a review of catastrophic drainage of moraine dammed lakes in british columbia abstract moraine dammed lakes are common in the high mountains of british columbia most of these lakes formed when valley and cirque glaciers retreated from advanced positions achieved during the little ice age many moraine dams in british columbia are susceptible to failure because they are steep sided have relatively low width to height ratios comprise loose poorly sorted sediment and may contain ice cores or interstitial ice in addition the lakes commonly are bordered by steep slopes that are prone to snow and ice avalanches and rockfalls moraine dams generally fail by overtopping and incision the triggering event may be a heavy rainstorm or an avalanche or rockfall that generates waves that overtop the dam the dam can also be overtopped by an influx of water caused by sudden drainage of an upstream ice dammed lake jokulhlaup melting of moraine ice cores and piping are other possible failure mechanisms failures of moraine dams in british columbia produce destructive floods orders of magnitude larger than normal streamflows most outburst floods are characterized by an exponential increase in discharge followed by an abrupt drop to background levels when the water supply is exhausted peak discharges are controlled by dam characteristics the volume of water in the reservoir failure mechanisms and downstream topography and sediment availability for the same potential energy at the dam site floods from moraine dammed lakes have higher peak discharges than floods from glacier dammed lakes the floodwaters may mobilize large amounts of sediment as they travel down steep valleys producing highly mobile debris flows such flows have larger discharges and greater destructive impact than the floods from which they form moraine dam failures in british columbia and elsewhere are most frequent following extended periods of cool climate when large lateral and end moraines are built a period of protracted warming is required to trap lakes behind moraines and create conditions that lead to dam failure this sequence of events occurred only a few times during the holocene epoch most notably during the last several centuries glaciers built large moraines during the little ice age mainly during the 1700s and 1800s and lakes formed behind these moraines when climate warmed in the 1900s twentieth century climate warming is also responsible for recent moraine dam failures in mountains throughout the world warming from the late 1800s until about 1940 and again from 1965 to today destabilized moraine dams with interstitial or core ice the warming also forced glaciers to retreat prompting ice avalanches landslides and jokulhlaups that have destroyed some moraine dams

the 1995 1998 eruption of the soufriere hills volcano montserrat wi eruption of the soufriere hills volcano began on 18 july 1995 after three years of elevated seismic activity four months of increasingly vigorous phreatic activity culminated in mid november 1995 with the initiation of dome growth growth rates increased unevenly through early march 1996 with fluctuations on time scales from hours to months since march 1996 gravitational collapse of the unstable dome flank has affected an ever increasing area with pyroclastic flows surges and ashfalls major collapse of the eastern flank on 17 september 1996 resulted in a sub plinian explosive eruption later that day by february 1997 the dome had outgrown the confines of the crater and begun to spill into the surrounding valleys a large collapse on 25 june 1997 caused pyroclastic flows and surges on the northern flanks and resulted in the only deaths of the eruption in august september and october 1997 vulcanian explosions followed further collapses on the western and northern flanks the largest event of the eruption occurred on 26 december 1997 with failure of the southwestern flank of the volcano producing a debris avalanche and large dome collapse pyroclastic flows dome growth ceased in early march 1998 but residual volcanic activity has continued and consists of ash venting mild explosions and dome collapse pyroclastic flows

the 1976 1982 strombolian and phreatomagmatic eruptions of white island new zealand eruptive and depositional mechanisms at a wet volcano white island is an active andesitic dacitic composite volcano surrounded by sea yet isolated from sea water by chemically sealed zones that confine a long lived acidic hydrothermal system within a thick sequence of fine grained volcaniclastic sediment and ash the rise of at least 106 m3 of basic andesite magma to shallow levels and its interaction with the hydrothermal system resulted in the longest historical eruption sequence at white island in 1976 1982 about 107 m3 of mixed lithic and juvenile ejecta was erupted accompanied by collapse to form two coalescing maar like craters vent position within the craters changed 5 times during the eruption but the vents were repeatedly re established along a line linking pre 1976 vents the eruption sequence consisted of seven alternating phases of phreatomagmatic and strombolian volcanism strombolian eruptions were preceded and followed by mildly explosive degassing and production of incandescent blocky juvenile ash from the margins of the magma body phreatomagmatic phases contained two styles of activity a near continuous emission of gas and ash and b discrete explosions followed by prolonged quiescence the near continuous activity reculted from streaming of magmatic volatiles and phreatic steam through open conduits frittering juvennile shards from the margins of the magma and eroding loose lithic particles from the unconsolidated wall rock the larger discrete explosions produced ballistic block aprons downwind lobes of fall tephra and cohesive wet surge deposits confined to the main crater the key features of the larger explosions were their shallow focus random occurrence and lack of precursors and the thermal heterogeneity of the ejecta this white island eruption was unusual because of the low discharge rate of magma over an extended time period and because of the influence of a unique physical and hydrological setting the low rate of magma rise led to very effective separation of magmatic volatiles and high fluxes of magmatic gas even during phreatic phases of the eruption while true strombolian phases did occur more frequently the decoupled magmatic gas rose to interact with the conduit walls and hydrothermal system producing phreatomagmatic eruptions the form of these wet explosions was governed by a delicate balance between erosion and collapse of the weak conduit walls if the walls were relatively stable fine ash was slowly eroded and erupted in weak near continous phreatomagmatic events when the walls were unstable wall collapse triggered larger discrete phreatomagmatic explosions

volcanic hazard assessment for ruapehu composite volcano taupo volcanic zone new zealand ruapehu is a very active andesitic composite volcano which has erupted five times in the past 10 years historical events have included phreatomagmatic eruptions through a hot crater lake and two dome building episodes ski field facilities road and rail bridges alpine huts and portions of a major hydroelectrical power scheme have been damaged or destroyed by these eruptions destruction of a rail bridge by a lahar in 1953 caused the loss of 151 lives other potential hazards with holocene analogues include strombolian and sub plinian explosive eruptions lava extrusion from summit or flank vents and collapse of portions of the volcano the greatest hazards would result from renewed phreatomagmatic activity in crater lake or collapse of its weak southeastern wall three types of hazard zones can be defined for the phreatomagmatic events inner zones of extreme risk from ballistic blocks and surges outer zones of disruption to services from fall deposits and zones of risk from lahars which consist of tongues down major river valleys ruapehu is prone to destructive lahars because of the presence of 107 m3 of hot acid water in crater lake and because of the surrounding summit glaciers and ice fields the greatest risks at ruapehu are to thousands of skiers on the ski field which crosses a northern lahar path three early warning schemes have been established to deal with the lahar problems collapse of the southeastern confining wall would release much of the lake into an eastern lahar path causing widespread damage this is a long term risk which could only be mitigated by drainage of the lake

quantifying the geomorphic impacts of a lake breakout lahar mount ruapehu new zealand at 11 18 h new zealand time gmt 12 on 18 march 2007 an impoundment of 0 01 10 6 m 3 of tephra collapsed releasing 1 3 10 6 m 3 of water from crater lake at 2536 m elevation on mount ruapehu the lahar traveled 200 km along the whangaehu river aerial lidar surveys of the upper 62 km of flow path were made before and after the lahar we present here the first large scale quantification of the geomorphic impact of the dam break flood along with the rates and controls on its sediment entrainment and deposition the flood mobilized a net value of 2 5 3 1 10 6 m 3 of boulders gravel and sand over the first 5 km of travel to form a lahar of at least 4 4 10 6 m 3 passing instruments at 6 9 km lidar volume transfer calculations match dynamic measurements made after a logarithmic increase in cumulative net sediment entrainment the lahar appeared to reach its maximum sediment carrying capacity at 22 km patterns of alternating sediment erosion and deposition occurred that dominantly reflect a combination of channel morphology and confinement on the local sediment carrying capacity of the flow

methods for assessing the stability of slopes during earthquakes a retrospective abstract during the twentieth century several methods to assess the stability of slopes during earthquakes were developed pseudostatic analysis was the earliest method it involved simply adding a permanent body force representing the earthquake shaking to a static limit equilibrium analysis stress deformation analysis a later development involved much more complex modeling of slopes using a mesh in which the internal stresses and strains within elements are computed based on the applied external loads including gravity and seismic loads stress deformation analysis provided the most realistic model of slope behavior but it is very complex and requires a high density of high quality soil property data as well as an accurate model of soil behavior in 1965 newmark developed a method that effectively bridges the gap between these two types of analysis his sliding block model is easy to apply and provides a useful index of co seismic slope performance subsequent modifications to sliding block analysis have made it applicable to a wider range of landslide types sliding block analysis provides perhaps the greatest utility of all the types of analysis it is far easier to apply than stress deformation analysis and it yields much more useful information than does pseudostatic analysis

depositional record of historic lahars in the upper whangaehu valley mt ruapehu new zealand implications for trigger mechanisms flow dynamics and lahar hazards mt ruapehu in the central north island of new zealand is one of the most lahar prone volcanoes in the world since historic observations began in 1861 ad more than 50 individual lahars have been recorded in the whangaehu valley alone the natural outlet to the summit crater lake these lahars have been triggered by a variety of mechanisms including explosive eruptions that displaced crater lake water over the outlet or ejected it onto the snow clad summit area of the volcano rain remobilisation of tephra deposits on steep slopes displacement over the outlet as a result of syn eruptive changes in lake bathymetry and lake break outs from crater lake following impoundment of excess water behind temporary barriers of tephra and or ice emplaced over the outlet however only 9 lahar deposits can be distinguished in the upper whangaehu valley on sedimentological stratigraphic geomorphic and petrological grounds and these are skewed towards either the largest or the most recent flows in some cases magnitude can be reconstructed from deposit geometry with the largest lahars producing the highest level terraces the coarsest deposits and crossing drainage divides into normally inactive channels this under representation of historic events reflects the low preservation potential of unconsolidated deposits in a steep alpine environment and the overprinting and recycling effect of large magnitude lahars that rework material down to bedrock and effectively reset the stratigraphic record development of magnitude frequency relationships for ruapehu lahars therefore requires the identification of lahar deposits in proximal medial and distal settings in order to ensure that the full range of events is represented

stability assessment of the crater lake te wai ā moe overflow channel at mt ruapehu new zealand and implications for volcanic lake break out triggers abstract the presence of lakes on active volcanoes gives rise to several unique volcano hydrologic hazards including those directly related to volcanic activity e g phreatic explosions and non volcanic phenomena e g lake outbursts mt ruapehu volcano hosts the 107 m3 crater lake te wai moe in the active summit crater making it prone to lahars due to the abundance of water stored at high elevation apart from eruptive periods when water is commonly ejected from the lake large lahar events can occur when portions of the crater rim fail during quiescent periods leading to partial lake drainage the latter occurred recently in 1953 and 2007 here we investigate the potential of future lahars due to rim failure at the current overflow channel considering several triggering scenarios during non eruptive periods the geomechanical properties of a matrix dominated breccia unit composing part of the overflow channel were analyzed using physical and mechanical laboratory methods these properties combined with previous geomechanical studies of lava units in the overflow channel were used in finite element and limit equilibrium method based groundwater and stability models groundwater models indicate that a low permeability barrier inside the crater rim is preventing water from seeping through the unconsolidated and potentially permeable breccia unit of the overflow channel the removal of this barrier or weathering of a resistive lava cap could cause water to seep through the overflow channel elevating the potential of collapse slope stability models indicate that under certain conditions the overflow channel is below a conservative threshold of stability and can be destabilized with continued mechanical or chemical weathering that reduces strength properties this is also true during high magnitude tectonic or volcanic earthquakes where large ground accelerations could result in several centimeters of displacement at the overflow channel corresponding to high hazard categories of stability in the worst case scenario modeled here full collapse of the overflow channel could result in the release of c 2 4 million m3 of lake water this could drive a lahar substantially larger than well documented historic events including the more common lahars produced during eruptions the identification of key factors affecting stability can be used to inform future monitoring and the risk of these high impact events

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

evolution of a vent hosted hydrothermal system beneath ruapehu crater lake new zealand a two year chemical monitoring program of ruapehu crater lake shows that it has evolved considerably since the volcano s more active eruptive periods in the early 1970s the present ph 20 c of 0 6 is about one half unit more acid than the baseline values in the 1970s whereas s cl ratios have increased markedly owing in part to declining hcl inputs into the lake but also to absolute increases in so4 levels which now stand at the highest values ever recorded increases in k mg and na mg ratios over the 20 year period are attributed to hydrothermal reaction processes in the vent which are presently causing dissolution of previously formed alteration phases such as natroalunite these observations combined with results of a recent heat budget analysis of the lake have led to the development of hydrothermal convection model for the upper portion of the vent possible vent lake chemical reaction processes between end member reactants have been modelled with the computer code chiller the results are consistent with the view that variations in lake chemistry which are initiated by the introduction of fresh magmatic material into the vent reflect the extent of dissolution reaction progress on the magmatic material and or its alteration products the results also provide insights into the role of such vent processes in the formation of high sulfidation type ore deposits

pyroclastic density currents resulting from the interaction of basaltic magma with hydrothermally altered rock an example from the 2006 summit eruptions of mount etna italy after 16 months of quiescence mount etna began to erupt again in mid july 2006 the activity was concentrated at and around the southeast crater sec one of the four craters on the summit of etna and eruptive activity continued intermittently for 5 months during this period numerous vents displayed a wide range of eruptive styles at different times virtually all explosive activities took place at vents at the summit of the sec and on its flanks eruptive episodes which lasted from 1 day to 2 weeks became shorter and more violent with time volcanic activity at these vents was often accompanied by dramatic mass wasting processes such as collapse of parts of the cone highly unusual flowage processes involving both old rocks and fresh magmatic material and magma water interaction the most dramatic events took place on 16 november when numerous rockfalls and pyroclastic density currents pdcs were generated during the opening of a large fracture on the se flank of the sec cone the largest pdcs were clearly triggered explosively and there is evidence that much of the energy was generated during the interaction of intruding magma with wet rocks on the cone s flanks the most mobile pdcs traveled up to 1 km from their source this previously unknown process on etna may not be unique on this volcano and is likely to have taken place on other volcanoes it represents a newly recognized hazard to those who visit and work in the vicinity of the summit of etna

a quantitative interpretation on possible correlations between intraplate seismic activity and interplate great earthquakes along the nankai trough abstract the tonankai earthquake occurred in 1944 along the nankai trough between the continental eurasian plate and the subducting philippine sea plate we investigated spatial and temporal correlations between the occurrence of this event and intraplate seismic activities in the inland region of southwest japan in order to elucidate the possible relationship and dynamic coupling between the 1944 tonankai and the 1946 nankaido earthquakes we calculated stress changes due to the tonankai earthquake by applying a three dimensional finite element method and compared them with post seismic activity agreement between them appears quite well at a depth of 10 km indicating that stress release in an e w direction associated with the tonankai earthquake may have reduced the seismic activity in the inland region particularly the observed drastic decrease of seismicity in the wakayama region just after this event can be explained by significant decrease of compressive stresses in the e w direction extensive seismicity quiescence preceding the 1946 nankaido earthquake which occurred adjacent to the source region of the tonankai event may be related to the enhancement of n s oriented compressive stress due to accelerating northward movement of the philippine sea plate therefore in addition to the decrease of stresses in the e w direction the increase of the n s oriented compressive stresses might play an important role to yield low seismic activity just after the tonankai event the calculated results show that the post seismic shear stress increased and the normal stress decreased near the hypocentral area of the 1946 nankaido earthquakes while the shear stress decreased and normal stress increased in its surrounding area on the fault this indicates that the tonankai earthquake made it easier for the rupture of the nankaido earthquake to originate at the observed hypocenter this triggering mechanism may explain the synchronous pattern of historical great interplate earthquakes along the nankai trough a great earthquake occurs in the western region within a few years after the first breakage in the eastern block

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

explosive activity and generation mechanisms of pyroclastic flows at arenal volcano costa rica between 1987 and 2001 explosive activity at arenal and associated tephra fall that has occurred over the 14 year period from 1987 2001 is described explosions have been notably variable in both frequency and size a marked decrease in both frequency and quantity of tephra fallout occurred in early 1998 until the end of 2001 grainsize distributions of cumulative tephra samples collected once a month are typically bimodal aggregation causing premature fallout of fine ash and possibly fallout from ash plumes produced by pyroclastic flows are considered responsible for the bimodality of fallout scanning electron microscopy of the glass component of tephra from single explosions show predominantly blocky and blocky fluidal clast types interpreted as being the product of vulcanian type explosions fragmentation of a mainly rigid degassed magma body and a minor molten component is inferred for these explosions pyroclastic flows were produced either associated with the larger explosions by a mechanism of column collapse 1987 1990 or unrelated to explosions by partial collapse of the crater wall 1993 1998 2000 2001 pyroclastic flow activity has migrated from west to north during the period reported pyroclastic flow deposits are variable in the quantity of juvenile material and any associated surge component large juvenile blocks were partially molten on emplacement and many have a typical cauliform texture blocks with both juvenile and lithic textures indicate that at the summit magma was in intimate contact with the pre existing edifice rather than as a simple open crater or lava pool crater wall collapse may have been promoted by the reduction in explosive activity which has increased the lava accumulation at the summit and in turn increased instability of the summit region thus although explosive activity has waned if the lava output is maintained the hazard of pyroclastic flows is likely to continue

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 earthquakes and their relationship to eruptions at ruapehu and ngauruhoe volcanoes abstract crustal earthquakes near ruapehu and ngauruhoe fall into two classes each of which can be subdivided on the one hand there are high frequency events 3 hz with sharp well defined phases mainly concentrated beneath ruapehu crater lake low frequency events the low frequency events resemble minakami s b type and explosion earthquakes but sometimes occur where no vent exists and rather deeper than his formal definition difficulty in applying minakami s classification rigorously and the fact that low frequencies may be due to abnormal attenuation of higher frequencies along the path rather than to their suppression or absence at the source has led to reclassification of earthquakes near the volcanoes into two broad groups tectonic and volcanic the former includes all high frequency earthquakes and those discrete events in which dominant low frequencies are due to path effects the latter includes multiple and emergent events which show evidence of prolonged or repetitive source mechanism dominant low frequencies are ascribed to occurrence in heat weakened material and high frequencies to instantaneous source mechanisms operating in competent rock the term volcano tectonic describes tectonic earthquakes within some arbitrary distance of a volcano at ngauruhoe and ruapehu volcanic earthquakes accompany explosive vent clearing eruptions subsequent open vent degassing and ash emission however although often powerful and prolonged usually occurs without earthquakes such activity is however frequently accompanied by volcanic tremor at ruapehu under closed vent conditions when lake temperature is low low frequency earthquakes up to magnitude ml 3 4 have occurred without any eruption five types of phreatic eruptions are identified at ruapehu each having a distinctive seismic pattern the three most explosive types appear to be generated by a chain reaction process and all involve flashing of water to steam the first by failure of the roof with little precursory seismicity after a closed vent period during which lake temperature decreases the second after prolonged heating of the lake and much preliminary volcanic tremor interpreted as due to rising magma and the third under open vent conditions in the wake of one of the two preceding types a fourth probably occurs in wet sediments near the base of the lake as a result of upward migration of hot gas and a fifth aseismic or accompanied by very weak volcanic tremor is associated with convective overturn within crater lake

the evolution of elastic moduli with increasing crack damage during cyclic stressing of a basalt from mt etna volcano article i nfo volcanic edifices such as mt etna italy are commonly subject to repeated cycles of stress over time due to the combination of magma emplacement from deep reservoirs to shallow depths and superimposed tectonic stresses such repeated stress cycles lead to anisotropic deformation and an increase in the level of crack damage within the rocks of the edifice and hence changes to their elastic moduli which are a key parameter for reliable modelling of deformation sources we therefore report results of changes in elastic moduli measured during increasing amplitude cyclic stressing experiments on dry and water saturated samples of etna basalt in all experiments the young s modulus decreased by approximately 30 over the total sequence of loading cycles and the poisson s ratio increased by a factor of approximately 3 0 5 microseismicity in terms of acoustic emission ae output was also recorded throughout each experiment our results demonstrate that ae output only re commences during any loading cycle when the level of stress where ae ceased during the unloading portion of the previous cycle is exceeded a manifestation of the kaiser stress memory effect in cycles where no ae output was generated we also observed no change in elastic moduli this result holds for both mechanical and thermal stressing our results are interpreted in relation to measurements of volcano tectonic seismicity and deformation at mt etna volcano

instabilities in the summit region of mount etna during the 1999 eruption during the 1999 eruption of mount etna sicily the summit of the volcano changed dramatically lavas erupted from a fissure on the southern flank of se cone formed a large compound flow field that buried a substantial part of the northern wall of valle del bove and the ground between there and se cone hot mass flow deposits formed on the eastern and western flanks of the chasm following a period of intense strombolian activity at the same time a new vent opened on the southern flank of se cone and there was a major rockfall from its summit seven weeks later part of the outer western rim of bocca nuova crater collapsed during another period of intense strombolian activity and lava emerged at a high effusion rate through the breached crater wall following a subsequent collapse of the bocca nuova crater rim a hot avalanche flowed a few hundred metres on top of the previous lava flow field similar deposits have been described on other volcanoes but their importance in the evolution of the summit of etna has not previously been recognised

inconsistent sea surface temperature and salinity changing trend in the northern south china sea since 7 0 ka bp abstract the south china sea scs is an important moisture and heat source in the asian monsoon system and its environmental changes influence economic and social stability in southeast asia and east asian previous records on sea surface temperature sst and salinity sss were mostly from one sediment core and or only showed fragmentary information it is hard to provide insights into the mechanisms of the overall paleoceanographical environmental variability in the northern scs in this study paired 18o and mg ca records of planktonic foraminifer globigerinoides ruber from core s0204b nearby the luzon strait 21 13 818 n 118 3 077 water depth 1822 m and core ghe 27l 19 85 n 115 34 e water depth of 1533 m in the central northern scs were analyzed so as to better understand the physical process of the sst and sss changes in the northern scs and its relationship with the tropical pacific the results demonstrate that the sst is relatively stable and seawater 18o 18osw values a salinity proxy shows a decrease trend since 7 0 ka bp in core s0204b by contrast sst and 18osw in core ghe 27l exhibit an overall increasing trend at the same time indicating apparent regional discrepancy on the changing trend of the sst and sss in the northern scs we suggest that the thermal and hydrographic conditions in core s0204b were primarily influenced by the outer western pacific water however the thermal and hydrographic conditions in core ghe 27l may be predominantly controlled by the weakened asian monsoon during the mid late holocene which was induced by the southern migration of intertropical convergence zone itcz and stronger ei nino southern oscillation

changes in whangaehu river lahar characteristics during the 1995 eruption sequence ruapehu volcano new zealand abstract during the 1995 ruapehu eruptive sequence multiple lahars occurred in the whangaehu river which drains ruapehu s crater lake during the earlier phreatic and phreatomagmatic eruptions lahars were generated by expulsion of waters from the lake but once the lake had emptied lahars were formed by remobilisation of seasonal snowpack laden with saturated freshly erupted tephra four types of lahars occurred during the eruptive sequence 1 initial snow slurry lahars composed of granular snow and ice incorporated by eruptively expelled crater lake waters which left behind frozen deposits with 2 5 20 clastic sediment 2 large dilute lahars generated as the volumes of ejected lake water increased and removed much of the readily available snow at least one third of the pre eruption crater lake volume was expelled during one day producing the largest lahars of the series these lahars were hyperconcentrated flows for up to 84 km from source leaving extensive deposits along the channel margins 3 concentrated lahars smaller volume lahars generated as the frequency of eruptions and volumes of expelled water declined these lahars were able to maintain high sediment concentrations measured at 46 52 by volume suspended sediment at 42 km from source their high sediment concentrations were maintained by erosion and incorporation of sand from the deposits of earlier flows which were lining the channel margins 4 remobilised tephra lahars generated following the two largest tephra eruptions of the sequence seasonal snowpack was covered by water saturated tephra warmer spring temperatures and heavy rainfall events caused collapse and remobilisation of snow and tephra producing several lahars in catchments draining eastern ruapehu

small fast moving flow like landslides in volcanic deposits the 2001 las colinas landslide el salvador abstract fast moving landslides are one of the most significant dangers deriving from slope instabilities landslides involving large volumes can develop in rock or debris avalanches with extreme mobility and enormous destructiveness nevertheless a relevant number of casualties and damages derive from small fast moving landslides with flow like behaviour the las colinas landslide occurred at santa tecla el salvador central america during a strong earthquake it slid off the northern flank of the balsamo ridge and resulted in almost 500 casualties and can be considered one of the most destructive landslides ever known earthquake shaking was amplified by the rock mass and the steep ridge topography we collected original geological geomorphological and geophysical data in the cordillera del balsamo area the involved materials ranging from lapilli to tuff layers of different strength have been mapped and characterized slope stability analyses have been performed both under static and dynamic conditions through limit equilibrium and finite element methods hazard zonation for this type of landslides requires the forecast of the movement velocity and final deposition area we used a fully two dimensional fem model to simulate landslide spreading downslope the developed code allows the use of different constitutive models and yield rules with the possibility to model and study internal deformation of the landslide mass as well material entrainment and deposition

geomechanical characterization of the volcaniclastic material involved in the 2002 landslides at stromboli during the 2002 eruption the nw flank of stromboli volcano southern italy experienced large landslides that produced tsunami waves with a maximum runup of 10 m in height this paper focuses on the geomechanical behavior of the loose volcaniclastic layers the weakest component of the deposit forming the volcano flank tests on the coarse grained volcaniclastic soil and on the rock material forming the grains were conducted in dry conditions a feature of the subaerial slope the rock material in spite of its high porosity exhibits relatively high stiffness and strength due to the remarkable continuity of the solid skeleton accordingly the volcaniclastic soil is characterized by high shear strength during shear tests however significant grain crushing occurs which partly explains the nonlinear shear strength envelope and the strain softening associated with contractive behavior grain crushing was also found to affect compressibility and its time dependency investigated under oedometric conditions

lahars of ruapehu volcano new zealand risk mitigation a dam break lahar resulting from the last eruption of ruapehu is expected when crater lake reaches a critical high level probably within the next 1 5 summers a high level of public consultation political decision making and ongoing scientific input has occurred to address the risks decisions about managing lahar risk have taken into account the fact that lahars are common on the active ruapehu volcano 2797 m and in valleys draining the mountain and that most lahars are generated by eruptions about half of which have no useful precursors lahars threaten new zealand s largest ski area and nationally important infrastructure public safety has been the main consideration but the need for long term risk mitigation and reducing impacts on tongariro national park world heritage area have also been important lahar mitigation on ruapehu now includes six lahar warning systems each with active response plans and some infrastructure isolated from or hardened against lahars

national seismic hazard model for new zealand 2010 update a team of earthquake geologists seismologists and engineering seis mologists has collectively produced an update of the national probabilistic seismic hazard psh model for new zealand national seismic hazard model or nshm the new nshm supersedes the earlier nshm published in 2002 and used as the hazard basis for the new zealand loadings standard and numerous other end user applica tions the new nshm incorporates a fault source model that has been updated with over 200 new onshore and offshore fault sources and utilizes new new zealand based and international scaling relationships for the parameterization of the faults the dis tributed seismicity model has also been updated to include post 1997 seismicity data a new seismicity regionalization and improved methodology for calculation of the seismicity parameters probabilistic seismic hazard maps produced from the new nshm show a similar pattern of hazard to the earlier model at the national scale but there are some significant reductions and increases in hazard at the regional scale the national scale differences between the new and earlier nshm appear less than those seen between much earlier national models indicating that some degree of consis tency has been achieved in the national scale pattern of hazard estimates at least for return periods of 475 years and greater online material table of fault source parameters for the 2010 national seismic hazard model