clast shape analysis and clast transport paths in glacial environments a critical review of methods and the role of lithology the reconstruction and tracing of transport paths in glaciated and other environments have a long tradition in the earth sciences we here present a dataset of clast shape samples from a worldwide selection of glaciated mountain environments in order to assess the reliability of this approach overall and the role of lithology on the performance of clast shape measurements in particular our findings demonstrate that the widely used ra c40 co variance approach is applicable to 63 of the 19 catchments investigated while the alternative rwr c40 approach is more widely applicable to 75 of these catchments a systematic assessment of mixing of lithologies at the catchment scale demonstrates that such mixing leads to pronounced overlaps between different control envelopes that had previously been separated thereby removing the discriminatory power of the method mixing of similar lithologies between different catchments shows an even more extreme loss of discriminatory power which strongly suggests that lithology plays a primary role in determining clast shape and that catchment specific processes are superimposed systematic analysis of the dataset also shows that nearly all catchments apart from two can be grouped into two types type i relates to sites in lesser mountain ranges and is characterised by dominantly blocky forms in the subglacial realm highlighting significant reworking processes type ii sites are dominantly in high mountain environments and characterised by a high similarity between subglacial and fluvial control envelopes this indicates that although reworking may be pronounced it is not necessarily effective enough to remove the platy shape that most likely results from extraglacial and supraglacial inputs our study highlights the potential of clast shape analysis as a tool that allows generic processes to be identified between catchments thereby enabling an understanding of debris cascades in glaciated mountain environments we finish with recommendations for ensuring that future clast shape studies are robust reproducible and comparable between different sites

mass movements in tropical volcanic terrains the case of teziutlan mexico abstract during the last decade soil degradation coupled with global climate changes has increased hydrogeological hazards in mexico in tropical volcanic terrains alteration processes have enhanced the formation of clay minerals that promote water retention and result in soil rock weakness intense seasonal rainfall can trigger the liquefaction and remobilization of these low resistance terrains during the first week of october 1999 heavy rains affected eastern mexico including puebla state as a consequence approximately 3000 mass movements consisting of rock and soil slides and slips debris flows and avalanches were generated in this area in the town of teziutlan puebla which is located on volcanic deposits a single mass movement event caused approximately 150 deaths in the present work we identified two types of mass movements in the teziutlan area type 1 superficial erosion of an unwelded ignimbritic sequence forming small detrital fans and type 2 thin soil slide debris flow from the remobilization of a volcanic sequence composed of clay rich paleosols interbedded with ashfall horizons the clay rich volcanic paleosols favored the formation of perched water tables on a hydraulic aquiclude positive pore water pressures triggered the failure based on these results the principal human settlement in the teziutlan area may be threatened by future debris flows which could cause serious harm to the dense population and severe damage to its infrastructure it is necessary to prevent future deaths and damage by installation of mitigative measures based on detailed studies without any further study it will not be possible to prevent and mitigate a natural disaster with the same magnitude as the 1999 catastrophic hydrogeological phenomena

gis based prediction method of landslide susceptibility using a rainfall infiltration groundwater flow model this paper describes a physical based model to predict rainfall induced landsides special attention was given to the introduction of a gis based model ys slope model yonsei slope model which can evaluate the susceptibility of landslides the model has been improved by incorporating the combined effects of groundwater flow and rainfall infiltration into the raster model the two dimensional darcy s law was used to reflect the effect of groundwater flow in the soil slope and the modified green ampt model which is a one dimensional infiltration model was selected to capture the effect of rainfall infiltration into the soil mass these elements were integrated into the infinite slope stability model for a rainfall induced landslide the proposed model was verified by comparing the results from existing models as well as an actual slope failure case that occurred in korea with further study the ys model could be adopted as a prediction method for rainfall induced landslides

submarginal debris transport and till formation in active temperate glacier systems the southeast iceland type locality abstract exhaustive sedimentological analysis of freshly exposed subglacial surfaces and moraines in southern iceland provides diagnostic sedimentological signatures of a debris transport pathways through active temperate glacier snouts and b till production in subglacial traction zones dominated by deforming layers three till end members are recognised based on stratigraphic architecture 1 thin and patchy tills over eroded bedrock 2 single push moraines and complexes and 3 overridden moraines or outwash fans typical till thicknesses are 0 10 1 40 m with each till relating to a deformation event driven by the seasonally tuned processes of glacier sub marginal shearing freeze on squeezing and bulldozing clast form trends demonstrate progressive modification towards mature forms in subglacial traction zones with till being clearly differentiated from scree and glacifluvial deposits clast macrofabric strengths are variable rarely matching those of laboratory shearing experiments except where obviously lodged clasts are abundant they also consistently record former glacier flow directions but localized variability is introduced by bedrock protuberances cavity infill clast interference and freshly imported plucked clasts within tills macrofabrics strengthen from lower b horizon to upper a horizon tills but at the outer edges of sub marginally thickening till wedges or push moraines seasonally driven cycles of squeezing flowage freeze on melt out and bulldozing give rise to a range of clast macrofabric strengths as well as superimposed deformation signatures this reflects two extremes of till emplacement including the more mobile flowing and often liquefied matrixes in push squeeze moraines and in contrast the lodgement deformation and ploughing at the thin end of sub marginal till wedges

late precambrian glacially related grooved and striated surfaces in the tillite group of central east greenland abstract the tillite group of central east greenland comprises five formations of which two are dominantly glacigenic the ulveso formation formerly lower tillite and the storeelv formation formerly upper tillite both of which embrace a wide range of facies including glaciomarine nearshore and terrestrial glacial sediments evidence of periodic terrestrial conditions is indicated especially by a variety of grooved and striated surfaces on the island ella o in the ulveso formation grooves of complex geometry 0 4 m wide and 0 3 m deep were cut into a cemented conglomerate horizon they are interpreted as having formed as a result of subglacial meltwater cavitation at the base of the storeelv formation boulders thought to have been dropped into partially cemented sandstone by floating glacier ice were largely planed off by a subsequent advance of grounded ice in the middle of the storeelv formation a striated boulder pavement occurs within diamictite on the basis of stone fabric striation orientation and cross bedding data this pavement is inferred to have formed by the packing of stones along a shear surface within an accumulating lodgement till such features have rarely been observed in pre pleistocene glacigenic sequences they imply that each glacigenic formation accumulated during a complex series of advances and retreats rather than just one

subsurface failure in spherical bodies a formation scenario for linear troughs on vesta s surface abstract many asteroids in the solar system exhibit unusual linear features on their surface the dawn mission recently observed two sets of linear features on the surface of the asteroid 4 vesta geologic observations indicate that these features are related to the two large impact basins at the south pole of vesta though no specific mechanism of origin has been determined further the orientation of the features is offset from the center of the basins experimental and numerical results reveal that the offset angle is a natural consequence of oblique impacts into a spherical target here we demonstrate that a set of shear planes develops in the subsurface of the body opposite to the point of first contact these subsurface failure zones then propagate to the surface under combined tensile shear stress fields after the impact to create sets of approximately linear faults on the surface comparison between the orientation of damage structures in the laboratory and failure regions within vesta can be used to constrain impact parameters e g the approximate impact point and likely impact trajectory

depositional controls on glacial facies associations in a basinal setting late proterozoic amadeus basin central australia abstract diamictites many established as being glacial in origin are globally distributed in late protezoic rocks their widespread occurrence is important in that it implies that significant climatic events occurred during the period between 900 and 600 ma however because of the age of the rocks correlations are poor and it is difficult to establish in a convincing manner whether these sediments were deposited synchronously during a major global ice age or if each occurrence of diamictite relates to local climatic or tectonic events since the biostratigraphy of these rocks is limited and only a small number of radiometric ages are available an alternative approach to correlation is necessary the most promising approach currently available appears to be the application of sequence stratigraphy and the careful evaluation of facies associations on a site by site basis before attempting global correlations late proterozoic diamictites occur in a number of intracratonic basins in a broad belt across the ancient australian craton two late proterozoic diamictite units both previously identified as glacial in origin are exposed in the intracratonic amadeus basin of central australia the areyonga formation the older of the two units forms the basis of this study the areyonga formation is contained within a major depositional sequence the areyonga sequence the bounds of which were determined by basin dynamics and eustatic sea level changes induced by an ice age of global dimensions during deposition of this sequence three major sedimentological systems were in operation along the northern margin of the basin glaciation dominated sedimentation in the south large volumes of sediment were deposited in a shallow marine setting whilst to the west braided streams supplied sediment to a major coastal plain and delta system all three systems operated within the same sea level and basinal constraints but each contributed sediment to the basin independently the glacial sediments of the areyonga sequence were deposited from a relatively small ice cap lying between the amadeus basin and the ngalia basin to the north sediments were deposited from two tongues of ice that extended about 100 km into the northeastern corner of the amadeus basin glacial sedimentation occurred in three stages determined by the initial fall and subsequent rise in eustatic sea level as the ice sheet grew and declined initially thick massive basal till units were deposited on an erosion surface intersected by subglacial and ice marginal channels they were then followed by thinner till units separated by channel like sandstone and conglomerate with associated boulder surfaces or concentrations that were deposited by an extensive subglacial drainage network finally the subglacial deposits grade into ice proximal and ice distal shallow marine sediments deposited in part by mass movement sedimentation appears to have been terminated by a major sea level fall in the ooraminna sub basin to the east rocks originally thought to have been deposited during a second glaciation appear to be part of a lowstand wedge formed during a sea level low following the areyonga glaciation a record of the second glaciation probably does not exist in the amadeus basin similarly diamictites in the inindia beds and originally correlated with the areyonga formation have been shown to belong to the non glacial lowstand wedge of the following sequence preservation of glacial sediments is most likely to occur in a basinal setting where depositional space is being actively created in the amadeus basin depositional space was created prior to deposition of the areyonga formation by subsidence following crustal extension that occurred approximately 150 m y previously the distribution of sequence boundaries and the succession of facies associations identified in the areyonga sequence provide the basis for a depositional model for glacial sedimentation during an ice age to be successful correlation of late proterozoic glacial sediments must be based on an understanding of these facies associations and their bounding depositional surfaces associations similar to those found in the amadeus basin have been documented in other proterozoic basins suggesting that the facies associations and relationships recorded in the areyonga sequence may form the basis for a generalized model for basinal sedimentation from an ice age of global significance if this is so it should be possible to determine if a sequence containing glacial sediments is part of a global climatic event or simply due to local conditions from a single site evaluation

glaciomarine deltaic deposition and ice marginal tectonics the loch don sand moraine isle of mull scotland detailed descriptions are given of sediments exposed in the loch don sand moraine isle of mull scotland two distinct sediment landform associations occur within the moraine i a gilbert type glaciomarine delta complex graded to ca 34 m ordnance datum and ii thrust moraines consisting of deformed sands and silts whereas previous studies have attributed the moraine to a single glacial readvance this paper shows that the delta and the thrust moraines formed during ice sheet deglaciation and the loch lomond readvance respectively depositional conditions and the palaeoenvironment for each stage of moraine formation are reconstructed during the loch lomond readvance till deposition and thrust moraine formation appear to have been controlled by drainage conditions in the marginal zone of the glacier

glacial advance and retreat sequences in a permo carboniferous section central transantarctic mountains episodes of glacial advance and retreat can be recognized through analysis of vertical facies sequences in the permo carboniferous pagoda formation of the beardmore glacier area antarctica the formation includes a remarkably complete record of continental sedimentation near the terminus of a temperate glacier facies sequence is pre eminent for inferring glacial advance and retreat other important criteria are abundance and geometry of sandstone interbedded with diamictite diamictite character and nature of bed contacts using these characteristics advance and retreat sequences 5 60 m thick are recognized a sharp contact with a striated surface and erosional relief overlain by structureless diamictite lodgement till is typical of grounded ice advance grounded ice retreat is characterized by structureless diamictite lodgement till overlain by crudely stratified diamictite melt out till and then by diamictite interbedded with sandstone and conglomerate flow till and glacio fluvial or glacio lacustrine deposits gradational contacts between shale overlain by diamictite and diamictite overlain by shale characterize advance and retreat respectively in subaqueous settings pauses in sediment accumulation minor fluctuations of the ice margin and or changes in subglacial dynamics are indicated by specific features within diamictite units such as probable frost wedge casts single layer boulder beds sharp sedimentary contacts and changes in diamictite character these minor events are superimposed upon the main advance retreat cycles study of both the overall facies sequence and of individual diagnostic structures albeit in an incomplete stratigraphic record permits a distinction between major and minor advance retreat events as many as six major advance retreat cycles exist in some pagoda sections but the number of cycles present varies in different sections

the geologically recent giant impact basins at vesta s south pole since 17 july 2011 nasa s spacecraft dawn has been orbiting the asteroid vesta the second most massive and the third largest asteroid in the solar system see the cover russell et al p 684 1 use dawn s observations to confirm that vesta is a small differentiated planetary body with an inner core and represents a surviving proto planet from the earliest epoch of solar system formation vesta is also confirmed as the source of the howardite eucrite diogenite hed meteorites jaumann et al p 687 2 report on the asteroid s overall geometry and topography based on global surface mapping vesta s surface is dominated by numerous impact craters and large troughs around the equatorial region marchi et al p 690 3 report on vesta s complex cratering history and constrain the age of some of its major regions based on crater counts schenk et al p 694 4 describe two giant impact basins located at the asteroid s south pole both basins are young and excavated enough amounts of material to form the vestoids a group of asteroids with a composition similar to that of vesta and hed meteorites de sanctis et al p 697 5 present the mineralogical characterization of vesta based on data obtained by dawn s visual and infrared spectrometer revealing that this asteroid underwent a complex magmatic evolution that led to a differentiated crust and mantle the global color variations detailed by reddy et al p 700 6 are unlike those of any other asteroid observed so far and are also indicative of a preserved differentiated proto planet 1 lookup doi 10 1126 science 1219381 2 lookup doi 10 1126 science 1219122 3 lookup doi 10 1126 science 1218757 4 lookup doi 10 1126 science 1223272 5 lookup doi 10 1126 science 1219270 6 lookup doi 10 1126 science 1219088

infiltration induced seasonally reactivated instability of a highway embankment near the eisenhower tunnel colorado usa abstract infiltration induced landslides are major natural hazards when they occur along highways they can impede traffic damage infrastructure and threaten public safety this paper presents a case study of an active landslide on an embankment of interstate 70 west of the eisenhower tunnel in central colorado usa records indicate that the hillslope under i 70 has moved episodically over the previous 40 years in the previous two decades the road surface has been displaced vertically by more than 60 cm the objective of this work is to develop a conceptual model capable of quantifying the seasonally reactivated landslide movement at the site inclinometer data of subsurface deformation and geologic and hydrologic mapping are used to develop the conceptual model as well as to constrain a numerical model a two dimensional hydro mechanical numerical model is used to test the conceptual model under three different infiltration rates during the period of snowmelt in the spring the framework used in the numerical model accounts for the major physical processes driving instability of the slope time dependent variably saturated flow the resultant changes in stress and induced deformation when the snowmelt water infiltrates into the slope the soil water content and the water table level vary accordingly these time dependent variations result in changes in soil matric suction effective stress and consequently change in slope stability the model calculates pore water pressures suction stress and the distribution of effective stress in the embankment slope at different times global factors of safety as a function of time are calculated along the predetermined sliding surface using effective stresses calculated with finite elements the slope stability assessment quantitatively confirms the conceptual model and is consistent with the displacements monitored at the site during the years of 2007 2009 it is shown that annual snowmelt infiltration of 60 100 cm of water can reduce the factor of safety by 6 enough to sustain landslide movement for as long as 8 months each year

direct detection of projectile relics from the end of the lunar basin forming epoch the lunar surface a key proxy for the early earth contains relics of asteroids and comets that have pummeled terrestrial planetary surfaces surviving fragments of projectiles in the lunar regolith provide a direct measure of the types and thus the sources of exogenous material delivered to the earth moon system in ancient 3 4 billion years ago ga regolith breccias from the apollo 16 landing site we located mineral and lithologic relics of magnesian chondrules from chondritic impactors these ancient impactor fragments are not nearly as diverse as those found in younger 3 4 ga to today regolith breccias and soils from the moon or that presently fall as meteorites to earth this suggests that primitive chondritic asteroids originating from a similar source region were common earth moon crossing impactors during the latter stages of the basin forming epoch

multiple subglacial till deposition a modern exemplar for quaternary palaeoglaciology the sedimentology of a vertical succession of alternating beds of massive and fissile diamictons on a orisjokull plateau icefield outlet foreland is employed to assess the evolution of subglacial traction tills at the margins of active temperate glaciers with deformable substrates where tills appear to form sub marginal incrementally thickened wedges that display multiple till emplacement events potentially of annual scale lodged boulders display strong a axes and surface striae alignments which parallel surface flutings indicating that fluting construction and till emplacement were related to moulding by consistent glacier flow from the ssw during the little ice age in contrast clast macrofabrics at the sub boulder size not unlike those reported from other icelandic tills are not as strong as would be expected in a subglacially sheared medium indicating shear strains too low for a steady state strain signature this separation of fabric data has isolated the strain signatures of the lodgement and deformation components of subglacial traction till whereby the orientations of the largest lodged clasts record high cumulative shear strains and those of the sub boulder sized clasts record greater susceptibility to deformation of their enclosing matrix this is likely due to the effect of clast collisions in clast rich till and the perturbations set up by the numerous large boulders consistent with observations on till fabrics in flutings and around lodged clasts a b plane macrofabric data display unusually high degrees of isotropy reflective of the more variable orientations of a b planes which are thought to reflect a b plane susceptibility to dip parallel or anastomosing shear planes a wide range of clast angularity values reflects the localized input of freshly plucked and hence relatively highly angular blocks to the deforming layer a characteristic of stepped bedrock profiles beneath the snouts of mountain glaciers finally we hypothesize that the massive and fissile units may represent a and b horizons of subglacial deforming layer couplets and that each couplet could record seasonal emplacement and partial inter couplet modification near the ice margin if the latter is the case then less than 1 m of subglacial till is advected to the glacier margin per annual deformation event

glacial origin of the cryogenian nantuo formation in eastern shennongjia area south china implications for macroalgal survival abstract the cryogenian period was characterized by global glaciations imposing extreme environmental stresses on early multicellular organisms globally distributed diamictite deposits are the major evidence for these glaciation events but the glacial origin of at least some of these diamictite deposits has been disputed complicating interpretations of the environmental conditions influencing the evolution of life in the cryogenian 720 635 ma in this study we conducted a systematic sedimentological investigation of the marinoan age 650 635 ma nantuo formation in six sections representing a 20 km long east west transect in the eastern shennongjia area of south china the nantuo formation which ranges in thickness from 2 m in the east to 300 m in the west comprises diamictite conglomerate lonestone bearing sandstone green siltstone and black shale facies the eastern sections e g longxi and wushanhu consist mainly of diamictite facies exhibiting micro scaled rotation structures microshear grain stacking grain to grain contacts and water escape structures supporting their deposition in a subglacial setting in contrast the western sections shijiahe liziping and songluo consist of massive and graded diamictite and conglomerate facies consistent with an origin as glacially induced submarine debris flows furthermore the lonestone bearing sandstone facies in these sections contain abundant dropstones and mud pellets within finely laminated turbidites indicating an ice rafted origin with locally reworking by turbidity currents the green siltstone and black shale facies lack glacigenic features and may represent late deglacial deposits based on thickness and facies variations among the study sections we infer that the nantuo formation records glacial sedimentation on a complex paleotopographic surface that was incised into the underlying bedrock with subglacial deposits to the east transitioning into glaciomarine deposits to the west of study area the distal songluo section likely records three cycles of glacial advance and retreat in the form of a facies alternation between diamictite and black shale consistent with a dynamically fluctuating ice margin in summary our sedimentological investigation supports a glacial origin for the nantuo formation in the eastern shennongjia area the occurrence of the benthic macroalgal dominated songluo biota in the black shale facies at songluo suggests that strong glacial retreats provided niches for macroalgal survival in the cryogenian glacial ocean

controls on early permian shelf deglaciation in the karoo basin of south africa abstract the late carboniferous to early permian glacigene dwyka group has at its top three types of transitions from diamictite to postglacial mudrock in the southern karoo the type 1 transition sequence consists of clast poor carbonate rich diamictite having a sharp contact with the overlying mudrocks this diamicton accumulated slowly by rain out and sediment gravity flow processes during sedimentation the polar ice front was stabilised by a possible ice shelf collapse of the ice shelf caused rapid ice margin retreat the type 2 transition sequence consists of clast poor diamictite with sandstone bodies overlain by mudrock with ice rafted debris or thin interbedded debris flow diamictites deposition of the diamictite facies occurred during oscillations of a subpolar ice front with short stable periods of surface melting of the ice resulting in the formation of small subaqueous outwash fans the type 3 transition sequence consists of bouldery diamictite interbedded with massive or sandstone bearing diamictite overlain by mudrock with ice rafted debris or thin interbedded debris flow diamictites the sequence represents highly unstable ice front conditions and fluctuating sea levels with periods of rapid deposition probably by collapsing ice streams climatic conditions may have alternated between polar and subpolar the type 1 transition sequence is predominant in the western part and the type 3 sequence in the eastern part of the karoo basin long term controls on deglaciation was climatic warming as gondwana drifted over the pole as well as changes in land sea configuration superimposed on these were local controls such as relative sea level changes presence of deformable substrate and meltwater production

subglacial sedimentary features in late palaeozoic sedimentary rocks central victoria australia abstract a section of late palaeozoic diamictite in the bacchus marsh formation in central victoria southeastern australia contains 1 1 striated boulders with long axes tilted up glacier 2 2 layers of pebbles lacking evidence of water sorting 3 3 thin sheets and lenses of sandstone 4 4 slab like and contorted sandstone bodies cut by closely spaced step fractures 5 5 thin slabs of rhythmically bedded siltstone and claystone the boulders indicate that the diamictite was deposited by lodgement beneath moving wet based glacial ice the sandstone sheets and lenses indicate periods of rapidly increasing subglacial water pressure and the deformed sandstone bodies indicate flow of some of the newly deposited diamicton in response to shear imparted by the overlying ice the pebble layers probably formed as a moving carpet of clasts close to the controlling obstacle size of the glacier during deposition from a layer of mobile subsole debris which then halted these features indicate changes in subglacial conditions that may have led to surging behaviour by the glacier the model of pebble layer formation allows an estimate of ice sliding velocity during layer formation and thus provides a method of quantifying one aspect of ice behaviour for a pre pleistocene glacier

the smart 1 lunar impact the smart 1 spacecraft impacted the moon on 3rd september 2006 at a speed of 2 km s 1 and at a very shallow angle of incidence 1 the resulting impact crater is too small to be viewed from the earth accordingly the general crater size and shape have been determined here by laboratory impact experiments at the same speed and angle of incidence combined with extrapolating to the correct size scale to match the smart 1 impact this predicts a highly asymmetric crater approximately 5 5 26 m long 1 9 9 m wide 0 23 1 5 m deep and 0 71 6 9 m3 volume some of the excavated mass will have gone into crater rim walls but 0 64 6 3 m3 would have been ejecta on ballistic trajectories corresponding to a cloud of 2200 21 800 kg of lunar material moving away from the impact site the shallow messier crater on the moon is similarly asymmetric and is usually taken as arising from a highly oblique impact the light flash from the impact and the associated ejecta plume were observed from earth but the flash magnitude was not obtained so it is not possible to obtain the luminous efficiency of the impact event

degree of impactor fragmentation under collision with a regolith surface laboratory impact experiments of rock projectiles some meteorites consist of a mix of components of various parent bodies that were presumably brought together by past collisions impact experiments have been performed to investigate the degree of target fragmentation during such collisions however much less attention has been paid to the fate of the impactors here we report the results of our study of the empirical relationship between the degree of projectile fragmentation and the impact conditions millimeter sized pyrophyllite and basalt projectiles were impacted onto regolith like sand targets and an aluminum target at velocities of up to 960 m s 1 experiments using millimeter sized pyrophyllite blocks as targets were also conducted to fill the gap between this study and the previous studies of centimeter sized rock targets the catastrophic disruption threshold for a projectile is defined as the energy density at which the mass of the largest fragment is the half of the original mass the thresholds with the sand target were 4 5 1 1 104 and 9 0 1 9 104 j kg 1 for pyrophyllite and basalt projectiles respectively these values are two orders of magnitude larger than the threshold for impacts between pyrophyllite projectiles onto aluminum targets but are qualitatively consistent with the fact that the compressive and tensile strengths of basalt are larger than those of pyrophyllite the threshold for pyrophyllite projectiles and the aluminum target agrees with the threshold for aluminum projectiles and pyrophyllite targets within the margin of error consistent with a previous result the threshold depended on the size of the rocks with a power of approximately 0 4 housen and holsapple 1999 destruction of rock projectiles occurred when the peak pressure was about ten times the tensile strength of the rocks

gis based weights of evidence modelling of rainfall induced landslides in small catchments for landslide susceptibility mapping landslide susceptibility mapping is a vital tool for disaster management and planning development activ ities in mountainous terrains of tropical and subtropical environments in this paper the weights of evidence modelling was applied within a geographical information system gis to derive landslide susceptibility map of two small catchments of shikoku japan the objective of this paper is to evaluate the importance of weights of evidence modelling in the generation of landslide susceptibility maps in relatively small catchments having an area less than 4 sq km for the study area in moriyuki and monnyu catchments northeast shikoku island in west japan a data set was generated at scale 1 5 000 relevant thematic maps representing various factors e g slope aspect relief flow accumulation soil depth soil type land use and distance to road that are related to landslide activity were generated using field data and gis techniques both catchments have homogeneous geology and only consist of cretaceous granitic rock thus bedrock geology was not considered in data layering during gis analysis success rates were also estimated to evaluate the accuracy of landslide suscepti bility maps and the weights of evidence modelling was found useful in landslide susceptibility mapping of small catchments

inter and intratill boulder pavements in the carboniferous hoyada verde formation of west argentina an insight on glacial advance retreat fluctuations in southwestern gondwana abstract two glacially abraded surfaces have been identified in the glaciomarine section of the carboniferous hoyada verde formation calingasta uspallata basin in west argentina the glacial erosion surfaces ges found in the hoyada verde section are boulder pavements one is an intertill boulder pavement developed as a single boulder layer resting on massive diamctites dmm and overlain by thick to thin bedded diamictites with ice rafted debris ird the second surface identified in recent field work can be described as an intratill boulder pavement it is also a single boulder layer but under and overlain by massive diamcitites dmm the intratill boulder pavement consists of a laterally discontinuous planar concentration of large clasts with faceted and striated upper surfaces it lies approximately 10 m below the intertill boulder pavement and is exposed on the southern closure of the hoyada verde anticline in both pavements the upper surfaces of the clasts are polished and striated the striae are parallel and subparallel to the a axes of the boulders and indicate similar paleoflow ice directions toward the s and s sw both pavements were probably originally laid down as residual gravel lag surfaces formed by the erosion of underlying diamict when wave and or tidal reworking was strong during a low stand and were subsequently abraded by advancing glaciers although both boulder pavements can be considered to be equivalent to glacial erosional surfaces ges caused by abrasion during a glacial advance and hence sequence boundaries form the sequence stratigraphic viewpoint their hierarchies are different the intertill boulder pavement demarks the demise of the mid carboniferous glacial episode in west argentina whereas the underlying intratill boulder pavement can be interpreted as the product of a minor fluctuation during the same glacial episode

the january 10 1997 pozzano landslide sorrento peninsula italy abstract from 1997 to 1999 a huge number of slides often turning into extremely rapid debris earth flows repeatedly affected the late quaternary volcaniclastic deposits mantling the carbonate slopes of campania region italy the sorrento peninsula was the epicentral district of the 1997 regional slope instability crisis some hundred shallow mass movements took place during january 1997 in this area these were the last episode of a long series of slope failure events dating back to mid 18th century results from geological and geomorphologic surveys are presented landslide mechanism and triggering factors are analysed for the most important mass movement which occurred during the january 9 11 1997 regional event on january 10 1997 at about 8 15 pm a rainfall induced debris slide debris flow occurred at pozzano province of naples mainly affecting the 79 ad pyroclastic products following a j path the landslide destroyed a private house and invaded the state road no 145 this event resulted in four deaths 22 persons injured and road closure for about 2 months there was less than 200 mm of rainfall in the 72 h period prior to the landslide although intense precipitation had occurred during a preceding 4 month period however the slope failure event was not preceded by an extreme short term antecedent rainfall as already noticed in previous landslides of this type in campania finally following a preliminary geotechnical characterization of volcaniclastic soils a slope stability back analysis was carried out which adopted the classical infinite slope scheme this analysis gave further evidence of the role played by pore pressure in reducing the overall shear strength of pyroclastic soils

survival of fossilised diatoms and forams in hypervelocity impacts with peak shock pressures in the 1 19 gpa range abstract previously it has been shown that diatom fossils embedded in ice could survive impacts at speeds of up to 5 km s 1 and peak shock pressures up to 12 gpa here we confirm these results using a different technique with diatoms carried in liquid water suspensions at impact speeds of 2 6 km s 1 these correspond to peak shock pressures of 3 8 19 8 gpa we also report on the results of similar experiments using forams at impact speeds of 4 67 km s 1 when carried in water and 4 73 km s 1 when carried in ice corresponding to peak shock pressures of 11 6 and 13 1 gpa respectively in all cases we again find survival of recognisable fragments with mean fragment size of order 20 25 m we compare our results to the peak shock pressures that ejecta from giant impacts on the earth would experience if it subsequently impacted the moon we find that 98 of impacts of terrestrial ejecta on the moon would have experienced peak pressures less than 20 gpa if the ejecta were a soft rock sandstone this falls to 82 of meteorites if the ejecta were a hard rock granite this assumes impacts on a solid lunar surface if we approximate the surface as a loose regolith over 99 of the impacts involve peak shock pressures below 20 gpa either way the results show that a significant fraction of terrestrial meteorites impacting the moon will do so with peak shock pressures which in our experiments permit the survival of recognisable fossil fragments

glaciogenic coarse clastics in a permo carboniferous bedrock trough in india a sedimentary model abstract physical aspects of sedimentation particularly of coarse clastics within a bedrock trough in the basal 28 5 m of the permo carboniferous talchir formation in west bokaro india have been addressed herein the trough fill facies assemblage bearing abundant signs of glacial activity was eventually buried under wave agitated open nearshore and shelf sediments analysis of several sedimentary characteristics and their interrelationship help to recognize various types of glacial sediments and their frequent resedimentation through various mass flow processes it brings to light plausible transportational and depositional mechanism facies patterns in relation to the various morphometric parts of the trough reveal a changing pattern of sedimentation whereas available palaeocurrent data indicate palaeoflows converging from the flanks and turning axis parallel on the floor of the trough trough filling through fan progradation initially from single but subsequently from multipoint sources failed to impart systematic changes in bed thickness clast size and composition in the sequence this continued till the major coastal onlapping attributed to rapid deglaciation a model with predictive generalization has been proposed for coarse clastic sedimentation in fjord like coastal glacier fed troughs on the basis of observations made herein

depositional models for the glaciomarine sequences of andean late paleozoic basins of argentina abstract diamictite bearing late paleozoic sequences of probably glacial origin crop out in three basins of western argentina 1 the tarija basin 2 the calingasta uspallata basin and 3 the central patagonian basin the tarija section shows clear evidence of soft sediment deformation in a shallow marine environment slump overfolds and hook like and pull apart structures are common in lenses of well sorted sandstones within a sequence mostly composed of massive matrix supported pebbly mudstones the overall shallowing upward trend of the section suggests alluvial progradation underlying fine grained rocks represent quiet water prodelta deposits the diamictites suggest a delta slope position and the overlying red mudstones with cross bedded sandstones and conglomerates correspond to delta plain deposits in the calingasta uspallata basin the hoyada verde formation represents the best example of an ice contact glaciomarine depositional system with minor gravity flow deposits massive matrix supported sandy diamictites associated with a boulder pavement together with sandstone and conglomerate channels represent grounded ice deposits grading to subglacial flow tills thin bedded matrix supported muddy diamictites with dropstones are the product of a process of gravity resedimentation debris flows and ice rafting pebbly shales represent shelf sedimentation with local deposition from floating ice the ansilta formation shows characteristic features of low and high turbidity current dominated environments basal diamictites resemble debris flow deposits and are associated with thickening upward sequences of bouma tb c turbidites and massive sandstones with fluid scape structures these two sections described above represent the end members of a continuum from glaciomarine rocks to gravity induced deposits formed by subaqueous reworking of glacial debris fine grained rocks associated with diamictites contain marine fossils belonging to the livipustula zone of westphalian age middle carboniferous the central patagonian diamictites appear to be clearly associated with classical turbidites with bouma sequences resedimented conglomerates and high density turbidity current sandstones the conglomerates and sandstones form composite channels with common amalgamation and internal scour surfaces the depositional models proposed for the diamictite bearing sequences of the three basins can be placed in a broader model which embraces several types of complex interactions among glaciomarine nearshore and gravity flow dominated environments

a systematic classification of glacial and periglacial environments facies and deposits abstract several aspects of the deposits formed in the glacial and periglacial environments are presented in order to establish a framework that can be used in various disciplines dealing with sedimentation under glacial and periglacial conditions the almost unlimited number of different deposits are grouped into 37 types that are all described briefly most of them are also illustrated by field examples mainly from poland these 37 types are grouped within 23 facies belonging to 3 continental glacial 3 continental periglacial and 3 marine periglacial subenvironments all environments subenvironments facies and deposits are defined and presented with a hierarchic code that enables unambiguous definition attention is paid to both the general characteristics of the various deposits as they have been described by previous investigators and to specific deposits that have been studied by the present authors the factors influencing peri glacial sedimentation are discussed briefly

analysis of rainstorm induced slide debris flows on natural terrain of lantau island hong kong abstract lantau island the largest outlying island of the territory of hong kong experienced a severe rainstorm on 4 5 november 1993 which induced 800 slope failures on natural terrain there detailed field investigations were carried out to study the failure modes in relation with various influencing factors it was found that the occurrence of slide debris flows has a close relationship with bedrock geology slope gradient vegetation cover and micro landform the failure modes of slide debris flows may be classified into translational slides and rotational slides and the former are predominant analysis of the hydrological response of colluvial slopes during the rainstorm indicated that the majority of the failures were caused by the development of a perched water table in the thin surface layer of colluvium of volcanic origin due to infiltration during the heavy rain undisturbed soil samples from south lantau have been subjected to anisotropically consolidated undrained compression tests at comparatively low stress levels constant deviatoric stress path tests cqd simulating the stress path in the field at in situ stress levels have been performed to investigate soil behavior the cqd test results indicate that the material of slopes at undisturbed state is brought to dilation because of the increase in pore water pressure caused by infiltration of rain water for a translational slide the displacement resulting from dilation may destroy cohesion along the failure surface and locally within the interior of the slide the surplus water during the intense rainstorm was able to equilibrate the reduction in pore pressure caused by dilation and the dilation and displacement may be further increased the strain softening after significant strains triggered debris flow mobilization however for a rotational slide the increase in pore water pressure caused by surplus water infiltration during the intense rainstorm could not equilibrate the reduction in pore pressure caused by dilation much or even all of the sliding block could not mobilize into a debris flow

evidence of glacial abrasion in the calingasta uspallata and western paganzo basins mid carboniferous of western argentina abstract evidence of glacial abrasion is present in the basal part of the carboniferous section of the calingasta uspallata and paganzo western argentina where subglacial and proximal glacial marine diamictites with pebbly dropstone shales constitute the dominant facies association intraformational striated pavements are exposed in the hoyada verde and leoncito formations of the calingasta uspallata basin marine invertebrate fossils levispustula zone in associated shales indicate a mid carboniferous age for both units a single layer striated boulder pavement is superbly exposed in the hoyada verde formation local a axis clast imbrication in the underlying bouldery diamictite and strong parallel striae on the flattened upper surfaces of boulders indicate a subglacial origin for the pavement paleo ice flow directions have an nne ssw strike the leoncito intraformational pavement is shaped on bioturbated fine grained sandstones with plant remains glacial striations are straight and parallel with subcircular cross sections dome like features are present in the surface which is covered in turn by a sandy bouldery diamictite four striated surfaces are present in the western paganzo basin three of them pavements at the san juan river valley loma de los piojos and agua hedionda are developed on basement rocks they contain parallel to subparallel striations nailhead striations crescentic gouges impact marks and furrows the pavements are overlain by thin up to 1 5 m laterally discontinuous diamictite beds with striated clasts some of them bullet shaped paleo ice flow directions are n ne directed an intraformational pavement is also present at the san juan river valley section it is carved on the top of the basal diamictite and exhibits furrows probably caused by subglacial soft sediment grooving the dispersion of paleo ice flow directions in the calingasta uspallata and paganzo basins indicates i regional slopes toward the north into a brackish water embayment and northwest into the open marine conditions ii glacial erosion by ice grounded below sea level and confined to the margins of the basins

an investigation of subglacial processes at the microscale from briksdalsbreen norway the subglacial processes at briksdalsbreen norway are examined by a combination of sedimentology thin section and scanning electron microscope sem analysis of till samples from an exposed subglacial surface and from beneath the glacier studies of a fluted surface indicate that subglacial deformation is occurring on a field scale with flutes forming behind most clasts 0 6 m high at the thin section scale 0 014 2 0 mm it is seen that deformation is by rotation and attenuation and is dependent on till texture at the sem scale 0 1 0 4 mm it is seen that erosion is controlled by abrasion and percussion which produces distinct grain styles as part of an erosional continuum overall it is shown that rotation and attenuation is a dominant process at all scales and that the clast interactions associated with different scale perturbations within the shear zone control erosion and deposition as well as landform and fabric production

clasts with stoss lee form in lodgement tills a discussion abstr act cla sls modifi ed b y glacial erosion a rc d escribed rrom lodge ment till s in front of the g lacier m yrd alsjokull south i cel and many cl asts show modifica ti on of their lower surfaces in th e sa me way as th e ir upper o nes h o wever the lower surfaces have a smooth ed do wn g lacier face and a trunca ted up g lacier fa ce which is th e o pposite o ri entatio n to that o f th e upper surfaces this so call ed d ouble sloss i ee form is interp re ted as a res ponse to basa l trans port over a brading ma teri als fo ll owing depos ition of th e clast a nd succeeded by g lacia l erosion it is sugges ted th a t clasts with a double stoss iee rorm are a diagnos ti c criteri on fo r subg lacial depos ition by lodgement furlh ermore the distributi o n and orienta tion of cl as ts with a stoss i ee form was in ves ti gated o n a ground mora ine surface 17 3 of2199 cl as ts with a n a ax is di a meter 30 cm had a stoss iee fo rm the proportion of clasts with th eir smoo th ed e nds facing up glacier within 22 5 of the ice fl o w directi on was 72 7 thus th e preferred stoss sid e ori enta tion is closely rela ted to th e ice mo vement a nd indica tes th e direc ti on from which th e ice came only 11 7 of bo ulders with a divergent stoss sid e ori ent a ti on a re located in conn ecti o n with annual mo rain es it is sugges ted th a t such bould ers have mainl y been re de posit ed beneath the ice a nd not at the ice rront by minor adva nces of the gl acier

flow and fracture maps for basaltic rock deformation at high temperatures understanding how the strength of basaltic rock varies with the extrinsic conditions of stress state pressure and temperature and the intrinsic rock physical properties is fundamental to understanding the dynamics of volcanic systems in particular it is essential to understand how rock strength at high temperatures is limited by fracture we have collated and analysed laboratory data for basaltic rocks from over 500 rock deformation experiments and plotted these on principal stress failure maps we have fitted an empirical flow law norton s law and a theoretical fracture criterion to these data the principal stress failure map is a graphical representation of ductile and brittle experimental data together with flow and fracture envelopes under varying strain rate temperature and pressure we have used these maps to re interpret the ductile brittle transition in basaltic rocks at high temperatures and show conceptually how these failure maps can be applied to volcanic systems using lava flows as an example c 2002 elsevier science b v all rights reserved

predictions for impactor contamination on ceres based on hypervelocity impact experiments new experiments predict that ceres should be extensively contaminated with meteoritic debris derived from the asteroid belt all types of impactors likely contribute to the contamination ceres may accrete debris more efficiently if it is ice rich because of enhanced projectile survival and retention in porous ice targets experiments indicate that if a silicate regolith lag protects subsurface ice then some of the projectile should be injected into the regolith during high angle impacts thereby hiding part of the projectile component from view if impacts excavate ice sublimation will gradually concentrate projectile relics into a surficial lag in contrast if the near surface lacks ice then accreted meteoritic debris should be distributed throughout a vertically mixed regolith high resolution images may reveal pristine projectile relics lining some crater floors moreover we predict that the surface of ceres is not exclusively endogenic and may be dominated by delivered exogenic debris

deep impact excavating comet tempel 1 deep impact collided with comet tempel 1 excavating a crater controlled by gravity the comet s outer layer is composed of 1 to 100 micrometer fine particles with negligible strength 1000 kelvins a large increase in organic material occurred during and after the event with smaller changes in carbon dioxide relative to water on approach the spacecraft observed frequent natural outbursts a mean radius of 3 0 0 1 kilometers smooth and rough terrain scarps and impact craters a thermal map indicates a surface in equilibrium with sunlight

boulder beds in the glaciogenic permo carboniferous dwyka formation in south africa single layer and massive boulder beds which include boulder pavements are sporadically distributed in the glaciogenic permo carboniferous dwyka formation these matrix supported beds consist of moderately to poorly sorted rounded boulders cobbles and pebbles with a clast composition similar to those in the underlying or overlying diamictite alternatively the clasts are composed of monolithic basement rock types the clasts show a long axis orientation which in the case of the boulder pavements is parallel to the striae on the pavements the various types of boulder beds have a similar mode of deposition and their subglacial origin is evidenced by the clast orientation clasts with stoss and lee sides stacking of clasts and the development of a cleavage in the matrix due to horizontal stresses exerted by the boulders in the subglacial sediment subglacial streams kame mounds subaqeously winnowed till or boulder beaches supplied the coarse debris which was entrained in the basal ice by plastic flow and regelation selective lodgement of the transported boulders occurred down glacier when the basal thermal conditions changed from cold freezing to warm melting the formation of the different types of boulder beds is thought to depend primarily on the concentration of coarse debris in the basal ice

laboratory impacts into dry and wet sandstone with and without an overlying water layer implications for scaling laws and projectile survivability scaling laws describing crater dimensions are defined in terms of projectile velocity and mass densities of the materials involved strength of the target and the local gravity here the additional importance of target porosity and saturation and an overlying water layer are considered through 15 laboratory impacts of 1 mm diameter stainless steel projectiles at 5 km s 1 into a an initially uncharacterized sandstone porosity 17 and b coconino sandstone porosity 23 the higher porosity dry sandstone allows a crater to form with a larger diameter but smaller depth than in the lower porosity dry sandstone furthermore for both porosities a greater volume of material is excavated from a wet target than a dry target by 27 30 comparison of our results with pi scaling dimensionless ratios of key parameters characterizing cratering data over a range of scales suggests that porosity is important for scaling laws given that the new data lie significantly beneath the current fit for ice and rock targets on a v versus 3 plot v gives cratering efficiency and 3 the influence of target strength an overlying water layer results in a reduction of crater dimensions with larger craters produced in the saturated targets compared to unsaturated targets a water depth of approximately 12 times the projectile diameter is required before craters are no longer observed in the targets previous experimental studies have shown that this ratio varies between 10 and 20 gault and sonett 1982 in our experiments 25 of the original projectile mass survives the impact

projectile remnants in central peaks of lunar impact craters unusual minerals observed in lunar craters were thought to originate from beneath the moon s surface numerical simulations show that rather than being vaporized much of the impactor material can survive in the crater implying that the unusual minerals come from the impactor and may not be indigenous to the moon

on subglacial stone pavements in till four pavements from central and western canada display uneven pavement surfaces abundant tilted and inverted stones reversed lee ends fine crossing striae in various directions weak striae around curves worn facets distributed evenly on rounded stones and till fabric girdles collectively inconsistent with the popular concept of stones firmly held in till being abraded by overriding ice based on these data new models are offered that involve stone rotation in viscously deforming till to produce deformation pavements in the specific model increased pore water pressure under moving ice locally mobilizes previously formed lodgment and or erosional pavements into deformation pavements in the more general model stones released from the sole of a wet based glacier rotate interact and settle into a viscous suspension zone in deforming till according to velocity density and viscosity gradients stone axes and striae settle into various orientations following dewatering and till stiffening conceptu

instability of partially saturated soil slopes due to alteration of rainfall pattern abstract the influence of climate change on rainfall patterns has the potential to alter stability of partially saturated soil slopes changes in rainfall patterns have a strong influence on stability of partially saturated soil slopes which recently have resulted in shallow landslides in this paper slope stability is assessed using a monolithically coupled finite element model for a deformable partially saturated soil subjected to surface infiltration of water numerical analysis solves for the matric suction distribution over a two dimensional cross section of a soil slope while varying permeability and considering a surface layer of soil with different permeability the formulation of hydraulic conductivity for a coupled analysis includes dependence on porosity and degree of saturation to illustrate the effects of water infiltration and deformation behavior in partially saturated soils numerical examples demonstrate that change in rainfall patterns may trigger slope instability earlier in the rainfall event than for rainfall events of the past assessment of these simulations can provide an indication of the potential influence of climate change on shallow landslides in many mountainous areas in south korea

performance of an unsaturated expansive soil slope subjected to artificial rainfall infiltration a major infrastructure project the south to north water transfer project has been proposed to carry potable water from the yangtze river region in the south to many arid and semi arid areas in the northern regions of china including beijing the proposed 1200 km middle route of the project is likely to be an open channel with a trapezoidal cross section at least 180 km of the proposed excavated canal will pass through areas of unsaturated expansive soils an 11 m high cut slope in a typical expansive clay with medium plasticity in zaoyang close to the middle route in hubei was selected for a comprehensive and well instrumented field study of the effects of rainfall infiltration two artificial rainfall events were created during a month of field investigation and monitoring prior to the rainfall events high soil suction was measured within the top 1 m of soil this high initial soil suction created an upward flux of water and moisture the abundant cracks and fissures near the ground surface p

a distributed slope stability model for steep forested basins a distributed physically based slope stability model dslam based on an infinite slope model a kinematic wave groundwater model and a continuous change vegetation root strength model is presented it is integrated with a contour line based topographic analysis and a geographic information system gis for spatial data extraction and display the model can be run with either individual rainfall events or long term sequences of storms these inputs can be either actual storm records or synthesized random events based on monte carlo simulation the model is designed to analyze rapid shallow landslides and the spatial distribution of safety factor fs in steep forested areas it can investigate the slope stability problem in both temporal and spatial dimensions for example the impact of timber harvesting on slope stability either at a given time or through an extended management period the probability of landslide occurrence for a given year and the delivery of landslide sediments to headwater streams the dslam model was applied in a steep forested drainage of cedar creek in the oregon coast ranges using actual spatial patterns of timber harvesting and measured rainfall during a major storm which triggered widespread landslides in that area in 1975 simulated volume and number of failures were 733 m3 and 4 respectively these values agreed closely with field measurements following the 1975 storm however the effect of parameter uncertainty may complicate this comparison for example when soil cohesion values of 2 0 and 3 0 kpa were used the failure volume changed by factors of 2 04 and 0 41 respectively compared with the average condition of 2 5 kpa used in the simulation for soil depths 30 higher and lower than the standard condition the failure volume changed by factors of 2 0 and 0 27 respectively when maximum root cohesion changed from 12 5 kpa average condition to 10 kpa the failure volume increased 1 73 fold for the case of 15 kpa the failure volume changed by a factor of 0 55 the simulated failures caused by the storm were mostly in hollows the simulations show that the spatial distribution of fs is controlled mainly by topography and timber harvesting patterns and is greatly affected by groundwater flow patterns during major rainstorms most areas with fs 3 0 corresponded with the distribution of blocks clear cut in 1968 and all elements with fs 2 0 were in areas clear cut in 1968 areas with low fs 1 0 1 6 expanded dramatically during the rainstorm and decreased at a slow rate after the storm factors of safety in hollows declined sharply during the storm

model for the prediction of shear strength with respect to soil suction experimental studies on unsaturated soils are generally costly time consuming and difficult to conduct shear strength data from the research literature suggests that there is a nonlinear increas

intertidal boulder pavements in the northeastern gulf of alaska and their geological significance abstract striated boulder pavements consisting of planar concentrations of clasts having striated upper surfaces are a common feature of glacigenic deposits but their origin is not well understood laterally extensive pavements are currently forming in the intertidal zone west of icy bay in the gulf of alaska pavements comprise armoured layers of interlocking boulders one clast thick that have been eroded from underlying outcrops of late cenozoic glaciomarine diamictites they originate essentially as lag surfaces along a high energy storm dominated mesotidal shoreline boulder pavements are either flat or show a nucleated plan form where successively smaller boulders have been accreted around a large core boulder nucleation imparts a hummocky surface topography to the pavements and suggests that some form of size sorting of clasts has occurred packing is promoted by repeated tamping of the clast lag by floating masses of glacier ice which become grounded across the intertidal zone at low tide repeated abrasion of the pavement surface by debris contained within ice blocks produces smooth flattened clast upper surfaces and short randomly oriented striations data from icy bay can be used to constrain the origin of laterally extensive boulder pavements exposed in late cenozoic glaciomarine sediments on middleton island the significance of such pavements in the geologic record is that they form along erosional unconformities and may identify sequence boundaries

the upper paleozoic pebbly mudstone facies of peninsular thailand and western malaysia continental margin deposits of paleoeurasia reply the phuket group in peninsular thailand and the singha formation in nw malaysia are of devonian to lower permian age these approximately 3000 m thick strata which are part of the se asian pebbly mudstone belt stretching from southern tibet to sumatra have been interpreted as continental margin deposits mitchell et al 1970 in contrast recent papers bunopas et al 1978 stauffer 1983 propose a glaciomarine origin these authors follow the scenario that parts of mainland se asia shan thai craton rifted away from gondwana during the lower carboniferous and collided with eurasia during the late triassic after crossing the tethys ocean under clockwise rotation of more than 180 degrees in this paper the arguments of these authors will be discussed and a sedimentological description will be given which shows that the pebbly mudstones are not glaciomarine sediments but rather of continental margin origin the investigations on phuket and langkawi islands when compared with newest results from central and north thailand clearly show that the shan thai craton was a part of or closely connected with palaeoeurasia indosinia during carboniferous and permian times comp helmcke 1985 the pebbly mudstones were deposited on the southern continental margin of this continent northern margin of tethys

the formation of a geometrical ridge network by the surge type glacier kongsvegen svalbard traditionally geometrical ridge networks are interpreted as the product of the flow of subglacial sediment into open basal crevasses at the cessation of a glacier surge crevasse fill ridges they are widely regarded as a characteristic landform of glacier surges understanding the range of processes by which these ridge networks form is therefore of importance in the recognition of palaeosurges within the landform record the geometrical ridge network at the surge type glacier kongsvegen in svalbard does not form by crevasse filling the networks consist of transverse and longitudinal ridges that can be seen forming at the current ice margin the transverse ridges form as a result of the incorporation of basal debris along thrust planes within the ice the thrusts were apparently formed during a glacier surge in 1948 longitudinal ridges form through the meltout of elongated pods of debris which on the glacier surface are subparallel to the ice foliation and pre date the surge this work adds to the range of landforms associated with glacier surges

two dimensional numerical modeling of the rheasilvia impact formation 1 we numerically modeled the formation of rheasilvia crater an enormous impact basin centered on asteroid 4 vesta s south pole using a trial and error method our models were adjusted to produce the best possible fit to rheasilvia s size and shape as observed during the vesta orbital stage of the dawn mission the final model yields estimates of the shock wave decay escaped material volume depth of excavation and other relevant characteristics to the extent allowed by the two dimensional axially symmetric approximation of the simplified arbitrary lagrangian eulerian hydrocode our model results permit interpretation of the dawn data on vesta s shape topographic crater profiles and the origin of the vestoid asteroid family as escaped ejecta from the rheasilvia crater

composition and mineralogy of dark material units on vesta vesta is the asteroid with the largest albedo variation among the known rocky solar system objects and shows a widespread occurrence of dark material dm and bright material bm units in the first observation phases by the dawn spacecraft two main extensions of low albedo areas were identified on vesta and found to be closely correlated with carbonaceous oh rich material in this work we use the hyperspectral data provided by the vir dawn imaging spectrometer onboard dawn to detect and analyze individual well defined dark material units we define dm units assuming a relative criterion i e reflectance lower than the surroundings by coupling visible and infrared images of the same area we are able to select real dark material units discarding false detections created by shadowing effects a detailed final catalogue of 123 dark units is presented containing the geographical parameters and the main spectral characteristics for each unit independently of the geological context of the dark units all dms show similar spectral properties dominated by the pyroxene absorption features as is the average spectrum of vesta this finding suggests a similar composition with the presence of darkening agents that also weaken pyroxene band depths the majority 90 of the dm units shows a positive correlation between low albedo and an oh band centered at 2 8 lm confirming the hypothesis that the darkening agents are carbonaceous chondrites probably delivered by low velocity impacts of primitive asteroids a comparison with laboratory spectra allows us to better constrain the size and the composition of the darkening agents these dm areas seem to be made of eucritic material the regolith grain size seems to be nearly constant around an average value of 25 lm and is quite homogenous at least in the first hundreds of meters beneath the vesta surface suggesting similar processing mechanisms for both dm and bm

infinite slope stability under steady unsaturated seepage conditions 1 we present a generalized framework for the stability of infinite slopes under steady unsaturated seepage conditions the analytical framework allows the water table to be located at any depth below the ground surface and variation of soil suction and moisture content above the water table under steady infiltration conditions the framework also explicitly considers the effect of weathering and porosity increase near the ground surface on changes in the friction angle of the soil the factor of safety is conceptualized as a function of the depth within the vadose zone and can be reduced to the classical analytical solution for subaerial infinite slopes in the saturated zone slope stability analyses with hypothetical sandy and silty soils are conducted to illustrate the effectiveness of the framework these analyses indicate that for hillslopes of both sandy and silty soils failure can occur above the water table under steady infiltration conditions which is consistent with some field observations that cannot be predicted by the classical infinite slope theory a case study of shallow slope failures of sandy colluvium on steep coastal hillslopes near seattle washington is presented to examine the predictive utility of the proposed framework

hypervelocity impact fragmentation of basalt and shale projectiles abstract results are presented for the fragmentation of projectiles in laboratory experiments 1 5 mm cubes and spheres of basalt and shale were impacted onto water at normal incidence and speeds from 0 39 to 6 13 km s 1 corresponding to peak shock pressures 0 7 32 gpa projectile fragments were collected and measured over 100 000 fragments in some impacts at sizes down to 10 m power laws were fitted to the cumulative fragment size distributions and the evolution of the exponent vs impact speed and peak shock pressure found the gradient of each of these power laws increased with increasing impact speed peak shock pressure the percentage of the projectiles recovered in the impacts was found and used to estimate projectile remnant survival in different solar system impact scenarios at the mean impact speed appropriate to that scenario for pluto the moon and in the asteroid belt approximately 55 40 and 15 respectively of an impactor could survive and be recovered at an impact site finally the catastrophic disruption energy densities of basalt and shale were measured and found to be 24 104 j kg 1 and 9 104 j kg 1 respectively a factor of 2 5 difference these corresponded to peak shock pressures of 1 to 1 5 gpa basalt and 0 8 gpa shale this is for near normal incidence impacts where tensile strength is dominant for shallow angle impacts we suggest shear effects dominate resulting in lower critical energy densities and peak shock pressures we also determine a method to ascertain information about fragment sizes in solar system impact events using a known size of impactor the results are used to predict projectile fragments sizes for the veneneia and rheasilvia crater forming impacts on vesta and similar impacts on ceres

delivering a projectile component to the vestan regolith abstract dark material on vesta may consist of carbonaceous chondrite like material delivered by impact events this study uses hypervelocity impact experiments to assess the viability of the impact delivery hypothesis experiments reveal that impact events deliver significant fractions of the projectile to the target during impacts at average vestan speeds hence dark material can plausibly be delivered to vesta by impacts with the projectile component accumulating in the regolith with time projectile retention is sensitive to impact angle ranging from 7 for 30 impacts measured from horizontal to 72 for vertical impacts averaged over the probability distribution of impact angles 17 of the projectile s mass remains in or near the crater projectile contaminated breccias largely remain inside the crater for vertical impacts in oblique impacts projectile contaminated pieces concentrate downrange beyond the crater rim based on experiments projectile delivery is expected for typical vestan impact conditions not only for extraordinary events such as low probability and very low speed e g

smart 1 end of life shallow regolith impact simulations the smart 1 end of life impact with the lunar surface was simulated with impacts in a two stage light gas gun onto inclined basalt targets with a shallow surface layer of sand this simulated the probable impact site where a loose regolith will have overlaid a well consolidated basaltic layer of rock the impact angles used were at 5 and 10 from the horizontal the impact speed was 2 km s 1 and the projectiles were 2 03 mm diameter aluminum spheres the sand depth was between approximately 0 8 and 1 8 times the projectile diameter implying a loose lunar surface regolith of similar dimensions to the smart 1 spacecraft a crater in the basement rock itself was only observed in the impact at 10 incidence and where the depth of loose surface material was less than the projectile diameter in which case the basement rock also contained a small pit like crater in all cases the projectile ricocheted away from the impact site at a shallow angle this implies that at the smart 1 impact site the crater will have a complicated structure with exposed basement rock and some excavated rock displaced nearby and the main spacecraft body itself will not be present at the main crater

fracture patterns in clasts of diamictites tillites fracture patterns in some of the clasts of the gowganda formation ontario are inconsistent with aqueous deposition and suggest that locally the diamictites are tillites similar fracture patterns have been found in the clasts of modern tills in the cascade mountains rare examples were also seen on the garvellachs scotland laboratory experiments indicate that such patterns can be developed by the impaction of one clast against another while surrounded by a compliant matrix the stresses which induced cracking were of the same order of magnitude as those which can be expected to occur in a sub glacial environment

unsaturated soil mechanics in rainfall induced flow landslides abstract rainfall induced flow landslides in coarse grained soils pose significant threats to populations and structures due to their high velocities long travel distance and the absence of definite warning signs during the pre failure stage the triggering phase of these phenomena is frequently related to rainfall events which significantly reduce matric suction in the shallower soil layers in this paper the processes leading to the onset of such phenomena are illustrated and some observations on their modelling are briefly recalled the failure stage at different scales is then modelled with reference to a case study from southern italy which draws on high quality experimental data sets from extensive in situ and laboratory investigation

the preservation of fossil biomarkers during meteorite impact events experimental evidence from biomarker rich projectiles and target rocks a devonian siltstone from orkney scotland shows survival of biomarkers in high velocity impact experiments the biomarkers were detected in ejecta fragments from experiments involving normal incidence of steel projectiles at 5 6 km s 1 and in projectile fragments from impact experiments into sand and water at 2 5 km s 1 the associated peak shock pressures were calculated to be in the range of 110 147 gpa for impacts of the steel projectiles into the siltstone target and hydrocode simulations are used to show the variation of peak pressure with depth in the target and throughout the finite volume projectiles thermally sensitive biomarker ratios including ratios of hopanoids and steranes and the methylphenanthrene ratio showed an increase in thermal maturity in the ejecta and especially the projectile fragments measurement of absolute concentrations of selected biomarkers indicates that changes in biomarker ratios reflect synthesis of new material rather than selective destruction their presence in ejecta and projectile fragments suggests that fossil biomarkers may survive hypervelocity impacts and that experiments using biomarker rich rock have high potential for testing survival of organic matter in a range of impact scenarios

origin and implications of non radial imbrium sculpture on the moon the widespread rimmed grooves lineations and elongate craters extending from the imbrium impact basin on the moon termed the imbrium sculpture includes a non radial component that is used to infer that the imbrium impactor was the size of a proto planet about half the diameter of vesta the pattern of rimmed grooves lineations and elongate craters around mare imbrium on the moon has been termed the imbrium sculpture rather than radiating from the centre of imbrium the grooves come from different locations reflecting the consequence of a giant oblique collision peter schultz and david crawford use the non radial trends in these patterns to infer that the imbrium impactor was a proto planet with a diameter about half that of the asteroid vesta on the basis of laboratory impact experiments shock physics codes and the observed groove widths the authors conclude that multiple fragments from each oblique basin forming impactor such as the one that formed imbrium should have survived planetary collisions and contributed to the heavy impact bombardment between 4 3 and 3 8 billion years ago rimmed grooves lineations and elongate craters around mare imbrium shape much of the nearside moon this pattern was coined the imbrium sculpture1 and it was originally argued that it must have been formed by a giant oblique 30 impact a conclusion echoed by later studies2 some investigators however noticed that many elements of the imbrium sculpture are not radial to imbrium thereby implicating an endogenic or structural origin3 4 here we use these non radial trends to conclude that the imbrium impactor was a proto planet half the diameter of vesta once part of a population of large proto planets in the asteroid belt such independent constraints on the sizes of the imbrium and other basin forming impactors markedly increase estimates for the mass in the asteroid belt before depletion caused by the orbital migration of jupiter and saturn5 moreover laboratory impact experiments shock physics codes and the groove widths indicate that multiple fragments up to 2 of the initial diameter from each oblique basin forming impactor such as the one that formed imbrium should have survived planetary collisions and contributed to the heavy impact bombardment between 4 3 and 3 8 billion years ago

influence of rainfall induced wetting on the stability of slopes in weathered soils abstract shallow failures of slopes in weathered soil are caused by infiltration due to prolonged rainfall these failures are mainly triggered by the deepening of the wetting band accompanied by a decrease in matric suction induced by the water infiltration this paper reports trends of rainfall induced wetting band depth in two types of weathered soils that are commonly found in korea both theoretical and numerical analyses for wetting band depth are presented based on the soil water characteristic curve obtained using filter paper as well as tensiometer tests it is found that the magnitude of wetting front suction plays a key role in the stability of slopes in weathered soils theoretical analysis based on modified green and ampt model tends to underestimate the wetting band depth for typical korean weathered soils it was also deduced that for korean weathered soils the factor of safety drops rapidly once the wetting band depth of 1 2 m reached

control of glacial quarrying by bedrock joints abstract a principal assumption of models that describe bedrock quarrying by glaciers is that cracks in the bed are small and isolated these cracks are assumed to grow slowly in response to glacial loading to eventually delimit the areas of quarried surfaces if this assumption is correct then quarried surface orientations will be controlled by orientations of principal stresses in the bed associated with sliding and resultant ice bed separation downglacier from rock ledges and roches moutonnees rather than by orientations of joints that predate glacial loading to test this hypothesis we compared orientations of quarried surfaces and preglacial joints in nine recently deglaciated forefields of glaciers in canada and switzerland with different bedrock lithologies and bedforms in all but one forefield quarried surfaces and major joint sets are coincident with orientations of quarried surfaces bearing no systematic relationship to sliding direction other than their obvious tendency to not face upglacier a difference in sliding direction of 64 between two areas of one glacier forefield had no effect on the orientation of quarried surfaces with the same joint set exploited in both areas these observations motivate a new characterization of subglacial bedrock that differs from that of existing quarrying models the bed is idealized as a group of rock blocks separated by preglacial joints slow crack growth necessary for quarrying would be confined to small bodies of rock bridges that connect the faces of joints this model of the bed does not allow it to be treated as an intact elastic solid with hydraulically isolated cracks as is usually assumed which would have a profound influence on characterization of quarrying mechanics

glacial abrasion and sliding their dependence on the debris concentration in basal ice a model of bedrock abrasion by a temperate glacier is developed that takes into account the significant impeding effect of scattered rock fragments at the ice rock interface on glacier sliding an increase in the debris concentration above a relatively low value can reduce the abrasion rate by decreasing both the flux of rock fragments and the effective forces which press fragments against the bed abrasion of a simple wavy bed is shown to be most rapid for a relatively low debris concentration above which the abrasion varies inversely with the debris content a similar concentration dependence of abrasion is expected for beds of arbitrary geometry but low roughness sliding glaciers will tend to abrade until the basal ice is nearly stagnant at which point rocks of all sizes start to lodge against the bed

the glaciation of dartmoor the southernmost independent pleistocene ice cap in the british isles the granite uplands of dartmoor have traditionally been considered to be relict permafrost and periglacial landscapes that lay beyond the limits of quaternary glaciations but a variety of landform evidence indicates that a plateau icefield existed on the northern part of the moor constituting the southernmost independent ice cap in the british isles overdeepened or weakly u shaped valley segments fringing north dartmoor document an early extensive phase of glaciation but the most convincing landform evidence relates to more recent valley based glacier occupancy a moraine ridge on the slipper stones represents the most unequivocal palaeo glacier on north dartmoor with a palaeo ela of c 460 m above sea level asl although this relates to the youngest and most restricted phase of glaciation a longer term ela is likely to be represented by the corn ridge proto cirque at 370 410 m asl more extensive valley glaciers are recorded in each of the major drainage basins of north dartmoor by arcuate and linear bouldery ridges and hummocky valley floor drift which are interpreted as latero frontal moraines deposited by outlet lobes of a plateau icefield recession of these lobes is marked by inset sequences of such ridges and occasional meltwater channels plateau ice was predominantly thin and protective and snowblow and preferential accumulation in valley heads facilitated the modest glacial erosion and debris transport recorded in the landforms and sediments it is proposed that the highest plateaux have been occupied by ice for the longest cumulative period of time throughout the quaternary average glacial conditions explaining the distribution of different tor types on northern dartmoor this also explains the lack of tors on the most expansive of the highest plateau terrain ice dispersal centres as the product of a average glacial conditions preferentially removing tors or dampening their production rates b the survival of high relief type 1 tors during glaciation if they occupy summits too narrow to develop significant plateau icefields and or ridges that are bypassed by faster moving ice in adjacent deep valleys and c the survival of subdued type 2 tors in areas glaciated less regularly during the quaternary simple ice flow modelling indicates that a plateau icefield type glaciation is required for significant ice flow to occur and confirms thin ice cover in particular on narrow summits thereby supporting the explanation of tor class distribution the modelling allows us to spatially correlate the geomorphological evidence of margin positions into two major stages and further indicates a strong altitude mass balance feedback leading to an ice cap that is not in balance with its climate and with an extent that is limited by the length of the cold phases rather than their severity

the variability of root cohesion as an influence on shallow landslide susceptibility in the oregon coast range decades of quantitative measurement indicate that roots can mechanically reinforce shallow soils in forested landscapes forests however have variations in vegetation species and age which can dominate the local stability of landslide initiation sites to assess the influence of this variability on root cohesion we examined scarps of landslides triggered during large storms in february and november of 1996 in the oregon coast range and hand dug soil pits on stable ground at 41 sites we estimated the cohesive reinforcement to soil due to roots by determining the tensile strength species depth orientation relative health and the density of roots 1 mm in diameter within a measured soil area we found that median lateral root cohesion ranges from 6 8 23 2 kpa in industrial forests with significant understory and deciduous vegetation to 25 6 94 3 kpa in natural forests dominated by coniferous vegetation lateral root cohesion in clearcuts is uniformly 10 kpa some 100 year old industrial forests have s

sedimentology and chronology of the advance and retreat of the last british irish ice sheet on the continental shelf west of ireland the last british irish ice sheet biis had extensive marine terminating margins and was drained by multiple large ice streams and is thus a useful analogue for marine based areas of modern ice sheets however despite recent advances from investigating the offshore record of the biis the dynamic history of its marine margins which would have been sensitive to external forcing s remain inadequately understood this study is the first reconstruction of the retreat dynamics and chronology of the western marine terminating margin of the last late midlandian biis analyses of shelf geomorphology and core sedimentology and chronology enable a reconstruction of the late midlandian history of the biis west of ireland from initial advance to final retreat onshore five ams radiocarbon dates from marine cores constrain the timing of retreat and associated readvances during deglaciation the biis advanced without streaming or surging depositing a bed of highly consolidated subglacial traction till and reached to within 20 km of the shelf break by 24 000 cal bp ice margin retreat was likely preceded by thinning grounding zone retreat and ice shelf formation on the outer shelf by 22 000 cal bp this ice shelf persisted for 2500 years while retreating at a minimum rate of 24 m yr and buttressing a 150 km long 20 km wide bathymetrically controlled grounding zone a large 150 km long arcuate flat topped grounding zone wedge termed here the galway lobe grounding zone wedge glgzw was deposited below this ice shelf and records a significant stillstand in biis retreat geomorphic relationships indicate that the biis experienced continued thinning during its retreat across the shelf which led to increased topographic influence on its flow dynamics following ice shelf break up and grounding zone retreat past the glgzw at this stage of retreat the western biis was comprised of several discrete asynchronous lobes that underwent several readvances sedimentary evidence of dilatant till deposition suggests that the readvances may have been rapid and possibly associated with ice streaming or surging the largest lobe extended offshore from galway bay and deposited the galway lobe readvance moraine by 18 500 cal bp further to the north an ice lobe readvanced at least 50 km offshore from killary harbour possibly by 15 100 cal bp the existing chronology currently does not allow us to determine conclusively whether these readvances were a glaciodynamic internally driven response of the ice sheet during deglaciation or were climatically driven following the 18 500 cal bp readvance the galway lobe experienced accelerated eastward retreat at an estimated rate of 113 m yr

the deep impact crater on 9p tempel 1 from stardust next abstract the stardust next sdn mission returned to comet 9p tempel 1 and viewed the site of the deep impact di collision just over one comet year later comparisons between pre impact images from the its camera on the di probe and sdn images reveal a 50 m diameter crater surrounded by a low rim about 180 m in diameter the removal of a small mound uprange but offset from the trajectory from the impact site can be related to changes in the evolution of ejecta a narrow 6 gap in the ejecta curtain downrange indicates that a ridge extending from the impact facing scarp downrange interrupted the final stages of cratering in one small region together these observations indicate that the di excavation crater diameter was about 200 m 20 m a value consistent with the ejected mass derived from earth and space based observations with the assumption that this mass represents only 10 20 of the total ejected mass as a result the di crater visible today is consistent with either a larger transient crater which collapsed or a central crater of a nested crater resembling an inverted sombrero the latter alternative would be expected from a layered target a loose particulate surface about 1 2 m deep over a slightly more competent substrate

alpine debris flows triggered by a 28 july 1999 thunderstorm in the central front range colorado on 28 july 1999 about 480 alpine debris flows were triggered by an afternoon thunderstorm along the continental divide in clear creek and summit counties in the central front range of colorado the thunderstorm produced about 43 mm of rain in 4 h 35 mm of which fell in the first 2 h several debris flows triggered by the storm impacted interstate highway 70 u s highway 6 and the arapahoe basin ski area we mapped the debris flows from color aerial photography and inspected many of them in the field three processes initiated debris flows the first process initiated 11 of the debris flows and involved the mobilization of shallow landslides in thick often well vegetated colluvium the second process which was responsible for 79 of the flows was the transport of material eroded from steep unvegetated hillslopes via a system of coalescing rills the third which has been termed the firehose effect initiated 10 of the debris flows and occurred where overland flow became concentrated in steep bedrock channels and scoured debris from talus deposits and the heads of debris fans these three processes initiated high on steep hillsides 30 in catchments with small contributing areas 8000 m2 however shallow landslides occurred on slopes that were significantly less steep than either overland flow process based on field observations and examination of soils mapping of the northern part of the study area we identified a relation between the degree of soil development and the process type that generated debris flows in general areas with greater soil development were less likely to generate runoff and therefore less likely to generate debris flows by the firehose effect or by rilling the character of the surficial cover and the spatially variable hydrologic response to intense rainfall rather than a threshold of contributing area and topographic slope appears to control the initiation process in the high alpine of the front range because debris flows initiated by rilling and the firehose effect tend to increase in volume as they travel downslope these debris flows are potentially more hazardous than those initiated by shallow landslides which tend to deposit material along their paths

mechanism of a long runout landslide triggered by the august 1998 heavy rainfall in fukushima prefecture japan abstract heavy rainfall from 26 to 31 august 1998 triggered many landslides in nishigo village of southern fukushima prefecture japan the hiegaesi landslide a long runout landslide with travel angle of 11 which occurred in loamy volcanic ash pumice layer and was deposited in a nearby rice paddy was investigated in an observation pit dug in the middle part of the landslide deposit the sliding zone just above the deflected rice plants was observed and it was confirmed that grain crushing occurred in the sliding zone the triggering and sliding mechanisms of this landslide then were investigated by ring shear tests in laboratory for the triggering mechanism one saturated naturally drained test test a torque controlled test and one saturated undrained test test b speed controlled test were conducted on the samples taken from the source area of the landslide even in the naturally drained test opening the upper drain valve of the shear box a temporary liquefaction occurred in the undrained test excess pore pressure was generated along with shearing and sliding surface liquefaction phenomenon was observed the effective stress and shear resistance finally decreased to near zero these results can explain the observed phenomenon of small friction resistance like a flow of liquid when the sliding mass slid out of the source area for the sliding mechanism of the landslide in the rice paddy saturated undrained test test c speed controlled test was performed on soil sample above the deflected rice plants the apparent friction angle obtained in this test was 8 in addition the residual friction angle measured after test b and test c was the same value of 41 combining with the observation on the shear zone in the ring shear box after test c it is concluded that during the sliding in rice paddy the undrained shear strength of the soil layer itself mainly influenced the high mobility of the landslide probably because the friction between rice plants and soils is greater than the undrained shear strength inside the soil mass

predicting the unconfined compressive strength of the breathitt shale using slake durability shore hardness and rock structural properties abstract compressive strength is the most widely used design parameter in the construction industry and in rock engineering for example bieniawski bieniawski z t estimating the strength of rock materials is j s afr inst min metall 1974 74 312 320 reported that mining engineers request the uniaxial compressive strength ucs more often than any other rock property however standards set for specimen preparation are very demanding therefore it is quite difficult and sometimes impossible to fulfill these requirements using weak rocks and especially shales this paper evaluates the use of the slake durability and shore hardness tests to estimate ucs based on laboratory correlations performed for this study and others and based on analysis of structural and physical material properties affecting both strength and durability

return to comet tempel 1 overview of stardust next results on february 14 2011 stardust next sn flew by comet tempel 1 the target of the deep impact di mission in 2005 obtaining dust measurements and high resolution images of areas surrounding the 2005 impact site and extending image coverage to almost two thirds of the nucleus surface the nucleus has an average radius of 2 83 0 1 km and a uniform geometric albedo of about 6 at visible wavelengths local elevation differences on the nucleus reach up to 830 m at the time of encounter the spin rate was 213 per day period 40 6 h and the comet was producing some 130 kg of dust per second some 30 of the nucleus is covered by smooth flow like deposits and related materials restricted to gravitational lows this distribution is consistent with the view that the smooth areas represent material erupted from the subsurface and date from a time after the nucleus achieved its current shape it is possible that some of these eruptions occurred after 1609 when the comet s perihelion distance decreased from 3 5 au to the current 1 5 au much of the surface displays evidence of layering some related to the smooth flows and some possibly dating back to the accretion of the nucleus pitted terrain covers approximately half the nucleus surface the pits range up to 850 m in diameter due to their large number they are unlikely to be impact scars rather they probably result from volatile outbursts and sublimational erosion the di impact site shows a subdued depression some 50 m in diameter implying surface properties similar to those of dry loose snow it is possible that the 50 m depression is all that remains of an initially larger crater in the region of overlapping di and sn coverage most of the surface remained unchanged between 2005 and 2011 in albedo photometric properties and morphology significant changes took place only along the edges of a prominent smooth flow estimated to be 10 15 m thick the margins of which receded in places by up to 50 m coma and jet activity were lower in 2011 than in 2005 most of the jets observed during the sn flyby can be traced back to an apparently eroding terraced scarp the dust instruments detected bursts of impacts consistent with a process by which larger aggregates of material emitted from the nucleus subsequently fragment into smaller particles within the coma

ice margin influence on glaciomarine sedimentation in the permo carboniferous dwyka formation from the southwestern karoo south africa a persistent sedimentary unit interbedded in massive diamictite over a distance of almost 400 km near the top of the permo carboniferous dwyka formation in the southwestern karoo consists of stratified diamictite rhythmite lonestone argillite and black shale the stratified diamictite facies association is interpreted as ice marginal debris flow the diamictite lonestone argillite facies association as proximal to intermediate debris flow debris rain and suspension settling and the shale diamictite facies association as distal debris flow and suspension settling deposits an analysis of the mudrock and diamictite facies relationships suggests deposition from a rapidly calving oscillating ice margin in the east and at a consistently retreating grounded ice margin with few icebergs in the west sediment sources volume of ice rafting resedimentation processes ice marginal recession and advance and configuration of the ice margin influenced the distribution of debris flow deposits and bergstone mud in the east and resulted in a near random facies arrangement due to a lack of icebergs in the west debris flow deposits and bergstone mud were poorly developed which reduced the number of facies transitions and variation resulting in a more systematic upward fining sequence

three dimensional microstructure of samples recovered from asteroid 25143 itokawa comparison with ll5 and ll6 chondrite particles in this study the three dimensional 3 d microstructure of 48 itokawa regolith particles was examined by synchrotron microtomography at spring 8 during the preliminary examination of hayabusa samples moreover the 3 d microstructure of particles collected from two ll6 chondrites ensisheim and kilabo meteorites and an ll5 chondrite tuxtuac meteorite was investigated by the same method for comparison the modal abundances of minerals especially olivine bulk density porosity and grain size are similar in all samples including voids and cracks these results show that the itokawa particles which are surface materials from the s type asteroid itokawa are consistent with the ll chondrite materials in terms of not only elemental and isotopic composition of the minerals but also 3 d microstructure however we could not determine whether the itokawa particles are purely ll5 ll6 or a mixture of the two no difference between the particles collected from rooms a and b of the sample chamber corresponding to the sampling sequence of the spacecraft s second and first touchdowns respectively was detected because of the statistically small amount of particles from room b

an extensive late holocene glacier advance of kotlujokull central south iceland this paper presents data on an extensive late holocene advance of kotlujokull a southeastern outlet glacier from the ice cap myrdalsjokull central south iceland during the advance basal till was deposited on top of a volcanic ash layer resting on lava hummocks remnants of this landscape are now seen 3 5 5 5 km in front of kotlujokull as a fragment surrounded by the myrdalssandur electron microprobe analysis of the volcanic ash shows that it is silicic and originates from the volcano katla underneath myrdalsjokull a c 14 ams date on a twig fragment sampled in the upper part of the volcanic ash layer provides a maximum age of the till of 1610 40 yr bp and this is supported by tephrochronological and geochemical analyses of the volcanic ash it is concluded that kotlujokull must have advanced more than 5 5 km from its present position after 1 6 kyr 13p this advance is much more extensive than the little ice age lia advance and took place in a relatively cold period also identified in the greenland ice cores and the diatom record in the seas surrounding iceland in the proglacial environment in front of the icelandic ice caps the preservation potential of older end moraines is strongly restricted due to intense glaciofluvial erosion therefore the lia end moraines have in many cases been interpreted as marking the outermost holocene glacier front position this study as well as other recent results stresses the fact that the lia glacial maximum in iceland may not be identical to the holocene glacial maximum and that far more case studies with well constrained dating control are needed c 2003 elsevier science ltd all rights reserved less

paleomagnetism of permian sedimentary rocks from tanzania and the permian paleogeography of pangea abstract we report new paleomagnetic results from karoo permian rocks in tanzania k1 and k3 redbeds and k5 siltstones and limestones from the songwe kiwira basin ndeke redbeds from the mikumi basin and group viii redbeds from the nyakatitu basin were sampled and thermally demagnetized palynologic data and lithologic correlations suggest that the k1 redbeds are lower permian and that the k3 ndeke and group viii redbeds as well as the k5 siltstones and limestones are upper permian stable magnetic directions were obtained from the k3 ndeke and group viii redbeds yielding an upper permain pole at 26 n 267 e characteristic remanence directions were also obtained from the k5 siltstones and limestones however because these directions define a pole 66 n 269 e that is very close to the upper cretaceous pole for africa and significantly different from the upper permian redbed poles these rocks may have been remagnetized the k1 redbeds did not yield stable results using our new results together with published permian poles for africa and the other gondwanan continents we revise the mean lower and upper permian poles for africa west gondwana and gondwana and investigate whether or not these revised poles can discriminate between the various pangea reconstructions proposed for the permian with any greater certainty than previous unrevised mean poles when compared to the mean lower and upper permian poles for laurussia we find that our revised west gondwanan and gondwanan poles do not necessarily provide stronger support for any particular pangea reconstruction than the previous poles therefore even though this study improves the paleomagnetic data base for gondwana for the permian it is not clear that the combination of our results with other paleomagnetic data from the gondwanan continents yields significant new insights about the permian configuration of pangea as suggested previously strong non dipole fields during the permian may provide an explanation for why it is not easy to discriminate with certainty between the various permain pangea reconstructions even with new paleomagnetic results

potential effects of subglacial water pressure fluctuations on quarrying water pressure fluctuations beneath glaciers may accelerate rock fracture by redistributing stresses on subglacial bedrock and changing the pressure of water in bedrock cracks to study the potential influence of water pressure fluctuations on the fracture of subglacial bedrock ice flow over a small bedrock step with a water filled cavity in its lee is numerically modeled and stresses on the bedrock surface are calculated as a function of transient water pressures in the cavity stresses on the bed are then used to calculate principal stress differences within the step rapid reductions in cavity water pressure increase principal stress differences in the bed increasing the likelihood of crack growth in the step and the formation of predominantly vertical fractures relatively impermeable bedrock may be most susceptible to fracturing during water pressure reductions because high water pressure in cracks within the rock can be maintained as water pressure decreases in cavities these results when considered in conjunction with the strong likelihood that increases in water pressure accelerate the removal of rock fragments loosened from the bed suggest that in zones of ice bed separation where water pressure fluctuations typically are large rates of quarrying may be higher than along other parts of glacier beds

rainfall induced landslides by deficit field matric suction in unsaturated soil slopes landslides are mainly triggered by decrease in the matric suction with deepening the wetting band by rainfall infiltrations this paper reports rainfall induced landslides in partially saturated soil slopes through a field study a comprehensive analysis on umyeonsan mt landslides in 2011 was highlighted the incident involves the collapse of unsaturated soil slopes under extreme rainfall event fundamental studies on the mechanism and the cause of landslides were carried out a number of technical findings are of interest including the failure mechanism of a depth of soil and effect of groundwater flow the downward movement of wetting band and the increase of groundwater level based on this an integrated analysis methodology for a rainfall induced landslide is proposed in this paper that incorporates the field matric suction for obtaining hydraulic parameters of unsaturated soil the field matric suction is shown to govern the rate of change in the water infiltration for the landslide analysis with respect to an antecedent rainfall special attention was given to a one dimensional infiltration model to determine the wetting band depth in the absence of the field matric suction the results indicate that landslide activities were primarily dependent on rainfall infiltration soil properties slope geometries vegetation and groundwater table positions the proposed methodology has clearly demonstrated both shallow and deep seated landslides and shows good agreement with the results of landslide investigations