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

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

recent dyke induced large scale block movement at mount etna and potential slope failure here we report the results of a geodetic survey undertaken on mount etna between 1981 and 1988 observed horizontal ground movements in the vicinity of the valle del bove caldera demonstrate that dyke emplacement during 1983 and 1985 resulted in the 2 8 m eastward displacement of a block of western caldera rim a history of past instability and collapse along the rim is indicated by the presence of large back rotated blocks of prehistoric volcanics1 furthermore the unusually linear form of the present western rim indicates past slope failure along north south aligned surfaces and therefore that dyke induced collapse may have been an important agent in caldera enlargement we suggest a self sustaining mechanism whereby the stress regime generated as a consequence of the caldera s existence results in the repeated injection of north south orientated dykes adjacent to the western rim2 3 dilation associated with magma intrusion leads in turn to periodic phases of slope instability and failure of the cliff wall causing a progressive westward migration of the western rim

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

from catastrophic collapse to multi phase deposition flow transformation seafloor interaction and triggered eruption following a volcanic island landslide abstract the current understanding of tsunamis generated by volcanic island landslides is reliant on numerical models benchmarked against reconstructions of past events as the largest historical event with timed tsunami observations the 1888 sector collapse of ritter island papua new guinea provides an outstanding opportunity to better understand the linked process of landslide emplacement and tsunami generation here we use a combination of geophysical imaging bathymetric mapping seafloor observations and sampling to demonstrate that the ritter landslide deposits are spatially and stratigraphically heterogeneous reflecting a complex evolution of mass flow processes the primary landslide mass was dominated by well bedded scoriaceous deposits which rapidly disintegrated to form an erosive volcaniclastic flow that incised the substrate over much of its pathway the major proportion of this initial flow is inferred to have been deposited up to 80 km from ritter the initial flow was followed by secondary failure of seafloor sediment over 40 km from ritter the most distal part of the 1888 deposit has parallel internal boundaries suggesting that multiple discrete units were deposited by a series of mass flow processes initiated by the primary collapse the last of these flows was derived from a submarine eruption triggered by the collapse this syn collapse eruption deposit is compositionally distinct from pre and post collapse eruptive products suggesting that the collapse immediately destabilised the underlying magma reservoir subsequent eruptions have been fed by a modified plumbing system constructing a submarine volcanic cone within the collapse scar through at least six post collapse eruptions our results show that the initial tsunami generating landslide at ritter generated a stratigraphically complex set of deposits with a total volume that is several times larger than the initial failure given the potential for such complexity there is no simple relationship between the volume of the tsunamigenic phase of a volcanic island landslide and the final deposit volume and deposit area or run out cannot be used to infer primary landslide magnitude the tsunamigenic potential of prehistoric sector collapse deposits cannot therefore be assessed simply from surface mapping but requires internal geophysical imaging and direct sampling to reconstruct the event

very shallow earthquakes and brittle deformation in active volcanic areas the eatnean region as an example abstract some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity h 1 2 km and the brittle deformation pattern of the etna volcano the magmatic composition and structural character of mt etna are described together with its geodynamic regional context after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity the high level of surficial seismicity the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of mt etna is a shallow seismotectonic domain structurally decoupled from the rest of the volcanic body this flank shows a tendency to slide in an eastern direction and is bound to the north by a left lateral oblique slip normal fault trending e w and in the south by an arcuate fault system with right lateral features right lateral oblique slip normal faults

seismicity of the caldera making eruption of mount katmai alaska in 1912 the seismic activity associated with the century s largest eruption and caldera collapse at mount katmai alaska during june 1912 was poorly understood and is studied here in detail the epicenter of the large shock of 10 june was long thought to be 140 km northeast of mount katmai but it is relocated to be 12 km west of mount katmai near the novarupta dome origin times surface wave magnitudes ms and broadband body wave magnitudes mb are assigned to 50 new shocks from instrumentally observed data of more than 60 worldwide milne s and other seismological stations of 50 shocks detected 14 have ms 6 0 and greater and the largest is 7 0 both the frequency magnitude relation and the mb ms relation apparently exhibit normal appearance for the alaskan region the strong earthquakes were concentrated in the nights of 6 and 7 june it is inferred that the substantial collapse of mount katmai took place in these two nights the total energy released in seismic waves is 7 1 1015 j corresponding to the energy of a single shock with ms 7 4 the total seismic moment is estimated to be 1 4 1020 nm from ms values this total moment can be interpreted in terms of failures caused by the total volume change of 5 km3 this volume agrees well with the estimated volume of the caldera collapse which presumably took place in response to transfer of supporting magma from beneath mount katmai toward novarupta

understanding etna flank instability through numerical models abstract as many active volcanoes mount etna shows clear evidence of flank instability and different mechanisms were suggested to explain this flank dynamics based on the recorded deformation pattern and character shallow and deep deformations mainly associated with both eruptive and seismic events are concentrated along recognised fracture and fault systems mobilising the eastern and south eastern flank of the volcano several interacting causes were postulated to control the phenomenon including gravity force magma ascent along the feeding system and a very complex local and or regional tectonic activity nevertheless the complexity of such dynamics is still an open subject of research and being the volcano flanks heavily urbanised the comprehension of the gravitative dynamics is a major issue for public safety and civil protection the present research explores the effects of the main geological features in particular the role of the subetnean clays interposed between the apennine maghrebian flysch and the volcanic products and the role of weakness zones identified by fracture and fault systems on the slope instability process the effects of magma intrusions are also investigated the problem is addressed by integrating field data laboratory tests and numerical modelling a bi and tri dimensional stress strain analysis was performed by a finite difference numerical code flac and flac 3d mainly aimed at evaluating the relationship among geological features volcano tectonic structures and magmatic activity in controlling the deformation processes the analyses are well supported by dedicated structural mechanical field surveys which allowed to estimate the rock mass strength and deformability parameters to take into account the uncertainties which inevitably occur in a so complicated model many efforts were done in performing a sensitivity analysis along a wnw ese section crossing the volcano summit and the valle del bove depression this was mainly devoted to evaluate the effect of topography geometry and rheological behaviour of the structural units the 3d numerical model extended 40 60 km was implemented to simulate the volcano deformation pattern first the role of the pleistocene subetnean clays was investigated then two structural weakness zones the pernicana fault system and the ne rift were introduced and their effects on the flank instability evaluated two extreme hydrogeological conditions drained and undrained were analysed the results are expressed in terms of stress strain field displacement pattern plasticity states and shear strain increments two main instability mechanisms were identified one at shallow depth with the sliding surface located inside the subetnean quaternary clay and another deep seated mechanism with a not continuous and less evident sliding surface developed inside the apennine maghrebian chain flysch bordered by active structures both mechanisms contribute to explain the present deformation pattern and some of the main structures of the etna flank the effect of magma pressure exerted on the active dyke walls during eruptions was then simulated and relations between magmatic activity and flank instability were preliminarily investigated

causes and mobility of large volcanic landslides application to tenerife canary islands abstract giant volcanic landslides are one of the most hazardous geological processes due to their volume and velocity since the 1980 eruption and associated debris avalanche of mount st helens hundreds of similar events have been recognised worldwide both on continental volcanoes and volcanic oceanic islands however the causes and mobility of these enormous mass movements remain unresolved tenerife exhibits three voluminous subaerial valleys and a wide offshore apron of landslide debris produced by recurrent flank failures with ages ranging from upper pliocene to middle pleistocene we have selected the la orotava landslide for analysis of its causes and mobility using a variety of simple numerical models first the causes of the landslide have been evaluated using limit equilibrium method and 2d finite difference techniques conventional parameters including hydrostatic pore pressure and material strength properties together with three external processes dike intrusion caldera collapse and seismicity have been incorporated into the stability models the results indicate that each of the external mechanism studied is capable of initiating slope failures however we propose that a combination of these processes may be the most probable cause for giant volcanic landslides second we have analysed the runout distance of the landslide using a simple model treating both the subaerial and submarine parts of the sliding path the effect of the friction coefficient drag forces and hydroplaning has been incorporated into the model the results indicate that hydroplaning particularly can significantly increase the mobility of the landslide which may reach runout distances greater than 70 km the models presented are not considered definite and have mainly a conceptual purpose however they provide a physical basis from which to better interpret these complex geologic phenomena and should be taken into account in the prediction of future events and the assessment of landslide related hazards

a new type of volcano flank failure the resurgent caldera sector collapse ischia italy 1 this study is the first description of recurrent and rapid lateral failure of the resurgent portion of a caldera complex the sliding planes and the characteristics of debris avalanche deposits resemble those of cone sector collapses but the main triggering mechanism proposed at ischia caldera italy is related to intermittent resurgence during the last 33 ka the increase in resurgence rate produced major collapses southward due to three main mechanisms that contributed to an increase in shear stress i magma driven uplift which produced increase in static loading ii faulting and associated deformation which induced tilting and steepening of the original layering and iii earthquake shaking due to coseismic faulting the largest episodes of flank failure occurred in the interval 8 6 5 7 ka bp these were followed by magma eruption and a decrease in the resurgence rate recognition of this phenomenon is particularly important in recent active calderas located near the coast as it can trigger tsunamis

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

catastrophic collapse at stratovolcanoes induced by gradual volcano spreading unlike ordinary mountains which are formed by slow uplift and erosion volcanoes are constructed rapidly as a consequence many are liable to massive flank failures leading to debris avalanches for example at mount st helens in 1980 such failures occur worldwide about once every 25 years ref 1 and even small ones can present a major hazard in particular if far reaching tsunamis are generated as at mayu yama in 1792 ref 2 previous work has tended to emphasize differences in eruption style associated with flank failure2 but here we focus on the fundamental structural causes of failure most volcanic failures are generated by magmatic intrusion and flank spreading3 we present evidence however that mombacho volcano in nicaragua experienced a previously unrecognized type of failure triggered by sub volcanic basement spreading notably collapses related to basement spreading do not require that the volcano be magma tically active and thus flank failure may pose a significant risk even at inactive volcanoes which are rarely monitored

development and recent activity of the san andres landslide on el hierro canary islands spain abstract extremely voluminous landslides with a long run out also known as megalandslides on oceanic volcanic islands are infrequent denudational processes on such islands at the same time they represent a major geological hazard that must be looked into to avoid negative consequences for the inhabitants of these islands their occurrence can be related to periods of intense seismo volcanic activity similar to that which occurred on el hierro island over 2011 2012 landslides on volcanic islands are studied using onshore and offshore geological geophysical and geomorphological records considering their unique triggering conditions e g lava intrusions eruptive vents magma chamber collapses previous work has pointed out similarities between specific cases of landslides on volcanic islands and deep seated gravitational slope deformations dsgsds which are typical in high mountain settings nevertheless the methodological approaches and concepts used to investigate dsgsds are not commonly applied on volcanic islands studies even though their use may provide new information about the development stage recent movements and future hazards therefore this approach for studying the san andres landslide sal on el hierro canary islands has been developed applying a detailed morphological field mapping an interpretation of digital elevation models structural measurements kinematic testing and a precise movement monitoring system the acquired information revealed a strong structural influence on the landslide morphology and the presence of sets of weakened planes acting as the sliding surfaces of the sal or secondary landslides within its body the presence of secondary landslides deep erosive gullies coastal cliffs and high on shore relative relief also suggests a high susceptibility to future landslide movement direct monitoring on the landslide scarps and the slip plane performed between february 2013 and july 2014 using an automated optical mechanical crack gauge with a precision of up to 10 2 mm detected creep movement in the order of 1 mm yr 1 with a persistent sinistral component as well as episodic horizontal and a subtle vertical movement this monitoring will continue in the future in order to verify the initial observations which instead of long term movement patterns could represent a landslide response to the period of an intense seismo volcanic activity during 2011 12

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

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

large scale mass wasting in ancient volcanic materials abstract giant landslides are significant hazards associated with many active volcanic edifices we describe a similar feature on ancient 4 ma volcanic deposits subject to active tectonism the landslide is approximately 3 km long by 1 km wide with an estimated depth of 400 m side margins are straight and parallel mimicking regional structure narrow valleys incised down these margins provide low strength side release surfaces between these is a giant slump consisting of at least four largely intact discrete blocks that have moved down dip a distance of 500 m a series of flows with areal extents ranging from 0 01 to 0 5 km 2 extends from the front of the failure the materials represent an eroded sequence of andesite flows on the flanks of a stratovolcano these have undergone two phases of hydrothermal alteration and are deeply weathered to low density 1040 80 kg m 3 silt 59 and clay 35 materials with strength properties typical of weathered silts c 26 3 kn m 2 42 8 the size and location of this landslide preclude detailed geotechnical investigation of the failure the worth of numerical stability analysis as an alternative technique in assessing the nature of the failure and hence the risk it poses to nearby communities is investigated sensitivity analysis identified likely conditions under which initial failure may have occurred analyses for sensitivity to strength and earthquake acceleration needed conversion to critical combinations f 1 0 of water table and strength acceleration to remove the overriding influence of water table fluctuations failure was likely initiated either by a high water table level 83 84 or some combination of intensity vii ix earthquake waves together with water table heights of 40 80 a general hazard assessment indicates that the risk associated with creep and catastrophic failure of the main mass is small whereas the risk from flow failures near the toe of the landslide may be high important parameters hydrological regime flow failure morphology age of initiation and rates of movement requiring closer investigation are identified development of a model is crucial to assessing the hazard associated with a feature such as that described here with limited resources a detailed stability analysis is a powerful tool as an initial stage in hazard analysis

theory of dike intrusion in a saturated porous solid a study of the pore pressure fields that develop around intruding dikes is described under the motivation that intruded geometry may be determined from pore pressures recorded in relatively remote monitoring wells the pore pressure fields induced around cylindrical and planar intrusions are described as analogues to moving point or line dislocations within an infinite saturated porous elastic medium the resulting transient pressure fields reduce to an equivalent steady state when viewed from the advancing front solutions for the moving point and line dislocations yield a dependence on common dimensionless groupings thus dimensionless pressure rise accompanying intrusion and recorded at a static location may be uniquely referenced to the dimensionless parameters representing emplacement velocity and time the resulting transient pressure response may be divided into two groups representing fast and slow emplacement where hydraulic parameters representing the host porous medium are known a priori both emplacement location and the cross sectional area may be determined uniquely for slow emplacement the intrusion rate may also be determined only a lower limiting intrusion rate may be discerned for fast emplacement field data are rare but two intrusive events at krafla iceland are examined using the proposed moving dislocation models predicted location and lower limiting intrusion rate of the krafla dikes compare favorably with field observation despite more than a 9 km separation to the monitoring well

age of the el golfo debris avalanche el hierro canary islands new contraints from laser and furnace 40ar 39 ar dating abstract the life cycle of ocean island volcanoes is commonly punctuated by large scale flank collapse events which may generate far reaching tsunami estimates exist though are poorly constrained for worldwide recurrence time intervals of giant landslides however individual events are often difficult to date the el golfo debris avalanche on the island of el hierro canary islands is a young feature although its exact formation age remains elusive using both furnace and laser heating 40 ar 39 ar dating techniques on groundmass separates we obtained new ages for the altitudinally highest lava flows cut by the el golfo landslide headwall as well as a post collapse lava flow erupted from within the embayment the new data significantly improve limits on the age of the debris avalanche which we propose occurred between 87 8 ka and 39 13 ka ago this age range raises doubts on the previously proposed correlation between this event and the glacial to interglacial transition at 130 ka

shallow structure beneath the central volcanic complex of tenerife from new gravity data implications for its evolution and recent reactivation abstract we present a new local bouguer anomaly map of the central volcanic complex cvc of tenerife spain constructed from the amalgamation of 323 new high precision gravity measurements with existing gravity data from 361 observations the new anomaly map images the high density core of the cvc and the pronounced gravity low centred in the las canadas caldera in greater detail than previously available mathematical construction of a sub surface model from the local anomaly data employing a 3d inversion based on growing the sub surface density distribution via the aggregation of cells enables mapping of the shallow structure beneath the complex giving unprecedented insights into the sub surface architecture we find the resultant density distribution in agreement with geological and other geophysical data the modelled sub surface structure supports a vertical collapse origin of the caldera and maps the headwall of the ca 180 ka icod landslide which appears to lie buried beneath the pico viejo pico teide stratovolcanic complex the results allow us to put into context the recorded ground deformation and gravity changes at the cvc during its reactivation in spring 2004 in relation to its dominant structural building blocks for example the areas undergoing the most significant changes at depth in recent years are underlain by low density material and are aligned along long standing structural entities which have shaped this volcanic ocean island over the past few million years

the giant submarine alika debris slide mauna loa hawaii probably represent multiple subsidence events before during and after the debris avalanches lower slopes of the slide contain distinctive lobate terraced deposits that are interpreted as having been emplaced more slowly prior to the debris avalanches estimated thicknesses of 50 200 m suggest volumes of 200 600 km 3 for the two lobes the combined volume of the entire slide and slump terrane is probably 1500 2000 km 3 the slide deposits predate a 13 ka coral reef and probably postdate the block faulted ninole basalt roughly dated as a few hundred thousand years old the alika slide or a similar deposit recognized on gloria images further north along the hawaiian ridge probably triggered a giant wave that washed 325 m high on lanai at about 100 ka slumping on mauna loa has been most intense adjacent to the large arcuate bend in its southwest rift zone as the rift zone migrated westward away from the growing kilauea volcano slumping events were probably triggered by seismic activity accompanying dike injection along the rift zone such massive slumps landslides and distal submarine turbidity flows appear to be widespread on the flanks of hawaiian volcanoes

multiple caldera collapses inferred from the shallow electrical resistivity signature of the las canadas caldera tenerife canary islands the las canadas caldera of tenerife lcc is a well exposed caldera depression filled with pyroclastic deposits and lava flows from the active teide pico viejo complex tpvc the caldera s origin is controversial as both the formation by huge lateral flank collapse s and multiple vertical collapses have been proposed although vertical collapses may have facilitated lateral slope failures and thus jointly contribute to the exposed morphology their joint contribution has not been clearly demonstrated using results from 185 audiomagnetotelluric amt soundings carried out between 2004 and 2006 inside the lcc our study provides consistent geophysical constraints in favour of multiple vertical caldera collapse one dimensional modelling reveals a conductive layer at shallow depth 30 1000 m presumably resulting from hydrothermal alteration and weathering underlying the infilling resistive top layer we present the resistivity distribution of both layers resistivity images the topography of the conductive layer across the lcc as well as a cross section in order to highlight the caldera s evolution including the distribution of earlier volcanic edifices the amt phase anisotropy reveals the structural and radial characteristics of the lcc

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

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

discovery of a huge sector collapse at the nisyros volcano greece by on land and offshore geological structural data abstract this study uses on land and offshore geological and structural data to demonstrate that a huge lateral collapse involved the se flank of nisyros volcano the collapse beheaded the summit part of the volcano and also involved the submarine portion of the slope producing a large debris avalanche deposit with a volume of about 1 km3 which has been recognized on the sea floor on land stratigraphic and structural data indicate that a thick succession of lava flows nikia lavas was emplaced in a huge horseshoe shaped depression open seaward and extending below the sea the magma feeding system in the volcano pre dating and following the collapse was structurally influenced by a dominant ne sw direction which is perpendicular to the newly recognised sector collapse the ne sw structural trend is consistent with the regional tectonic structures found offshore around nisyros and with the related nw se extension direction we suggest that the lateral magma pressure produced by repeated magma injections along tectonic discontinuities contributed to destabilise the volcano flank the occurrence of a pyroclastic deposit that mantled the scar left by the collapse suggests that a magma batch might have been injected inside the volcano and triggered the collapse the lavas of the pre collapse edifice have been deposited in alternating submarine and subaerial environments suggesting that vertical movements might also be a major triggering mechanism for large lateral collapses recognition of this phenomenon is particularly important in recent active island or coastal volcanoes as it can trigger tsunamis

growth and persistence of hawaiian volcanic rift zones hawaiian volcanic rift zones are modeled by representing the rifts and adjacent volcano flanks as long ridges with the geometry of flattened triangular prisms the intrusion of dikes along the axis of a rift requires a mechanism to generate the appropriate dike trapping stress field within the prism possible factors that affect the state of stress in the prism include multiple dike intrusion along the ridge axis faulting and gravitational sagging of the topography in extreme models with very steep slopes and high poisson s ratio corresponding to the gelatin models of rift zones by fiske and jackson 1972 results of finite element calculations indicate that gravity induced stresses are sufficient to trap a dike into propagating within the prism and parallel to the rift zone as proposed by fiske and jackson however the mechanism does not work for gently sloping flanks or a more acceptable poisson s ratio of about 0 25 additionally trapping stresses in the gravity loading and density stratification models will not persist after a few dike injection episodes therefore in mature hawaiian rift zones with possibly thousands of dikes additional processes must act to control the stresses that permit continued dike intrusion and rift persistence it is proposed that accommodation to dike emplacement occurs by slip on deep faults possibly of the type proposed for the 1975 kalapana hawaii earthquake as suggested by others for this earthquake the faults could coincide with the contact of the volcano with the seafloor within the weak seafloor sediments such faulting not only provides a means for the flanks to adjust continuously to intrusions but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis other possible faulting mechanisms such as shallow gravity slides and normal faulting of the flanks do not appear to favor rift zone persistence in this model the horizontal stress generated by a standing column of magma at the time of dike emplacement the stresses in the ridges and the fault strength are coupled this results in a feedback between the maximum height that magma can rise along the rift fault friction and fault width through this feedback the slope of the volcano flank is controlled by the fault friction when applied to kilauea volcano the model yields an estimate for the coefficient of fault friction as high as 0 39 assuming normal hydrostatic pore fluid pressure an implication of this model supported by other studies is that rift intrusion and lateral spreading could be major contributors to volcano growth

geological and geochemical legacy of a cold early mars 1 we consider the hypothesis that mars never experienced an early warm wet period and the implications of a continuously cold martian climate for the hydrology and geochemistry of the planet geomorphic evidence previously interpreted to indicate a more temperate early climate can be explained by cold climate processes and the transient flow of liquid water at the surface rather than a terrestrial like hydrological cycle in this scenario freezing and confinement of crustal aquifers lead to the eruption of water or brines to the surface hesperian events formed massive ice sheets and triggered floods that carved the outflow channels while smaller present day aqueous eruptions are responsible for the seepage and gully like landforms identified in high resolution imaging this process may have fluxed a significant volume of groundwater to the surface and the polar caps a primordial source of groundwater reconciles the present d h isotopic ratio of the atmosphere with fractionating atmospheric escape and a primordial martian d h inferred from hydrous phases of snc meteorites a cold early climate and a thin co2 atmosphere are consistent with the ubiquity of primary igneous minerals and the apparent absence of secondary minerals and copious carbonates on the surface aqueous eruptions introduced soluble chloride and sulfate salts into martian soils leaving clays and carbonates within the crust if the martian crust hosts a deep biosphere aqueous eruptions can bring organisms or their chemical signature to the surface the biotic component of any recent eruptions may be preserved in transient ice in cold traps on the surface

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

importance of gravitational spreading in the tectonic and volcanic evolution of mount etna the interaction between gravity and thermal effects largely determines the structural and magmatic evolution of volcanic constructs at scales spanning several orders of magnitude from small cones to the oceanic crust1 3 although gravitational spreading is a direct consequence of this interaction and a fundamental process in volcano growth it is rarely recognized as such here we describe a striking example of this process at etna volcano in italy the volcano and its clay rich substratum are slowly spreading towards the east and south driven by gravity spreading produces extensional structures in the summit region and contpressional structures at the base of the volcano eastward movement of the volcanic edifice over a stationary magma supply may be the cause of an apparent westward migration of volcanic activity as gravitational spreading seems to control the location and magnitude of shallow seismicity and flank eruptions an appreciation of its effects could become an essential element of future volcanic hazard evaluation our model proposed here for etna may also be relevant to a reinterpretation of the geological history of a number of other volcanoes

stability analysis of hawaiian island flanks using insight gained from strength testing of the hsdp core abstract hawaiian island flank failures are recognized as the largest landslide events on earth reaching volumes of several thousand cubic kilometers and lengths of over 200 km and occurring on an average of once every 100 000 years the 3 1 km deep hawaii scientific drilling project hsdp enabled an investigation of the rock mass strength variations on the island of hawaii schiffman p watters r j thompson n walton a w 2006 hyaloclastites and the slope stability of hawaiian volcanoes insights from the hawaiian scientific drilling project s 3 km drill core journal of volcanology and geothermal research 151 1 3 217 228 this study builds on that of schiffman et al schiffman p watters r j thompson n walton a w 2006 hyaloclastites and the slope stability of hawaiian volcanoes insights from the hawaiian scientific drilling project s 3 km drill core journal of volcanology and geothermal research 151 1 3 217 228 by considering more in depth rock mass classification and strength testing methods of the hsdp core geotechnical core logging techniques combined with laboratory strength testing methods show that rock strength differences exist within the edifice comparing the rock strength parameters obtained from the various volcano lithologies identified weak zones suggesting the possible location of future slip surfaces for large flank failures relatively weak rock layers were recognized within poorly consolidated hyaloclastite zones with increases in strength based on degree of alteration subaerial and submarine basalt flows are found to be significantly stronger with the aid of digital elevation models cross sections have been developed of key flank areas on the island of hawaii limit equilibrium slope stability analyses are performed on each cross section using various failure criteria for the rock mass strength calculations based on the stability analyses the majority of the slopes analyzed are considered stable in cases where instability i e failure is predicted decreased rock mass quality strength of the altered and highly poorly consolidated lithologies is found to have a significant influence these lithologies are present throughout the hawaiian islands representing potential failure surfaces for large flank collapses failure criterion input parameters are considered in sensitivity analyses as are the influences of certain external stability factors such as sea level variation and seismic loading

stability of a collapsing volcano stromboli italy limit equilibrium analysis and numerical modelling abstract stromboli is an active island volcano belonging to the aeolian archipelago italy in the last 13 ka it experienced four lateral collapses affecting its northwestern flank with its most recent volcanic crisis december 2002 associated with landslides and related tsunami events this paper presents the first stability analysis of the stromboli volcanic edifice the main input is the geotechnical model of the volcano defined on the basis of stratigraphical lithological material properties and structural data collected from in situ surveys and laboratory tests two dimensional stability analysis was performed by limit equilibrium methods lem and finite difference modelling flac 4 0 code mainly focusing on the subaerial part of stromboli s nw flank sciara del fuoco the variability of the safety factor was studied by deterministic sensitivity and probabilistic analysis focusing on the effect of external forces such as magma pressure and seismicity as potential triggering mechanisms of lateral collapse the lem analyses were developed considering a maximum depth of 150 350 m for the sliding surface to which correspond collapse volumes of 95 000 185 000 m 3 m respectively the study shows that without external forces the investigated rock mass is stable and that the tectonic seismicity of the area alone does not destabilize the studied slope on the contrary magma pressure in dykes can represent a destabilizing factor numerical modelling results are concordant with those from lem in addition the simulation reveals that deformations and superficial landslides preannounce and contribute to retrogressive plasticization and maybe to failure surface deepening shallow submarine landslides represent a possible triggering mechanism and the landslide events of 30 december 2002 consistently fit the simulated evolution flac has revealed to be a useful tool for modelling such a complex system it allowed to calibrate the response of the geotechnical model test the validity of the assumptions simulate the stress strain evolution and prepare a possible model for future scenarios

a deep scar in the flank of tenerife canary islands geophysical contribution to tsunami hazard assessment abstract among the high intensity on earth tsunami generating events seismicity submarine landslides and volcano lateral collapses are the most important ward s h 2001 landslide tsunami j geophy res 106 11201 11215 holcomb r t searle r c 1991 large landslides from oceanic volcanoes mar geotech 10 19 32 tinti s bortolucci e romagnoli c 2000 computer simulations of tsunamis due to the sector collapse ar stromboli italy j volcano geotherm res 96 103 128 ward s n day s 2003 ritter island volcano lateral collapse and the tsunami of 1888 geophys j int 154 891 902 macguire w j 2003 volcano instability and lateral collapse revista 1 33 45 offshore bathymetry studies highlighted huge accumulations of large mass waste flows up to thousands cubic kilometres inherited from past lateral collapses or submarine landslides le friant a boudon g deplus c villemant b 2003 large scale flank collapse events during the activity of montagne pelee martinique lesser antilles j geophys res 108 ecv13 moore j g et al 1989 prodigious submarine landslides on the hawaiian ridge j geophys res 94 17465 17484 which spread over more than 100 km off the northern tenerife canary islands coastline watts a b masson d g 1995 a giant landslide on the north flank of tenerife canary islands j geophys res 100 24487 24498 although mechanics and dynamics triggering such catastrophic events follow from combined complex processes and interactions hurlimann m garcia piera j o ledesma a 2000 causes and mobility of large volcanic landslides application to tenerife canary islands j volcano geotherm res 103 121 134 masson d g et al 2002 slope failures on the flanks of the western canary islands earth sci rev 57 1 35 reid m e sisson t w brien d l 2001 volcano collapse promoted by hydrothermal alteration and edifice shape mount rainier washington geology 29 779 782 potential movable volume is an unavoidable parameter to quantify and constrain tsunamigenic hazard numerical modelling of a tsunami generated by the potential la palma landslide concluded that high amplitude waves threaten north atlantic shorelines ward s n day s j 2001 cumbre vieja volcano potential collapse and tsunami at la palma canary islands geophys res lett 28 397 400 new audiomagnetotelluric results provide for the first time a good estimation of the icod valley tenerife canary islands volume a potential giant landslide threatening the same shorelines two profiles image its electrically conductive roots with a characteristic of a u shaped cross section thought to be the consequence of previous landslides by this study we show that north atlantic ocean shorelines might be exposed to a destructive tsunami generated by a subaerial lateral collapse of at least 120 km 3 during the next strong felsic eruptive activity of the teide pico viejo complex this article highlights the degree of urgency of carrying out geophysical investigations on the flanks of most volcanic islands prone to potential flank collapse these investigations will contribute to the understanding of their structure a key parameter in the sliding process finally all results should be included in model providing a global map of tsunami hazard assessment

turbidite record of frequency and source of large volume 100 km3 canary island landslides in the last 1 5 ma implications for landslide triggers and geohazards during the last two decades numerous studies have focused on resolving the landslide histories of the canary islands issues surrounding the preservation and dating of onshore and proximal submarine landslide deposits precludes accurate determination of event ages however submarine landslides often disaggregate and generate sediment gravity flows volcaniclastic turbidites sampled from madeira abyssal plain piston cores represent a record of eight large volume failures from the western canary islands in the last 1 5 ma during this time there is a mean recurrence rate of 200 ka while the islands of el hierro and tenerife have individual landslide recurrences of 500 ka and 330 ka respectively deposits from the 15 ka el golfo landslide from el hierro and 165 ka icod landslide from tenerife are examined this study also identifies potential deposits associated with the orotava 535 ka guimar 850 ka and rogues de garcia landslides 1 2 ma from tenerife el julan 540 ka and el tinor 1 05 ma landslides from el hierro and the cumbre nueva landslide 485 ka from la palma seven of eight landslides occurred during major deglaciations or subsequent interglacial periods which represent 55 of the time however all of the studied landslides occur during or at the end of periods of protracted island volcanism which generally represent 60 of the island histories although climate may precondition failures it is suggested that volcanism presents a more viable preconditioning and trigger mechanism for canary island landslides

the influence of thermal and cyclic stressing on the strength of rocks from mount st helens washington stratovolcanoes and lava domes are particularly susceptible to sector collapse resulting from wholesale rock failure as a consequence of decreasing rock strength here we provide insights into the influence of thermal and cyclic stressing on the strength and mechanical properties of volcanic rocks specifically this laboratory study examines the properties of samples from mount st helens chosen because its strength and stability have played a key role in its history influencing the character of the infamous 1980 eruption we find that thermal stressing exerts different effects on the strengths of different volcanic units increasing the heterogeneity of rocks in situ increasing the uniaxial compressive stress generates cracking the timing and magnitude of which was monitored via acoustic emission ae output during our experiments aes accelerated in the approach to failure sometimes following the pattern predicted by the failure forecast method kilburn 2003 crack damage during the experiments was tracked using the evolving static young s modulus and poisson s ratio which represent the quasi static deformation in volcanic edifices more accurately than dynamic elastic moduli which are usually implemented in volcanic models cyclic loading of these rocks resulted in a lower failure strength confirming that volcanic rocks may be weakened by repeated inflation and deflation of the volcanic edifice additionally volcanic rocks in this study undergo significant elastic hysteresis in some instances a material may fail at a stress lower than the peak stress which has previously been endured thus a volcanic dome repeatedly inflated and deflated may progressively weaken possibly inducing failure without necessarily exceeding earlier conditions

volcanic dry avalanche deposits identification and comparison with nonvolcanic debris stream deposits abstract a volcanic dry avalanche deposit is defined as a volcaniclastic deposit formed as a result of a large scale sector collapse of a volcanic cone associated with some form of volcanic activity avalanche transport occurred in response to the gravitational field in a manner similar to the transport of nonvolcanic debris streams e g hsu 1975 such deposits are characterized by megablock structure deformed and fractured large blocks up to several hundreds meters in diameter a megablock preserves original layering intrusive contacts or weathered surfaces of the source volcanic edifice surface topography of the deposit is characterised with hummocky relief ratios of fell height to travel distance for volcanic dry avalanche deposits are between 0 18 and 0 06 this range is similar but smaller than the value of 0 58 to 0 08 for nonvolcanic debris stream deposit this similarity suggests similar transportation mechanisms excessive travel distances as defined by hsu 1975 calculated for volcanic dry avalanche deposits give values larger than for debris stream deposits of the same volume the difference is explained by lower rigidity of the collapsing mass due to the existence of soft pyroclastic layers alteration around the vent development of fractures owing to new cryptodome intrusion and boiling of supercritical fluid contained within the collapsed mass

lateral collapses and active sedimentary processes on the northwestern flank of stromboli volcano italy abstract the marine volcaniclastic system extending to 3 km water depth on the northwest flank of stromboli volcano has been surveyed using seismo acoustic profiling multibeam bathymetry deep towed long range side scan sonar imaging and box core sampling deposits and sea floor topography record repeated flank collapses that have occurred during the last 13 ka and created the present sciara del fuoco scar an extensive 170 km2 debris avalanche deposit characterized by subdued hummocks megablocks is buried by turbidites formed from gravity currents that originated in sciara del fuoco the currents were mainly deflected along the margin of the avalanche deposit but also spilt over onto it the turbidites reflect topographic flow stripping and their thinning towards slightly steeper slopes indicates that some material that settled there drained further downslope as secondary higher concentration flows the estimated volume of the entire fan shaped bulge amounts to 12 2 5 km3 about 3 5 km3 of which is attributed to the post collapse sedimentation the remaining 8 5 2 5 km3 is in the order of the volume computed for the material removed by the multiple sector collapses that affected the nw stromboli flank two units are identified in the distal part of the bulge through the recognition of their fronts and these indicate a layered structure for successive debris avalanche deposits granulometric and particle type characterization of seabed samples shows clast population evolution with sedimentary transport distance from the main entrance point of debris in sciara del fuoco to the confluence with the stromboli canyon and into the marsili basin some 45 km from the island changes in particle populations are due to selective sedimentation and also mixing with a wide range of terrigenous detritus brought by currents that descended the main stromboli canyon from the continental shelf abundant fine sand and silt is produced at the volcano and occurrence of mainly coarse grained material along the channel to the marsili basin indicates that a considerable volume of volcaniclastic material from stromboli lies in the sedimentary succession accumulating on the distal basin floor where a deep sea fan is growing

conditions favouring catastrophic landslides on tenerife canary islands catastrophic failures of volcano flanks represent one of the most hazardous geological phenomena these immense mass movements originate either by increasing the destabilizing forces driving forces or by reducing the strength of the materials involved or both the study of large volcanic landslides on tenerife suggests that the presence of weak residual soils palaeosols in combination with the pre existence of deep narrow canyons created by fluvial erosion have played a fundamental role in the initiation of large scale sector collapses of the volcanic edifice regardless of the triggering mechanism considered residual soils strongly reduce the material strength during undrained loading while pre existing canyons control the lateral limits of the landslide the existence of a wet climate in some sectors of the island favours these circumstances

emplacement of dikes sills and crustal magma chambers at divergent plate boundaries abstract a model of dike emplacement at divergent plate boundaries is developed which predicts that below the uppermost 1 3 km of the oceanic crust the number and lengths of dikes in any particular swarm should increase but that the thickness should decrease with depth in the crust these predictions are supported by field observations it is proposed that rapid injections of dikes at divergent plate boundaries may temporarily alter the normal stress field in such a way that at a certain level in the crust subsequent dikes change into sills such sills may develop into crustal magma chambers either when many nearby sills combine into a large one or when an initial sill absorbs the magma of many dikes that enter it in a rapid succession while the sill is liquid for the fastest spreading ridges the initial thickness of a sill that is to develop into a crustal chamber need only attain 20 m whereas at the slowest spreading ridges the initial thickness must exceed 170 m because thin sills are much more likely to form than thick sills the probability of sills developing into crustal chambers increases with dike intrusion frequency hence with spreading rate furthermore the model predicts first that with increasing spreading rate the length of the chamber along the ridge axis should increase and second that the most likely site for magma chambers is at depths of 2 4 km both these predictions are supported by available data

submarine volcanism surrounding tenerife canary islands implications for tectonic controls and oceanic shield forming processes abstract using high resolution bathymetric data 97 seamounts within two large submarine areas n and se of tenerife have been identified and studied in detail main dimensions and associated parameters of these seamounts have been measured allowing a morphometric and morphologic classification on a shape basis in order to be certain of their volcanic origin several restrictive criteria were applied conical shape with maximum height 150 m basal ratio 1 aspect ratio 0 1 to the initial tally obtaining finally 31 regular shapes that can be identified without any reasonable doubt as volcanic seamounts these are very similar to submarine volcanoes described elsewhere on the sea floor most of these volcanic seamounts are aligned along two lines that follow the main volcano tectonic trends of the canary archipelago the nw se line crosses the island while the ne sw line coincides with a seismically active reverse fault that separates the tenerife and gran canaria insular blocks the distribution of the submarine volcanism to the north of tenerife permits a better knowledge of the island from its base on the sea floor and defines the tectonic control of the growth of the shield between 4 and 2 ma therefore the evolution of the submarine edifice of tenerife shows that the widespread parasite or satellite eruption centres are also very important in the overall growth of large shield edifices of volcanic islands

real data results of kirchhoff elastic wave migration although kirchhoff integral migration has attracted considerable attention for seismic data processing since the early 1970s it like all other seismic migration methods is only applicable to compressional p waves because of a recent surge of interest in shear s waves kuo and dai 1984 developed the kirchhoff elastic p and s wave migration kewm formulation and migration principle for the case of source and receiver noncoincidence they obtained encouraging results using two dimensional 2 d synthetic surface data from various geometric elastic models including a dipping layer a composite dipping and horizontal layer and two layers over a half space

styles of volcano induced deformation numerical models of substratum flexure spreading and extrusion the gravitational deformation of volcanoes is largely controlled by ductile layers of substrata using numerical finite element modelling we investigate the role of ductile layer thickness and viscosity on such deformation to characterise the deformation we introduce two dimensionless ratios a volcano radius ductile layer thickness and b viscosity of ductile substratum failure strength of volcano we find that the volcanic edifice spreads laterally when underlain by thin ductile layers a 1 while thicker ductile layers lead to inward flexure a 1 the deformation style is related to the switch from predominantly horizontal to vertical flow in the ductile layer with increasing thickness increasing a structures produced by lateral spreading include concentric thrust belts around the volcano base and radial normal faulting in the cone itself in contrast flexure on thick ductile substrata leads to concentric normal faults around the base and compression in the cone in addition we show that lower viscosities in the ductile layer low b lead to faster rates of movement and also affect the deformation style considering a thin ductile layer if viscosity is high compared to the failure strength of the volcano high b then deformation is coupled and spreading is produced however if the viscosity is low low b substratum is effectively decoupled from the volcano and extrudes from underneath it in this latter case evidence is likely to be found for basement compression but corresponding spreading features in the volcano will be absent as the cone is subject to a compressive stress regime similar to that produced by flexure at volcanoes where basement extrusion is operating high volcano stresses and outward substratum movement may combine to produce catastrophic sector collapse an analysis of deformation features at a volcano can provide information about the type of basement below it a useful tool for remote sensing and planetary geology also knowledge of substratum geology can be used to predict styles of deformation operating at volcanoes where features have not yet become well developed or are obscured

momentum transfer and friction in the debris of rock avalanches when a mass of loose dry purely frictional material slides down an incline after release at a given velocity the runout the distance the centre of gravity of the displaced mass moves from its initial position depends on momentum transfer within the mass this can be estimated from the profile of the debris accumulation which also allows more accurate calculation of apparent angles of sliding friction in rockfall avalanches the apparent extreme mobility of the elm and frank slides typical rockfall avalanches is explained by momentum transfer in a loose dry purely frictional material with an angle of friction of 30 key words mass wasting momentum transfer landslide accumulation rock avalanche runout distance

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

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

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

coastal evolution on volcanic oceanic islands a complex interplay between volcanism erosion sedimentation sea level change and biogenic production abstract the growth and decay of oceanic hotspot volcanoes are intrinsically related to a competition between volcanic construction and erosive destruction and coastlines are at the forefront of such confrontation in this paper we review the several mechanisms that interact and contribute to the development of coastlines on oceanic island volcanoes and how these processes evolve throughout the islands lifetime volcanic constructional processes dominate during the emergent island and subaerial shield building stages during the emergent island stage surtseyan activity prevails and hydroclastic and pyroclastic structures form these structures are generally ephemeral because they can be rapidly obliterated by marine erosion with the onset of the subaerial shield building stage coastal evolution is essentially characterized by rapid but intermittent lateral growth through the formation of lava deltas largely expanding the coastlines until they typically reach their maximum extension with the post shield quiescence in volcanic activity destructive processes gradually take over and coastlines retreat adopting a more prominent profile mass wasting and marine and fluvial erosion reshape the landscape and if conditions are favorable biogenic processes assume a prominent role post erosional volcanic activity may temporarily reverse the balance by renewing coastline expansion but islands inexorably enter in a long battle for survival above sea level reef growth and or uplift may also prolong the island s lifetime above the waves the ultimate fate of most islands however is to be drowned through subsidence and or truncation by marine erosion

the spectrum of persistent volcanic flank instability a review and proposed framework based on kīlauea piton de la fournaise and etna abstract persistent motion of the south flank of k lauea volcano hawai i has been known for several decades but has only recently been identified at other large basaltic volcanoes namely piton de la fournaise la reunion and etna sicily thanks to the advent of space geodetic techniques nevertheless understanding of long term flank instability is based largely on the example of k lauea despite the large differences in the manifestations and mechanisms of the process when viewed through a comparative lens for example the rate of flank motion at k lauea is several times that of etna and piton de la fournaise and is accommodated on a slip plane several km deeper than is probably present at the other two volcanoes gravitational spreading also appears to be the dominant driving force at k lauea given the long term steady motion of the volcano s south flank regardless of eruptive intrusive activity whereas magmatic activity plays a larger role in flank deformation at etna and piton de la fournaise k lauea and etna however are both characterized by heavily faulted flanks while piton de la fournaise shows little evidence for flank faulting a helpful means of understanding the spectrum of persistent flank motion at large basaltic edifices may be through a framework defined on one hand by magmatic activity which encompasses both magma supply and edifice size and on the other hand by the structural setting of the volcano especially the characteristics of the subvolcanic basement or subhorizontal intravolcanic weak zones a volcano s size and magmatic activity will dictate the extent to which gravitational and magmatic forces can drive motion of an unstable flank and possibly the level of faulting of that flank while the volcano s structural setting governs whether or not a plane of weakness exists beneath or within the edifice and can facilitate flank slip considering persistent flank instability using this conceptual model is an alternative to using a single volcano as a type example especially given that the example is usually k lauea which defines an extreme end of the spectrum and can provide a basis for understanding why flank motion may or may not exist on other large basaltic volcanoes worldwide

a sliding consolidation model for flow slides a model is proposed for the behaviour of flow slides in loose cohesionless materials in which the debris spreads out as a uniform sheet excess pore fluid pressures are assumed to be generated for example by undrained loading arising from the collapse of metastable structure in the source area of the flow slide under the influence of these the leading element of the debris moves downslope by basal sliding consolidating as it does so by single upward drainage as a result the pore pressure at the base of the element eventually decays to a value that brings the element to rest hence defining the run out of the flow slide the model is applicable in principle to subaqueous and subaerial flow slides and to pore fluids consisting of water gas or both of these the predictions of the model are tested against the observed behaviour and measured properties of the 1966 flow slide at aberfan south wales the results show that a sliding consolidation model provides a possible mechanism for that event

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

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

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