structural analysis of the early stages of catastrophic stratovolcano flank collapse using analogue models many major volcanic flank collapses involve the failure of low angle strata in or under the edifice such failures produce voluminous destructive debris avalanches that are a major volcanic hazard at socompa las isletas mombacho and parinacota volcanoes field studies have shown that during catastrophic flank collapse a significant segment of their substrata was detached and expelled from beneath the volcanic edifice and formed a mobile basal layer on which the sliding flanks were transported previous studies have proposed that gravitational flank spreading was likely involved in the onset of sudden substrata failure the early stages of this particular type of flank collapse can be modelled under laboratory conditions using analogue models this allows us to study the development of structures accommodating early deformation of the sliding flank during catastrophic collapse in the experiments the detached substratum segment low viscosity basal layer was modelled with a silicone layer and the overlying stratovolcano with a layered sand cone the first structure developed in the models is a graben rooted in the low viscosity basal layer this graben forms the limits of the future avalanche amphitheatre and divides the sliding flank into a toreva domain upper sliding flank and a hummock domain lower sliding flank these domains display distinctive structural patterns and kinetic behaviour normal faults develop in the toreva domain and inside the graben while the hummock domain is characterised by transtensional structures the hummock domain also over thrusts the lower amphitheatre sides which allows subsequent sideways avalanche spreading measurements show that horizontal speeds of the hummock domain are always higher than that of the toreva domain during model collapse the main role played by the low viscosity basal layer during this type of collapse is to control the size shape and structural complexity of the sliding flank it also transmits mass and momentum from the toreva to the hummock domain

volcano tectonic controls and emplacement kinematics of the iriga debris avalanches philippines mt iriga in southeastern luzon is known for its spectacular collapse scar that was possibly created in 1628 ad by a 1 5 km3 debris avalanche the debris avalanche deposit dad covered 70 km2 and dammed the barit river to form lake buhi the collapse has been ascribed to a non volcanic trigger related to a major strike slip fault under the volcano using a combination of fieldwork and remote sensing we have identified a similar size older dad to the southwest of the edifice that originated from a sector oblique to the underlying strike slip fault both deposits cover wide areas of low waterlogged plains to a distance of about 16 km for the oldest and 12 km for the youngest hundreds of metre wide and up to 50 m high hummocks of intact conglomerate sand and clay units derived from the base of the volcano show that the initial failure planes cut deep into the substrata in addition large proportions of both dad consist of ring plain sediments that were incorporated by soft sediment bulking and extensive bulldozing an ignimbrite unit incorporated into the younger dad forms small less than 5 m high discrete hummocks between the larger ones both debris avalanches slid over water saturated soft sediment or ignimbrite and spread out on a basal shear zone accommodated by horst and graben formation and strike slip faults in the main mass the faults are listric and flatten into a well developed basal shear zone this shear zone contains components from the substrate and has a diffuse contact with the intact substrata long transport normal ridges in the distal parts are evidence of compression related to deceleration and bulldozing the collapse orientation and structure on both sectors and dad constituents are consistent with collapse being a response to combined transtensional faulting and gravity spreading iriga can serve as a model for other volcanoes such as mayon that stand in sedimentary basins undergoing transtensional strike slip faulting

fogo volcano cape verde islands seismicity derived constraints on the mechanism of the 1995 eruption seismic data recorded in the vicinity of the active vent of the 1995 fogo eruption global volcanism network bulletin 1995 20 3 2 4 is used to constrain the associated stress field and deformation using the frequency content of the seismograms to distinguish between brittle fracture of cold host rock and deformation in the vicinity of the intruding magma a sub vertical dyke with 060 strike is identified as the feeder of the eruption and delineated down to a depth of about 4 km the local stress field during the eruption is estimated from composite focal mechanisms besides the expected 3 direction normal to the dyke a group of focal solutions point to a stress field with nearly dyke parallel 3 which is interpreted as a re adjustment of the edifice following the eruption maybe partially controlled by gravity this effect may have increased the instability of the steep eastern flank of the island since the deformation detected during the magma drainback is compatible with predominantly dip slip motion on east dipping surfaces

the krafla geothermal field iceland 1 analysis of well test data extensive modeling studies of the krafla geothermal field in iceland are presented in a series of four papers this first paper describes the geological settings of the field and the analysis of well test data the geothermal system at krafla is very complex with a single phase liquid reservoir overlying a two phase reservoir the reservoir rocks are volcanic with sequences of basalt flows hyloclastics and intrusions the fluid flow in the reservoir is fracture dominated considerable pressure transient data from injection tests have been gathered from the krafla wells these data are analyzed to yield the transmissivity distribution in the reservoir system as the data are complicated by various factors wellbore effects nonisothermal effects two phase flow and fractured rocks the applicability of conventional well test analysis methods is questionable the authors have developed a methodology to analyze injection tests for such systems the results obtained show that the transmissivity of the krafla reservoir is low averaging 2 darcy meters dm the average transmissivity of most commercially successful geothermal fields is an order of magnitude higher

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

experiments on rift zone evolution in unstable volcanic edifices large ocean island volcanoes frequently develop productive rift zones located close to unstable flanks and sites of older major sector collapses flank deformation is often caused by slip along a decollement within or underneath the volcanic edifice we studied how such a stressed volcanic flank may bias the rift zone development the influence of basal lubrication and lateral flank creep on rift development and rift migration is still poorly constrained by field evidence here our analog experiments provide new insights we injected colored water into gelatin cones and found systematic orientations of hydro fractures dikes propagating through the cones at the base of the cone diverse friction conditions were simulated by variation of the basal creep conditions we modeled radial dike swarms collinear rift zones and three armed rift systems it is illustrated that a single outward creeping flank is sufficient to modify the entire rift architecture of a volcano the experiments highlight the general unsteadiness of dike swarms and that the distribution and alteration of weak substratum may become a major player in shaping a volcano s architecture

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

climate forcing of volcano lateral collapse evidence from mount etna sicily in this study we present evidence for early holocene climatic conditions providing circumstances favourable to major lateral collapse at mount etna sicily the volcano s most notable topographic feature is the valle del bove a 5 x 8 km cliff bounded amphitheatre excavated from the eastern flank of the volcano its origin due to prehistoric lateral collapse is corroborated by sturtzstrom deposits adjacent to the amphitheatre s downslope outlet but the age nature and cause of amphitheatre excavation remain matters for debate cosmogenic 3 he exposure ages determined for eroded surfaces within an abandoned watershed flanking the valle del bove support channel abandonment ca 7 5 ka bp as a consequence of its excavation in a catastrophic collapse event watershed development was largely dictated by pluvial conditions during the early holocene which are also implicated in slope failure a viable trigger is magma emplacement into rift zones in the eastern flank of a water saturated edifice leading to the development of excess pore pressures consequent reduction in sliding resistance detachment and collapse such a mechanism is presented as one potential driver of future lateral collapse in volcanic landscapes forecast to experience increased precipitation or melting of ice cover as a consequence of anthropogenic warming

cyclical slope instability and volcanism related to volcano tectonism in resurgent calderas the ischia island italy case study abstract the results of a detailed stratigraphic study carried out in the areas located to the east and south west of mt epomeo at ischia are presented and compared with those of previous geological archaeological and historical investigations to show the relationships among caldera resurgence volcanism and slope instability in the past 5 5 ka resurgence at ischia began at about 30 ka b p and occurred through intermittent uplifting and tectonic quietness phases during the past 5 5 ka reactivation of faults and related volcanic activity was accompanied by emplacement of deposits generated by surface gravitational movements these deposits were generated in four main phases dated between 5 5 and 2 9 ka around 2 9 ka between 2 6 and 2 3 ka and between 2 3 and 1 9 ka respectively deposits formed by gravitational movements preceded and followed the emplacement of volcanic rocks testifying that slope instability was induced by vertical movements which also activated and or reactivated faults and fractures that fed volcanism the results of this study therefore suggest that although slope failure can occur as a consequence of a variety of factors resurgence has to be considered a factor inducing a particularly intense slope instability resurgence is accompanied by activation of faults and renewal of volcanism causing oversteepening of the slopes and generating seismicity that could trigger surface gravitational movements furthermore the availability of large amount of loose material rapidly accumulated along the slopes during eruptions favors landslide generation

relationship between the flank sliding of the south east crater mt etna italy and the paroxysmal event of november 16 2006 over the last 2 years the south east crater sec at mt etna italy has been characterised by the intermittent emission of lava flows often accompanied by paroxysmal episodes with violent strombolian activity and or lava fountains one of the most intense and intriguing episodes occurred on november 16 2006 during strombolian and effusive activity from the very top of the sec at the eastern base of the crater a violent and short lasting outburst generated a 300 m high eruptive curtain of finely fragmented magma and steam which collapsed in a few seconds giving rise to a small but significant pyroclastic flow the paroxysm was preceded by progressive sliding of the eastern flank of the sec edifice which led to the formation of a large niche previously published models explain the outburst as due to rapid vaporisation of water contained in sediments on contact with hot lava flowing along the flank of the sec or alternatively to gravitational collapse of a destabilised portion of the eastern flank of the crater however several lines of evidence suggest that these models do not adequately explain the paroxysm which we propose was associated with the explosive emission of magma during the rapid opening of an ese wnw oriented fracture at the eastern base of the sec moreover geochemical data of the products associated with this episode show that they are the most primitive and gas rich among those erupted during the entire 2006 period we suggest that the paroxysm of november 16 2006 which occurred at base of the sec was a magma outburst due to rapid ground fracturing related to a drop in confining pressure upon the underlying dyke consequent to the sliding of the eastern flank of the sec cone specifically the unloaded shallow portion of the feeding dyke did not restrain the arrival of a new batch of gas rich magma which worked its way out by fracturing the base of the niche at its weakest point this paroxysm appears significant because it reveals the potential development of syn eruptive dynamics acting directly on the uppermost portion of the plumbing system which is able to generate pyroclastic flows even on basaltic volcanoes such as mount etna

sedimentary signatures of cyclic growth and destruction of stratovolcanoes a case study from mt taranaki new zealand abstract the long term behaviour of andesite stratovolcanoes is characterised by a repetition of edifice growth phases followed by collapse this cyclic pattern represents a natural frequency at varying timescales in the growth dynamics of stratovolcanoes worldwide around the 130 ka mt taranaki egmont volcano new zealand coastal cliff successions at 20 40 km distance comprise repeating packages of lithologically and sedimentologically distinctive mass flow deposits varying depositional mechanisms and source properties of these units record growth and collapse cycles of the central edifice these are used to construct a model for cyclic volcaniclastic sedimentation in the surrounds of stratovolcanoes during edifice construction phases thick packages of tabular predominantly monolithologic hyperconcentrated flow and debris flow deposits accumulate with intercalated tephra beds the mass flow units commonly contain large proportions of fresh pumice or juvenile lithic andesite intervals of quiescence separating eruptive periods are characterised by landscape re adjustment accompanied by deposition of fluvial and aeolian sediments along with steady accretion of medial ash in contrast brief episodes of destruction are marked by wide spread distinctively clay rich polylithologic debris avalanche deposits and related marginal debris flow units the growth stages can be terminated by an eruption triggered sector collapse or by external forces once the edifice exceeds a critical stable height or profile dependent on eruptive style and local geo tectonic conditions once the edifice becomes metastable regional tectonic earthquakes or shallow level intrusion events are likely triggers for collapse although the resulting debris avalanches represent the greatest individual hazard from such andesite stratovolcanoes their frequency is relatively low compared with other types of mass flows generated during edifice growth phases accurate forecasts of future hazard from mass flow events are therefore dependent on recognition of both the frequency of a stratovolcano s growth cycle and its current position in that cycle

the lifecycle of mid ocean ridge seamounts and their prodigious flank collapses abstract volcanic seamounts are spectacular bathymetric features representing undersea mountains comparable in size to volcanic islands they are often sites of active volcanism represent major marine habitats and contain potentially globally significant commodities of trace metals however we know comparatively little about how they form the extent of their volcanic lifecycle and what risks they pose from periodic flank collapse here we study a uniquely extensive 43 myr record of volcaniclastic and calciclastic turbidites accumulated on the madeira abyssal plain in the ne atlantic which originate from large submarine landslides from the adjacent great meteor cruiser seamount complex on the flanks of the mid atlantic ridge these turbidites present the first long term temporal record of the recurrence magnitude and emplacement mechanism of seamount flank collapses from a single seamount complex throughout its lifecycle landslides from the great meteor cruiser seamount complex are comparable size to those from the canary islands with average volumes of 30 40 km3 but can be as large as 130 km3 comparable to many volcanic island landslides these seamount landslides were predominantly multi stage failures similar to those form neighbouring volcanic islands but in contrast occurred preferentially during sea level lowstands we show that volcanic seamounts above mantle plumes have long protracted lifecycles and that substantial flank failures are capable of occurring at all stages of development temporal change in turbidite composition has for the first time enabled reconstruction of the inception around 43 45 myrs ago ascension taking around 20 25 myrs emergence after 30 myrs and later recession last 9 myrs cessation in volcanism last 4 myrs and subsidence of the seamounts from 2 myrs onwards these seamounts above a mantle plume have taken around 26 myrs to emergence above sea level from inception while their volcanic island contemporaries only took 2 to 5 myrs here we use the history of turbidites derived from landslides from the seamounts to show how the seamounts developed and suffered mass wasting during their life cycles

structural consequences of cohesion in gravitational instabilities triggered by fluid overpressure analytical derivation and experimental testing abstract the critical taper theory of coulomb wedges has been classically applied to compressive regimes accretionary prisms fold and thrust belts and more recently to gravitational instabilities following the initial hypothesis of the theory we provide an alternative expression of the exact solution for a non cohesive wedge by considering the balance of forces applied to the external surfaces then we use this approach to derive a solution for the case of cohesive wedges we show that cohesion has conspicuous structural effects including a minimum length required for sliding and the formation of listric faults the stabilizing effect of cohesion is accentuated in the foremost thin domain of the wedge defining a required minimum failure length mfl and producing sliding of a rigid mass above the detachment this mfl decreases with less cohesion a smaller coefficient of internal friction larger fluid overpressure ratio and steeper upper and basal surfaces for the wedge listricity of the normal faults depends on the fluid overpressure magnitude within the wedge for moderate fluid overpressure normal faults are curved close to the surface and become straight at depth in contrast where fluid overpressure exceeds a critical value corresponding to the fluid pressure required to destabilize the surface of a noncohesive wedge the state of stress changes and rotates at depth the faults are straight close to the surface and listric at depth becoming parallel to the upper surface if the wedge is thick enough we tested some of these structural effects of a cohesive wedge on gravitational instabilities using analogue models where cohesive material was subjected to pore fluid pressure the shape of the faults obtained in the models is consistent with the predictions of the theory

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

dykes and structures of the ne rift of tenerife canary islands a record of stabilisation and destabilisation of ocean island rift zones many oceanic island rift zones are associated with lateral sector collapses and several models have been proposed to explain this link the north east rift zone nerz of tenerife island spain offers an opportunity to explore this relationship as three successive collapses are located on both sides of the rift we have carried out a systematic and detailed mapping campaign on the rift zone including analysis of about 400 dykes we recorded dyke morphology thickness composition internal textural features and orientation to provide a catalogue of the characteristics of rift zone dykes dykes were intruded along the rift but also radiate from several nodes along the rift and form en echelon sets along the walls of collapse scars a striking characteristic of the dykes along the collapse scars is that they dip away from rift or embayment axes and are oblique to the collapse walls this dyke pattern is consistent with the lateral spreading of the sectors long before the collapse events the slump sides would create the necessary strike slip movement to promote en echelon dyke patterns the spreading flank would probably involve a basal decollement lateral flank spreading could have been generated by the intense intrusive activity along the rift but sectorial spreading in turn focused intrusive activity and allowed the development of deep intra volcanic intrusive complexes with continued magma supply spreading caused temporary stabilisation of the rift by reducing slopes and relaxing stress however as magmatic intrusion persisted a critical point was reached beyond which further intrusion led to large scale flank failure and sector collapse during the early stages of growth the rift could have been influenced by regional stress strain fields and by pre existing oceanic structures but its later and mature development probably depended largely on the local volcanic and magmatic stress strain fields that are effectively controlled by the rift zone growth the intrusive complex development the flank creep the speed of flank deformation and the associated changes in topography using different approaches a similar rift evolution has been proposed in volcanic oceanic islands elsewhere showing that this model likely reflects a general and widespread process this study however shows that the idea that dykes orient simply parallel to the rift or to the collapse scar walls is too simple instead a dynamic interplay between external factors e g collapse erosion and internal forces e g intrusions is envisaged this model thus provides a geological framework to understand the evolution of the nerz and may help to predict developments in similar oceanic volcanoes elsewhere

rift zone reorganization through flank instability in ocean island volcanoes an example from tenerife canary islands the relationship between rift zones and flank instability in ocean island volcanoes is often inferred but rarely documented our field data aerial image analysis and 40ar 39ar chronology from anaga basaltic shield volcano on tenerife canary islands support a rift zone flank instability relationship a single rift zone dominated the early stage of the anaga edifice 6 4 5 ma destabilization of the northern sector led to partial seaward collapse at about 4 5 ma resulting in a giant landslide the remnant highly fractured northern flank is part of the destabilized sector a curved rift zone developed within and around this unstable sector between 4 5 and 3 5 ma induced by the dilatation of the curved rift a further rift arm developed to the south generating a three armed rift system this evolutionary sequence is supported by elastic dislocation models that illustrate how a curved rift zone accelerates flank instability on one side of a rift and facilitates dike intrusions on the opposite side our study demonstrates a feedback relationship between flank instability and intrusive development a scenario probably common in ocean island volcanoes we therefore propose that ocean island rift zones represent geologically unsteady structures that migrate and reorganize in response to volcano flank instability

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

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

source characteristics of earthquakes in the michoacan seismic gap in mexico we investigated the source characteristics of large earthquakes which occurred in the michoacan mexico seismic gap during the period from 1981 to 1986 in relation to historical seismicity in the region the rupture pattern of the michoacan gap during this period can be characterized by a sequential failure of five distinct asperities before 1981 the michoacan gap had not experienced a large earthquake since 1911 when an m s 7 8 earthquake occurred the recent sequence started in october 1981 with the playa azul earthquake which broke the central part of the gap body wave modeling indicates that the playa azul earthquake is 27 km deep with a seismic moment of 7 2 10 27 dyne cm it is slightly deeper than the recent michoacan earthquakes and its stress drop is higher suggesting a higher stress level at depths in the michoacan gap the seismic moment of the 19 september 1985 m w 8 1 earthquake was released in two distinct events with the rupture starting in the northern portion of the seismic gap and propagating to the southeast with low moment release through the area already broken by the 1981 playa azul earthquake the rupture propagated further southeast with an m w 7 5 event on 21 september 1985 another aftershock occurred on 30 april 1986 to the northwest of the 19 september main shock body wave modeling indicates that this event has a simple source 10 sec long at 21 km depth and fault parameters consistent with subduction of the cocos plate 280 12 and 70 and m 0 2 0 to 3 1 10 26 dyne cm m w 6 8 to 6 9 although this distribution of asperities is considered characteristic of the michoacan gap whether the temporal sequence exhibited by the 1981 to 1986 sequence is also characteristic of this gap or not is unclear it is probable that depending on the state of stress in each asperity the entire gap may fail in either a single large event with a complex time history or a sequence of moderate to large events spread over a few years the seismic moment and the time since the last earthquake in michoacan in 1911 fit an empirical relation between moment and recurrence time found for the guerrero oaxaca region of the mexico subduction zone

coeval strombolian and vulcanian type explosive eruptions at panarea aeolian islands southern italy in this paper we document the evolution of the emergent panarea dome in the aeolian islands southern italy placing particular emphasis on the reconstruction of the explosive events that occurred during the final stage of its evolution two main pyroclastic successions exposing fall deposits with different compositions have been studied into detail the andesitic palisi succession and the basaltic punta falcone succession the close in time deposition of the two successions the dispersal area and grain size distribution of the deposits account for their attribution to vents located in the western sector of the present island and erupting almost contemporaneously vents could have been aligned along nne trending regional fracture systems controlling the western flank of the dome and possibly its collapse laboratory analyses have been devoted to the characterization of the products of the two successions that have been ascribed to vulcanian and to strombolian type eruptions respectively the vulcanian eruption started with a vent clearing phase that occurred by sudden decompression of a pressurized magma producing ballistic bombs and a surge blast and the development of a vulcanian plume vulcanian activity was almost contemporaneous to strombolian type fall out eruptions the coeval occurrence of basaltic and andesitic eruptions from close vents and the presence of magmatic basaltic enclaves in the final dacitic lava lobe of the dome allow us to speculate that the intrusion of a basaltic dyke played a major role in triggering explosive eruptions the final explosive episodes may have been caused by extensional tectonics fracturing the roof of a zoned shallow magma chamber or by the intrusion of a new basaltic magma into a more acidic and shallow reservoir intrusion most likely occurred through the injection of dykes along the western cliff of the present panarea island inducing the collapse of the western sector of the dome

the proximal part of the giant submarine wailau landslide molokai hawaii abstract the main break in slope on the northern submarine flank of molokai at 1500 to 1250 m is a shoreline feature that has been only modestly modified by the wailau landslide submarine canyons above the break in slope including one meandering stream were subaerially carved where such canyons cross the break in slope plunge pools may form by erosion from bedload sediment carried down the canyons west molokai volcano continued infrequent volcanic activity that formed a series of small coastal sea cliffs now submerged as the island subsided lavas exposed at the break in slope are subaerially erupted and emplaced tholeiitic shield lavas submarine rejuvenated stage volcanic cones formed after the landslide took place and following at least 400 500 m of subsidence after the main break in slope had formed the sea cliff on east molokai is not the headwall of the landslide nor did it form entirely by erosion it may mark the location of a listric fault similar to the hilina faults on present day kilauea volcano the wailau landslide occurred about 1 5 ma and the kalaupapa peninsula most likely formed 330 5 ka molokai is presently stable relative to sea level and has subsided no more than 30 m in the last 330 ka at their peak west and east molokai stood 1 6 and 3 km above sea level high rainfall causes high surface runoff and formation of canyons and increases groundwater pressure that during dike intrusions may lead to flank failure active shield or postshield volcanism with dikes injected along rift zones and high rainfall appear to be two components needed to trigger the deep seated giant hawaiian landslides

faulting assisted lateral collapses and influence on shallow magma feeding system at ollague volcano central volcanic zone chile bolivia andes abstract the role played by the regional tectonics and relationships between volcanic structures and their shallow magmatic feeding system are of paramount importance in understanding multiple lateral collapse events and thus for hazard assessment in active volcanoes ollague 21 18 s 68 11 w andean central volcanic zone chile bolivia border is an active andesite dacite composite volcano developed on a regional nw striking extensional fault system that bisects the volcanic edifice geological and stratigraphic studies on the summit part of the cone together with new 40ar 39ar dating and petrographic and geochemical major trace elements analyses have allowed us to delineate the volcanic history of ollague and recognize multiple deformation and lateral collapse events the evolution of ollague appears to be characterized by four stages of volcano building separated by three main events of deformation of the cone these deformation events developed progressively by downthrow of the sw sector of the volcano 800 ka along the nw striking normal fault propagating from the substrate to a final catastrophic failure 300 ka of the sw sector and debris avalanche emplacement both nw trending regional tectonics and weakness of the edifice caused by the successive deformation and collapse events are responsible for both the geometric variations of the shallow magma feeding system and the coexistence of summit and parasitic dacitic vents central and lateral vents shifted in a sw trending direction i e perpendicular to the tectonic trend and along the axis of the collapse movement and developed along a nw trending alignment i e parallel to the main tectonic trend and collapse scarps

flank instability assessment at kick em jenny submarine volcano grenada lesser antilles a multidisciplinary approach using experiments and modeling kick em jenny kej located ca 8 km north of the island of grenada is the only active submarine volcano of the lesser antilles volcanic arc previous investigations of kej revealed that it lies within a collapse scar inherited from a past flank instability episode to assess the likelihood of future collapse we employ here a combined laboratory and modeling approach lavas collected using a remotely operated vehicle rov provided samples to perform the first rock physical property measurements for the materials comprising the kej edifice uniaxial and triaxial deformation experiments showed that the dominant failure mode within the edifice host rock is brittle edifice fractures such as those at champagne vent will therefore assist the outgassing of the nearby magma filled conduit favoring effusive behavior these laboratory data were then used as input parameters in models of slope stability first relative slope stability analysis revealed that the sw to n sector of the volcano displays a deficit of mass volume with respect to a volcanoid ideal 3d surface slope stability analysis using a limit equilibrium method lem showed that kej is currently stable since all values of stability factor or factor of safety fs are greater than unity the lowest values of fs were found for the sw nw sector of the volcano the sector displaying a mass volume deficit although currently stable kej may become unstable in the future instability severe reductions in fs could result for example from overpressurization due to the growth of a cryptodome our modeling has shown that instability induced flank collapse will most likely initiate from the sw nw sector of kej therefore mobilizing a volume of at least ca 0 7 km3 the mobilization of ca 0 7 km3 of material is certainly capable of generating a tsunami that poses a significant hazard to the southern islands of the west indies

was a dacite dome implicated in the 9 500 b p collapse of mt ruapehu a palaeomagnetic investigation constraining the process by which volcanoes become unstable is difficult several models have been proposed to explain the driving forces which cause volcanic edifices to catastrophically collapse these include models for destabilisation of volcanic flanks by wedging due to dyke intrusion and the weakening of mechanical properties by pressurisation of pore fluids it is not known which if any of the models are relevant to particular sector collapse events recent developments in the palaeomagnetic estimation of emplacement temperatures of volcaniclastic rocks have shown that even relatively low emplacement temperatures can be recorded by volcaniclastics with high fidelity we have carried out a palaeomagnetic study of emplacement temperatures to investigate the role of igneous activity in the initiation of the 9 500 b p murimotu sector collapse of mt ruapehu new zealand this debris avalanche deposit has three fades which are stratigraphically superimposed and the lowermost fades contains three lithological assemblages representing different segments of the edifice which were transported with little internal mixing within the flow we have determined that some of the dacite bearing assemblage 1 fades 1 was hot 350 c during transport and emplacement whereas none of the other lithological assemblages of fades contained hot material our interpretation is that a dacite dome was active on the ancient ruapehu edifice immediately prior to the murimotu sector collapse the partially cooled carapace of the dome and material shed from this part was incorporated into the avalanche deposit along with cold lavas and volcaniclastics we have not found evidence for incorporation of material at or close to magmatic temperatures at least in the sampled locations our palaeomagnetic work allows us to develop a comprehensive new palaeomagnetic classification of volcaniclastics

gravitational spreading and formation of new rift zones on overlapping volcanoes large volcanic edifices are often shaped by the coalescence of adjacent volcanoes as well as intrusive rift zones and gravitational spreading to better understand the structure of such volcanoes we designed analogue experiments simulating gravitational spreading of an edifice made by overlapping cones of different age and examined the formation of rift zones the results allow distinction of two main rift geometries i spreading edifices of similar age that partly overlap tend to develop a rift zone approximately perpendicular to the boundary of both volcanoes such a rift zone causes two volcanoes to grow together and form an elongated topographic ridge ii partly overlapping volcanoes of different age are spreading at different rates and thus form a rift zone parallel to the boundary of both volcanoes such a rift zone causes two volcanoes to structurally separate the results are widely applicable for large volcanoes subject to rifting and flank spreading which we demonstrate for reunion island and for southern hawaii

ground deformation monitoring of a potential landslide at la palma canary islands abstract the southern part of the island of la palma comprises a north south oriented volcano known as the cumbre vieja the steep gradient and high aspect ratio of the volcano coupled with the prospect of future episodes of magma intrusion highlight the potential for large scale lateral collapse of the volcano as recorded earlier in the history of la palma and elsewhere in the canary islands historic eruptions of the cumbre vieja have occurred high up on the western flank of the volcano and along a single rift zone along the crest of the volcano the geometry of the recent activity and faulting which occurred during an eruption in 1949 indicates that a discontinuity may be present beneath the western flank of the volcano along which a future collapse may occur to identify any displacement of the western flank overlying the discontinuity a ground deformation network has recently been established on the volcano the initial network spanned the fault system that developed on the upper flanks of the cumbre vieja during the 1949 eruption this small network was measured in 1994 1996 and 1997 using infrared electronic distance measurement in 1997 the network was enlarged and re occupied using the global positioning system to incorporate the west flank and the southern part of the island although the results show that apparent displacements recorded during this period are within the error margins of the techniques employed the apparent movement vectors do suggest a coherent westward displacement of stations to the west of the 1949 fault system additional occupations of the network over the next few years will however be required to determine the reality or otherwise of this apparent coherent movement and thus to decide whether or not the western flank of the cumbre vieja is currently sliding seaward if not it can be inferred that the volcano is stable during inter eruptive periods

volcanic rifting at martian grabens 1 a large fraction of surface extension on mars occurred at segmented grabens having width length ratios akin to oceanic rifts on earth association with volcanic landforms such as pit craters clearly suggests interconnection between tectonic and magmatic processes a martian rift evolution model is proposed on the basis of new geomorphological and structural interpretations of imagery high resolution digital elevation models dems scaled experimental modeling and three dimensional boundary element modeling of magmatic and tectonic processes and a comparison with terrestrial rifts the dems were obtained from mars observer laser altimeter viking orbiter stereo images or a combination of both comparison of terrestrial rifts included afar iceland and the east pacific rise the ambient extensional stress field induced by regional body forces is combined at depth with decompression melting and mantle plume thermal anomaly resulting in emplacement of elongated magma reservoirs along the grabens injection of dikes above the reservoirs and flood basalt eruption result in a reservoir underpressurization of up to hundreds of mpa and induces surface collapse each collapse event is associated with an eruption of volcanic volumes akin to those of individual flow eruptions in large terrestrial igneous provinces the geometry and mechanisms of graben formation and surface collapse are described and used to infer reservoir depth and width we conclude from this study that giant dike swarms akin to typical giant terrestrial dike swarms are unlikely to underlie the volcanic martian grabens on the basis one graben one dike rather every volcanic graben segment appears to own a local dike swarm perhaps analogous to the dike swarms in the icelandic fissure zones index terms 5475 planetology solid surface planets tectonics 8149 5480 planetology solid surface planets volcanism 8450 6225 planetology solar system objects mars 8121 tectonophysics dynamics convection currents and mantle plumes 8010 structural geology fractures and faults keywords rifting graben pit crater magma chamber dyke

multiple edifice collapse events in the eastern mexican volcanic belt the role of sloping substrate and implications for hazard assessment abstract the citlaltepetl cofre de perote volcanic chain forms an important physiographic barrier that separates the central altiplano 2500 masl from the gulf coastal plain gcp 1300 masl the abrupt eastward drop in relief between these provinces gives rise to unstable conditions and consequent gravitational collapse of large volcanic edifices built at the edge of the altiplano eastward sloping substrate caused by the irregular configuration of the basement rocks is the dominant factor that controls the direction of collapsing sectors in all major volcanoes in the region to be preferentially towards the gcp these collapses produced voluminous debris avalanches and lahars that inundated the well developed drainages and clastic aprons that characterize the coastal plain large catastrophic collapses from citlaltepetl las cumbres and cofre de perote volcanoes are well documented in the geologic record some of the avalanches and transformed flows have exceptionally long runouts and reach the gulf of mexico traveling more than 120 km from their source so far no direct evidence has been found for magmatic activity associated with the initiation of these catastrophic flank collapses apparently instability of the volcanic edifices has been strongly favored by very intense hydrothermal alteration abrupt topographic change and intense fracturing in addition to the eastward slope of the substrate the reactivation of pre volcanic basement structures during the late tertiary and the e w to ene ssw oriented regional stress regimes may have played an important role in the preferential movement direction of the avalanches and flows in addition to magmatic hydrothermal processes high amounts of rainfall in the area is another factor that enhances alteration and eventually weakens the rocks it is very likely that seismic activity may be the principal triggering mechanism that caused the flank collapse of large volcanic edifices in the eastern mexican volcanic belt however critical pore water pressure from extraordinary amounts of rainfall associated with hurricanes or other meteorological perturbation cannot be ruled out particularly for smaller volume collapses there are examples in the area of small seismogenic debris flows that have occurred in historical times showing that these processes are not uncommon assessing the stability conditions of major volcanic edifices that have experienced catastrophic sector collapses is crucial for forecasting future events this is particularly true for the eastern mexican volcanic belt where in many cases no magmatic activity was associated with the collapse therefore edifice failure could occur again without any precursory warning

digital photogrammetry as a tool in analogue modelling applications to volcano instability abstract three techniques of digital photogrammetry have been applied successfully to laboratory analogue models to study surface displacements caused by various volcano deformation types firstly side perspective videos are used to differentiate profile displacements between cryptodome intrusion models and models deforming by ductile inner core viscous flow both models show similar morphologic features including a bulged flank and an asymmetric upper graben however differences in displacement trajectories of the bulge crest reflect upward intrusion push contrasting with essentially downward displacement vectors of weak core models the other two techniques use vertical views correlated automatically either as time sequence monoscopic views or as coeval stereoscopic pairs this exploits to a maximum the method s potential by imaging surface displacements over the whole model successive monoscopic photograms because they suffer only moderate numerical processing for topographic effect removal can detect very small displacements occurring early in deformation processes as illustrated by analysis of intrusion models the monoscopic method allows prediction of fault locations and main displacement locations it can also anticipate the principal strain directions and separate different deformation stages on the other hand the stereo photogrammetry technique although more complicated provides topography and volume changes as well as pictures of surface displacements in three dimensions results are presented for the spreading of volcano models on a ductile substratum and viscous cored cones we have found digital photogrammetry to be a useful tool for analogue modelling because it provides quantitative data on surface displacements including movement invisible to the eye as well as topographic changes it is a good method for investigating and comparing different deformation mechanisms it is especially useful for interpretation of displacement patterns obtained from monitoring of natural active volcanoes in fact results of the methods used in the laboratory can be directly compared with field data from geodetic or photogrammetric surveys as at mount st helens in 1980

new insight into the factors leading to the 1998 flank collapse and lahar disaster at casita volcano nicaragua during unusually high rainfall associated with hurricane mitch in 1998 a flank collapse leading to a disastrous lahar occurred at casita volcano nicaragua the lack of a similar failure during a rainfall event of comparable magnitude in 1982 tropical storm alleta suggests that additional factors influenced the 1998 collapse we have investigated the potential contribution of erosional flank undercutting seismic activity and anthropogenic land cover change at the collapse site except for seismic events prior to mitch which may have increased flank instability none of these factors appears significant instead for failure to occur the following conditions were required 1 highly fractured slope material allowing deep and rapid infiltration of meteoric water 2 a less permeable underlying layer to obstruct drainage 3 strong continuous antecedent rainfall to build up high pore water pressure and 4 episodic high intensity precipitation during mitch to generate recurrent pressure waves prerequisite 1 was provided by edifice wide deformation towards the south east seismic activity and proximity to a prominent fault and local subsidence condition 2 was met by clay rich layers resulting from hydrothermal alteration more than 1 900 mm of rain fell in the 6 months prior to mitch without significant interruption while intense episodic precipitation occurred during the hurricane satisfying conditions 3 and 4 respectively the main difference with alleta was that it occurred at the beginning of the rainy season and therefore without sufficient antecedent rainfall anthropogenic activity including land cover change did not affect slope stability i e the hazard however vulnerability was generated when two towns were established in the lowlands south of casita on top of previous lahar deposits it was greatly increased when approximately 4 km of forest between the collapse site and the towns were cleared paving the way for a largely unobstructed debris flow deforestation also facilitated erosion along the flanks to provide about 78 of the material contained in the lahar when it destroyed the towns killing more than 2 500 people

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

sector collapses and large landslides on late pleistocene holocene volcanoes in kamchatka russia on kamchatka detailed geologic and geomorphologic mapping of young volcanic terrains and observations on historical eruptions reveal that landslides of various scales from small 0 001 km3 to catastrophic up to 20 30 km3 are widespread moreover these processes are among the most effective and most rapid geomorphic agents of 30 recently active kamchatka volcanoes at least 18 have experienced sector collapses some of them repetitively the largest sector collapses identified so far on kamchatka volcanoes with volumes of 20 30 km3 of resulting debris avalanche deposits occurred at shiveluch and avachinsky volcanoes in the late pleistocene during the last 10 000 yr the most voluminous sector collapses have occurred on extinct kamen 4 6 km3 and active kambalny 5 10 km3 volcanoes the largest number of repetitive debris avalanches 10 during just the holocene has occurred at shiveluch volcano landslides from the volcanoes cut by ring faults of the large collapse calderas were ubiquitous large failures have happened on both mafic and silicic volcanoes mostly related to volcanic activity orientation of collapse craters is controlled by local tectonic stress fields rather than regional fault systems specific features of some debris avalanche deposits are toreva blocks huge almost intact fragments of volcanic edifices involved in the failure some have been erroneously mapped as individual volcanoes one of the largest toreva blocks is mt monastyr a 2 km3 piece of avachinsky somma involved in a major sector collapse 30 40 ka bp long term forecast of sector collapses on kliuchevskoi koriaksky young cone of avachinsky and some other volcanoes highlights the importance of closer studies of their structure and stability

the morphology of the submarine flanks of volcanic ocean islands a comparative study of the canary and hawaiian hotspot islands the submarine flanks of volcanic islands are shaped by volcanic constructional processes landslides erosion sediment deposition and tectonic movements we use a newly acquired multibeam sonar dataset from the westerly canary islands el hierro la palma and tenerife to develop a comparison with the hawaiian islands which suggests differences in the processes constructing and modifying their flanks landslides affect the flanks of both island groups debris avalanches fast moving shallow landslides have left smooth chutes and blocky deposits in both cases but blocks within some hawaiian avalanche deposits are markedly larger we attribute the larger block sizes in the hawaiian islands to the fact that their avalanches were relatively unconfined whereas many canary and hawaiian avalanches with small block sizes appear to have been constrained down narrow chutes forcing interactions between blocks within the flows and encouraging disintegration furthermore the hawaiian avalanches with the largest blocks initiated near sea level whereas many of the canary avalanches initiated above sea level so hydraulic resistance of water entering cracks may be an additional factor in resisting block disintegration during flow slow moving deep seated slumps or volcanic spreading have produced submarine benches and tabular escarpments due to thrust faulting adjacent to several hawaiian rift zones but are not well developed in the canaries although volcanic morphology is partly obscured by sedimentation in the canaries we are able to interpret lava terraces around the deep flanks of el hierro which are similar to those found in the hawaiian islands however cones rather than terraces are the most common volcanic forms in the canary islands implying that flank eruptions have involved magma with significant volatile contents assuming that volatile contents dictate whether cones or terraces are formed these differences may ultimately originate from the different building rates of the two island groups for example the lack of evidence for high level magma chambers in the canaries associated with their lower outputs implies that there is less possibility for degassing of magma below the summit before lateral intrusion down rift zones hence cones rather than lava terraces are more commonly observed the apparent lack of slumping or volcano spreading could also reflect a lack of driving pressure from extensive high level magma chambers in the canaries

impact of the goce gravity mission on ocean circulation estimates the impact of a geoid model derived from the goce gravity mission on estimates of large scale oceanic transports is investigated using an inverse model of the north atlantic because its precision would match the precision of satellite altimeters goce would significantly improve estimates of ocean dynamic topography and would thus provide information on ocean surface velocities the impact of this information in terms of uncertainties in volume transports would be limited in the deep ocean by the presence of noise in the density field but it would be significant in the upper ocean with for instance a 26 reduction of the uncertainty in the top 100 m layer at 48 n this impact is comparable in magnitude to the impact on top to bottom transport uncertainties found by ganachaud and co workers but it is achieved here with realistic error bars in the density field this result shows that the improvement in hydrographic data assumed by these authors is not a prerequisite to a significant impact of future gravity missions

thermal weakening of the carbonate basement under mt etna volcano italy implications for volcano instability abstract the physical integrity of a sub volcanic basement is crucial in controlling the stability of a volcanic edifice for many volcanoes this basement can comprise thick sequences of carbonates that are prone to significant thermally induced alteration these debilitating thermal reactions facilitated by heat from proximal magma storage volumes promote the weakening of the rock mass and likely therefore encourage edifice instability such instability can result in slow gravitational spreading and episodic to continuous slippage of unstable flanks and may also facilitate catastrophic flank collapse understanding the propensity of a particular sub volcanic basement to such instability requires a detailed understanding of the influence of high temperatures on the chemical physical and mechanical properties of the rocks involved the juxtaposition of a thick carbonate substratum and magmatic heat sources makes mt etna volcano an ideal candidate for our study we investigated experimentally the effect of temperature on two carbonate rocks that have been chosen to represent the deep heterogeneous sedimentary substratum under mt etna volcano this study has demonstrated that thermal stressing resulted in a progressive and significant change in the physical properties of the two rocks porosity wet i e water saturated dynamic poisson s ratio and wet vp vs ratio all increased whilst p and s wave velocities bulk sample density dynamic and static young s modulus dry vp vs ratio and dry dynamic poisson s ratio all decreased at temperatures of 800 c the carbonate in these rocks completely dissociated resulting in a total mass loss of about 45 and the release of about 44 wt of co 2 uniaxial deformation experiments showed that high in situ temperatures 500 c significantly reduced the strength of the carbonates and altered their deformation behaviour above 500 c the rocks deformed in a ductile manner and the output of acoustic emissions was greatly reduced we speculate that thermally induced weakening and the ductile behaviour of the carbonate substratum could be a key factor in explaining the large scale deformation observed at mt etna volcano our findings are consistent with several field observations at mt etna volcano and can quantitatively support the interpretation of 1 the irregularly low seismic velocity zones present within the sub volcanic sedimentary basement 2 the anomalously high co 2 degassing observed 3 the anomalously high vp vs ratios and the rapid migration of fluids and 4 the increasing instability of volcanic edifices in the lifespan of a magmatic system we speculate that carbonate sub volcanic basement may emerge as one of the decisive fundamentals in controlling volcanic stability