the topography and morphology of low shields and associated landforms of plains volcanism in the tharsis region of mars abstract the morphology and topography of volcanic landforms provide critical information to the investigation of their tectonic setting and the physical characteristics e g rheology of their eruption products their investigation is also an important prerequisite for studies of comparative planetology e g the comparison between surface features of the earth and other planetary bodies numerous small and low shield volcanoes on mars and associated vents and lava flows have previously been compared to terrestrial plains style volcanism which is defined as being an intermediate style between flood basalts and the hawai ian shields this study investigates the topography and morphology of martian landforms associated with plains volcanism using mola moc themis hrsc and hirise data low shields and other landforms of plains volcanism on mars display similarities with terrestrial basaltic volcanic fields and we do not observe any features that do not have morphologic analogues on earth the most typical landforms of martian plains style volcanism are low shields defined as volcanic shields with diameters of typically less than 50 km heights of a few hundred meters only and extremely shallow flank slopes of less than 0 5 other surface features related to plains style volcanism on mars are craters fissure vents cinder and spatter cones lava flows that are commonly associated with lava channels and tubes lava inflation features and volcanic rift zones our results reconfirm the viking orbiter based conclusion that plains volcanism in the eastern snake river plains is perhaps the best terrestrial morphological analogue for these martian surface features icelandic shields distinct structures in hawai i and other basaltic landforms also show similarities to martian plains volcanism sinuous rilles previously not described in association with plains volcanism on mars are interpreted as evidence for high eruption rates the extremely shallow flank slopes of the low shields suggest the eruption of shield building lavas with low viscosity which might be the result of high eruption temperatures high effusion rates a low si and a high mg content along with a possible high fe content or a combination of these factors the spatial distribution of low shield clusters in tharsis does not show any obvious association with large scale tectonic features plains volcanism might represent a relatively recent type of volcanism on mars which is not related to mantle plumes but to a zone of partial melting in an anomalously warm mantle underneath a thickened crust schumacher and breuer geophys res lett 34 l14202 doi 10 1029 2007gl030083 2007

morphometry of terrestrial shield volcanoes abstract shield volcanoes are described as low angle edifices built primarily by the accumulation of successive lava flows this generic view of shield volcano morphology is based on a limited number of monogenetic shields from iceland and mexico and a small set of large oceanic islands hawaii galapagos here the morphometry of 158 monogenetic and polygenetic shield volcanoes is analyzed quantitatively from 90 meter resolution srtm dems using the morvolc algorithm an additional set of 24 lava dominated shield like volcanoes considered so far as stratovolcanoes are documented for comparison results show that there is a large variation in shield size volumes from 0 1 to 1000 km3 profile shape height basal width h wb ratios mostly from 0 01 to 0 1 flank slope gradients average slopes mostly from 1 to 15 elongation and summit truncation although there is no clear cut morphometric difference between shield volcanoes and stratovolcanoes an approximate threshold can be drawn at 12 average slope and 0 10 h wb ratio principal component analysis of the obtained database enables to identify four key morphometric descriptors size steepness plan shape and truncation hierarchical cluster analysis of these descriptors results in 12 end member shield types with intermediate cases defining a continuum of morphologies the shield types can be linked in terms of growth stages and shape evolution related to 1 magma composition and rheology effusion rate and lava pyroclast ratio which will condition edifice steepness 2 spatial distribution of vents in turn related to the magmatic feeding system and the tectonic framework which will control edifice plan shape and 3 caldera formation which will condition edifice truncation

a new method to estimate the overtopping and overflow discharge at over washed and breached dikes abstract most of the experience collected on wave overtopping is concentrated on emerged or zero freeboard structures and only few experiments are available on over washed dikes the experience on submerged crest conditions is principally related to rubble mound structures and limited to the wave reflection and transmission processes the existing tools for the prediction of the average wave overtopping discharge q at dikes are therefore targeted to represent overtopped structures leading to cautious estimates at over washed dikes and unrealistic overestimations in case of catastrophic scenarios such as breached dikes this paper proposes a new conceptual and practical method for the prediction of q that is valid for both over washed and fully breached dikes it consists of three physically based formulae whose coefficients are fitted on a new numerical database of smooth structures under variable wave attack the predictions are compared with the new numerical results and the data and the tools available from the literature i e experimental data formulae and neural network the new method gives a more realistic representation of the overtopping and overflow processes reducing significantly the overestimation in case of breaching and being at least as accurate as the existing tools in case of over washing

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

wave reflection from coastal structures in design conditions based on an extensive database of more than 4000 data this paper analyses wave reflection for various types of coastal structures in design conditions such as smooth rock and armour unit slopes a new simple formula has been developed that relates the reflection coefficient to the breaker parameter and seems to fit all kinds of revetment materials by changing two coefficients these coefficients depend only on the correct roughness factor provided by recent research on overtopping discharges the effects on reflection due to composite slopes and to low crests are also examined and proper extensions of the formula are provided 2008 elsevier b v all rights reserved

how do deep water volcanoes grow abstract deep water volcanoes are emplaced in water depths 1 0 km and are widespread along continental margins and in ocean basins whilst the external morphology of deep water volcanoes can be mapped using bathymetric surveys their internal structure and true volume remain enigmatic it is thus difficult to determine how deep water volcanoes grow we investigate 13 late miocene to quaternary deep water volcanoes that are imaged in 3d by seismic reflection data from the northern south china sea which allow us to quantify their external morphology and examine their internal structure these deep water volcanoes were emplaced in water depths 1 5 km are relatively small 15 mpa which are typical of water depths 1 5 km inhibited degassing and fragmentation of ascending magma and thus erupted lava this lack of degassing and fragmentation permitted effusive eruptions during the latter stages of volcanism our models for volcano growth in the deep submarine realm demonstrate the power of using 3d seismic data when investigating the internal structure and total volume of deep water volcanoes

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

small domes on venus probable analogs of icelandic lava shields on the basis of observed shapes and volumetric estimates we interpret small dome like features on radar images of venus to be analogs of icelandic lava shield volcanoes using morphometric data for venusian domes in aubele and slyuta in press as well as our own measurements of representative dome volumes and areas from tethus regio we demonstrate that the characteristic aspect ratios and flank slopes of these features are consistent with a subclass of low icelandic lava shield volcanoes lils lils are slightly convex in cross section with typical flank slopes of 3 plausible lava shield production rates for the venusian plains suggest formation of 53 million shields over the past 0 25 ga the cumulative global volume of lava that would be associated with this predicted number of lava shields is only a factor of 3 4 times that of a single oceanic composite shield volcano such as mauna loa the global volume of all venusian lava shields in the 0 5 20 km size range would only contribute a meter of resurfacing over geologically significant time scales thus venusian analogs to lils may represent the most abundant landform on the globally dominant plains of venus but would be insignificant with regard to the global volume of lava extruded as in iceland associated lavas from fissure eruptions probably dominate plains volcanism and should be evident on the higher resolution magellan radar images

a swarm of small shield volcanoes on syria planum mars this study focuses on the volcanism in syria planum located at the center of the tharsis bulge at an altitude of 6 to 8 km above mars datum syria planum was previously recognized as a center for the tectonic activity of tharsis but not as a major locus for volcanic activity despite its centrality over the bulge using high resolution images from the high resolution stereo camera on mars express combined with mars observer laser altimeter data we have characterized a volcanic system that reveals a number of very interesting aspects of mars volcanism we identified a swarm of tens of coalesced shallow volcanic edifices typically 10 30 km diameter 0 1 0 2 km high and with slopes around 0 5 these characteristics are similar to those of small shield volcanoes found in iceland in addition an intermediate sized volcano which is the source of lava flows that extend over 200 km is observed west of this shield swarm our study characterizes a previously unrecognized volcanic assemblage on mars which appears to be much more developed than was documented before in terms of morphology inferred origin and periodicity of eruption the estimated lava flux of the syria planum volcanoes is of the same order as the lava flux of tharsis montes these characteristics suggest that syria planum experienced a very specific style of volcanism which we dated to the hesperian period

dynamical modeling of flow in cumulus filled boundary layers abstract a primitive equation planetary boundary layer pbl model is constructed and applied to simulate the downwind evolution of coupled dynamic thermodynamic and cloud properties in the pbl over warmer mean a multilayered approach is adopted to model the inversion capped convective pbl filled with shallow cumuli stratocumulus clouds or cloud free air vertically varying turbulent and convective cloud fluxes are constructed from recently published parameterization schemes this model is designed to simulate some influences of cloud vertical mixing and horizontal advection on surface winds over much of the world s oceans an initial application is the local simulation of trade wind flow using a one dimensional version of the model modeled vertical momentum flux and wind in the cumulus filled baroclinic pbl agree well with observations confirming the validity of the momentum parameterization scheme applications to two dimensional simulation of a moderate cold surge over a warm ocean show the enh

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

an ensemble study of wet season convection in southwest amazonia kinematics and implications for diabatic heating dual doppler radar data from the tropical rainfall measuring mission large scale biosphere atmosphere experiment in amazonia trmm lba field campaign are used to determine characteristic kinematic and reflectivity vertical structures associated with precipitation features observed during the wet season in the southwest region of amazonia case studies of precipitating systems during trmm lba as well as overarching satellite studies have shown large differences in convective intensity associated with changes that develop in low level easterly flow east regime er and westerly flow west regime wr this study attempts to examine the vertical kinematic and heating structure of convection across the spectrum of precipitation features that occurred in each regime results show that convection in the er is characterized by more intense updrafts and larger radar reflectivities above the melting level in agreement with results from lightning detection networks these regime differences are consistent with contrasts in composite thermal buoyancy between the regimes above the boundary layer the environment in the er is characterized by a greater virtual temperature excess for near surface rising parcels both regimes showed a peak in intensity during the late afternoon hours as evidenced by radar reflectivity and

p type and s type pahoehoe a study of vesicle distribution patterns in hawaiian lava flows abstract two main types of hawaiian pahoehoe lava p type pipe vesicle bearing and s type spongy are characterized their origin is inferred from features of the vesicle sizes and abundances particularly in their chilled margins which record frozen in the vesicle population at the time and place of solidification s type margins are distinctly more vesicular than p type porosity and vesicle size and range in s type margins are highest at the vent vesicle size reaches a minimum in medial areas and then increases while porosity decreases onto the flatter ground of the coastal terrace the vesicles are inferred to be part of the complement of bubbles that was present at the vent modified by loss and coalescence during travel in lava tubes the minimum porosity occurs on the coastal terrace and is the result of degassing during a longer residence time in lava tubes there the systematically lower porosity of p type margins than s type is attributed to a still longer residence allowing more time for bubble coalescence and loss p type pahoehoe is common only on flatter ground such as the coastal terrace it is found where tumuli and lava rises are widespread and where extensive networks of lava expansion clefts occur through which lava moving below the surface crust can lose gas without significant cooling additionally p type pahoehoe shows clear evidence that a strong inward movement and growth of bubbles took place from the outermost selvage into an inner selvage concentration zone a mechanism that might cause this inward movement is surface tension operating against deforming forces in the steep viscosity gradient of flow margins causing down gradient bubble translation inward movement does not usually occur in the upper crust of thick 2 m flow units because of the absence of strong deforming forces in the shallow velocity gradient there many of the larger bubbles that entered the inner selvage rose buoyantly to form pipe vesicles p type pahoehoe is characterized by sampled profiles across 20 flow units continued gas loss through surface clefts caused a general overall reduction in vesicle content within each flow unit to less than that in the upper crust and the pronounced depletion of vesicles from its lower half is attributed to scavenging by ascending pipe bubbles in a small proportion of flow units overall gas loss was small and a median gas blister fed by pipe bubbles developed instead

morphology and mechanism of eruption of postglacial shield volcanoes in iceland postglacial icelandic shield volcanoes were formed in monogenetic eruptions mainly in the early holocene epoch shield volcanoes vary in their cone morphology and in the areal extent of the associated lava flows this paper presents the results of a study of 24 olivine tholeiite and 7 picrite basaltic shield volcanoes for the olivine tholeiitic shields the median slope is 2 7 the median height 60 m the median diameter 3 6 km the median aspect ratio height against diameter 0 019 and the median cone volume 0 2 km3 the picritic shield volcanoes are considerably steeper and smaller a shield volcano cone forms from successive lava lake overflows which are of shelly type pahoehoe a widespread apron surrounding the cone forms from tube fed p type pahoehoe the slopes of the cones have a a planar or slightly convex form b a concave form or c a convex concave form a successive stage of a shield volcano is determined on the basis of cone morphology and lava assemblages a shield producing eruption has alternating episodes of lava lake overflows and tube fed delivery to the distal parts of the flow field in the late stages of eruption the cone volume increases in response to the increased amount of rootless outpouring on the cone flanks normally only a small percentage of the total erupted volume of a shield volcano sometimes as little as 1 3 is in the shield volcano cone itself the main volume being in the apron of the shield

radar observations of the kinematic microphysical and precipitation characteristics of two mcss in trmm lba 1 dual doppler and polarimetric radar observations are used to analyze two mesoscale convective systems mcss that occurred during the tropical rainfall measuring mission large scale biosphere atmosphere field campaign the mcss formed in different meteorological regimes based on profiles of atmospheric wind and thermodynamic data the first mcs event 26 january 1999 was a squall line that formed in low level easterly flow and had an intense leading line of convection in contrast the 25 february 1999 mcs formed in low level westerly flow and was best characterized by stratiform precipitation with embedded convective elements the radar analyses suggest that the mcss were distinct in terms of overall vertical structure characteristics in particular polarimetric radar cross sections indicated the presence of an active mixed phase zone in the easterly mcs that was largely absent in the westerly case the easterly mcs had considerably more precipitation ice in the middle to upper troposphere compared to the westerly mcs composite analyses showed that the easterly mcs had higher peak reflectivities and a smaller reflectivity gradient above the 08c level in convective regions of the storm compared to the westerly mcs event moreover mean profiles of both vertical air motion and vertical mass transport in the convective portion of the easterly mcs were larger over a factor of 2 at some heights below the 08 c level than those in the westerly event these observations suggest that the easterly and westerly wind regimes in the southwest amazon region produce convection with different vertical structure characteristics similar to regimes elsewhere in the global tropics e g maritime continent index terms 3314 meteorology and atmospheric dynamics convective processes 3329 meteorology and atmospheric dynamics mesoscale meteorology 3354 meteorology and atmospheric dynamics precipitation 1854 3374 meteorology and atmospheric dynamics tropical meteorology keywords microphysics tropical precipitation polarimetric radar mesoscale convective system

systematic morphometric characterization of volcanic edifices using digital elevation models abstract quantitative characterization of the size and shape of volcanic edifices is an essential step towards the understanding of factors controlling volcano growth and morphology the recent advent of digital elevation models dems with worldwide coverage offers the opportunity to systematically document the morphometry of all types of volcanoes using quantitative well formalized methodologies we present a methodology for the morphometric characterization of volcanic edifices after reviewing previous studies on volcano morphometry and the various existing dem sources we describe an integrated procedure that uses a dem and its derived products slope curvature to extract a coherent set of morphometric parameters for a given volcanic edifice edifice boundaries are manually defined by searching for breaks in slope around the base the parameters describe the overall size basal and summit region area and widths height volume planar shape ellipticity and irregularity index of elevation contours profile shape height width ratios and slope of the edifice similar parameters for relatively large depending on dem spatial resolution summit craters calderas are also computed slope values and ellipticity and irregularity indexes are extracted for successive height intervals providing detailed information of volcano shape as a function of height the number of secondary peaks is also estimated the method is tested on thirteen composite volcanoes in nicaragua using three dem datasets 90 m srtm 30 m aster g dem and an 80 m topographic map derived dem and the resulting parameters are evaluated in terms of boundary delineation and dem source finally the parameters obtained for the nicaraguan volcanoes are discussed as an illustrative example of the type of data and information that can be extracted systematically for volcanoes worldwide

contrasting palaeoenvironments of the mid late miocene dunedin volcano southern new zealand climate or topography abstract at the mid late miocene boundary a northward shift occurred in the subtropical front neighbouring the new zealand continental landmass the terrestrial palaeoenvironment of new zealand concurrently underwent a period of cooling the dunedin volcanic group in southern new zealand spans the mid late miocene boundary and the sedimentary deposits from kaikorai valley and double hill within this group contain diverse and well preserved floral assemblages we used terrestrial palaeoclimate proxies clamp climate leaf analysis multivariate program and ba bioclimatic analysis to determine the paleoenvironment at southern mid latitudes during the mid late miocene transition our results indicate that the mid late miocene climate of the dunedin volcano was warm temperate to subtropical mean annual temperature mat 17 19 c at double hill similar to modern coastal queensland and cool to warm temperate mat 12 14 c at kaikorai valley similar to modern northern new zealand winter temperatures at kaikorai valley were distinctly cooler 6 8 c differing aspect i e north vs south facing may have played a part in determining solar radiation particularly in an area of high relief such as the dunedin volcano because kaikorai valley was situated facing south and double hill facing north the two sites would have received differing radiative fluxes particularly in winter thereby possibly influencing the local environment biota and potentially also the palaeoclimate signal produced by floral proxies this study provides evidence for the temperature decline in terrestrial palaeoenvironments at mid latitudes caused by the northward movement of the subtropical front and strengthening of the antarctic circumpolar current during the mid late miocene

small volcanic edifices and volcanism in the plains of venus the most widespread terrain type on venus consists of volcanic lowland plains several styles of volcanism are represented in the plains the most extensive volcanic units consist of flood lavas the largest of which have volumes of the order of thousands of cubic kilometers as with terrestrial flood lavas they are inferred to have erupted at high effusion rates they show a range of radar backscatter characteristics indicating different surface textures and ages small edifices on the plains occur mainly in clusters associated with fracture belts the majority are shield volcanoes that may be up to a few tens of kilometers across but are generally 10 km or less in diameter volcanic cones have the same size range volcanic domes have diameters up to several tens of kilometers and volumes of the order of 100 km3 these are interpreted as being constructed of lava erupted with a relatively high effective viscosity and thus possibly composed of more silicic lava for many domes the flanks were unstable during and afte eruption and suffered gravity sliding that produced steep scalloped outer margins because of the high atmospheric pressures on venus explosive activity is less likely to occur than on earth however n a few plains areas there is evidence of pyroclastic deposits surrounding craters indicating that volatile contents in some of the magmas may be high in comparison to earth the clusters of small volcanic edifices are considered to be analogous to plains volcanism similar to that of the snake river plain of idaho there may also be analogues with terrestrial volcanic clusters associated with mid oceanic ridges

shape rheology and emplacement times of small martian shield volcanoes abstract this paper focuses on the shape of 31 shield volcanoes of small to intermediate size a few tens of kilometers in diameter in 5 regions of mars tempe terra syria planum pavonis mons arsia mons and central elysium planitia a model for the shape of these shield volcanoes is applied based upon the concept of porous flow of an unconfined aquifer proposed by lacey et al lacey a ockendon j r turcotte d l 1981 on the geometrical form of volcanoes earth planet sci lett 54 1 139 143 and developed by turcotte and schubert turcotte d schubert g 2002 geodynamics cambridge university press second edition the agreement between the topographic profiles and the theoretical shape suggests that the model is appropriate and can be used to derive the product of flow rate and viscosity q estimates of q are found to be homogeneous within a given volcanic region but show large differences from one region to another values generally decreasing with age from oldest to youngest intrinsically the method cannot separate the flow rate from the viscosity but independent observations on individual lava flows in syria planum and central elysium planitia suggest that this evolution may be explained by decreasing magma viscosity with age independent constraints on the viscosity are used to interpret q variations between volcanic regions except for tempe terra and within error bars relative effusion rates are essentially independent of volcano volumes suggesting that the size of a shield volcano is principally controlled by the duration of volcanic activity the specificity of central elysium planitia is emphasized with highest flow rates associated with lowest lava viscosity however the lower viscosities at central elysium planitia cannot totally explain low q values considering the equation of magma flow through a dike from a magma chamber at depth to the shield we suggest that lower volatile contents and or deeper magma chambers may contribute to the decrease of q values with time finally the emplacement times of the 31 shield volcanoes were calculated using a calibration based upon terrestrial volcanoes mauna loa eldborgir and skjalbrei ur emplacement times of martian volcanoes calculated in this way range from a few hundred thousand years tempe terra to a few tens of thousands of years central elysium planitia despite the simplicity of the model the quality of the fits and the internal consistency of the results are reasonable encouraging development of more advanced models linking shield volcano shape to rheological properties of lavas and their characteristic time scales of emplacement

extraterrestrial lava lakes abstract active lava lakes are rare on earth with only ten documented examples all formed by lavas of basaltic composition and housed inside summit craters or calderas the existence of lava lakes on other planetary bodies may imply similarities in either composition or volcano tectonic settings and so has important implications for understanding the link between melt production and volcanism we review lava lakes on earth and other planets particularly active caldera like features interpreted to be currently containing active lava lakes on jupiter s moon io and features interpreted as remnants of lava lakes on venus and mars mercury and the moon do not boast the major calderas or shield volcanoes of their larger rocky neighbors partly due to a horizontally compressive tectonic regime arising from global contraction that makes it difficult to move melts through the upper crust we discuss the evidence for active lava lakes on io and show how modeling based on terrestrial lava lakes can reveal how these phenomena differ on both bodies the superficial similarities do not necessarily imply that the plumbing is similar observations of the largest lava lake on io loki patera provide insight into the nature of ionian lava lakes in general which may be more similar to eruptive episodes on the east pacific rise on earth which lead to temporary lava lakes although temporal data for io s lava lake activity are scarce studies of temporal variability of lava lakes on earth are useful for providing ground truth for comparisons future studies of earth by remote sensing and field observations and of io by both ground based observations and future missions are needed to answer many questions including why lava lakes rare on earth appear to be common on io

observed structure of mesoscale convective systems and implications for large scale heating mesoscale convective cloud systems that produce large amounts of rain in mid latitudes and most of the rain in the tropics consist of a combination of convective and stratiform cloud the convective regions contain numerous deep cells that are often but not always arranged in lines the stratiform region is an outgrowth of the convective ensemble it lies adjacent to the convective region and is seeded by ice particles detrained from convective towers sometimes it lies to the rear of a propagating convective line while on other occasions it surrounds the convection the heating of the large scale environment by a mesoscale convective system is affected by both the convective and stratiform regions although processes such as melting and radiation are important the net heating by a system is dominated by condensation and evaporation associated with vertical air motions this paper reviews recent observational evidence regarding the mean vertical motion profiles in the convective and stratiform regions of mesoscale convective systems and the implications of these mean motions for the vertical distribution of heating of the large scale environment in both the convective and the stratiform regions vertical motions have been determined by various techniques including composites of rawinsonde and aircraft wind data single and dual doppler precipitation radar analyses and wind profiler observations in stratiform regions these data consistently show mean vertical velocity that is upward in the upper troposphere and downward in the lower troposphere the level separating upward from downward motion is located from 0 to 2 km above the 0 c level depending on location within the stratiform region diagnostic calculations show that these vertical motion profiles imply heating of the upper troposphere and cooling of lower levels by stratiform region processes data on vertical motions in the convective regions are less consistent from case to case these data sometimes indicate that the mean vertical velocity in convective regions is maximum in the lower troposphere in other cases the data indicate a maximum in the high troposphere diagnostic calculations show that heating profiles diagnosed from these two types of profile are quite different the first having a maximum of heating in the lower troposphere while the second has a maximum in the middle troposphere although it is difficult to determine whether or not the differences in estimates arise from different types of observations analysis methods or sampling strategies it seems likely that they stem from differences in the large scale environment of the different mesoscale systems the ubiquitous occurrence of stratiform regions in mesoscale convective systems and hurricanes together with their consistent heating profiles which systematically concentrate heating in upper levels while cooling lower levels are a major consideration in evaluating the interaction of mesoscale systems with the large scale environment however the consistency of the stratiform profiles from case to case indicates that the variability of net convective plus stratiform heating profiles from case to case lies primarily in the variation of the convective region profiles from one case to another it is suggested that future work should focus on the convective region vertical profiles of vertical motion and heating and on the large scale environmental factors that may control the variation of these profiles from case to case

dimmuborgir a rootless shield complex in northern iceland the origin of dimmuborgir a shield like volcanic structure within the younger laxa lava flow field near lake m vatn in northern iceland has long been questioned new airborne laser mapping light detection and ranging lidar combined with ground penetrating radar results and a detailed field study suggests that dimmuborgir is a complex of at least two overlapping rootless shields fed by lava erupting from the nearby ludentarborgir crater row this model builds upon previous explanations for the formation of dimmuborgir and is consistent with observations of rootless shield development at k lauea volcano hawaii the larger rootless shields at dimmuborgir 1 1 5 km in diameter elliptical in plan view 30 m in height and each with a 500 m wide summit depression were capable of storing as much as 2 3 106 m3 of lava they were fed by lava which descended 30 60 m in lava tubes along a distance of 3 km from the crater row the height difference generated pressure sufficient to build rootless shields at dimmuborgir in a timescale of weeks the main summit depressions inferred to be drained lava ponds could have emptied via a 30 m wide 5 m deep channel with estimated effusion rates of 0 7 7 m3 s 1 and minimum flow durations of 5 50 days we argue that the pillars for which dimmuborgir is famed are remnants of lava pond rims at various stages of disintegration that formed during pond drainage

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

models of ice melting and edifice growth at the onset of subglacial basaltic eruptions 1 models of the early stages of basaltic eruptions beneath temperate glaciers are presented that consider the evolving sizes of volcanic edifices emplaced within subglacial cavities the cavity size reflects the competing effects of enlargement by melting and closure by downward ductile deformation of the ice roof which occurs when the cavity pressure is less than glaciostatic due to meltwater drainage eruptions of basaltic magma from fissures and point sources are considered which form either hemicylindrical or hemispherical cavities the rate of roof closure can therefore be estimated using nye s law the cavity size edifice size and depth of meltwater above the edifice are predicted by the model and are used to identify two potential eruption mechanisms explosive and intrusive when the cavity is considerably larger than the edifice hydroclastic fragmentation is possible via explosive eruptions with deposition of tephra by eruptionfed aqueous density currents when the edifice completely fills the cavity rising magma is likely to quench within waterlogged tephra in a predominantly intrusive manner the models were run for a range of magma discharge rates ice thicknesses and cavity pressures relevant to subglacial volcanism in iceland explosive eruptions occur at high magma discharge rates when there is insufficient time for significant roof closure the models correctly predict the style of historic and pleistocene subglacial fissure eruptions in iceland and are used to explain the contrasting sedimentology of basaltic and rhyolitic tuyas the models also point to new ways of unraveling the complex coupling between eruption mechanisms and glacier response during subglacial eruptions

three long lava flows in north queensland the kinrara toomba and undara basaltic lava flows are from 55 to 160 km long and range in age from 13 to 190 ka the lavas were emplaced down low gradients 0 2 to 0 4 with volumes ranging up to 30 km3 they were not unusually hot at eruption 1130 1160 nor unusually fluid gentle topography controlled the flows and shallow drainage lines captured them lava tubes operated in places and some drained to form caves injection under surface crust was widespread producing inflation features ranging from tumuli and low plateaus to extensive ridges sustained eruption was essential for the development of the long flows but each is composite with pauses between successive pulses that partially covered the earlier longer flows the lava structures are mainly pahoehoe but some a a lavas are present of the three volcanoes involved undara is a simple low angle lava cone with a 200 m wide crater toomba is a low angled cone with several eruption centers and kinrara has a deep crater with evidence of strong fountaining effusion rates are not known but may have been relatively low similar to those observed in hawaiian volcanoes lava tubes most of which remained undrained are believed to have been of major importance in flow emplacement given the evidence of successive flows and the time needed to develop widespread inflation it is suggested that the two long flows over 100 km involved many decades of eruption

a low relief shield volcano origin for the south kaua i swell 1 the south kaua i swell sks is a 110 km x 80 km ovoid bathymetric feature that stands 2 km high and abuts the southern flank of the island of kaua i the origin of the sks was investigated using multibeam bathymetry and acoustic backscatter gravity data radiometric ages and geochemistry of rock samples most of the sks rock samples are tholeiitic in composition with ages of 3 9 5 4 ma indicating they were derived from shield volcanism the ages and compositions of the sks rocks partially overlap with those of the nearby ni ihau kaua i and west ka ena volcano complexes the sks was originally described as a landslide however this interpretation is problematic given the ovoid shape of sks its relatively smooth flat to convex surface and the lack of an obvious source region that could accommodate what would be one of earth s most voluminous 6 x 103 km3 landslides the morphology size and the surrounding gravity anomaly are more consistent with the sks being a low relief shield volcano which was partially covered with a small volume of landside debris from south kaua i and later with some secondary volcanic seamounts a shield origin would imply that hawaiian and possibly other hotspot shield volcanoes can take on a wider variety of forms than is commonly thought ranging from tall island building shields to smaller edifices such as ka ena ridge and mahukona to even lower relief volcanoes represented by the sks and possibly the south west o ahu volcanic field

volcanoes as elastic inclusions their effects on the propagation of dykes volcanic fissures and volcanic zones in iceland mechanically many volcanoes may be regarded as elastic inclusions either softer with a lower young s modulus or stiffer with a higher young s modulus than the host rock matrix for example many central volcanoes stratovolcanoes composite volcanoes are composed of rocks that are softer than the crustal segments that host them this is particularly clear in iceland where central volcanoes are mostly made of soft rocks such as rhyolite pyroclastics hyaloclastites and sediments whereas the host rock is primarily stiff basaltic lava flows most active central volcanoes also contain fluid magma chambers and many have collapse calderas fluid magma chambers are best modelled as cavities in three dimensions or holes in two dimensions entire calderas as holes and the ring faults themselves which commonly include soft materials such as breccias as soft inclusions many hyaloclastite basaltic breccias mountains partly buried in the basaltic lava pile also function as soft inclusions modelling volcanoes as soft inclusions or holes we present three main numerical results the first using the hole model shows the mechanical interaction between all the active central volcanoes in iceland and in particular those forming the two main clusters at the north and south end of the east volcanic zone evz the strong indication of mechanical interaction through shared dykes and faults in the northern cluster of the evz is supported by observations the second model using a soft inclusion shows that the torfajokull central volcano which contains the largest active caldera in iceland suppresses the spreading generated tensile stress in its surroundings we propose that this partly explains why the proper rift zone northeast of torfajokull has not managed to propagate through the volcano apparently torfajokull tends to slow down the rate of southwest propagation of the rift zone part of the evz the third model again using a soft inclusion indicates how the lateral propagation of a segment of the 1783 laki fissure became arrested in the slopes of the hyaloclastite mountain laki

widespread inflation and drainage of a pāhoehoe flow field the nesjahraun þingvellir iceland this study describes the emplacement of the nesjahraun a basaltic lava flow that entered the lake ingvallavatn sw iceland high resolution remotely sensed data were combined with fieldwork to map the flow field onshore the nesjahraun exhibits a variety of textures related to the widespread inflation and collapse of a p hoehoe flow field its emplacement is interpreted as follows initially the eruption produced sheet p hoehoe in the central part of the flow field the lava has a platy ridged surface which is similar to some other lava flows in iceland and on mars here the texture is interpreted to have formed by unsteady inflation of the brittle crust of stationary sheet p hoehoe causing it to break into separate plates the ridges of broken p hoehoe slabs formed as the plates of crust moved vertically past each other in a process similar to the formation of shatter rings upstream fresh lava overflowed repeatedly from channels and tubes covering the surface with shelly p hoehoe formation of a 250 m wide open channel through the flow field allowed the inflated central part of the flow to drain rapidly this phase produced a lava which eroded the channel walls carrying broken p hoehoe slabs lava balls and detaching large 200 m long rafts of compound shelly p hoehoe lava much of this channelized lava flowed into the lake leaving a network of drained channels and tubes in the upstream part of the flow as in other locations the platy ridged texture is associated with a low underlying slope and high eruption rate here its formation was possibly enhanced by lateral confinement hindered entry into the lake and an elevated vent location we suggest that formation of this type of platy ridged lava where the plates are smooth and the ridges are slabs of broken p hoehoe can occur without significant horizontal transport as the surface crust is broken into plates in situ this reconstruction of the emplacement of the nesjahraun also demonstrates that high resolution aerial survey data are extremely useful in the mapping and measurement of lithofacies distributions in large flow fields but that fieldwork is still necessary to obtain the detailed textural information necessary to interpret them

the snake river plain idaho representative of a new category of volcanism studies of the volcanic geology of the snake river plain idaho and comparison with other basaltic regions suggest a new category of volcanic activity termed basaltic plains volcanism typified by the snake river plain this style of volcanism is intermediate between basaltic flood or plateau eruptions and hawaiian volcanism characteristics that are common to both hawaiian and plains volcanism are multiple lava flow units which erupt primarily from point sources formation of low shields and frequent emplacement through lava tubes or channels characteristics that are common to both flood basalts and plains volcanism are high volume flows vents aligned along rift zones and planar surfaces the recognition of plains volcanism in other areas provides a means to interpret the style of eruption and volcanic history

the morphology and formation of flow lobe tumuli on icelandic shield volcanoes three types of tumuli are recognized on monogenetic shield volcanoes in iceland namely 1 lava coated tumuli 2 upper slope tumuli and 3 flow lobe tumuli flow lobe tumuli grade into lava rises which are larger inflation structures but both structures have a similar mode of emplacement the areal distribution of flow lobe tumuli in the flow field differs from that of lava coated tumuli and upper slope tumuli flow lobe tumuli are frequent in the medial and distal parts of pahoehoe flow fields whereas the other two tumulus types are more frequent in the proximal parts of the flow fields the flow lobe tumuli also differ from the two other tumulus types as regards their morphology they are significantly larger have shallower flanks and do not have extensive outflows from the cracks the vesicle distribution within the flow lobe tumuli is similar to that of p type flow lobes a fairly dense zone is situated between the upper and lower vesicular zones each flow lobe tumulus is an individual lobe that inflates and forms tension cracks in the lava crust major lava tubes are mostly absent from the areas where flow lobe tumuli form and therefore the emplacement of flow lobe tumuli must be related to secondary short lived pathways of lava the flow lobe tumuli inside the flow fields of icelandic shield volcanoes are morphologically identical to those flow lobe tumuli that are found in the margins of flow fields of other icelandic volcanoes these observations allow us to model the flow lobe tumuli as morphological variants of p type flow lobes forming along terminating secondary lava paths flow lobe tumuli form at low lava supply rates of the order of 10 2 10 5 m3 s and are generated by inflation of the lava crust as a result of magmatic overpressure in the associated lava core we model the tumulus as a circular elastic plate that becomes uplifted inflated and fractured by a uniform magmatic overpressure at its bottom we conclude that 1 the effective thickness of the lava crust that is subject to bending is 0 2 0 4 m and remains essentially constant during the formation of the tumulus and 2 for flow lobe tumuli that are supplied with magma from tubes that originate in overflow from the lava lake of a shield volcano the elevation difference between the tumuli and the surface of the source lava lake is commonly around 100 m this elevation difference can give rise to a static magmatic overpressure of 2 5 mpa in the tumulus whereas the overpressure needed to form a typical flow lobe tumulus is only 0 2 1 mpa

vertical motion diabatic heating and rainfall characteristics in north australia convective systems very high frequency wind profiler data are used to study the vertical draught structure within 13 tropical mesoscale convective systems mcss near darwin australia during the 1989 90 and 1990 91 wet seasons these studies are supported by single doppler radar soundings and surface rainfall data to correlate radar reflectivity thermal buoyancy and surface rainfall patterns with vertical air motion structures because of darwin s unique location at the southern tip of the maritime continent vertical draughts in both the monsoon maritime and monsoon break continental convective regimes can be observed the break regime mcss six in total were all squall lines characterized by a leading line of convection with heavy precipitation and trailing stratiform rainfall containing a characteristic radar bright band these mcss exhibited a pronounced life cycle pattern and were all sampled by the profiler in the mature to dissipating stages in contrast the monsoon systems seven in total were composed of regions of stratiform cloud with embedded convective bands which moved on shore in the monsoonal flow results from the darwin rain gauge network indicated that the majority of the total rainfall in each mcs break and monsoon was associated with the convective portion of the system the break regime mcss were all characterized by a low level 4 km updraught peak associated with convective cells on the leading edge of each squall line trailed by deeper convective updraughts in the middle and upper troposphere for the monsoon cases the lower troposphere convective updraughts were typically less than those in the squall lines yet were stronger in the upper troposphere the low level differences in the convective updraughts were consistent with the smaller virtual temperature excess in the monsoon soundings as well as the larger vertical radar reflectivity gradients observed in monsoon convection consistent with the differences in vertical air motion patterns diabatic heating and moistening profiles for the monsoon mcss were characterized by a higher level heating and drying peak compared with the break mcss the results have important implications for cumulus parametrizations in numerical models since the large scale circulation is sensitive to the vertical distribution of diabatic heating in tropical mcss

volcanism and hydrothermalism on a hotspot influenced ridge comparing reykjanes peninsula and reykjanes ridge iceland abstract current estimates indicate that the number of high temperature vents one of the primary pathways for the heat extraction from the earth s mantle at least 1 per 100 km of axial length scales with spreading rate and should scale with crustal thickness but up to present shallow ridge axes underlain by thick crust show anomalously low incidences of high temperature activity here we compare the reykjanes ridge an abnormally shallow ridge with thick crust and only one high temperature vent known over 900 km axial length to the adjacent subaerial reykjanes peninsula rp which is characterized by high temperature geothermal sites confined to four volcanic systems transected by fissure swarms with young holocene volcanic activity multiple faults cracks and fissures and continuous seismic activity new high resolution bathymetry gridded at 60 m of the reykjanes ridge between 62 30 n and 63 30 n shows seven axial volcanic ridges avr that based on their morphology geometry and tectonic regime are analogues for the volcanic systems and fissure swarms on land we investigate in detail the volcano tectonic features of all mapped avrs and show that they do not fit with the previously suggested 4 stage evolution model for avr construction instead we suggest that avr morphology reflects the robust or weak melt supply to the system and two or more eruption mechanisms may co exist on one avr in contrast to 4 stage evolution model our interpretations indicate that unlike on the reykjanes peninsula faults on and around avrs do not cluster in orientation domains but all are subparallel to the overall strike of avrs orthogonal to spreading direction high abundance of seamounts shows that the region centered at 62 47 n and 25 04 w between avr 5 and 6 is volcanically robust while the highest fault density implies that avr 1 and southern part of avr 6 rather undergo period of melt starvation based on our observations and interpretations we expect all of the avrs on reykjanes ridge to be hydrothermally active but morphological and hydrographic settings of this ridge may cause hydrothermal plumes to be quickly dispersed and diluted due to exposure to strong bottom currents therefore combined ctd and autonomous vehicles surveys are probably the most efficient methods for hydrothermal exploration along the reykjanes ridge