volcanology greek inflation circa 1600 bc a petrology study of the bronze age minoan eruption on the greek island of santorini finds that the sub volcanic magma reservoir was recharged in spurts during the decades to months that preceded the eruption see letter p 77 timothy druitt and co authors have studied pre eruptive magmatic processes and their timescales using chemically zoned crystals from the late 1600s bc minoan caldera forming eruption on the island of santorini greece despite the large volume of erupted magma and the 18 000 year gestation period between the minoan and the previous major eruption recharge of the magma reservoir seems to have occurred during the century before eruption and mixing between different magma batches was still taking place during the final months these observations have implications for monitoring strategies at long dormant but potentially active caldera systems such as long valley in california yellowstone in wyoming and campi flegrei in italy

magma reservoir response to transient recharge events the case of santorini volcano greece igneous bodies are built incrementally by episodic magma injection events that vary in rate and duration such recharge events can either grow an upper crustal magma reservoir or trigger an eruption this bifurcation in behavior remains poorly constrained but is essential to volcanic hazard assessment here we use a numerical model that couples the thermal and mechanical processes in a magma reservoir to study the evolution of the santorini magmatic system greece over the past 20 k y our results constrain the recharge rate and duration that are necessary to trigger an eruption for the known long term average inflow rate of 10 3 km3 yr the size of the chamber and its exsolved volatile content are dominant controls on the critical recharge rate and duration that will trigger an eruption our model successfully reproduces the main features of the minoan eruption and nea kameni activity providing volume estimates for the active part of the current subvolcanic reservoir as well as information regarding the presence of exsolved volatiles thermomechanical models offer a new framework to integrate the historic eruption record with geodetic measurements and provide a context to understand the past present and future of active volcanic centers

submarine volcanoes along the aegean volcanic arc abstract the aegean volcanic arc has been investigated along its offshore areas and several submarine volcanic outcrops have been discovered in the last 25 years of research the basic data including swath bathymetric maps air gun profiles underwater photos and samples analysis have been presented along the four main volcanic groups of the arc the description concerns i paphsanias submarine volcano in the methana group ii three volcanic domes to the east of antimilos volcano and hydrothermal activity in southeast milos in the milos group iii three volcanic domes east of christiana and a chain of about twenty volcanic domes and craters in the kolumbo zone northeast of santorini in the santorini group and iv several volcanic domes and a volcanic caldera together with very deep slopes of several volcanic islands in the nisyros group the tectonic structure of the volcanic centers is described and related to the geometry of the arc and the neotectonic graben structures that usually host them the ne sw direction is dominant in the santorini and nisyros volcanic groups located at the eastern part of the arc where strike slip is also present whereas nw se direction dominates in milos and methana at the western part where co existence of e w disrupting normal faults is observed the volcanic relief reaches 1100 1200 m in most cases this is produced from the outcrops of the volcanic centers emerging usually at 400 600 m depth and ending either below sea level or at high altitudes of 600 700 m on the islands hydrothermal activity at relatively high temperatures observed in kolumbo is remarkable whereas low temperature phenomena have been detected in the santorini caldera around kameni islands and in the area southeast of milos in methana and nisyros hydrothermal activity seems to be limited in the coastal areas without other offshore manifestations

evaluation of morphometric parameters of drainage networks derived from topographic maps and dem in point of floods an evaluation of morphometric parameters of two drainage networks derived from different sources was done to determine the influence of sub basins to flooding on the main channel in the havran river basin balikesir turkey drainage networks for the sub basins were derived from both topographic maps scaled 1 25 000 and a 10 m resolution digital elevation model dem using geographic information systems gis blue lines representing fluvial channels on the topographic maps were accepted as a drainage network which does not depict all exterior links in the basin the second drainage network was extracted from the dem using minimum accumulation area threshold to include all exterior links morphometric parameters were applied to the two types of drainage networks at sub basin levels these parameters were used to assess the influence of the sub basins on the main channel with respect to flooding the results show that the drainage network of sub basin 4 where a dam was constructed on its outlet to mitigate potential floods has a lower influence morphometrically to produce probable floods on the main channel than that of sub basins 1 3 and 5 the construction of the dam will help reduce flooding on the main channel from sub basin 4 but it will not prevent potential flooding from sub basin 1 3 and 5 which join the main channel downstream of sub basin 4 therefore flood mitigation efforts should be considered in order to protect the settlement and agricultural lands on the floodplain downstream of the dam in order to increase our understanding of flood hazards and to determine appropriate mitigation solutions drainage morphometry research should be included as an essential component to hydrologic studies

the santorini volcanic complex and its relation to the stratigraphy and structure of the aegean arc greece abstract the santorini complex is the most active volcano of the southern aegean volcanic arc its relationship to the surrounding area was examined by using a dense set of seismic reflection profiles three seismic units were recognized in the surrounding area unit a consists of generally strong subparallel continuous reflectors into which two subunits a1 and a2 were distinguished that are unconformable in the upper slopes and the shelves and conformable at lower sectors the age of unit a which consists mainly of volcaniclastic sediments is considered quaternary unit b consists of faulted and slightly folded strong continuous reflectors that pinch out at lower basin margin sectors than unit a its age is mainly pliocene its sediments are probably terrigenous and it was deposited in the basins at the early and middle stages of their formation finally unit c represents the acoustic mainly metamorphic basement the dominant tectonic structure in the area is the ne sw trending normal faults superimposed on earlier e w normal faults the santorini complex includes one caldera at santorini and one crater at columbus about 7 km to the northeast the caldera of santorini consists of four deep basins depth from 290 to 390 m the columbus volcano has a well defined crater with a single basin depth 500 m and was formed in 1650 a d by an underwater explosion the start of volcanic activity of santorini which initiated in the early pleistocene and continues up until today may be related to the change in the normal fault orientation from e w to ne sw and to the unconformity between units a and b

a comparison of frequency ratio and fuzzy logic models for flood susceptibility assessment of the lower kosi river basin in india the kosi megafan region of eastern bihar india comprising of eight districts is regularly afflicted by large floods that cause extensive damage mapping the possible inundation susceptible zones in the region accurately is therefore paramount for land resource conservation and livelihood preservation this paper compares the relative efficiency of two flood zonation methods the frequency ratio and fuzzy logic models for flood susceptibility evaluation and delineation flooded extents from two past events were combined to create the training dataset which was then compared individually with respective maps of 12 well documented causal factors of inundation to gauge their relative influence on the flood spread these were merged using the two models to generate the respective flood susceptibility maps which were subsequently validated using the receiver operating characteristics curve and the seed cell area index methods results revealed that an enhanced fuzzy logic model prepared by assigning relative weights to the respective causal factors as obtained from their analysis in the frequency ratio model was more accurate and robust in demarcating flood susceptibility zones as was further ascertained by comparison with a recent flood event thereby providing a novel way to merge these methods the western and southern tracts of the region were found to be more inundation prone with the greatest risk posed along the narrow interfluve between the kosi and ganga rivers prior to their confluence further east the districts most likely to be inundated were identified by computing their respective proportionate areas under the very highly susceptible flood class

new insights into the initiation and venting of the bronze age eruption of santorini greece from component analysis the late seventeenth century bc minoan eruption of santorini discharged 30 60 km3 of magma and caldera collapse deepened and widened the existing 22 ka caldera a study of juvenile cognate and accidental components in the eruption products provides new constraints on vent development during the five eruptive phases and on the processes that initiated the eruption the eruption began with subplinian phase 0 and plinian phase 1 phases from a vent on a ne sw fault line that bisects the volcanic field during phase 1 the magma fragmentation level dropped from the surface to the level of subvolcanic basement and magmatic intrusions the fragmentation level shallowed again and the vent migrated northwards during phase 2 into the flooded 22 ka caldera the eruption then became strongly phreatomagmatic and discharged low temperature ignimbrite containing abundant fragments of post 22 ka pre minoan intracaldera lavas phase 3 phase 4 discharged hot fluidized pyroclastic flows from subaerial vents and constructed three main ignimbrite fans northwestern eastern and southern around the volcano the first phase 4 flows were discharged from a vent or vents in the northern half of the volcanic field and laid down lithic block rich ignimbrite and lag breccias across much of the nw fan about a tenth of the lithic debris in these flows was subvolcanic basement new subaerial vents then opened up probably across much of the volcanic field and finer grained ignimbrite was discharged to form the e and s fans if major caldera collapse took place during the eruption it probably occurred during phase 4 three juvenile components were discharged during the eruption a volumetrically dominant rhyodacitic pumice and two andesitic components microphenocryst rich andesitic pumices and quenched andesitic enclaves the microphenocryst rich pumices form a textural mineralogical chemical and thermal continuum with co erupted hornblende diorite nodules and together they are interpreted as the contents of a small variably crystallized intrusion that was fragmented and discharged during the eruption mostly during phases 0 and 1 the microphenocryst rich pumices hornblende diorite andesitic enclaves and fragments of pre minoan intracaldera andesitic lava together form a chemically distinct suite of ba rich zr poor andesites that is unique in the products of santorini since 530 ka once the minoan magma reservoir was primed for eruption by recharge generated pressurization the rhyodacite moved upwards by exploiting the plane of weakness offered by the pre existing andesite diorite intrusion dragging some of the crystal rich contents of the intrusion with it

multi risk interpretation of natural hazards for settlements of the hatay province in the east mediterranean region turkey using srtm dem many scientists have recently alarmed natural hazards due to global climate change such natural disasters are coastal inundation in response to sea level rise and or river flooding caused by heavy rain falls additionally earthquakes and etc in terms of natural hazards one of the most sensitive and culturally significant areas in turkey is the hatay province in the east mediterranean region the hatay province is located on such a region which is not only vulnerable to coastal inundation and river flooding but also is a tectonically and seismically sensitive area in this study for taking conservation measures against the natural hazards beforehand and decision making on any future land planning a digital terrain model and a 3d fly through model of the hatay province were generated then quantitatively and or qualitatively interpreted by employing the shuttle radar topographic mission digital elevation model besides stream drainage patterns lineaments and structural geological features were extracted for natural hazard risk interpretation of settlements and their relationships among the landscape characteristics were exhibited by combining tectonic information previously confirmed regarding the sea level rise the coastal inundation risk map indicates that the most vulnerable areas are coastlines of iskenderun arsuz payas and samandag respectively by after analyzing the digital terrain of the study region and stream drainage patterns the karasu valley zone where the amik plain settlements of antakya iskenderun arsuz payas and samandag with their flood plains have the most flooding risk in decreasing order respectively when a heavy raining occurs finally analysis of tectonics has revealed that antakya iskenderun hassa kirikhan samandag payas arsuz altinozu kumlu and hacipasa regions have the most sensitivity to earthquake disaster in the study region

the measurement of thermal conductivity of solids with a transient linear heat source on the plane surface of a poorly conducting body abstract during the last ten years the transient hot wire method for measuring thermal conductivity of ocean bottom muds and other soft materials has been adapted for measuring the conductivity of solid rocks because it is cheaper and quicker than the steady state methods such as the divided bar this is done by embedding the hot wire in the form of a hypodermic needle or a ribbon flush into the surface of a block of a poorly conducting material when a flat surface of a specimen is placed on the surface of such a sensor the line source can be said to diffuse heat into an infinite half space if one neglects the heat absorbed by the poorly conducting block into which the needle is embedded the rate of the temperature rise of the line source with respect to the logarithm of time elapsed since turning on the heater is inversely proportional to the conductivity in practice the rates of temperature rise are compared for the unknown and for a standard specimen a fused silica plate in our case the percentage of the total heat flowing into the sensor block is in general different for the standard and for the unknown thus possibly creating an error when the conductivity of the sensor block is neglected it was determined experimentally that the temperature rise for a silica plate is decreased only by 1 3 by the heat absorbed by the material of the sensor block an empirical equation is proposed to correct errors arising from this source this correction needs to be used only for materials of conductivity less than 2 mcal cm c s the equation gives somewhat larger but still acceptable conductivity values for substances in the range of 0 208 3 25 mcal cm c s as shown in table 1 and fig 2 for measurements on common rocks corrections for the heat diffused into the material of the sensor block can be neglected

deep sea drilling project heat flow and models of the rifted west rockall margin downhole thermal measurements for the southwest rockall bank rifted margin made on deep sea drilling project leg 81 plus those previously made on leg 48 give six reliable heat flow values in the narrow range 62 71 mw m 2 with an average of 66 5 mw m 2 the temperatures were obtained using a self contained downhole temperature recording device a long probe is inserted through the drill bit into the undisturbed sediments below the bottom of the hole at intervals during drilling the thermal disturbance from the penetration was extrapolated to equilibrium in situ temperatures using the cylindrical decay function the thermal conductivities have been measured on core samples using the needle probe method supplemented with porosity conductivity relations heat production in the sedimentary volcanic sequence above basement probably makes a negligible contribution to the heat flow there is no systematic heat flow trend with water depth which ranges from 1650 to 1900 m or with position and the mean value is not significantly different from that expected from pure oceanic crust of age equal to the approximately 50 ma time of rifting however the unloaded basement depth is over 1 km shallower than expected for normal oceanic crust of the 50 ma rifting age the heat flow combined with subsidence data fits a simple rifting model with crustal stretching and thinning by a factor of 3 or 4 over a zone at least 100 km wide occurring about 50 ma the heat production in the stretched crust is taken to contribute 4 mw m 2 based on a prerift structure comparable to once adjacent north america a major uncertainty in thermal and subsidence models for the margin is the effect of the earlier iceland hot spot which produced extensive margin volcanism on the northern british isles and greenland and shoaling of the oceanic crust at about the time of west rockall rifting

channel networks a geomorphological perspective the study of channel networks has been dominated since 1966 by the random model however recent work has shown 1 that although the topological properties of small networks conform to the random model more closely than those of large ones even small networks exhibit systematic deviations from topological randomness and 2 that the topological and length properties of channel networks are controlled to a large degree by the spatial requirements of subbasins and the need for these subbasins to fit together in space by the size sinuosity and migration rate of valley bends and by the length and steepness of valley sides the factors that control the density properties of channel networks vary with the scale of the investigation and the geomorphic processes governing channel initiation although progress has been made toward a satisfactory stream junction angle model further work is needed the evolution of channel networks has been investigated by a variety of methods including the development of conceptual and simulation models the monitoring of small scale badland and experimental drainage basins and the substitution of space for time the morphology of most channel networks is largely inherited from the past or strongly influenced by inherited forms inasmuch as there is no way of ever knowing the origin or complex history of such networks the use of stochastic models in their study seems unavoidable

gas hydrate stability and the assessment of heat flow through continental margins summary a prominent feature across some continental margins is a bottom simulating reflector bsr this seismic reflection generally coincides with the depth predicted for the base of the gas hydrate stability field because the occurrence of gas hydrates is controlled by temperature and pressure conditions it has been suggested that bsrs mark an isotherm and they have therefore been used to estimate the heat flow through continental margins crucial parameters are the temperature at bsr depth and at the seafloor and the thermal conductivity structure between the bsr and the seabed however very often the required parameters are not available and therefore they have been derived from models for gas hydrate stability and empirical relationships to obtain thermal conductivities from seismic velocities here we use downhole temperature thermal conductivity porosity and logging data from 10 ocean drilling program odp sites drilled into and through the gas hydrate field to investigate the quality of estimates our analyses and application of constraints to the makran margin off pakistan indicate the following i the temperature at bsr depth could be approximated by a seawater methane system although capillary forces chemical impurities or non equilibrium conditions can lower or increase the temperature if calibration by heat probe measurements is possible errors of geothermal gradients are less than 10 per cent otherwise uncertainties of 20 per cent or even higher may arise in addition seasonal variations of bottom water temperature have to be considered because they may affect thermal gradients by up to y10 per cent ii the impact of typical quantities of low thermal conductivity gas hydrate on the bulk thermal conductivity is insignificant iii the thermal conductivity profile between the bsr and the seabed can generally be approximated by a mean value thus iv seabed measurements should be used instead of empirical relationships which may produce errors of 5 30 per cent consequently in addition to high quality seismic data a prerequisite should be a large data set of thermal conductivities and oceanographic data heat probe measurements are recommended to constrain geothermal gradients in this case the uncertainty of heat flow is 5 10 per cent of the estimated heat flow if these data are not available errors uncertainties can reach 50 60 per cent of the calculated value

reconstructing the tephra dispersal pattern from the bronze age eruption of santorini using an advection diffusion model the advection diffusion model tephra2 has been used in conjunction with the downhill simplex method dsm and one at a time oat inversion methods to reconstruct the eruption conditions and seasonality consistent with the deposit patterns from the bronze age minoan eruption of santorini we investigated three datasets representing different depositional environments proximal terrestrial distal terrestrial and deep sea core in order to determine source conditions such as plume height erupted mass and grain size and recreate the tephra fall deposit from the plinian co ignimbrite and combined eruptive phases the results of the dsm and oat method agreed adequately well with each other for erupted mass plume height and grain size distribution both approaches were able to successfully recreate the plinian deposit but estimating conditions that created the co ignimbrite and deep sea core dataset were less successful the reduced agreement is the result of the low quantity 6 to 28 deposit points and quality inconsistent deposit depths at localities adjacent to each other of the datasets and the different dynamics between co ignimbrite and plinian columns with the former not well represented in the model different sampling methods between archaeological and volcanological disciplines and post depositional processes which have acted on the tephra deposits since the bronze age can explain the discrepancy between these computed and observed deposits the seasonality of the minoan eruption was investigated by using seasonal wind profiles for winter spring summer and autumn we find that the bronze age eruption of santorini is likely to have during the spring and summer months with a main dispersal axis aligned east crete would have received very little ash fall and the eruption would not have caused much disruption to the life of the inhabitants of the island

gis multi criteria decision analysis for assessment and mapping of neotectonic landscape deformation a case study from crete this study of drainage systems in a tectonically active region is based on the geographical information systems gis integration of data from an analytic hierarchy process ahp and a weighted linear combination wlc procedure with multiple criteria data a set of thematic maps were produced based on existing geological maps and freely available aster global dem elevation data using various geological information i e lineaments and lithologies geomorphometric indices i e slope gradient drainage density stream frequency and the topographic wetness index and morphotectonic indices i e amplitude of relief and stream length gradient that highlight areas of neotectonic landscape deformation the weights of the factors were determined using ahp and wlc a neotectonic landscape deformation index nldi is computed as the sum of the various weighted factors to provide a map of nldi distribution across the study region western crete the main objective of this study was to analyse and map the intra basin spatial variations in neotectonic landscape deformation five classes very low to very high were determined high to very high deformation zones are linked with known and newly detected active fault zones the methodology could be developed into a low cost technique for assessing seismic hazard guiding disaster risk reduction activities it can provide an alternative to the interferometric synthetic aperture radar insar approach for highlighting zones of neotectonic deformation particularly in regions where dense vegetation or snow cover renders insar ineffective

evolution of santorini volcano dominated by episodic and rapid fluxes of melt from depth santorini volcano in greece was thought to be continually charged by small injections of magma measurements of surface deformation show that magma equivalent to 10 50 of that emitted in previous small eruptions has been injected beneath santorini since january 2011 implying that the volcano is instead charged by rapid episodic fluxes of melt

volcano tectonic evolution of the polygenetic kolumbo submarine volcano santorini aegean sea abstract here we show for the first time the 3d structural evolution of an explosive submarine volcano by means of reflection seismic interpretation four to five vertically stacked circular and cone shaped units consisting mainly of volcaniclastics build the kolumbo underwater volcano which experienced its first eruption 70 ka ago and its last explosive eruption 1650 ad 7 km ne of santorini volcano southern aegean sea the summed volume of volcaniclastics is estimated to range between 13 22 km3 the entire kolumbo volcanic complex has a height of 1 km and a diameter of 11 km all volcaniclastic units reveal the same transparent reflection pattern strongly suggesting that explosive underwater volcanism was the prevalent process growth faults terminate upwards at the base of volcaniclastic units thus representing a predictor to an eruption phase similarities in seismic reflection pattern between kolumbo and near by volcanic cones imply that the smaller cones evolved through explosive eruptions as well hence the central aegean sea experienced several more explosive eruptions 23 than previously assumed thus justifying further risk assessment however the eruption columns from the smaller volcanic cones did not reach the air and consequently no sub aerial pyroclastic surge was created the anydros basin that hosts kolumbo volcanic field opened incrementally nw to se and parallel to the pliny and strabo trends during four major tectonic pulses prior to the onset of underwater volcanism

santorini eruption radiocarbon dated to 1627 1600 b c precise and direct dating of the minoan eruption of santorini thera in greece a global bronze age time marker has been made possible by the unique find of an olive tree buried alive in life position by the tephra pumice and ashes on santorini we applied so called radiocarbon wiggle matching to a carbon 14 sequence of tree ring segments to constrain the eruption date to the range 1627 1600 b c with 95 4 probability our result is in the range of previous less precise and less direct results of several scientific dating methods but it is a century earlier than the date derived from traditional egyptian chronologies

historical bathymetric charts and the evolution of santorini submarine volcano greece historical bathymetric charts are a potential resource for better understanding the dynamics of the seafloor and the role of active processes such as submarine volcanism the british admiralty for example have been involved in lead line measurements of seafloor depth since the early 1790s here we report on an analysis of historical charts in the region of santorini volcano greece repeat lead line surveys in 1848 late 1866 and 1925 1928 as well as multibeam swath bathymetry surveys in 2001 and 2006 have been used to document changes in seafloor depth these data reveal that the flanks of the kameni islands a dacitic dome complex in the caldera center have shallowed by up to 175 m and deepened by up to 80 m since 1848 the largest shallowing occurred between the late 1866 and 1925 1928 surveys and the largest deepening occurred during the 1925 1928 and 2001 and 2006 surveys the shallowing is attributed to the emplacement of lavas during effusive eruptions in both 1866 1870 and 1925 1928 at rates of up to 0 18 and 0 05 km3 a 1 respectively the deepening is attributed to a load induced viscoelastic stress relaxation following the 1866 1870 and 1925 1928 lava eruptions the elastic thickness and viscosity that best fits the observed deepening are 1 0 km and 1016 pa s respectively this parameter pair which is consistent with the predictions of a shallow magma chamber thermal model explains both the amplitude and wavelength of the historical bathymetric data and the present day rate of subsidence inferred from insar analysis

comparison of basin morphometry analyses derived from different dems on two drainage basins in turkey morphometric analyses provide important data about basins and their drainage networks many data sources which are produced from different techniques can be used in this analysis two areas which have similar areal and formal features but have different vegetation density were selected as study areas kabisre and koyunluyusufozu basin selected parameters were implemented to both basins using five different datasets aster gdem srtm dem alos dsm 30 m and topo dems 30 m and 10 m the topo dems were produced from 1 25 000 scaled digitized topographical maps the morphometric analyses result of topo dems 10 m resolution was used as the benchmark data for comparing the results of the other data sources as a result srtm dems gave the most compatible results with the results of reference data for the study area of kabisre basin that has heavy vegetation and the alos dsms gave the closest results to the reference data in study area on koyunluyusufozu basin that is deprived of vegetation

deep sea drilling project geothermal measurements a review in this article the geothermal measurements made from the scientific drilling ship glomar challenger are evaluated edited and reviewed for a number of sites the heat flow values given in the initial reports of the deep sea drilling project have been revised less than half of the boreholes in which thermal measurements were attempted gave reliable data by the end of the deep sea drilling project dsdp in 1983 reliable borehole heat flow measurements had been obtained at some 80 sites in all of the world oceans except the arctic the reliable values are considered to represent the deeper heat flux to within 20 for a few the accuracy is within 5 most temperature measurements have been obtained using probes penetrating the undisturbed sediments at the bottom of the hole at subbottom depths of between 75 m and 250 m although some data have been obtained at depths less than 30 and over 1000 m temperatures have been obtained a significant distance into the crust in eight holes the main general conclusions are as follows 1 there are no large or systematic differences between borehole heat flow values and oceanographic probe values obtained nearby such a test of shallow penetration oceanographic probe measurements was one of the first objectives of the dsdp heat flow program 2 there are very few clear smooth changes of borehole heat flow with depth in areas with thick sedimentary sections that are indicative of either long term bottom water temperature changes tens to thousands of years or large heat production in the sediments vertical migration of sediment interstitial pore water is suggested by nonlinear temperature depth profiles at a few sites particularly where the sediment is relatively thin and the temperature gradient is high 3 temperatures in the crustal parts of deep sea drill holes exhibit a wide range of behavior generally indicating hydrothermal circulation in the upper crust at five sites seawater is inferred to be moving down the holes into the crust indicating low formation pressures and very high permeability in the upper crust in two deep holes however such flow is limited to above several hundred meters into the crust and heat fluxes close to theoretical cooling lithosphere values for the age of the crust 6 and 7 ma are found at greater depth these sites suggest that hydrothermal circulation may be concentrated at shallow depths in the crust summary tables are presented of the heat flow data considered to be reliable after review and revision and an appendix provides detailed comments on all the measurements for which data are available geothermal measurements are continuing on the new ocean drilling program ship joides resolution

suitability of spaceborne digital elevation models of different scales in topographic analysis an example from kerala india digital elevation model dem deriving conventionally from contour data of topographic maps provides sufficient information regarding the continuously varying topographic surface of the earth though spaceborne dems are increasingly being used in earth environmental applications suitability of various freely available spaceborne dems e g advanced spaceborne thermal emission and reflection aster shuttle radar topography mapping mission srtm global multi resolution terrain elevation data gmted for topographic and geomorphometric analyzes in tropical regions is yet to be ascertained in this paper comparability of these spaceborne dems among themselves and also with the dem topo prepared from digital contour data of topographic maps is assessed results show that various primary and secondary derivatives of aster and srtm dems provide relatively better precision and substantial agreement with the corresponding parameters derived from topo among the spaceborne dems srtm has relatively higher vertical accuracy root mean square error 17 05 m compared to aster 24 09 m and gmted 32 85 m the vertical accuracy of all the spaceborne dems strongly depends on the relief and ruggedness of the terrain as well as the type of vegetation it is proposed that in the absence of other available and acceptable elevation datasets srtm and aster are equally competent for geomorphometric analysis in tropical regions while gmted shows significant loss of terrain information due to coarser spatial resolution

heat flow determination in three dsdp boreholes near the japan trench the first deep borehole determinations of temperature gradients and heat flow of the landward wall of the japan trench and forearc were made on ipod dsdp leg 57 these heat flow values are based on temperature logs corrected to equilibrium using a detailed model of the drilling disturbance heat flow values on a deeply submerged terrace landward of the trench slope break are 28 and 32 mw m sup 2 a measurement in the midslope terrace basin on the landward wall of the trench yielded a value of 22 mw m sup 2 the results are in good agreement with earlier seafloor measurements and indicate that most of the forearc area is characterized by heat flow about one half of that over oceanic lithosphere seaward of the trench our observations indicate only a small increase of heat flow from the trench to the volcanic arc in agreement with thermal models which suggests that the subduction of the relatively cold oceanic plate continues to dominate the temperature structure for distances of up to 250 km landward of the trench the temperature profile in the borehole on the midslope terrace indicates possible vertical flow of pore waters hundreds of conductivity determinations were made usingmore a new technique less

the treatment of flat areas and depressions in automated drainage analysis of raster digital elevation models methods developed to process raster digital elevation models dem automatically in order to delineate and measure the properties of drainage networks and drainage basins are being recognized as potentially valuable tools for the topographic parameterization of hydrological models all of these methods ultimately rely on some form of overland flow simulation to define drainage courses and catchment areas and therefore have difficulty dealing with closed depressions and flat areas on digital land surface models some fundamental assumptions about the nature of these problem topographic features in dem are implicit in the various techniques developed to deal with them in automated drainage analysis the principal assumptions are 1 that closed depressions and flat areas are spurious features that arise from data errors and limitations of dem resolution 2 that flow directions across flat areas are determined solely by adjacent cells of lower elevation and 3 that closed depressions are caused exclusively by the underestimation of dem elevations it is argued that while the first of these assumptions is reasonable given the quality of dems generally available for hydrological analysis the others are not rather it seems more likely that depressions are caused by both under and overestimation errors and that flow directions across flat areas are determined by the distribution of both higher and lower elevations surrounding flat areas two new algorithms are introduced that are based on more reasonable assumptions about the nature of flat areas and depressions and produce more realistic results in application these algorithms allow breaching of depression outlets and consider the distribution of both higher and lower elevations in assigning flow directions on flat areas the results of applying these algorithms to some real and hypothetical landscapes are presented 1998 john wiley sons ltd

drainage morphometry and its influence on hydrology in an semi arid region using srtm data and gis an attempt has been made to study drainage morphometry and its influence on hydrology of peddavanka watershed south india drainage networks for the sub basins were derived from topographical map 1 50 000 and shuttle radar topographic mission srtm digital elevation model dem data used for preparing elevation slope and aspects maps geographical information system gis was used in evaluation of linear areal and relief aspects of morphometric parameters the study reveals that srtm dem and gis based approach in evaluation of drainage morphometric parameters and their influence on hydrological characteristics at watershed level is more appropriate than the conventional methods the mean bifurcation ratio r b of the entire basin is 3 88 which indicate that the drainage pattern is not much influenced by geological structures viii sub basin have high elongation ratio r e basin relief b h ruggedness number rn and time of concentration t c it indicates that the erosion and peak discharges are high in these basins therefore the construction of the check dams and earth dams will help in reducing peak discharge on the main channel these studies are very useful for implementing rainwater harvesting and watershed management

geophysical prospecting on the santorini islands a program of geophysical research was carried out as a preliminary stage of study of the santorini volcanic group this area is of remarkable geothermal and volcanological interest and the definition of a volcanological structural model is the starting point for an understanding of the local geodynamic processes

quantitative geomorphology applied to fluvial dynamic in aviles and moneta basins tierra del fuego southern argentina the morphometric characteristics of the moneta river basin are compared to those of the aviles river basin both are located in the north of the province of tierra del fuego in argentina and they also have their catchment area in the same range the sierras del bosque runoff on the ne oriented slopes forms the aviles river basin while runoff on the se slopes forms the moneta river basin the analysis was made in two different scales the first as a general scale of the basin and the second as the catchment sector upper middle and lower the quantitative analysis was applied in order to know the behavior of these two fluvial systems for the analysis a cartographic basis scale to 1 20 000 was used which was made on a mosaic of images from google earth the altimetric information was obtained throughout a digital elevation model of 45 m spatial resolution srtm45 shuttle radar topographic mission the indices used were rr rb ish and dd to characterize the geological and geomorphological context and rl re if ct and ca to infer the behavior of the runoff in the catchment it was established that the moneta river basin reaches 6 in order of hierarchy its main channel is 65 52 km long the re determines an elongated basin the ct obtained in the basin is 0 96 whereas the sub basin level was identified to a maximum value of the o3 sm 10 1 46 the dd is low 1 94 km km2 which is directly proportional to the intensity of rainfall and the slopes of the area considered the comparison made at the same scale between basins determines specific fluvial characteristics of each sector upper middle and lower

neotectonic control on drainage systems gis based geomorphometric and morphotectonic assessment for crete greece abstract geomorphic indices can be used to examine the geomorphological and tectonic processes responsible for the development of the drainage basins such indices can be dependent on tectonics erosional processes and other factors that control the morphology of the landforms the inter relationships between geomorphic indices can determine the influence of regional tectonic activity in the shape development of drainage basins a multi criteria decision analysis mcda procedure has been used to perform an integrated cluster analysis that highlights information associated with the dominant regional tectonic activity factor analysis fa and analytical hierarchy process ahp were considered within that procedure producing a representation of the distributed regional tectonic activity of the drainage basins studied the study area is western crete located in the outer fore arc of the hellenic subduction zone one of the world s most tectonically active regions the results indicate that in the landscape evolution of the study area especially the western basins tectonic controls dominate over lithological controls

flood hazard assessment of upper jhelum basin using morphometric parameters morphometric parameters can be useful tools to provide general understanding of physical characteristics of drainage basin with respect to floods to evaluate the flood influencing factors in the upper jhelum basin we delineate the upper jhelum basin into ten sub basins followed by extraction of drainage network and morphometric parameters using advanced spaceborne thermal emission and reflection radiometer digital elevation model and topographic maps in geographic information system the overall flood potential was determined on the basis of compound value obtained for all morphometric parameters of each sub basin the analysis reveals that in general the northeastern segment of the upper jhelum basin reveals comparative higher flood potential than the southwestern segment the tributaries such as lidder veshav arapal arapat and bring exhibit greater potential to produce peak flows during rainfall events while the tributaries like dudhganga rambiara sandran romushi and sasara express moderate to low flood potential respectively the results of this study are likely to be very useful for effective flood hazard mitigation in upper jhelum floodplain

squeesar and gps ground deformation monitoring of santorini volcano 1992 2012 tectonic implications abstract the santorini volcanic complex svc has been in a dormant state for the last 60 years until january 2011 when upward influx of magma reawakened the volcano with intense radial ground deformation and inter caldera seismicity that lasted until january 2012 but declined afterwards this paper aims to study the ground deformation and the inferred tectonic implications of the svc for the period 1992 2012 mainly based on the squeesar technique and dgps campaign results of our local network which incorporates available data on internet from several continuous gps stations established on the island the spatial deformation of the svc during the quiet period 1992 2010 was deduced by joint analysis of ers1 and 2 and envisat it was found that the intra caldera palaea kammeni shield volcano was being uplifted 2 3 mm yr with increasing rate whilst the adjacent nea kammeni shield volcano was being subsided up to 6 mm yr with increasing rate the rest of the svc showed a velocity field varying from 1 to 2 mm yr indicating a rather linear deformation during that period the results from the gps network are in full agreement with the squeesar results based on the results of squeesar analysis of 12 envisat images and dgps cgps data to end 2012 the deformation for the unrest period 2011 2012 was non linear being characterized by strong radial deformation in the northern part of the caldera 50 120 mm yr and accelerating values 130 mm yr 2 combined gps squeesar mogi modeling indicated a source located north of nea kammeni at a shallow depth however a progressively decreasing rate in deformation was noted at most gps cgps station components after january 2012 indicating magma settlement consistent with the constantly decreasing rate of the inter caldera seismicity the faulting features seem to have a key role in the evolution of the deformation which continues up the end 2012 but at a very low level

stratigraphic relations of santorini s intracaldera fill and implications for the rate of post caldera volcanism we propose a new volcanological interpretation of santorini s intracaldera fill deposits as revealed by seismic reflection profiles this interpretation along with supplementary gravity and geophysical studies reveals three distinct volcaniclastic units 1 3 from top to bottom these units are attributed to 1 modern infilling sediment 2 shallow marine phreatomagmatic volcanism associated with the relatively recent formation of the kameni islands and 3 downfaulted minoan pyroclastic deposits which formed during caldera collapse towards the end of the bronze age eruption estimates of the volumes of the seismic units and kameni islands yield a dense rock equivalent magma volume of 4 85 0 7 km 3 the average rate of volcanism over the past c 3641 years is estimated at 1 3 10 3 km 3 a 1 and is similar to the rate since the ad 1707 eruption of 1 2 10 3 km 3 a 1 based on historical lava volume estimates

seismic imaging of santorini subsurface constraints on caldera collapse and present day magma recharge abstract volcanic calderas are surface depressions formed by roof collapse following evacuation of magma from an underlying reservoir the mechanisms of caldera formation are debated and predict differences in the evolution of the caldera floor and distinct styles of magma recharge here we use a dense active source seismic tomography study to reveal the sub surface physical properties of the santorini caldera in order to understand caldera formation we find a 3 km wide cylindrical low velocity anomaly in the upper 3 km beneath the north central portion of the caldera that lies directly above the pressure source of the 2011 2012 inflation we interpret this anomaly as a low density volume caused by excess porosities of between 4 and 28 with pore spaces filled with hot seawater vents that were formed during the first three phases of the 3 6 ka late bronze age lba eruption are located close to the edge of the imaged structure the correlation between older volcanic vents and the low velocity anomaly suggests that this feature may be long lived we infer that collapse of a limited area of the caldera floor resulted in a high porosity low density cylindrical volume which formed by either chaotic collapse along reverse faults wholesale subsidence and infilling with tuffs and ignimbrites phreatomagmatic fracturing or a combination of these processes phase 4 eruptive vents are located along the margins of the topographic caldera and the velocity structure indicates that coherent down drop of the wider topographic caldera followed the more limited collapse in the northern caldera this progressive collapse sequence is consistent with models for multi stage formation of nested calderas along conjugate reverse and normal faults the upper crustal density differences inferred from the seismic velocity model predict differences in subsurface gravitational loading that correlate with the location of 2011 2012 edifice inflation this result supports the hypothesis that sub surface density anomalies may influence present day magma recharge events we postulate that past collapses and the resulting topographical and density variations at santorini influence magma focusing between eruptive cycles a feedback process that may be important in other volcanoes

backarc tectonism volcanism and mass wasting shape seafloor morphology in the santorini christiana amorgos region of the hellenic volcanic arc abstract in subduction zone backarcs extensional deformation and arc volcanism interact and these processes together with mass wasting shape the seafloor morphology we present a new bathymetric map of the santorini christiana amorgos backarc region of the hellenic subduction zone by merging high resolution multibeam swath data from the r v langseth proteus seismic experiment with existing maps the map together with knudsen subbottom echosounding profiles reveal that recent tectonism volcanism and mass wasting are more prevalent in the santorini amorgos region on the east side of santorini than in the christiana basin on the west side in the santorini amorgos region large normal faults form the anydros and anafi basins where normal fault segments overlap two nearby accommodation zones generate a relay ramp and the adjoining anydros synclinal horst with associated complex faulting and elevated seismicity the ongoing normal faulting in the santorini amorgos region is accompanied by potentially tsunamigenic submarine landsliding we identified a large submarine landslide along the santorini amorgos fault and a smaller landslide with an overlying debris chute along the amorgos fault volcanic activity is also focused in this eastern region along the kolumbo lineament within the anydros basin within the christiana basin we discovered the proteus knoll and adjacent buried edifice we suggest that this is an older volcanic edifice formed along the hellenic volcanic arc between santorini and milos around santorini itself features formed during and immediately after the late bronze age eruption dominate the seafloor morphology such as the northern strait and wrinkled seafloor pyroclastic flow deposits this topography is continually reshaped at a smaller scale by ongoing mass wasting we infer that the earthquake volcanic and tsunami activity of the santorini amorgos region is a consequence of focused northwest southeast extension as the southeastern aegean moves away from the attico cycladic complex in response to slab breakup and rollback

caldera formation on santorini and the physiography of the islands in the late bronze age the caldera of santorini is a composite structure with a subsidence history extending over 100 ka or more geomorphological mapping shows that the present day caldera wall is a complex assemblage of cliff surfaces of different ages and that collapse at santorini has repeatedly exhumed earlier caldera cliffs and unconformities cliffs bounding the southern southeastern and northwestern rims of the caldera are morphologically fresh and probably formed during or soon after the minoan eruption in the late bronze age the well scalloped shape of these cliffs is attributed to large scale rotational landslip around the margins of the minoan caldera the deposit from one landslip is preserved subaerially minoan landslips in southeast santorini detached along the basement unconformity exposing a cliff of the prevolcanic island the caldera wall in the north northeast and east preserves evidence for three generations of cliff those of minoan age and two earlier generations of caldera wall the two early calderas can be dated relative to a well established statigraphy of lavas and tuffs the presence of in situ minoan tephra plastered onto the present day caldera wall provides evidence that these ancient caldera cliffs had already been exhumed prior to the minoan eruption field relationships permit reconstruction of the physiography of bronze age santorini immediately before the minoan eruption the reconstruction differs from some previously published versions and is believed to be the most accurate to date bronze age sa ntorini had a large flooded caldera formed 21 ka ago this caldera must have acted as an excellent harbour for the bronze age inhabitants of the island the 3 6 ka minoan eruption deepened and widened the extant caldera the volume of minoan collapse 25 km3 is in good agreement with published estimates for the volume of discharged magma if between 5 and 8 km3 of minoan ignimbrite ponded as intracaldera tuff

caldera development during the minoan eruption thira cyclades greece the well known caldera of thira santorini greece was not formed during a single eruption but is composed of two overlapping calderas superimposed upon a complex volcanic field that developed along a ne trending line of vents before the minoan eruption of 1400 b c thira consisted of three lava shields in the northern half of the island and a flooded depression surrounded by tuff deposits in the southern half andesitic lavas formed the overlapping shields of the north and were contemporaneous with and in many places interbedded with the southern tuff deposits although there appears to be little difference between the composition of magmas erupted differences in eruption style indicate that most of the activity in the northern half of the volcanic field was subaerial producing lava flows whereas in the south eruptions within a flooded depression produced a sequence of mostly phreatomagmatic tuffs many of these tuffs are plastered onto the walls of what appears to have been an older caldera most probably associated with an eruption of rhyodiacitic tephra 100 000 years ago the minoan eruption of about 1400 b c had four distinct phases each reflecting a different vent geometry and eruption mechanism the minoan activity was preceded by minormore eruptions of fine ash 1 the eruption began with a plinian phase from subaerial vent s located on the easternmost of the lave shields 2 vent s grew toward the sw into the flooded depression subsequent activity deposited large scale base surge deposits during vent widening by phreatomagnetic activity 3 the third eruptive phase was also phreatomagmatic and produced 60 of the volume of the minoan tuff this activity was nearly continuous and formed a large featureless tuff ring with poorly defined bedding less

evidence from cosmic ray exposure cre dating for the existence of a pre minoan caldera on santorini greece cosmic ray exposure cre dating was performed on the caldera cliffs of santorini with the aim of detecting cliff segments predating the minoan eruption 17th century bce the methodology involved the determination of in situ produced cosmogenic 36cl concentration in basaltic to rhyodacitic whole rocks cropping out in the cliffs after the samples were processed following the chemical protocol of 36cl preparation for silicate rocks 36cl concentrations were measured by accelerator mass spectrometry ams important challenges during the implementation procedure were related to large amounts of radiogenic 36cl complex modeling of inherited 36cl and dominance of the thermal and epithermal low energy neutron capture production pathway nevertheless quantitative assessments on the basis of the contribution of the low energy neutron capture pathway percent to the total production rate validated the calculated cre dates current cre ages demonstrate that an ancient caldera existed on pre minoan santorini occupying at least the northern half of the modern day caldera

quantitative comparative geomorpholgical analysis of fluvial and karst relief of florida karst relief of central florida and fluvial relief of the florida panhandle were analyzed and compared on the basis of standardized samples of karst and fluvial topography derived from digital databases in a gis environment comparative geomorphological analyses of the two distinct genetic relief types were performed on the basis of morphometric parameters derived for each type of relief in general as well as differentially for hypsometric intervals of paleo marine terraces with the assumption of relative stability of tectonic conditions of the underlying carbonate platform the comparative analyses conducted indicate overall higher values of the morphometric parameters in the fluvial relief compared to those in the karst relief this is a consequence of more than two times higher rates of fluvial denudation compared to the karst denudation rates 0 23 vs 0 11 mm year respectively differential analyses with respect to the paleo marine terrace intervals reveal significant quantitative morphological differences between the upper older and lower younger terrace intervals in the karst and fluvial relief in the two older terrace intervals fluvial and karst denudation rates range from 0 07 to 0 09 mm year while in the younger terrace intervals fluvial denudation shows more than two times higher rates than the karst denudation 0 22 and 0 55 vs 0 11 and 0 19 mm year indicating that fluvial processes in the study area are more effective than the respective karst processes this is clearly reflected in the higher values of vertical dissection and denudated sediment volume in the fluvial relief in the younger terrace intervals while the increased karst denudation rates are not yet reflected in the respective morphometric parameters due to the slower morphologic response overall long term karst denudation ranging from 0 07 to 0 19 mm year is derived by volumetric analysis of the denudated sediment and as such accounts for the effects of both chemical and mechanical denudation consequently they are significantly higher than the previously calculated short term solutional denudation rates although their values fall in the mid range of theoretical estimations with respect to climatic conditions of the study area the obtained fluvial denudation rates ranging from 0 07 to 0 55 mm year are similar to previous estimates of long term fluvial denudation

geochemical and isotopic changes in the fumarolic and submerged gas discharges during the 2011 2012 unrest at santorini caldera greece a geochemical survey of fumarolic and submerged gases from fluid discharges located in the nea kameni and palea kameni islets santorini island greece was carried out before during and after the unrest related to the anomalously high seismic and ground deformation activity that affected this volcanic system since january 2011 our data show that from may 2011 to february 2012 the nea kameni fumaroles showed a significant increase of h2 concentrations after this period an abrupt decrease in the h2 contents accompanied by decreasing seismic events was recorded a similar temporal pattern was shown by the f cl so4 2 and nh4 concentrations in the fumarolic condensates during the sharp increase of h2 concentrations when values up to 158 mmol mol were measured the 13c co2 values which prior to january 2011 were consistent with a dominant co2 thermometamorphic source have shown a significant decrease suggesting an increase of mantle co2 contribution light hydrocarbons including ch4 which are controlled by chemical reactions kinetically slower than h2 production from h2o dissociation displayed a sharp increase in march 2012 under enhanced reducing conditions caused by the high h2 concentrations of may 2011 february 2012 the general increase in light hydrocarbons continued up to july 2012 notwithstanding the contemporaneous h2 decrease the temporal patterns of co2 concentrations and n2 ar ratios increased similarly to that of h2 possibly due to sealing processes in the fumarolic conduits that diminished the contamination related to the entrance of atmospheric gases in the fumarolic conduits the compositional evolution of the nea kameni fumaroles can be explained by a convective heat pulse from depth associated with the seismic activation of the ne sw oriented kameni tectonic lineament possibly triggered by either injection of new magma below nea kameni island as apparently suggested by the evolution of the seismic and ground deformation activity or increased permeability of the volcanic plumbing system resulting from the tectonic movements affecting the area the results of the present study demonstrate that the geophysical and geochemical signals at santorini are interrelated and may be precursory signals of renewed volcanic activity and encourage the development of interdisciplinary monitoring program to mitigate the volcanic risk in the most tourist visited island of the mediterranean sea

heat transfer through the sediments of the mounds hydrothermal area galapagos spreading center at 86 w heat transfer processes at the mounds area of the galapagos spreading center at 86 w are revealed by temperatures measured at 10 m intervals in the 30 10m sediment at each of 12 holes at dsdp leg 70 sites 506 509 and by temperatures of up to five thermistors on eleven 8 12 m long piston cores the 325 needle probe values show a significant linear increase of thermal conductivity with depth in each core about half of the temperature thermal resistance profiles are nonlinear and are fit to a steady state vertical pore water advection model results indicate high and variable total heat flow and localized hydrothermal discharge at 10 8 m s associated with individual mounds recharge is indicated at similar rates in the low heat flow belt 5 km south of the mounds and is suggested at slower rates in the intermediate heat flow 0 17 0 42 w m2 belt surrounding the mounds heat flow high possible slow entrained recharge within 100 m of discharging mounds is suggested also suggested is strong local discharge along the major fault bounding the mounds crustal block to the north about 95 km north of the spreading axis at dsdp site 510 temperatures in the 114 m sediment cover on 2 7 m y crust are linear consistent with the suggestion that the hydraulic resistance of this layer is sufficient to seal off free hydrothermal exchange between basement and bottom water the combination of heat flow data and the physical properties data of karato and becker this issue suggests that 50 m of sediment may be a threshold thickness for sealing of hydrothermal circulation within basement where the topography is smooth we suggest that the formation of mounds may be associated with the forced localization of hydrothermal discharge through the sediment as its thickness approaches this threshold value

recent geodetic unrest at santorini caldera greece 1 after approximately 60 years of seismic quiescence within santorini caldera in january 2011 the volcano reawakened with a significant seismic swarm and rapidly expanding radial deformation the deformation is imaged by a dense network of 19 survey and 5 continuous gps stations showing that as of 21 january 2012 the volcano has extended laterally from a point inside the northern segment of the caldera by about 140 mm and is expanding at 180 mm yr a series of spherical source models show the source is not migrating significantly but remains about 4 km depth and has expanded by 14 million m3since inflation began a distributed sill model is also tested which shows a possible n s elongation of the volumetric source while observations of the current deformation sequence are unprecedented at santorini it is not certain that an eruption is imminent as other similar calderas have experienced comparable activity without eruption

constraining the landscape of late bronze age santorini prior to the minoan eruption insights from volcanological geomorphological and archaeological findings abstract one of the best known places on earth where volcanology meets archaeology and history is the volcanic island of santorini thira greece it is famous for the cataclysmic late bronze age minoan plinian eruption which destroyed the minoan culture that flourished on the island hosting a central flooded caldera bay and within that the active islands of palaea and nea kameni santorini volcano has been the focus of international research efforts for over one and a half centuries in this paper we summarize recent findings and related ideas about the minoan physiography of the island also known as strongyli from a volcanological geomorphological and archaeological point of view as proposed as early as the 1980s a central caldera bay existed prior to the late bronze age probably characterised by a smaller size and located in the northern part of the present day caldera this earlier caldera bay was formed during the previous plinian eruption called cape riva eruption c 22 000 years ago within the caldera bay a central island pre kameni existed named after the present day kameni islands high precision radioisotopic dating revealed that pre kameni started to grow c 20 000 years ago whereas volcanologists have accepted and refined the caldera concept archaeologists have generally favoured the theory of an exploded central cone instead of a pre existing central caldera however analysis of the flotilla fresco one of the wall paintings found in the bronze age settlement of akrotiri reveals the interior of a late bronze age caldera that may be interpreted as a realistic landscape approximately 3600 years ago the island of strongyli was destroyed during the explosive vei 7 minoan eruption pre kameni was lost by this eruption but its scattered fragments together with other parts of strongyli can be recovered as lithic clasts from the minoan tuffs on the basis of photo statistics and granulometry of the lithic clasts contained in the minoan tuffs complemented by volumetric assessment of the erupted tephra and digital elevation model dem analysis of alternative models for the pre eruptive topography the volume of pre kameni can be constrained between 1 6 and 3 0 km3 whereas the volume of the destroyed portion of the ring island of strongyli between 9 1 and 17 1 km3 of these the larger values are considered more realistic and imply that most of the destroyed part of strongyli was incorporated as lithic components in the minoan tuffs whereas up to 3 km3 of strongyli might have been downfaulted and sunken during caldera formation and is not accounted for in the lithics

automatically derived catchment boundaries and channel networks and their hydrological applications abstract a method of generating drainage networks and catchment boundaries from gridded ground elevation data a digital terrain model is presented the method includes an algorithm for coping with localised low points in the data the paper suggests two objective ways of comparing the conventionally mapped with the automatically generated drainage network emphasis is placed on the way that this approach is capable of benefiting a variety of hydrological applications in particular the automatic estimation of flow statistics from catchment characteristics

morphotectonic analysis and gnss observations for assessment of relative tectonic activity in alaknanda basin of garhwal himalaya india abstract alaknanda basin in the garhwal himalaya india is a tectonically active region owing to ongoing crustal deformation erosion and depositional processes active in the region active tectonics in this region have greatly affected the drainage system and geomorphic expression of topography and provide an ideal natural set up to investigate the influence of tectonic activity resulting from the india eurasia collision we evaluated active tectonics by using high resolution digital elevation model dem based on eight geomorphic indices stream length gradient index valley floor width to height ratio hypsometric integral drainage basin asymmetry transverse topography symmetry factor mountain front sinousity index bifurcation ratio and basin shape index and seismicity in eight subbasins of alaknanda basin the integrated product relative tectonic activity index tai map was classified into three classes such as highly active with values ranging up to 2 0 moderately active with values ranging from 2 0 to 2 25 and less active with values 2 25 further the results were compared with relatively high crustal movement rate of 41 10 mm y computed through high precession global navigation satellite system gnss based continuous operating reference station cors data thus we concluded that this new quantitative approach can be used for better characterization and assessment of active seismotectonic regions of the himalaya and elsewhere

spatial distribution of channel heads in the polish flysch carpathians article i nfo one of the key topics in modern geomorphology is the identification of locations where the drainage network begins however there still exists a gap in the research literature in the area of channel head location in flysch regionscharacterizedbyunique hydrogeological conditions in thisstudy we haveidentifiedthe spatial distribu tionofchannelheadsanddeterminedthresholdvaluesofmorphometricparametersforcatchmentscontributing to channel heads in the polish flysch carpathians we surveyed a total of 401 channel heads on the main ridge of the polonina wetlinska range using gps the dem was used to identify 16 physiographic parameters for each catchment and statistical correlations between catchment parameters were also calculated we compared field data versus the drainage network produced using a topographic map and dem the channel head density based on field mapping is five times higher than the density estimated using a topographic map and 250 lower than that obtained from a dem most channel heads are recharged by very small catchment areas the threshold value for catchment size has been shown to be about 0 01 km 2 the mean slope gradient responsible for channel head formation is 18 in the study area given the very small size of catchment areas contributing to channel heads in the study area remote sensing methods are not useful fieldwork is still the best method of mapping channel heads the distribution of channel heads across the polonina wetlinska range in the polish flysch carpathians cannot be described using simple relationships correlations between topographic attributes that are common in other physiographic regions are not very clear in flysch areas

morphotectonic analysis of aripal basin in the north western himalayas india an evaluation of tectonics derived from geomorphic indices abstract himalayan river basins are exposed to continuous erosion and deformational processes the main goal of this paper is to characterize the tectonic activity as it acts as a controlling factor in the development of landforms in the tectonically active terrains research was carried out in the aripal basin which lies to the south east of kashmir valley one of the right bank tributary of river jhelum the geomorphic indices and morphometric parameters are determined using advanced spaceborne thermal reflection and emission radiometer aster 30 m digital elevation model the low mountain front sinuosity smf 1 3 s type hypsometric curve with high hypsometric integral hi 0 35 low valley floor width to valley height ratios vf

seismic volcanostratigraphy of large volume basaltic extrusive complexes on rifted margins large volume extrusive basaltic constructions have distinct morphologies and seismic properties depending on the eruption and emplacement environments the presence and amount of water is of main importance while local rift basin configuration erosion and resedimentation determine the overall geometry of the volcanic constructions we have developed the concept of seismic volcanostratigraphy a subset of seismic stratigraphy to analyze volcanic deposits imaged on seismic reflection data the method places special focus on identification and mapping of seismic facies units and the volcanological interpretation of these units interpretation of seismic reflection data along the atlantic and western australia rifted margins reveals six characteristic volcanic seismic facies units named 1 landward flows 2 lava delta 3 inner flows 4 inner seaward dipping reflectors inner sdr 5 outer high and 6 outer sdr these units are interpreted in terms of a five stage tectonomagmatic volcanic margin evolution model comprising 1 explosive volcanism in a wet sediment broad basin setting 2 subaerial effusive volcanism forming gilbert type lava deltas along paleoshorelines 3 subaerial effusive volcanism infilling a fairly narrow rift basin 4 shallow marine explosive volcanism as the injection axis is submerged below sea level and finally 5 deep marine sheet flow or pillow basalt volcanism further erosion and resedimentation processes are particularly important during the shallow marine stages seismic volcanostratigraphy provides important constraints on rifted margin development in particular on the prevolcanic basin configuration relative timing of tectonomagmatic events total amount of volcanic rocks location of paleoshorelines and margin subsidence history these parameters give key boundary conditions for understanding the processes forming volcanic margins and other large volume basaltic provinces

vent development during the minoan eruption 1640 bc of santorini greece as suggested by ballistic blocks abstract the minoan eruption on santorini greece was a major plinian caldera forming event that occurred at ca 1640 bc the eruption is generally divided into four distinct phases 1 plinian phase 2 phreatomagmatic base surge 3 ash flow phase and 4 non welded ignimbrite many ballistic blocks mostly consisting of older lava fragments with diameters up to several meters were ejected during phases 2 and 3 as caldera collapse followed the eruption the precise vent location is unknown but its position during phase 1 has been inferred from the pumice isopachs of the plinian deposits the location of the vent during the following phases has been estimated by measuring thickness variations flow directions within the pyroclastic flows and impact directions of ballistic blocks in this study the vent location has been estimated by analysis of the size distribution of the ballistic blocks phase 2 blocks show no clear size dependant distribution pattern blocks ranging between 0 15 and 1 60 m in diameter are found throughout almost the entire deposit but are concentrated in the southeastern parts and within a circle of 14 km diameter thus suggesting a maximum range of at least 6 7 km the center of that circle is regarded as the most probable ejection region it is proposed that the subaerial vent of phase 1 developed into an fracture opening to the sw along the general tectonic trend very large blocks up to 3 m in diameter or possibly more were also ejected during phase 3 with the largest ones being found only in the northern half of the island group near the caldera rim it therefore appears that at least one other vent opened in the northern half of the caldera possibly as a new sw ne trending fracture

on the reliability of lithospheric constraints derived from models of outer rise flexure summary we evaluate the common practice of utilizing elastic models of outer rise flexure to constrain lithospheric parameters such as mechanical thickness and ambient in plane force we numerically compute synthetic flexural profiles consistent with empirically determined constraints on lithospheric rheology and representative trench type boundary conditions and misfit minimization is utilized to determine the analytical solution to elastic plate flexure that most closely resembles each synthetic profile we then determine if it is possible to use the best fitting elastic solutions to recover the lithospheric mechanical thickness and level of in plane force that were assumed during the numerical computation of the synthetic profiles this methodology is analogous to the common practice of estimating lithospheric parameters by modelling bathymetric profiles with analytical descriptions of elastic plate flexure our results unequivocally indicate that in plane force cannot be reliably constrained in this manner such an approach does not even allow the qualitative nature of in plane force to be distinguished i e compressional versus tensional although in principle elastic plate models may provide reliable constraints on the mechanical thickness of oceanic lithosphere in practice uncertainties associated with bathymetric noise and the level of in plane force may in some instances render such constraints unreliable

morphometric diversity of supply limited and transport limited river systems in the himalayan foreland abstract the indo gangetic basin exhibits highly diverse hydro geomorphic settings that influence the hydrology sediment production and transport rates of the rivers draining this region and this in turn is manifested in morphometric diversity of river systems the rivers draining the western gangetic plains wgp show incised channels attributable to high stream power and low sediment yield in contrast the rivers draining the eastern gangetic plains egp have formed aggradational landforms such as megafans due to low stream power and high sediment yield for a better process understanding of the causal factors of such spatial inhomogeneities in a river basin a morphometric characterization of its hinterland is necessary in this work a set of morphometric parameters such as stream network longitudinal profile and hypsometric curve have been integrated with data on sediment connectivity and stream power index to establish the form process relationships in two contrasting basins the upper ganga basin ugb and the upper kosi basin ukb the results of this study suggest that high sediment flux in the ukb is attributed to high rainfall steep topography unstable channel longitudinal profiles and high sediment connectivity a large part of these sediments gets deposited within the channel belt in the alluvial reaches and is remobilized during high flow events however the ugb produces fewer sediments due to low rainfall mild topography stable channel longitudinal profile and low sediment connectivity also the presence of a major dam at tehri further reduces the functional sediment connectivity in the upper ganga basin

drainage networks from grid digital elevation models current algorithms that deduce the drainage network from a digital elevation model dem represented by a regular array of surface elevations share a fault unless the terrain is rugged the derived water channels tend to flow in parallel lines along preferred directions engendered by the sampling grid orientation we present a simple solution to the problem a second difficulty is the presence of noise that creates artificial pits we briefly describe a method which deals with pits in what we believe to be a more efficient manner for virtual memory environments than previous efforts our system has treated dems of nearly 9 000 000 pixels we show how depth first search of the resulting drainage network permits segmentation of the dem into basins by various criteria analysis of stream sediment anomaly dilution profiles improved hydrological models and other applications

analyzing the drainage system anomaly of zagros basins implications for active tectonics abstract morphometric analysis of hierarchical arrangement of drainage networks allows to evaluate the effects of external controls especially tectonics on basin development in this study a quantitative method for calculation of stream s hierarchical anomaly number is introduced morphometric parameters such as hierarchal anomaly index a percent of asymmetry factor paf basin shape bs basin length to mean width ratio bl bmw stream s bifurcation ratio rb bifurcation index r drainage density dd drainage frequency df and anticline s hinge spacing hs of 15 basins in zagros mountains were examined results show that the strong correlations exist between pairs a paf r 0 844 a bs r 0 732 a bl bmw r 0 775 a r r 0 517 paf bl bmw r 0 519 bs r r 0 659 bl bmw r r 0 703 hs a r 0 708 hs paf r 0 529 and hs bs r 0 516 the variations in trend of anticlines control the shape of basins so that where anticlines hinges become closer to each other in the downstream direction basin become narrower downward and hence the a increases the more uplifted northeastern anticlines cause the trunk river of the basins to migrate toward the younger anticlines in southwest and hence a increases because the trunk river receives a lot of first order streams data reveal that the rate of a is higher in elongated synclinal basins due to the decrease in the intensity of deformation from northeast toward southwest of zagros the hinge spacing of anticlines increases southwestwards data reveal that the variation in hinge spacing of anticlines strongly controls the basin s shape and tilting as well as the hierarchical anomaly of drainage system since the elongation and tilting of basins are associated with the variations in rates of folding uplift and hinge spacing of anticlines it can be concluded that the hierarchical anomaly of drainages in studied basins is controlled by the intensity of zagros tectonic activities

morphometric analysis of the river thamirabarani sub basin in kanyakumari district south west coast of tamil nadu india using remote sensing and gis the quantitative analysis of the drainage morphometric system is vital to understand the hydrological and environmental interaction and its processes of an area the present study deals with quantitative characteristics of morphometry of steep slope and short length sub basin of r thamirabarani in kanyakumari district tamilnadu india using geospatial technology in this study the digital elevation model data product aster dem landsat etm image and survey of india topographical map were used to delineate slope relief and drainage system structures such as drainage pattern stream order stream network and stream length of the sub basin using arcgis 9 3 software the morphometric analysis deals with hydrologic processes such as stream frequency bifurcation ratio circulatory ratio and length of overland flow of the sub basin area and their influences on the local morphologic landforms the quantitative measurement of these characteristics is used to explore the basin s contribution to the hydrological cycle and the shape size and formation of the local landscapes in the region moreover the hypsometric analysis and denudation rate were estimated for understanding the quantitative geomorphological characteristics of the sub basin the relationship of the morphometric parameters reveals that the drainage network is strongly controlled by geological and geomorphological structures of the area the geometry of streams exhibits dendritic drainage pattern associated with coarse drainage texture in primary order of streams present on hilly terrain surface and semi dendritic pattern in higher stream order flow on less elevated surface with gentle slope the drainage density of the study area ranges from 0 1 to 1 89 km km2 and the maximum density value was found along the higher stream order the mean bifurcation ratio of this area is 4 21 and the high ratio was measured between the third and fourth order of stream segments the morphometry of this area is depicted by the length of the stream segment drainage pattern and stream flow direction which are influenced by relief steep slope and local geological structure furthermore the sub basin is found to be strongly elongated in shape with a length of 42 78 km and the circularity ratio of this area is measured as 0 33 and elongation ratio as 0 57 the textural dissection of the landforms shows low drainage density in the high elevated hilly terrain in the north and high level in the plain areas in the southern part the values of the circulatory ratio length of overland flow and elongation ratio are relatively close to one another and the relationship among them shows their influences on the process of surface runoff and sediment deposition along the estuary landforms in the study area moreover it is observed that the hypsometric curve of this study area is characterized by convex up shape in nature and represents the youth stage inequilibrium of landscapes consequently the hypsometric integral value 0 49 reflects the distribution of a major volume of the landmass 435 32 km2 at relatively low elevations 180 m the morphometric parameters induced denudation rate of this study area is 65 14 t km2 year and indicates the occurrence of a wide range of denudation intensities throughout the sub basin which is relatively proportional to the suspended sediment yield that is transported in the suspension per unit area based on the realistic output it is proved that remote sensing and gis are effective tools for morphometric studies of the drainage basin

sedimentology of the krakatau 1883 submarine pyroclastic deposits the majority of tephra generated during the paroxysmal 1883 eruption of krakatau volcano indonesia was deposited in the sea within a 15 km radius of the caldera two syneruptive pyroclastic facies have been recovered in scuba cores which sampled the 1883 subaqueous pyroclastic deposit the most commonly recovered facies is a massive textured poorly sorted mixture of pumice and lithic lapilli to block sized fragments set in a silty to sandy ash matrix this facies is indistinguishable from the 1883 subaerial pyroclastic flow deposits preserved on the krakatau islands on the basis of grain size and component abundances a less common facies consists of well sorted planarlaminated to low angle cross bedded vitric enriched silty ash entrance of subaerial pyroclastic flows into the sea resulted in subaqueous deposition of the massive facies primarily by deceleration and sinking of highly concentrated deflated components of pyroclastic flows as they traveled over water the basal component of the deposit suggests no mixing with seawater as inferred from retention of the fine ash fraction high temperature of emplacement and lack of traction structures and no significant hydraulic sorting of components the laminated facies was most likely deposited from low concentration pyroclastic density currents generated by shear along the boundary between the submarine pyroclastic flows and seawater the krakatau deposits are the first well documented example of true submarine pyroclastic flow deposition from a modern eruption and thus constitute an important analog for the interpretation of ancient sequences where subaqueous deposition has been inferred based on the facies characteristics of encapsulating sedimentary sequences

revised estimates for the volume of the late bronze age minoan eruption santorini greece the late bronze age minoan eruption of santorini greece occurred from within an existing caldera low temperature pyroclastic flow emplacement on shallow slopes outside the caldera can only be consistent with the caldera being filled with eruption products that are not preserved field observations and seismic reflection surveys suggest that this missing material has been downfaulted the volume of the caldera infill is estimated as 18 26 km 3 dense rock equivalent dre increasing the total of the minoan eruption deposits to 78 86 km 3 dre and making it the largest known holocene eruption this study highlights a general mechanism whereby caldera eruption volumes could be significantly underestimated

digital elevation model networks demon a model of flow over hillslopes for computation of contributing and dispersal areas current algorithms for computing contributing areas from a rectangular grid digital elevation model dem use the flow routing model of o callaghan and mark 1984 which has two major restrictions 1 flow which originates over a two dimensional pixel is treated as a point source nondimensional and is projected downslope by a line one dimensional moore and grayson 1991 and 2 the flow direction in each pixel is restricted to eight possibilities we show that large errors in the computed contributing areas result for any terrain topography divergent convergent or planar we present a new model called digital elevation model networks demon which avoids the above problems by representing flow in two dimensions and directed by aspect demon allows computation of both contributing and dispersal areas demon offers the main advantage of contour based models e g moore et al 1988 the representation of varying flow width over nonplanar topography while having the convenience of using rectangular grid dems

reheating of old oceanic lithosphere deductions from observations deep wide oceanic basins are the only regions of old seafloor where depth is truly representative of thermal isostasy when the depths of these basins are corrected for the effect of sediment accumulation and variation in crustal thickness the principal non thermal factors have been eliminated we collect the most precise and reliable values of heat flow for the same basins from multi penetration measurements with in situ thermal conductivity or deep sea drilling thermal gradients backed up by surface surveys the 9 data points that result from this selection process have been plotted on a depth versus heat flow graph and compared to published thermal models of lithosphere when considered without regard to age all the points fall at greater depths than predicted by the plate models with constant temperature lower boundaries and remarkably close to boundary layer cooling with parameters determined from the pre 80 ma depth and heat flow history of the ocean floor they are differentiated by their heat flows not much by their depths and the order they plot in along the heat flow axis is random with respect to crustal age modeling of discrete reheating events shows that near boundary layer conditions are re established after about 40 myr but corresponding to a younger than real age the data therefore favor discrete reheating events rather than a continuously hot basal boundary as implicitly assumed by the plate model lithospheric reheating appears to start only on ocean floor 100 ma the data alone cannot discriminate between a few discrete reheating events due to convective peel off at the base of the lithosphere or one or more catastrophic events however the distribution of points from the blake bahama basin is more consistent with distal reheating associated with the bermuda hotspot than local convective peel off

decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano caldera forming volcanic eruptions are low frequency highimpact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days with devastating effects on local and global scales1 because no such eruption has been monitored during its long build up phase the precursor phenomena are not well understood geophysical signals obtained during recent episodes of unrest at calderas such as yellowstone usa and campi flegrei italy are difficult to interpret and the conditions necessary for large eruptions are poorly constrained2 3 here we present a study of pre eruptive magmatic processes and their timescales using chemically zoned crystals from the minoan caldera formingeruption of santorini volcano greece4 which occurred in the late 1600s bc the results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption5 6 despite the large volume of erupted magma4 40 60 cubic kilometres and the 18 000 year gestation period between the minoan eruption and the previous major eruption most crystals in the minoan magma record processes that occurred less than about 100 years before the eruption recharge of the magma reservoir by large volumes of silicic magma and some mafic magma occurred during the century before eruption and mixing between different silicicmagmabatches was still taking place during the final months final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period with major growth phases immediately before eruption these observations have implications for the monitoring of long dormant but potentially active caldera systems