the properties and genesis environments of south atlantic cyclones a new climatology of south atlantic cyclones is produced to provide new insights into the conditions leading to genesis in different regions of the domain cyclones are identified and tracked based on the relative vorticity at 850 hpa computed from the ncep cfsr winds the characteristics of the cyclones are obtained by diagnostic variables sampled within a radial distance from the cyclone centers to produce the spatial distribution of cyclone properties at the time of genesis also cyclone centered composites are used to analyze the cyclone structure and evolution during their genesis there are four main cyclogenesis regions in the south atlantic ocean the southern brazilian coast se br 30 circ text s over the continent near the la plata river discharge region la plata 35 circ text s the southeastern coast of argentina arg 40 circ text s 55 circ text s and the southeastern atlantic se sao centered at 45 circ text s and 10 circ text w we found that cyclogenesis northward of 35 circ text s occurs mainly due to low level forcing associated with moisture transport in the summer and is associated with upper level forcing in the winter due to a strong baroclinic environment southward of 35 circ text s cyclones develop in a high baroclinic environment throughout the year with only a small influence from moist processes the cyclone composites reveal that se br and se sao cyclones are associated with secondary development the la plata cyclones development is influenced by an orographic low in their early stages and arg cyclones are influenced by thermal advection as an essential mechanism in the reduction of static stability

upper mantle structure of the northern cascadia subduction zone previous knowledge of the structure of the cascadia subduction zone north of the canada united states border has been derived from a variety of geophysical studies that accurately delineated the downgoing juan de fuca plate from the offshore deformation front to depths of 50 60 km beneath south central vancouver island and the georgia strait little is known however of the structure of the cascadia subduction zone farther westward and to greater depths in the upper mantle we have assembled a set of some 1100 teleseismic traveltimes from events recorded on the western canadian telemetered network to augment a previously existing data set recorded on the washington regional seismograph network the composite data set is inverted for upper mantle structure below washington oregon and southwestern british columbia we analyze the new northern portion of the model between 48 5 50 n and 118 127 w which provides the first images of the deep slab structure in this region the model is parameterized using s

fracturing of etnean and vesuvian rocks at high temperatures and low pressures abstract the mechanical properties of volcanic rocks at high temperatures and low pressures are key properties in the understanding of a range of volcanological problems in particular lava flow dynamics the measurement of these properties on extrusive volcanic samples under the appropriate pressure and temperature conditions has a direct application in the assessment of volcanic hazards a new triaxial deformation cell has been designed to obtain mechanical strength data on rock samples at temperatures up to 1000 c and pressures up to 30 mpa significantly the cell uses large cylindrical rock specimens 25 mm diameter by 75 mm long never previously employed in such a high temperature apparatus the large specimen size is necessary to test volcanic rocks with their large crystals and vesicles the design of this novel apparatus is presented its operating temperature and pressure range encompasses the conditions of an advancing flow from the vent to the front as well as the conditions of the volcanic rocks hosting magma at equivalent depths of up to 2 km experimental results are presented for tests on vesuvian and etnean rocks results show that the vesuvius and the etnean rocks remain fully brittle up to 600 c with typical strengths of 90 mpa and 100 mpa and young s moduli of 60 gpa and 40 gpa respectively above these temperatures the elastic modulus and compressive strength decreases steadily in both the vesuvian and etnean rocks reaching 10 of the original values at 900 c and 800 c respectively when partial melting occurred full melting occurs at 1100 c in the vesuvian rock and at 1040 c in the etnean rock results also show that confining pressure has only a small effect on the strength of the rock at these low pressures and that strain rates are important at high temperatures fracture energy release rates have been calculated and show an inversely proportional relationship with temperature results reveal why fracturing is important on the crust of the lava flow as much as at the flow front where the flow has almost completely solidified but still maintains high temperatures these results put quantitative limits on models where fracturing processes play an important role

thermoelastic deformation associated with a lava tube active lava tubes have much higher temperatures than the surrounding rocks any change in the tube temperature produces a change in the temperature distribution in the rocks and induces a thermoelastic deformation in them we calculate such a deformation by solving the equilibrium equation of linear thermoelasticity we assume that the initial temperature distribution in the medium is the steady state solution of the heat equation for a very long cylindrical tube at constant temperature embedded in a medium with uniform thermal conductivity we calculate the displacement and stress fields in the medium following to a temperature change of the tube a temperature increase produces a dilatation of the medium and a contraction of the tube while a temperature decrease produces the opposite effect for a temperature change equal to 100 k thermal stresses in the order of 10 mpa are produced which are large enough to fracture the rocks surrounding the tube

continental signature of a ridge trench triple junction northern vancouver island south of the juan de fuca pacific north america triple junction located off northern vancouver island there is subduction and to the north there is oblique convergence along the queen charlotte transform fault in the mid tertiary periods of extension including crustal thinning and volcanism formed queen charlotte basin heat flow on northern vancouver island 67 mw m2 is the same as in queen charlotte basin to the north but it decreases abruptly to the south over a distance of 70 km to an average value of 46 mw m2 compared to the rest of the island the northern island has more subdued topography a lower mean elevation slightly higher bouguer gravity values and lower seismicity late tertiary volcanics which occur only on the northern part of the island geochemically resemble the tertiary masset formation which formed during periods of extension in queen charlotte basin these data are consistent with a tertiary history including periods of extension for northern vancouver island similar to queen charlotte basin and distinguish it from the rest of vancouver island the southern boundary of this northern block extends northeastward from brooks peninsula approximately above the inferred northern edge of the subducted juan de fuca plate and parallel to a series of linear magnetic anomalies associated with a northeasterly trending fault zone the abrupt transition in observed heat flow is most likely associated with the edge of the subducted plate which produces large temperature differences at depths of 30 40 km the time constant for these thermal effects to reach the surface conductively indicates that this boundary has been stable over tens of millions of years and therefore the location of the subducting plate s northern edge must have been stationary or moving very slowly over this period consequently it is likely that the triple junction has been located on average for the last 40 myr off brooks peninsula

on the dynamics of the juan de fuca plate the juan de fuca plate is currently fragmenting along the nootka fault zone in the north while the gorda region in the south shows no evidence of fragmentation this difference is surprising as both the northern and southern regions are young relative to the central juan de fuca plate we develop stress models for the juan de fuca plate to understand this pattern of breakup another objective of our study follows from our hypothesis that small plates are partially driven by larger neighbor plates the transform push force has been proposed to be such a dynamic interaction between the small juan de fuca plate and the pacific plate we aim to establish the relative importance of transform push for juan de fuca dynamics balancing torques from plate tectonic forces like slab pull ridge push and various resistive forces we first derive two groups of force models models which require transform push across the mendocino transform fault and models which do not intraplate stress orientations computed on the basis of the force models are all close to identical orientations of predicted stresses are in agreement with observations stress magnitudes are sensitive to the force model we use but as we have no stress magnitude observations we have no means of discriminating between force models model stresses in the north and the south of the juan de fuca plate are similar breakup along the nootka fault zone and not in the gorda region can be explained if the local strength of a lithosphere column depends on lithospheric age stresses are invariant to whether or not transform push is acting on the mendocino transform fault we therefore conclude that the introduction of this extra plate driving force is not required by observations for the juan de fuca plate fl 2001 elsevier science b v all rights reserved

numerical study of explosively developing extratropical cyclones in the northwestern pacific region abstract numerical simulations of six explosively developing extratropical cyclones in the northwestern pacific ocean region are conducted using a regional mesoscale numerical model the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 cyclones are categorized according to the locations where they form and develop okhotsk japan sea oj cyclones originate over the eastern asian continent and develop over the sea of japan or the sea of okhotsk pacific ocean land po l cyclones also form over the asian continent and develop over the northwestern pacific ocean and pacific ocean ocean po o cyclones form and develop over the northwestern pacific ocean two cases the most extreme and normal deepening rate cases for each cyclone type are selected and simulated simulations show that the extreme cyclone of each type is characterized by a different mesoscale structure and evolutionary path which strongly reflect the larger scale environment a

plate boundary deformation between the pacific and north america in the explorer region abstract one of the consequences of plate tectonics is that a spreading ridge will eventually approach a subduction zone the problem whether the possible break up of the approaching ridge will lead to the development of independent micro plates or not is still unresolved some 4 million years ago the interaction between the juan de fuca ridge and the cascadia subduction zone resulted in ridge fragmentation in the explorer region there are two proposed post miocene kinematic models one that proposes the presence of a micro plate and the other that treats the region as a transform deformation zone or so called pseudo plate we use earthquake strain rates derived from 74 events since 1948 to estimate a long term velocity field for the region by comparing this result with the predicted velocity fields for both models we try to discriminate between the two the earthquake strain rates indicate the presence of a transform deformation zone between the north american nam and pacific pac plates the velocity field derived from the inversion of the earthquake strain rates indicates that seismic activity takes up 50 30 1 of the pac nam relative motion nuvel 1a demets et al 1994 effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions geophys res lett 21 2191 2194 within the seismogenic layer of this zone and is indistinguishable in direction from the nuvel 1a pac nam model the presence of this explorer transform zone is consistent with the strain rate and velocity field for the pseudo plate model and indicates that seismicity defines a new plate boundary zone between the pacific and north american plates earthquake derived strain rates are low along the nootka transform which accommodates relative motion between the juan de fuca and north american plates the cause for the absence of significant seismic slip along this transform is unclear and may be closely linked to the fact that the adjacent cascadia subduction zone is locked the micro plate model which we reject predicts sw ne convergence in the eastern explorer region and this is inconsistent with the earthquake strain rates as well as with surface fault observations

climatology and dynamics of the link between dry intrusions and cold fronts during winter part ii front centred perspective the conceptual picture of an extratropical cyclone typically includes a cold front and a dry intrusion di behind it by objectively identifying fronts and dis in ecmwf era interim data for 1979 2014 part i quantified the climatological relationship between cold fronts and dis driven by the finding that front intensity and frontal precipitation are enhanced in the presence of dis here we employ a front centred perspective to focus on the dynamical and thermodynamical environment of cold fronts with and without dis in the northern hemisphere winter distinguishing between trailing fronts that connect to a parent cyclone and isolated fronts examples of dis behind each type illustrate the baroclinic environment of the trailing front and the lack of strong temperature gradients across the isolated front composite analyses of north atlantic and north pacific fronts outline the major differences in the presence of dis compared to similar fronts but without dis in their vicinity the magnitude and spatial structure of the modification by dis depends on the front intensity yet generally with dis trailing fronts occur with stronger slp dipole deeper upper tropospheric trough stronger 10 m wind gusts enhanced ocean sensible and latent heat fluxes in the cyclone cold sector and heavier precipitation isolated weak fronts exhibit similar behaviour with different spatial structure this study highlights the central role of dis for shaping the variability of fronts and their associated environment and impact

the distal segment of etna s 2001 basaltic lava flow etna s 2001 basaltic lava flow provided a good example of the distal flow segment between the flow front and stable channel across which the flow evolves from channel contained to dispersed this zone was mapped with meter precision using lidar data collected during 2004 and 2005 these data supported by field mapping show that the flow front comprised eight lobes each 10 to 20 m high the flow front appears to have advanced not as a single unit but as a series of lobes moving forward one lobe at a time primary lobes were centered on the channel axis and marginal lobes were off axis the lobes advanced as breakouts of low yield strength lava from the flow core of the stalled flow front marginal lobes were abandoned and contributed to marginal levees flanking the transitional channel for etna s 2001 flow the transitional channel is 140 m wide 700 m long and fed a 240 m long zone of dispersed flow the change from stable to transitional channel occurred at a major reduction in slope above this the stable channel is 5 2 km long 55 to 105 m wide and bounded by 15 to 25 m high levees and the stable channel is located over a previous channel in a final stage of activity lava ponding at the break in slope that marks the terminus of the stable channel put pressure on the eastern levee causing it to fail liberated lava then fed a final break out to the east similar flow front features occur at other volcanoes indicating that similar processes are characteristic of dispersed flow zones

a simplified two component model for the lateral growth of pahoehoe lobes unconfined pahoehoe lobes composed of networks of numerous pahoehoe toes often show a transverse profile with central thickening and crude bilateral symmetry the overall widths of individual lobes are often relatively constant compared to the large diversity in widths of individual toes these observations collectively suggest that there is a lateral self confinement mechanism at the scale of a lobe although previous correlated random walk models successfully address the nature of this mechanism the underlying physical processes are still not clearly understood here we propose a simplified two component model for the lateral self confinement mechanism the model assumes that the surface crust retains an inner hot core until its overpressure surpasses the strength of the crust it also assumes that fracturing of the crust occurs at the top of the flow where the crust has the weakest strength and then a breakout of the hot core spills out to form a new flow unit episodic fracturing and subsequent coalescence of multiple toes form a broad lobe which is then considered theoretically to behave as a single large flow unit although simplified the model can determine the inflated thickness necessary to fracture the crust and the width scale of the lateral spreading with a self confinement effect the model also provides theoretical support for the correlated random walk model for pahoehoe emplacement

a model for the opening of ephemeral vents in a stationary lava flow abstract a model is proposed for the opening of ephemeral vents in the solid front of a stationary lava flow the front is considered to be a viscoelastic shell which deforms due to the pressure exerted on it by the inner fluid lava the vent opens when the normal stress in the front overcomes the tensile strength of solid lava cooling of the front is considered and the increase in crust thickness as the isothermal surface at the solidus temperature deepens into the lava body is calculated the thermal effect is negligible if the timescale for the opening of ephemeral vents is on the order of days as is often observed considering stationary flow lengths of a few hundred meters this timescale corresponds to an average viscosity of the crust of 10 12 pa s assuming reasonable values of the crust strength and initial thickness observation of ephemeral vents on mount etna is found to be consistent with the model predictions

development of lava tubes in the light of observations at mauna ulu kilauea volcano hawaii during the 1969 1974 mauna ulu eruption on kilauea s upper east rift zone lava tubes were observed to develop by four principal processes 1 flat rooted crusts grew across streams within confined channels 2 overflows and spatter accreted to levees to build arched roofs across streams 3 plates of solidified crust floating downstream coalesced to form a roof and 4 pahoehoe lobes progressively extended fed by networks of distributaries beneath a solidified crust still another tube forming process operated when pahoehoe entered the ocean large waves would abruptly chill a crust across the entire surface of a molten stream crossing through the surf zone these littoral lava tubes formed abruptly in contrast to subaerial tubes which formed gradually all tube forming processes were favored by low to moderate volume rates of flow for sustained periods of time tubes thereby became ubiquitous within the pahoehoe flows and distributed a very large proportionof the lava that was produced during this prolonged eruption tubes transport lava efficiently once formed the roofs of tubes insulate the active streams within allowing the lava to retain its fluidity for a longer time than if exposed directly to ambient air temperature thus the flows can travel greater distances and spread over wider areas even though supply rates during most of 1970 1974 were moderate ranging from 1 to 5 m3 s large tube systems conducted lava as far as the coast 12 13 km distant where they fed extensive pahoehoe fields on the coastal flats some flows entered the sea to build lava deltas and add new land to the island the largest and most efficient tubes developed during periods of sustained extrusion when new lava was being supplied at nearly constant rates tubes can play a major role in building volcanic edifices with gentle slopes because they can deliver a substantial fraction of lava erupted at low to moderate rates to sites far down the flank of a volcano we conclude therefore that the tendency of active pahoehoe flows to form lava tubes is a significant factor in producing the common shield morphology of basaltic volcanoes

surface wave tomography of the gulf of california 1 we measured interstation fundamental mode rayleigh wave phase velocities using data from the nars baja seismic network located around the gulf of california a region average shear velocity model and a set of azimuthally anisotropic phase velocity maps are obtained from these data the average shear velocity structure shows a strong low velocity zone underlying a thin lid and the data are suggestive of low velocities down into the transition zone the phase velocity maps display signatures of sedimentary layers crustal thickness variations upwelling under the plate boundary and the presence of the subducted farallon microplate remnants beneath the gulf the upper mantle features inferred from this study provide new seismic evidence on the tectonic evolution of the region

the effect of large scale flow on low level frontal structure and evolution in midlatitude cyclones abstract observational and modeling studies documented in the literature indicate that the large scale flow has an important effect on the structure and evolution of low level fronts in midlatitude cyclones the purpose of this paper is to address the role of the large scale flow on low level cyclone frontal structure and evolution through a combined observational and idealized modeling approach analyses of two observed cyclone cases embedded in large scale diffluence and confluence respectively are presented to illustrate two possible cyclone frontal structures and evolutions specifically the cyclone moving into a diffluent high amplitude ridge becomes meridionally elongated and possesses a strong meridionally oriented cold front and a weak warm front the cold front rotates into the warm front forming an occluded front in the manner of the norwegian cyclone model as indicated by the narrowing of the thermal ridge connecting the warm sector to the cyclone center in contrast the cyclone moving i

current tectonics of northern cascadia from a decade of gps measurements 1 global positioning system gps measurements to study regional deformation were initiated in northern cascadia in the late 1980s and early 1990s on the basis of a decade of gps data we derive a crustal velocity field for nw washington sw british columbia the permanent and campaign gps velocities are defined with respect to north america in the itrf2000 reference frame velocity uncertainties are estimated using a model of time series noise spectra this new velocity field is the basis for interpretation of the tectonics of the northern cascadia subduction system gps velocities are interpreted in terms of interseismic loading of the megathrust using different coupling models our data confirm that the upper part of the megathrust is nearly fully locked an exponential model for the downdip transition zone gives slightly better agreement with the data compared to the common linear transition the landward decrease of forearc strain loading is smaller than predicted by any of the current subduction interseismic models this could be a consequence of a small 0 3 mm yr long term motion of the southern vancouver island forearc with respect to north america or of a concentration of interseismic strain across the elastically weaker cascadia volcanic arc in northern vancouver island our velocity field supports the existence of an independent explorer microplate currently underthrusting underneath north america at least up to brooks peninsula further north gps velocities indicate transient and or permanent deformation of northernmost vancouver island related to the interaction with the explorer microplate and possibly with the queen charlotte transform margin

conclusion recommendations and findings of the red seed working group red seed stands for risk evaluation detection and simulation during effusive eruption disasters and combines stakeholders from the remote sensing modelling and response communities with experience in tracking volcanic effusive events the group first met during a three day long workshop held in clermont ferrand france between 28 and 30 may 2013 during each day presentations were given reviewing the state of the art in terms of a volcano hot spot detection and parameterization b operational satellite based hot spot detection systems c lava flow modelling and d response protocols during effusive crises at the end of each presentation set the four groups retreated to discuss and report on requirements for a truly integrated and operational response that satisfactorily combines remote sensors modellers and responders during an effusive crisis the results of collating the final reports and follow up discussions that have been on going since the workshop are given here we can reduce our discussions to four main findings 1 hot spot detection tools are operational and capable of providing effusive eruption onset notice within 15 min 2 spectral radiance metrics can also be provided with high degrees of confidence however if we are to achieve a truly global system more local receiving stations need to be installed with hot spot detection and data processing modules running on site and in real time 3 models are operational but need real time input of reliable time averaged discharge rate data and regular updates of digital elevation models if they are to be effective the latter can be provided by the radar photogrammetry community 4 information needs to be provided in an agreed and standard format following an ensemble approach and using models that have been validated and recognized as trustworthy by the responding authorities all of this requires a sophisticated and centralized data collection distribution and reporting hub that is based on a philosophy of joint ownership and mutual trust while the next chapter carries out an exercise to explore the viability of the last point the detailed recommendations behind these findings are detailed here

risk evaluation detection and simulation during effusive eruption disasters lava ingress into a vulnerable population will be difficult to control so that evacuation will be necessary for communities in the path of the active lava followed by post event population infrastructural societal and community replacement and or relocation there is a pressing need to set up a response chain that bridges scientists and responders during an effusive crisis to allow near real time delivery of globally standard products for a timely and adequate humanitarian response in this chain the scientific research groups investigating lava remote sensing and modelling need to provide products that are both useful to and trusted by the crisis response community requirements for these products include a formats that can be immediately integrated into a crisis management procedure and b in an agreed and stable standard a review of current capability reveals that we are at a point where the community can provide such a response as is the aim of the red seed risk evaluation detection and simulation during effusive eruption disasters working group this book is the first production of this group and is intended not only as a directory of current capabilities and operational service providers but also as a statement of intent and need while providing a simulation designed to demonstrate how a truly pan disciplinary response to an effusive crisis could work

the mechanical properties of solidified polyethylene glycol 600 an analog for lava crust abstract the strength of lava crust and the role of that crust in determining lava flow dynamics and morphology are of fundamental importance in modeling lava flow behavior great improvements to flow models have been made by combining theoretical analysis with the results from analog experiments using polyethylene glycol peg 600 wax which solidifies just below room temperature and can be used to simulate solidifying flows however a paucity of experimental data on the mechanical properties of solid peg 600 has limited the quantitative interpretation of the role of crust in these experiments we have therefore conducted experiments to measure the mechanical properties tensile strength shear strength and young s modulus of solidified peg 600 at temperatures and strain rates similar to those employed in analog experiments the mechanical properties of peg 600 can be modeled by a power law function of temperature with the tensile strength exhibiting an additional dependence on strain rate at intermediate temperatures marked changes in the temperature dependence of the young s modulus and in the character of failure surfaces indicate a transition from brittle to ductile behavior we find that the strength of solid peg 600 at experimental temperatures and strain rates exceeds that inferred for the crust on active laboratory flows by four orders of magnitude this discrepancy is best explained by the presence of a thin visco elastic layer separating the solid surface from the fluid interior of peg 600 flows a model that has been suggested to explain the behavior of some basaltic lava flows

seismic low velocity layer at the top of subducting slabs observations predictions and systematics abstract layered structure persists at the tops of subducting plates to depths in excess of 150 km a low velocity channel several km thick produces guided seismic guided waves which indicate that the top of the downgoing plate remains coherent and probably has not eclogitized to 150 km depth the surrounding medium has seismic velocities 3 6 faster than standard earth models as inferred from direct travel times presumably because the waveguide lies atop cold descending lithosphere however guided waves travel more slowly several tests with full waveform synthetics show that the guided waves can be observed only if excited by sources that lie near or within the low velocity channel thus the frequent observation of dispersed body waves indicates that intermediate depth earthquakes tend to lie in waveguides also receivers must be favorably placed observations for seven circum pacific subduction zones show such signals which can be explained as low velocity channels 2 8 km thick velocity anomalies within low velocity channels are largest at shallowest depths up to 14 slower than surroundings at depths less than 150 km diminishing to

do microplates in subduction zones leave a geological record active microplate boundaries in ocean continent subduction zones may induce deformation of the overlying plate and spatial or geochemical variations in the volcanic arc we discuss two modern cases the first is the south gorda juan de fuca plate boundary in the cascadia subduction zone where there is little or no effect on the overriding plate and the oceanic plate takes up much of the deformation the second case is the cocos rivera plate boundary in the middle america trench where the overlying colima graben contains substantial deformation in a zone extending from the trench to the volcanic arc and the sub duction related volcanism is spatially and geochemically complex we apply these observations to boundaries of the arguello monterey guadalupe and magdalena microplates which existed in the subduction zone west of baja california at various times from 20 to 12 5 ma the past positions of these boundaries relative to baja california are constrained by global plate reconstructions closure of the gulf of california and an estimate of extension in the mexican basin and range province existing regional mapping and our additional reconnaissance mapping show that paleocene to eocene fluvial and marine sedimentary rocks south of ensenada along the western baja california peninsula and eastward to the mid miocene volcanic arc are undeformed limited available data reveal no major spatial or geochemical variations in the mid miocene volcanic arc that might correlate with the past positions of the microplate boundaries thus these microplate boundaries had little to no effect on the overriding continental plate the nature of guadalupe and magdalena interactions with north america may have been closer to the south gorda juan de fuca example with possible internal deformation of the microplates the monterey and arguello microplates may have behaved like the modern explorer plate with largely strike slip motion relative to north america during their last stages of existence tectonic patterns similar to these examples may be expected from other plate boundaries where a plate is fragmenting as it enters a subduction zone e g the aluk plate in the trench beneath west antarctica in early tertiary time whether these microplates subsequently become attached to the overriding continental plate or to a larger oceanic plate and whether this causes deformation in the region of the former subduction zone may depend on the velocities of the nearby major plates and the relative orientations of the microplate boundaries

new constraints on subduction zone structure in northern cascadia summary a detailed passive seismic experiment was carried out across southwestern british columbia and northwestern washington to investigate the structure of the subducting juan de fuca plate and mantle wedge in cascadia and its relation to intraslab seismicity as part of the polaris project 31 three component broad band stations were deployed in an approximately linear array spanning southern vancouver island the gulf and san juan islands watcom county and the british columbia lower mainland p wave coda from 41 teleseismic events have been employed in formal inversions for fine scale shear velocity structure our results indicate a structure very similar to that identified across a comparable profile in central oregon the continental moho is evident at the eastern end of the profile near 35 km depth but disappears towards georgia strait puget sound a prominent low s velocity zone is clearly evident below southern vancouver island dipping eastwards through georgia strait puget sound and coincides with the e reflection zone originally identified in lithoprobe studies structure below the e layer is much less prominent and varies intermittently along the array based on the observations and interpretations of similar structures beneath oregon alaska and south america and its projection to mantle depths we suggest that the low velocity e layer represents the dehydrating oceanic crust of the subducting juan de fuca plate this interpretation is consistent with recent seismicity studies that place shallow wadati benioff events within the oceanic mantle and implies that the oceanic crust is 6 8 km shallower beneath vancouver island than previously assumed as in oregon we interpret the diminished signature of oceanic crust below a depth of 45 km to signal the presence of eclogitization which in turn supplies water to serpentinize the overlying forearc mantle

seismotectonics of the explorer region 1 the explorer region offshore western canada is a tectonically complex area surrounded by the pacific north america and juan de fuca plates existing tectonic models for the region differ fundamentally proposed plate configurations range from multiple independent plate fragments to an explorer plate now fused to north america along the continental margin and cut by pacific north america transform faults in the west we present new seismological data constraining the region s current tectonics we use three component regional waveforms to determine the source parameters of 84 earthquakes with magnitude greater than 4 combined with 34 harvard centroid moment tensor solutions they represent the region s largest earthquake source parameter data set obtained by robust waveform modeling techniques in addition we perform joint epicenter determination to relocate larger earthquakes recorded since 1918 the source parameters and improved locations provide a consistent tectonic picture earthquake slip vector azimuths along the pacific plate boundary change smoothly and are significantly less northerly oriented than the pacific north america plate motion direction requiring an independent explorer plate the present day pacific explorer boundary is formed by transform faults subparallel to the revere dellwood wilson fault plate motion vectors indicate that the winona block is part of the explorer plate current explorer motion is more northerly than indicated by magnetic anomalies prior to 2 ma implying a recent change possibly coinciding with a northwestward ridge jump near explorer plate s northern end transferring the winona block from the pacific to the explorer plate in response to these plate motion changes the region north of the western sovanco fracture zone was assimilated into the pacific plate the region around the eastern sovanco fracture zone characterized by broadly distributed seismicity is composed of well defined sets of conjugate faults bounding rotating crustal blocks earthquake fault strikes agree with the dominant northwest southeast fault sets however the conjugate sets must be also active to fully accommodate present day explorer plate motion the sw portion of the strike slip nootka fault zone the explorer juan de fuca plate boundary is well defined by focused seismicity however its full extent under nootka island remains unresolved the explorer north america boundary shows sporadic low magnitude seismicity our explorer north america rotation pole predicts convergence varying from negligible at the boundary s northwest end to 2 cm yr at the se end this convergence can be accommodated either by subduction or by crustal thickening extending to the north american continent we favor subduction based on low deformation rates observed by onshore gps sites the present explorer plate system configuration is a result of stepwise reorientation of the explorer ridge system each step successively reducing the subduction rate relative to north america

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

plate deformation at depth under northern california slab gap or stretched slab plate kinematic interpretations for northern california predict a gap in the underlying subducted slab caused by the northward migration of the pacific north america juan de fuca triple junction however large scale decompression melting and asthenospheric upwelling to the base of the overlying plate within the postulated gap are not supported by geophysical and geochemical observations we suggest a model for the interaction between the three plates which is compatible with the observations in this slab stretch model the juan de fuca plate under coastal northern california deforms by stretching and thinning to fill the geometrical gap formed in the wake of the northward migrating mendocino triple junction the stretching is in response to boundary forces acting on the plate the thinning results in an elevated geothermal gradient which may be roughly equivalent to a 4 ma oceanic lithosphere still much cooler than that inferred by the slab gap model we show that reequilibration of this geothermal gradient under 20 30 km thick overlying plate can explain the minor neogene volcanic activity its chemical composition and the heat flow in contrast to northern california geochemical and geophysical consequences of a true slab gap can be observed in the california inner continental borderland offshore los angeles where local asthenospheric upwelling probably took place during the miocene as a result of horizontal extension and rotation of the overlying plate the elevated heat flow in central california can be explained by thermal reequilibration of the stalled monterey microplate under the coast ranges rather than by a slab gap or viscous shear heating in the mantle

air sea interaction processes influencing the development of a shapiro keyser type cyclone over the subtropical south atlantic ocean this study analyzes the impacts of latent and sensible heat exchanges between the atmosphere and the ocean in a non explosive shapiro keyser type cyclogenesis event that occurred over the southwestern south atlantic ocean the synoptic evolution shows a relatively strong warm front and a cold frontal fracture during the system s development and a warm seclusion in its mature stage characterizing a shapiro keyser type cyclone numerical experiments with the arw wrf model version 3 3 were used to investigate the influences of sensible and latent fluxes on the track of the surface low intensity of the fronts and coupling of the lower and upper troposphere the simulations indicate that in the presence of these fluxes the cyclone underwent greater intensification had a longer life time and longer trajectory and presented a typical southeastward movement in the absence of these fluxes the cyclone developed a weaker warm front with consequent reduction of diabatic heating due to grid scale precipitation along it this reduced the negative pressure tendency southeast of the cyclone center and the surface cyclone moved northeastward showing a decoupling of the lower and upper level waves a consequence of this anomalous tracking is the location of the surface cyclone beneath the upper level trough axis where there is no upper level divergence associated with cyclonic vorticity advection contributing to the further system intensification numerical experiments suggest that for this shapiro keyser type cyclone the air sea interaction processes are crucial to obtain a cyclone with features similar to the observations

explorer deformation zone evidence of a large shear zone and reorganization of the pacific juan de fuca north american triple junction recently collected multibeam bathymetry and hydroacoustic earthquake data are used to investigate the recent tectonics of the explorer juan de fuca ridge systems the boundaries between the pacific and northern juan de fuca plates the bathymetric and seismic evidence presented is consistent with a zone of shear extending well south of the sovanco fracture zone to include the heck and heckle seamounts and potentially as far south as the springfield seamounts and cobb offset along the juan de fuca ridge this indicates that the triple junction between the pacific juan de fuca north american plates may be reorganizing southward to establish at the cobb offset

motion of the rivera plate since 10 ma relative to the pacific and north american plates and the mantle abstract to better understand the influence of rivera plate kinematics on the geodynamic evolution of western mexico we use more than 1400 crossings of seafloor spreading magnetic lineations along the pacific rivera rise and northern mathematician ridge to solve for rotations of the rivera plate relative to the underlying mantle and the pacific and north american plates at 14 times since 9 9 ma our comparison of magnetic anomaly crossings from the undeformed pacific plate to their counterparts on the rivera plate indicates that significant areas of the rivera plate have deformed since 9 9 ma dextral shear along the southern edge of the plate from 3 3 2 2 ma during a regional plate boundary reorganization deformed the rivera plate farther into its interior than previously recognized in addition seafloor located north of two rupture zones within the rivera plate sutured to north america after 1 5 ma anomaly crossings from these two deformed regions thus cannot be used to reconstruct motion of the rivera plate finite rotations that best reconstruct pacific plate anomaly crossings onto their undeformed counterparts on the rivera plate yield stage spreading rates that decrease gradually by 10 between 10 and 3 6 ma decrease rapidly by 20 after 3 6 ma and recover after 1 ma the slowdown in pacific rivera seafloor spreading at 3 6 ma coincided with the onset of dextral shear across the then incipient southern boundary of the rivera plate with the pacific plate the available evidence indicates that the rivera plate has been an independent microplate since at least 10 ma contrary to published assertions that it fragmented from the cocos plate at 5 ma motion of the rivera plate relative to north america has changed significantly since 10 ma in concert with significant changes in pacific rivera motion a significant and robust feature of rivera north america motion not previously recognized is the cessation of margin normal convergence and thus subduction from 2 6 to 1 0 ma along the entire plate boundary followed by a resumption of trench normal subduction along the southern half of the rivera north america plate boundary after 1 0 ma motion of the rivera plate relative to the underlying mantle since 10 ma has oscillated between periods of landward motion and seaward motion the evidence suggests that the torque exerted by slab pull on this young and hot oceanic plate is either minimal or is effectively counterbalanced by forces that resist its motion

transient phenomena in vesicular lava flows based on laboratory experiments with analogue materials realistic lava flow models require a comprehensive understanding of the rheological properties of lava under a range of stress conditions previous measurements have shown that at typical eruption temperatures lavas are non newtonian this is commonly attributed to the formation and destruction of crystal networks in the present study the effects of bubbles on the time dependent non newtonian properties of vesicular melts are investigated experimentally using analogue materials the shear thinning behaviour of bubbly liquids is shown to be dependent on the previous shearing history this thixotropic behaviour which was investigated using a rotational vane viscometer is caused by delayed bubble deformation and recovery when subjected to changes in shear stress the viscoelastic transition and the transient flow behaviour of analogue fluids were studied using both a rotational vane viscometer and oscillatory shear apparatus these experiments have shown that vesicular suspensions are viscoelastic fluids with a yield strength power law rheology and a non zero shear modulus these properties are also found in polymer fluids commonly used as analogue materials for lava such as gum rosin we show that when materials with this rheology are accelerated in channels they may be fragmented and when they flow through a narrowing conduit pulsating flow can develop as a consequence of a transition from slip to non slip conditions at the conduit wall this has important implications both for effusive and explosive volcanic eruptions

a model for the formation of lava tubes by roofing over a channel the formation of lava tubes is a common phenomenon on some basaltic volcanoes such as etna a model for tube formation by roofing of a channel is proposed and involves first describing lava as a bingham liquid flowing down a slope it is further assumed that lava flows in a channel with rectangular cross section as a result of heat loss into the atmosphere a crust is gradually formed on the upper surface of the flow and this crust eventually welds to the channel levees we assume that a lava tube is formed when such a crust is sufficiently thick to resist the drag of the underlying flow and to sustain itself under its own weight the minimum thickness of the crust satisfying such conditions depends on the tensile strength and shear strength of the crust itself assuming that the growth of the crust produces a downflow linear increase of the shear stress at the interface between flowing lava and the crust the distance is evaluated between the eruption vent and the point where the tube is formed the model predicts that if the flow rate is constant the thickness of the flow increases as the crust fragments grow and weld to each other and the velocity of the crust decreases to zero once the lava tube is formed the initial flow rate can be achieved by a flow thickness smaller than the vertical size of the tube with the same viscous dissipation this may explain why under steady state conditions the lava level inside a tube is frequently lower than the roof of the tube itself

the neogene alert bay volcanic belt of northern vancouver island canada descending plate edge volcanism in the arc trench gap abstract the alert bay volcanic belt trends northeasterly across northern vancouver island coincident with the trace of the subducted juan de fuca explorer plate edge volcanism began in the west at brooks peninsula about 8 ma ago but occurred in most centers 3 5 1 ma ago there is a suggestion of eastward migration of activity and shift from basalt to dacite or rhyolite with time most of the volcanism was coincident with a time of rapid changes in the geometry of subduction as inferred from offshore magnetic patterns and with a hiatus in mainland cascade volcanic arc activity geometry and chronometry suggest this is a descending plate edge volcanic belt where disruption of steady state plate consumption patterns triggered magma genesis chemically the rocks are quite variable with divergent fractionation trends one trend resembles that of mull hebrides with a plagiophyric basalt of transitional alkaline subalkaline mildly tholeiitic and aluminous character which differentiated to clinopyroxene andesite and eventually to tholeiitic rhyolite and mildly tholeiitic calc alkaline dacite both of k poor magma type the other trend is like the cascades with aluminous aphyric calc alkaline basalt hornblende and or hypersthene andesite and k poor dacite this divergent character is also evident in ba rb nb and zr fractionation trends major and trace element discriminant diagrams generally identify the basalts as within plate types the 87 sr 86 sr isotope ratio is relatively low averaging 0 70325 and shows no trend with rock type or differentiation series oxygen in the entire suite is relatively heavy 18 o averaging 7 1 even the basalts are 18 o enriched oxygen shows no trend with degree of hydration rock type or series these isotopic and chemical data are compatible with minor crustal contamination of mafic primary magmas followed by fractional crystallization under different oxidation and hydration conditions

the northern limit of the subducted juan de fuca plate system analysis of data recorded at an array of three component broadband seismograph stations deployed on northern vancouver island and the adjacent british columbia mainland at the northern end of the cascadia subduction zone provides the first constraints on the s wave velocity structure of this region and permits us to define the northern limit of the subducted juan de fuca plate system during a 2 year period more than 80 teleseisms were recorded at our five stations the method of receiver function analysis was used to constrain the s velocity structure to upper mantle depths beneath the northern three stations a relatively simple continental crust is interpreted with a well defined moho near 37 39 km depth an upper crustal s velocity discontinuity at these stations is interpreted as the top of the high velocity rocks of the wrangellia terrane in contrast more complicated structure dominated by pronounced low velocity zones dipping to the ne are interpreted beneath our southern two stations the shallower low velocity zone is 6 8 km thick has an s velocity contrast of 0 6 1 1 km s and lies within the continental crust this feature is similar to a pronounced low velocity layer the e zone imaged beneath southern vancouver island the deeper low velocity zone is interpreted as the subducted oceanic crust we interpret the pronounced change in s velocity structure that we observe as the northern limit of the subducted oceanic plate beneath vancouver island this change coincides with significant changes in topography heat flow gravity and geochemistry

ephemeral plate tectonics at the queen charlotte triple junction three plate boundaries the queen charlotte transform the cascadia subduction zone and the juan de fuca ridge meet in a complex triple junction offshore vancouver island some interpretations of the plate tectonics of the region have included the explorer ridge the dellwood knolls and the tuzo wilson volcanic field as part of the spreading system requiring up to three triple junctions in the region new seabeam bathymetry interpreted with existing regional data sets indicate that the dellwood knolls and tuzo wilson volcanic field are not independent plate boundaries but the result of leaky transform tectonics between two overlapping transform faults seismicity shows that the explorer plate is being deformed by pacific north american relative motion as a new transform plate boundary forms and cuts off the explorer ridge the system is evolving to a single triple junction at the northern terminus of the juan de fuca ridge where it meets the nootka deformation zone thus the explorer microplate which was spawned 5 ma is an ephemeral adjustment to mechanical difficulties at the triple junction this new model implies that the explorer subduction zone is no longer active ephemeral oceanic microplates have also existed at pacific north american triple junctions off southern california and baja california

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

morphology of the explorer juan de fuca slab edge in northern cascadia imaging plate capture at a ridge trench transform triple junction the explorer plate is a young oceanic microplate that accommodates relative motion between the pacific juan de fuca and north america plates near northern vancouver island canada the northern limit of explorer plate juan de fuca subduction and the fate of the slab in northern cascadia are poorly understood we use passive teleseismic recordings from an array of polaris broadband seismic stations to image crustal and upper mantle structure beneath northern vancouver island into the interior of british columbia a clear signature of subducted material extends northeast from the brooks peninsula at crustal levels beneath georgia strait and the mainland deep into the mantle to 300 km depth complexity in slab morphology results from juan de fuca ridge subduction and toroidal flow around the slab edge in agreement with geophysical and geological data we propose a tectonic model for the explorer plate in which its separation from the juan de fuca plate is caused by the thermomechanical erosion of the slab edge and slab thinning at shallow levels both of which slow convergence with north america and lead eventually to plate capture

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

structure and evolution of subtropical cyclone anita as evaluated by heat and vorticity budgets this paper explores the evolution of subtropical cyclone anita which occurred near the east coast of brazil 19 s 37 w in march 2010 thermodynamic and dynamic processes during anita s lifecycle are investigated using the heat and vorticity budget equations the cyclone developed with hybrid characteristics and moved anomalously to the southwest where it coupled with an upper level cut off low during the mature phase this coupling was the main dynamical mechanism for further cyclone deepening anita then remained quasi stationary about 30 s 47 w for two days due to an upper level dipole pattern which prevented earlier displacement of the upper level low counterpart when the dipole pattern dissipated the cyclone moved southeast and underwent extratropical transition whilst merging with a mid latitude frontal cyclone diabatic heating and horizontal temperature advection are found to be essential for the subtropical development during extratropical transition it is instead diabatic cooling together with adiabatic cooling and warm air advection that act as the main mechanisms to influence the local temperature tendencies at low levels low level cyclonic tendencies were mostly due to convergent flow and the residual vorticity partially destroyed the vorticity tendencies produced by the divergence term moreover in regions and levels where convection could explain some of the vorticity tendencies it is found that apparent sinks of cyclonic vorticity were related to negative vorticity due to divergence i e convergent flow whilst apparent sources were related to positive vorticity due to divergence i e divergent flow

partial melting of slab window margins genesis of adakitic and non adakitic magmas abstract when a mid ocean spreading ridge subducts it typically splits apart at depth to form two tapered slab edges separated by asthenospheric mantle within a slab window we examine the fate of the slab edges using simplified slab window geometries specific thermal parameters and assumptions regarding shear stress and slab hydration six fundamental zones of slab anatexis are identified and classified according to expected melt and restite compositions non adakitic melts of granodioritic to tonalitic composition are generated along the plate edges at depths of 5 65 km whereas adakitic melts form proximal to the edges at depths of 25 90 km as anatexis proceeds the subducted crust is converted to a migmatite of slab melt and eclogitic restite much of the migmatite may shear away from the slab and become incorporated into the mantle the melts will rise and leave behind fragments of restite within mantle peridotite if the peridotite is part of the overriding plate then the restite fragments may become long term residents of the continental lithospheric mantle however if the restite becomes entrained in the asthenosphere it may undergo upwelling and melting or flow away as ductile streaks to become long term mantle heterogeneities slab windows are thereby identified as important sites for slab melting and geochemical replenishment of the mantle