laboratory simulation of clast abrasion brewer paul lewin j 2002 laboratory simulation of clast abrasion earth surface processes and landforms 27 pp 145 164 rae2008

backthrusting in accretionary wedges backthrusting of the rear of the accretionary wedge arcward over the rocks of the forearc basin is a common aspect of accretionary tectonics an older assumption that backstops of accretionary wedges dip back toward the arc and that accreted material is emplaced below such backstops is contradicted by observations from many active forearcs that indicate 1 backthrusting is common 2 forearc basins are nearly ubiquitous associates of accretionary wedges and 3 forearc basement where imaged appears to diverge from the sedimentary package dipping under the wedge while the overlying sediments are often lifted up against it backthrusting may be favored where relief is high between the crest of the wedge and the surface of the forearc basin because the relief must be supported by shear stress along the backthrust we find ratios of lt lb averaging 2 64 0 8 where lt is the horizontal distance from the crest of the wedge to the front of the toe and lb is the distance from the crest of the wedge to the surface projection of the backthrust this ratio is predicted to increase with total convergence and with sedimentation because the toe undergoes higher deformation rates than the backthrust and sedimentation in the trench favors outbuilding of the toe whereas sedimentation in the forearc basin tends to cancel the gravitational component of the driving stress for the backthrust

quantitative roundness analysis of coastal boulder deposits abstract the sedimentology of coastal boulder deposits cbd is little known these deposits and especially the largest clasts within them which commonly weigh many 10s of tonnes are of increasing interest because they attest to extreme energy wave events acting well above the high tide mark in some cases 40 m above high water and 100 m inland recent observations have made clear that storm waves rather than tsunami are important in both creating and activating these deposits but beyond that we know little about their hydrodynamics or the relative frequency of boulder movement and how this might vary with topographic setting roundness is a first order characteristic that preserves a record of deposit reworking it can tell us whether clasts move around much after they have been created from bedrock or whether they are emplaced into cbd with little or no subsequent transport but because roundness has historically been difficult to measure most roundness estimates in the literature are based on qualitative visual assessment and are therefore of limited analytical value fully reproducible roundness measurements are possible however and in the case of boulders they can be acquired quite easily using the kirkbride 2005 device in combination with a trigonometric formula presented here cbd at locations in ireland and scotland provide a test case demonstrating the utility of quantitative boulder roundness measurements the 567 clasts we measured are generally angular but a substantial proportion shows some degree of rounding most importantly there are demonstrable consistent patterns relating topography and roundness there is a strong and unsurprising inverse correlation between clast roundness and deposit elevation there is no first order relationship between roundness and inland distance but there is a power law inverse relationship between rounding and steepness ratio of elevation to distance inland the greatest degree of rounding is found in cbd located at the back of gentle coastal platforms with gradual slopes these relationships provide new insights into cbd sedimentology which we hope will be probed and tested in future studies

impressive abrasion rates of marked pebbles on a coarse clastic beach within a 13 month timespan abstract in this paper the abrasion rate on a coarse clastic beach was evaluated by calculating the volume loss recorded on indigenous pebbles within a 13 month timespan the experiment was carried out at marina di pisa italy on an artificial beach that was built to counteract the erosion processes affecting this sector of the coast a total of 240 marble pebbles 120 rounded and 120 angular were marked using the rfid technology and injected on the beach the volume loss measured after consecutive recovery campaigns was progressively increasing reaching the maximum value after 13 months 61 overall the average volume loss is consistent between rounded and angular pebbles at any time 59 3 and 64 2 after 13 months respectively meaning that the roundness is not a primary control factor on abrasion rate the pebbles that did not reach such abrasion rates after 8 and 10 months volume loss less than 20 were found at heights equal or greater than 2 m above mean sea level on the crest of the storm berm that formed during the strongest storms this implies that the highest wearing is achieved in the lower portion of the backshore which is also the area that underwent major topographic modifications here sea water action might also exert chemical influence on the pebbles adding to the mechanical abrasion the main result of this research indicating an impressive volume loss on beach pebbles in a short timespan could be of key importance for coastal managers the optimization of coarse sediment beach nourishments is also relevant taking into right consideration that the volume loss due to sediment abrasion might exceed 50 of the original fill volume just after 1 year in the most dynamic portion of the beach

deformation and sedimentation along a developing terrane suture eastern sunda forearc indonesia the collision of the eastern sunda arc with northwest australia has resulted in the development of a suture between the sumba ridge and sawu timor terranes along a zone of intraforearc convergence the developing suture varies from the low angle sawu thrust with attendant mud diapirs in the sumba basin to high angle reverse faults near a basement high of the underthrust sumba ridge terrane bottom currents associated with the flow of pacific ocean deep water into the indian ocean have eroded the terranes and subsequently deposited the detritus in an assemblage of contourites along the suture this study reveals the high structural variability of a terrane suture and the oceanographic influence on the deposition of overlap assemblages

tectonic history of sumba island indonesia since the late cretaceous and its rapid escape into the forearc in the miocene abstract the island of sumba lies within the sunda banda forearc and contains volcanic plutonic and volcaniclastic rocks that record a history of arc volcanism extending from late cretaceous 80 ma or earlier to oligocene 31 ma time during the late cretaceous sumba formed part of a great indonesian volcanic arc system near southeastern eurasia between late cretaceous and early miocene time sumba remained part of that arc system which ceased to be volcanically active by 31 ma during the late miocene 18 ma sumba as part of the relict arc system was situated near the present site of alor and wetar at 16 ma sumba was torn from the relict arc and began to move at a velocity of 50 mm yr in a west south westerly direction volcanism along the modern banda arc soon followed by 7 ma sumba finally came to rest after having moved 450 km into the forearc we interpret the rapid motion of sumba into the forearc as a discrete block to have been a response to the collision between australia and indonesia in the area of timor the savu basin possibly originated as an arc crestal rift which then opened behind sumba as the latter moved westward over the past 16 my more than 3 km of sediment have been deposited in the savu basin by erosion from the surrounding islands sumba stopped moving to the west south west at 7 ma after reaching approximately its present location since then the island has ceased to be a discrete tectonic fragment and has behaved as an integral part of the forearc during the past 7 my compressional tectonics within the forearc has led to elevation of the rocks exposed on sumba by as much as 4 km

high resolution fluvial records of holocene environmental changes in the sahel the yame river at ounjougou mali west africa abstract the yame river in the bandiagara plateau dogon country mali is characterised by extensive alluvial sedimentary records particularly in the 1 km long ounjougou reach where holocene floodplain pockets are inset in the pleistocene formations these alluvial records have been investigated via geomorphologic fieldwork and sedimentologic and micromorphologic analyses and are supported by 79 radiocarbon dates the alluvial deposits of the valley floor correspond to a vertical accretion of 3 10 m the reconstruction of fluvial style changes provides evidence of four main aggradation periods from 11 500 to 8760 cal bp the alluvial architecture and grain size parameters indicate a wandering river this period included phases of pulsed high energy floods and avulsion related to a northward shift of the summer monsoon to around 14 n after 11 500 cal bp from 7800 to 5300 cal bp a swampy floodplain environment with standing water pools within a sudanian savanna woodland mosaic corresponds to the culmination of the holocene humid period from 3800 cal bp onwards rhythmic sedimentation attests to an increase in the duration and or intensity of the dry season giving a precise date for the local termination of the holocene optimum period during the last two millennia and for the first time during the holocene the alluvial formations are progressively restricted whereas the colluvial deposits increase indicating strong soil erosion and redeposition within the watershed related to an increase in human impact four major periods are characterised by incision i1 ante 11 500 i2 8760 7800 i3 6790 6500 cal bp i4 2400 1700 cal bp pointing to dramatic changes in fluvial style they result from high energy flood flows during dry spells and confirm the capacity of the floodplain pocket in the upstream reach of the sahelian belt to record rapid holocene climatic change

on the profile evolution of three artificial pebble beaches at marina di pisa italy abstract in this paper the profiles of three artificial coarse grained beaches located at marina di pisa tuscany italy were monitored from april 2008 to may 2009 in order to define the response of the beaches to major storms that occurred during the study two beaches are similar the third differs in length and in the level of protection being less than half the length of the others and devoid of an offshore submerged breakwater the work was achieved by means of accurate topographic surveys intended to reconstruct the beach profile from the backshore up to the foreshore upper shoreface transition step the surveys were performed with an rtk gps instrument which provided extremely precise recording of the beach the most significant features of the beaches were tracked during each survey in particular the landward foot of the storm berm the crest of the storm berm the coastline and the step crest were monitored five cross shore transects were traced on each beach along these transects any meaningful slope change was recorded to obtain accurate sections of the beach the field datasets were processed with autocad software to compare the beach profile evolution during the year long research the results showed a comparable evolution of the twin beaches the resulting storm berm retreat of about 15 to 19 m is a remarkable feature considering the coarse grain size and the offshore protection due to the absence of the breakwater the third beach was characterized by even higher values of recession over 20 m and showed hints of wave reflection related processes after the huge steep storm berm had been formed and grown after the high energy events these processes were not as evident on the twin beaches these results underline the different response of three similar protection schemes and the importance that frequent monitoring of the beach morphology holds when it comes to coastal management issues

thermal history of australian passive margin cover sequences accreted to timor during late neogene arc continent collision indonesia abstract paleotemperature indicators and apatite fission track analysis of australian continental margin cover sequences accreted to the active banda arc continent collision indicate little to no heating during rapid late neogene uplift and exhumation thermal maturation patterns of vitrinite reflectance conodont alteration and illite crystallinity show that peak paleotemperatures ppt increase with stratigraphic and structural burial the highest ppt is found in the northern hinterland of the accretionary wedge which was beneath progressively thicker parts of the upper plate towards the north major discontinuities in the pattern of ppt are associated with the position of major thrust ramps such as those forming the ramelau kekneno arch rka ppt for upper triassic to neogene strata south of the rka are 60 80 c which are similar to and in many cases lower than correlative and age equivalent units drilled on the nw australian shelf permian to lower triassic sedimentary strata thrust over younger units within and north of the rka have ppt of 100 220 c thrust sheets accreted beneath the upper plate have ppt approximately 90 c higher than those frontally accreted metamorphism of the northernmost units of these sequences yield ppt of 300 c thrust stacking yields an inverted thermal profile of ppt decreasing discontinuously downward and to the south towards the foreland the timing of ppt is constrained by apatite fission track ages from mostly triassic continental margin cover sequences ages of upper triassic units are primarily coeval with deposition and show little evidence of thermal annealing whereas those of lower triassic units are almost completely annealed and range from 1 8 0 5 19 2 9 7 ma the clustering of apatite fission track ages into two distinct groups indicates that the upper boundary of the partial annealing zone has remained for some time at a triassic stratigraphic interval in the slope and rise of the nw australian continental margin the position of this zone on the present shelf is higher in the stratigraphic column due to the greater thickness of post breakup shelf facies units thrust stacking of rise slope and shelf units produces an inverted vertical profile of increasing apatite fission track age with depth lack of any long confined track lengths in apatite from all of the units requires rapid and recent exhumation of the thrust stack which is coincident with rapid phases of pliocene pleistocene exhumation documented throughout timor these data preclude pre late miocene tectonic burial or pre pliocene exhumation of the nw australian continental margin

bottom current controlled sand deposits a review of modern shallow to deep water environments abstract different examples of modern marine sand accumulations generated or strongly influenced by the action of bottom currents are here presented they are drawn from a variety of tectonic and morphological settings and grouped into three water depth zones deep water 2000 m mid water 300 2000 m and outer shelf upper slope 50 300 m deposits in the first two of these depth zones are normal contourites according to their original definition heezen and hollister 1971 being those sediments that have been transported and deposited by contour currents in deep water environments those deposited at shallower depths under the influence of surficial geostrophic currents combined with other hydrodynamic factors shelf currents induced by wind tide and waves gyres internal waves etc are more properly referred to as outer shelf upper slope bottom current sands or shallow water bottom current sands we have elaborated a facies model for each bathymetric zone deep water sandy contourites are relatively rare thin and very thin bedded highly bioturbated and mainly of bioclastic composition they are interbedded with muddy contourites and pelagites or in some areas with turbidites in the latter case thin bottom current reworked sandy tops of turbidites provide a different and distinct facies mid water sandy contourites are more common ranging up to a metre in thickness and may form extensive sandy sheets in a variety of slope bank and channel settings they are mainly of mixed siliciclastic bioclastic composition typically bioturbated and associated with muddy silty contourites in coarsening up fining up complete or truncated sequences shallow water bottom current sands occur in particular outer shelf upper slope settings where they may develop relatively thick 1 20 m laterally extensive sheets covered by fields of sandwaves megaripples and ribbons internal structures may be preserved along with much bioturbation their composition varies from mainly siliciclastic to bioclastic and they may be interbedded with both inner shelf facies and slope hemipelagites the principal factors that control the deposition of sandy contourites and shallow water bottom current sands are the hydrodynamic regime of the basin the availability of coarse grained sandy sediments and the physiographic context of the area swept by the currents the greater the depth the finer and rarer the bottom current or sandy contourite deposits global sea level and climatic changes and the time involved in the depositional history play an ultimate role in the development of important sand accumulations of this sort by controlling the ocean circulation pattern and its long term persistence from the present analysis we conclude that mid depth sandy contourites are the most commonly found in modern environments and that shallow water bottom current sands constitute the most significant potential oil reservoirs to be found in the geological record

longshore transport of cobbles on a mixed sand and gravel beach southern hawke bay new zealand abstract few large scale field measurements of longshore sediment transport have been undertaken on beaches composed of coarse sediments in part owing to difficulties associated with measurement in energetic swash zones in which large clasts are moving here we present results from a field experiment in which passive integrated transponder tags were used to investigate patterns of cobble transport over 8 months on a mixed sand and gravel beach on the east coast of new zealand the study objectives were to document rates of alongshore transport and measure rates of cobble abrasion under field conditions cobble recovery rates were highly variable over the study period with 30 60 recovery at site 1 compared to much lower 0 20 recovery rates at sites 2 and 3 consistent uni directional patterns of net alongshore sediment transport were observed the median cobble transport rate was approximately 500 m over 207 days indicating long term net northward transport rates on the order of 2 2 5 m day results highlight a number of factors in addition to longshore energy flux that are important for understanding the observed patterns in particular across shore sediment transport during storms may have been smaller at site 1 than the other sites owing to lesser wave exposure this is partly responsible for higher cobble recovery rates at this site and also an increased amount of time during which cobbles were able to be transported alongshore on the lower beachface unique to this study results demonstrate the use of pit tags to provide direct measurement of cobble abrasion under natural processes repeat weight measurement on individually tracked cobbles show that after 207 days the median loss was 11 3 g or 1 8 of total weight there was a general trend of abrasion increasing with net transport distance but longshore cobble movement was highly variable ranging from 130 to 2500 m

seismological evidence for shallow thrusting north of the timor trough summary the eastern sunda arc in indonesia is the site of subduction of the continental crust of australia and its shallow seismicity is manifested by infrequent large ms 7 earthquakes that occur near the volcanic arc within the upper plate rather than as interplate events beneath the forearc in the same region volcanic activity has ceased and small shallow earthquakes are rare we examine two of the larger earthquakes the events of 1962 may 15 ms 7 2 and 1977 august 27 ms 7 0 the 1977 event occurred north of central timor and the inversion of long period p and sh waves indicates a nearly pure thrust mechanism at a depth of 10 km below sea level and a seismic moment of 4 1 1026 dyne cm the p wave nodal planes for this solution strike roughly parallel to the mapped trace of a thrust zone the wetar thrust zone at the southern margin of the backarc basin and the south nodal dipping plane is consistent with the sense of thrusting on this thrust zone a broad zone of compressional deformation is evident in seismic reflection profiles over the epicentral region of the 1977 event and gravity data suggest that a small amount of either isostatically uncompensated crustal thickening or flexure of the underthrusting plate has occurred the 1962 earthquake occurred approximately 300 km north east of the 1977 earthquake and near the eastern end of the volcanically quiet section of the banda arc the similarity of the few available waveforms to those at the same stations for the 1977 event suggests a similar source mechanism modelling of pdif waveforms for the 1962 event indicates a depth of less than 40 km and a preferred centroidal depth of 20 km for which a seismic moment of 5 1026 dyne cm is estimated these fault plane solutions indicate that most of the seismic energy released by the collision between australia and the sunda arc is generated by faulting within the overriding plate and we infer that a major change in the plate geometry is imminent we suggest that most of the relative convergence between the plates is accommodated by thrusting of the marginal basin the banda sea southward beneath the arc and that the present geometry represents the initial stage of the reversal of the arc s polarity

slumping and sliding in miocene and recent developing arc basins onshore and offshore sumba indonesia abstract neogene slidemasses in eastern sumba are discussed and compared to neogene and quaternary analogues in seismic profiles from the offshore lombok and savu basins the onshore examples were deposited in deep marine base of slope environments within the reach of large amounts of clastics derived from a volcanic arc i e in a setting comparable to that of the recent slides onshore three types of slides are distinguished ranging from mud clast rich debris flows type 1 their possible seismic origin is discussed elongate lenticular slumps type 2 to over 100 m thick slide masses of intimately mixed and folded strata together with rafts of less deformed sediments type 3 the offshore analogues may be twice as thick both in the field and in the seismic profiles such slides are found at various superimposed levels five superimposed units can be distinguished in a seismic profile in the savu basin near the westernmost extension of the offshore sumba ridge a giant blocky slide occurs all slide masses are located on slopes with increasing gradients due to differential vertical movements tectonically induced oversteepening is therefore considered a main cause of failure in outcrops the upper surfaces of the slides are almost flat this contrasts with a hummocky topography seen in some of the offshore examples

late quaternary river development in the southwest chad basin osl dating of sediment from the komadugu palaeofloodplain northeast nigeria the komadugu river system is the major nigerian tributary to lake chad its large alluvial complex represents an important archive of the late quaternary environmental history of the chad basin modern floodplains are incised into an older fluvial terrace that extends over 5000 km2 evidence from satellite images suggests that the ancient river system was dammed up by the bama beach ridge during high stands of mega lake chad this caused the formation of extensive wetlands with a chaotic network of relic channels the first set of luminescence ages presented here fits well into the previously established environmental history of the chad basin both the early and mid holocene pluvial periods as well as a final relatively humid period during the late holocene are reflected by point bar to overbank deposits or channel fills the onset of the holocene was characterised by erosion of older dune fields as indicated by grain size distributions of the alluvium satellite images and sedimentological observations show that the floodplain was dominated by meandering channels shifted by frequent avulsion reflecting a high variability in precipitation and discharge patterns at the beginning and end of holocene humid periods copyright 2007 john wiley sons ltd

a submarine slide scar and channel filled with slide blocks and megarippled globigerina sands of possible contourite origin from the pliocene of sumba indonesia abstract early pliocene deep water sequences estimated depositional depth 1 2 km near kambatatana sumba island include a slide scar which evolved into a channel the channel measures over 120 m in width and 20 m in depth after an initial phase of sliding overall quiescene is marked by a burrowed surface the overlying fill consists of intimately associated current and slide deposits the former are characterized by climbing megaripples with set heights of 0 3 1 2 m indicating suspension rich currents these megaripples mainly consist of foraminiferal and washed out from pliocene pelagic chalks and marls mixed with some shallow water benthos the slide blocks display the lithology of the underlying pliocene sediment and vary in size from a few cm to 15 m some blocks underwent deformation during sliding whereas others retained their original shape comparison with data from analogous modern settings suggests that the channel was located at the transition between a relatively steep and more gentle submarine slope syntectonic deformation related to gradual uplift of sumba probably induced locally steeper slopes on the distal part of a sediment starved miocene turbidite fan which originally was inclined at an angle of around 2 the general slope during the pliocene is estimated to have been less 1 1 30 the origin of the megarippled foraminiferal sand units is uncertain but they may have been supplied by contour currents presently shaping parts of the seafloor morphology in this region

collisional melange development geologic associations of active melange forming processes with exhumed melange facies in the western banda orogen indonesia analysis of block assemblages matrix clay mineral composition and microfauna and offshore seismic reflection profiles reveal that the bobonaro melange in the timor region is sourced from mud rich australian continental margin sequences that are remobilized during accretion and form various facies depending on the structural conditions of emplacement melange facies include broken formation matrix rich mud injections and classic mixed block in clay facies each of these are distinguished by varying degrees of remobilization mixing and dispersion at different structural positions across the orogenic wedge the most important structural control is whether melange was generated beneath or in front of upper plate banda forearc basement banda terrane at the present collisional deformation front in the timor trough seismic reflection profiles show that melange forms mostly by stratal detachment and fluid assisted remobilization above a basal decollement propagating laterally along overpressured jurassic to cretaceous clay rich sequences of the distal australian continental margin the broken clay rich material injects upward through faults to form intrusive bodies at the base of slope cover sediment to form mud ridges at the surface similar patterns of stratal disruption are exposed onshore in the pliocene kolbano fold and thrust wedge of southern timor which is structurally contiguous with the timor trough deformation front melange in the kolbano mountains is mostly broken formation and matrix rich injections of mud from jurassic and cretaceous units deformation mechanisms include intense layer parallel extension associated with emplacement by mud diapirs that rise from near the decollement upward to the surface along fault conduits in the hinterland of the orogenic wedge east timor and northern west timor melange is dominantly of mixed block in clay facies with large blocks derived from roof thrust sheets of intermixed banda terrane and maubisse formation units at the structural base of these thrust sheets is the sonnebait disruption zone sdz which formed the initial suture between the banda terrane and structurally underthrust australian continental margin sequences during the late miocene to early pliocene the thickest accumulations of mixed block in clay melange in the timor region are found at the southern edge outlet of the sdz near the central and viqueque synorogenic basins the extent of block dispersion and mixing in the sdz is indicative of intense shear strains perhaps induced by an oversupply of accretable material when the suture zone was clogged by underthrusting of the australian continental margin

measuring pebble abrasion on a mixed sand and gravel beach using abrasion baskets abstract the abrasion of sediments on mixed sand and gravel beaches has important consequences for local sediment budgets as abrasion often accounts for the major loss of beach volume here we report an innovative method using abrasion baskets to measure abrasion in the swash zone of mixed sand and gravel beaches this method offers significant advantages over laboratory based tumbler experiments traditionally used to determine abrasion rates the very high recovery rate from our method is also a significant advantage over previous field methods using radio frequency identification technology to measure abrasion where tagged particles are often lost either three or five abrasion baskets were placed across the swash zone on a mixed sand and gravel beach at timaru south island new zealand to measure the abrasion occurring on labeled sediments placed in the baskets over two experiments results showed measurable abrasion across the swash zone with higher abrasion rates occurring in the middle of the swash zone and lower rates towards the swash limit and at the breaker zone results also illustrate the role of changing wave energy on abrasion loss a relationship between particle size and abrasion rate was also found similar to previous laboratory results reported in the literature our preliminary experiments lead us to define an abrasion zone and this idea may help shape future research on abrasion processes on mixed sand and gravel beaches

holocene lake mega chad palaeoshorelines from space during the holocene a giant lake known as lake mega chad lmc extended over more than 350 000 km2 in southern sahara morphodynamic features of sedimentary systems outlining the lmc palaeoshorelines have been identified by the joint analyses of new topographic images digital elevation model acquired by radar interferometry and landsat thematic mapper images here we characterize for the first time at the scale of the chad basin a wave dominated sedimentary system including river deltas longshore sandridges beach ridges spits and a wave ravinement surface they provide new evidence of the environmental impact of quaternary climate changes in the sahelo saharan area continental trade winds controlled the longshore drift in the northern part of the palaeolake two distinct lmc episodes dated as lower and middle holocene are clearly identified contemporaneous with the two phases of wetter conditions usually recognized in central and northern africa

the wetar back arc thrust belt eastern indonesia the effect of accretion against an irregularly shaped arc the 350 km long east west trending wetar back arc thrust belt in eastern indonesia is a result of the collision of australia with the indonesian island arc along the northwest margin of wetar island a short 50 km section of the thrust belt trends northeast coincident with the offset of the indonesian arc by the newly discovered left lateral wetar atauro fault which runs along the shelf region and trends northeast the wetar atauro fault may be viewed as a large scale lateral ramp or wrench fault separating the eastern wetar thrust belt from the western wetar thrust belt the interaction of strike slip faulting and back arc thrust faulting creates several arc blocks whose geometry strongly affects the structure of the deformed wedge of sediment accreting in the wetar back arc thrust belt the varying orientations of the arc backstop make the wetar back arc thrust belt a perfect laboratory for the study of oblique convergence along most of its length the wetar thrust belt parallels the arc slope however along the northeast trending offset in the thrust belt seamarc ii side scan sonar plus seismic reflection data show that the trend of the thrust belt is not parallel to the trend of the arc slope rather it is intermediate between the trend of the arc slope and the perpendicular to the expected convergence direction the side scan images allow us to map the geometry of four main thrust faults the wetar liran atauro and alor faults the wetar liran and atauro faults trend northeast parallel to the thrust front and do not have an en echelon relationship the westernmost fault in the survey area the alor fault trends almost east west the orientation of the wetar atauro fault is consistent with a maximum principal stress within the arc oriented between 8 and 23 west of north depending on the internal coefficient of friction this agrees well with the p axes of nearby earthquake focal mechanisms which trend consistently west of north suggesting that the regional principal tectonic compression is oriented west of north because the thrust belt is oblique to the arc slope we infer the structural directions are influenced by both the arc backstop and by the regional tectonic stress the tectonic compression due to arc continent collision in this region may be modified by the arc geometry in several ways 1 the stress necessary to support the arc topography may be significant close to the arc 2 the change in thickness of the elastic part of the lithosphere may cause a concentration of tectonic stress and 3 the difference in material properties between the relatively rigid arc bulldozer and the weak basin sedimentary fill may be an important factor in producing a thrust belt that conforms roughly to the shape of the arc the structure of the wetar back arc thrust zone demonstrates that the development of small rigid blocks within a major collision zone may produce complex structural patterns and local directions of shortening that are highly oblique to the main direction of plate convergence

rise and fall of the eastern great indonesian arc recorded by the assembly dispersion and accretion of the banda terrane timor abstract new age petrochemical and structural data indicate that the banda terrane is a remnant of a jurassic to eocene arc trench system that formed the eastern part of the great indonesian arc the arc system rifted apart during eocene to miocene supra subduction zone sea floor spreading which dispersed ridges of banda terrane embedded in young oceanic crust as far south as sumba and timor in timor the banda terrane is well exposed as high level thrust sheets that were detached from the edge of the banda sea upper plate and uplifted by collision with the passive margin of nw australia the thrust sheets contain a distinctive assemblage of medium grade metamorphic rocks overlain by cretaceous to miocene forearc basin deposits new u pb age data presented here indicate igneous zircons are less than 162 ma with a cluster of ages at 83 ma and 35 ma 40ar 39ar plateau ages of various mineral phases from metamorphic units all cluster at between 32 38 ma these data yield a cooling curve that shows exhumation from around 550 c to the surface between 36 28 ma after this time there is no evidence of metamorphism of the banda terrane including its accretion to the edge of the australian continental margin during the pliocene these data link the banda terrane to similar rocks and events documented throughout the eastern edge of the sunda shelf and the banda sea floor

holocene landscape evolution of the manga grasslands ne nigeria evidence from palaeolimnology and dune chronology this paper presents a synthesis of results from investigations into palaeolimnology and dune chronology in the manga grasslands and adjacent areas of ne nigeria in order to reconstruct the evolution of this semi arid landscape since the late glacial a marked wet phase gave way to a fall in lake levels during the late glacial dune emplacement was active at this time to the south of the manga grasslands but seems to have been absent from the grasslands themselves wet conditions prevailed during much of the early to mid holocene accompanied by periods of significant barchanoid dune reactivation a marked deterioration in climate and vegetation commenced around 4 1 ka bp leading to the formation of the present day semi arid landscape the data suggest that there have been major changes in humidity in this part of subsaharan west africa during the late glacial to holocene and that the relationship between changes in precipitation and aeolian activity is complex

fluvial system dynamics of sudano sahelian zone during the late holocene the yame river dogon country mali abstract in west africa most palaeoenvironmental studies have focused on the role of climatic change on the environment because of the richness of its deposits the yame river mali a tributary of the niger river offers an opportunity to reconstruct the evolution of this fluvial system in comparison with both climatic and anthropogenic changes during the late holocene to investigate more closely the spatio temporal response of the fluvial system sedimentary analyses were conducted on seven reaches distributed along the 137 km length of the yame valley this approach testifies of the possibility for each time slice and river reach 1 to reconstruct the fluvial style and processes and 2 to estimate the sediment storage volume reflecting sediment distribution patterns results reveal a wide variability of the sedimentary cascade suggesting contrasting responses to external and local controls humid 4200 2900 cal bp 450 24 cal bp or arid 2350 1700 cal bp phases have been recorded in fluvial archives while an intensification in erosion and sediment supplies even during the arid period 2900 2350 cal bp and the 20th century may be associated with an increase in human pressure two other periods are related to both climate and anthropogenic factors during 1700 1400 cal bp phase huge sediment supplies can be explained mainly by the reactivation of both hydrological processes and human occupation after an intense and long arid event dispersed sediment sinks recorded during the 450 24 cal bp period originate from the combination of intensification of colluvial processes and a wet phase context originating from global climatic change thus this study provides evidence that climate is the strongest driver for the fluvial response of these semi arid and tropical rivers while human disturbance appear as a secondary factor due to the high sensitivity of the environment to climate variability in such areas

seasonal patterns of coarse sediment transport on a mixed sand and gravel beach due to vessel wakes wind waves and tidal currents direct measurements of coarse sediment gravel transport are presented and analyzed from a mixed sand and gravel beach on bainbridge island puget sound wa that is exposed to wind waves vessel wakes and tidal currents in order to quantify the relative role of different forcing mechanisms and the corresponding time scales of morphological response radio frequency identification rfid passive integrated transponder pit technology is implemented in two coincident yearlong tracking studies of sediment particles and complemented with beach profile surveys and meteorological and hydrodynamic measurements the sampling of the gravel tracers provides sufficient resolution to reveal the dominant seasonal transport patterns which include a range of wave climates during winter storms the predominant transport is due to wind waves in an alongshore uni directional process whereas tides and wakes play a relatively minor role in non storm intervals transport is brought about by the combination of vessel wakes and tidal currents although tidal currents are not sufficient to initiate sediment movement alone the combination of tidal currents and vessel wakes generate significant transport and provide a mechanism for post storm recovery re distributing sediment onshore morphologic response occurs as a seasonal fluctuation of the upper beach profile from steep to flat and in sediment composition from gravel to coarse sand between non storm and storm conditions respectively these results which are unique in their duration suggest that mixed sand and gravel beaches experience different modes of behavior over the range of forcing conditions observed during a typical year they point to the need for including grain composition in modeling mixed sand and gravel beach response and the need for long term observations of both forcing and response

transport trajectories of smart pebbles on an artificial coarse grained beach at marina di pisa italy implications for beach morphodynamics abstract in this paper transport pathways for coarse sediments were studied on an artificial pebble beach located at marina di pisa tuscany italy radio frequency identification rfid technology was used to trace the pebbles the rfid technique is an inexpensive and reliable methodology that is used to address sediment displacement along the coastline the use of low frequency radio signals 125 khz enabled the detection of the marked pebbles within a range of 40 cm on the underwater and subaerial portions of the beach about one hundred pebbles were sampled on the beach and paired with passive transponders the tracers were released along a series of cross shore transects march 2009 the pebbles were injected on the fair weather berm on the swash zone and on the step crest along each transect the recovery campaign was carried out in may 2009 fifty three pebbles were detected this number is rather high given the intensity of the three storms that hit the coast during the period of the experiment and the significant reworking that this beach is subjected to even under fair weather conditions the analysis of the tracer pathways highlighted twofold convergent longshore movement on the beach the trajectories indicated that the longshore movement dominated the cross shore movement but there was no prevailing transport direction to explore the morphology of the sea bottom fronting the beach a topographic survey was carried out using an echo sounder the survey showed the presence of two distinct shoals 20 m off the coastline that are responsible for the resulting coarse sediment transport these results confirm that even mild sea bottom irregularities may significantly affect sediment transport dynamics along a beach suggesting that accurate planning for defense schemes such as artificial coarse replenishment must begin with an in depth knowledge of the morphology of the sea floor such information may increase the durability and or the efficiency of the intervention

abrasion model of downstream changes in grain shape and size along the williams river australia 1 modeling pebble abrasion during bed load transport is of fundamental importance in fluvial geomorphology as it may help to understand downstream fining patterns along gravel bed rivers here we review a recently published analytical abrasion model called box equations which can simultaneously track the shape and size evolution of large pebble populations as the cumulative effect of binary collisions between particles the model predicts that pebble shapes move away from the sphere and develop sharp edges due to collisional abrasion by sand we present a field study on the downstream evolution of basalt particle shape and size along the williams river in the hunter valley australia pebbles get flatter and thinner and several aquafacts i e abraded pebbles with sharp edges emerge in the downstream reaches both suggesting the importance of abrasion by sand applying box equations with a few fitted parameters we present a numerical simulation which reproduces both the shape and size evolution of pebbles along the williams river the simulation allows tracking of the shape and size evolution of individual particles as well revealing an interesting phenomenon that particle size controls shape evolution box equations in combination with existing transport concepts provide a framework for future shape and size evolution studies in sedimentary environments in particular they may help to assess the relative importance of size selective transport versus abrasion in causing downstream fining in gravel bed rivers

cenozoic evolution of the savu basin indonesia forearc basin response to arc continent collision abstract a seismo stratigraphic analysis of the savu basin relates the evolution of a complexly evolved forearc basin to the late miocene recent collision with australia initial early miocene subsidence of the outer forearc basin and the subsequent development of a middle late miocene volcanic proto arc located in the south of the basin both resulted from the late oligocene early miocene eastward propagation of the java timor trench block faulting of the relatively thick continental forearc basement probably determined the rather irregular and scattered pattern of middle late miocene volcanic centres just north of the accretionary prism the forearc basement is flexed down and reshaped into a trenchward dipping backstop that facilitates backthrusting of the accretionary prism the southern forearc basement probably acted as a barrier against compression the thickness of this continental basement is suggested to be a critical factor in the response of the forearc to continent collision owing to its strength the savu basin did not react to collision by the development of northward verging inter arc thrusts in contrast it responded to the underthrusting of continental crust by reactivation of the basement ridges this resulted in the differentiation of the forearc basin into a presently extinct and uplifted miocene south savu basin and a pliocene recent active north savu basin the simultaneous late miocene recent uplift of large segments of the outer forearc and subsidence of the north savu basin is interpreted to result from tectonic underplating of continental material and uplift caused by the buoyancy of the subducted continental crust the relatively recent decoupling of this crust from the oceanic slab and the subsequent isostatic rebound may superimpose the initial effects of post collision extension on arc continent collision

backstop geometry and accretionary mechanics of the sunda margin the convergent sunda margin off indonesia displays all geological features characteristic of an accretion dominated subduction zone a combined interpretation of prestack depth migrated seismic reflection data and velocity information gained from refraction studies is supplemented by high resolution bathymetric data and for the first time allows the exact mapping of backstop regimes initially the outer high evolved as material was pushed against a static rigid arc framework backstop underlying a forearc basin increasing material strength of the outer high due to lithification formed a dynamic backstop which controls accretion today an out of sequence thrust marks the transition from the recent active frontal accretionary prism to the outer high and may be traced in the seismic and bathymetric data over the whole extent of the study area the existence of a static as well as a dynamic backstop controls the forearc geometry and is associated with the segmentation of the forearc which is observed in regimes of frontal as well as of oblique subduction mass balance calculations which account for porosity changes and metamorphism indicate a subduction history dominated by accretionary processes since the late eocene accretion is associated with the low values of basal friction inferred for the sunda margin structural investigations of conjugate fault planes indicate a very weak basal detachment effective stress analyses reveal that intrinsically weak material causes the high strength ratio of the detachment to the overlying sediments whereas overpressuring within the frontal accretionary prism is negligible

the west pacific geodynamic model abstract between the asian and australian continents on the western side and the general subduction of the central pacific on the eastern side the west pacific presents two types of subduction towards the continents and towards the ocean as a consequence at the present day there are two main types of marginal seas the japan sea and the south china sea and in the geological past two types of orogenesis the japanese and the taiwanese types these are the models of the two main orogenic belts respectively the circum pacific and tethyan for a long period of the past the alps and the mediterranean sea were the tectonic model of reference however with the increase in geological studies oceanographic research geophysical surveying the west pacific gradually became an alternative model which grew more useful with each passing day the present day trench island arc marginal sea system appears to be a good model for the first stages of orogenic belts whereas the mountains of the east eurasian margins provide an example of the completion of formation of such belts the coexistence of different stages of mountain building is the main reason for the increasing interest shown by earth scientists in the west pacific

continental margin tectonics submarine accretionary prisms submarine accretionary prisms are sites of incipient mountain building where sediments and rocks of the deep ocean are uplifted deformed and ultimately transformed to continental crust accretionary prisms develop at sites of lithospheric convergence that is subduction zones commonly accretionary prisms form along continental margins although accretionary prisms may also occur adjacent to island arcs which are ultimately coalesced into continental landmasses here we review the studies of submarine accretionary prisms during the past four years with primary focus on the contributions of geoscientists from the united states

holocene fluvial dynamics in the ne nigerian savanna some preliminary interpretations abstract the development of the main northeast nigerian river complex the komadugu system is reconstructed and the possible relation to holocene environmental changes is investigated at this stage of research some field work concentrating on the lithostratigraphy of the alluvial deposits has been carried out along the middle and lower courses of the komadugu yobe and the komadugu gana and is supported by laboratory analyses of sediments and soils the data obtained so far confirm earlier suggestions that the alluvium can be distinguished into late holocene floodplain deposits and a wider fossilized terrace complex that may reflect a rather palustrine to lacustrine palaeoenvironment possibly related to the early and mid holocene lake megachad

radio frequency identification rfid technology applied to the definition of underwater and subaerial coarse sediment movement abstract in this paper radio frequency identification technology has been applied to track both underwater and subaerial displacement of pebbles along an artificial coarse beach at marina di pisa italy several preliminary laboratory tests have been performed to adapt the rfid technique for underwater use which has been the primary impediment to this promising approach to the study of coarse sediment transport and movement tests showed the reliability of low frequencies for this kind of work since they enable good signal transmission and reception through water passive abs plastic transponders were inserted into about 100 pebbles and released onto the beach in march 2009 a core 125 reader was chosen as the operating antenna to continuously transmit low frequency 125 khz signals an acoustic signal toned whenever a pebble was detected while the unambiguous identification code of the pebble is shown immediately on the screen of a laptop connected to the reader the positions of the pebbles were recorded with a total station after two months may 2009 74 marked pebbles were retrieved 77 of the total the positions of the retrieved pebbles were also recorded with the total station thus allowing calculation of the coarse sediment transport tendency about 60 of the recovered pebbles 44 out of 74 were found on the upper shoreface the analysis of the marked pebble trajectories revealed a divergent transport movement in the northernmost sector of the beach this movement was probably triggered by an irregularity of the submerged breakwater fronting the shoreline the southern sector is characterised by chaotic pathways related to the formation and evolution of beach cusps this outcome highlights and confirms the importance of a complete definition of the beach system with no separation between the underwater and the subaerial portion of the shore when it comes to sediment transport and movement this successful application of rfid technology to the underwater environment provides a chance to broaden understanding of a topic in need of further study

luminescence chronology of the bama beach ridge chad basin north eastern nigeria the mega lake chad palaeo beach ridge is covered by aeolian deposits the elevation 320 335 and 338 m a s l is the rim to the southwestern shores of mega lake chad and the initial deposits of this palaeo beach are believed to have been guided by a neotectonic fault line trending nnw sse luminescence dating was conducted on quartz grains extracted from sedimentary layers of the ridge section samples from the highest point on the ridge have revealed that aeolian deposits covering the ridge date from 3 3 0 31 ka at 2 m to 6 6 0 64 ka at about 5 m a water laid deposit of fine to medium sands from 5 m to 8 m depth has ages of 6 1 0 54 to 9 6 0 7 ka and fine medium to coarse sand from 10 to 17 m depth have ages from 18 4 1 5 to 26 4 9 3 ka

short term displacements of marked pebbles in the swash zone focus on particle shape and size abstract in this paper two short term experiments with tracers on a mixed beach are presented the aim was to understand how the size and shape of pebbles can affect their transport under low energy conditions sediment transport was studied by means of rfid technology to univocally monitor every single marked pebble a size subdivision of injected pebbles was conducted based on three classes big from 5 5 to 6 5 phi medium from 5 to 5 5 phi and small from 4 5 to 5 phi two recoveries were realised 6 and 24 h after the injection during a single day the wave motion was very low in the first experiment and low to moderate in the second never exceeding 0 4 m the results showed that discs are less dynamic than spheres but can cover greater distances regarding the sediment size big pebbles are less dynamic if compared to finer classes and they move preferentially down the swash zone towards the step or do not move up slope if already at the step very low and steady energy conditions facilitate cross shore and offshore movement of pebbles rather than a slight raise in wave height producing predominant longshore transport even with non marginal displacements low to moderate energy conditions can also produce some trend displacement based on the pebble shape even though t tests showed that shape was not statistically significant for pebble displacement the displacements of medium and small sized pebbles show a statistical dissimilarity compared to the big ones to refine the velocity estimation necessary to initiate pebble movement the threshold velocity formulas known up to now should involve the shape parameter especially for the short term better knowledge of the relationship between the sediment s characteristics and dynamics is critical to forecast the durability of replenishment material and to establish the suitability of fill material relative to native beach material hence a better understanding of the role of particle characteristics is necessary

origin of the sumba forearc basement abstract an interpretation of acoustic basement structures in the eastern sunda western banda forearc region suggests structural continuity between sumba and northern timor the area between sumba and timor is delineated as a zone of continuous structures without major strike slip offsets these structures trend east west in the west but gradually change towards the east into ne sw trending structures a major ne sw trending discontinuity west of sumba between 117 30 and 118 30 e marks the transition between an intraoceanic volcanic arc system in the west and a volcanic arc continent collision zone in the east the extent of the sumba basement suggests either a common late jurassic rift drift history for both sumba and northern timor or an early miocene magmatic welding of two continental fragments of different origin resulting in structural continuity between two microplates the first explanation implies that sumba originated from the north west australian continental margin south of tethys from which it drifted away in the late jurassic the second hypothesis which is favoured proposes a northern provenance of sumba the island would then originate from the south east asian continent north of tethys from which it was detached in the eocene

juxtaposed sequence stratigraphy temporal spatial variations of sedimentation and development of modern forming forearc lichi melange in north luzon trough forearc basin onshore and offshore eastern taiwan an overview abstract the south china sea oceanic lithosphere has been subducting eastward beneath the huatung basin philippine sea plate since the early miocene 18 ma the subduction is followed by the oblique collision between the luzon arc and the subducting eurasian plate from 6 5 ma the north luzon trough forearc strata and the luzon arc are then obducted northwestward as the coastal range eastern taiwan in the last 1 ma the collision propagates southward and is presently active in the region offshore se taiwan integrating seismic surveys offshore and a detailed forearc stratigraphy study onshore the coastal range this paper overviews the characteristics of forearc deformation dynamic sequence stratigraphy temporal spatial variations of forearc sedimentation and stratigraphic correlation onshore and offshore forearc sequences in response to the oblique convergent tectonics north of 20 n combining onshore and offshore forearc geology together allows us to reconstruct a structural evolution of the north luzon trough forearc basin from subduction through collision to obduction and to discuss the mechanism and processes responsible for developments of the modern forming forearc lichi melange during the active taiwan orogeny seismic surveys offshore show that forearc deformation in the subduction zone is primarily caused by increase of rear prism slope and west vergent thrusting of forearc strata along the prism top since the early forearc sedimentation east vergent backthrusting occurs during the late forearc sedimentation and propagates arcward when the volcanic arc collides with the accretionary prism in the collision zone bivergent thrusting leads to a development of the forearc huatung ridge popup as a bathymetric high which further controls the sedimentation of the younger forearc sequence in the collision zone in response to the syn sedimentation deformation forearc depocenter shifts progressively eastward forearc stratigraphy thus changes from two mega sequences bounded by an unconformity in the subduction zone to three mega sequences juxtaposed from west to east unconformably in the collision zone as a consequence the forearc deformation and stratigraphy in the oblique collision zone off se taiwan show a characteristic temporal spatial pattern that the lowest mega sequence with the most intensive deformation occurs restrictedly in the west whiles the middle and the upper mega sequences with mild deformation crop out in the center and the eastern part of the forearc basin respectively detailed biostratigraphy study using planktonic foraminifera and calcareous nannoplanktons indicates that the forearc strata onshore the coastal range are also composed of three sequences lower unit s 1 6 5 5 8 ma middle unit s 2 5 8 3 0 ma and upper unit s 3 a structure reconstruction reveals that the north luzon trough forearc strata have experienced multiple stages of thrust deformation from subduction through collision to obduction these deformations account for the mechanism and processes to develop the modern forming highly sheared ssz bearing forearc lichi melange tectonically in the western coastal range during the last 1 ma

the use of passive integrated transponder pit tags to trace cobble transport in a mixed sand and gravel beach on the high energy oregon coast usa abstract cobble transport is investigated on a mixed sand and gravel beach on the high energy oregon coast using radio frequency identification technology rfid to detect passive integrated transponder pit tags inserted in the gravels pit tags are glass encapsulated transponders that are activated when an antenna passes near them with each tag characterized by its own unique identification number the tags are sealed within the cobbles minimizing any effect on the hydrodynamic character of the particles the tags draw power from the antenna itself and have a potential lifespan of up to 50 years pit tags are simple to use and inexpensive permitting the release and tracking of large numbers of gravel particles as a result pit tags have tremendous potential for examining the complexities of particle movement and the parameters that control their distribution on the beach our experiments have been conducted at cape lookout state park on the northern oregon coast on a composite beach where a seasonally variable sand beach fronts a mixed sand and gravel beach with the latter impacted by waves only during the winter when the sand beach is cut back a total of 400 cobble tracers have been released at five different locations subsequent monitoring of the gravel tracers revealed that they can be detected up to 1 m below the surface of the beach using a 1 0 m diameter antenna and up to 0 5 m below the surface using a smaller 0 3 m diameter antenna while their positions were determined using a trimble 5700 5800 rtk dgps survey system gravel tracer recovery rates were found to vary significantly between the different release points from as high as 90 recovery after 8 months to a low of 18 after 17 months the lowest recovery rates are thought to be due to the extent of aggradation of the sandy beach during the summer partially covering the gravel berm and burying the tracer particles to depths where they could not be detected by the antennas used with our rfid system relocation of the gravel tracers has revealed a predominant northward migration of the cobbles and locally demonstrate a strong cross shore transport both upslope and downslope movements initial attempts to examine the relationship between the transport distances and particle sizes and shapes have thus far revealed that the larger gravels are tending to outrun the smaller particles this is despite the fact that both small and large particles were found to be capable of being transported both short and long distances in contrast our results revealed no relationships between particle shape and distance moved in time it is expected that the pit tag tracers may begin to yield more definitive patterns of sorting the results did highlight that the gravel movement occurs predominantly near the sand gravel beach junction on the profiles a region dominated by a higher incidence of wave breaking and strong swash activity finally our analyses revealed the potential for using pit tags to provide field assessments of the abrasion rates of gravel particles having already found measurable degrees of weight loss to abrasion in our experiments

earthquake occurrence along the java trench in front of the onset of the wadati benioff zone beginning of a new subduction cycle 1 spatial distribution of earthquake foci in the central part of the sunda arc was analyzed using global seismological data the analysis revealed the existence of a distinct strip of earthquakes distributed along the java trench separated by a trench parallel 50 150 km wide aseismic link from seismicity belonging to the wadati benioff zone of the recently subducting slab the seismicity pattern at the plate margin corresponds well with the morphology of the seafloor the along trench seismicity correlates with the position of the java trench and the onset of the wadati benioff zone correlates with the java trough the gps measurements performed in three analogous structural units of the neighboring sumatran convergent margin point to substantial differences in velocities of movement of the respective units and correlate with the spatial distribution of earthquake foci we interpret the distinct along trench seismicity as a consequence of the onset of a new subduction cycle due to the rapid convergent movement of the indo australian plate relative to the aseismic lithospheric link

seismicity pattern an indicator of source region of volcanism at convergent plate margins abstract the results of detailed investigation into the geometry of distribution of earthquakes around and below the volcanoes korovin cleveland makushin yake dake oshima lewotobi fuego sangay nisyros and montagne pelee at convergent plate margins are presented the isc hypocentral determinations for the period 1964 1999 based on data of global seismic network and relocated by engdahl van der hilst and buland have been used the aim of this study has been to contribute to the solution of the problem of location of source regions of primary magma for calc alkaline volcanoes spatially and genetically related to the process of subduction several specific features of seismicity pattern were revealed in this context i a clear occurrence of the intermediate depth aseismic gap idag in the wadati benioff zone wbz below all investigated active volcanoes we interpret this part of the subducted slab which does not contain any teleseismically recorded earthquake with magnitude greater than 4 0 as a partially melted domain of oceanic lithosphere and as a possible source of primary magma for calc alkaline volcanoes ii a set of earthquakes in the shape of a seismically active column sac seems to exists in the continental wedge below volcanoes korovin makushin and sangay the seismically active columns probably reach from the earth surface down to the aseismic gap in the wadati benioff zone this points to the possibility that the upper mantle overlying the subducted slab does not contain large melted domains displays an intense fracturing and is not likely to represent the site of magma generation iii in the continental wedge below the volcanoes cleveland fuego nisyros yake dake oshima and lewotobi shallow seismicity occurs down to the depth of 50 km the domain without any earthquakes between the shallow seismically active column and the aseismic gap in the wadati benioff zone in the depth range of 50 100 km does not exclude the melting of the mantle also above the slab iv any earthquake does not exist in the lithospheric wedge below the volcano montagne pelee the source of primary magma could be located in the subducted slab as well as in the overlying mantle wedge v frequent aftershock sequences accompanying stronger earthquakes in the seismically active columns indicate high fracturing of the wedge below active volcanoes vi the elongated shape of clusters of epicentres of earthquakes of seismically active columns as well as stable parameters of the available fault plane solutions seem to reflect the existence of dominant deeply rooted fracture zones below volcanoes these facts also favour the location of primary magma in the subducting slab rather than in the overlying wedge we suppose that melts advancing from the slab toward the earth surface may trigger the observed earthquakes in the continental wedge that is critically pre stressed by the process of subduction however for definitive conclusions it will be necessary to explain the occurrence of earthquake clusters below some volcanoes and the lack of seismicity below others taking into account the uncertainty of focal depth determination from global seismological data in some regions

updrift river mouth migration on cuspate deltas two examples from the coast of tuscany italy the configuration of the arno and ombrone deltas italy is evaluated the terminal courses of the rivers forming these deltas face the dominant wave orthogonal this configuration came about during rapid delta progradation as a consequence of increased river sediment input due to widespread deforestation within the catchment area a prevailing phenomenon from the early middle ages to the xviii century the rivers attained and maintained their directions as the result of the increased accretion rate on the less exposed downdrift side of the delta on the more exposed updrift side delta growth caused the shoreline to gradually rotate so that it directly faced the waves approaching the coast here due to the lower refraction wave energy per shore unit increased whilst accretion rate decreased this rotation of the shoreline induced longshore inversion on the updrift side whereas today cusp erosion is restoring the original drift direction

short and medium term response to storms on three mediterranean coarse grained beaches abstract the storm response of three italian coarse grained beaches was investigated to better understand the morphodynamics of coarse clastic beaches in a microtidal context two of the studied sites are located on the eastern side of the country portonovo and sirolo and the third one marina di pisa is on the western side portonovo and sirolo are mixed sand and gravel beaches where the storms approach from two main directions se and ne marina di pisa is a coarse grained gravel dominated beach exposed to storms driven by sw winds gravel nourishments were undertaken in recent years on the three sites beach topography was monitored measuring the same network of cross sections at a monthly i e short term to seasonal frequency i e medium term geomorphic changes were examined before and after storm occurrences by means of profile analyses and shoreline position evaluations the beach orientation and the influence of hard structures are the main factors controlling the transport and accumulation of significant amount of sediments and the consequent high variability of beach morphology over the medium term for marina di pisa storms tend to accumulate material towards the upper part of the beach with no shoreline rotation and no chance to recover the initial configuration sirolo and portonovo showed a similar behaviour that is more typical of pocket beaches both beaches show shoreline rotation after storms in a clockwise or counter clockwise direction according to the incoming wave direction the wider and longer beach at sirolo allows the accumulation of a thin layer of sediment during storms rather than at portonovo where given its longshore and landward boundaries the beach material tends to accumulate in greater thickness after storms sirolo and especially portonovo can quickly recover the initial beach configuration as soon as another storm of comparable energy approaches from the opposite direction of the previous one large morphological variations after the storm on mixed sand and gravel beaches do not necessarily mean a slower recovery of surface topography and shoreline position considering that all the three beaches were recently nourished with gravel it emerged that the differences between the nourishment and the native material in terms of size and composition seem to have an important influence on the dynamics of the sediment stock considering that recent studies have remarked the high abrasion rate of gravel further understanding of the evolution of nourishment material with time is needed the peculiar behaviour of gravel material artificially added to an originally sandy beach suggests the need to modify the widely used classification of jennings and shulmeister 2002 adding a fourth additional beach typology which could represent human altered beaches

holocene dust records from the west african sahel and their implications for changes in climate and land surface conditions we reconstructed aeolian dust accumulation during the holocene from two radiocarbon dated lake sediment sequences from the manga grasslands in northeastern nigeria in order to investigate long term changes in the harmattan dust system over west africa and evaluate their possible causes flux values were low in the early holocene decreasing further to a minimum at around 6 2 kyr b p after which time they increased steadily until around 2 kyr b p and then more sharply after this time the long term variations in dust flux agree broadly with changes in the exposed area of the lake chad basin to the northeast of the study sites which vary inversely with the volume of paleolake megachad more proximal sources of dust including the fine fraction of local dune sand and floodplains of nearby rivers have also made a contribution to the total dust load during times of enhanced dune and fluvial activity sharp rises in dust flux over the past century may be related to human activity broad patterns of change in dust flux during the holocene agree with other reconstructions over the same period however we see no evidence for a stepped rise during the middle holocene as seen at some sites from the northeastern tropical atlantic suggesting that controls on the harmattan dust system have differed from those affecting dust deposition elsewhere across northern africa