stratigraphy of the 1902 and 1929 nuee ardente deposits mt pelee martinique mild nuee ardentes in 1902 1903 and 1929 1930 at mt pelee formed high aspect ratio h a r deposits i e deposits with a high thickness extent ratio in the riviere blanche channel several violent nuees ardentes from may to august 1902 yielded low aspect ratio l a r deposits unevenly blanketing an area of 58 km2 on the southwestern flank of the volcano three closely spaced nuees ardentes on august 30 additionally affected 56 km2 on the southeastern flank the l a r deposits are divided into eight stratigraphic units u1 u8 either compound or consisting of a single flow unit the deposits of the largest nuees ardentes on may 8 20 and august 30 1902 are identified as u1 u3 and u8 respectively and can be traced over most of the area individual l a r flow units are lenticular and show large erratic lateral variations of thickness and grain size most flow units consist of three distinct beds bed 1 is a few centimeters thick lenticular fines depleted layer bed 2 is the thickest layer and contains more silt sized ash than bed 1 it is normally graded as a whole though reverse grading may occur in the lower part bed 2 generally consists of two parts bed 2a nonbedded and bed 2b finer grained and laminated with cross bedding and duned structures bed 3 is a thin silty capping layer which contains accretionary lapilli the distribution of the l a r flow units especially of the coarse grained facies suggests that they were formed from overpressured blast flows expanding radially from the vent at a high rate in the same manner as the laterally directed blast of mount st helens on may 18 1980 the transport system of the major 1902 nuees ardentes was an inflated relatively low concentration turbulent cloud as suggested by several lines of evidence 1 the transported material was able to cross ridges up to 300 m high 2 many scour and fill and other erosional features can be observed in the deposits at any distance from the vent 3 survivors within the devastated area on may 8 did not experience a dense low profile cloud but instead a choking hot ash laden cloud 4 many human corpses in st pierre remained where they fell instead of having floated away if the current flow surge terminology were to be used the 1902 blast flows would be better considered as pyroclastic surges the normally graded multi layered structure of the flow units is also consistent with deposits primarily formed from relatively low concentration flows

the sensitivity of subannual and intraseasonal tropical variability to model ocean mixed layer depth 1 the influence of air sea interaction on subannual and intraseasonal tropical variability is explored through analysis of three long simulations of the commonwealth scientific and industrial research organisation atmospheric general circulation model gcm with differing ocean specifications a coupled ocean gcm a simple 50 m mixed layer model or climatological sea surface temperatures sst together with 50 year simulations with mixed layer depths of 10 m and 20 m the analysis focuses initially on a signal similar to a madden julian oscillation mjo contained in the first two empirical orthogonal functions eof of monthly anomalies of tropical 807 hpa winds in january in the coupled model time lag regression is used to demonstrate that these patterns propagate eastward although at only half the speed of the mjo and induce perturbations to the australian monsoon the specified sst model shows no such propagation similar results are then obtained using daily data filtered to retain subannual periods the eastward propagation speed is faster in the shallower mixed layer cases with the 10 m case producing speeds close to observations in the interactive models surface energy fluxes force sst anomalies propagating ahead of the eof convergence these fluxes are largely consistent with evaporation perturbed by wind anomalies to the monsoon westerlies augmented by solar radiation the sst anomalies then further perturb the winds as is confirmed by a separate sst perturbation experiment from the examination of other seasons it is seen that air sea interaction generally enhances the amplitude of the mjo like patterns it also enhances their eastward propagation along westerly wind bands analysis of zonal wave number one winds confirms the strong sensitivity to mixed layer depth in the amplitude and period of the eastward propagating component particularly during september through february the results suggest that air sea interaction may be important to the mjo provided that the ssts are sufficiently responsive to the atmospheric patterns

magmatology of mt pelee martinique f w i iii fractional crystallization versus magma mixing the mineralogical and chemical compositions of the magmas emplaced during the three successive stages of mt pelee s activity ca 0 4 0 2 ma ca 0 1 ma 19 500 y b p 13 500 y b p remained relatively constant all magmas are cogenetic in a broad sense and result from the combination of two major petrogenetic processes fractional crystallization witnessed by gabbroic and dioritic cumulates fichaut et al 1989 this issue and magma mixing evidenced by textural mineralogical and chemical heterogeneities gourgaud et al 1989 this issue the study of heterogeneous eruptions e g the ash and scoria flows second stage and the 1902 1929 block and ash flows demonstrates that the basic and acid magmas involved have small but significant geochemical differences the distribution of compatible mg sc co and hygromagmaphile th la ta hf elements indicates that fractional crystallization played a dominant role in the genesis of the second stage products whereas magma mixing was dominant in the 1902 1929 lavas geological mineralogical and geochemical constraints are used to propose models of magma chambers the second stage deposits are considered to be the result of the discharge of the magmas stored in a chemically stratified ca 2 3 km3 magma chamber tentatively described as a cylinder or a parallelepiped of large vertical extent tens of km but small horizontal section some hundreds of meters by contrast the young 13 500 y b p deposits of mt pelee are thought to originate from a small 1 km3 and shallow ca 10 km in depth chamber filled with andesitic to dacitic magmas the periodic intrusion of basic magmas presumably from a deeper chamber causes magma mixing which triggers the eruption of heterogeneous and hybrid products

hydrothermal circulation beneath mount pelee inferred by self potential surveying structural and tectonic implications abstract self potential sp surveys were made on mount pelee volcano martinique island french west indies in 1991 and 1992 in order to recognize its hydrothermal system the associated groundwater channeling and the main superficial structures of the massif almost 70 km of profiles were carried out with an average sample spacing of 50 m measurements essentially reveal negative sp anomalies down to 1700 mv with high gradients 1 83 mv m due to the infiltration of meteoric water into the massif rims of summit calderas morne macouba and etang sec present sharp negative sp anomalies on the western northern and eastern flanks negative sp anomalies indicate no upward water flow beneath mount pelee summit on the southwestern volcano flank a 3 5 6 km horseshoe shaped structure corresponding to a southwest flank collapse event older than 25 000 years bp is clearly identified by the sp mapping high gradients border the inner southern rim from morne calebasse to st pierre town and the caribbean sea along the northern rim of the horseshoe shaped structure the negative sp anomalies give place to a positive sp anomaly up to 200 mv of sw ne trend this zone covers the area of two active hot springs sources chaudes and puits chaud 40 65 c marine magnetic surveys and bathymetry show that the horseshoe shaped structure spreads into the caribbean sea up to about 10 km from the coast buried structural discontinuities are evidenced inside the flank collapse structure the upper one deviates the groundwater flow coming from the summit toward the south flank where the flow finds an indentation to expand again downwards this discontinuity is either an old hypothetical caldera rim partly destroyed by the collapse of the south southwestern flank and covered by recent pyroclastic deposits or more probably the trace of a bulge landslide a circulation model of the hydrothermal waters is proposed rainfall 5 6 m year is partly drained inside the summital calderas and the flank collapse zone through pyroclastic flows down to an impermeable basement there the groundwater constitutes perched aquifers at the contact of the bulge landslide or of the hypothetical old caldera rim along the inner northern border of the flank collapse structure the phreatic water is reheated warm groundwater flows along the northern avalanche structure rim and discharges near the coast in ground and marine outcrops of medium temperature finally the main part of the meteoric water is channeled along the old caldera rim or along the bulge landslide towards the south flank of mount pelee where some gaps in the rim exist there the groundwater finds again a subhorizontal gravitational circulation along mount pelee slopes into the caribbean sea

case study of a volcanic geothermal system mount pelee martinique abstract mount pelee is one of the active volcanoes of the lesser antilles arc with more than 20 eruptions during the last 5000 years despite this abundant potential heat flow there are few surface manifestations indicative of the existence of a large high temperature hydrothermal system a few na hco 3 so 4 type hot springs with emergence temperatures not exceeding 65 c occur on the south and west flanks of the volcano two small hydrothermal eruptions occurred in 1792 and 1851 on the southwestern flank on the site of now extinct sulfur springs the heat source provided by the mount pelee magma chamber should occur according to petrologic data at shallow depth 5 8 km beneath the summit region we assume abundant groundwater recharge to take place within the central calderas where faults and magmatic conduits provide vertical channelways for deep infiltration of cold meteoric water this would be expected to depress a presumed nacl hydrothermal system located deep in the core of the volcano upwelling of high temperature fluids and gases is thought to be found at the periphery of the central calderas along the arcuate caldera related faults and or along regional faults and any permeable stratigraphic levels connected to the central caldera structure steam heating of shallow meteoric waters by a degassing nacl system could produce a na hco 3 so 4 type system which would develop preferentially on the periphery of the central caldera structure or even outside it in an adjacent zone of fracture permeability caldera or regional faults where cold meteoric flows are less abundant this na hco 3 so 4 system is assumed to be located beneath the south flank of the volcano and the major upflow zone seems to be the southern limit of the intermediate caldera as evidenced by the location of hot springs and hydrothermal eruptions the scarcity of thermal manifestations on mount pelee is not surprising in view of its groundwater hydrogeology the na hco 3 so 4 fluids which ascend will be masked wherever a highly permeable subhorizontal aquifer occurs near the surface and they commonly mix with cold waters before discharging

measurement of self affinity on surfaces as a trial application of fractal geometry to landform analysis abstract landforms which are often referred to as good examples of fractal geometry are considered to be self affine because they appear flatter as the viewing point is moved farther away the line scaling method which can express the self affinity of various curves including self similar curves as a limiting case by separately scaling two coordinates was expanded and applied to surfaces developing in three dimensional space area scaling method for the purpose of deriving a parameter which might be useful in landform analysis the variance of height change z 2 surface area s and basal area a measured in a number of scaling unit areas of various sizes can be scaled as z 2 s z and a s a indicating the self affinity of these surfaces z 2 and a then are scaled to each other as z 2 a h and h z a in the of land surfaces h v z because a is always close to 1 this means that h is equivalent to the scaling hurst exponent h 0 h h measured by the area scaling method closely reproduced the initially introduced h values of computer generated fractional brownian surfaces although vertical exaggeration can make a surface look very different from the original appearance the measured values of h do not change significantly owing to vertical exaggeration the h value seems to express a relief texture essential for the surface a surface with minor h has a greater local roughness relative to the total relief than surfaces with large h the area scaling method then was applied to actual landforms in two areas of well dissected low mountains using equally scaled topographic maps with the same grid spacing 25 m grid on 1 5000 maps the obtained values of h are considered reasonable for the difference in relief texture shown by the block diagrams of these areas h values which were evaluated for four different landscapes on 1 25 000 topographic maps with a 125 m grid moreover also seem to indicate their relief texture expressed by the 125 m grid spacing h values obtained by the area scaling method may become a useful parameter to express the degree of self affinity or relief texture of landform surfaces although more research is necessary to establish the reliability of the h parameter for landform analysis

the structure and evolution of seasonal wind anomalies over the near equatorial eastern indian and western pacific oceans abstract the longitude height time evolution of seasonally averaged wind anomalies over the near equatorial eastern indian and western pacific oceans is examined using multiyear time series derived from a network of eight rawinsonde stations data at six pressure levels between 850 and 150 mb are considered the first two modes of an empirical orthogonal function analysis of zonal wind fluctuations are cross correlated at lag with spatial structures suggesting that the dominant pattern of variability on seasonal time scales is best described as a propagating oscillation this space time structure is confirmed using a complex empirical orthogonal function analysis which indicates that over half of the interseasonal zonal wind variance at these stations is associated with an eastward propagating mode denoted e1 wind anomalies described by e1 are negatively correlated in the upper and lower troposphere at each station and are out of phase between the southern tip of india and the central pacific so

revised chronostratigraphy of recurrent ignimbritic eruptions in dominica lesser antilles arc implications on the behavior of the magma plumbing system ignimbritic eruptions represent catastrophic events due to the magma volume involved and the related consequences on earth s environment in relation with the released gases and the tephra dispersal dominica has been recognized as hosting one of the major ignimbritic eruptions of the last 200 ky in the lesser antilles arc called the roseau tuff but more recent works have evidenced several pumiceous events instead of a single large one here we propose a revised chronostratigraphy of the explosive activity that occurred in the last tens of thousands years based on three field trips new 14c ages detailed lithological and geochemical investigations in particular a precise characterization of trace element glass chemistry this eruptive history reconstruction is mainly based on outcrops along the coast and in the valley since the luxury vegetation in the center of the island mostly precludes sections close to the central volcanic centers we thus confirm that the roseau event has been overestimated and that we may recognize five main ignimbritic events grande savane layou 51 ka grand bay roseau 33 ka grand fond 24 ka we discuss the possible volcanic center at their origin in addition to correlations with some plinian events of lower magnitude that were identified in the roseau valley and in the southern part of dominica this study may help to better constrain the eruptive history of the most active volcanic island of the lesser antilles arc which has important implications on hazard mitigation

diversity of eruptive styles inferred from the microlites of mt pelee andesite martinique lesser antilles abstract we have studied the compositional and textural characteristics of plagioclase microlites from several dome forming eruptions dome block and ash flows and surges and plinian fallouts of the recent period of activity of mt pelee in order to infer magma ascent dynamics dome forming and plinian samples display a wide range of plagioclase microlite compositions from an 35 to an 90 and an 55 to an 90 respectively microlites with compositions an 50 60 crystallized from a mafic melt that intruded the andesitic reservoir in proportion of 10 vol during magma ascent in the conduit the fraction number density and morphology of the decompression induced microlites compositions 50 60 suggest that the plinian magmas experienced a nucleation dominated crystallization regime with high undercooling in contrast magmas from domes and block and ash flows were dominated by a growth regime with low undercooling and the surges were influenced by both regimes according to these crystallization regimes and new experimental data on h 2 o content of the matrix glasses we propose magma relative ascent rates and fragmentation pressures for the different eruptive styles observed at mt pelee that may explain why surges are explosive events and why they may or may not be followed by a plinian event

large scale flank collapse events during the activity of montagne pelee martinique lesser antilles 1 a horseshoe shaped structure already identified on the southwestern flank of montagne pelee martinique lesser antilles arc was previously interpreted as resulting of a flank collapse event but no debris avalanche deposits were observed at the time new offshore high resolution bathymetry and geophysical data aguadomar cruise december 1998 to january 1999 r v l atalante lead us to identify three debris avalanche deposits on the submarine western flank of montagne pelee extending down to the grenada basin they display morphological fronts and hummocky morphology on bathymetric data speckled pattern on backscatter data and hyperbolic facies on 3 5 khz and seismic profiles new on land geological studies lead us to identify two other horseshoe shaped structures on the same flank of the volcano the three submarine deposits have been traced back to the structures identified on land which confirms the occurrence of repeated flank collapse events during the evolution of montagne pelee the ages of the last two events are estimated at 9 ka and 25 ka on the basis of 14c and 238u 230th dates every flank collapse produced debris avalanches which flowed down to the caribbean sea we propose that the repeated instabilities are due to the large asymmetry of the island with western aerial and submarine slopes steeper than the eastern slopes the asymmetry results from progressive loading by accumulation of volcanic products on the western slopes of the volcano and development of long term gravitational instabilities meteoric and hydrothermal fluid circulation on the floor of the second flank collapse structure also creates a weakened hydrothermalized area which favors the recurrence of flank collapses

intraseasonal oscillations in sea level along the west coast of the americas abstract hourly observations of coastal sea level at stations from peru to british columbia are analyzed for low frequency content a space time contour plot of sea level from four years of data during the 1971 75 period shows the meridional structure of the seasonal cycle and interannual variability associated with the 1972 73 el nino oscillations with intraseasonal periods of 36 73 days are also evident coherent over alongshore distances of several thousand kilometers further investigation using spectral methods and empirical orthogonal function analysis in the frequency domain reveals in particular that intraseasonal sea level variability has a peak in spectral density along the coasts of south america central america and mexico with high coherence from near the equator tumaco 2 n north to central california 34 n and south to at least callao 12 s phase propagation north of the equator is poleward at 150 200 kilometers day atmospheric pressure alongshore wind stress and wind stress cu

new insights into the recent eruptive and collapse history of montagne pelee lesser antilles arc from offshore marine drilling site u1401a iodp expedition 340 abstract marine tephrochronology provides a good alternative to study the eruptive history of volcanic islands and overcome the problem of poorly preserved on land outcropping here we provide new observations on the recent volcanological evolution

scaling tidal channel geometry with marsh island area a tool for habitat restoration linked to channel formation process 1 hydraulic geometry and related analyses are often used to investigate tidal channel geometry and evolution and inform marsh restoration an alternative approach is presented that avoids calculating tidal prism and allows analysis of additional channel metrics it relies on scaling relationships between marsh island surface area and various metrics of the set of tidal channels draining each island in the skagit delta marshes washington united states total channel surface area and length and surface area of the largest channel draining an island scaled disproportionately with island area suggesting restoration of a 100 ha site would be preferable to restoration of 10 separate 10 ha sites to maximize channel length and area a model of channel formation through random island conglomeration replicated observed scaling patterns linking channel scaling to blind channel evolution from river distributaries channel size and complexity varied spatially with significant deficits in an eroding marsh isolated from river distributaries and riverine sediments

mt pelee martinique may 8 and 20 1902 pyroclastic flows and surges abstract the distribution stratigraphic relationships and fragmental components of the may 8 and 20 1902 pyroclastic flows from mt pelee martinique together with eyewitness accounts suggest the following explanation for those eruptions the eruptions were vertically directed magmatic perhaps initiated phreatically and contained abundant juvenile lithics from congealed magma of the dome and neck this resulted in a two part eruption column having 1 a dense lithic charged part which collapsed into the crater and flowed out of a pre existing notch in its side giving rise to pyrochlastic flows and 2 a magmatically derived column containing gases juvenile vitric material and crystals which largely by passed the neck and dome and escaped into the atmosphere all of the energy of the flows was apparently focused through the notch they emerged fully turbulent and flowed down riviere blanche gravity segregation of large and abundant fragments soon resulted in a dense high concentration poorly fluidized block and ash flow confined to the valley leaving above a fully turbulent high energy ash cloud surge as the ash cloud surge moved down the mountain it continued to expand outward the process of gravity segregation continued as the ash cloud surge expanded resulting in secondary block and ash underflows toward st pierre the secondary block and ash flows developed on a gently sloping upland surface 100 m or more above the valley of riviere blanche the turbulent fragment depleted surges above the secondary block and ash flows maintained sufficient energy to devastate the landscape outward to about 3000 m including st pierre the surges refracted around obstacles and in one place moved up a small valley in a direction opposite to the main flows

applying tidal landform scaling to habitat restoration planning design and monitoring abstract tidal channels are structurally and functionally prominent features in tidal marshes so their restoration is central to marsh restoration prominent design questions in tidal marsh restoration include how many tidal channels can a restoration site support and thus how many dike breaches should be made to restore tidal inundation and tidal channels how much total channel surface area will be supported by a restored marsh and thus how many fish shrimp or other organisms can be supported by restored channel habitat these basic design questions can be addressed by landscape allometry which describes the proportional relative rates of change in a system between two entities of particular interest in the case of marsh restoration between the amount of marsh area to be restored and a wide variety of measures of tidal channel network geometry this paper briefly reviews the development of landscape allometry insights that it provides into landforms and related ecological patterns and its utility and application to marsh restoration planning design and monitoring its practical application is illustrated in a conceptual restoration design that is the basis for a current restoration project

the past 5 000 years of volcanic activity at mt pelee martinique f w i implications for assessment of volcanic hazards the history of mt pelee martinique was subdivided into three stages based on field geology and 14c data the two first stages constructed an ancient mt pelee and an intermediate cone between 0 4 m y and 19 500 y b p the third or present stage started 13 500 years ago after a repose of 6 000 years this paper focuses on the activity of mt pelee during the past 5 000 years as a means to assess and zone volcanic hazards of the 23 magmatic eruptions during the past 5 000 years the ages of 21 eruptions of this period are based on 75 new 14c dates the types of phenomena and distribution of pyroclasts relate to four main types of activity the first type consists of pumice and ash flows that are not preceded by a plinian fall two eruptions named p6 and p4 illustrate this type for which the mixture of gas ash and pumice simply overflow the vent and flood several valleys the second type differs from the first by the occurrence of a preliminary moderate plinian fall stage four eruptions p5 p31 p2 and p1 illustrate this type two eruptions p32 and p33 experienced cataclysmic plinian explosions and pumiceous surges the third type is related to dome growth with the rise of viscous spines and the production of related block and ash flows five eruptions 1929 sept 1902 1904 npm nab2 and nmp illustrate this type the fourth type is characterized by violent ejection of more or less heterogeneous nuees ardentes the direction of the blast dictated by the morphology of the crater has been towards the south several times at mt pelee four eruptions may 1902 nab1 nrp2 and nrp3 belong to this type future magmatic eruptions at mt pelee will very likely belong to one of these four types assessment of hazards at mt pelee is based upon the behavior of the volcano during the past 5 000 years because 1 recognition of past magmatic eruptions is quite complete and well dated and 2 no structural change has occurred in the volcano a probabilistic and statistical approach has been tentatively followed stochastic models of wickman indicate a the chance that contemporary abnormal seismic and or phreatic activity at the volcano would signal an impending magmatic eruption is 20 percent b mt pelee exhibits a complex loading time behavior that may be related to the buffering effect of a magma chamber time is needed following a single or several closely spaced eruptions to establish conditions to initiate a new eruption and c if the 1929 event can be regarded as the last episode of the major 1902 eruption the volcano could remain in a dormant stage with respect to magmatic events for another century

magmatology of mt pelee martinique f w i i magma mixing and triggering of the 1902 and 1929 pelean nuees ardentes abstract at mt pelee martinique f w i the 1902 and 1929 nuees ardentes occurred before the final emplacement of the dome at an early phase during the eruption the first 1902 nuees ardentes on may 8 and may 20 were also the most destructive corresponding products present heterogeneous textures with the occurrence of mafic enclaves banded and emulsified lavas the terminal dome is andesitic and texturally homogeneous these features are compatible with 1 co eruption of two contrasted magmas basalt and dacite 2 interaction between the two magmas which led to intermediate andesitic compositions 3 a predominantly mechanical magma mixing process the evolution of which could be observed during the eruption a similar evolution appeared in the 1929 sequence mineralogical evidence depends essentially on phenocryst transfers between basaltic and dacitic magmas and their paragenetic implications frequent disequilibrium features wide compositional ranges polymodal distribution of plagioclase and strong zoning of phenocrysts all these features occur in the mingled hybrids as well as in blended mixtures the chemical compositions of the juvenile magma of nuees ardentes range from basalt or basaltic andesite mafic enclaves to dacite clear host lavas with all intermediate and predominant andesite composition the terminal dome is andesitic and from major and trace element data it is interpreted as the result of a basalt dacite mixing nevertheless a fractional crystallization process is necessary to generate the acid component from the basic one we suggest a model comprising a double magma chamber with a shallow reservoir dacitic in composition and a deep reservoir where the mafic magma is stored the rising mafic magma intersects the superficial chamber inducing magma mixing and rapidly triggering an explosive pelean eruption the early eruptive activity associated with a deep seated mafic injection intersecting a differentiated shallow chamber immediately reaches a climax we emphasize the necessity for quick detection of such a rising mafic magma since the superficial chamber has a relatively short time lag before an explosive and dangerous eruption

geographic variation in puget sound tidal channel planform geometry tidal channels are central elements of salt marsh hydrodynamics sediment dynamics and habitat to develop allometric models predicting the number and size of tidal channels that could develop following salt marsh restoration channels were digitized from aerial photographs of puget sound river delta marshes salt marsh area was the independent variable for all dependent channel planform metrics tidal channel allometry showed similar scaling exponents for channel planform metrics throughout puget sound simplifying comparisons between locations y intercepts of allometric relationships showed geographic variation which multiple regression indicated was associated with tidal range and storm significant wave height channel size and complexity were positively related to tidal range and negatively related to wave height four case studies each with paired regions of similar tidal range and contrasting wave environments further indicated wave environment affected channel geometry wave mediated sediment delivery may be the mechanism involved with wave sheltered areas experiencing relative sediment deficits such that some salt marshes in puget sound are already suffering sea level rise impacts that are reflected in their channel network geometry

eruption dynamics inferred from microlite crystallization experiments application to plinian and dome forming eruptions of mt pelee martinique lesser antilles decompression experiments have been conducted to simulate syn eruptive crystallization in volcanic conduits to infer magma ascent rates and conditions during dome forming and plinian eruptions of silicic arc volcanoes the experiments were carried out on starting material with the composition of mt pele e rhyolitic interstitial melt 76 wt sio2 and consisted of three consecutive steps hydration decompression and annealing hydration saturated and undersaturated was performed at 8508c and 200mpa and was followed by isothermal decompression either linearly or stepwise to a final pressure pf of 30 or 5 10mpa decompression rates range from 0 003 to 25mpamin 1 decompression durations of 15 min to 40 days two samples were cooled by 258c and 508c during a 3 day step at pf subsequent to decompression the samples were held for up to 15 days at pf the experiments generated three types of crystals as products of pre syn and post decompression crystallization the experiments basically differ from previous studies in that they are specifically designed to discriminate crystal nucleation from growth and to evaluate the influence of pre decompression crystals on the decompression induced crystallization the effects of pre decompression crystals decompression rate undercooling pf and terminal cooling have been determined on plagioclase nucleation growth morphology and composition the main results suggest a positive correlation between decompression rate and the number density of plagioclase crystals nucleated at pf and highlight the effect of pre decompression crystals in further decompression induced crystallization the relations between the decompression conditions and the plagioclase characteristics have been used to infer mt pele e eruption dynamics suggesting that 1 plinian magmas ascend from the reservoir within less than 1h 1 10 m s 2 dome and block and ash flow magmas ascend within more than 2 5 days giving time for syn decompression crystallization around pre existent microlites 3 dome magmas provide evidence for long stagnation and cooling at low pressure and 4 surge magmas ascend without significant crystallization within less than 4 days and massively nucleate plagioclase at very low pressure the extent and violence of dome destruction may depend on the size or age of the dome with large or old domes favouring mildly explosive block and ash flows whereas small or young protodomes may generate highly explosive surges

the primitive volcano of mount pelee its construction and partial destruction by flank collapse abstract the geology of mount pelee the active volcano of martinique lesser antilles has been actively studied during the past decade this paper reviews the current knowledge about the oldest least well known part of the volcano here called paleo pelee and the relations between paleo pelee and the mont conil volcanic complex paleo pelee consists mostly of volcanic breccias with a few lava flows it differs in this respect from neighbouring active volcanoes such as the grande decouverte soufriere in guadeloupe and the soufriere in st vincent the oldest products of which are mainly lava flows paleo pelee initially formed a regular cone which was comparable in size with the present edifice it is now largely eroded and its products form prominent radial ridges on the western flank of mount pelee these are buried under younger deposits on the eastern flank the uniformly andesitic breccias of paleo pelee are for the most part brecciated lava flows it is inferred that the activity of mount pelee was less explosive at this stage than during following periods neo pelee the paleo pelee formations overlap those of mont conil the geology of mont conil is poorly known however its lowest exposed products are submarine andesitic breccias cut by many dikes this contrasts with paleo pelee where all breccias are of subaerial origin pleistocene limestones are interbedded within the mont conil breccias between 120 and 150 m above sea level though mont conil seems to be closely linked to mount pelee on the basis of available petrological data a major uplift must have occurred sometime during or after the construction of mont conil and forms a recognizable geological boundary between the two volcanic systems the paleo pelee edifice was partially destroyed by a flank collapse event that occurred on the southwest flank during the early stage 40 000 20 000 y b p of neo pelee this event is evidenced by a large 6 2 5 km horseshoe shaped structure which is limited by well preserved morphological scarps on land and by a 300 m offshore scarp as shown by seabeam bathymetry paleo pelee breccias and lava flows are truncated by the boundary of the collapse structure lava domes occupied the upslope part of the structure at a later time these domes are intersected by the present crater etang sec which has probably been the active vent for at least 2000 years the active crater is located at the intersection between the flank failure depression and an older caldera formed at the paleo pelee stage but probably enlarged later the flank failure structure appears as a major structure of the volcano and creates a strong structural asymmetry in the edifice this fact should be considered when dealing with such various aspects as the hydrogeology of the volcano the structural control of past and future eruptions and the volcanic hazards

the influence of air sea interaction on the madden julian oscillation the role of the seasonal mean state the csiro mark 3 general circulation model at t63 resolution is used to explore the potential effect of air sea interaction in enhancing the eastward propagation of the madden julian oscillation mjo principal component analysis is used to define a seasonal lower tropospheric wind signal when the model is coupled with an interactive ocean the monsoon wind anomalies in december february djf propagate from the indian ocean to the pacific ocean in versions with a thinner mixed layer the propagation speed approaches that seen in the observational era40 data set however in the non interactive model with specified sea surface temperatures ssts there is no propagation similar contrasts are seen in other seasons the upper tropospheric long wave signal determined through spectral analysis is also more realistic in the coupled model although power around the 80 day period remains too large positive sst anomalies form to the east of low level convergence in part due to evaporative flux that is modified by the mean monsoon westerly belt in djf interannual variations in this belt appear to have an effect on the propagation of the wind anomalies in the coupled model while only the amplitude varies in the non interactive model this contrast is also seen in partitions of years by the state of enso propagation of the mjo signal is faster and extends farther into the pacific in el nino years in observations and the coupled model although model biases in particular a short westerly belt appear to limit the effect it is concluded that air sea interaction is potentially very important to the mjo and its interannual variability and that the westerly belt has an influence on its evolution

construction and destruction of mont pelee volcano volumes and rates constrained from a geomorphological model of evolution this study presents long term volumes and construction rates for the mont conil mont pelee volcano and rate estimates at which volcanic activity creates relief an algorithm shapevolc is used to numerically model topographic surfaces volcano morphology is analyzed using current digital elevation model in combination with mapped geology to produce 10 paleotopographies at the end of four constructional stages and three destructional events volumes of each constructional stage were estimated at about 35 2 km3 26 2 km3 8 3 km3 and 2 5 km3 for a total cumulative erupted volume of 72 2 km3 we estimate that mont pelee accounted for about 10 of the lesser antilles arc production in the last 100 kyr the volcano has been built at an average rate of 0 13 km3 kyr during the last 550 kyr during that time construction rates varied by a factor of 15 from 0 04 km3 kyr in early stages up to 0 52 km3 kyr after the second flank collapse volumes displaced by each flank collapse were estimated at 14 7 km3 8 8 km3 and 3 5 km3 thus about 37 of the total constructed volume integrated over the volcano s lifetime the rate at which flank collapses removed material off the island is 0 15 km3 kyr in contrast long term erosion rates outside collapsed areas are estimated at about 0 05 0 7 km3 kyr or 11 km3 of material removed this latter rate is not negligible which strengthens the importance of taking into account recurrent small erosional events on the geomorphological evolution of a volcanic island in a tropical context

basin wide zonal wind stress and ocean thermal variations in the equatorial pacific ocean wind data obtained from the model results of the european centre for medium range weather forecasts ecmwf for the equatorial pacific ocean from 1985 to 1992 were employed to study the basin wide distributions for various constituents of zonal wind stress forcing the ocean by the individual constituent of zonal wind stress the upper ocean thermal variation was investigated using a linear analytical ocean model the interannual variation of zonal wind stress is largest in amplitude in the west central part of the basin and is dominated by an eastwardly propagating wave the upper layer thickness perturbation h shows an evolving eastward propagation over the region where the interannual wind stress variation occurs while to the east and west the region changes nearly in phase the evolution of h agrees well with the evolution of upper ocean heat content anomaly estimated from the tropical atmosphere ocean tao moored array the annual cycle of zonal wind stress can be described properly by a combination of annual and semiannual variations the annual variation of zonal wind stress was found to propagate westward with relative maxima out of phase to the west and east of the west central pacific the semiannual variation is stationary and is largest in amplitude in the western basin forced by the two components of the annual cycle of zonal wind stress the evolution of h shows a westward propagation this does not correlate well with the pattern of the evolution of the annual cycle of upper ocean heat content which emanates from the east central pacific and shows both eastward and westward propagation the seemingly anomalous eastward propagation is mainly related to the abrupt change during the relaxation intensification period of the easterly wind stress the abrupt change of the annual zonal wind stress variation in both time and space is then critical for the evolution of the pattern of the annual ocean response

magma degassing process during plinian eruptions abstract to assess magma degassing processes during plinian eruption noble gas abundances and isotopic ratios have been determined in pumices by crushing under vacuum samples come from plinian eruptions which occur along different subduction zones in addition two pumice samples come from the azores hotspot all samples are characterized by a systematic enrichment in neon over argon a depletion of krypton relative to argon and an isotopically fractioned 38 ar 36 ar ratio these features do not depend on geological setting or on pumice age or eruption intensity however they are similar for pumices from the same eruption a correlation is observed between 84 kr 36 ar and the 38 ar 36 ar ratio this illustrates that only one physical process is at the origin of the fractionation we propose here a model of kinetic magma degassing before fragmentation to explain the elemental and isotopic fractionation noble gases diffuse in a magma shell surrounding a preexisting bubble the model put forward an alternative to the model of pinti et al 1999 in which diffusion occurs after pumice quenching in plinian plume the model explains measurements and shows the rapidity of the magma degassing process in the conduit few hundreds of seconds

air sea coupled modes on intraseasonal and interannual time scales over the tropical western pacific dominant phase relationships between sea surface temperature sst high cloud cover hcc and zonal wind at 850 mbar on intraseasonal and interannual time scales in the warm pool region of the western pacific are examined using the complex empirical orthogonal function ceof analysis two air sea coupled modes that is an intraseasonal mode and an interannual mode are statistically extracted it is found that in the intraseasonal mode the area of maximum sst anomaly lies to the east of the center of the active large scale convection area and therefore positive sst anomalies exist at the easterly anomaly area the existence of high sst at the easterly anomaly area provides a favorable condition for a large scale disturbance to propagate eastward though the evaporation wind feedback mechanism may also favor its eastward propagation if the mean wind is easterly it is seen that the intraseasonal mode is very similar to the advective mode proposed by lau and shen 1988 with respect to the phase relationship however since the time evolution of the intraseasonal mode does not always coincide with the variations of east west sst gradient over the tropical western pacific this mode requires another mechanism other than the east west sst advection causing the advective mode on one hand the interannual mode has a characteristic that the phase relation of 850 mbar zonal wind u is different in each region of the tropical western pacific whereas the sst is almost in phase with hcc the predominant growth of the mode defined in the key region 0 10 n 130 160 e corresponds to the life cycle that occurs when the el nino southern oscillation enso begins develops and decays this verifies that the enso is one of the prominent phenomena in the air sea interactive system on the interannual time scale on the other hand the mode over the tropical pacific around the dateline explains the air sea coupling when large scale convection is not very active it is thus clear that evident differences of air sea coupling exist between the intraseasonal time scale and the interannual time scale it is also determined that the strength of air sea coupling varies with year in both time scales the above results provide a clue for understanding the mechanism of multiscale air sea coupling in the tropics

merapi volcano java indonesia and merapi type nuee ardente a particular nuee ardente type merapi type avalanche nuee has been defined at the merapi volcano because of its prominent role in the recent activity of the volcano gravity plays a significant role during the eruption

the recent pumice eruptions of mt pelee volcano martinique part ii grain size studies and modeling of the last plinian phase p1 abstract some aspects of the last pumice eruption p1 recorded at mt pelee volcano martinique and dated at 650 years b p are quantified during this event plinian falls were followed by pumice flows channelled by the valleys plinian deposits crop out over the entire mt pelee massif and significant volumes fell upon the ocean grain size studies of the fall deposits show a median md which generally ranges from 2 25 to 3 8 and a sorting coefficient of between 1 33 and 2 75 the main volcanological parameters are tmax thickness up to 15 m f fragmentation of 10 wt of clasts less than 1 mm in size and d dispersal of about 900 km2 the total volume of the tephra is estimated at 0 95 km3 and the duration of the eruption at 1 5 3 h which liberated a total thermal energy of 0 4 1025 ergs with a mass eruption rate of between 3 8 and 7 0 107 kg s 1 the column height is calculated to be 20 22 km and the initial muzzle velocities between 230 and 310 m s 1 for blocks 0 4 0 7 m in diameter these parameters suggest that the eruption was a relatively small plinian eruption

tropical intraseasonal oscillations appearing in a gfdl general circulation model and fgge data part ii structure abstract space time spectral and filter analyses are made of the structure of the tropical intraseasonal oscillations appearing in a gfdl 30 wavenumber spectral general circulation model and the fgge iiib data set the model s tropical zonal velocity exhibits spectral peaks with periods of 40 50 and 25 30 days at wavenumber 1 for six individual years although the 40 50 day peak is not as pronounced as that found in the fgge dataset both the eastward moving 40 50 and 25 30 day oscillations take the form of a kelvin rossby wave pattern in the upper troposphere and a rossby mode in the lower troposphere they also take the form of a latitudinally tilted walker cell which is modified by a meridional convergence in the boundary layer