the infiltration of fine matrices into coarse grained alluvial sediments and its implications for stratigraphical interpretation traps designed to simulate the framework gravel of natural streams and installed in a coarse grained channel allow the identification and differentiation of the processes governing the infiltration of fines into bed interstices vertical patterns of matrix distribution reflect the relative importance of variables acting at both the surface of the channel bed and within the bed sediments differences in grain size and therefore pore size of the framework exercise a strong controlling influence an armour layer of coarse particles superimposed on comparatively finer sub surface bed material common to many coarse grained rivers is shown to encourage the clogging of near surface pores with matrix fines below the obstruction interstices may be protected from incursion and the gravel framework is often left open this is the reason for patchy concentrations of matrices often reported in the stratigraphical literature in contrast a uniform size grading of the bed sediment or an upwards fining leads to a more uniform packing of the interstices with matrix flood history is shown to be an important determinant of both the size distribution and the spatial distribution of matrices and is useful in providing a dynamic explanation of the variability of matrices observed from place to place in ancient deposits

currents associated with abnormal quiet days in sq h summary declination data have been analysed on nqds and aqds for the years 1963 64 65 such an analysis indicates that there is a larger southward current in the morning and a larger northward current in the afternoon on nqds than aqds in both the northern and southern hemispheres the strength of this current is found to be imf dependent taken in conjunction with the previous analyses of the h data it is concluded that on aqds the sq h amplitude is affected by a reduction in the current of a large current vortex which extends over both hemispheres and is part of the normal sq h current system such a current is driven by diurnal winds variations in the strength of the wind thus contributing to the day to day variability of the sq h amplitudes aqds therefore represent days of small amplitude in the general day to day variability the imf dependence arises due to complicated current systems that flow on aqds and which are associated with high latitude phenomena and generally have their focus at latitudes 60 similar to those found by takeda araki

detecting volcanism on titan and venus with microwave radiometry the detection by spaceborne instrumentation of infrared thermal emission from volcanic eruptions is well established on earth but is challenged on venus and titan by their optically thick atmospheres microwave radiometry in principle offers the ability to detect emission from surface thermal anomalies on these worlds due to greater atmospheric transparency microwaves also offer the prospect of sensing the shallow subsurface and thus may detect warmth from lava flows for longer than surface infrared emission however satellite microwave instruments typically have low spatial resolution 10s of km so volcanic heat is diluted in the wide instrument footprint we examine the prospects for the detection of volcanic deposits by microwave given likely planetary eruption rates and lava flow deposit geometries using mt etna as a template nondetection of prominent hotspots in cassini data may imply that the resurfacing rate is lower than 2 km3 yr five times smaller than the expression of an earth like fraction of geothermal heat flow as latent heat in extrusive volcanism

ut variation of internal sq currents and the oceanic effect during 1980 march 1 18 summary ut variation of the internal part of sq currents is examined using the geomagnetic data during 1980 march 1 18 and the effect of the ocean is found the ratio of the internal currents to the external increases when the external current vortex comes above the atlantic and pacific oceans and the internal current vortex shifts to the oceans when the external vortex approaches the edge of the oceans the existence of the ocean increases the total induced current by about 30 per cent and this amount is consistent with model calculations for sq by previous workers

deformation associated with the 1997 eruption of okmok volcano alaska 1 okmok volcano located on umnak island in the aleutian chain alaska is the most eruptive caldera system in north america in historic time its most recent eruption occurred in 1997 synthetic aperture radar interferometry shows deflation of the caldera center of up to 140 cm during this time preceded and followed by inflation of smaller magnitude the main part of the observed deformation can be modeled using a pressure point source model the inferred source is located between 2 5 and 5 0 km beneath the approximate center of the caldera and 5 km from the eruptive vent we interpret it as a central magma reservoir the preeruptive period features inflation accompanied by shallow localized subsidence between the caldera center and the vent we hypothesize that this is caused by hydrothermal activity or that magma moved away from the central chamber and toward the later vent since all historic eruptions at okmok have originated from the same cone this feature may be a precursor that indicates an upcoming eruption the erupted magma volume is 9 times the volume that can be accounted for by the observed preeruptive inflation this indicates a much longer inflation interval than we were able to observe the observation that reinflation started shortly after the eruption suggests that inflation spans the whole time interval between eruptions extrapolation of the average subsurface volume change rate is in good agreement with the long term eruption frequency and eruption volumes of okmok

surface deformation and coherence measurements of kilauea volcano hawaii from sir c radar interferometry the shuttle imaging radar c x synthetic aperture radar sir c x sar radar on board the space shuttle endeavor imaged kilauea volcano hawaii in april and october 1994 for the purpose of measuring active surface deformation by the methods of repeat pass differential radar interferometry observations at 24 cm l band and 5 6 cm c band wavelengths were reduced to interferograms showing apparent surface deformation over the 6 month interval and over a succession of 1 day intervals in october a statistically significant local phase signature in the 6 month interferogram is coincident with the pu u o o lava vent interpreted as deformation the signal implies centimeter scale deflation in an area several kilometers wide surrounding the vent peak deflation is roughly 14 cm if the deformation is purely vertical centered southward of the pu u o o caldera delays in the radar signal phase induced by atmospheric refractivity anomalies introduce spurious apparent deformation signatures at the level of 12 cm peak to peak in the radar line of sight direction though the phase observations are suggestive of the wide area deformation measured by global positioning system gps methods the atmospheric effects are large enough to limit the interpretation of the result it is difficult to characterize centimeter scale deformations spatially distributed over tens of kilometers using differential interferometry without supporting simultaneous spatially distributed measurements of refractivity along the radar line of sight studies of the interferometric correlation of images acquired at different times show that l band is far superior to c band in the vegetated areas even when the observations are separated by only 1 day these results imply longer wavelength instruments are more appropriate for studying surfaces by repeat pass observations

new formulae for estimating lava flow volumes at mt etna volcano sicily a new data set of etna lava flows erupted since 1868 has been compiled from eight topographic maps of the volcano published at intervals since then volumes of 59 flows or groups of flows were measured from topographic difference maps most of these volumes are likely to be considerably more accurate than those published previously we cut the number of flow volumes down to 25 by selecting those examples for which the volume of an individual eruption could be derived with the highest accuracy this refined data set was searched for high correlations between flow volume and more directly measurable parameters only two parameters showed a correlation coefficient of 70 or greater planimetric flow area a 70 and duration of the eruption d 79 if only short duration 18 days flows were used flow length cubed l3 had a correlation coefficient of 98 using combinations of measured parameters much more significant correlations with volume were found dh had a correlation coefficient of 90 h is the hydrostatic head of magma above the vent and 92 where w is mean width and e is the degree of topographic enclosure and a combination of the two 97 these latter formulae were used to derive volumes of all eruptions back to 1868 to compare with those from the complete data set values determined from the formulae were on average lower by 16 dh 7 and 19

channel aggradation below chew valley lake somerset u k variations of channel substrate composition are described for a regulated river which has experienced channel change since dam completion sediment samples were obtained using bulk grab sampling and freeze coring data derived from the two methods are shown to differ bulk sample data describe the bed surface layer its grain size variations are related to bedform freeze core data describe the sub surface structure and the fine size grades the gravel framework supported substrate of the control reaches constrasts with the sand dominated substrate of the aggraded reach although in both cases the substrate coarsens upwards in the former this relates to the development of a sand matrix within the gravel framework substrate and in the latter sand bed channel to the progressive addition of a gravel component towards the surface which is related to the process of channel change at the local scale bedform is shown to exert an important control on the character of substrate change induced by flow regulation

on the nature of abnormal quiet days in sq hs summary it is well known that the time of occurrence of the minimum in the horizontal component of the earth s magnetic field hmin on quiet days at a mid latitude station on the poleward side of the sq focus shows considerable variability from day to day this variability has previously been discussed in terms of the incidence of so called abnormal quiet days aqd arbitrarily defined for the station hartland as quiet days when hmin occurred outside an interval of 2 hr centred on the most common time of 1130 lt aqds have some interesting properties which have been documented but their precise nature and cause have not been elucidated in this paper we report the results of a study of aqds as identified at hartland using a chain of northern hemisphere stations situated approximately along the 0 longitude meridian and extending on both sides of the sq focus it is found that there are two effects on aqds i a northward component field varying in lt is superposed at all latitudes throughout the day so reducing the amplitude of the normal sq h variation at stations poleward of the focus and increasing it on the equatorward side ii a southward perturbation field of most probable magnitude 6 0 nt for the period studied is imposed for about 4 hr at a fixed ut at all latitudes so constituting an aqd event which can lead to the occurrence of hmin at an anomalous local time for a station poleward of the focus it is shown that the aqd event may be of large geographical extent and that it is related to the interplanetary magnetic field all the main properties of aqd occurrences are explained and it is suggested that much of the day to day variability in the amplitude and phase of the normal sq h variation probably also arises from the occurrence of aqd events at times close to the diurnal turning points

the july august 2001 eruption of mt etna sicily the july august 2001 eruption of mt etna stimulated widespread public and media interest caused significant damage to tourist facilities and for several days threatened the town of nicolosi on the s flank of the volcano seven eruptive fissures were active five on the s flank between 3 050 and 2 100 m altitude and two on the ne flank between 3 080 and 2 600 m elevation all produced lava flows over various periods during the eruption the most voluminous of which reached a length of 6 9 km mineralogically the 2001 lavas fall into two distinct groups indicating that magma was supplied through two different and largely independent pathways one extending laterally from the central conduit system through radial fissures the other being a vertically ascending eccentric dike furthermore one of the eccentric vents at 2 570 m elevation was the site of vigorous phreatomagmatic activity as the dike cut through a shallow aquifer during both the initial and closing stages of the eruption for 6 days the magma column feeding this vent was more or less effectively sealed from the aquifer permitting powerful explosive and effusive magmatic activity while the eruption was characterized by a highly dynamic evolution complex interactions between some of the eruptive fissures and changing eruptive styles its total volume 25 106 m3 of lava and 5 10 106 m3 of pyroclastics was relatively small in comparison with other recent eruptions of etna effusion rates were calculated on a daily basis and reached peaks of 14 16 m3 s 1 while the average effusion rate at all fissures was about 11 m3 s 1 which is not exceptionally high the eruption showed a number of peculiar features but none of these except the contemporaneous lateral and eccentric activity represented a significant deviation from etna s eruptive behavior in the long term however the 2001 eruption could be but the first in a series of flank eruptions some of which might be more voluminous and hazardous placed in a long term context the eruption confirms a distinct trend initiated during the past 50 years toward higher production rates and more frequent eruptions which might bring etna back to similar levels of activity as during the early to mid seventeenth century

the equatorial electrojet an integrated treatment of observations and models of the undisturbed equatorial electrojet is presented previous reviews have concentrated on particular aspects of the electrojet phenomenon such as ground magnetic variations the counterelectrojet or e region electron density irregularities and associated plasma instabilities here accomplishments during the past 15 years involving all aspects of the phenomenon are covered and where possible interrelated observational and theoretical studies during recent years have emphasized the local time longitude vertical and latitudinal structure of electric fields and currents in the electrojet this review similarly places its emphasis along these lines and by necessity involves a detailed examination of electrodynamic coupling with the neutral atmosphere tidal oscillations in temperature composition and winds the review concludes with an assessment of current knowledge concerning the equatorial electrojet and suggestions for the future direction of observational and theoretical research on electrodynamical processes in the equatorial ionosphere

the large and destructive 1669 ad eruption at etna volcano reconstruction of the lava flow field evolution and effusion rate trend the 1669 ad flank eruption was the most destructive event on etna volcano in historical times 700 bc and provided because of the presence of numerous quarries and subsurface data the opportunity for a unique case study in which we directly measured the thickness of the lava field moreover analysis of historical documents allowed reconstruction of the temporal evolution of the lava field and estimation of the average effusion rate one hundred and thirty eight thickness measurements acquired from field surveys and subsurface data allowed us to divide the lava field into 12 zones of homogenous mean thickness and to calculate a total lava volume of 607 105 106 m3 corresponding to an average effusion rate of 58 10 m3 s this new volume differs by 24 up to 64 from previously published values the temporal evolution of the cumulative volume and average effusion rate were reconstructed for the first fourteen days from field data and analysis of historical records a short initial phase was characterized by a rapid increase in effusion rate which reached a peak of 640 m3 s after 3 days this was followed by a longer phase in which the flow rate decreased the first 14 days were crucial for the development of the lava field and in this time it covered 72 of its final area and produced most of the damage thereafter the growth of a complex lava tube network promoted lava field lengthening to the city of catania 17 km away from the vent effusion rate trends like those of the 1669 eruption can be adopted for future investigations aimed at assessing the effects of similar events on etna s most highly urbanized area and at other effusive basaltic volcanoes

factors controlling the morphology of monogenetic basaltic volcanoes the holocene volcanism of gran canaria canary islands spain abstract a detailed morphometric analysis was performed on the 24 holocene eruptions of gran canaria a nearly circular island located at the centre of the canary islands spain developed as result of the eastward movement of the african plate over a mantle hotspot rigorous field work was carried out to generate a palaeogeomorphological reconstruction of the holocene eruptions of gran canaria to obtain pre and post eruption digital terrain models dtms these eruptions were of strombolian monogenetic basaltic volcanism style with respect to the cones feeder fissures determine their location and some morphological features as crater openings which are usually perpendicular to the slope direction in addition the trade winds influence the final volcanic edifice shape and the extent of the pyroclastic sheet like fall deposits for the lava flows the most significant controls are the eruption rate affecting the maximum distance travelled and the gully slope and shape that condition their flow path concerning volcanic hazard and risk assessment the applied methodology has led to a better understanding of the recent eruptions and foresees the location and nature of future eruptions

on the latitude of the sq h focus at sunspot minimum summary the latitude of the sq h focus along the 0 longitude meridian in the northern hemisphere has been determined for all the quiet days as determined from the aa indices for the sunspot minimum years 1963 64 65 it is shown that a most of the large variability of the focus latitude is due to the effect of a superposed northward magnetic field that is present on aqds and which tends to move the apparent focus latitude poleward in the northern hemisphere and b a smaller equatorward motion is caused by the negative aqd events that occur in the 0830 1330 lt range when these two classes of days are removed from the data set the focus latitude is found to be completely contained within the range 36 48 for the months march october with an average value of 41 5 2 3 whilst in winter the range is larger with an average value of 36 7 3 4 however since the magnitude of the superposed northward field is longitude dependent it may be present even on days not classed as aqds it is shown that much of the variability in the focus latitude of the normal days along the 0 longitude meridian is caused by variations in the amplitude of the superposed northward field

assessing the effects of consecutive sediment control dams using a numerical hydraulic experiment to model river bed variation abstract in the kotaki river valley japan the fossa magna has produced a large scale collapse and landslide zone debris flows occur annually in the kotaki river which has headstreams in the hakuba range altitude 2267 m located in niigata prefecture sediment related disasters occur over extensive areas from headwater to downstream cities and in a variety of forms this will produce large quantities of upstream sand in the future which may cause flooding through the deposition of sediment near downstream junctures in such a river it is necessary to control sediment runoff from the upper stream and prevent extreme changes in the height of the downstream riverbed to protect people and properties from sediment related disasters consecutive sediment control dams are erected these dams are built into the upstream areas of mountain streams to accumulate sediment suppressing its production and flow on the kotaki river in areas of the river where the mtl is exposed the potentially large quantity of sediment discharge during floods was reduced by installing three sets of slit barriers to prevent landslides while allowing the passage of fish this dam system was modelled after extant slit barriers of this nature previous investigations of temporal changes in sediment regulating function and sediment outflow in river sections with continuous slit barriers have incorporated many unknown factors we performed a numerical simulation of a section of the kotaki river containing slit barriers to prevent landslides and examined the characteristics affecting sediment regulating functions

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

an investigation of the causes of abnormal quiet days in sq h summary from a study of abnormal quiet days aqds along the 0 meridian between 14 and 60 n it was found butcher brown that the minimum in h at stations on the poleward side of the sq h focus was formed by a small negative substorm event when the normal sq h amplitude was reduced by a superposed northward field in this paper we consider both the aqd event and the superposed northward field as a function of longitude and also consider in more detail the latitude variation of the superposed northward field from such a study it is concluded that 1 the aqd event is definitely due to a small magnetospheric substorm event 2 the superposed northward field varies smoothly with longitude falling to zero some 110 from the longitude of its maximum amplitude 3 the superposed northward field has a variation with geomagnetic latitude tending to zero near 20 and 70 n with a maximum near 55 n in summer and 35 n in winter 4 there is some evidence that the effect of the imf penetrates into the mid latitude e region and its effect is latitude dependent although the evidence supports the suggestion that the currents responsible for the superposed northward field flow in the e region no suggestion as to the origin of the driving force of the currents is forthcoming

biases of submerged bulk and freeze core samples freeze coring and bulk sampling are routine methods used to sample subsurface spawning gravel under shallow water both methods have limitations freeze coring is not believed to representatively sample coarse grain sizes and the sample volumes are relatively small conversely when bulk sampling even within an enclosure some fine sediment is suspended and washed away from the sample this paper assesses the biases in sampling performance between the two methods and determines whether the loss of fines that occurs when bulk sampling could be predicted and thus corrected for at six riffles the spawning substrate was sampled under approximately 50 cm of water with a bulk sample and three adjacent freeze cores for each riffle data from the two samples were combined using the method of fripp and diplas 1993 and the resultant composite sample was compared with the original freeze core and bulk samples to assess the relative precision and biases of the two techniques on average the d50 of the bulk samples was 4 mm larger and a one third loss of the 16 mm compared with composite samples based on six samples taken from six riffles the amount of sediment finer than 0 5 mm lost using our bulk sampling technique with an enclosure appears to be predictable and correctable copyright 2005 john wiley sons ltd

dams and geomorphology research progress and future directions dams impose changes of flow and sediment transfer that drive changes of channel form along the downstream regulated river these changes have been described for more than 50 years but process form relationships have only been advanced with the establishment of a conceptual framework during the 1970s and then the extension of monitoring data and advancement of remote sensing technologies particularly over the past 20 years this paper reviews these developments and identifies three influential themes i channel dynamics ii the role of riparian vegetation and iii channel change as the driver of ecological change changes can be rapid in semi arid regions but elsewhere relaxation periods may extend to millenia in these latter cases regime or steady state models should be replaced by models of transient states applied to the reach scale in order to respond to the needs of river managers over decadal timescales

structural changes in the currents and fields of the equatorial electrojet due to zonal and meridional winds the authors describe calculations of the effects of zonal and meridional winds on the equatorial electrojet vis a vis the observed features by solving the electrodynamic equations vertical shears in the zonal winds can cause significant changes in the electrojet beyond about 2 degree latitude at the magnetic equator these changes are less than about 10 the width latitudinal and the thickness altitudinal of the jet are changed by as much as 100 by these shears when the width is decreased the intensity of the current densities in meridional plane is increased steady not varying with altitude zonal winds are ineffective these results are discussed in comparison with those of earlier authors meridional winds cause substantial cross equatorial currents leading to considerable asymmetry in the distribution of the electrojet current density as inferred by the ground base and rocket borne magnetometers the electrojet center is shifted to about 0 5 degree south of the equator by a steady northward wind of speed 100 m s the deviations in the magnitude of the electrojet current produced by the meridional winds are significant only beyond plus minus 2 degree off the equator structures in the vertical profiles of the eastward current density observed by rocket borne magnetometers a few degrees off the equator canmore be accounted for by the zonal wind shears less

day to day variability of geomagnetic hourly amplitudes at low latitudes summary a study of the variability of the amplitude of sq at a fixed hour from one day to the next at nine stations from the dip equator to about 22 north of it has produced interesting results the amplitude and sign of the variability change virtually randomly making the mean practically zero the variability occurs at all hours of the day its magnitudes in the components d h and z have the same diurnal variation which peaks in the noon period like sq h in low latitudes and a weak seasonal variation that peaks at the june solstice local summer it is demonstrated that changes in the current intensities of the equatorial electrojet eej and the worldwide part of the sq w sq current layers have contrasting phases and can sometimes be in antiphase indeed the changes are mostly independent inclusion of the magnetic element d revealed that the eej current system has not only an east west but also a north south component the study shows that the meridional component of the eej current intensity evidenced at the kodaikanal and annamalainagar stations is an integral part of the zonal component at trivandrum this confirms the results of rastogi 1996 and validates those of onwumechili 1997 the results suggest that ionospheric conductivity mainly controls the magnitude while the electric field and ultimately winds mainly control the phase and randomness of the day to day variability of the hourly amplitudes of sq the random component is attributed to local and or regional atmospheric winds probably of gravity wave origin

rapid morphological changes at the summit of an active volcano reappraisal of the poorly documented 1964 eruption of mount etna italy while the eruptive record of mount etna is reasonably complete for the past 400 years the activity of the early and late 1960s which took place at the summit is poorly documented in the scientific literature from 1955 to 1971 the central and northeast craters were the sites of long lived mild strombolian and effusive activity and numerous brief episodes of vigorous eruptive activity which led to repeated overflows of lava onto the external flanks of the volcano a reconstruction of the sequence of the more important of these events based on research in largely obscure and nearly inaccessible sources permits a better understanding of the eruption dynamics and rough estimates of erupted volumes and of the changes to the morphology of the summit area during the first half of 1964 the activity culminated in a series of highly dynamic events at the central crater including the opening of a fissure on the e flank of the central summit cone lava fountains voluminous tephra emission prolonged strong activity with continuous lava overflows and growth of large pyroclastic intracrater cones among the most notable processes during this eruption was the breaching of a section of the crater wall which was caused by lateral pressure of lava ponding within the crater comparison with the apparently similar summit activity of 1999 allows us to state that a lava overflows from large pit craters at the summit are often accompanied by breaching of the crater walls which represents a significant hazard to nearby observers and that b eruptive activity in 1999 was much more complex and voluminous than in 1964 for 1960s standards however the 1964 activity was the most important summit eruption in terms of intensity and output rates for about 100 years causing profound changes to the summit morphology and obliterating definitively the former central crater

atmospheric limitations to repeat track radar interferometry in its recent radar imaging mission the shuttle imaging radar satellite sir c devoted three days to repeat track interferometry we have analyzed the data from a test site in the mojave desert of california although good topography 10 m on 21 m postings was obtained most of the error was caused by turbulent water vapor in the lower atmosphere spatial structure of 6 km and all smaller sizes was observed the rms one way time delay was found to be 0 24 cm essentially identical results were obtained at two wavelengths 24 and 5 7 cm

classification of geomorphological effects downstream of dams abstract the effects of dams on downstream geomorphology are reviewed and a typology is devised consisting of nine cases the classification can be seen as a further development of lane s balance between water discharge sediment load grain size and river slope depending on changes in released water flow and changes in released sediment load relative to the transport capacity of the flow it is possible to estimate resulting cross sectional geomorphology the longitudinal extent of changes and their variability with time and the tributary response to altered mainstream cross section changes are also discussed

height and latitude structure of electric fields and currents due to local east west winds in the equatorial electrojet using the equivalent electrical circuit method for the theoretical treatment of the local wind effects on the equatorial electrojet the height structures of electric fields and currents that are generated by height varying east west winds in the electrojet region have been calculated for theoretical model wind sturctures and for a variety of experimentally observed wind structures the results bring out clearly the nature and extent of the local wind effects on the height and latitude structures of the equatorial electrojet the more important conclusions of the present study are a the vertical wind shears associated with tidal winds and gravity waves can generate significantly large electric fields and east west currents in the equatorial electrojet eej b the wind generated electric fields and currents are characterized by large height gradients latitudinal gradients and reversals of direction c at the magnetic equator wind generated electric fields and currents are often small 10 30 in comparison with the eastward electric field generated polarization field and east west currents around noon hours d at geomagnetic latitudes of 3 and beyond the wind generated currents and electric fields often exceed those caused by the eastward electric field e beyond 2 the neutral winds can drastically alter the intensity and latitudinal structure of the eej depending upon the magnitude and height location of the wind shear f the observed variabilities in the width and latitude structure of the eej can arise from the effects of such east west winds that have been observed experimentally

evidence for short spatial correlation lengths of the noontime equatorial electrojet inferred from a comparison of satellite and ground magnetic data 1 the current density of the noontime equatorial electrojet eej as determined from champ data is highly variable between successive passes of the satellite which are separated by 23 in distance and 93 min in time an open question is to which extent this variability is caused by temporal or spatial variations in the ionosphere another important question is the connection between eej and global solar quiet sq current systems we try to answer these questions by comparing the eej current density estimated from highquality scalar magnetic field measurements of the champ satellite with the magnetic horizontal intensity variations at six equatorial observatory pairs distributed across the globe data taken during the period 2000 2002 were used for the present study we apply corrections for the effect of local time lt and sq fields by estimating the correlation coefficients between the ground and satellite data as a function of distances between measurements new insights into the spatial structure of the eej have been obtained the high correlation when champ passes directly over an observatory decays quickly in eastern and western directions typically within 15 of longitudinal separation between satellite and observatory the correlation falls well below the statistical significance level this observation holds for all longitude sectors interestingly the correlation between champ inferred eej strength and observatory differences breaks down for the observatory pairs outside of a 4 latitudinal band this implies that the eej and sq variations are uncorrelated for periods up to 1 hour additionally it was found that monitoring of the eej can be performed best if the reference observatory is 4 to 5 apart from the dip equator

volumetric characteristics of lava flows from interferometric radar and multispectral satellite data the 1995 fernandina and 1998 cerro azul eruptions in the western galapagos we have used a suite of remotely sensed data numerical lava flow modeling and field observations to determine quantitative characteristics of the 1995 fernandina and 1998 cerro azul eruptions in the western galapagos islands flank lava flow areas volumes instantaneous effusion rates and average effusion rates were all determined for these two eruptions for which only limited syn eruptive field observations are available using data from spot topsar ers 1 and ers 2 we determined that the 1995 fernandina flow covers a subaerial area of 6 5 106 m2 and has a subaerial dense rock equivalent dre volume of 42 106 m3 field observations atsr satellite data and the flowgo numerical model allow us to determine that the effusion rate declined exponentially from a high of 60 200 m3 s 1 during the first few hours to 5 m3 s 1 prior to ceasing after 73 days with a mean effusion rate of 4 16 m3 s 1 integrating the atsr derived exponentially declining effusion rate over the eruption duration produces a total subaerial submarine dre volume of between 27 and 100 106 m3 the range in values being due to differing assumptions about heat loss characteristics only values in the higher part of this range are consistent with the independently derived subaerial volume using spot topsar ers 1 and ers 2 data we determine that the 1998 cerro azul flow is 16 km long covers 16 km2 and has a dre volume of 54 106 m3 flowgo produces at vent velocity and effusion rate values of 11 m s 1 and 600 m3 s 1 respectively the velocity value agrees well with the 12 m s 1 estimated in the field the mean effusion rate total dre volume duration was 7 47 m3 s 1 dike dimensions fissure lengths and pressure gradients along the conduit based on magma chamber depth estimates of 3 5 km produce mean effusion rates for the two eruptions that range over nearly four orders of magnitude the range being due to uncertainty in the magma viscosity dike dimensions and pressure gradient between magma chamber and vent although somewhat consistent with mean effusion rates from other techniques their wide range makes them less useful the exponentially declining effusion rates during both eruptions are consistent with release of elastic strain being the driving mechanism of the eruptions our results provide independent input parameters for previously published theoretical relationships between magma chamber pressurization and eruption rates that constrain chamber volumes and increases in volume prior to eruption as well as time constants of exponential decay during the eruption the results and theoretical relationships combine to indicate that at both volcanoes probably 25 30 of the volumetric increase in the magma chamber erupted as lava onto the surface in both eruptions the lava flow volumes are less than 1 of the magma chamber volume

seismicity and time lagged lava output at mount etna a new method of long term forecasting at a destructive volcano time averaged seismic moments m0 of earthquakes in the etna region between 1874 and 1998 show good inverse correlations with functions of time lagged volumetric lava output rates at mount etna the highest correlation coefficients are for a time lag of 25 yr because earthquake activity precedes lava emission the relationship can be used to forecast lava output years in advance the method has valuable potential for forward planning at a destructive volcano and applying it to the immediate future it is predicted that 170 50 106 m3 of lava will be erupted from mount etna between the years 2007 and 2015 this is about half the volume of lava erupted between 1987 and 1995

estimating lava volume by precision combination of multiple baseline spaceborne and airborne interferometric synthetic aperture radar the 1997 eruption of okmok volcano alaska interferometric synthetic aperture radar insar techniques are used to calculate the volume of extrusion at okmok volcano alaska by constructing precise digital elevation models dems that represent volcano topography before and after the 1997 eruption the posteruption dem is generated using airborne topographic synthetic aperture radar topsar data where a three dimensional affine transformation is used to account for the misalignments between different dem patches the preeruption dem is produced using repeat pass european remote sensing satellite data multiple interferograms are combined to reduce errors due to atmospheric variations and deformation rates are estimated independently and removed from the interferograms used for dem generation the extrusive flow volume associated with the 1997 eruption of okmok volcano is 0 154 spl plusmn 0 025 km sup 3 the thickest portion is approximately 50 m although field measurements of the flow margin s height do not exceed 20 m the in situ measurements at lava edges are not representative of the total thickness and precise dem data are absolutely essential to calculate eruption volume based on lava thickness estimations this study is an example that demonstrates how insar will play a significant role in studying volcanoes in remote areas

the application of a long range laser scanner for monitoring volcanic activity on mount etna abstract there is a requirement for rapid remote monitoring of ground deformation of volcanoes especially during eruptions a long range reflector less laser scanning instrument manufactured by riegl laser measurement systems was used on mount etna in october 2000 and its potential for monitoring ground surface changes associated with volcanic activity was evaluated the 3dlm lr1 scanner system can measure distances up to 2 km with an accuracy of 25 mm in typical conditions measurement rates range from 1 point per second at 2 km to 4 points per second at 10 m the system also records reflective intensity and this proved useful in distinguishing between different types of volcanic material cloud and gas obscured some measurements but the scanning nature of the instrument coupled with effective data filtering software allowed robust digital terrain models to be created

upper atmosphere wind systems during reverse equatorial electrojet events days of reversed equatorial electrojet were identified at trivandrum india and in order to seek a global wind change in the dynamo region responsible for these events upper atmosphere winds at a height of 99 km at saskatoon canada were examined during northern winter and also in april and september the reversed electrojets were accompanied by reversals of the eastward wind at saskatoon the winter events generally occurred during a stratwarm no changes in the winds were detected during summer reversed electrojets

lava effusion rate definition and measurement a review measurement of effusion rate is a primary objective for studies that model lava flow and magma system dynamics as well as for monitoring efforts during on going eruptions however its exact definition remains a source of confusion and problems occur when comparing volume flux values that are averaged over different time periods or spatial scales or measured using different approaches thus our aims are to 1 define effusion rate terminology and 2 assess the various measurement methods and their results we first distinguish between instantaneous effusion rate and time averaged discharge rate eruption rate is next defined as the total volume of lava emplaced since the beginning of the eruption divided by the time since the eruption began the ultimate extension of this is mean output rate this being the final volume of erupted lava divided by total eruption duration whether these values are total values i e the flux feeding all flow units across the entire flow field or local i e the flux feeding a single active unit within a flow field across which many units are active also needs to be specified no approach is without its problems and all can have large error up to 50 however good agreement between diverse approaches shows that reliable estimates can be made if each approach is applied carefully and takes into account the caveats we detail here there are three important factors to consider and state when measuring giving or using an effusion rate first the time period over which the value was averaged second whether the measurement applies to the entire active flow field or a single lava flow within that field and third the measurement technique and its accompanying assumptions

geomorphological reconstruction and morphometric modelling applied to past volcanism accurate and precise morphometric modelling can be extended to past eruptions after a careful palaeogeomorphological reconstruction of volcanic landforms in an oceanic island this reconstruction was used to derive the pre post eruption and present day digital elevation models dem the correct pixel size interpolation method and quality of these dems are discussed the process in a geographical information system framework of the geological information of cone lava flow and tephra fall deposits together and the aforementioned dems allowed the determination of main morphological features of these volcanic landforms and their derivatives the calibration and validation of morphometric modelling were performed on simulated volcanic landforms and verified by a case study a typical holocene monogenetic basaltic eruption at gran canaria island spain

on the latitudinal variations of the ionospheric electric field during magnetospheric disturbances a joint alert campaign was organized during the month of october 1980 by the incoherent scatter radars in the american sector namely jicamarca arecibo millstone hill and chatanika the campaign which met with success was designed to study the behavior of the ionospheric electric field as a function of latitude during magnetically active conditions the arecibo data in this campaign support present and previous observations at jicamarca that suggest that when the convection e field suddenly decreases the alfven layer shielding field becomes unbalanced and penetrates the plasmasphere while this type of observation is reasonably convincing others are more difficult to categorize we suggest that beside the high latitude electric fields time varying auroral conductivity models will have to be considered in order to understand the morphology of the low latitude e field disturbances we present the first correlation analysis and determination of the amplitude ratio of the disturbed zonal electric field at 30 geometric latitude arecibo to the field at 0 jicamarca other highlights of the paper are a discussion of dp2 which may help clarify the controversy surrounding it and a discussion of the sensitivity of low and mid latitude radars to disturbances of magnetospheric origin we show that this sensitivity maximizes at the magnetic equator

topographic analyses of k lauea volcano hawai i from interferometric airborne radar we analyze digital topographic data collected in september 1993 over a 500 km2 portion of k lauea volcano hawai i by the c band 5 6 cm wavelength topographic synthetic aperture radar topsar airborne interferometric radar field surveys covering an 1 km2 area of the summit caldera and the distal end of an 8 m thick a flow indicate that the 10 m spatial resolution topsar data have a vertical accuracy of 1 2 m over a variety of volcanic surfaces after conversion to a common datum topsar data agree favorably with a digital elevation model dem produced by the u s geological survey usgs with the important exception of the region of the ongoing eruption which postdates the usgs dem this dem comparison gives us confidence that subtracting the usgs data from topsar data will produce a reasonable estimate of the erupted volume as of september 1993 this subtraction produces dense rock equivalent dre volumes of 392 439 and 90 106 m3 for the pu u k pa ianah and episode 50 53 stages of the eruption respectively these are 124 89 and 94 of the volumes calculated by staff of the hawaiian volcano observatory hvo but do not include lava of k pa ianah and episodes 50 53 that flowed into the ocean and are thus invisible to topsar accounting for this lava increases the topsar volumes to 124 159 and 129 of the hvo volumes including the 2 m uncertainty derived from the field surveys produces topsar derived volumes for the eruption as a whole that range between 81 and 125 of the usgs derived values the vesicularity and ocean corrected topsar volumes yield volumetric eruption rates of 4 5 4 5 and 2 7 m3 s for the three stages of the eruption which compare with hvo derived values of 3 6 2 8 and 2 1 m3 s respectively our analysis shows that care must be taken when vertically registering the topsar and usgs dems to a common datum because c band topsar penetrates only partially into thick forest and therefore produces a dem within the tree canopy whereas the usgs dem is adjusted for vegetation

sediment continuity through the upland sediment cascade geomorphic response of an upland river to an extreme flood event hillslope erosion and accelerated lake sedimentation are often reported as the source and main stores of sediment in the upland sediment cascade during extreme flood events while upland valley floodplain systems in the transfer zone have the potential to influence sediment continuity during extreme events their geomorphic response is rarely quantified this paper quantifies the sediment continuity through a regulated upland valley fluvial system st john s beck cumbria uk in response to the extreme storm desmond 4 6 december 2015 flood event a sediment budget framework is used to quantify geomorphic response and evaluate sediment transport during the event field measurements show 6500 710 t of sediment was eroded or scoured from the river floodplains banks and bed during the event with 6300 570 t of sediment deposited in the channel or on the surrounding floodplains 6 of sediment eroded during the flood event was transported out of the 8 km channel floodplain sediment storage was seen to be restricted to areas of overbank flow where the channel was unconfined results indicate that rather than upland floodplain valleys functioning as effective transfer reaches they instead comprise significant storage zones that capture coarse flood sediments and disrupt sediment continuity downstream

sedimentation within a regulated river channel change induced by tributary sediment injection to a regulated gravel bed river is described for the river rheidol u k eighteen years after dam closure morphological and sedimentological data are presented for an aggrading reach a primary lobate bar appears to have initiated flow separation and the subsequent construction of channel side berms hydraulic sorting has operated to produce both longitudinal and lateral particle size reduction and selective particle size dispersal appears to be an important process influencing channel change the channel is adjusting to a lower width depth ratio form of smaller capacity and with a steeper slope