element simulations of gravitational volcanic deformation 1 deformation structures and geometries 1 we have carried out two dimensional particle dynamics simulations of granular piles subject to frictional coulomb failure criteria to gain a first order understanding of different modes of gravitational deformation within volcanoes under uniform basal and internal strength conditions granular piles grow self similarly developing distinctive stratigraphies morphologies and structures piles constructed upon cohesive substrates exhibit particle avalanching forming outward dipping strata and angle of repose slopes systematic decreases in basal strength lead to progressively deeper and steeper internal detachment faults and slip along a basal decollement landslide forms grade from shallow slumps to deep seated landslide and finally to axial subsidence and outward flank displacements or volcanic spreading surface slopes decrease and develop concave up morphologies with decreasing decollement strength depositional layers tilt progressively inward spatial variations in basal strength cause lateral transitions in pile structure stratigraphy and morphology this approximation of volcanoes as coulomb granular piles reproduces the richness of deformational structures and surface morphologies in many volcanic settings the gentle slopes of hawaiian volcanoes and olympus mons on mars suggest weak basal decollements that enable volcanic spreading high angle normal faults favored above weak decollements are interpreted in both settings and may explain catastrophic sector collapse in hawaii and broad aureole deposits surrounding olympus mons in contrast steeper slopes and shallow detachment faults predominate in the canary islands thought to lack a weak decollement favoring smaller more frequent slope failures than predicted for hawaii the numerical results provide a useful predictive tool for interpreting dynamic behavior and associated geologic hazards of active volcanoes