a model for the formation of lava tubes by the growth of the crust from the levees 1 we propose a model to explain lava tube formation by the growth of crust slabs from the levees of a channel toward its center involving solid surface fragments the flow dynamics are described with the steady state solution of the navier stokes equation in a rectangular channel for a newtonian homogeneous isotropic and incompressible fluid the cooling of a lava flow is described by the mechanism of heat conduction into the atmosphere the presence of levees is taken into account both in the dynamical and in the thermal model as long as the flow cools a solid layer forms at the surface much thicker near the levees than at the center of the channel the crust that has formed breaks under the effects of the applied stresses solid blocks slow the fluid down the shear stress at the interface between crust and fluid lava increases and the flow thickens using the thin elastic plate approximation we determine conditions allowing a crust to resist both the action of the shear stress due to the drag of the underlying fluid and the tensile stress due to the weight of the crust itself detecting the required crust thickness and distances from the eruptive vent where the tube can form

formation of lava tubes and extensive flow field during the 1991 1993 eruption of mount etna detailed mapping during the 1991 1993 eruption of mount etna has shown that there is a relationship between tumuli ephemeral vents lava tubes and their parent lava flows during this eruption many tubes formed in stationary inflated a a lava flows ephemeral vents at the fronts of these stationary flows and above lava tubes fed secondary lava flows many of which subsequently developed new tubes the resulting complex network of tubes ephemeral vents and secondary flows was responsible for most of the widening thickening and lengthening of the 1991 1993 etna lava flow field the supply of relatively uncooled lava via tubes to distal parts of this flow field allowed lava to flow 3 km farther from the vent than the longest channel fed lava flow our observations suggest that lava tubes play a more important role in the formation of extensive a a flow fields on etna than has previously been recognized

missing aragonitic biota and the diagenetic evolution of heterozoan carbonates a case study from the oligo miocene of the central mediterranean abstract several previous studies have addressed the diagenetic evolution of heterozoan carbonate assemblages generally it is assumed that early diagenetic processes in heterozoan settings are mainly destructive including abrasion and dissolution on the sea floor constructive diagenesis cementation is delayed to later stages in the burial environment with pressure solution of calcitic grains acting as a cement source this paper presents a study of oligo miocene inner to outer ramp heterozoan carbonates from the central mediterranean maltese islands and sicily indicating that early diagenetic processes are more important than previously assumed four to five different cement types including fibrous two types of epitaxial bladed and blocky cement are distinguished based on transmitted light microscopy cathodoluminescence microscopy allowed a differentiation between primary high mg calcitic fibrous and epitaxial cement i and primary low mg calcitic epitaxial cement ii bladed and blocky cements stable isotope data indicate cement precipitation from marine marine derived and meteoric waters trace element analyses point to cementation in an open system maltese islands and a closed system sicily our investigations show that the majority of constructive diagenetic processes in these rocks occurs rather early in the shallow marine burial environment which is transitional between the marine seafloor and the deep burial diagenetic environment the main cement source in this environment is assumed to be aragonite we suggest careful consideration of the importance of aragonitic components in fossil heterozoan settings which seem to be more abundant than previously assumed and can act as a major early cement source due to the low preservation potential of these components detailed geochemical studies are necessary to detect aragonite as the cement source our findings also have implications when considering the reservoir qualities of these rocks because primary porosity can be occluded early and secondary porosity is not preserved

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

stress field in the continental part of china derived from temporal variations of seismic activity abstract the seismic activity in east asia during the last 3000 years and more has systematically been analyzed a quantitative estimate has been attempted for the seismicity during the last 500 years employing a statistical approach the earthquake generating stresses in and around china have been investigated by analyzing the relationships of the temporal variations of seismicity in various regions of east asia seismicities in the region from the northern part of the north south seismic belt of china nsb using events with m 7 to the japan trench using events with m 7 5 through north china using events with m 7 south china using events with m 6 and the korean peninsula using events with m 6 5 were investigated they all show high activity from about the 16th century to the beginning of the 18th century the activity then subsided until the beginning of the 20th century from the beginning of the 20th century the activity of each region has risen again and remains high now the short term variations of seismicity since 1900 in north china the korean peninsula and japan also exhibit the same pattern synchronous variations of seismicity in these regions imply that regional earthquake generating stress fields between the japan trench and the northern part of the nsb of china originate under common tectonic conditions and that there is a transmission of the tectonic force from the subduction of the pacific ocean plate along the japan trench to the northern part of the nsb through the korean peninsula and north china the seismic activities since 1900 in south china using events with m 5 the taiwan using events m 7 3 and the ryukyu regions using events with m 6 7 were found to be high between 1900 and 1940 this high activity was followed by a quiet period starting from around 1945 since 1960 the active period has continued up to the present time these results suggest that the earthquake generating stress fields between taiwan and south china seem to be formed under common tectonic conditions i e due to the transmission of the tectonic force resulting from the subduction of the philippine sea plate along the ryukyu trench and the collision between the philippine sea plate and the eurasian plate in the taiwan region during this century the tibetan plateau using events with m 6 8 and the xinjiang region using events with m 7 were seismically active from 1900 to 1916 then from around 1931 to 1955 and lately from around 1970 to the present these active periods correspond to those using events with m 7 7 at the boundary regions between the indo australian and the eurasian plate this implies that the earthquake generating stress fields in and around west china result from the transmission of the tectonic forces originating from the collision of the indo australian plate and the eurasian plate along the himalayan mountain range

geologic structure and neotectonics of the north african continental margin south of sicily abstract marine geological and geophysical data together with drilling information indicate that the north african passive continental margin has been subjected to extension and wrenching after it collided with the northern part of sicily the area of the tripolitania basin jarrafa trough melita and medina bank and the ragusa malta plateau has formed part of a sinking passive margin since the dispersal of gondwanaland at about 180 my ago as observed from geohistory diagrams a record of rifting in a nw se direction accompanied by dextral shear along the southern troughs is observed in seismic reflection data the rifting started during the neocomian and lasted until the eocene when activity became minor a pre middle miocene period of northward subduction of oceanic crust is inferred from the geology in ne sicily uplift of the northern part of the african margin after collision in the middle miocene is seen in wells in southern sicily after the messinian a rift and dextral shear zone established itself across the african margin from the strait of sicily to the medina ridge in the lonian basin the zone is marked by up to 1 7 km deep grabens narrow active wrench faulted channels volcanic fissures and local uplifted keilhorsts such as malta this zone which varies in width from 100 to 35 km forms the southern boundary of a microplate which includes sicily we speculate that the present motion of this microplate is partly due to the eastward movement of the calabrian arc with the sicilian block over the last remaining oceanic lithosphere in the eastern mediterranean

the petrology and palaeoenvironment of the sortino group miocene of se sicily evidence for periodic emergence the sortino group of carbonates consists of three formations which developed on a shallow marine shelf during tortonian and lower messinian times the two lower formations contain three bioherms and are intercalated with thick volcaniclastic sequences the youngest formation is dominated by shoal water lagoonal and peri tidal carbonates early submarine lithification is well developed within the bioherms and consists of construction by both algae and invertebrates the development of peloidal micrites and isopachous fringe growth superimposed upon these are a series of both meteoric phreatic and vadose textures related to episodic emergence of the bioherms these features include bladed cements showing cathodoluminescence pendent cements brecciation alveolar texture and palaeosols the sicilian strata may be directly correlated with the maltese islands sequence and collectively exhibit the effects of fluctuating mediterranean sea levels at an early stage in the late miocene salinity crisis

the distribution and palaeoenvironment of early miocene phosphorites of southeast sicily and their relationships with the maltese phosphorites abstract several phosphatic limestone localites occur within the irminio member ragusa formation of the western hyblean of southeast sicily in areas of maximum development such as around sampieri and modica the phosphatized intraslcast dominated deposits attain a thickness of up to 0 6m and are associated with a phosphatized underlying hardground thin and possibly discontinous spreads of phosphatized intraclast form a broader zone beyond the central semi autochthonous zone microfossil analysis of associated strata demonstrates that all occurences of phosphatized strata within the irminio member are restricted to a single level of probable late burdigalian early miocene age the bed correlates well both biostratigraphically and lithologically with the upper main phosphorite conglomerate bed of the maltese islands which lie c 95 km south of the sicilian province five more distinct phosphorite beds occur in the maltese islands being best developed in the western and northern parts of the islands they range in age from aquitanian to late burdigalian these are principally francolite replaced micrate conglomerates which may be associated with phosphatized underlying hardgrounds in places a major central mediterranean phosphatogenic province of early miocene age is postulated inorder to account for the simultaneous occurrence of phosphorites in sicily and malta

mechanisms of formation of lava tubes 1 we propose a model to describe lava tube formation considering lava as a newtonian fluid moving downslope in a rectangular channel we obtain flow velocity using an analytical steady state solution of the navier stokes equation shear stress is also calculated from velocity for a newtonian incompressible and isotropic fluid a 2 d model with heat flux assigned at the upper surface is introduced to describe lava cooling by radiation into the atmosphere and to obtain the flow temperature lava crust is considered as a plastic body and its rheology is described through the introduction of the yield strength as a function of temperature it describes the capacity of crustal structure to prevent shear deformation for lower shear stress values when lava temperature becomes lower than the solidus value ts a superficial thin solid layer develops in regions where shear stress xy is smaller than yield strength the model shows how the competition between these two functions xy and controls the development of crust width and the possible transition from a mobile crust to a stationary roof for typical parameter values of lava channels on mount etna crust develops in the central part of the flow laterally limited by two crust free regions we analyze the effects of some typical channel irregularities on surface shear stress and as a consequence on crust width growth we consider a variation of channel width and ground slope finding that crust widening is favored by channel widening or slope reduction in both cases the decrease in shear stress produces an increase in the fraction of channel width occupied by solid crust given a set of initial conditions defining eruptive parameters and channel features the model provides critical values of channel width and ground slope that allow tube formation the effect of different effusion rates on crust development is also studied with the result that tube formation is favored by low flow rates corresponding to lower values of xy

facies analysis and palaeoenvironmental interpretation of the late oligocene attard member lower coralline limestone formation malta the oligocene represents a key interval during which coralline algae became dominant on carbonate ramps and luxuriant coral reefs emerged on a global scale so far few studies have considered the impact that these early reefs had on ramp development consequently this study aimed at presenting a high resolution analysis of the attard member of the lower coralline limestone formation late oligocene malta in order to decipher the internal and external factors controlling the architecture of a typical late oligocene platform excellent exposures of the lower coralline limestone formation occurring along continuous outcrops adjacent to the victoria lines fault reveal in detail the three dimensional distribution of the reef associated facies a total of four sedimentary facies have been recognized and are grouped into two depositional environments that correspond to the inner and middle carbonate ramp the inner ramp was characterized by a very high energy shallow water setting influenced by tide and wave processes this setting passed downslope into an inner ramp depositional environment which was colonized by seagrass and interfingered with adjacent areas containing scattered corals the middle ramp lithofacies were deposited in the oligophotic zone the sediments being generated from combined in situ production and sediments swept from the shallower inner ramp by currents compositional characteristics and facies distributions of the attard ramp are more similar to the miocene ramps than to those of the eocene an important factor controlling this similarity may be the expansion of the seagrass colonization within the euphotic zone this expansion may have commenced in the late oligocene and was associated with a concomitant reduction in the aerial extent of the larger benthonic foraminifera facies stacking pattern analysis shows that the depositional units parasequences at the study section are arranged into transgressive regressive facies cycles this cyclicity is superimposed on the overall regressive phase recorded by the attard succession furthermore a minor highstand correlated with the ru4 ch1 sequence and subsequent minor lowstand ch2 sequence have been recognized the biota assemblages of the attard member suggest that carbonate sedimentation took place in subtropical waters and oligotrophic to slightly mesotrophic conditions the apparent low capacity of corals to form wave resistant reef structures is considered to have been a significant factor affecting substrate stability at this time the resulting lack of resistant mid ramp reef frameworks left this zone exposed to wave and storm activity thereby encouraging the widespread development of coralline algal associations dominated by rhodoliths

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

formation and evolution of strike slip faults rifts and basins during the india asia collision an experimental approach the processes which have governed the formation and evolution of large tertiary strike slip faults during the penetration of india into eastern asia are investigated by means of plane strain indentation experiments on layered plasticine models the steady state deformation of plasticine obeys a power creep flow law e c t n the stress exponent n is between 6 and 9 at 25 c uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening a process observed for strain rates ranging from 3 5 10 5 to 3 6 10 3 s 1 fault or shear zones form after only 7 10 bulk strain subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine a series of nine plane strain indentation experiments shows the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence the ubiquity of strain softening in experimental deformation of a variety of rocks as well as the widespread occurrence of shear zones in nature suggest that long term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain the deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision induced strikeslip faulting in asia particularly to total offsets and rates of movements on the faults the experiments simulate the evolution of the western ends of the strike slip faults which have probably been analogous to trench fault fault triple junctions the experiments also illustrate mechanisms for the formation of extensional basins such as the south china sea north china basin and andaman sea near active continental margins the basins which appear to absorb terminal offsets along major strike slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts the existence of distinct phases of strike slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous non steady state deformation of the continental lithosphere

relation between characteristics of seismic activity and neotectonics in honshu japan abstract the nature of the occurrence of earthquakes in and around the honshu region of japan has been studied from the viewpoint of the relation with its neotectonics honshu island japan consists of two large crustal blocks one is northeast japan and the other is southwest japan the junction of these two blocks is the northern part of the fossa magna which crosses the central part of honshu tectonic forces in the crust by which shallow earthquakes occur in the inner zone of southwest japan are considered to be transmitted from northeast japan through this junction due to the transmission of these tectonic forces the earthquake activity in the inner zone of southwest japan shows some significant characteristics that are closely related to major events in northeast japan in particular occurrences of large earthquakes along the eastern edge of the japan sea provide clear evidence of this in some regions in southwest japan seismic activity increases after the occurrence of large earthquakes along the eastern edge of the japan sea in the northern part of the fossa magna region the seismic activity increases over a period of a few years after a large event along the eastern edge of the japan sea such evidence of seismic activity indicates that force transmission exists from the east to the west crustal block of honshu island japan

sedimentary and tectonic evolution of the eastern hyblean plateau southeastern sicily during late cretaceous to quaternary time abstract two palaeogeographic domains have been distinguished in the cretaceous quaternary sequences which crop out in the hyblean region of southeastern sicily in the northeast shallow water algal bryozoan calcarenites of oligocene miocene age overlie either cretaceous rudist limestones or volcanics further to the northeast the stratigraphic gap increases as the miocene limestone thins and in the a g i p well catania 10 plio pleistocene sediments and volcanics directly overlie upper jurassic rocks in the southwestern part of the hyblean plateau pelagic sediments occupy the cretaceous miocene interval they were deposited in a shallow basin dipping gently towards the southwest the transition between the two zones is marked by much evidence of synsedimentary tectonic activity such as widespread slumping and the development of megabreccias composed of cretaceous and eocene blocks the palaeogeographic picture is one of carbonate reefs and volcanic seamounts developing in the upper cretaceous they formed platforms fault bounded to the west and southwest from which were derived the detrital sediments found in the basin and occasional spectacular gravity slides in present day terms the structural high probably corresponds to the northeastern margin of the hyblean plateau and in part to the siracusa syracuse malta escarpment the pattern is little changed in the upper miocene with volcanoclastics of phreatomagmatic origin intercalated with coral bioherms overlying algal bryozoan calcarenites upper tortonian lower messinian limestones with a restricted fauna indicate a shallow water environment which grades up into continental conditions in the eastern hyblean plateau the tertiary sequence is capped by pliocene submarine to subaerial mafic lava flows lower pleistocene sediments consist of biocalcarenites and clays which fill deep graben delimited by plio pleistocene faults the inshore continuation of the malta syracuse escarpment system of faults from a tectonic standpoint the hyblean region a gently deformed segment of the african continental margin acted as a foreland during tertiary times a cretaceous eocene tectonic phase was responsible for the palaeogeographic pattern which existed during most of the cenozoic the present pattern is the result of three main tectonic phases following the regional upper miocene uplift of early middle pliocene plio pleistocene and middle pleistocene recent age which influenced the tectonic evolution of the present ionian coast and the malta syracuse escarpment

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

controls of facies and sediment composition on the diagenetic pathway of shallow water heterozoan carbonates the oligocene of the maltese islands relatively few studies have so far addressed diagenetic processes in heterozoan carbonates and the role that sediment composition and depositional facies exert over diagenetic pathways this paper presents a study of oligocene shallow water heterozoan carbonates from the maltese islands we investigate stratigraphic distribution abundance and timing of diagenetic features and their relationship to sediment composition and depositional facies the studied carbonate rocks comprise rud to packstones of the heterozoan association predominantly containing coralline red algae bryozoans echinoids and benthic foraminifers xrd analyses show that all high mg calcite has been transformed to low mg calcite and that no aragonite is preserved diagenetic processes include dissolution of aragonitic biota neomorphism of high mg calcitic biota to low mg calcite and cementation by fibrous bladed epitaxial and blocky cements stable isotopes on bulk rock integrated with petrographic data suggest that the study interval was not exposed to significant meteoric diagenesis we interpret early cementation to have taken place in the marine and marine burial environment the distribution and abundance of early diagenetic features determining the diagenetic pathway can be related to the primary sediment composition and depositional texture sorting and micrite content are important controls over the abundance of diagenetic features

morphometric analysis of lava flow units case study over lidar derived topography at mount etna italy abstract high resolution lidar derived digital elevation models of volcanic areas can significantly improve knowledge of lava flow morphology and emplacement mechanisms here we focus on single flow units presenting a new semi automatic procedure which provides a quantitative analysis of their shape the method relies on the automatic processing of the elevation profiles obtained on transects orthogonal to the flow unit axis the initial phase of the mount etna flank eruption from september 2004 is taken as test case and the procedure is applied on an active lava flow which was emplaced on the eastern flank of the volcano the main topographic dataset used is a 2 m resolution digital elevation model obtained from a lidar survey starting from the axis of a lava flow unit our method yields morphometric data on the flow unit at a 2 m spacing calculating parameters including flow width channel width the heights of the levees inward and outward slope of levees and estimating pre emplacement slope along the axis the procedure is embedded in a customized gis which allows easy processing handling and displaying of data the procedure has also been applied to another flow unit emplaced during the october november 1999 overflow from the bocca nuova crater results show that the channel width seems to accommodate first order trends of the pre emplacement slope along the flow unit axis while it is little affected by high frequency changes in slope in contrast flow unit width and flow unit thickness are apparently influenced by small scale changes in slope the different emplacement conditions of the two flow units are reflected by the overall contrasting morphologies as shown by the different average thickness and by the different ratios between i flow width vs channel width and ii flow unit section area vs channel width the new method provides an enhanced systematic and thorough morphometric description of flow units which may improve the understanding of the emplacement mechanisms of lava flows on earth and other planets

late tortonian lower messinian miocene palaeogeography of se sicily information from two new formations of the sorting group abstract a thick volcanoclastic biohermal and lagoonal sequence of strata succeeds the siracusa limestone member monti climiti formation of se sicily this overlying sequence may be divided into two new formations on the basis of lithostratigraphy petrology and palaeontology the older formation here named the carlentini formation is predominantly a thick volcanoclastic sequence but with two intervening carbonate horizons faunas are rare within the volcanic strata but may be abundant and associated with corals and patch reefs within the two carbonate levels the younger formation here named the monte carrubba formation is almost exclusively composed of oolitic grainstones and lagoonal wackestones peritidal carbonates are developed in the northeast of the area faunas are frequently of low diversity euryhaline mollusc associations are dominant although pecten vigolenesis occurs in the lower beds collectively the new formations span the late tortonian lower messinian time interval and may be correlated with the calcare di base of the main sicilian basin to the west the palaeoenvironmental reconstruction suggests that both formations were deposited around the sw margins to a low island or landmass lying to the north of the hyblean region

sedimentology and palaeoenvironment of the southeast sicilian tertiary platform carbonates abstract a thick succession of shelf and shelf slope carbonates is developed in southeastern sicily sedimentological aspects of the oligocene to tortonian sequence including distribution and palaeoenvironmental factors are considered a new formation and four new members are proposed in the upper part of the succession the region comprises a western half typically exhibiting the principal deeper water planktonic facies including marls and an eastern area displaying typically inner shelf carbonates and an attenuated succession coralline algal limestones and calcarenites are more typical of this latter region but there are also some volcanic intercalations an attempt is made to relate the hyblean succession to that of the maltese islands which lie at the southern end of this tertiary carbonate platform

surface temperature measurements of active lava flows on kilauea volcano hawai i systematic hand held radiometer measurements of lava surface temperatures in active flows and tubes on kilauea volcano hawai i reveal complexities that cannot be resolved in remotely sensed data from aircraft or satellites using portable infrared minolta land cyclops radiometers we measured surface temperatures of flows at various distances from their sources and investigated cooling rates and the development of crust our measurements suggest that the upper surface of these lava flows can be split into a minimum of four thermal components core 1050 c visco elastic skin 750 900 c rigid solid crust 750 c and flow margins 175 c for the a a flows investigated a cool rigid crust characteristically developed in the central part of channels within 30 m of the source vent and incandescent lava was exposed in the marginal shear zones of channels this affects the heat loss and morphology of lava in active channels our investigations of temperature distributions on pahoehoe flow fields reveal temperature anomalies of up to 150 c above active tubes and tumuli

focal depths and fault plane solutions of earthquakes under the tibetan plateau we compare synthetic and recorded p wave forms to place constraints on the focal depths and fault plane solutions of 16 crustal earthquakes beneath the highest parts 4000 m of the tibetan plateau fault plane solutions for all 16 events show combinations of normal and strike slip faulting with t axes oriented approximately east west none of these solutions show thrust faulting thus the data corroborate previous inferences that the active tectonics are dominated by east west extension focal depths for all 16 events are less than 15 km and appear to be between 5 and 10 km this style of deformation and these depths of faulting are similar to those in the basin and range province of the western united states two intermediate depth events below the crust of southern tibet also show primarily normal faulting with east west t axes the solution for one discussed by chen et al 1981 is unambiguous the solution for the other the event of august 1 1973 27 59 n 89 17 e 85 10 km mb 4 9 is less certain both apparently occurred in the mantle beneath a thick aseismic lower crust and their occurrence suggests that brittle deformation occurs there in response to a stress field similar to that operating at shallow depths beneath tibet

viscous newtonian laminar flow in a rectangular channel application to etna lava flows we introduce a 3d model for near vent channelized lava flows we assume the lava to be an isothermal newtonian liquid flowing in a rectangular channel down a constant slope the flow velocity is calculated with an analytical steady state solution of the navier stokes equation the surface velocity and the flow rate are calculated as functions of the flow thickness for different flow widths and the results are compared with those of a 2d model for typical etna lava flow parameters the influence of levees on the flow dynamics is significant when the flow width is less than 25 m the model predicts the volume flow rate corresponding to the surface velocity taking into account that both depend on flow thickness the effusion rate is a critical parameter to evaluate lava flow hazard we propose a model to calculate the effusion rate given the lava flow width the topograhic slope the lava density the surface flow velocity and either the lava viscosity or the flow thickness

flow and convective cooling in lava tubes tube fed basaltic lava flows with lengths ranging from 10 to 200 km are inferred to exhibit similar amounts of cooling to explain the wide range of implied cooling rates we consider forced convection as a dominant cooling process in lava tubes and present solutions that express mean temperature versus distance down the tube as a function of flow rate and flow cross section our models treat forced convective thermal losses in steady laminar flow through a lava tube with constant temperature walls and constant material properties we explore the effects of different wall temperature and heat flux rate boundary conditions for circular tube and parallel plate flows over a range of tube sizes plate spacings eruption temperatures and volume flow rates results show that nonlinear cooling rates over distance are characteristic of constant wall temperature for a piecewise parallel plate circular tube model this provides the best fit to temperature observations for hawaiian tubes such a model may also provide an explanation for the very low 10 c cooling observed in 10 km long hawaii tube flows and inferred in longer 50 to 150 km tube fed flows in queensland the forced convective cooling model may also explain similar flow morphologies for long tube fed basaltic lava flows in a wide variety of locations since small variations in eruption temperature or flow rate can accommodate the entire range of flow lengths and cooling rates considered our results are consistent with previous suggestions that long basaltic flows may be a reflection of low slopes a particularly steady moderate eruption rate and well insulated flow rather than of high discharge rates

palaeoenvironment and palaeogeography of miocene marls from southeast sicily and the maltese islands abstract tortonian marls and clays are extensively developed in southeast sicily macrofaunas are sparsely distributed in these strata except for a new section at musenna hill in the vittoria scoglitti area this section together with two other coastal sequences of about the same age are described for the first time their abundant faunas are recorded ecological requirements for these faunas are considered and some attempt is made to place them into the known sicilian miocene stratigraphy the musenna hill section shows a particularly close relationship to the upper part of the miocene blue clay formation of the maltese islands both from the viewpoint of sediment and macrofauna the maltese faunas are recorded in detail for the first time and ecological and palaeogeographical information is considered an attempt at an overall regional palaeoenvironmental reconstruction is made for the maltese and southeast sicilian parts of the central mediterranean for tortonian times

role of heat advection in a channeled lava flow with power law temperature dependent rheology 1 the cooling of a lava flow both in the transient and the steady state is investigated considering that lava rheology is pseudoplastic and dependent on temperature lava exits from the vent with constant velocity and flows down a slope under the effect of gravity force inside a channel of rectangular cross section we consider that cooling of lava is caused by thermal radiation into the atmosphere and thermal conduction at the channel walls and at the ground the heat equation is solved numerically in a 3 d computational domain and the solution is tested to evaluate the numerical errors we study the steady state and the initial transient period of lava cooling results indicate that the advective heat transport significantly modifies the cooling rate of lava slowing down the cooling process since the lava velocity depends on temperature the cooling rate depends on the effusion temperature velocity profiles are modified during cooling showing two marginal static zones where the crust can form and remain stable the fraction of crust coverage is calculated under the assumption that the solid lava is a plastic body with temperature dependent yield strength we numerically confirm that heat advection cannot be neglected in the mechanism of formation of lava tubes

effects of the curvature of a lava channel on flow dynamics and crust formation summary bends in lava channels are often observed in volcanic fields the curvature of a channel affects flow dynamics and surface morphology and may be a trigger for the formation of lava tube we propose a model to describe the effects of curvature on velocity shear stress and the formation of crust at the flow surface lava is described as a newtonian homogeneous isotropic and incompressible fluid the steady state solution of the navier stokes equation is found for a unidirectional flow in cylindrical coordinates the flow levees are described as arcs of concentric circumferences with their centres in the origin of the coordinate system under the assumption that the gravity force has no radial component in the bend the fluid moves parallel to the levees the velocity is assumed to depend on the radial coordinate only as an effect of curvature velocity and shear stress are asymmetric with respect to the centre of the channel the maximum of surface velocity is shifted toward the internal levee and the shear stress has larger values close to the internal levee this effect is greater for wider channels heatradiationandconvectionintotheatmosphereareconsideredasthemaincooling mechanisms and the temperature distribution along the channel is calculated crust formation at the flow surface is considered under the assumption that solid lava is a plastic body the amount of crust coverage is mainly controlled by the channel width narrow channels have a greater coverage than wide channels for a given radius of curvature the effect of a bend is to favour the crust growth toward the internal levee while the crust coverage toward the external levee decreases the presence of a bend in a lava channel may favour the formation of a lava tube the analytical solution will serve as a benchmark for numerical models understanding the mechanism of formation of lava tubes is crucial to the simulation of actual lava flows and to evaluation of the associated hazard

observations on basaltic lava streams in tubes from kilauea volcano island of hawai i from 1986 to 1997 the pu u o o kupaianaha eruption of kilauea produced a vast pahoehoe flow field fed by lava tubes that extended 10 12 km from vents on the volcano s east rift zone to the ocean within a kilometer of the vent tubes were as much as 20 m high and 10 25 m wide on steep slopes 4 10 a little farther away from the vent some tubes formed by roofing over of lava channels lava streams were typically 1 2 m deep flowing within a tube that here was typically 5 m high and 3 m wide on the coastal plain 1 tubes within inflated sheet flows were completely filled typically 1 2 m high and several tens of meters wide tubes develop as a flow s crust grows on the top bottom and sides of the tubes restricting the size of the fluid core the tubes start out with nearly elliptical cross sectional shapes many times wider than high broad flat sheet flows evolve into elongate tumuli with an axial crack as the flanks of the original flow were progressively buried by breakouts temperature measurements and the presence of stalactites in active tubes confirmed that the tube walls were above the solidus and subject to melting sometimes the tubes began downcutting progressive downcutting was frequently observed through skylights a rate of 10 cm d was measured at one skylight for nearly 2 months

sedimentology and palaeoecology of a miocene coralline algal biostrome from the maltese islands abstract a large coralline algal biostrome 20 km 5 km 16 m thick is well exposed in western malta and eastern gozo the biostrome is composed of limestones largely constructed by in situ coralline algae or transported algal debris some sediments are dominated by rhodoliths and others by crustose coralline frameworks six facies are distinguished crustose algal marl crustose algal wackestone rhodolith pavement algal branch packstone crustose pavement and algal crust packstone each facies is characterised by different rhodolith morphologies and coralline crusts which are constructed mainly bymesophyllum commune the coralline morphogenesis is related to the palaeoenvironmental conditions the biostrome is thought to have developed from a series of relic sand ridges to form a low relief platform of moderate depths containing a mosaic of sedimentary facies the sequence is affected by growth faulting which divides the biostrome into eight units

temporal variations in seismic and volcanic activity and relationship with stress fields in east asia abstract the temporal characteristics in seismic and volcanic activity and relationship with seismogenic stress in east asia were analyzed mainly based on the qualitative and statistical analysis of historical and instrumental earthquake data a long term synchronous variation in seismicity since 1400 a d exists in the intraplate region from northeastern china to the inner zone of southwest japan through the korean peninsula short term synchronous variation in seismicity since 1900 is also found in the region from northeastern china and the korean peninsula to the western part of the inner zone of southwest japan historical volcanic activity in and around the korean peninsula is closely correlated with active seismicity the seismogenic stress field in this intraplate region may be formed under the common tectonic conditions due to the regional tectonic forces originating from the collision between the indo australian and the eurasian plates in the west and the combined effects of subduction of the pacific and the philippine sea plates around the izu and tokai area in the east and the regional vertical force by uplifting of upper mantle the direction of the regional forces is almost parallel to the great circle connecting the eastern part of the himalayas to japan the intraplate regions from northeastern china and the korean peninsula to the western part of the inner zone of southwest japan may be responding as a unitary block to the regional tectonic force and comprising a province with a common seismogenic stress field in the eastern part of the eurasian plate

channeled flow analytic solutions laboratory experiments and applications to lava flows although channeled lava flows are common in basaltic volcanism relationships between channel morphology eruption and emplacement parameters and lava properties are not well understood several models have commonly been used to constrain these relations but they have not been well tested on natural or simulated lava flows over a wide range of parameter space here we test the accuracy and assumptions of a moderately simple analytic rectangular channel solution by comparing the behavior of well controlled laboratory polyethylene glycol peg channeled flows to the analytic solution for isothermal steady newtonian flow in a rectangular channel with constant dimensions this analytic solution agrees well with laboratory measurements volumetric effusion rates q m3 s 1 calculated from the analytical model using measured peg flows as input yield ratios of qcalculated qpumped of 0 2 to 3 6 and flow rates calculated from a best fit surface velocity profile to measured velocities give more accurate ratios of 0 8 to 1 2 we find a very weak dependence of solution accuracy on slope attributable to flow front effects within the laboratory flows we subsequently apply the solution to several subaerial and submarine terrestrial flows as well as extraterrestrial channeled flows over a wide range of flow parameters viscosity ranges and flow rates obtained using measured channel dimensions and assumed lava properties are plausible interestingly the resulting extraterrestrial estimates of viscosities and flow rates tend to fall closer to known terrestrial measurements and estimates of channel flow than to previous planetary estimates we therefore suggest that the analytic newtonian rectangular channel flow model is a more appropriate physical model for many channeled terrestrial and planetary flows than the newtonian infinite sheet flow and approximation to bingham channel flow widely used previously

thermal anomaly at the earth s surface associated with a lava tube abstract lava tubes are frequently encountered in volcanic areas the formation of lava tubes has strong implications on the volcanic hazard during effusive eruptions the thermal dissipation of lava flowing in a tube is reduced in respect to the lava flowing in an open channel so the lava may threaten areas that would not be reached by flows in open channels for this reason it is important to detect the presence of lava tubes in this work we propose a model to detect the presence and the characteristics of lava tubes by their thermal footprint at the surface we model numerically the temperature distribution and the heat flow both in the steady and the transient state and we take into account the principal thermal effects due to the presence of an active lava tube i e the conduction to the ground and the atmosphere the convection and the radiation in the atmosphere we assume that lava fluid is at high temperature in motion inside a sloping tube under the gravity force the thermal profile across the tube direction in particular the width of the temperature curve allows to evaluate the depth of the tube the values of maximum temperature and of tube depth allow to estimate the area of the tube section the shape of the temperature curve and its asymmetry can give information about the geometry of the tube if we observe volcanic areas at different times by thermal cameras we can detect anomalies and evaluate their causes during an eruption in particular we can evaluate whether they are due to active lava flows or not and what is their state for lava tubes we can connect thermal anomalies with lava tube position characteristics and state

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