heat flow in the baltic shield results of the lithospheric geothermal modelling abstract the results of heat flow measurements performed within the baltic shield and in its closest neighbourhood are reviewed the regional distribution of the heat flow density is presented as a heat flow map the characteristic heat flow density amounts to 35 40 mw m 2 and is notably smaller than heat flow in the surrounding areas the radiogenic heat production within the crust contributes to the observed surface heat flow by about 15 20 mw m 2 this permits to estimate the moho heat flow in the most stable parts of the shield to about 20 mw m 2 and over 25 30 mw m 2 in the surrounding platform to the south and east relatively low moho temperatures of 350 500 c characterize the crust mantle boundary of the shield increasing to 600 700 c beneath the shield margins the thermal thickness of the lithosphere of the shield can attain more than 200 km

deep seated gravitational slope deformations related landslides and tectonics abstract deep seated gravitational slope deformations and their relationships with tectonic deformation of rocks is considered to examine the viewpoint of tectonics as a causative factor in slope deformation first a distinction is made between the different types of deep seated gravitational slope deformation then the geomorphological and structural effects of the different macrostructural deformations induced by tectonics on the scale of the whole deforming ridge is briefly discussed finally some case studies that represent either verified or possible cases of gravity deformation in response to tectonic activity are used as illustration

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

crustal heat production and mantle heat flow in central and eastern europe abstract the conversion of seismic velocity p into radiogenic heat production a enables the distribution of crustal heat sources to be estimated this technique was used to assess the mantle moho heat flow for 49 seismic velocity depth profiles located along five continental traverses in central and eastern europe the effect of pressure and temperature on p was taken into account as was the age dependence of a the uppermost part of the crust is dominated by microcracks that may have allowed a certain redistribution of radioactive elements by deep groundwater migration furthermore owing to the highly variable value of the pressure derivative of v p in the uppermost crust the use of a a p relationship is problematic within this depth range this radioactivity enriched zone the thickness of which can be determined from the parameters of the heat flow heat production relationship was therefore treated separately according to the model adopted for the upper crust the moho heat flow ranges from 14 to 26 mw m 2 in the stable continental areas such as the shields or ancient platforms younger terrains are characterized by elevated moho heat flows of 20 to 40 mw m 2 and the moho heat flow may eventually attain values over 50 mw m 2 in regions characterized by very high surface heat flow such as the pannonian basin for example the present data were compared with crustal models proposed by other authors moho heat flow estimates based on a simple exponential distribution of heat sources valid for the whole crust might be too high if applied to stable continental crust our data confirm a considerable variability in the mantle heat flow corresponding to the large scale tectonothermal evolution with a generally lower moho heat flow typical of consolidated stable continental crust the discrepancy in relation to the above estimates can be accounted for by a heat generation hump beneath an upper zone of exponential decline

thermomechanical lithospheric structure of the central fennoscandian shield abstract the deep seismic sounding dss profiles baltic including its southern continuation the sovetsk kohtla jarve skj profile sveka the northern part of babel polar fennia and pechenga kovdor kostomuksha were used in studying the present day thermomechanical structure of the central fennoscandian shield these profiles are located in different tectonic units which represent different stages in precambrian crustal and lithospheric growth first present day geotherms were constructed for several points along the dss profiles successively strength envelopes were calculated using the obtained geotherms and rheological flow laws variations in strain rate were also considered in the computations of the strength envelopes the integrated crustal and lithospheric strengths the thicknesses of the mechanically strong crust msc and mechanically strong lithosphere msl and the rheological thickness of the lithosphere were derived from these strength envelopes the obtained mechanical structures for different regions were analysed and compared with other geophysical data e g seismicity depth and isotherm depth distributions the rheological results show lateral variations in the lithospheric strength reflecting the geometry of the lithosphere and following roughly the same trend as the geochronological development of the fennoscandian shield the mechanical structure shows distinct decoupling of the weak lower crust and the strong upper mantle particularly with a wet rheology this decoupling interrupts the transmission of the differential stress from the brittle upper crust to the ductile lower crust and through it to the mantle lithosphere the weak lower crustal layer is also detected with a dry rheology in the svecofennian area whereas in the archaean side it is not distinct the assumed frictional transition temperature of 350 c varies between the depths of 25 and 44 km with an average value of 35 km this is in good agreement with the observed focal depth limit of 31 km consequently it seems that the velocity weakening velocity strengthening explains best the real lower boundary of seismicity

prehistoric fault offsets of the hilina fault system south flank of kilauea volcano hawaii historical accounts of earthquakes on the island of hawaii date only to 1823 but lava flows as old as 1500 3000 years b p contain fault offsets from prehistoric earthquakes the m7 2 1975 kalapana earthquake produced over 25 km of fault rupture along the hilina fault system we compare fault offsets in prehistoric lava flows with kalapana earthquake fault offsets in neighboring 1969 1974 mauna ulu lava flows to estimate the frequency of prehistoric major earthquakes on the hilina fault system horizontal and vertical fault offset rates across the hilina fault system are 4 0 to 12 0 and 2 0 to 20 0 mm yr respectively based on lava flows 750 years b p age assuming prehistoric earthquakes produced similar fault offsets compared to the kalapana earthquake three to five events are recorded in 400 750 years b p old lava flows yielding recurrence intervals of 260 80 years vertical fault offsets in prehistoric lava flows suggest that hanging wall rotation of the hilina fault system contributes to fault offset the assumption that past faulting resulted from prehistoric earthquakes with similar magnitude and fault offset to the kalapana earthquake is an oversimplification large south flank earthquakes most likely do not have uniform recurrence intervals

failure of volcano slopes magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse their role is twofold involving both driving and resisting forces first flank stability is diminished by magmastatic and magma overpressures and steepened slopes that accompany intrusion second excess pore pressures in potential failure zones can be generated as a result of intrusion related mechanical or thermal straining of the rock fluid medium pressurized retrograde boiling in high level magma chambers or hydrothermal fluid circulation also earthquakes may aid collapse through inertial forces and shaking induced pore pressure generation these excess pore pressures reduce the sliding resistance as shown for wedge shaped slide blocks for selected cases the destabilizing influence of mechanically induced pore pressures is maximized as the intruded width or corresponding overpressure of the intrusion is increased the destabilizing influence of thermally induced pore pressures is conditioned by the seve

discrete element simulations of gravitational volcanic deformation 1 deformation structures and geometries 1 we have carried out two dimensional particle dynamics simulations of granular piles subject to frictional coulomb failure criteria to gain a first order understanding of different modes of gravitational deformation within volcanoes under uniform basal and internal strength conditions granular piles grow self similarly developing distinctive stratigraphies morphologies and structures piles constructed upon cohesive substrates exhibit particle avalanching forming outward dipping strata and angle of repose slopes systematic decreases in basal strength lead to progressively deeper and steeper internal detachment faults and slip along a basal decollement landslide forms grade from shallow slumps to deep seated landslide and finally to axial subsidence and outward flank displacements or volcanic spreading surface slopes decrease and develop concave up morphologies with decreasing decollement strength depositional layers tilt progressively inward spatial variations in basal strength cause lateral transitions in pile structure stratigraphy and morphology this approximation of volcanoes as coulomb granular piles reproduces the richness of deformational structures and surface morphologies in many volcanic settings the gentle slopes of hawaiian volcanoes and olympus mons on mars suggest weak basal decollements that enable volcanic spreading high angle normal faults favored above weak decollements are interpreted in both settings and may explain catastrophic sector collapse in hawaii and broad aureole deposits surrounding olympus mons in contrast steeper slopes and shallow detachment faults predominate in the canary islands thought to lack a weak decollement favoring smaller more frequent slope failures than predicted for hawaii the numerical results provide a useful predictive tool for interpreting dynamic behavior and associated geologic hazards of active volcanoes

the variation of heat generation density and seismic velocity with rock type in the continental lithosphere abstract the petrophysical properties radioactive heat generation compressional wave velocity and density are related to rock type in crystalline rocks the cation fraction in the rock forming minerals is applied to determine the relationships quantitatively heat generation exhibits considerable variation with rock type as well as with the geologic age of the rocks therefore the relation between heat generation and rock type has been split into a relation for phanerozoic rocks and another for precambrian rocks which exhibit significantly lower heat generation only 1 3 of that of phanerozoic rocks the interrelations between the petrophysical properties are applied to fennoscandia precambrian terrane and southern bavaria northern alpine foreland phanerozoic rocks to estimate the heat generation by radioactivity in the crust and the heat flow density from the upper mantle

forced oscillations on the equatorial atlantic basin during the seasonal response of the equatorial atlantic program 1983 1984 a subset of data from an array of eight inverted echo sounders and a meteorological station deployed and maintained for 15 months in the equatorial atlantic as part of the seasonal response of the equatorial atlantic program are analyzed to determine the variability of forced oscillations of the basin the analysis is done to study both low and high frequency variability at low frequencies the equatorial basin responds as a whole to the seasonally varying winds the dominant signal is the annual cycle of the equatorial system as a composite of the response to the strong seasonal wind curl that is maximum in the western basin and the part of the zonal transfer to mass associated with the seasonal equatorial upwelling and downwelling system three bands of energy appear as dominant in the combined spectrum of the ocean and the atmosphere at higher frequencies 20 30 days 13 16 days and the inertial gravity wave band each one of the bands is analyzed and discussed instability waves are detected on the echo sounder records the waves have periods centered at 30 2 days and propagate westward with a wavelength of 1000 km and a phase speed of 0 35 m s the most energetic oscillation in the analyzed wind records is at periods centered around 14 days the response of the ocean to this oscillation has a meridional distribution with maximum amplitude at 3 n the most significant oceanic oscillations in the inertial gravity band are centered at 5 2 and 3 5 days from the study of their meridional structure it is concluded that those oscillations correspond to forced inertial gravity waves with meridional structures corresponding to the meridional numbers n 1 and n 3 respectively

seasonal variation of the gulf of guinea thermal structure data from 6 temperature sections are combined with other sequal focal data along 4 w from the coast 5 n to 3 s to study the seasonal variation of the temperature field in the gulf of guinea during 1983 the equatorial upwelling begins during mid april approximately 1 1 2 months before the climatic mean but has a normal amplitude and duration the upwelling on the coast at abidjan occurs approximately 1 1 2 months after the equatorial upwelling and precedes its climatic mean by 2 weeks at the equator vertical displacements of isotherms within the thermostad are complicated by an anomalous warming of the thermostad in may between the thermostad and the deeper thermocline at 230 m the seasonal isotherm displacement amplitude has a minimum at greater depths it increases again in all respects the fluctuation of the thermal field at the equator is similar to the climatic mean but displaced forward in time by 1 1 2 months

validation of an equatorial atlantic simulation model using inverted echo sounder data changes in the vertically averaged temperature of the water column observed over a 12 month period at eight locations in the tropical atlantic with inverted echo sounders are described in terms of empirical orthogonal functions these modes are compared with those from a similar analysis for data from a general circulation model of the tropical atlantic the method proves to be useful for the validation of models

the post collisional stabilization of thickened crust in the southern urals abstract the urals are characterized by a depression of the moho to a depth of 57 km this structure is interpreted as a relic orogenic root which has been conserved because no significant post collisional processes occurred however there is evidence that voluminous post collisional magmatism affected the lower crust in this paper we use thermal finite element models to quantify the influence of the post collisional magmatism on the stabilization of the root we show that at least 70 of the heat producing elements migrated in granitic melts from the lower crust to the upper crust as a result the crustal heat flow reduced and the lithosphere could stabilize at a thickness of 180 km furthermore we propose that a granulite metamorphic event during the thermal relaxation of the collision zone prevented the 57 km thick crust from delamination these results strongly indicate that post collisional processes were necessary for the stabilization of the uralian crust and lithosphere

rock mass strength and slope stability of the hilina slump kīlauea volcano hawai i abstract stability of the hilina slump on the south flank of k lauea volcano hawai i is investigated using slope stability analyses based on rock mass mechanics the hilina slump is an active example of the giant landslides that are observed around submarine flanks of ocean island volcanoes based on edifice topology along with derived rock mass strength and deformability parameters slope stability analyses predict that the geometries of present day failure surfaces of the hilina slump are shallow located at less than 3 5 km depth below the upper surface of the edifice the failure surfaces at the base of the hilina slump are predicted to be structurally independent from a previously interpreted subjacent detachment at the contact between the k lauea edifice and the oceanic crust based on these model results the hilina slump is envisioned to ride atop the south flank of k lauea as it spreads seaward along this slipping basal detachment under present day slope and sea level configurations local horizontal ground accelerations greater than 0 4 0 6 g are predicted to cause slip along failure surfaces within hilina slump therefore dynamic stress changes due to slip along the subjacent detachment may potentially trigger slip along failure surfaces of the hilina slump model derived stability and failure surface geometries can account for the distinct observed distribution of slip along specific hilina faults following the m fa 7 9 1868 ka u and m s 7 2 1974 kalapana earthquakes further the spatial distribution of south flank aftershocks m 1 5 recorded between 1950 and 1976 are consistent with the predicted distribution of potential earthquake induced slip of the hilina faults

rheological structure and dynamical response of the dss profile baltic in the se fennoscandian shield abstract numerical modelling was applied to study the present day state of stress and deformation under different tectonic loading conditions at the seismic baltic skj profile in south eastern finland and in estonia the finite element method was used to solve the numerical problem the two dimensional model was constructed using the results from both seismic and thermal studies along the profile the model is 700 km long and 200 km deep and is roughly divided into an inhomogeneous laterally layered crust and a homogeneous mantle lithosphere both the linear elastic and non linear elasto plastic rheologies were used elasto plasticity was achieved by calculating a rheological strength as a function of depth along the profile different tectonic load cases were analysed with displacement force and pressure type boundary conditions also the effect of different strain rates was investigated the results suggest that even with relatively low compressive stress levels the lower crust deforms in a plastic manner for a wet crustal rheology when applying a dry crustal rheology plastic yielding is attained only with much higher stress fields

rapid deformation of the south flank of kilauea volcano hawaii the south flank of kilauea volcano has experienced two large magnitude m 7 2 and m 6 1 earthquakes in the past two decades global positioning system measurements conducted between 1990 and 1993 reveal seaward displacements of kilauea9s central south flank at rates of up to about 10 centimeters per year in contrast the northern side of the volcano and the distal ends of the south flank did not displace significantly the observations can be explained by slip on a low angle fault beneath the south flank combined with dilation deep within kilauea9s rift system both at rates of at least 15 centimeters per year

crustal temperature and mantle heat flow in europe abstract the map of the surface heat flow in europe was supplemented by the crustal thickness pattern and data on crustal radioactivity and transformed to the mantle moho heat flow distribution using a model of radioactivity decreasing exponentially with depth a z a 0 exp z d with a0 2 wm 3 and d 10km we computed generalized one dimensional steady state conductive temperature depth curves for the major tectonic units of europe the available information on the heat flow tectonic age heat flow heat generation and heat flow crustal thickness relationships were summarized and discussed in terms of crustal structure the mohorovicic discontinuity is clearly not an isothermal surface neither is the outflow of heat from the upper mantle constant but both parameters may vary within broad limits the moho temperature can be as low as 280 c in the shield areas however it can exceed 900 c in some young intrarnontane depressions or rift structures regional variations of the moho heat flow can be as large as 30 40 mwm 2 the value of the moho temperature reflects primarily the tectonic stabilization of the crust as a result of the deep seated processes in the upper mantle

rapid deformation of kilauea volcano global positioning system measurements between 1990 and 1996 campaign global positioning system gps measurements from 1990 to 1996 are used to calculate surface displacement rates on kilauea volcano hawaii the gps data show that the south flank of the volcano which has generated several large earthquakes in the past 3 decades is displacing at up to 8 cm yr to the south southeast the summit and rift zones are subsiding with maximum subsidence rates of 8 cm yr observed a few kilometers south of the summit caldera elastic dislocation modeling of the gps data suggests that the active sources of deformation include deep rift opening along the upper east and east rift zone fault slip along a subhorizontal fault near the base of the volcano and deflation near the summit caldera a nonlinear optimization algorithm was used to explore the parameter space and to find the best fitting source geometry there is a broad range of model geometries that fit the data reasonably well however certain models can be ruled out including those that have shallow rift opening or shallow fault slip some offshore aseismic slip on a fault plane that dips between 258 north northwest and 88 south southeast is required best fitting slip and rift opening rates are 23 28 cm yr although rates as low as 10 cm yr are permitted by the data

modes of variability of the 1983 thermocline signal acoustic travel time series from an array of nine inverted echo sounders deployed along the equator and in the north equatorial countercurrent necc are decomposed into empirical orthogonal functions eof to analyze the dominant frequencies of oscillations in the thermocline field at low frequencies the first eof mode describes the seasonal signal shows the reversal of the necc and separates the behavior of the gulf of guinea from the rest of the basin the second eof mode shows rapid changes in the depth of the thermocline in short periods of time on the equator at 10 w and at 3 n 38 30 w comparison with a simulation model by philander and pacanowski shows that the theoretical time series behave in a similar way at these two locations at high frequencies the modes show oscillations in the inertia gravity wave band

molten core model for hawaiian rift zones abstract kilauea volcano s east rift zone erz is extraordinary in that abundant lateral dike intrusions and rift zone widening associated with seaward slip of the south flank over a basal fault may have allowed an extensive molten core to develop the rift zones of mauna loa and the southwest rift zone swrz of kilauea do not appear to have such extensive molten cores perhaps because of a diminished role of flank slip a molten core may efficiently convey pressure and transport magma to distant sites along the rift zone this concept helps to explain the long low profile of kilauea as viewed along the axis of the erz the combined influence of a molten core and flank slip helps to explain the varied repertoire of magmatic events at kilauea i propose that the 1975 m 7 2 earthquake marked a fundamental change of activity at kilauea from shallow dike injection above the molten core and largely effusive edifice growth to chiefly endogenous growth by deep dike intrusion below the molten core dike intrusion slowed during the 1983 1991 pu u o o eruption sequence because inflation of the magmatic system the engine of intrusion and flank slip processes was retarded by continuous magma loss via the molten erz core to a low elevation vent site

geodynamics and rheology of the lithosphere along the dss profile sveka in the central fennoscandian shield abstract numerical modelling was carried out to investigate the rheological structure and properties of the northern part of the deep seismic sounding dss profile sveka this profile is located in central finland and it crosses the lake ladoga bothnian bay zone llbb which is the border between the proterozoic and the archaean domains data from seismic thermal electromagnetic and gravitational studies are used as initial parameters and also for analysing the results mainly dss data are used to construct the subsurface structures rheological and thermal models with different material properties are calculated first these results are then applied to the two dimensional finite element model of the sveka profile the rheologically defined model is furthermore subjected to compressive boundary conditions and the resulting response is suggested to give some understanding of the present day state of stress and deformational conditions in the lithosphere the rheology of the dss profile sveka seems to be fairly strong the proterozoic lower crust of the model is weaker than the archaean one finite element modelling shows that with moderate stress fields the crust remains still intact and only minor deformational areas are found these include brittle deformation in the uppermost proterozoic crust and plastic deformation in the lowermost crust lower crustal yielding present in few model cases is limited to very narrow zones at depths which are very close to the moho boundary changing the lower crustal composition from dry to wet reduces the strength in the lower crust remarkably which enables plastic deformation in the lowermost crust similar results are obtained with reduction of the strain rate value

the forced annual reversal of the atlantic north equatorial countercurrent abstract we analyze the variability of the thermal structure associated with the atlantic north equatorial countercurrent necc and its relation to the seasonally varying winds the analysis performed allows us to establish the period of time and the region where the necc reverses direction west of 25 w the depth of the thermocline in the southern side of the necc 4 to 7 n annually oscillates 180 out of phase to the oscillations on the northern side 7 to 10 n east of 25 w the thermocline rises and falls nearly in phase across the countercurrent if the flow can be uniquely presumed from the thermal structure the necc disappears during the boreal spring in the western basin the reversal of phase from north to south over one part of the ocean but no the other is shown to be mirrored in the annual variation of the curl of the stress induced at the surface by the winds in order to quantify this result the different terms of the vorticity equation are calculated from the data we conclude that t

filling of flexural moats around large volcanoes on venus implications for volcano structure and global magmatic flux the absence of topographic moats and concentric normal faulting around large volcanoes on venus is attributed to filling of the annular flexural depression by lava flows from the central edifice large volcanoes on venus are characterized by prominent approximately conical edifices surrounded by relatively flat flow aprons the surfaces of both of these constructional components consist dominantly of radially oriented flows from analytic plate flexure models we generate a synthetic stratigraphy for venus volcanoes from which we calculate the volume of material filling the flexural moats to the level of the flow apron the total volume of volcano associated extrusive lavas including moat fill can be an order of magnitude greater than the volume of the edifice alone extended to all large volcanoes on venus this procedure yields estimates for magmatic flux on venus comparable to the present terrestrial intraplate extrusive flux but this scenario is nonetheless consistent with observations of areally limited resurfacing since the most recent global resurfacing event the absence of flexure related tectonic features around most large volcanoes by the arguments advanced here is attributable to masking by apron flows and low stresses in the apron moat fill on venus a volcanic edifice and associated moat filling material constitute a single structurally coherent unit large volcanoes on venus thus appear to be structurally distinct from those on earth and mars

later stages of volcanic evolution of la palma canary islands rift evolution giant landslides and the genesis of the caldera de taburiente the islands of la palma and el hierro form the western end of the hotspot induced canary islands chain both islands are at present in the earliest and fastest shield building stage of growth and show many similarities with the hawaiian islands la palma shows two very distinct phases of volcanic construction 1 a pliocene submarine volcanic and intrusive series interpreted as an uplifted seamount at least 1500 m above present sea level and 2 a subaerial volcanic series erupted in the past 2 m y taburiente volcano initially formed the northern part of the island and then extended to the south forming a ridge cumbre nueva ridge that was partially destroyed about 560 ka by a giant lateral collapse the cumbre nueva collapse possibly involving 180 200 km 3 of subaerial volcanic material the northwest boundary of the cumbre nueva collapse formed a vertical scarp that enlarged by headward erosion formed the spectacular depression of caldera de taburiente cumbre vieja volcano a north south elongated rift forms the southern half of la palma and constitutes its last stage of growth including all eruptive activity in the past 125 k y detailed field observations mapping and high precision radiometric dating have allowed reconstruction of the growth and structural changes of the cumbre vieja volcano interactions between eruption rates coastal erosion and glacio eustatic sea level change allow stratigraphic subdivision of the edifice the structure of the volcano has been controlled for most of its history by a rift system with a clearly dominant north south and less distinct north east and north west volcanic rift zones the rift reorganization of the volcano to a single north south rift since 7 ka and the opening of faults during the 1949 eruption probably reflect increasing instability of the west flank of the volcano

a heat production model of a shield area and its implications for the heat flow heat production relationship the pikwitonei and sachigo subprovinces of central manitoba provide a cross sectional view of the superior province crust to constrain thermal models of the crust we measured heat production and thermal conductivity in rocks from this terrain using standard gamma ray spectrometry and divided bar techniques these data when used in a two dimensional model of shield crust show that estimates of surface heat flow and surface heat production yield the well known linear relationship between surface heat production and surface heat flow observed for heat flow provinces this demonstrates that determinations of heat production with depth based on inversion of the linear heat production heat flow relationship are non unique

the north equatorial countercurrent observed during the programme francais ocean climat dans l atlantique equatorial experiment in the atlantic ocean july 1982 to august 1984 observations from programme francais ocean climat dans l atlantique equatorial focal cruises in 1982 and 1984 have confirmed that in the central atlantic ocean the north equatorial countercurrent necc has a well defined seasonal regime with a very reduced flux during spring the main core of the necc always lies between 4 n and 6 n focal observations have also shown that a long term change of necc may occur and contribute to the development of an el nino type event in the eastern atlantic ocean

anomalously low heat flow density in eastern karelia baltic shield a possible palaeoclimatic signature abstract we report new heat flow density hfd values in seven drill holes in the kamennye lakes area in eastern karelia russia approximately at latitude 63 15 n longitude 36 10 e the investigated holes are 250 750 m deep and they intersect archaean ultrabasic serpentinites and talc carbonate rocks measured gradients range from 0 8 to 3 7 mk m 1 and the apparent hfd values from 2 4 to 11 6 mw m 2 the holes are not technically disturbed by fluid flow or any drilling effects average heat production of the rocks as analysed in the core samples of the deepest measured hole is 0 25 w m 3 but the low heat production is not a critical factor in producing the low hfd values this is due to refraction of heat as shown with 2 d conductive simulations of heat transfer in a low heat production formation surrounded by higher heat production hydrogeological disturbances can be ruled out by the presence of saline groundwater in the sections deeper than 150 400 m and low topographic variation in the area as well as peclet number estimates which suggest negligible convective heat transfer in the bedrock all the temperature profiles are curved indicating recent palaeoclimatic disturbances inversion studies with singular value decomposition techniques yielded a climatic warming of about 1 0 1 5 k which started 150 200 years ago and was preceded by a cool period which lasted about 100 years nevertheless recent climatic changes cannot explain the very low apparent hfd values but long period effects of the weichselian glaciation are sufficient to decrease the hfd values to the levels measured these effects were investigated with forward simulations and suggest that present temperature gradients in the range of 1 4 mk m 1 in the uppermost 1 km can be created by a very cold ground temperature 10 to 15 c during the glaciation time 60 11 ka ago

terrestrial heat flow and groundwater circulation in the bedrock in the central baltic shield abstract unpublished heat flow measurements from 17 drillholes in finland central baltic shield are presented the holes range from 270 to 1080 m in depth sharp vertical changes in the heat flow density and in the temperature gradient indicating groundwater flow disturbances were detected in eight holes the variations in heat flow were typically of the order of 5 10 mw m 2 in many cases the groundwater flow concept was supported by geological logs and other borehole measurements which indicated the existence of fracture zones at the same depths as the flow the flow zones were usually encountered at depths of less than 500 m but flows between fracture zones in the holes were detected even deeper at as much as 930 m according to recent groundwater studies in the same holes the water flowing in the fracture zones seems to be fresh or only slightly saline in composition this can be taken as an indication of relatively rapidly circulating groundwater in contrast to the more saline and more stagnant groundwater encountered deeper in the holes the results indicate that disturbances in heat flow induced by groundwater flow may be much more common in areas of crystalline bedrock than has previously been realized the apparent heat flow densities mean 35 0 3 0 mw m 2 agree well with values published previously from the central baltic shield but the results from southern and western finland indicate regionally above average heat flow values 45 mw m 2

recurrent large scale landsliding on the west flank of la palma canary islands a large area of debris avalanche deposits has been discovered on the western submarine flanks of the island of la palma multibeam bathymetry and its derivative backscatter data towed ocean bottom instrument tobi sidescan sonar images and 3 5 khz and airgun seismic reflection data have been used to identify at least two and possibly as many as four major landslide events the youngest of the events the cumbre nueva debris avalanche extends onshore into the valleys bounded by the caldera de taburiente and cumbre nueva ridge which mark the degraded collapse scars radiometric dating of the volcanic flows in the headwall indicate an age of between 536 and 125 ka for this landslide the debris avalanche covers an area of 780 km2 has a maximum thickness of 500 m and has an estimated volume of 95 km3 older deposits collectively referred to as the playa de la veta debris avalanche complex are probably as the name indicates an amalgamation of at least two or three events rather than the result of a single catastrophic failure the playa de la veta debris avalanche complex is associated onshore with an unconformity dated as late matuyama 1 ma to 800 ka it covers an area of 1200 km2 has a maximum thickness of 1300 m and may represent a total volume of up to 650 km3 the greater thicknesses and limited areas occupied by debris avalanches on the western flank of la palma compared to other landslides in the canary archipelago suggest that the la palma landslide masses have relatively low mobility the different debris avalanche lobes formed by each landslide event are separated by channels 2 2 5 km wide the clear relationship between channel position and the boundaries of each debris avalanche lobe indicates that debris avalanches control later channel formation and pathways the relief of the submarine flanks of the la palma volcanoes in the areas of island slope unaffected by landslides is mainly the result of constructional volcanic processes however the older submarine slopes such as in the northern taburiente volcano may also have been modified by smaller scale submarine mass wasting and sediment flows

the 1998 debris avalanche at casita volcano nicaragua investigation of structural deformation as the cause of slope instability using remote sensing abstract during hurricane mitch in 1998 a debris avalanche occurred at casita volcano nicaragua resulting in a lahar that killed approximately 2500 people the failure that initiated the avalanche developed at a pre existing cliff part of the headwall of a gravitational slide of approximately 1 8 km 2 in plan view that cuts the southern flank of the volcano structural analysis primarily based on a high resolution dem has shown that this slide is caused by edifice deformation casita s eastern side is spreading radially outwards forming a convex concave profile and steepening original slopes this deformation is possibly facilitated by millennia of persistent hydrothermal alteration of the volcano s core the gravity slide has some typical features of smaller slumps such as steep headwalls an inner flatter area and a pronounced basal bulge fronted by thrusts the headwall is the source of the 1998 avalanche as well as several previous mass movements edifice deformation has led to extensive fracturing of the hydrothermally altered andesitic source rock increasing instability further field evidence indicates that the gravity slide is still actively deforming and with steep headscarps remaining the hazard of future avalanches is increasing the analysis presented here shows how small but highly damaging landslides can occur during the deformation of a volcanic edifice we show that identification of instability is possible with remote sensing data and minimal reconnaissance work implying the possibility of similar efficient and cost effective analysis at other volcanoes known to host extensive hydrothermal systems we demonstrate this with a simple structural analysis of two similar stratovolcanoes orosi costa rica and maderas nicaragua

lithospheric thermal structure in the baltic shield summary steady state heat conduction modelling was carried out to calculate the crustal temperature field and thermal lithosphere thickness in the baltic shield the radiogenic sources at the surface were fixed depending on the age of the crust below the uppermost 10 kilometres a relationship between heat generation and p wave velocity was applied and seismic structure was used to define individual crustal blocks of specific thermal parameters small scale surface heat flow density anomalies are interpreted as lateral variations of heat generation within the upper part of the crust whereas the large anomaly in the southern part of the shield is attributed to an anomalously high mantle heat flow density the results are shown on maps outlining mantle heat flow density moho temperature and thermal lithosphere thickness a relationship between subcrustal temperature and moho depth was found except for southern sweden the lithospheric thickness is found to exceed 200 km in the bothnian gulf northern central finland and part of the kola peninsula where temperatures at the moho are less than 500 c the temperature gradient at the top of the mantle has on the average a value of 7 5 mk m and the mantle heat flow density varies from 19 to 25mwm 2 towards the south the lithospheric thickness decreases until it attains a value lower than 100km under southern sweden in this latter area the moho temperature and mantle heat flow density are remarkably high 700 900 c and 30 45 mw m 2 respectively as well as the temperature gradient which amounts to 10 mk m

geothermal modelling of the lithosphere in the central baltic shield and its southern slope lithospheric temperature and heat flow density hfd were studied in the central baltic fennoscandian shield and its subsurface continuation to the south along a transect trending from eastern finland to southern estonia the transect represents an example of a low hfd 30 mw m 2 archaean craton on a thick 150 190 km lithosphere surrounded by early and middle proterozoic mobile belts on a thinner 110 150 km lithosphere with slightly elevated hfd 35 55 mw m 2 numerical 2 d conductive models were constructed in which peridotite solidus temperatures were assigned to those depths which correspond to the seismically determined lithosphere asthenosphere boundary this technique was found to reduce the effect of uncertainties in heat production and thermal conductivity values on the simulation results upper crustal heat production values for the finnish terrain were taken from published geochemical analyses of outcropping rocks for the estonian terrain new heat production values were measured from core samples representing nineteen deep boreholes middle and lower crustal lithologies were estimated with the aid of the deep seismic vpvs data and corresponding heat production values were adapted from global xenolith averages and from data for granulites cropping out in other precambrian areas the results of the modelling suggest that the lithosphere and moho depth variations are only weakly reflected in the measured surface heat flow data which are mainly controlled by heat sources in the upper crust the simulated heat flow densities at 50 km depth approximately at the moho are relatively low and range from 12 mw m 2 at the archaean northeastern end to 19 mw m 2 on the proterozoic southwestern end of the transect simulated temperatures at 50 km depth increase from northeast to southwest ranging from 450 550 c in eastern finland to about 650 c in estonia sensitivity of the simulations to parameter changes was studied by varying the heat production and thermal conductivity values the extreme values for the moho temperature estimates thus obtained may be about 50 k lower or 100 k higher than the values above the corresponding sensitivity of the moho hfd is about 6 mw m 2 and of the surface hfd 5 20 mw m 2 respectively

north brazil current retroflection and transports 1 a subset of data collected as a part of a larger program the north brazil current rings nbcr experiment is analyzed to study the variability of the transport of the north brazil current nbc and its relation with the shedding of rings it is concluded that there is a direct relation between the latitude of penetration the number of rings shed and the intensity of the nbc the data set consists of dynamic height time series derived from three inverted echo sounders and a shallow pressure gauge deployed along a section perpendicular to the south american coast between the continent and 7 n and between 48 and 45 w velocity and hydrographic data collected during the nbcr cruises are also analyzed and used to validate the results the 15 month mean transport of the nbc is 16 2 sv the 18 month mean of the retroflected southeastward flow is 22 2 sv both flows display considerable variability the retroflected southeast flow reaches its maximum value during september 1999 near the time when the climatological north equatorial countercurrent necc reaches its maximum strength and it is minimum when the climatological necc reverses or is not present in the basin the mean difference between the nbc flow and the retroflected flow during august december 1999 when the necc is fully established is 7 sv the excess in the retroflected flow is due to north atlantic water joining the retroflected flow from the south atlantic the combination of both flows constitutes the necc

faulting in the south flank of kilauea volcano hawai i abstract models developed to explain the deformation of kilauea volcano largely rely on seismic and geodetic data that cover only a short period of activity kilauea s active south flank contains two normal fault systems the koa e and hilina systems that must reflect longer term deformation of the edifice the scale and origin of these faults is poorly understood both fault systems consist of en echelon fault segments that have significant interaction and linkage the presence of relay ramps between fault segments systematic stepping senses and slip and displacement data all suggest that the fault systems link down to individual larger faults the hilina fault system hfs is 42 km long and 9 km deep while the koa e fault system kfs is underlain by two to three smaller faults the largest of which is at least 14 km long and 4 km deep and possibly extends down to the basal thrust at 9 km depth we suggest that the hfs has developed as a result of differential slip on the thrust at the base of the edifice and that footwall uplift on the hfs causes antithetic faulting in the south flank which provides a new explanation of the origin of the kfs

morphometric properties of martian volcanoes 1 mars orbiter laser altimeter mola data have been used to construct digital elevation models dem of the martian volcanoes in order to determine height flank slope caldera depth and volumes summit elevations range from 21 1 km to 0 5 km and relief varies from 1 0 km to almost 22 km average flank slopes are in the range of 1 to 10 consistent with basaltic shield volcanism the very low slopes of highland patera are also consistent with pyroclastic volcanism minimum volumes range from 1012 to 1015 m3 estimates of the time required to build these volcanoes on the basis of long term terrestrial eruption rates range from hundreds of thousands to tens of millions of years

deep temperatures and lithospheric thickness along the european geotraverse abstract one dimensional steady state heat conduction models in the crust and upper mantle for 24 areas along the european geotraverse egt show that temperatures are higher beneath young geological regions at the moho they range from 450 to 825 c heat flowing out from the mantle varies from 18 to 72 mw m2 and the contribution of crustal heat flow density evaluated by the correlation between seismic velocity and the abundance of radioactive elements accounts for about 48 of the surface heat flow density the temperature gradient below moho from about 5 to 23 mk m is low where the surface heat flow density reaches its minimum values the depth at which the geotherms reach 0 85 of the mantle melting temperature is greater in the precambrian and caledonian areas with a maximum value of about 195 km under the early proterozoic scandinavian shield in the hercynian and alpine areas this depth is generally lower higher values maximum 150 km coincide with the orogenic belts and the continental block of sardinia and corsica under the ligurian sea and the sardinian channel the lithospheric thickness decreases remarkably to about 50 km globally the lithosphere thickness is controlled by the mantle heat flow density which decreases according to a power law with an increase in the lithosphere asthenosphere depth

low frequency meandering of the atlantic north equatorial countercurrent four 19 month time series of indirect measurements of dynamic height were obtained in the tropical atlantic along 28 w at 0 3 6 and 9 n with three inverted echo sounders and one current meter mooring the series were analyzed to study the time latitude variability of the north equatorial countercurrent necc the eastward flow associated with the necc was present at 28 w from 3 to 9 n during most of the observed period except in march april 1983 and april may 1984 periods that coincided with the onset of the wind at the equator the amplitude of the necc s annual cycle was maximum at 6 n and was larger in 1983 than in 1984 the analysis of the time latitude variability of differences in dynamic height shows a long period meridional shift of the necc the core of the current attains its northernmost location during august september in both years and its southernmost location during march april in 1983 and march in 1984 the location of the core is directly related to the position of the intertropical convergence zone from the time series of dynamic height obtained from the indirect measurements geostrophic velocities and transports were estimated and compared with direct observations of currents and values obtained from hydrographic casts

styles of volcano induced deformation numerical models of substratum flexure spreading and extrusion the gravitational deformation of volcanoes is largely controlled by ductile layers of substrata using numerical finite element modelling we investigate the role of ductile layer thickness and viscosity on such deformation to characterise the deformation we introduce two dimensionless ratios a volcano radius ductile layer thickness and b viscosity of ductile substratum failure strength of volcano we find that the volcanic edifice spreads laterally when underlain by thin ductile layers a 1 while thicker ductile layers lead to inward flexure a 1 the deformation style is related to the switch from predominantly horizontal to vertical flow in the ductile layer with increasing thickness increasing a structures produced by lateral spreading include concentric thrust belts around the volcano base and radial normal faulting in the cone itself in contrast flexure on thick ductile substrata leads to concentric normal faults around the base and compression in the cone in addition we show that lower viscosities in the ductile layer low b lead to faster rates of movement and also affect the deformation style considering a thin ductile layer if viscosity is high compared to the failure strength of the volcano high b then deformation is coupled and spreading is produced however if the viscosity is low low b substratum is effectively decoupled from the volcano and extrudes from underneath it in this latter case evidence is likely to be found for basement compression but corresponding spreading features in the volcano will be absent as the cone is subject to a compressive stress regime similar to that produced by flexure at volcanoes where basement extrusion is operating high volcano stresses and outward substratum movement may combine to produce catastrophic sector collapse an analysis of deformation features at a volcano can provide information about the type of basement below it a useful tool for remote sensing and planetary geology also knowledge of substratum geology can be used to predict styles of deformation operating at volcanoes where features have not yet become well developed or are obscured

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

thermocline displacement across the atlantic north equatorial countercurrent during 1983 two time series of thermocline displacement across the north equatorial countercurrent are derived from pairs of inverted echo sounders which straddle the countercurrent along the 28 w and 38 30 w meridians the observations reported are from february to september 1983 from mid may to the end of the record the thermocline deepens to the south and shallows to the north of the countercurrent suggesting a continual strengthening of the countercurrent the rate of increase of the thermocline slope at the western meridian is about twice that at 28 w as expected from historical data an empirical orthogonal functions eof analysis of the four sounders finds the dominant mode accounting for 64 of the variance this is compared to an eof analysis of model results by philander and pacanowski where the forcing is provided by the historical average wind field with the model the dominant mode is almost the entire response 92 of the variance the time dependence of the observed mode tracks that derived from the model during the overlapping seasons

ground deformation monitoring of a potential landslide at la palma canary islands abstract the southern part of the island of la palma comprises a north south oriented volcano known as the cumbre vieja the steep gradient and high aspect ratio of the volcano coupled with the prospect of future episodes of magma intrusion highlight the potential for large scale lateral collapse of the volcano as recorded earlier in the history of la palma and elsewhere in the canary islands historic eruptions of the cumbre vieja have occurred high up on the western flank of the volcano and along a single rift zone along the crest of the volcano the geometry of the recent activity and faulting which occurred during an eruption in 1949 indicates that a discontinuity may be present beneath the western flank of the volcano along which a future collapse may occur to identify any displacement of the western flank overlying the discontinuity a ground deformation network has recently been established on the volcano the initial network spanned the fault system that developed on the upper flanks of the cumbre vieja during the 1949 eruption this small network was measured in 1994 1996 and 1997 using infrared electronic distance measurement in 1997 the network was enlarged and re occupied using the global positioning system to incorporate the west flank and the southern part of the island although the results show that apparent displacements recorded during this period are within the error margins of the techniques employed the apparent movement vectors do suggest a coherent westward displacement of stations to the west of the 1949 fault system additional occupations of the network over the next few years will however be required to determine the reality or otherwise of this apparent coherent movement and thus to decide whether or not the western flank of the cumbre vieja is currently sliding seaward if not it can be inferred that the volcano is stable during inter eruptive periods

geothermal flow and phenomena in two swedish localities north of the arctic circle summary temperature measurements in eight holes reaching vertical depths between 287 and 1100m below ground surface in the malmberget area lat 67 10 n long 20 40 e gr and the kiruna area lat 67 52 n long 20 9 e gr in the swedish precambrian are reported the mean equilibrium heat flow in this part of the swedish shield after climatic correction is 52 6 1 7mwm 2 the mean uncorrected heat flow is 46 6 mwm 2 comparison with other shield areas shows that in common with the s african and indian shields the north swedish shield has a greater heat flow than the remaining shield areas of the world

growth structure instability and collapse of canarian volcanoes and comparisons with hawaiian volcanoes recent onshore and offshore investigations in the canarian archipelago especially in the western islands of la palma and el hierro have greatly improved the understanding of the genesis and evolution of these islands and allow interesting comparisons with other hotspot induced oceanic island volcanoes especially the hawaiian archipelago genesis induced by hotspot activity and consequently shield and post erosional stages of growth allow the definition of similar main stratigraphic units the canarian and hawaiian volcanoes show common constructional and structural features such as rift zones progressive volcano instability and multiple gravitational collapses however the canaries present some important geological differences from the prototypical hotspot volcanoes of the hawaiian islands particularly the absence of significant subsidence the canarian volcanoes remain emergent until completely mass wasted by gravitational collapses and erosion volcanic formations over 20 million years are observable in outcrop in the canaries including the seamount stages of growth in several of the islands

structure and composition of the precambrian crust along the polar profile in the northern baltic shield abstract along the 500 km long polar profile the continental crust of the northern baltic shield consists of several archaean and early proterozoic crustal segments in the south in the karelian province the upper crust consists of a 3 1 2 6 ga old archaean substratum with a 0 6 km thick low to medium grade volcanosedimentary cover here shallow basin facies rocks of the central lapland complex have been thrust northwards onto the karasjok kittila greenstone belt the repeatedly folded cover rocks form linear troughs between domes and culminations of granitoids the 47 48 km thick crust of the karelian province is of a shield type it is characterised by a low velocity layer interpreted as a horizon of decollement below the supracrustal and granitoid rocks in the lapland granulite belt early proterozoic high grade metapelites and metapsammites with minor metaigneous intercalations have been thrust to the southwest they are separated from the underlying karelian province by the tectonic mixture zone of the tanaelv belt in the interpretations two alternative models are given for the shape of the lapland granulite belt it is either a synformal nappe or a ne dipping body pinching out at depth and overthrust from the north by the archaean inari terrain both the lapland granulite belt and the inari terrain have a 42 44 km thick crust with a relatively thin lower crust marked by lower seismic velocities the early proterozoic polmak pasvik pechenga belt separates the archaean inari terrain from the archaean sorvaranger terrain in the north this belt is interpreted as a suture zone which continues to depth it may either dip steeply towards irregularities in the moho or form a sw dipping low angle plane below the lapland granulite belt the northernmost part of the baltic shield is concealed beneath a 0 7 km thick very low grade metamorphic late proterozoic cover this cover is divided into two parts by the trollfjord komagelv strike slip fault here the crust is again of a normal shield type with a thickness of 42 46 km

growth of large volcanoes on venus mechanical models and implications for structural evolution the structure tectonics and evolution of large volcanoes on venus as revealed by data from the magellan mission appear to be distinct from those on earth and mars to determine the conditions and processes that account for these differences we model the evolution of stress and deformation in growing volcanic edifices on venus using the finite element method large volcanoes on venus are characterized by topographically prominent conical edifices surrounded by relatively flat flow aprons the surfaces of both edifice and apron consist dominantly of radially oriented flows tectonic features usually the surface expression of shallowly intruded dikes also have predominantly radial orientations features similar to hawaiian style linear rift zones or large scale flank failure common on large volcanoes on earth and mars are absent by comparing predictions of faulting for models with detached and welded basal boundary conditions with the observed tectonic features we determine that a welded condition is more likely horizontal compressive stresses transmitted into edifices across welded basal boundaries are inversely proportional to elastic lithosphere thickness te contravening stress increments from magma chamber expansion differential thermal contraction or buoyant loading from beneath the crust or lithosphere are required to reorient principal stresses in the edifice so that magma ascent and radial dike formation are favored incremental volcano growth results in stress distributions that decrease with height in the edifice dike intrusion is easiest in the uppermost youngest layers consistent with the observed shallow radial dikes on venus volcanoes small values of te greatly inhibit the formation of large shields in that conical edifice topography cannot be supported and large contravening stresses are required for further growth large volcano formation is much more likely at large te where more moderate contravening stresses are sufficient for growth the near surface manifestation of mantle upwelling on venus may thus depend on te in that the response to upwellings beneath thin or nonexistent lithosphere is likely to be dominantly ductile leading to the formation of coronae but a thick elastic lithosphere is required to support the growth of the largest volcanoes the transitional value of te between these modes of evolution likely depends on the horizontal scale of the upwelling

crustal heterogeneities and the thermal structure of the continental crust the observed linear relationship between surface heat flow q0 and the radiogenic heat production of near surface rocks a0 discovered almost two decades ago has been a primary tool used to infer the distribution of heat production in the continental crust recent evidence on the nature of compositional heterogeneities in the continental crust has led us to reexamine the q0 a0 relationship and the likely implications for the thermal structure of the lower continental crust numerical simulations of crustal thermal models indicate that some interpretations derived from this relation may be flawed in particular the length scale determined from the q0 a0 function normally thought to describe the depth distribution of crustal heat sources is significantly affected by the horizontal scale of crustal heterogeneity as a consequence most estimates of lower crustal heat flow and lower crustal temperatures obtained using heat flow data with the q0 a0 relationship are overestimates this overestimation is proportionally largest in areas of low mantle heat flux such as cratons where basal heat flux may be overestimated by more than a factor of two

the morphology of the submarine flanks of volcanic ocean islands a comparative study of the canary and hawaiian hotspot islands the submarine flanks of volcanic islands are shaped by volcanic constructional processes landslides erosion sediment deposition and tectonic movements we use a newly acquired multibeam sonar dataset from the westerly canary islands el hierro la palma and tenerife to develop a comparison with the hawaiian islands which suggests differences in the processes constructing and modifying their flanks landslides affect the flanks of both island groups debris avalanches fast moving shallow landslides have left smooth chutes and blocky deposits in both cases but blocks within some hawaiian avalanche deposits are markedly larger we attribute the larger block sizes in the hawaiian islands to the fact that their avalanches were relatively unconfined whereas many canary and hawaiian avalanches with small block sizes appear to have been constrained down narrow chutes forcing interactions between blocks within the flows and encouraging disintegration furthermore the hawaiian avalanches with the largest blocks initiated near sea level whereas many of the canary avalanches initiated above sea level so hydraulic resistance of water entering cracks may be an additional factor in resisting block disintegration during flow slow moving deep seated slumps or volcanic spreading have produced submarine benches and tabular escarpments due to thrust faulting adjacent to several hawaiian rift zones but are not well developed in the canaries although volcanic morphology is partly obscured by sedimentation in the canaries we are able to interpret lava terraces around the deep flanks of el hierro which are similar to those found in the hawaiian islands however cones rather than terraces are the most common volcanic forms in the canary islands implying that flank eruptions have involved magma with significant volatile contents assuming that volatile contents dictate whether cones or terraces are formed these differences may ultimately originate from the different building rates of the two island groups for example the lack of evidence for high level magma chambers in the canaries associated with their lower outputs implies that there is less possibility for degassing of magma below the summit before lateral intrusion down rift zones hence cones rather than lava terraces are more commonly observed the apparent lack of slumping or volcano spreading could also reflect a lack of driving pressure from extensive high level magma chambers in the canaries

lithospheric structure of the mid norwegian margin comparison between the more and voring margins the lithospheric structure across the more margin has been studied by integrating regional elevation gravity geoid and heat flow data together with available seismic and geological data our results show that the moho depth varies from 42 km beneath the caledonides to 20 15 km beneath the basin and to 13 16 km in the oceanic domain the lithosphere thins in a step like manner from 160 km inland to 60 80 km in the oceanic domain a comparison with the voring margin reveals that both margins have similar crustal and lithospheric structures major dissimilarities are 1 the volume of underplating beneath the ocean continent boundary 2 the lithospheric thickness beneath the caledonian front 3 the lithospheric thickness beneath the distal parts of the margins the heat transfer across the voring transform margin the secular variation of lithospheric thickness with age and the jump of the aegir spreading ridge are responsible for these differences

deep structure of the voring margin the transition from a continental shield to a young oceanic lithosphere the present day lithospheric structure across the norwegian margin in the voring region is presented the voring margin is characterized by the presence of large volume of magmatic underplating thick mesozoic basins and prominent crustal thinning results from recent deep seismic experiments in the voring basin and voring marginal high and 3 d gravity modelling have been implemented in a regional 2 d lithospheric transect that runs from the norwegian caledonian belt to the oceanic domain crossing the transition between the precambrian fennoscandian baltic shield and the cenozoic northern north atlantic oceanic lithosphere the modelling approach integrates elevation gravity geoid and heat flow data under the assumptions of thermal steady state and local isostasy the results confirm and refine the major trends of the crustal geometry which is characterized by a moho depth varying from about 45 km beneath the caledonian thrusts to 30 km beneath the trondelag platform to 20 14 km beneath the voring basin and to 13 km in the oceanic domain the lithosphere thins from the norwegian caledonian belt 190 km thick to the oceanic domain 60 km in a stepwise manner reflecting the progressive seawards migration of lithospheric deformation since the paleozoic our lithospheric thickness results are different from those predicted by post rift lithospheric cooling models in the oceanic domain observed residual bathymetry 600 m is interpreted as the remaining effect of a deep seated thermal perturbation during the upper cretaceous which would also produce a heat flow anomaly of 15 mw m 2 alternatively residual bathymetry can be interpreted in the absence of thermal anomalies as produced by depletion of the sublithospheric mantle extending down to 130 230 km depth depending on the density contrast 10 30 kg m 3

numerical simulation of earthquake faults with gouge toward a comprehensive explanation for the heat flow paradox the particle based lattice solid model is used to simulate transform faults with and without fault gouge stick slip frictional behavior is observed in two dimensional numerical experiments of model faults both with and without gouge when no gouge is present the fault is strong and the heat generation and stress drops are correspondingly high in disaccord with observations surrounding the heat flow paradox in contrast when a gouge is specified the fault is weak and the heat generation as well as stress drops are low in quantitative agreement with observational constraints the heat flow is low on average and during short periods of aseismic creep seismic efficiencies are compatible with observationally based bounds counter intuitively the fault strength decreases as the intrinsic friction between particles is increased beyond a given threshold the mechanism for low fault strength and heat is rolling and jostling of fault gouge grains during slip this allows macroscopic movement of the fault with only minimal slip between surfaces of the gouge grains as this dynamical mechanism operates during seismic and aseismic slip it provides an explanation for the lack of a heat flow anomaly in both the seismic and creeping parts of the san andreas fault the simulation results provide the first comprehensive and quantitative possible explanation of the heat flow paradox and suggest that fault gouge plays a fundamental role on the dynamics of earthquake faults whether rolling and jostling of fault gouge particles provides the explanation for the heat flow paradox in nature remains to be validated by observation evidence

a three dimensional integrated density and thermal model of the fennoscandian lithosphere abstract a three dimensional geophysical model of the crust and upper mantle for fennoscandia and adjacent regions is presented seismic results gravity field and heat flow data were used for the construction of the model the layers which were allocated from seismic data and distribution of p wave velocities in these layers served as a basis of the initial seismic model empirical equations of interrelation between velocity heat generation and density were used for transforming the seismic model to thermal and density models the influence of pressure and temperature on physical properties was investigated and taken into account statistical parameters of the interrelation between velocity heat generation and density were used when solving the inverse problems for geothermal and gravity data a brief description of the mathematical principles of integrated interpretation is also given as a result 3 d models of distribution of heat generation temperature and density in the crust and upper mantle were obtained these data are represented in horizontal and vertical cross sections outlining physical parameters for various depth levels finally regional geological data are correlated with the obtained density variations in the crust

terrestrial heat flow and radiogenic heat production in finland the central baltic shield abstract heat flow density and radiogenic heat production of the bedrock were studied in finland in part of the central baltic fennoscandian shield heat flow data were collected from 35 holes 270 1080 m deep the heat production values at the sites were determined from the drill core samples by gamma ray spectrometry the areal variation in heat production was studied with the aid of k u and th analyses of 1054 glacial till samples collected for the geochemical atlas of finland a heat production map constructed from this data set revealed a strong areal variation that can be attributed to the known lithological geochemical and tectonic features of the bedrock in general heat production seems to increase with decreasing geological age the presented data strongly suggest that the southern and western parts of finland are geothermally anomalous apparent heat flow density 38 68 mw m 2 surface heat production 2 0 w m 3 in contrast to the other parts of the country mw m 2 w m 3 the heat production heat flow density plots were constructed from apparent and palaeoclimatically corrected heat flow densities the heat production values were determined from both drill core samples and till samples the plot constructed from the till data and apparent heat flow densities which yielded a scale depth of 10 8 2 6 km and a reduced heat flow density of 15 8 4 9 mw m 2 was considered the most reliable the results are discussed in terms of crustal fracturing and deep groundwater flow if the crystalline bedrock is approached as a medium consisting of blocks internally conductive but bounded by fracture zones in which heat is transported by groundwater flow an alternative hypothesis can be constructed for interpreting the linear heat production heat flow density plots according to this hypothesis the scale depth and reduced heat flow densities refer only to the geothermal properties of the uppermost bedrock block in the present study this concept is supported by results from deep electromagnetic and seismic soundings

the vertical distribution of radiogenic heat production in the precambrian crust of norway and sweden geothermal implications the present geology of southern scandinavia offers the unique opportunity to sample deep and intermediate levels from the same crustal section for both heat flow and heat production in the central part of southern norway amphibolite facies terranes appear to lie on top of the same deeper crustal formations which crop out on their western and eastern margins an extensive data set on the geochemistry of all types of rocks in the region culled from the literature is used to derive values for radiogenic heat production for each kind of crustal facies using constraints from heat flow data in the same area allows a reliable model of the distribution of crustal heat production the average heat production of granulite facies terranes is 0 4 w m similar to values in other parts of the world for amphibolite facies rocks the value is 1 6 w m the present shield also includes heat producing element enriched granites formed in later events and the average heat production of presently exposed crust is 2 7 m using heat flow and radioactivity data from ten stations the reduced heat flow in the area is 22 2 mw m this corresponds to the heat flow at the top of 28 km of deep crustal facies implying that the mantle heat flow is probably as low as 10 mw m over the whole crustal thickness the average amount of radiogenic heat is 31 mw m

high frequency oscillations and their correlation with the wind forcing during the first sequal year two arrays of inverted echo sounders one along the equator and the other across the north equatorial countercurrent are analysed together with a wind record from st peter and st paul rocks the dominant high frequency feature along the equator is an energetic oscillation with a period of 5 8 days that shows strong coherence with the meridional component of the wind the sounder at 3 n 28 w on the other hand shows a high degree of coherence with the zonal component of the wind at a period of 4 5 days comparison of these measurements in 1983 with measurements made in 1979 suggest considerable non stationarity

the socompa collapse and avalanche event failure of the northwestern flank of the socompa volcano north chile about 7000 years ago created a 40 km long debris avalanche deposit the deposit is remarkably well exposed we have combined spectral reflectance data field observations and analysis of digital topographic surfaces to reconstruct the sequence of collapse events and to constrain the volumes and sources of materials comprising the avalanche collapse involved three principle components the debris avalanche deposit itself volume 26 km3 after 30 expansion large slide blocks 11 km3 and detached blocks 23 km3 which remained in the upper part of the amphitheatre the debris avalanche deposit comprised two main units and seven subunits landsat thematic mapper data enabled estimation of the proportions of spectrally distinct lithological components within these heterogeneous units about 35 of the deposit area is composed of ignimbrites and gravels derived from a 100 200 m thick slice of basement rock underlying the northwestern flank of the volcano dacite domes and lavas originally situated in the southern and western parts of the amphitheatre constitute much of the remainder of the deposit blocks composed largely of sequences of lavas and pyroclastic deposits originally located in the northern and eastern parts of the amphitheatre slid coherently 7 km northwestwards and accumulated near the mouth of the amphitheatre modelling of locations of centroids in the original cone and of displaced components shows that potential energy loss during collapse was 3 8 1017 j cf 0 7 1017 j for mount st helens 1980 significantly components of the avalanche with least potential energy travelled the furthest laterally perhaps demonstrating efficient transfer of momentum from rear to front of the avalanche retrogressive flank failures of the original cone contributed successive components to the avalanche most of these combined to form a single moving mass but some appear to have been emplaced separately