seismicity of the koyna region and regional tectonomagmatism of the western margin india recent findings on the meso cenozoic tectonomagmatism and deep seated anomalous geophysical structures suggest a close linkage between the seismicity of the koyna region the westernghat uplift wg u and associated thermomechanical and fluid activities the wg u seems to be the result of late cretaceous thermal mobilization erosion of the deccan trap cover and superposition of compressional stress the association of seismicity with uplift seems to result from movement of deep seated heat and fluids volatiles along the edges or boundary faults of the uplift because the force required for crustal deformation depends on the relief observed gradients in relief may be attributed to the differential erosion rates and heat inputs due to the time gap of 50 ma in the break ups and plume activities on the eastern and western sides and consequence magmatism further the geology and tectonics strongly indicate that the western margin wm is a relic of a mobile arm ma that included madagascar and which formed a part of the proterozoic mobile belt of greater india fort 85 ma the mobile nature of the wm facilitates mantle upwellings and transient elevation of isotherms at depth raising the possibility of intermittent metamorphism and greater deformation superposition of the ongoing compression and uplift induced forces make local permeability and pore fluid pressure vital in triggering the seismic slip over the peninsular shield certain representative model calculations have been carried out to estimate change in the e m induction characteristics caused by an intermittent hydraulic connectivity the results show a drop in the resistivity which could be a useful monitoring index the close connection of uplift and fluid activity as discussed here seems applicable for other active parts of the south indian shield sis also

temporally and spatially uniform rates of erosion in the southern appalachian great smoky mountains we measured 1 0 be in fluvial sediment samples n 27 from eight great smoky mountain drainages 1 330 km 2 results suggest spatially homogeneous sediment generation on the 10 4 10 5 yr time scale and 100 km 2 spatial scale at 73 11 t km 2 yr 1 equivalent to 27 4 m m y of bedrock erosion this rate is consistent with rates derived from fission track long term sediment budget and sediment yield data all of which indicate that the great smoky mountains and the southern appalachians eroded during the mesozoic and cenozoic at 30 m m y in contrast unroofing rates during the paleozoic orogenic events that formed the appalachian mountains were higher 10 2 m m y erosion rates decreased after termination of tectonically driven uplift enabling the survival of this ancient mountain belt with its deep crustal root as an isostatically maintained feature in the contemporary landscape

mesoscale analysis of the activation of a cold front during cyclogenesis summary the archetypal mesoscale structure of an ana cold front comprises a narrow cold frontal rainband ncfr associated with line convection embedded within a wide cold frontal rainband wcfr due to the slantwise ascent associated with a strong transverse front mesoscale circulation whereas most mesoscale observational studies have concentrated on this mature stage the present paper explores by means of a detailed case study how such a mature frontal system develops from pre existing features the study is based upon the synthesis of data spanning many scales in the form of satellite imagery observations from conventional and multi parameter doppler radar and surface reports together with diagnostics from an operational mesoscale forecast model the cold frontal zone in this case is characterized by multiple cold fronts the dominant second cold front is studied in detail from the point of view of its evolution and its relationship to neighbouring fronts especially the leading front associated with the initial polar front cloud band the dominant cold front started as a shallow rope cloud in the cold sector and at a fairly early stage it produced a ncfr due to line convection then over a period of only a few hours a dry intrusion and an associated strong direct transverse front circulation led to the formation of a canopy of mid level cloud and a wcfr the wcfr was attributable not only to the rearward ascending outflow from the line convection but also to the re invigoration of ascent within the initial polar front cloud band that the line convection was undercutting although the transverse circulation was probably intensified by precipitation processes it is inferred that it was mainly a manifestation of the larger scale environmental flow that existed independently of the major precipitation features

river drainage patterns in the new zealand alps primarily controlled by plate tectonic strain the persistence of dendritic drainage patterns implies that rivers reorganize after a tectonic perturbation preserving no long term record of that tectonic event numerical simulations of the evolution of drainage patterns in the southern alps new zealand however reveal rivers that resist reorganization and thus preserve a record of plate tectonic strain over 10 million years

thin lithosphere asthenosphere boundary beneath eastern indian craton the lithosphere asthenosphere boundary lab separates the hard and rigid outer layer of the earth lithosphere and the weaker hotter and deeper part of the upper mantle asthenosphere and plays a pivotal role in plate tectonics however its definitive detection especially beneath the cratons is proving elusive one of the geophysical tools used to map the lab beneath the cratons is through magnetotelluric mt observations the resistivity at boundary falls in the range of 5 25 m and can be explained by the presence of a small amount of water in the asthenosphere possibly inducing partial melt here we report thickness of the lab in one of the oldest dated ancient cratons of india eastern indian craton eic of 3 3 gyr from mt studies the two prominent phase sensitive strike directions one each for crust and mantle and the presence of resistive continental lower crust act as a window to mantle in resolving deeper electrical conductivity structures beneath eic our results show that the lab beneath the eic is at 95 km the region is interesting as the electrical properties of the crust and mantle and the moho depth are similar to those of the slave craton canada 4 0 gyr but the depth of the lab beneath the eic is half that of the slave craton as cratonic signatures depicted by ultrapotassic rocks from gondwana coal fields close to eic are preserved at least till early cretaceous 117 ma it is likely that himalayan orogeny could have played a major role in delamination of the lithospheric roots of the eic in addition to attendant seismicity

cloud resolving model simulations of multiply banded frontal clouds an idealized two dimensional cloud resolving model is used to investigate the formation and temporal evolution of multiply banded clouds in frontal zones radar observations often show both upright and slantwise convection in the circulations associated with such bands the aim is to examine the interaction between upright and slantwise convection and to determine the mechanisms leading to multiple banding a warm bubble is used to initiate convection in the frontal zone which has an initial thermodynamic profile based on observations further triggering occurs and banded clouds evolve the initially upright plumes become tilted due to the so called am adjustment process upscale development observed multiple bands in frontal zones are frequently attributed to the release of conditional symmetric instability csi however in these simulations there is no evidence of the release of csi despite the fragmentation of slantwise bands into multiple layers in the mid troposphere successive triggering of upright convection is instead associated with a spreading cold pool driven by evaporative cooling in the slanted downdraughts triggering can occur on both the warm and cold air sides of the frontal zone and is sensitive to the microphysical parametrization used

observations of dual slantwise circulations above a cool undercurrent in a mesoscale convective system a series of mesoscale convective systems mcss was observed in the uk during one of the intensive observation periods iop 3 in the convective storm initiation project csip a detailed case study of one of the mcss involving some novel interpretation of single doppler radar data reveals the evolution of stacked slantwise circulations associated with elevated upright convection a feature of this occasion was the existence near the surface of a strong undercurrent of cool air flowing against the direction of travel of the storm the air feeding both the upright and slantwise ascent originated not from near the surface but rather from layers between 1 and 3 km the upright convection was intense at first and was accompanied by a region of dry subsidence surrounding it together with the alternating layers of slantwise ascent and descent within the storm s precipitation area when the elevated upright convection weakened vigorous slantwise motions continued for some time but their slope decreased from the initial 1 in 4 to 1 in 9 the lowermost layer of slantwise descent corresponded to a moderately intense rear inflow jet the rear inflow jet did not penetrate the cool undercurrent and reach the surface instead beneath where it impacted the warm air capping the undercurrent the undercurrent took on the structure of a gravity wave without stagnation the raised head of the undercurrent lifted overlying air of high wet bulb potential temperature sufficiently to overcome the convective inhibition copyright c 2010 royal meteorological society

drainage network dynamics and knickpoint evolution in the ebro and duero basins from endorheism to exorheism abstract the study of fluvial network rearrangement provides a key to understand past and future landscape evolution large perturbations of hydrographic basins such as the change from endorheism to exorheism have repercussions in the steady or disequilibrium state of the basins and their drainage divides such transitions from internal to external drainage imply a major lowering of the geomorphological base level causing a major retreating knickpoint wave that separates the upstream low relief area inherited from the endorheic period from the downstream incised area subsequently the water divide migrates to reach an equilibrium in which erosion rates at both sides of the divide are similar previous fluvial analyses suggest that both the duero and ebro drainage networks the two largest catchments in iberia experienced a change from endorheism to exorheism sometime between the late miocene and the pliocene fluvial capture evidence argues for a pliocene westward migration of the ebro duero divide implying an area decrease for the duero fluvial network victim in favor of the ebro aggressor we used river profiles knickpoint distribution and chi map calculation to understand the different degree of erosion of the duero and the ebro catchments and the dynamics of their drainage network the results show an equilibrated ebro drainage network in contrast with a disequilibrium in the erosional state of the duero drainage which remains reorganizing and adapting to the newly imposed atlantic base level we identified at least two knickpoint wave trains in the duero drainage resulting from the onset of exorheism a fast propagating wave through the cover and a low propagating wave affecting the bedrock field evidence and topographic analysis suggest a westward migration of the ebro duero divide resulting in an ongoing headward erosion of the ebro against the duero catchment chi analysis provides the degree of disequilibrium of the drainage network indicating a large scale aggressor role for the duero and a victim role for the ebro we interpreted this seeming contradiction as the result of a different time scale perspective local divide observations indicate a victim duero in the short term whereas basin scale dynamics support a victim role for the ebro fluvial network in the long term multi million year time scales

new physical evidence of the role of stream capture in active retreat of the blue ridge escarpment southern appalachians abstract the blue ridge escarpment of the southern appalachian mountains is a striking and rugged topographic feature of the ancient passive margin of eastern north america the crest of the escarpment generally coincides with an asymmetric regional drainage divide separating steep streams of the escarpment face from low gradient streams of the blue ridge upland recent exhumation and erosion rate studies suggest that the escarpment has evolved by inland erosional retreat but the mechanism timing and magnitude of retreat remain poorly understood longitudinal stream profiles and slope drainage area relationships of several upland basins draining the divide have led to the identification of 14 previously unknown fluvial terrace deposits preserved at the escarpment crest these relict terraces and the associated beheaded drainages indicate the role of large stream capture events in producing ongoing escarpment retreat through landward divide migration and subsequent topographic adjustment terrace location and preservation suggest that rectilinear drainage patterns and divide asymmetry generate discrete high order captures and episodes of rapid localized retreat that collectively produce slower evolution of the escarpment at large while overall retreat magnitude and rate remain unknown roundness of terrace alluvium suggests that the most recent captures have locally produced tens of kilometers of retreat within the limited preservation lifetime of the deposits in contrast with recent numerical modeling and cosmogenic studies these data show the potential for stream capture and divide migration to sustain passive margin escarpment evolution long after the cessation of rifting the fluvial record of divide retreat preserved atop the blue ridge escarpment suggests the potential for using field methods to better constrain the histories of younger taller and potentially more dynamic passive margin escarpments

lithologic controls on landscape dynamics and aquatic species evolution in post orogenic mountains abstract determining factors that modify earth s topography is essential for understanding continental mass and nutrient fluxes and the evolution and diversity of species contrary to the paradigm of slow steady topographic decay after orogenesis ceases nearly all ancient mountain belts exhibit evidence of unsteady landscape evolution at large spatial scales external forcing from uplift from dynamic mantle processes or climate change is commonly invoked to explain the unexpected dynamics of dead orogens yet direct evidence supporting such inferences is generally lacking here i use quantitative analysis of fluvial topography in the southern appalachian mountains to show that the exhumation of rocks of variable erosional resistance exerts a fundamental autogenic control on the evolution of post orogenic landscapes that continually reshapes river networks i characterize the spatial pattern of erodibility associated with individual rock types and use inverse modeling of river profiles to document a 150 m base level fall event at 9 3 ma in the upper tennessee drainage basin this analysis combined with existing geological and biological data demonstrates that base level fall was triggered by capture of the upper tennessee river basin by the lower tennessee river basin in the late miocene i demonstrate that rock type triggered changes in river network topology gave rise to the modern tennessee river system and enhanced erosion rates changed sediment flux and dispersal patterns and altered bio evolutionary pathways in the southeastern u s a a biodiversity hotspot these findings suggest that variability observed in the stratigraphic geomorphic and biologic archives of tectonically quiescent regions does not require external drivers such as geodynamic or climate forcing as is typically the interpretation rather my findings lead to a new model of inherently unsteady evolution of ancient mountain landscapes due to the geologic legacy of plate tectonics

on the dependence of boundary layer ventilation on frontal type 1 case study simulations with idealized tracers have been used to determine the relationship between the dynamics and conceptual representations of different midlatitude frontal systems and the amount distribution and time scale of boundary layer ventilation by these systems the key features of ventilation by a kata and ana cold frontal system are found to be quantitatively and also often qualitatively similar to the main ventilation pathways which are the conveyor belts cloud head and other convection the conveyor belts and cloud head occur within cloud implying that they can be identified using satellite imagery differences in the transport by the two systems can be related to their conceptual representations and include a sensitive dependence on the diurnal cycle for the kata but not the ana cold frontal case

transient landscape dynamics across the southeastern australian escarpment passive margin escarpments provide some of the best examples for large scale transient landscape evolution despite the relative simplicity of their geological setting when compared with active orogenic systems many open questions exist concerning their modes and rates of evolution we use catchment wide denudation rates calculated from cosmogenic nuclides concentrations and high resolution topographic analysis to constrain landscape dynamics across the south eastern australian escarpment we determined denuda tion rates of 15 mm ka in the lowlands at the foot of the escarpment and of 10 mm ka in the highlands while catchment draining the escarpment face display rates in the 20 60 mm ka range these denudation rates along a passive margin escarpment are among the highest in the world and show greater sensitivity to topographic gradients when compared to other passive margin settings we interpret this situation as resulting from the intermediate precipitation regime of our study area as opposed to drier or wetter settings where hillslope processes can be inhibited due to water availability or deep weathering profiles and vegetation feedbacks respectively combined with the extraction of topographic metrics across the escarpment these rates allow us to constrain efficiency coefficients for fluvial incision and hillslope diffusion that are similar to other independent estimates in this region these coef corresponding author ficients are used to calculate an escarpment retreat rate of 40 to 80 mm ka over the last 100s of ka our analysis of high resolution hillslope morphological properties suggests widespread small scale disequilibrium across this landscape illustrating the pervasiveness of transience across all spatial scales in this geomorphological setting

fluvial landscape response time how plausible is steady state denudation whether or not steady state topography and denudation are probable states depends on the timescale of system response to tectonic and climatic perturba tions relative to the frequency of those perturbations this paper presents analytical derivations of algebraic relations for the response time of detachment limited fluvial bedrock channel systems both to tectonic and climatic perturbations detachment limited fluvial erosion is described by the stream power incision model and the derivations are limited to the applicability of that model all factors likely to influence system response time that are not adequately captured by the stream power incision model will tend to increase the response time the calculations presented thus provide minimum estimates of landscape response time and therefore over predict the prob ability of attaining and sustaining steady state topography and denudation the central range of taiwan is used as a case study to estimate response times in a landscape often argued to be in steady state model parameters are fit to modern stream profiles by assuming that the topography represents a quasi steady state form estimated response times generally range from 0 25 to 2 5 ma depending on the non linearity of the incision rule and the magnitude and type of perturbation thus it may be reasonably argued that steady state topography and denudation are likely to prevail during periods of climatic stability response time is sufficiently short compared with plate tectonic timescales however rapid climatic fluctuation in the quaternary appears to preclude the attainment of steady state conditions in modern orogens motivation

reply to comments by david m schultz on cloud resolving model simulations of multiply banded frontal clouds october a 2005 131 2617 2637

stream capture as driver of transient landscape evolution in a tectonically quiescent setting we use unique fluvial gravel deposits preserved atop a regional drainage divide to confirm the role of stream capture in driving 250 m of incision in the transient roanoke river basin of the appalachian mountains united states gravel provenance constrains the pre capture position of the divide indicating that 225 km 2 of basin area were abruptly connected to the base level of the capturing stream the resulting wave of incision is currently manifest as major knickzones separating adjusting reaches from relict headwaters resembling streams of the new river basin from which the roanoke river was captured the unusual preservation of the unconsolidated gravels on small relict surfaces adjacent to bedrock gorges indicates extreme spatial variability in erosion rates within the roanoke basin which is the first documented example of a transient passive margin basin connected to a capture event by stranded fluvial debris our results show the potential for stream capture across an asymmetric drainage divide to drive major transient incision independent of external forcings such as climate change or tectonic uplift a continuation of this process will lead to eventual capture of 7000 km 2 of the new river basin in the relatively near geologic future

the sting at the end of the tail damaging winds associated with extratropical cyclones strong surface winds often accompany the low level jets that occur along the cold fronts of extratropical cyclones but there is evidence that the strongest surface winds occur in a distinctly different part of a certain class of cyclone the most damaging extratropical cyclones go through an evolution that involves the formation of a bent back front and cloud head separated from the main polar front cloud band by a dry slot when the cyclone attains its minimum central pressure the trailing tip of the cloud head bounding the bent back front forms a hook which goes on to encircle a seclusion of warm air the most damaging winds occur near the tip of this hook the sting at the end of the tail observations of the great storm of october 1987 in south east england are re examined in some detail to study this phenomenon the cloud head is shown to have a banded structure consistent with the existence of multiple mesoscale slantwise circulations air within these circulations leaves the hooked tip of the cloud head and enters the dry slot much faster than the rate of travel of the cloud head tip implying rapid evaporation and diabatic cooling immediately upwind of the area of damaging surface winds the circumstantial evidence from the observational study leads one to hypothesize that the mesoscale circulations and the associated evaporative heat sinks may play an active role in strengthening the damaging winds regardless of how important this role may be the evolution of the cloud pattern seen in satellite imagery is a useful tool for nowcasting the occurrence and location of the worst winds copyright 2004 royal meteorological society

exploring fractionation models for martian magmas 1 martian primary compositions i e magmas that did not experience fractionation and or contamination after extraction from the mantle occur as a subset of martian meteorites and a few lavas analyzed on the planet s surface by rovers eruptions of primary magmas are rare on earth and presumably on mars previous studies of fractional crystallization of martian primary magmas have been conducted under isobaric conditions simulating idealized crystallization in magma chambers polybaric fractionation which occurs during magma ascent has not been investigated in detail for martian magmas using the melts algorithm and the pmelts revision we present comprehensive isobaric and polybaric thermodynamic calculations of the fractional crystallization of four primary or parental martian magmas humphrey fastball y 980459 shergottite and nakhlite parental melts using various pressure temperature paths oxygen fugacities and water contents to constrain how these magmas might evolve we then examine whether known martian alkaline rock compositions could have formed through fractional crystallization of these magmas under the simulated conditions we find that isobaric and polybaric crystallization paths produce similar residual melt compositions but given sufficient details we may be able to distinguish between them we calculate that backstay gusev crater likely formed by fractionation of a primary magma under polybaric conditions while jake m gale crater may have formed through melting of a metasomatized mantle crustal assimilation or fractional crystallization of an unknown primary magma the best fits for the backstay composition indicate that consideration of polybaric crystallization paths can help improve the quality of fit when simulating liquid lines of descent

the role of mesoscale instabilities in the sting jet dynamics of windstorm tini sting jets sj occur as an additional region of low level strong winds in some shapiro keyser type extra tropical cyclones while sjs are widely accepted as being distinct from the warm and cold conveyor belts the mechanisms responsible for their occurrence are still not fully understood here we determine the relative importance of the release of mesoscale instabilities and synoptic scale cyclone dynamics so addressing an area of current debate numerical weather prediction simulations of a sj containing windstorm are analysed and lagrangian trajectories used to assess the evolution of and mesoscale atmospheric instabilities e g symmetric and inertial instabilities in the descending airstream the sj undergoes a two stage descent cooling via sublimation followed by a large acceleration accompanied by instability release combined tilting and stretching of vorticity play a major role in the local onset of instability on the airstream vorticity and frontogenesis fields have a narrow slantwise banded structure in the cloud head and around the sj the descending sj modifies the widespread frontolysis expected from the large scale dynamics alone in the frontal fracture region a coarser resolution simulation also generates strong winds in the frontal fracture region although these are significantly weaker than in the higher resolution simulation the sj airstream in the coarser resolution simulation undergoes a weaker descent without instability generation and descends in a widespread frontolytic region hence while the sj undergoes a process of destabilisation that enhances its descent and acceleration in the higher resolution simulation enhancing the strong winds already generated by the synoptic scale cyclone dynamics this destabilisation does not occur in the sj produced by a coarser resolution simulation resulting in weaker winds this analysis reveals the synergy between the paradigms of sj occurrence through the release of mesoscale instabilities and synoptic scale cyclone dynamics and demonstrates that the current debate may in part be a consequence of the model resolutions used by different studies

cloud top striations above ana cold frontal circulations satellite images occasionally show regular arrays of cloud top striations within mesoscale cloud features associated with vigorous ana cold frontal circulations observational case studies with a variety of types of radar are presented to show that the striations are due to bands of upright upper level convective cells these convective cells form at the top of the rearward sloping ascent part of a transverse frontal circulation which in one of the cases studied had a multi layered structure fed in turn by upright line convection lifting air from the boundary layer this coexistence and interdependence of upright and slantwise forms of convection may not in itself be uncommon what is less usual in these results is the way in which the upper level convection is manifested as bands or striations orientated roughly parallel to the wind shear at cloud top level but almost perpendicular to the strong thermal wind shear in the underlying frontal zone a behaviour that may be specific to vigorous ana cold frontal systems the striations have a large wavelength 30 to 55 km but we are unaware of any simple dynamical mechanism that can account for the convection being organized on this scale the striations are regarded as an important indicator of accompanying adverse weather earlier studies have suggested that such striations are associated with rapid cyclogenesis and surface gusts one of the cases presented here falls into this category the other more detailed case study is notable for the rainfall associated with the vigorous frontal circulations copyright 2002 royal meteorological society

a new theory of the origin and evolution of the deccan traps india abstract the deccan traps india represent one of the largest continental flood basalts and its origin and phases of evolution have remained puzzling for the earth science community an integrated analysis of available geochronological geochemical and geophysical data of post mesozoic volcanism clearly rejects the dominating theory of origin from a hot spot e g la reunion at about 23 s 55 e in the indian ocean the deccan traps show imprints of three events belonging to a worldwide peak magmatism series matching with a galactic catastrophism cyclicity of 33 m y study further reveals that the deccan magmas were not directly derived by the partial melting of the deep mantle but appear to have their origin at a depth of less than 40 km as a consequence of crustal rifting and secondary melting caused by the rise of geoisotherms due to frictional heating generated at the lithospheric asthenospheric boundary during india s fast south north journey from antarctica

escarpment retreat in sedimentary tablelands and cuesta landscapes landforms mechanisms and patterns abstract although the general concept that escarpments in layered rocks retreat through time was offered more than 150 years ago recognizing the exact mechanisms patterns and rates of retreat remains a challenge in this paper we provide the state of the art of the theme of escarpment retreat reviewing both the classic contributions often forgotten but important case studies and the latest research in separate parts of the paper we discuss 1 terminology applied to the geomorphology of escarpments 2 the main assumptions and pathways of long term evolution of escarpments including conceptual models presented so far 3 processes involved in cliff retreat mainly weathering mass movements and erosion 4 the role of spring erosion and fluvial processes leading to fluvial dissection and development of canyons present in many tablelands 5 the possible role of climate change in escarpment evolution 6 rates of escarpment retreat in conclusions we summarize the major advances in our understanding of escarpment evolution of the last two three decades such as the recognition of the key role of emerging groundwater in non uniform escarpment retreat of an important role of silica dissolution and underground removal of dissolved solids increasing appreciation of rock properties in governing the patterns of escarpment retreat the proposal that cliffs do not necessarily retreat via catastrophic rock slope failures but may disintegrate in situ and the first attempts to date escarpment retreat using cosmogenic isotopes finally the remaining gaps and possible research priorities for the future are identified

shrinking and splitting of drainage basins in orogenic landscapes from the migration of the main drainage divide climate and in particular the spatial pattern of precipitation is thought to affect the topographic and tectonic evolution of mountain belts through erosion numerical model simulations of landscape erosion controlled by horizontal tectonic motion or orographic precipitation result in the asymmetric topography that characterizes most natural mountain belts and in a continuous migration of the main drainage divide the effects of such a migration have however been challenging to observe in natural settings here i document the effects of a lateral precipitation gradient on a landscape undergoing constant uplift in a laboratory modelling experiment in the experiment the drainage divide migrates towards the drier leeward side of the mountain range causing the drainage basins on the leeward side to shrink and split into smaller basins this mechanism results in a progressively increasing number of drainage basins on the leeward side of the mountain range as the divide migrates such that the expected relationship between the spacing of drainage basins and the location of the main drainage divide is maintained i propose that this mechanism could clarify the drainage divide migration and topographic asymmetry found in active orogenic mountain ranges as exemplified by the aconquija range of argentina

pattern and tempo of great escarpment erosion extensive geological geophysical structural and geochronological data suggest that the locations of great escarpments bordering passive margins are exceptionally stable and are probably determined by crustal structure together the data do not support the established paradigm of ongoing significant and parallel escarpment retreat rather thermochronologic data and sedimentary sequences in ocean basins suggest that initial tectonically controlled rift escarpments undergo rapid and significant erosion only during the earliest stages of seafloor spreading development of stable passive margin escarpments follows this period of intense erosion escarpments increase in sinuosity as embayments retreat more rapidly than interfluves measurements of 24 escarpments suggest that sinuosity and the rate at which it increases depends upon the location of maximum uplift the geometry of the preescarpment drainage system and margin age all data suggest that the location of passive margin escarpments does not change significantly over time

rate and processes of river network rearrangement during incipient faulting the case of the cahabon river guatemala deeply incised river networks are generally regarded as robust features that are not easily modified by erosion or tectonics although the reorganization of deeply incised drainage systems has been documented the corresponding importance with regard to the overall landscape evolution of mountain ranges and the factors that permit such reorganizations are poorly understood to address this problem we have explored the rapid drainage reorganization that affected the cahabon river in guatemala during the quaternary sediment provenance analysis field mapping and electrical resistivity tomography ert imaging are used to reconstruct the geometry of the valley before the river was captured dating of the abandoned valley sediments by the be 10 al 26 burial method and geomagnetic polarity analysis allow us to determine the age of the capture events and then to quantify several processes such as the rate of tectonic deformation of the paleovalley the rate of propagation of post capture drainage reversal and the rate at which canyons that formed at the capture sites have propagated along the paleovalley transtensional faulting started 1 to 3 million years ago produced ground tilting and ground faulting along the cahabon river and thus generated differential uplift rate of 0 3 0 1 up to 0 7 0 4 mm y 1 along the river s course the river responded to faulting by incising the areas of relative uplift and depositing a few tens of meters of sediment above the areas of relative subsidence then the river experienced two captures and one avulsion between 700 ky and 100 ky the captures breached high standing ridges that separate the cahabon river from its captors captures occurred at specific points where ridges are made permeable by fault damage zones and or soluble rocks groundwater flow from the cahabon river down to its captors likely increased the erosive power of the captors thus promoting focused erosion of the ridges valley fill formation and capture occurred in close temporal succession suggesting a genetic link between the two we suggest that the aquifers accumulated within the valley fills increased the head along the subterraneous system connecting the cahabon river to its captors and promoted their development upon capture the breached valley experienced widespread drainage reversal toward the capture sites we attribute the generalized reversal to combined effects of groundwater sapping in the valley fill axial drainage obstruction by lateral fans and tectonic tilting drainage reversal increased the size of the captured areas by a factor of 4 to 6 at the capture sites 500 m deep canyons have been incised into the bedrock and are propagating upstream at a rate of 3 to 11 mm y 1 deepening at a rate of 0 7 to 1 5 mm y 1 at this rate 1 to 2 million years will be necessary for headward erosion to completely erase the topographic expression of the paleovalley it is concluded that the rapid reorganization of this drainage system was made possible by the way the river adjusted to the new tectonic strain field which involved transient sedimentation along the river s course if the river had escaped its early reorganization and had been given the time necessary to reach a new dynamic equilibrium then the transient conditions that promoted capture would have vanished and its vulnerability to capture would have been strongly reduced

the sting at the end of the tail model diagnostics of fine scale three dimensional structure of the cloud head this is the second in a series of papers on the sting at the end of the tail a mesoscale region of potentially damaging surface winds that can occur close to the evaporating tip of a cloud head wrapped around the bent back front of an extratropical cyclone in the first paper the sting phenomenon was identified from a purely observational study of the great storm of october 1987 in the present paper an observationally validated forecast run from a high resolution numerical weather prediction model is used to examine the evolving three dimensional structure of the sting phenomenon it is shown that the damaging surface winds in the october 1987 storm were due to a well defined mesoscale sting jet sj identifiable as a coherent ensemble of trajectories originating in cloudy air at about 650 hpa there is evidence of multiple mesoscale slantwise circulations and the sj appears to form within the descending part of these circulations air within the sj descends to the 900 hpa level over a period of about 4 h during which time it accelerates from less than 20 to above 45 m s 1 with extremes greater than 50 m s 1 although the wet bulb potential temperature of air in the sj remains constant during its descent to 900 hpa evaporation leads to a reduction of up to 5 k or more in dry bulb potential temperature in some parts of the jet the sj is situated behind the primary cold front and is distinct from the associated warm conveyor belt low level jet it is also distinct from the cold conveyor belt low level jet which remains below and behind it as the sj skirts the bent back front crown copyright 2005

a review of numerical modeling studies of passive margin escarpments leading to a new analytical expression for the rate of escarpment migration velocity abstract passive margins are geomorphological features that have historically attracted much attention from the modeling community in particular many numerical modeling studies have attempted to explain the longevity of steep escarpments that formed along continental edges at the transition between low elevation coastal plains and high elevation continental interiors such as along the coasts of africa and south america on both sides of the south atlantic ocean in this paper i review the wide and diverse body of observational constraints gathered to constrain the formation and evolution of passive margins escarpments as well as the various mechanisms that have been proposed to explain their anomalously high topography i then compile and summarize the findings of numerous numerical modeling studies that have been performed in the past twenty years to explain their formation and evolution i show that many of these studies converged to agree that the longevity of passive margin escarpments depends on how rapidly they become and remain regional drainage divides and that this is primarily controlled by the flexural isostatic rebound associated with the erosion of the high elevation continental interior to better quantify these findings i derive and present a new analytical expression for the migration velocity of an escarpment once it has become a drainage divide this expression is validated by a series of numerical experiments using 1d and 2d high resolution landscape evolution models interestingly these models also predict that the rate of erosion at or near escarpments can be several orders of magnitude smaller than the rate of escarpment retreat this may explain the apparent discrepancy between the low estimates of present day erosion rates obtained mostly from cosmogenic nuclide studies 10m myr and the long term rates of escarpment retreat 1km myr

coupled numerical analytical approach to landscape evolution modeling the earth s topography is shaped by surface processes that operate on various scales in particular river processes control landscape dynamics over large length scales whereas hillslope processes control the dynamics over smaller length scales this scale separation challenges numerical treatments of landscape evolution that use space discretization large grid spacing cannot account for the dynamics of water divides that control drainage area competition and erosion rate and slope distribution small grid spacing that properly accounts for divide dynamics is computationally inefficient when studying large domains here we propose a new approach for landscape evolution modeling that couples irregular grid based numerical solutions for the large scale fluvial dynamics and continuum based analytical solutions for the small scale fluvial and hillslope dynamics the new approach is implemented in the landscape evolution model dac divide and capture the geometrical and topological characteristics of dac s landscapes show compatibility with those of natural landscapes a comparative study shows that even with large grid spacing dac predictions fit well an analytical solution for divide migration in the presence of horizontal advection of topography in addition dac is used to study some outstanding problems in landscape evolution i the time to steady state is investigated and simulations show that steady state requires much more time to achieve than predicted by fixed area calculations due to divides migration and persistent reorganization of low order streams ii large scale stream captures in a strike slip environment are studied and show a distinct pattern of erosion rates that can be used to identify recent capture events iii three tectono climatic mechanisms that can lead to asymmetric mountains are studied each of the mechanisms produces a distinct morphology and erosion rate distribution application to the southern alps of new zealand suggests that tectonic advection precipitation gradients and non uniform tectonic uplift act together to shape the first order topography of this mountain range copyright 2014 john wiley sons ltd

super mobility of hot indian lithosphere negi j g pandey o p and agrawal p k 1986 super mobility of hot indian lithosphere tectonoph vsics 131 147 156 the great mobility of the indian subcontinent during the last 180 million years 9000 km of south north motion with an anticlockwise rotation of about 60 o has long been a major puzzle for theorists of plate tectonics a relative analysis of the available heat flow data the estimated temperature depth regime of india and the gravity anomalies reveals that the indian lithosphere does not have the characteristics of a typical shield zone and that it has higher radioactivity smaller viscous drag decidedly low viscosity of 10 p lower density and a well defined low velocity zone as compared to other shield areas of the world these factors appear to contribute significantly to the faster northward movement of the thin indian lithosphere as compared to the almost immobile african plate

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

modeling the evolution of loess covered landforms in the loess plateau of china using a dem of underground bedrock surface the evolution of loess covered landforms is largely controlled by the pre quaternary underlying bedrock terrain which is one of the most important factors in understanding the formation mechanism of the landforms this study used multiple data sources to detect 1729 outcropping points of underlying terrain in order to construct a digital elevation model dem of the paleotopography of an area of the loess plateau subject to severe soil erosion four terrain characteristics including terrain texture slope gradient the hypsometric curve and slope aspect were used to quantify topographic differences and reveal the loess deposition process during the quaternary a loess thickness map was then created to show the spatial distribution of loess deposits in the test area finally the geomorphological inheritance characteristics of the loess covered landforms were evaluated in different landform divisions the results showed the significant inheritance of modern topography from the underlying topography with a similar general relief trends the average thickness of loess deposits was computed to be 104 6 m with the thickest part located in the xifeng loess tableland area in addition the slope aspects of the north and northwest seem to have favored quaternary loess deposition which supported the hypothesis of an eolian origin for loess in china the modem surface has lower topographic relief compared to the underlying terrain due to loess deposition crown copyright c 2013 published by elsevier b v all rights reserved

scape charts from numerical weather prediction model fields abstract although the scape concept is strictly only meaningful for quasi two dimensional flows it can be given a precise definition for flows satisfying the conditions governing the semigeostrophic approximation for this type of balanced flow it is argued that scape corresponds to the positive area on the tephigram when the environment curve defines the thermodynamic state along a semigeostrophic vortex line a procedure for the calculation of scape as a numerical model diagnostic is described and is applied to an operational model analysis prior to the great storm which struck southern england on 16 october 1987 values of scape greater than 1000 j kg 1 are found over a large area near the embryo storm since the degree of slantwise stability or instability is widely considered to be relevant to the intensity of cyclogenesis and rainband formation scape charts may be of some utility to the bench forecaster

tectonic and climatic controls on rift escarpments erosion and flexural rebound of the dhofar passive margin gulf of aden oman we investigate the respective roles of climatic parameters and the flexural rigidity of the lithosphere in the erosion history and behavior of two adjacent rift escarpments along the northern coast of the gulf of aden in oman at this 25 myr old passive margin we define a type 1 scarp which is high sharp crested and has retreated 25 30 km inland from its master fault and a type 2 scarp which exhibits a more rounded profile lower relief and still coincides with its mapped normal fault trace since about 15 ma the margin has been seasonally affected by monsoon precipitation but with contrasting effects at the type 1 and type 2 escarpments depending on the position of the intertropical convergence zone in the geologic past during peak monsoon conditions both scarps experienced heavy rainfall and runoff whereas during monsoon starved conditions such as today the type 2 scarp experienced a foggy moist climate while the type 1 scarp remained much drier in order to assess the relative effects of climate and flexural parameters on the present day morphology of the dhofar margin we present onedimensional numerical models of erosion and flexure along two profiles representative of the type 1 and type 2 scarps unlike most surface process models previously published where present day topography is the only criterion by which to evaluate the quality of model outputs model behavior here is additionally constrained by independent estimates of denudation provided by geological cross sections well defined fault traces and other stratigraphic markers the best fitting models indicate that the type 1 escarpment formed under relatively arid climatic conditions and was affected by significant erosion recession and flexural uplift due to a low 7 km effective elastic thickness in contrast the morphology of the type 2 fault scarp was smoothed by a more humid climate but a high effective elastic thickness 15 km prevented it from uplifting or receding in addition we show that the sedimentary load acting at the foot of the escarpments exerts significant influence on their morphological evolution though this parameter is often neglected in other scarp evolution models

continental rifting and drainage reversal the clarence river of eastern australia the clarence river on australia s east coast has an anomalous drainage pattern its right bank tributaries are markedly barbed suggesting reversal whereas tertiary volcanism has disrupted its left bank drainage the southeast flowing clarence is closely aligned with the northwest flowing condamine river just across the continental divide the condamine clarence alignment is continued by a large southern tributary the orara river which flows northwest away from the sea to meet the southeast flowing clarence a broad river with a quite different character flows east from near the orara clarence junction to the sea this is essentially an overflow channel this series of aligned streams the condamine clarence orara represents the remains of an earlier northwest flowing stream that extended the full length of the clarence moreton basin an eastern extension of the great artesian basin during the jurassic the clarence moreton basin was filled with sediments from the surrounding highlands including those to the east of the present coastline continental rifting from late cretaceous times onwards led to the opening of the tasman sea causing the reversal and beheading of the original northwest flowing streams and the formation of the great escarpment the evolution of the clarence river does not fit into most conventional geomorphic paradigms such as cycles climatic geomorphology or steady state landforms it is the result of a succession of unique events on a very long timescale and as such is a classic example of evolutionary geomorphology

erosional dynamics flexural isostasy and long lived escarpments a numerical modeling study erosional escarpments are common features of high elevation rifted continents fission track data suggest that these escarpments form by base level lowering and or marginal uplift during rifting followed by lateral retreat of an erosion front across tens to hundreds of kilometers previous modeling studies have shown that this characteristic pattern of denudation can have a profound impact upon marginal isostatic uplift and the evolution of offshore sedimentary basins yet at present there is only a rudimentary understanding of the geomorphic mechanisms capable of driving such prolonged escarpment retreat in this study we present a nonlinear two dimensional landscape evolution model that is used to assess the necessary and sufficient conditions for long term retreat of a rift generated escarpment the model represents topography as a grid of cells with drainage networks evolving as water flows across the grid in the direction of steepest descent the model accounts for sediment production by weathering fluvial sediment transport bedrock channel erosion and hillslope sediment transport by diffusive mechanisms and by mass failure numerical experiments presented explore the effects of different combinations of erosion processes and of dynamic coupling between denudation and flexural isostatic uplift model results suggest that the necessary and sufficient conditions for long term escarpment retreat are 1 incising bedrock channels in which the erosion rate increases with increasing drainage area so that the channels steepen and propagate headward 2 a low rate of sediment production relative to sediment transport efficiency which promotes relief generating processes over diffusive ones 3 high continental elevation which allows greater freedom for fluvial dissection and 4 any process including flexural isostatic uplift that helps to maintain a drainage divide near an escarpment crest flexural isostatic uplift also facilitates escarpment retreat by elevating topography in the vicinity of an eroding escarpment thereby increasing channel gradients and accelerating erosion which in turn generates additional isostatic uplift of all the above conditions high continental elevation is common to most rift margin escarpments and may ultimately be the most important factor

attribution of strong winds to a cold conveyor belt and sting jet a high resolution version of the wrf weather research and forecasting model has been used to study the fine structure of a cloud head and its associated cold conveyor belt jet cj and sting jet sj in an intense extratropical cyclone that produced damaging surface winds in northern ireland and central scotland on 3 january 2012 the model was run with many different initialisation times and physical parametrisations and a run was selected that verified well against a variety of observations new methods have been devised to visualise the 3d structure of the cj and sj and to attribute strong surface winds to one or other of them and the validity of regarding the sj as a semi lagrangian feature has been assessed the model suggests that whereas the cj remained mainly below the 850hpa level as it circulated around the bent back front the sj consisted of a stream or streams of air within the bent back frontal zone that first ascended from close to the surface into the middle and upper level parts of the cloud head before descending from evaporating cloud filaments at the tip of the cloud head and reaching the top of the boundary layer slightly ahead of the cj the simulations did not support the idea that either the evaporation or conditional symmetric instability csi played a major role in the development of these jets the strong gusts up to 47ms 1 w hich were recorded on the north coast of ireland appear to have been due mainly to the cj which by then was undercutting the sj the sj was responsible for stronger surface winds than the cj several hours earlier during the initial stage of frontal fracture but only for a limited period

stacked slantwise convective circulations it is well known that classical ana cold fronts tend to be characterized by mesoscale circulations in which upright line convection feeds a layer of concentrated rearward slantwise ascent occasionally however as in the case study presented in this paper two and sometimes more of these mesoscale circulations coexist within the same cold frontal zone the two slantwise circulations described were observed to be stacked one above the other with a vertical wavelength of less than 2 km although it is often suspected that the circulations at ana cold fronts are enhanced by mesoscale processes such as conditional symmetric instability csi or m adjustment it is notoriously difficult to discriminate between these circulations and the larger scale transverse circulation within which they are embedded the occurrence in this study of multiple circulations with small vertical scale helps to distinguish them from the large scale circulation and this has motivated the detailed examination of this case mesoscale circulations of the kind described are difficult to detect numerical weather prediction nwp models even high resolution models do not usually represent them and conventional observations do not show them clearly this study takes advantage of observations from a high resolution microwave doppler radar plus a high resolution analysis of ultra high frequency wind profiler radar data analysed in the context of output from an operational mesoscale nwp model the study defines the mesoscale structure of the event sufficiently carefully to provide a basis for future idealized modelling studies to investigate the possible roles of csi and m adjustment both of which appear to play a part in the maintenance of the circulations

dynamic reorganization of river basins river networks evolve as migrating drainage divides reshape river basins and change network topology by capture of river channels we demonstrate that a characteristic metric of river network geometry gauges the horizontal motion of drainage divides assessing this metric throughout a landscape maps the dynamic states of entire river networks revealing diverse conditions drainage divides in the loess plateau of china appear stationary the young topography of taiwan has migrating divides driving adjustment of major basins and rivers draining the ancient landscape of the southeastern united states are reorganizing in response to escarpment retreat and coastal advance the ability to measure the dynamic reorganization of river basins presents opportunities to examine landscape scale interactions among tectonics erosion and ecology

numerical modeling of fluvial strath terrace formation in response to oscillating climate many river systems in western north america retain a fluvial strath terrace rec ord of discontinuous downcutting into bedrock through the quaternary their importance lies in their use to interpret climatic events in the headwaters and to determine long term incision rates terrace formation has been ascribed to changes in sediment supply and or water discharge produced by late quaternary climatic fluctuations we use a one dimensional channel evolution model to explore whether temporal variations in sediment and water discharge can generate terrace sequences the model includes sediment transport vertical bedrock erosion limited by alluvial cover and lateral valley wall erosion we set limits on our modeling by using data collected from the terraced wind river basin two types of experiments were performed constant period sinusoidal input histories and variable period inputs scaled by the marine 18 o rec ord our simulations indicate that strath terrace formation requires input variability that produces a changing ratio of vertical to lateral erosion rates straths are cut when the channel floor is protected from erosion by sediment and are abandoned and terraces formed when incision can resume following sediment cover thinning high sediment supply promotes wide valley floors that are abandoned as sediment supply decreases in contrast wide valleys are promoted by low effective water discharge and are abandoned as discharge increases widening of the valley floors that become terraces occurs over many thousands of years the transition from valley widening to downcutting and terrace creation occurs in response to subtle input changes affecting local divergence of sediment transport capacity formation of terraces lags by several thousand years the input changes that cause their formation our results suggest that use of terrace ages to set limits on the timing of a specific event must be done with the knowledge that the system can take thousands of years to respond to a perturbation the incision rate calculated in the field from the lowest terrace in these systems will likely be higher than the rate calculated by using older terraces because the most recent fluvial response in the field is commonly downcutting associated with declining sediment input since the last glacial maximum this apparent increase in incision rates is observed in many river systems and should not necessarily be interpreted as a response to an increase in rock uplift rate

the impact of deformation strain on the formation of banded clouds in idealized modelling experiments experiments are performed using an idealized version of an operational forecast model to determine the impact on banded frontal clouds of the strength of deformational forcing low level baroclinicity and model representation of convection line convection is initiated along the front and slantwise bands extend from the top of the line convection elements into the cold air this banding is attributed primarily to m adjustment the cross frontal spreading of the cold pool generated by the line convection leads to further triggering of upright convection in the cold air that feeds into these slantwise bands secondary low level bands form later in the simulations these are attributed to the release of conditional symmetric instability enhanced deformation strain leads to earlier onset of convection and more coherent line convection a stronger cold pool is generated but its speed is reduced relative to that seen in experiments with weaker deformational strain because of inhibition by the strain field enhanced low level baroclinicity leads to the generation of more inertial instability by line convection for a given capping height of convection and consequently greater strength of the slantwise circulations formed by m adjustment these conclusions are based on experiments without a convective parametrization scheme experiments using the standard or a modified scheme for this model demonstrate known problems with the use of this scheme at the awkward 4 km grid length used in these simulations copyright 2008 royal meteorological society

the development of negative moist potential vorticity in the stratiform region of a simulated squall line abstract this paper presents evidence on the development of negative moist potential vorticity mpv or moist symmetric instability msi in the stratiform region of a midlatitude squall line based on a three dimensional 3d numerical simulation of a case that occurred on 10 11 june 1985 during the preliminary regional experiment for storm central pre storm the results show that the stratiform region though convectively stable to pure vertical displacement is considerably unstable to slantwise displacement along the system s broad front to rear ftr saturated ascending flow it is found that this instability evolves from boundary layer convective instability that has previously been removed by upright convection over the leading portion of the squall system the negative mpv in the stratiform region is mainly the result of upward and rearward transport of the low level convectively unstable air along the sloping ftr ascending flow and of processes that reverse the signs of both the convective stab

thermal evolution of the indian shield and its subjacent mantle abstract the estimate of the paleothermal state at 3 ga of the indian shield is deduced using pressure and temperature estimates from the mineral assemblages combined with models of the heat transport mechanism and depth distribution of radiogenic heat in the crust we find that at 3 ga ago the mean thermal gradient within the crust reduced heat flow and mean mantle temperature were 28 c km 1 08 h f u and 2350 c respectively

high moho temperature in the indian shield abstract moho temperatures in the indian shield region are estimated using step exponential and power law models of the depth variation of radiogenic heat with temperature dependent thermal conductivity the moho temperatures and heat flows are around 550 600 c and 0 8 hfu 33 mwm 2 in the southern part of the indian shield and 850 900 c and 0 95 hfu 40 mwm 2 in its northern part it is argued that such high temperatures and their lateral variations may contain signatures of deccan trap volcanism and himalayan orogeny the implications of the temperature estimates on some related crustal parameters viz p n wave velocity curie isotherm depth and melting point temperature at moho depth are also indicated

expression of active tectonics in erosional landscapes understanding the manner and degree to which topography in active mountain ranges reflects deformation of the earth s surface remains a first order goal of tectonic geomorphology a substantial body of research in the past decade demonstrates that incising channel systems play a central role in setting relationships among topographic relief differential rock uplift rate and climatically modulated erosional efficiency this review provides an introduction to the analysis and interpretation of channel profiles in erosional mountain ranges we show that existing data support theoretical expectations of positive monotonic relationships between channel steepness index a measure of channel gradient normalized for downstream increases in drainage area and erosion rate at equilibrium and that the transient response to perturbations away from equilibrium engenders specific spatial patterns in channel profiles that can be used to infer aspects of the forcing these aspects of channel behavior lay the foundation for a series of case studies that we use to illustrate how focused quantitative analysis of channel morphology can provide insight into the spatial and temporal dynamics of active deformation although the complexities of river response to climate lithology and uplift patterns mean that multiple interpretations of topographic data alone will always possible we show that application of stream profile analysis can be a powerful reconnaissance tool with which to interrogate the rates and patterns of deformation in active mountain belts

geothermal structure in a seismoactive region of central india the geothermal structure beneath a seismoactive region of central india has been determined by using two independent geophysical parameters i e p n velocity and curie point depth which are temperature dependent p n velocity has been determined by reanalyzing deep seismic sounding dss records obtained for this region surface heat flow has been computed using the p n velocity data from this region and found to be 55 5 mw m 2 curie point depths have been derived from the magnetic satellite data in this region and reveal an identical value of heat flow of around 56 4 mw m 2 we estimated temperatures of 600 700 c at a moho depth of 39 km by using surface heat flow ranging from 50 to 60 mw m 2 and a simple 1 d geothermal model the present study suggests the presence of a brittle ductile transition high strength zone ranging in depth from 20 to 35 km where the temperatures range from 350 to 550 c we also suggest that the nucleation of earthquakes in this region took place in a relatively high strength zone this is supported by the fact that the focal depths of all the recent earthquakes from 1978 to 2000 of magnitude 3 5 lie in this zone of high strength

parcel theory in three dimensions and the calculation of scape slantwise convective available potential energy scape is a measure of the degree to which the atmosphere is unstable to conditional symmetric instability csi it has until now been defined by parcel theory in which the atmosphere is assumed to be nonevolving and balanced that is two dimensional when applying this two dimensional theory to three dimensional evolving flows these assumptions can be interpreted as an implicit assumption that a timescale separation exists between a relatively rapid timescale for slantwise ascent and a slower timescale for the development of the system an approximate extension of parcel theory to three dimensions is derived and it is shown that calculations of scape based on the assumption of relatively rapid slantwise ascent can be qualitatively in error for a case study example of a developing extratropical cyclone scape calculated along trajectories determined without assuming the existence of the timescale separation show large scape values for parcels ascending from the warm sector and along the warm front these parcels ascend into the cloud head within which there is some evidence consistent with the release of csi from observational and model cross sections this region of high scape was not found for calculations along the relatively rapidly ascending trajectories determined by assuming the existence of the timescale separation

observational synthesis of mesoscale structures within an explosively developing cyclone an observational case study is presented of a rapidly developing uk cyclone on 30 october 2000 to reveal the rich diversity of coexisting mesoscale structures in the vicinity of the cloud head dry slot and polar front cloud band the mesoscale structures include multiple rain bands due to upright convection originating in the boundary layer stacked slantwise convective circulations at middle levels cloud top striations due to upright convection originating at high levels above the polar front cloud band multiple sub structure within the cloud head and inertia gravity waves in the region of the tropopause fold the emphasis of the analysis synthesis is on the inter relationships between the various mesoscale structures issues raised by this study include i the interaction between upright and slantwise convection including the effects of evaporation in the dry slot ii the possible roles of inertia gravity waves and conditional symmetric instability in triggering organizing the dry slot convective rain bands and the sub structure within the cloud head and iii the relationship between the dry slot rain bands and the multiple structures within the cloud head this study is limited to documenting these relationships controlled experiments with high resolution mesoscale models will be required to establish cause and effect and to assess their importance copyright 2005 royal meteorological society

in situ low relief landscape formation as a result of river network disruption the relict landscapes of southeast tibet are being formed in situ as a result of river drainage reorganization that renders rivers unable to balance tectonic uplift so these landscapes may not provide an unaltered record of past geomorphic conditions high elevation low relief surfaces or relict landscapes are generally thought to be uplifted old landscapes that preserve past tectonic and environmental conditions rong yang et al have tested current models of landscape evolution using digital topographic analysis of so called relict landscapes in southeast tibet and yunnan province china dramatic scenery boasting up to 3 km of relief encompassing the gorges of the yangtze mekong and salween rivers they find that the region may not provide an unaltered record of past geomorphic conditions rather these landscapes form in situ as a result of river drainage reorganization that renders rivers unable to balance tectonic uplift landscapes on earth retain a record of the tectonic environmental and climatic history under which they formed landscapes tend towards an equilibrium in which rivers attain a stable grade that balances the tectonic production of elevation and with hillslopes that attain a gradient steep enough to transport material to river channels equilibrium low relief surfaces are typically found at low elevations graded to sea level however there are many examples of high elevation low relief surfaces often referred to as relict landscapes1 2 or as elevated peneplains3 these do not grade to sea level and are typically interpreted as uplifted old landscapes preserving former more moderate tectonic conditions4 here we test this model of landscape evolution through digital topographic analysis of a set of purportedly relict landscapes on the southeastern margin of the tibetan plateau one of the most geographically complex climatically varied and biologically diverse regions of the world we find that in contrast to theory the purported surfaces are not consistent with progressive establishment of a new steeper river grade and therefore they cannot necessarily be interpreted as a remnant of an old low relief surface we propose an alternative model supported by numerical experiments in which tectonic deformation has disrupted the regional river network leaving remnants of it isolated and starved of drainage area and thus unable to balance tectonic uplift the implication is that the state of low relief with low erosion rate is developing in situ rather than preserving past erosional conditions

on the interpretation of the distinctive pattern of geomagnetic induction observed in northwest india the geomagnetic variation data from the 1979 indian array experiment have been reanalyzed and reexamined using the hypothetical event analysis technique the contour map of the z h ratio replicates distinctive anomaly in northwest india previously delineated in maps of the fourier coefficients the anomaly reveals the presence of a significant conductor under the ganga basin the contour map has been used to derive a response profile perpendicular to the strike of the anomaly for comparison with 2 d numerical models an excellent fit was found for a conductor at a depth of 32 km with a width of 110 km and a conductivity contrast of 1000 this result places the conductor deep within the lithosphere in the absence of supporting data the origin of the conductor is difficult to resolve however it is thought to be related to pressure released partial melting caused by fracturing of the indian crust during the collision of india with asia

delineation of intra crustal horizon in eastern dharwar craton an aeromagnetic evidence abstract a correlative study of two mutually independent geophysical properties like magnetic susceptibility variations and shear wave velocity structure of the crust has been carried out in a part of the eastern dharwar craton of indian peninsular shield analysis of the aeromagnetic anomaly field over an area of 35 000 km 2 comprising the peninsular gneissic basement complex and a part of cuddapah basin has resulted in identification of two distinct magnetic horizons one at a depth of 2 km and the other at a depth of 12 km correlation of these results with the inferences made by the inversion of rayleigh wave phase velocity and other geophysical studies has confirmed the presence of a crustal layer at a depth of 12 km this horizon has been inferred to be the depth to the lower boundary of the upper crust in this region

tectonics and thermal structure of western satpura india abstract increased seismicity and occurrences of hot springs having surface temperature of 36 58 c are observed in the central part of india 74 81 e 20 25 n where the ne trending middle proterozoic aravalli mobile belt meets the ene trending satpura mobile belt earlier deep seismic sounding dss studies along thuadara sendhwa sindad profile in the area has showed mesozoic sediments up to around 4 km depth covered by deccan trap and the moho depth with a boundary velocity p n of 8 2 km s in the present study surface heat flow of 48 4 mw m 2 has been estimated based on p n velocity which agrees with the value of heat flow of 52 4 mw m 2 based on curie point isotherms estimates the calculated temperature depth profile shows temperature of 80 120 c at the basement which is equivalent to oil window temperature in mesozoic sediments and around 570 635 c at moho depth of 38 43 km and the thermal lithosphere is about 110 km thick which is comparatively higher than those of adjoining regions the present study reveals the brittle ductile transition zone at 14 41 km depth temperature around 250 600 c where earthquake nucleation takes place

switching between alternative responses of the lithosphere to continental collision summary we study possible responses to arc continent or continent continent collision using numerical models our short term integration models show that the initial stage of deformation following continental collision is governed by the competition between three potential weakness zones 1 mantle wedge 2 plate interface and 3 lower continental crust depending on which of these is the weakest zone in the system three different responses can be recognized 1 subduction polarity reversal 2 continuation of subduction and 3 delamination and back stepping subduction polarity reversal occurs if the mantle wedge is the weakest zone in the system this happens only if the viscosity of the mantle wedge is at least one order of magnitudelowerthantheaverageviscosityofthelithosphere incontinent continentcollision one additional condition needs to be satisfied for subduction polarity reversal to occur for the subducting lithosphere the ratio of the viscosity of the lower continental crust to the viscosity of the upper lithospheric mantle must be equal to or higher than 0 006 the time required for polarity reversal depends on several parameters the convergence rate the sinking velocity of the detached slab and the relative strength of the mantle wedge arc and backarc the response to collision is continued subduction if the plate interface is the weakest zone and is delamination and back stepping if the lower continental crust is the weakest area in the system our finding that a low viscosity wedge is a prerequisite for a reversal of subduction polarity agrees with inferences about regions for which subduction polarity reversal has been proposed

persistent drainage migration in a numerical landscape evolution model 1 numerical landscape evolution models driven by uniform vertical uplift often develop a static drainage network and a precise balance between uplift and erosion small scale physical models of uplifting drainage basins however continually reorganize by ridge migration and do not reach an ideal steady state here i show that the presence or absence of persistent drainage migration in a bedrock numerical landform evolution model depends on the flow routing algorithm used to determine upstream contributing area the model version that uses steepest descent routing achieves an ideal steady state while the model version that uses bifurcation routing results in continually evolving drainage basins even under conditions of uniform vertical uplift bedrock erodibility precipitation and landsliding threshold this result suggests that persistent drainage migration can occur by erosional processes alone this result has important implications for numerical modeling methodology our understanding of the natural variability of landform evolution and the interpretation of thermochronological data

evolution of a cold front encountering steep quasi 2d terrain coordinated aircraft observations on 8 9 december 2001 during improve 2 abstract research aircraft observations from the 8 9 december 2001 case of the second phase of the improvement of microphysical parameterization through operational verification experiment improve 2 describe the evolution of a wide cold frontal rainband wcfr during its eastward advance from the pacific coastline to a point 200 km inland over the cascade mountains of oregon this analysis has two objectives first to illustrate the rapid weakening of the circulation associated with a landfalling wcfr and the relationship of these changes to terrain induced airflow modifications and second to quantify the degree to which this weakening impacted cloud microphysical properties such as liquid water content ice particle concentrations and precipitation rate the kinematic structure of the wcfr is detailed using doppler radar observations from a noaa p 3 aircraft while some concomitant cloud microphysical properties are documented using flight level measurements from the university of washington convai

the root of branching river networks models and field measurements together show that the branching patterns of fine scale river networks are the result of coupled instabilities in the erosional processes that drive valley incision the mechanisms that create the familiar patterns seen in branching river networks are poorly understood here the authors use a simple numerical model together with field measurements to establish that the branching patterns of fine scale river networks are the result of coupled instabilities in the erosion processes involved in valley widening and channel incision this means that river networks are not a consequence of random topology but of erosional mechanics and the branching patterns can provide information about the geological and environmental conditions during their formation branching river networks are one of the most widespread and recognizable features of earth s landscapes and have also been discovered elsewhere in the solar system1 2 but the mechanisms that create these patterns and control their spatial scales are poorly understood theories based on probability3 4 5 or optimality3 6 7 8 have proven useful9 but do not explain how river networks develop over time through erosion and sediment transport here we show that branching at the uppermost reaches of river networks is rooted in two coupled instabilities first valleys widen at the expense of their smaller neighbours and second side slopes of the widening valleys become susceptible to channel incision each instability occurs at a critical ratio of the characteristic timescales for soil transport and channel incision measurements from two field sites demonstrate that our theory correctly predicts the size of the smallest valleys with tributaries we also show that the dominant control on the scale of landscape dissection in these sites is the strength of channel incision which correlates with aridity and rock weakness rather than the strength of soil transport these results imply that the fine scale structure of branching river networks is an organized signature of erosional mechanics not a consequence of random topology

uplift histories from river profiles 1 longitudinal river profiles where elevation of a river bed is plotted as a function of distance along the river bed contain information about uplift rate when a region adjacent to a reference level e g sea level is uplifted a rapid change in gradient occurs near the river mouth the erosional process causes this change in gradient to migrate upstream thus a river profile is effectively a tape recording of the uplift rate history provided that the erosional process can be adequately parameterized here we use a non linear equation to relate the shape of a river profile z x to uplift rate history u t if erosion is assumed to be dominated by knickpoint retreat an inverse model can be formulated and used to calculate uplift rate histories our model builds upon standard stream profile analysis which focuses on the relationship between profile slope and drainage area we have applied this analytical approach to river profiles from the bie dome angola calculated uplift rate histories agree with independent geologic estimates

solutions of the stream power equation and application to the evolution of river longitudinal profiles 1 erosion by bedrock river channels is commonly modeled with the stream power equation we present a two part approach to solving this nonlinear equation analytically and explore the implications for evolving river profiles first a method for non dimensionalizing the stream power equation transforms river profiles in steady state with respect to uniform uplift into a straight line in dimensionless distance elevation space second a method that tracks the upstream migration of slope patches which are mathematical entities that carry information about downstream river states provides a basis for constructing analytical solutions slope patch analysis explains why the transient morphology of dimensionless river profiles differs fundamentally if the exponent on channel slope n is less than or greater than one and why only concave up migrating knickpoints persist when n 1 at migrating knickpoints slope patches and the information they carry are lost a phenomenon that fundamentally limits the potential for reconstructing tectonic histories from bedrock river profiles stationary knickpoints which can arise from spatially varying uplift rates differ from migrating knickpoints in that slope patches and the information they carry are not lost counterparts to migrating knickpoints called stretch zones are created when closely spaced slope patches spread to form smooth curves in distance elevation space these theoretical results are illustrated with examples from the california king range and the central apennines

magsat data and curie depth below deccan flood basalts india ground and airborne magnetic data are severely disturbed due to random susceptibility variations in deccan flood basalts however magnetic satellite magsat data over the deccan flood basaltic region of the indian subcontinent exhibit filtering of surficial noise three passes over deccan traps show a low at about 20 n latitude and a high at about 23 n latitude spectral analysis of these passes and an available 2 d magsat vertical intensity map indicate a deep 40 4 km magnetic interface it is interesting to note that the determination of curie depth from magsat matches and confirms the geothermal data model the estimates correspond to the moho depth derived from gravity and deep seismic sounding studies the study suggests a continental shield like geothermal gradient of about 14 c km below the area

comments on cloud resolving model simulations of multiply banded frontal clouds by m pizzamei s l gray and k a browning october a 2005 131 2617 2637

magsat scalar anomaly map of india and a part of indian ocean magnetic crust and tectonic correlation magnetic scalar anomaly maps over india and a part of the indian ocean are prepared from the magsat data using an average of the observed field in a grid of 1 1 the magsat scalar anomaly map thus obtained is characterised by highs over the indian shield and large lows over the himalayas centered over tibet plateau a ne sw magnetic trend emanating from ne india and spreading almost over the entire peninsular shield is the single most prominent feature of the map which might be related to the stress system or deepseated structural trends associated with plate motion the deccan traps are reflected by nosing of the magnetic contours the shillong massif is characterised by a separate anomaly which deflects the ne sw magnetic trend referred to above a magnetic crustal map prepared from this magsat scalar anomaly using the principles of harmonic inversion yields a thickness of 30 km under the cambay basin and the western part of the narmada son lineament for a magnetization of 2a m suggesting a higher subsurface thermal gradient in this area and therefore a tectonically active region a maximum thickness of 40 42 km is found under the regions of aravallis singhbhum and south of the narmada son lineament which are precambrian stable cratons major lineaments and faults are reflected as variations in the thickness of the magnetic crust along these lines the himalayas are chaaracterised by an average thickness of 35 36 km with a thickening of 2 4 km under the tibet plateau and shillong massif the magsat anomaly in the northern part of the indian ocean can be accounted for by a thickening of 8 km in the magnetic crust the center of this crustal thickening derived from the magsat anomaly after appropriate correction for the inclination of the earth s magnetic field in this region coincides with the wellknown indian ocean gravity and geoid lows

a statistical framework to quantify spatial variation in channel gradients using the integral method of channel profile analysis 1 we present a statistical technique for analyzing longitudinal channel profiles our technique is based on the integral approach to channel analysis drainage area is integrated over flow distance to produce a transformed coordinate which has dimensions of length assuming that profile geometry is conditioned by the stream power law defined as e kamsn where e is erosion rate k is erodibility a is drainage area s is channel gradient and m and n are constants the slope of a transformed profile in elevation space should reflect the ratio of erosion rate to channel erodibility raised to a power 1 n this quantity is often referred to as the channel steepness and represents channel slope normalized for drainage area our technique tests all possible contiguous segments in the channel network to identify the most likely locations where channel steepness changes and also identifies the most likely m n ratio the technique identifies locations where either erodibility or erosion rates are most likely to be changing tests on a simulated landscape demonstrate that the technique can accurately retrieve both the m n ratio and the correct number and location of segments eroding at different rates where model assumptions apply tests on natural landscapes illustrate how the method can distinguish between spurious channel convexities due to incorrect selection of the m n ratio from those which are candidates for changing erodibility or erosion rates we also show how given erosion or uplift rate constraints the method can be used to constrain the slope exponent n

2 d inversion of geomagnetic deep sounding data near ujjain guna india summary the inductive response of a hypothesized conductor located between ujjain and guna india has been modelled in the absence of a satisfactory fit from forward numerical modelling 2 d inversion of the anomaly profile of z h ratio has revealed the main conductor to be situated below ujjain guna with an offset and another secondary conductor in the form of a jointed body the main conductor is at a depth of 23 km from the surface thickness being 20 km and the resistivity 3 m the jointed secondary conductors are at depths of 31 km and 28 km with thicknesses of 14 km and 21 km and resistivities 3 m and 5 m respectively the resistivity contrast with the background is a factor of 1600 or even slightly more the possibility of mineralization on the flanks of the subsurface granitic intrusion cannot be ruled out however partial melting of the subsurface granites seems to be another plausible explanation for the high conductivity contrast

airborne radar observations of a cold front during fastex1 abstract a detailed analysis using airborne doppler radars of an oceanic cold front associated with precipitation core and gap regions is presented the precipitation cores appear to form as a result of the combined effects of horizontal shearing instability and the advection of hydrometeors by the core relative winds in contrast to previous schematic models it is shown that a strong surface discontinuity does not exist along the entire length of the precipitation core the southern section of the core can be accompanied by an abrupt discontinuity and lighter precipitation while the northern section can be associated with more slowly changing variables but heavier precipitation the peak updrafts at the leading edge of the front appeared to be primarily driven by frictional convergence and the acceleration of the vertical vorticity in the boundary layer the overall motion of the cold front was not well predicted using density current theory even though the kinematic structure of the front resembled cla

lateral migration of hillcrests in response to channel incision in soil mantled landscapes 1 we investigate lateral migration of hillcrests in response to vertical offsets or transient incision rates of channels bordering these hillcrests in soil mantled landscapes for hillslopes undergoing sediment transport that is linearly proportional to the slope the hillcrest offset distance is one quarter of the ratio of the vertical offset between the channels to the relief of the symmetric hillslope if channels are downcutting at different rates the speed of hillcrest migration will depend on the ratio of the downcutting rates and the density ratio which is the ratio of the bulk density of the bedrock to the bulk density of the soil the density ratio plays a fundamental role in determining the transient response of the hillcrest lower density ratios lead to faster transient responses to changes in channel downcutting rates other parameters that affect the transient response of the hillcrest are the magnitude of transient differences in downcutting between the two channels the time averaged incision rate and a ratio of the elevation of the hillslope to a length that characterizes the decay in soil production with increasing soil thickness different parameters will be important for different sediment flux laws the profile of soil thickness reacts to transient changes in downcutting at a different rate than surface topography hillslopes experiencing transient channel downcutting may have surface topography that is symmetric about the hillcrest but will at the same time have a soil thickness profile that is asymmetric

evidence of transient topographic disequilibrium in a landward passive margin river system knickpoints and paleo landscapes of the new river basin southern appalachians the upper new river basin of the southern appalachian mountains a major tributary of the modern ohio river represents the unglaciated headwaters of the tertiary teays river system of eastern north america dating of relict fluvial gravels have suggested that new river incision may be outpacing lowering of the surrounding uplands but physical evidence of transient topographic disequilibrium has yet to be identified we use focused topographic analysis of the upper new river basin to delineate a perched low relief paleo landscape that is experiencing transgressive dissection due to incision by the new river and its tributaries accelerated incision has decoupled hillslopes from the drainage network generating knickpoints which represent the boundary between remnants of the paleo landscape and actively adjusting topography downstream steepening of hillslopes downstream of knickpoints suggests dynamic headward migration which along with knickpoint occurrence throughout the drainage network is inconsistent with the development of fixed stream profile convexities atop strike extensive geologic contacts in the absence of tectonic forcing we favor a climatically forced drop in external base level as driver of the incision pattern we observe plio pleistocene glacial damming and diversion of the teays river to form the modern ohio river lowered regional base level for the study area potentially forcing the paleo landscape developed during the teays era to adjust to the modern drainage pattern the upper new river may therefore represent the potential for glacially driven drainage rearrangement to drive transient topographic evolution hundreds of kilometers away from the ice margin long after the disappearance of ice sheets copyright 2013 john wiley sons ltd

the origin of large local uplift in extensional regions large localized uplift is commonly observed in continental regions undergoing extension these observations can be modelled by planar high angle normal faulting of an elastic upper crust overlying an inviscid lower crust isostasy provides the necessary driving force the model quantifies the role of flexural rigidity density variations in the crust and erosion and deposition of sediment

sting jets in extratropical cyclones a review this paper reviews the current state of knowledge of sting jets in extratropical cyclones sting jets were formally identified in 2004 by the pioneering work of keith browning reviewing this and subsequent studies we define the sting jet as a coherent air flow that descends from mid levels inside the cloud head into the frontal fracture region of a shapiro keyser cyclone over a period of a few hours leading to a distinct region of near surface stronger winds it therefore lies above the cold conveyor belt during some stage its life but at least in some cases descends to reach the top of boundary layer ahead of the cold conveyor belt it is not attributed to a specific mechanism in this definition we conclude that it is likely that a continuum of sting jet descent and speed up mechanisms exists at one extreme is balanced descent partly associated with frontolysis in the frontal fracture region more horizontally small scale and stronger frontolytic descent may occur associated with weak stability to slantwise convective downdraughts instability to slantwise convective downdraughts may occur in some systems leading to multiple slantwise convective downdraughts associated with the release of conditional symmetric instability and even possibly symmetric instability the global climatology of sting jets and the interaction between the atmospheric boundary layer and sting jets are revealed as specific areas where more research is needed finally we describe eight myths and misunderstandings that exist in the current literature with the aim of guiding future research into the sting jet phenomenon

evidence for nonlinear diffusive sediment transport on hillslopes and implications for landscape morphology steep soil mantled hillslopes evolve through the downslope movement of soil driven largely by slope dependent transport processes most landscape evolution models represent hillslope transport by linear diffusion in which rates of sediment transport are proportional to slope such that equilibrium hillslopes should have constant curvature between divides and channels on many soil mantled hillslopes however curvature appears to vary systematically such that slopes are typically convex near the divide and become increasingly planar downslope this suggests that linear diffusion is not an adequate model to describe the entire morphology of soil mantled hillslopes here we show that the interaction between local disturbances such as rainsplash and biogenic activity and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient our proposed transport law 1 approximates linear diffusion at low gradients and 2 indicates that sediment flux increases rapidly as gradient approaches a critical value we calibrated and tested this transport law using high resolution topographic data from the oregon coast range these data obtained by airborne laser altimetry allow us to characterize hillslope morphology at 2 m scale at five small basins in our study area hillslope curvature approaches zero with increasing gradient consistent with our proposed nonlinear diffusive transport law hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope such that large changes in erosion rate will correspond to small changes in gradient therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering where hillslope erosion is dominated by nonlinear diffusion rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient

climatic control of bedrock river incision bedrock river incision drives the development of much of earth s surface topography and thereby shapes the structure of mountain belts and modulates earth s habitability through its effects on soil erosion nutrient fluxes and global climate although it has long been expected that river incision rates should depend strongly on precipitation rates quantifying the effects of precipitation rates on bedrock river incision rates has proved difficult partly because river incision rates are difficult to measure and partly because non climatic factors can obscure climatic effects at sites where river incision rates have been measured here we present measurements of river incision rates across one of earth s steepest rainfall gradients which show that precipitation rates do indeed influence long term bedrock river incision rates we apply a widely used empirical law for bedrock river incision to a series of rivers on the hawaiian island of kaua i where mean annual precipitation ranges from 0 5 metres to 9 5 metres ref 12 over 70 per cent of the global range and river incision rates averaged over millions of years can be inferred from the depth of river canyons and the age of the volcanic bedrock both a time averaged analysis and numerical modelling of transient river incision reveal that the long term efficiency of bedrock river incision across kaua i is positively correlated with upstream averaged mean annual precipitation rates we provide theoretical context for this result by demonstrating that our measurements are consistent with a linear dependence of river incision rates on stream power the rate of energy expenditure by the flow on the riverbed these observations provide rare empirical evidence for the long proposed coupling between climate and river incision suggesting that previously proposed feedbacks among topography climate and tectonics may occur