volcanic edifice slip events recorded on the fault plane of the san andres landslide el hierro canary islands abstract volcanic flank collapses often result in giant debris avalanches that are capable of travelling tens of kilometres across the ocean floor and generating tsunamis that devastate distant communities the san andres landslide on el hierro canary islands represents one of the few places in the world where it is possible to investigate the landslide mass and fault planes of a volcanic collapse structure in this study a new conceptual model for the development of this enormous slump is presented on the basis of structural geological and geomorphological measurements petrological and microstructural analyses and cosmogenic radionuclide dating structural geological and geomorphological measurements indicate that the fault plane records two distinct events petrological and microstructural analyses demonstrate that a thin layer of frictionite covers the surface of the fault in contact with an oxidised tectonic breccia that transitions into the underlying undeformed basanite host rock this frictionite comprises a heterogeneous cataclastic layer and a translucent silica layer that are interpreted to represent two separate slip events on the basis of their architecture and crosscutting relationships cosmogenic 3he dating reveals a maximum exposure age of 183 17 ka to 52 17 ka arguments are presented in support of the idea that the first slip event took place between 545 ka and 430 ka prior to significant clockwise rotation of el hierro and the second slip event took place between 183 ka and 52 ka perhaps in association with one of the giant debris avalanches that occurred around that time this is the first time that more than one slip event has been recognised from the fault plane of the san andres landslide it is also believed to be the first time a silica layer resulting from frictional melt has been described in a volcanic setting

oceanic propagation of a potential tsunami from the la palma island 1 the likelihood of a large scale tsunami from the la palma island is considered small by most nevertheless the potential catastrophic consequences call for attention here we report on numerical simulations of a tsunami that might result from the extreme case of a flank collapse of the cumbre vieja volcano at the la palma island done by combining a multimaterial model for the wave generation with boussinesq models for the far field propagation our simulations show that the slide speed is close to critical effectively generating an initial wave of several hundred meters height our main focus is the wave propagation which is genuinely dispersive in the far field propagation becomes increasingly complex due to the combined effects of dispersion refraction and interference in the direction of propagation constructive interference of the trailing waves are found to decrease the decay of the maximum amplitude with distance compared to classical asymptotic theory at transatlantic distances thus the commonly used hydrostatic models fail to describe the propagation consequences of the la palma scenario would be largest at the canary islands but our findings also suggests that the whole central atlantic would face grave consequences however the largest surface elevations are smaller than the most pessimistic reports found in literature we also find undular bores towards the shorelines of america

insights into the emplacement dynamics of volcanic landslides from high resolution 3d seismic data acquired offshore montserrat lesser antilles we present results from the first three dimensional 3d marine seismic dataset ever collected over volcanic landslide deposits acquired offshore of the soufriere hills volcano on the island of montserrat in the lesser antilles the 3d data enable detailed analysis of various features in and around these mass wasting deposits such as surface deformation fabrics the distribution and size of transported blocks change of emplacement direction and erosion into seafloor strata deformational features preserved on the surface of the most recent debris avalanche deposit deposit 1 reveal evidence for spatially variant deceleration as the mass failure came to rest on the seafloor block distributions suggest that the failure spread out very rapidly with no tendency to develop longitudinal ridges an older volcanic flank collapse deposit deposit 2 appears to be intrinsically related to large scale secondary failure of seafloor sediments we observe pronounced erosion directly down slope of a prominent headwall where translational sliding of well stratified sediments was initiated deep reaching faults controlled the form and location of the headwall and stratigraphic relationships suggest that sliding was concurrent with volcanic flank collapse emplacement we also identified a very different mass wasting unit between deposit 1 and deposit 2 that was likely emplaced as a series of particle laden mass flows derived from pyroclastic flows much like the recent since 1995 phase of deposition offshore montserrat but at a much larger scale this study highlights the power of 3d seismic data in understanding landslide emplacement processes offshore of volcanic islands highlights 3d seismic data show new detail of volcanic landslide deposits offshore montserrat volcanic flank collapse material has been diverted around seafloor topographic highs this bending during emplacement has caused pronounced erosion into seafloor strata erosion can destabilize seafloor slopes which then fail as translational slides block distributions and surface deformation give insight into debris avalanche style

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

possible tornado like tracks on mars distinct atmospheric conditions suggest that dark ephemeral filamentary lineations on the martian surface may be formed during the passage of intense atmospheric vortices

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

multiple related flank collapses on volcanic oceanic islands evidence from the debris avalanche deposits in the orotava valley water galleries tenerife canary islands abstract catastrophic flank collapses are common on oceanic islands of volcanic origin and often recognizable from the resulting morphology as large u shaped embayments however post collapse volcanic activity can infill such features thereby obscuring them this study takes advantage of a dense network of long sub horizontal galleries for groundwater extraction in the flank collapse structure of the orotava valley tenerife canary islands this impressive landform is located in the overlapping zone of the ne rift and the canadas edifice of this volcanic island three debris avalanche deposits dads have been identified inside the waterworks bored into the valley s western sector the deeper layer the lower dad l dad was previously described under the local name of mortalon this deposit lies unconformably over older volcanic rocks where a prominent shear zone is developed here interpreted as the detachment plane of a massive rockslide the l dad was therefore produced during the large failure event the orotava landslide ol which carved the depression two younger dads much smaller in volume and not previously described were also identified in the underground strata the intermediate i dad and upper dad u dad both correlate well with the thick breccia deposits cropping out at the base of the marine cliff along the western coast of the valley the i dad and u dad are conformably intercalated between the lava flows and other volcanics infilling the depression and their bases are erosive depositional features without structural deformation zones below them their stratigraphic setting and geometrical reconstruction indicate that both deposits were emplaced after the valley was formed by the ol event in two successive failures here called western orotava landslides wols the younger called wol 2 was dated at 494 22 ka using the 40ar 39ar method these two subaerial failures affected the upper eastern flank of the canadas iii edifice previously destabilized when the ol failure event carved a steep wall at its foot the western lateral escarpment of the orotava valley

combining 3d seismics eyewitness accounts and numerical simulations to reconstruct the 1888 ritter island sector collapse and tsunami the 1888 ritter island volcanic sector collapse triggered a regionally damaging tsunami historic eyewitness accounts allow the reconstruction of the arrival time phase and height of the tsunami wave at multiple locations around the coast of new guinea and new britain 3d seismic interpretations and sedimentological analyses indicate that the catastrophic collapse of ritter island was preceded by a phase of deep seated gradual spreading within the volcanic edifice and accompanied by a submarine explosive eruption as the volcanic conduit was cut beneath sea level however the potential impact of the deep seated deformation and the explosive eruption on tsunami genesis is unclear for the first time it is possible to parameterise the different components of the ritter island collapse with 3d seismic data and thereby test their relative contributions to the tsunami the modelled tsunami arrival times and heights are in good agreement with the historic eyewitness accounts our simulations reveal that the tsunami was primarily controlled by the displacement of the water column by the collapsing cone at the subaerial submarine boundary and that the submerged fraction of the slide mass and its mobility had only a minor effect on tsunami genesis this indicates that the total slide volume when incorporating the deep seated deforming mass is not directly scalable for the resulting tsunami height furthermore the simulations show that the tsunamigenic impact of the explosive eruption energy during the ritter island collapse was only minor however this relationship may be different for other volcanogenic tsunami events with smaller slide volumes or larger magnitude eruptions and should not be neglected in tsunami simulations and hazard assessment

mesoscale linear streaks on mars environments of dust entrainment abstract variable surface albedo features on mars are likely caused by the entrainment and deposition of dust by the wind most discrete markings are associated with topographic forms or with regional slopes that serve to alter the effective wind shear stress on the surface some of the largest variable features here termed mesoscale linear streaks are up to 400 km in length and repeatedly occur in one of the smoothest regions of mars amazonis planitia their orientations and apparent season of variability as observed by viking and mars orbiter cameras indicate linear streak formation by enhanced surface wind stresses during regional or local dust storms and during the initial stages of global dust storms they provide an example of the ability of large scale winds without significant local enhancement to initiate dust motion on mars the sizes and spacing of the linear streaks may be controlled by boundary layer rolls the repetitive formation of these streaks over a span of more than 11 mars years gives one measure of the stability of mars eolian processes

mass movement slope streaks imaged by the mars orbiter camera narrow fan shaped dark streaks on steep martian slopes were originally observed in viking orbiter images but a definitive explanation was not possible because of resolution limitations pictures acquired by the mars orbiter camera moc aboard the mars global surveyor mgs spacecraft show innumerable examples of dark slope streaks distributed widely but not uniformly across the brighter equatorial regions as well as individual details of these features that were not visible in viking orbiter data dark slope streaks as well as much rarer bright slope streaks represent one of the most widespread and easily recognized styles of mass movement currently affecting the martian surface new dark streaks have formed since viking and even during the mgs mission confirming earlier suppositions that higher contrast dark streaks are younger and fade brighten with time the darkest slope streaks represent 10 contrast with surrounding slope materials no small outcrops supplying dark material or bright material for bright streaks have been found at streak apexes digitate downslope ends indicate slope streak formation involves a ground hugging flow subject to deflection by minor topographic obstacles the model we favor explains most dark slope streaks as scars from dust avalanches following oversteepening of air fall deposits this process is analogous to terrestrial avalanches of oversteepened dry loose snow which produce shallow avalanche scars with similar morphologies low angles of internal friction typically 10 30i for terrestrial loess and clay materials suggest that mass movement of low cohesion martian dusty air fall is possible on a wide range of gradients martian gravity presumed low density of the air fall deposits and thin unresolved by moc failed layer depths imply extremely low cohesive strength at time of failure consistent with expectations for an air fall deposit of dust particles as speed increases during a dust avalanche a growing fraction of the avalanching dust particles acquires sufficient kinetic energy to be lost to the atmosphere in suspension limiting the momentum of the descending avalanche front the equilibrium speed where rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front descends decreases with decreasing gradient this mechanism explains observations from moc images indicating slope streaks formed with little reserve kinetic energy for run outs on to valley floors and explains why large distal deposits of displaced material are not found at downslope streak ends the mass movement process of dark and bright slope streak formation through dust avalanches involves renewable sources of dust only leaving underlying slope materials unaffected areas where dark and bright slope streaks currently form and fade in cycles are closely correlated with low thermal inertia and probably represent regions where dust currently is accumulating not just residing

the evolution of volcanic systems following sector collapse abstract sector collapses affect volcanic edifices across all tectonic settings and involve a rapid redistribution of mass comparable in scale to the largest magmatic eruptions the eruptive behaviour of a volcano following sector collapse provides a test of theoretical relationships between surface loading and magma storage which imply that collapse driven unloading may lead to changes in eruption rate and erupted magma compositions large sector collapses are infrequent events globally with all historical examples being relatively small in comparison to many of the events documented in the geological record as a result exploration of the impacts of sector collapse on eruptive behaviour requires detailed investigation of prehistoric collapses but this is often hindered by poorly resolved stratigraphic relationships and dating uncertainties nevertheless observations from a number of volcanoes indicate sharp changes in activity following sector collapse here a global synthesis of studies from individual volcanoes in both arc and intraplate settings is used to demonstrate a number of common processes in post collapse volcanism multiple examples from large 5 km3 sector collapses in arc settings show that collapse may be followed by compositionally anomalous large volume and often effusive eruptions interpreted to originate via disruption of a previously stable upper crustal reservoir these anomalous eruptions highlight that magma compositions erupted during periods of typical i e unperturbed by sector collapse volcanism may not be representative of the range of compositions stored within a vertically extensive crustal reservoir if eruptible magma is not present upper crustal reservoirs may rapidly solidify following collapse without further eruption allowing more mafic compositions to ascend to the surface with only limited upper crustal modification resulting in edifice regrowth at temporarily elevated eruption rates subsequent re establishment of an upper crustal reservoir further supports a relationship between surface loading and crustal storage but long term chemical and mineralogical differences between pre and post collapse evolved magmas imply that a newly developed reservoir can overprint the influence of a preceding reservoir forming a spatially and compositionally distinct plumbing system these broad patterns are replicated in intraplate settings despite differences in scale and melting processes current evidence suggests that post collapse evolution of intraplate volcanoes can be explained by unloading induced destabilisation of the magma plumbing system rather than increased melt production what emerges from an apparently diverse set of observations is a systematic behaviour that strongly supports a coupling between edifice growth and magma ascent storage and pressurisation eruption rates erupted compositions and the style of volcanism at any particular system may thus be modulated from the surface and long term shifts in surface behaviour may occur without any changes in the deep parts of magmatic systems observations of sharp post collapse changes in erupted compositions including the ascent of primitive mafic magmas also require a crystal dominated mid to upper crustal reservoir consistent with recent models of crustal magmatic systems

thermal inertia of crater related wind streaks on mars data from the thermal emission spectrometer tes on board the mars global surveyor spacecraft are used to analyze the structure of and materials comprising crater related wind streaks comparisons of high resolution tes albedo and tes based thermal inertia values within and adjacent to the streaks allow us to constrain the properties of the streaks and gain insight into their physical structure the majority of the analyzed type i bright depositional streaks are distinct from the surrounding terrain in albedo but not in thermal inertia we conclude that these streaks consist of thin deposits of bright material greater than 1 pm thick but less than 1 3 mm thick the majority of the analyzed type i dark erosional streaks identified from viking images are now indistinct from the surrounding terrain in both albedo and thermal inertia we conclude that these streaks have been covered by a thin deposit of bright material greater than 1 m thick but less than 1 3 mm thick all of the analyzed type ii dark depositional streaks are distinct from the surrounding terrain in both albedo and thermal inertia we conclude that these streaks consist of deposits greater than a few centimeters thick in this case we were also able to use the thermal inertia values to estimate the particle sizes of the deposited material the values correspond to a broad range of sand sized particles easily mobilized by wind supporting the deflation deposition theory of type ii streak formation

elysium planitia lava flows crater count chronology and geological implications mars global surveyor mgs and viking images allow analysis of chronological and geological relations among lava flows in southern elysium planitia based on crater populations mgs and viking images clearly show morphological features of lava flows with some extremely sparsely cratered young flow units atop somewhat older surfaces there is no evidence of substantial dust mantling on the young flows and hence we infer that the crater populations date not sediment accumulation but the lava flows themselves the youngest flows have some of the lowest crater densities that we have seen on mars some 1 of lunar mare values at crater diameters below about 180 to 500 m we infer that thin scattered volcanic flows some tens of meters thick have been emplaced atop stratigraphic units within the last 100 myr and possibly within the last 10 myr volcanism is thus a continuing process in the recent geologic history of mars and this must constrain geophysical models of the planet

combinations of volcanic flank and seafloor sediment failure offshore montserrat and their implications for tsunami generation recent seafloor mapping around volcanic islands shows that submarine landslide deposits are common and widespread such landslides may cause devastating tsunamis but accurate assessment of tsunami hazard relies on understanding failure processes and sources here we use high resolution geophysical data offshore from montserrat in the lesser antilles to show that landslides around volcanic islands may involve two fundamentally different sources of sediment island flank and larger seafloor sediment failures and can occur in multiple stages a combination of these processes produces elongate deposits with a blocky centre associated with island flank collapse surrounded by a smoother surfaced deposit that is dominated by failed seafloor sediment the failure of seafloor sediment is associated with little marginal accumulation and involves only limited downslope motion submarine landslide deposits with similar blocky and smooth surfaced associations are observed in several locations worldwide but the complex emplacement processes implied by this morphological relationship can only be revealed by high resolution geophysical data such complexity shows that the volume of landslide deposits offshore of volcanic islands cannot simply be used in tsunami models to reflect a single stage collapse of primary volcanic material by applying predictive equations for tsunami amplitude to investigate general scenarios of volcanic island landslide generation we show that the tsunami hazard associated with volcanic island collapse remains highly significant volcanic flank failures even if relatively small may generate large local tsunamis but associated seafloor sediment failures even if they have a much greater volume have a substantially lower potential for tsunami generation

ritter island volcano lateral collapse and the tsunami of 1888 summary in the early morning of 1888 march 13 roughly 5 km 3 of ritter island volcano fell violently into the sea northeast of new guinea this event the largest lateral collapse of an island volcano to be recorded in historical time flung devastating tsunami tens of metres high on to adjacent shores several hundred kilometres away observers on new guinea chronicled 3 min period waves up to 8 m high that lasted for as long as 3 h these accounts represent the best available first hand information on tsunami generated by a major volcano lateral collapse in this article we simulate the ritter island landslide as constrained by a 1985 sonar survey of its debris field and compare predicted tsunami with historical observations the best agreement occurs for landslides travelling at 40 m s 1 but velocities up to 80 m s 1 cannot be excluded the ritter island debris dropped little more than 800 m vertically and moved slowly compared with landslides that descend into deeper water basal friction block models predict that slides with shorter falls should attain lower peak velocities and that 40 ms 1 is perfectly compatible with the geometry and runout extent of the ritter island landslide the consensus between theory and observation for the ritter island waves increases our confidence in the existence of mega tsunami produced by oceanic volcano collapses two to three orders of magnitude larger in scale

new views of mars eolian activity materials and surface properties three vignettes from the mars global surveyor mars orbiter camera prior to the mars global surveyor mgs mission a very general view had emerged in which martian surface materials were seen as consisting of a mixture of bright dust dark sand and rocks the configuration of these materials and the winds that transport and deposit sand and dust have been thought to be directly linked to the albedo patterns that have been observed on mars for centuries high spatial resolution images 1 4 20 m pixel obtained by the mgs mars orbiter camera moc between september 15 1997 and july 4 1999 provide new information about the physical nature of the windblown material on the martian surface and show that the pre mgs view was much too simple in addition to bright dust and dark sand moc images show evidence of bright sediment that can be transported by saltation e g sand and dark material that can be transported in suspension e g silt new views of eolian wind streaks in daedalia planum show that part of this region thought to be mantled by bright dust based upon viking and mariner observations is instead covered by a thin veneer of bright windblown sand moc images of sinus sabaeus and parts of syrtis major two regions thought to be sandy based upon viking era observations exhibit thick mantles that are inferred to consist of fine grained sediment deposited from eolian suspension low albedo wind streaks in western arabia terra are also dark mantles and their association with eroded crater floors and megaripples dunes on these floors suggest that these particular wind streaks are deposits of silt sized material that was only briefly suspended before settling to the surface moc images also show evidence that some eolian dunes are active on mars today i e in 1998 and 1999 the evidence for activity is largely based upon wind and avalanche induced streaks superposed on or eroded into seasonal frost on high latitude dune fields moc images show that some other dunes are inactive but the albedo of dunes relative to surrounding terrain is not a good indicator of dune activity because some inactive dunes are not mantled by dust inactive dunes are best identified by superposed features such as impact craters landslide deposits and yardangs

the influence of edifice slope and substrata on volcano spreading gravitational volcano spreading is caused by flow of weak substrata due to volcanic loading and is now a process known to affect many edifices the process produces extension in the upper edifice evidenced by graben and normal faults and compression at the base seen in strike slip faults and thrusts where spreading is identified host volcanoes have a range of fault densities variable rift and graben shapes and different degrees of structural asymmetry previous studies have suggested a link between edifice shape and structure and the proportion of brittle to ductile material in the substrata or lower edifice we study this link using refined sand cone analogue models standing on a brittle ductile sand silicone substrata two scenarios have been investigated the first mainly represents oceanic volcanoes with a ductile layer within the edifice type i where there is an outer ductile free surface the second represents most continental volcanoes that have ductile substrata type ii we apply the model results to natural examples and develop quantitative relationships between slope brittle ductile ratio fault density spreading rate and structural style displacement fields calculated from stereophotogrammetry show significant differences between different slope models we find that more faults are produced when the cone is initially steeper or when the brittle substratum is thinner however the effect of the brittle layer dominates over that of slope the strike slip movements are found to be an essential feature in the spreading mechanism and the graben are in fact transtensional features strike slip and graben faults make a conjugate flower pattern the structures produced are well organised for type ii edifices but they are poorly organised for type i models type i models represent good analogues for oceanic volcanoes that are commonly affected by large slumps bounded by an extensional zone and lack of well formed sector graben the well observed connection between oceanic volcano rifts and large landslide slumps is confirmed to be a consequence of spreading

wind streaks on mars meteorological control of occurence and mode of formation abstract why do some craters on mars produce depositional wind streaks while others produce erosional ones there is no evidence to suggest that crater morphology or topography plays the determining role some craters can form either type of streak at different times of the martian year suggesting that the controlling factor is meteorological we propose that atmospheric stability is the determining factor a stable atmosphere should lead to blocking of the wind flow by crater rims producing wind shadows over distances comparable to those of observed bright streaks such conditions should prevail in a belt about the equator at the time of major dust storms as the atmosphere becomes more transparent following the end of the dust storms the rate of surface heating increases and the stability of the atmosphere is reduced under such conditions blocking is not expected flow over obstacles results in increased surface stress downwind conditions which encourage the formation of erosional dark streaks these ideas are shown to be consistent with the seasons at which erosional and depositional streaks are formed as well as with their distribution on the planet specifically the scheme explains why craters which have both erosional and depositional streaks occur only within a very restricted latitude belt

large scale volcanic cone collapse the 1888 slope failure of ritter volcano and other examples from papua new guinea a largely submarine avalanche amphitheatre that formed catastrophically in 1888 on ritter volcano has been identified from a bathymetric survey collapse of the volcano in 1888 therefore is considered to have been caused by rapid large scale slope failure rather than by cauldron subsidence as previously supposed escarpments of pre historic slope failures are common on other papua new guinea volcanoes directions of avalanching on some volcanoes in the bismarck volcanic arc appear to be controlled by a regional stress pattern and those for some volcanoes in the fly highlands province on mainland papua new guinea point away from the regional centre of pliocene uplift large amphitheatres such as at doma peaks in the fly high lands province probably originated by multiple collapses

pacific basin tsunami hazards associated with mass flows in the aleutian arc of alaska abstract we analyze mass flow tsunami generation for selected areas within the aleutian arc of alaska using results from numerical simulation of hypothetical but plausible mass flow sources such as submarine landslides and volcanic debris avalanches the aleutian arc consists of a chain of volcanic mountains volcanic islands and submarine canyons surrounded by a low relief continental shelf above about 1000 2000 m water depth parts of the arc are fragmented into a series of fault bounded blocks tens to hundreds of kilometers in length and separated from one another by distinctive fault controlled canyons that are roughly normal to the arc axis the canyons are natural regions for the accumulation and conveyance of sediment derived from glacial and volcanic processes the volcanic islands in the region include a number of historically active volcanoes and some possess geological evidence for large scale sector collapse into the sea large scale mass flow deposits have not been mapped on the seafloor south of the aleutian islands in part because most of the area has never been examined at the resolution required to identify such features and in part because of the complex nature of erosional and depositional processes extensive submarine landslide deposits and debris flows are known on the north side of the arc and are common in similar settings elsewhere and thus they likely exist on the trench slope south of the aleutian islands because the aleutian arc is surrounded by deep open ocean mass flows of unconsolidated debris that originate either as submarine landslides or as volcanic debris avalanches entering the sea may be potential tsunami sources to test this hypothesis we present a series of numerical simulations of submarine mass flow initiated tsunamis from eight different source areas we consider four submarine mass flows originating in submarine canyons and four flows that evolve from submarine landslides on the trench slope the flows have lengths that range from 40 to 80 km maximum thicknesses of 400 800 m and maximum widths of 10 40 km we also evaluate tsunami generation by volcanic debris avalanches associated with flank collapse at four locations makushin cleveland seguam and yunaska sw volcanoes which represent large to moderate sized events in this region we calculate tsunami sources using the numerical model topics and simulate wave propagation across the pacific using a spherical boussinesq model which is a modified version of the public domain code funwave our numerical simulations indicate that geologically plausible mass flows originating in the north pacific near the aleutian islands can indeed generate large local tsunamis as well as large transoceanic tsunamis these waves may be several meters in elevation at distal locations such as japan hawaii and along the north and south american coastlines where they would constitute significant hazards

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

tectonics of the new guinea region the new guinea region evolved within the obliquely and rapidly converging australian and pacific plate boundary zone it is arguably one of the most tectonically complex regions of the world and its geodynamic evolution involved microplate formation and rotation lithospheric rupture to form ocean basins arc continent collision subduction polarity reversal collisional orogenesis ophiolite obduction and exhumation of ultra high pressure metamorphic rocks we describe the major onshore and offshore tectonic and geologic components including plate boundaries seismicity faults and magmatism and we integrate these with emerging ideas about mantle dynamics to evaluate the cenozoic tectonic evolution of new guinea future research opportunities to resolve the mantle structure beneath new guinea will enable mantle dynamics to be linked to lithospheric and surface processes virtually all plate tectonic and mantle processes have been active in the new guinea region throughout the cenozoic and as such

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

substrate deformation associated with the jocotitlan edifice collapse and debris avalanche deposit central mexico abstract an impressive debris avalanche deposit is preserved at jocotitlan volcano in central mexico the northern flank of this edifice collapsed 9690 years b p resulting in a 80 km 2 covering clast supported deposit that lacks substantial matrix fine weak or hydrothermally altered materials the deposit can be subdivided into three morphologically distinct areas which are each accompanied by specific and often unique deformation features in the underlying and adjacent volcaniclastic and lacustrine sediments from these features a complex history of pre and syn avalanche events was reconstructed beginning with edifice spreading on the weak substrate material prior to and in preparation of part of the flank collapse event the north eastern flank in particular was strongly coupled with the deforming substrate material as is still evident in its extensional profile and the unique mode of failure during the catastrophic event resulting in the deposition of what resembles non volcanic blockslide deposits rather than the typical hummocky volcanic debris avalanche morphology this latter type of failure occurred at the north western flank of jocotitlan volcano where few signs of substrate interactions are preserved in a deposit dominated by large conical hummocks in addition to substrate response interaction with pre avalanche topography in the eastern deposit area facilitated the emplacement of a lobe roughly perpendicular to the flank failure direction at apparent high emplacement velocity and with longitudinal ridges as its most striking surface expression

volcano collapse and tsunami generation in the bismarck volcanic arc papua new guinea during a cruise on the r v kilo moana in 2004 we mapped 12 debris avalanches from volcanoes in the bismarck volcanic arc estimated their sizes and computed the size of potential tsunami run up in major local population centers from these features we used the towed side scan instrument hawaii mr1 the hull mounted em120 system for swath bathymetry and backscatter intensity a shallow penetration chirp system several bottom camera tows and selected cores we calibrate our computations with the known tsunami run up of the ritter collapse even the small collapses may have had significant run up on near by coastlines had any of the collapses we have identified occurred in modern times each would affect a presently populated region of the coastline to a moderate or significant degree

submarine landslide deposits of the historical lateral collapse of ritter island papua new guinea abstract the march 13th 1888 collapse of ritter island in papua new guinea is the largest known sector collapse of an island volcano in historical times one single event removed most of the island and its western submarine flank and produced a landslide deposit that extends at least 70 km from the headwall of the collapse scar we have mapped and described the deposits of the debris avalanche left by the collapse using full coverage multibeam bathymetry side scan sonar backscatter intensity mapping chirp seismic reflection profiles towcam photographs of the seafloor and samples from a single dredge applying concepts originally developed on the 1980 mount st helens collapse landslide deposits we find that the ritter landslide deposits show three distinct morphological facies large block debris avalanche matrix rich debris avalanche and distal debris flow facies restoring the island s land and submarine topography we obtained a volume of 4 2 km3 for the initial collapse about 75 of which is now forming the large block facies at distances less than 12 km from the collapse scar the matrix rich facies volume is unknown but large scale erosion of the marine sediment substrate yielded a minimum total volume of 6 4 km3 in the distal debris flow and or turbidite deposits highlighting the efficiency of substrate erosion during the later history of the landslide movement although studying submarine landslide deposits we can never have the same confidence that subaerial observations provide our analysis shows that well exposed submarine landslide deposits can be interpreted in a similar way to subaerial volcano collapse deposits and that they can in turn be used to interpret older incompletely exposed submarine landslide deposits studying the deposits from a facies perspective provides the basis for reconstructing the kinematics of a collapse event landslide understanding the mechanisms involved in its movement and deposition and so providing key inputs to tsunami models

aeolian behavior of dust in a simulated martian environment the behavior of aeolian dust particles 1 2 microns m in diameter was analyzed in a simulated martian environment three main areas have been investigated 1 characterizing spectral and aeolian properties of martian particles and natural wind blown terrestrial dust in order to identify a suitable surrogate martian dust 2 emplacement of the material in the simulated martian environment and 3 experimental procedures and testing in the martian surface wind tunnel marswit the first phase of the study involved choosing a terrestrial dust that closely resembled martian dust data accumulated from various sources suggest that martian dust is derived from the weathering of basaltic parent material nontronite clay being a good candidate composition a commercial clay carbondale red clay crc was determined to be an appropriate surrogate martian dust using a compressed air dust ejection system an air entrained dust cloud was generated which settled to cover the test section in the marswit this method best replicated the natural acrodynamic settling process presumed to exist on mars low pressure experiments were performed in the marswit facility located at the nasa ames research center moffett field california two separate wind tunnel floors were used for these experiments one provided an aerodynamically smooth surface flow and the other was an aerodynamically rough surface flow initial and momentary particle movement was recorded at friction velocities as low as 2 m s however the dust never reached fluid saltation threshold because individual particles less than 10 m typically do not saltate but pass into suspension an estimated dust flux of 3 7 x 10 7 g cm 2 s was determined for a friction velocity of 2 m s this flux could suspend about 10 000 metric tons of dust per second over the surface of mars the dust behavior on the smooth surface was markedly different than on the rough surface under martian conditions application of the processes described above to the martian environment suggests that on rocky surfaces dust suspension would first occur whereas smooth plains would require higher wind speeds for dust entrainment

low albedo surfaces and eolian sediment mars orbiter camera views of western arabia terra craters and wind streaks 1 high spatial resolution 1 5 to 6 m pixel mars global surveyor mars orbiter camera images obtained september 1997 to june 2001 show that each of the large dark wind streaks of western arabia terra originate at a barchan dune field on a crater floor the streaks consist of a relatively thin 1 m coating of sediment deflated from the dune fields and their vicinity in most cases this sediment drapes over a previous mantle that more thickly covers nearly all of western arabia terra no concurrent eolian bedforms are found within the dark streaks nor do any dunes climb up crater walls to deliver sand via saltation to the streaks the relations between dunes wind streak and subjacent terrain imply that dark toned grains finer than those that comprise the dunes are lifted into suspension and carried out of the craters to be deposited on the adjacent terrain previous eolian physics and thermal inertia studies suggest that under modern martian conditions such grains likely include silt 3 9 62 5 m very fine sand 62 5 125 m and possibly fine sand to 210 m the streaks change in terms of extent relative albedo and surface pattern over periods measured in years however through june 2001 very little evidence for recent eolian activity dust plumes storms dune movement was observed

mars orbiter camera geodesy campaign during the geodesy campaign in may and june 1999 the wide angle system of the mars global surveyor mars orbiter camera imaged the visible surface of mars from latitudes 70 s to 90 n over 90 of this portion of the planet was covered at two viewing angles to obtain side looking stereo at a resolution of 250 m pixel and convergence angles of 21 27 continuous radiometric spacecraft tracking during this period provided precise orbit determination of spacecraft location this data set will become the basis of a new image mosaic of mars with the potential to exceed the geodetic precision and image quality of those presently available

from gradual spreading to catastrophic collapse reconstruction of the 1888 ritter island volcanic sector collapse from high resolution 3d seismic data abstract volcanic island flank collapses have the potential to trigger devastating tsunamis threatening coastal communities and infrastructure the 1888 sector collapse of ritter island papua new guinea in the following called ritter is the most voluminous volcanic island flank collapse in historic times the associated tsunami had run up heights of more than 20 m on the neighboring islands and reached settlements 600 km away from its source this event provides an opportunity to advance our understanding of volcanic landslide tsunami hazards here we present a detailed reconstruction of the 1888 ritter sector collapse based on high resolution 2d and 3d seismic and bathymetric data covering the failed volcanic edifice and the associated mass movement deposits the 3d seismic data reveal that the catastrophic collapse of ritter occurred in two phases 1 ritter was first affected by deep seated gradual spreading over a long time period which is manifest in pronounced compressional deformation within the volcanic edifice and the adjacent seafloor sediments a scoria cone at the foot of ritter acted as a buttress influencing the displacement and deformation of the western flank of the volcano and causing shearing within the volcanic edifice 2 during the final catastrophic phase of the collapse about 2 4 km3 of ritter disintegrated almost entirely and traveled as a highly energetic mass flow which incised the underlying sediment the irregular topography west of ritter is a product of both compressional deformation and erosion a crater like depression underlying the recent volcanic cone and eyewitness accounts suggest that an explosion may have accompanied the catastrophic collapse our findings demonstrate that volcanic sector collapses may transform from slow gravitational deformation to catastrophic collapse understanding the processes involved in such a transformation is crucial for assessing the hazard potential of other volcanoes with slowly deforming flanks such as mt etna or kilauea

a gravitational spreading origin for the socompa debris avalanche abstract socompa volcano arguably provides the world s best exposed example of a sector collapse derived debris avalanche deposit new observations lead us to re interpret the origin of the sector collapse we show that it was triggered by failure of active thrust anticlines in sediments and ignimbrites underlying the volcano the thrust anticlines were a result of gravitational spreading of substrata under the volcano load about 80 of the resulting avalanche deposit is composed of substrata formerly residing under the volcano and in the anticlines the collapse scar can be traced up to 5 km from the edifice truncating two spreading related anticlines which collapsed in the event outcrops near the volcano preserve evidence of edifice material being carried along on top of mobilised substrata on the north side of the scar the avalanche motion was initially at right angles to the failure edge structural relations indicate that immediately prior to collapse the substrata disintegrated became effectively liquidised and were ejected from beneath the edifice catastrophic mobilisation of substrata probably resulted from breakdown of ignimbrite clasts and cement it may have occurred through progressive rock fracture by high shear strain during spreading material ejected from under socompa formed a layer on which volcanic edifice debris was transported this interpretation of events explains the puzzling observation that avalanche units with the lowest gravitational potential energy moved the furthest it can also account for avalanche motion normal to the collapse scar walls ignimbrites and other rock types probably capable of similar behaviour underlie many other volcanoes identification of spreading at other sites could therefore be a first step towards assessment of the potential for this style of catastrophic sector collapse

a parametric study of tsunamis generated by submarine slides in the ormen lange storegga area off western norway tsunami generation by submarine slides have been a major concern in the risk assessment for the ormen lange gas field off western norway tsunamis are analysed with a numerical model supplemented by an analytical one both models show how slide extensions and slide dynamics influence the tsunamigenic potential for a large region several combinations of slide parameters were tested and the product of initial acceleration and the volume of the slide gave the best correlation with the maximum surface elevation for the near coastal domain

source of the tsunami generated by the 1650 ad eruption of kolumbo submarine volcano aegean sea greece the 1650 ad explosive eruption of kolumbo submarine volcano aegean sea greece generated a destructive tsunami in this paper we propose a source mechanism of this poorly documented tsunami using both geological investigations and numerical simulations sedimentary evidence of the 1650 ad tsunami was found along the coast of santorini island at maximum altitudes ranging between 3 5 m a s l perissa southern coast and 20 m a s l monolithos eastern coast corresponding to a minimum inundation of 360 and 630 m respectively tsunami deposits consist of an irregular 5 to 30 cm thick layer of dark grey sand that overlies pumiceous deposits erupted during the minoan eruption and are found at depths of 30 50 cm below the surface composition of the tsunami sand is similar to the composition of the present day beach sand but differs from the pumiceous gravelly deposits on which it rests the spatial distribution of the tsunami deposits was compared to available historical records and to the results of numerical simulations of tsunami inundation different source mechanisms were tested earthquakes underwater explosions caldera collapse and pyroclastic flows the most probable source of the 1650 ad kolumbo tsunami is a 250 m high water surface displacement generated by underwater explosion with an energy of 2 1016 j at water depths between 20 and 150 m the tsunamigenic explosion s occurred on september 29 1650 during the transition between submarine and subaerial phases of the eruption caldera subsidence is not an efficient tsunami source mechanism as short and probably unrealistic collapse durations 5 min are needed pyroclastic flows cannot be discarded but the required flux 106 to 107 m3 s 1 is exceptionally high compared to the magnitude of the eruption

on the characteristics of landslide tsunamis this review presents modelling techniques and processes that govern landslide tsunami generation with emphasis on tsunamis induced by fully submerged landslides the analysis focuses on a set of representative examples in simplified geometries demonstrating the main kinematic landslide parameters influencing initial tsunami amplitudes and wavelengths scaling relations from laboratory experiments for subaerial landslide tsunamis are also briefly reviewed it is found that the landslide acceleration determines the initial tsunami elevation for translational landslides while the landslide velocity is more important for impulsive events such as rapid slumps and subaerial landslides retrogressive effects stretch the tsunami and in certain cases produce enlarged amplitudes due to positive interference in an example involving a deformable landslide it is found that the landslide deformation has only a weak influence on tsunamigenesis however more research is needed to determine how landslide flow processes that involve strong deformation and long run out determine tsunami generation

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

interaction between magma intrusion and flank dynamics at mt etna in 2008 imaged by integrated dense gps and dinsar data 1 global positioning system gps and differential interferometric synthetic aperture radar dinsar data collected from july 2007 to july 2008 on mt etna are analyzed to define the dynamics preceding and accompanying the onset of the eruption on 13 may 2008 short and long term comparisons have been made on both gps and radar data covering similar time windows thanks to the availability of three gps surveys the year before the eruption onset an increase in the seaward movement of the ne flank of the volcano has been detected in the few months before the dike intrusion the gps ground deformation pattern also shows a slight inflation centered on the western side of the volcano in the preeruptive long term comparison from july 2007 to may 2008 the gps has been integrated with dinsar data by the sistem approach to take advantage of the different methodologies and provide high spatial sampling of the 3 d ground displacement pattern we inverted the sistem results to model the pressure source causing the observed preeruptive inflation the subsequent emplacement of the eruptive dike was imaged by two gps surveys carried out on a dense network over the uppermost part of the volcano on 6 and 13 may i e a few days before and a few hours after the beginning of the eruption we inverted this comparison to define the position geometry and kinematics of the dike the dike intrusion was also imaged by dinsar data with temporal baselines of 2 3 months which confirm strong displacements localized on the summit area rapidly decreasing toward the middle flanks of the volcano as detected by very short term gps data furthermore the comparison between dinsar and gps data highlighted the presence of a depressurizing source localized beneath the upper southwestern area acting just after the dike intrusion finally the long period 1 year gps and dinsar data were integrated by sistem to finely depict the 3 d ground deformation pattern with the highest spatial resolution the long period data allowed the complex kinematics of the volcano to be finely imaged and highlighting the interaction between flank dynamics and magma injection

dust devils on mars columnar cone shaped and funnel shaped clouds rising 1 to 6 kilometers above the surface of mars have been identified in viking orbiter images they are interpreted as dust devils confirming predictions of their occurrence on mars and giving evidence of a specific form of dust entrainment

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

observations of martian surface winds at the viking lander 1 site partial failure of the wind instrumentation on the viking lander 1 vl1 in the martian sub tropics 22 5 n has limited previous analyses of meteorological data for this site we describe a method for reconstructing surface winds using data from the partially failed sensor and present and analyze a time series of wind pressure and temperature at the site covering 350 mars days sols at the beginning of the mission during early summer winds were controlled by regional topography but they soon underwent a transition to a regime controlled by the hadley circulation diurnal and semidiurnal wind oscillations and synoptic variations have been analyzed and compared with the corresponding variations at the viking lander 2 middle latitude site 48 n diurnal wind oscillations were controlled primarily by regional topography and boundary layer forcing although a global mode may have been influencing them during two brief episodes semidiurnal wind oscillations were controlled by the westward propagating semidiurnal tide from sol 210 onward comparison of the synoptic variations at the two sites suggests that the same eastward propagating wave trains were present at both sites at least following the first 1977 great dust storm but discordant inferred zonal wave numbers and phase speeds at the two sites cast doubt on the zonal wave numbers deduced from analyses of combined wind and pressure data particularly at the vl1 site where the signal to noise ratio of the dominant synoptic waves is relatively small

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