carbon sequestration activated by a volcanic co 2 pulse during ocean anoxic event 2 ninety four million years ago during ocean anoxic event 2 there was a marked increase in the burial of organic carbon in marine sediments measurements of stomata in fossil leaves show that the two main pulses of carbon burial were associated with a decline in atmospheric co2 levels of up to 26 the cretaceous ocean anoxic event 2 about 94 million years ago is thought to be linked to extensive volcanism which triggered a biogeochemical chain of events that eventually led to widespread marine anoxia and a remarkable increase in carbon burial in marine sediments1 2 3 it has been suggested that the event was accompanied by a substantial decrease in atmospheric co2 concentrations4 but the quantification of the drawdown remains controversial5 6 here we reconstruct atmospheric co2 concentrations throughout the ocean anoxic event from counts of the stomata in fossil leaves and use terrestrial carbon isotopes to link the reconstruction to marine records of the event7 8 we find that before the onset of ocean anoxia atmospheric co2 concentrations increased by 20 over background levels of 370 100 70 ppm this was part of a long term rise in atmospheric co2 levels presumably caused by volcanism which reached a peak of 500 400 180 ppm however two pulses of extensive carbon burial during the ocean anoxic event as indicated by positive carbon isotope excursions are associated with decreased atmospheric co2 concentrations we conclude that the sequestration of marine organic carbon led to a decrease in atmospheric co2 concentration of up to 26 during ocean anoxic event 2

dynamic analysis and field investigation of a fluidized landslide in guanling guizhou china abstract on june 28 2010 a large catastrophic landslide was triggered by a heavy rainfall in guanling guizhou china this catastrophic event destroyed two villages and caused 99 casualties the landslide involved the failure of about 985 000 m 3 of sandstone from the source area the displaced materials traveled about 1300 m with a descent of about 400 m covering an area of 129 000 m 2 with the final volume being accumulated to be 1 840 000 m 3 approximately to provide information for hazard zonation of similar type of landslides in the same area we used a dynamic model dan3d to simulate the runout behavior of the displaced landslide materials and found that a combined frictional vollemy model could provide the best performance in simulating this landslide and the runout is precisely duplicated with a dynamic friction angle of 30 and a pore pressure ratio r u of 0 55 for the materials at the source area and with vollemy parameters of friction coefficient f 0 1 dimensionless and turbulent coefficient 400 m s 2 the simulated results indicated that the duration of the movement is estimated at about 60 s for a mean velocity 23 m s to examine the effectiveness of simulation by means of dan3d and also to evaluate the reactivation potential of these displaced landslide materials depositing on the valley we used electrical resistivity tomography ert method to survey the depth and internal structure of landslide deposits the ert results showed that dan3d gave a good prediction on the shape and runout distance of the landslide deposits although the predicted maximum depths of landslide deposit on some areas were differing from those obtained by ert method

numerical modelling of entrainment deposition in rock and debris avalanches abstract rock and debris avalanches as well as debris flows are characterized by peculiar behaviour influenced by geometry of the initial failure surface topography involved materials involved and water content during their motion rock avalanches can entrain large volumes of sediments both in a dry and in a saturated state entrained dry material has generally the consequence to reduce the total landslide runout whereas entrainment of almost saturated material can have more complex consequences we use a finite element code to simulate the motion of a moving landslide mass on materials with different properties and along very sharp topographies erosion and deposition can be modelled as well as interaction with obstacles of different characteristics we present two examples of the modelling problems and capabilities we simulated the runout of a rock avalanche on a ground formed by alluvial material under dry and saturated conditions this material can be entrained and plowed by the impacting and running rock avalanche material sensitivity of the erosion and transport mechanisms has been analysed by performing different analyses the simulated case study is the 6 10 5 m 3 arvel rock avalanche 1922 switzerland for which a reliable set of pre and post failure observations is available final geometry mass redistribution velocities and runup are used to validate the model capabilities and study the effects of different material properties

a two layer numerical model for simulating the frontal plowing phenomenon of flow like landslides abstract many flow like landslides entrain material from their paths during motion at the flow front and along the lateral margins the sliding mass can plow into the path material pushing or entraining the existing soil although plowing can be a dominant mechanism for landslide mobility little attention has been paid to this phenomenon in comparison with other entraining mechanism such as basal scouring therefore establishing a suitable mathematical description is still a challenge in this paper a two layer finite difference model is proposed to simulate frontal plowing the frontal erodible mass and the sliding mass are simplified as two separate layers based on the assumption that they are immiscible in their propagation processes the interaction i e thrusting and shear between the two layers is simulated by the normal force and shear force acting on the two layer interface the governing equations for the two layer model are deduced from the mass and momentum conservations of a soil column and transformed into a finite difference form for numerical solving then the proposed model is tested in the back analysis of the ximiaodian landslide which is a typical loess flow like landslide located at the south bank of the jing river china the modeling results show that frontal plowing has significant influence on the propagation of this landslide especially on the final topography of the deposit without considering this effect the thickness of the final deposit tends to be underestimated while the propagation duration area and distance are likely to be overestimated the proposed model can provide more accurate and reliable simulations for rapid flow like landslides with frontal plowing phenomenon

geomorphology landslide boost from entrainment the mechanisms that govern the growth of debris flows are largely unclear hampering efforts to assess natural hazards in landslide prone areas experiments suggest that high bed water content increases flow velocity and mass entrainment in landslides

dynamic modelling of entrainment in rapid landslides entrainment of path material is an important feature of many rapid landslides the associated increases in volume and changes in flow character can significantly influence mobility a simple material entrainment algorithm based on the assumption of natural exponential growth with displacement has been incorporated into a new computer model designed to simulate rapid landslide motion across 3d terrain the user controls the growth rate and can also implement a change in rheology at the onset of entrainment a hypothetical example is used to demonstrate the influence of the mass and momentum transfer assumptions a back analysis of the 1999 nomash river landslide is included to show that the simple model is capable of simulating the bulk characteristics of a complex event involving substantial entrainment key words landslides debris flows rock avalanches entrainment erosion dynamic modelling

positive feedback and momentum growth during debris flow entrainment of wet bed sediment debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep debris mantled slopes the flows can then grow dramatically in size and speed as they entrain material from their beds and banks but the mechanism of this growth is unclear indeed momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged here we use data from large scale experiments to assess the entrainment of bed material by debris flows we find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows the increased pore pressure facilitates progressive scour of the bed reduces basal friction and instigates positive feedback that causes flow speed mass and momentum to increase if dryer bed sediment is entrained however the feedback becomes negative and flow momentum declines we infer that analogous feedbacks could operate in other types of gravity driven mass flow that interact with erodible beds the mechanisms by which debris flows acquire mass and momentum as they entrain material are unclear large scale experiments suggest that the pore pressure of wet bed sediment increases as the flow moves over the bed leading to reduced friction and progressive scouring of the base

entrainment of bed material by earth surface mass flows review and reformulation of depth integrated theory earth surface mass flows such as debris flows rock avalanches and dam break floods can grow greatly in size and destructive potential by entraining bed material they encounter increasing use of depth integrated mass and momentum conservation equations to model these erosive flows motivates a review of the underlying theory our review indicates that many existing models apply depth integrated conservation principles incorrectly leading to spurious inferences about the role of mass and momentum exchanges at flow bed boundaries model discrepancies can be rectified by analyzing conservation of mass and momentum in a two layer system consisting of amoving upper layer and static lower layer our analysis shows that erosion or deposition rates at the interface between layers must in general satisfy three jump conditions these conditions impose constraints on valid erosion formulas and they help determine the correct forms of depth integrated conservation equations two of the three jump conditions are closely analogous to rankine hugoniot conditions that describe the behavior of shocks in compressible gasses and the third jump condition describes shear traction discontinuities that necessarily exist across eroding boundaries grain fluid mixtures commonly behave as compressible materials as they undergo entrainment because changes in bulk density occur as the mixtures mobilize and merge with an overriding flow if no bulk density change occurs then only the shear traction jump condition applies even for this special case however accurate formulation of depth integrated momentum equations requires a clear distinction between boundary shear tractions that exist in the presence or absence of bed erosion

entrainment of debris in rock avalanches an analysis of a long run out mechanism many rock avalanches entrain and liquefy saturated soil from their paths evidence for this includes mud displaced from the margins of rock avalanche deposits substrate material smeared along the base of deposits extrusion of liquefied soil upward through the deposits and increases of volume a hypothesis first suggested in 1881 and since reinforced by several authors suggests that entrainment of substrate material increases mobility although the process has been discussed in the literature for more than 100 years few detailed and quantitative descriptions exist the main purpose of this paper is to describe two recent cases from british columbia canada where rockslides entrained substrate on a very large scale influencing the character of the events estimated volume balance curves based on detailed field mapping are provided for both cases dynamic analyses are carried out using a numerical model and using the same set of rheological parameters the mechanism of material entrainment and displacement is discussed the data suggest that rapid rock failures entraining very large quantities of saturated substrate material represent a special type of landslide transitional between rock avalanche and debris avalanche many rock avalanches can thus be seen as end members of a continuum of phenomena involving rock failure followed by interaction with saturated substrate

downslope volume enlargement of a debris slide debris flow in the 1999 hiroshima japan rainstorm abstract following a heavy rainstorm on 29 june 1999 hundreds of slope failures occurred in granitic mountains in hiroshima prefecture japan among these events a highly mobile landslide termed the kameyama landslide in this paper which occurred in kameyama area of hiroshima city was the most catastrophic and was investigated in detail the displaced soil mass from the source area of this landslide traveled about 300 m and deposited a volume more than 10 times as great as that in the source area the landslide originated in and traversed a valley shaped concave slope covered by pre existing colluvial debris deposits in addition a spring was visible in the source area and very shallow ground water was observed in an observation pit dug in the source area thus it is inferred that the ground water table rose quickly during the rainfall and that this rise triggered the slope failure in the source area based on a field survey along the landslide cross section a possible explanation for the mechanism of the landslide was obtained the displaced soil mass from the source area impacted the debris deposit in the path of the landslide thus triggering liquefaction failure of the saturated part of debris the original landslide and the liquefied debris then moved downslope as a single mass to examine this assumption ring shear tests were performed on samples taken from the source area undrained ring shear tests on the saturated samples showed that the sample is highly liquefiable and liquefaction failure could have been triggered in the debris deposits by a very small impact from the displaced soil mass of the initial failure in addition laboratory tests simulating the impacts on the debris deposits at natural water content i e unsaturated at the survey time 2 days after the failure showed that although shear failure could be caused by the assumed impact force the displaced soils stopped after a few centimeters displacement indicating that existence of a saturated zone in debris deposits is prerequisite for this kind of failure

interplay of rheology and entrainment in debris avalanches a numerical study flow type landslides are a major global hazard they occur worldwide and are responsible for a large number of casualties significant structural damage to property and infrastructure and economic losses the features of debris avalanches are particularly important as they involve open slopes and affect triangular source areas when initial slides turn into avalanches through further failures or eventual soil entrainment in this paper the propagation stage of debris avalanches is numerically modelled to provide information such as the propagation pattern of the mobilized material and its velocity thickness and run out distance the use of a depth integrated model has the following advantages i it adequately accommodates the irregular topography of real slopes which greatly affects the evolution of the propagation stage and ii it is less time consuming than full three dimensional approaches the model is named geoflow sph and has previously been applied to theoretical experimental and re

study of the 1920 haiyuan earthquake induced landslides in loess china many large scale landslides induced by earthquakes have been reported in loess soils they often cause catastrophes because they travel long distances at high velocity to clarify the mechanism of these landslides field survey was performed on the landslides triggered by the haiyuan earthquake china 1920 and a series of ring shear tests was conducted on the loess soils collected from a landslide the field surveys revealed that most of the loess landslides triggered by the haiyuan earthquake occurred on concave slopes gentler than 15 with long runout distance showing very small equivalent friction angle cyclic ring shear tests on saturated specimens in the undrained condition showed that when cyclic shear stress was applied to a loose loess specimen pore pressure was built up gradually before the failure and after that large pore pressure was quickly generated due to the failure of loess soil structure meanwhile to investigate the mechanism that produces the high mobility of loess landslides ring shear tests were conducted on loess specimens with large shear displacement of up to several meters under the undrained condition and it was found that the initial normal stress has no effects and overconsolidation ratio has little if any effects on the apparent friction angle in the steady state for loess soils results of tests on soils at different saturation degrees revealed that the reduction in shear strength results more likely from the generation of pore water pressure not of pore air pressure

field testing of irrigation effects on the stability of a cliff edge in loess north west china as it is not uncommon that irrigation has triggered landslides in the chinese loess plateau a full scale field testing in a typical cracked plateau in heifangtai gansu province of china to simulate such phenomenon was conducted in the study piezometers were installed to measure the groundwater and crackmeters as well as inclinometers were used to measure the slope movement water was pumped from the nearby source daily to simulate the irrigation process there was a sharp increase of pore pressure in the undisturbed loess below the crack when the inclinometer registered considerable movement due to the inflow of water via the crack such increase in pore pressure also dissipated rapidly eventually the irrigation water daylighted at the major cracks from the face of the plateau leading to local failures the results show that cracks have significant effects on the flow of the irrigation water into the ground the rapid rise in the local pore water pressure had reduced the stability of the slope

landslides triggered by the 1949 khait earthquake tajikistan and associated loss of life abstract earthquake triggered landslides are a major geological hazard in central asia in july 1949 the m7 4 khait earthquake triggered many hundreds of landslides in a mountainous region near the southern limit of the tien shan mountains central tajikistan these landslides involved widespread rock slope failure as well as large numbers of flowslides in loess that mantles the steep slopes of the region in the yasman valley hundreds of loess landslides coalesced to form a massive loess flow est vol 245 mm 3 that travelled up to 20 km on a slope of only 2 in an adjacent valley the khait landslide involved transformation of an earthquake triggered rockslide into a very rapid flow by the entrainment of saturated loess into its movement it travelled 7 41 km over a vertical distance of 1421 m with an estimated average velocity of 30 m s we estimate its volume as 75 mm 3 an order of magnitude less that previously published estimates the khait landslide was simulated using dan the number of casualties due to earthquake triggered landslides in the epicentral region was considerable approximately 4000 people were killed in the yasman valley loess flow as 20 villages kishlaks were overwhelmed in the khait landslide alone we estimate ca 800 people lost their lives when the villages of khait and khisorak were overrun by rapidly moving debris our data indicates that a total of approximately 7200 people were killed by earthquake triggered landslides in the epicentral region of the khait earthquake and that in terms of loss of life the 1949 yasman valley loess flow was one of the most destructive landslides in recent history

bed scour by debris flows experimental investigation of effects of debris flow composition debris flows can grow greatly in size by entrainment of bed material enhancing their runout and hazardous impact here we experimentally investigate the effects of debris flow composition on the amount and spatial patterns of bed scour and erosion downstream of a fixed to erodible bed transition the experimental debris flows were observed to entrain bed particles both grain by grain and en masse and the majority of entrainment was observed to occur during passage of the flow front the spatial bed scour patterns are highly variable but large scale patterns are largely similar over 22 5 35 channel slopes for debris flows of similar composition scour depth is generally largest slightly downstream of the fixed to erodible bed transition except for clay rich debris flows which cause a relatively uniform scour pattern the spatial variability in the scour depth decreases with increasing water gravel grain size and clay fraction basal scour depth increases with channel slope flow velocity flow depth discharge and shear stress in our experiments whereas there is no correlation with grain collisional stress the strongest correlation is between basal scour and shear stress and discharge there are substantial differences in the scour caused by different types of debris flows in general mean and maximum scour depths become larger with increasing water fraction and grain size and decrease with increasing clay content however the erodibility of coarse grained experimental debris flows gravel fraction 0 64 is similar on a wide range of channel slopes flow depths flow velocities discharges and shear stresses this probably relates to the relatively large influence of grain collisional stress to the total bed stress in these flows 30 50 the relative effect of grain collisional stress is low in the other experimental debris flows 5 causing erosion to be largely controlled by basal shear stress

depositional facies diagenesis and reservoir quality of ivishak sandstone sadlerochit group prudhoe bay field abstract the sadlerochit group is a large fan delta system comparable in size to the modern kosi river wet alluvial fan of nepal and india braided stream processes distributed chert gravel and quartz and chert sand in radial fashion to construct the subaerial part of the fan delta fluvial energy slope of the fan surface and grain size decrease in a north to south basinward direction there is also a decrease in scale of sedimentation units from source area seaward facies of the subaerial fan delta can be broadly categorized as midfan delta alternating conglomerate and sandstone distal fan delta chiefly sandstone and abandoned channel fill overbank and pond facies mudstone siltstone fine grained sandstone seaward of the subaerial fan delta are the delta front and rodelta facies subaerial fan delta and delta front facies compose the ivishak sandstone which grades basinward into the kavik shale a prodelta facies diagenetic effects were gradually superimposed on the sediments deposited in the sadlerochit fan delta system the sedimentary facies and in particular their textural characteristics seem to control the side and degree of diagenesis including enhancement of porosity and permeability comparison of permeability trends among the facies of the ivishak sandstone with permeability patterns displayed by unconsolidated sands with analogous grain size and texture indicates that the general trends that existed in the ivishak sediments are still recognizable in spite of the diagenetic overprint end of article last page 286

landslide mobility and hazards implications of the 2014 oso disaster abstract landslides reflect landscape instability that evolves over meteorological and geological timescales and they also pose threats to people property and the environment the severity of these threats depends largely on landslide speed and travel distance which are collectively described as landslide mobility to investigate causes and effects of mobility we focus on a disastrous landslide that occurred on 22 march 2014 near oso washington usa following a long period of abnormally wet weather the landslide s impacts were severe because its mobility exceeded that of prior historical landslides at the site and also exceeded that of comparable landslides elsewhere the 8 10 6 m 3 landslide originated on a gently sloping

the hypermobility of huge landslides and avalanches abstract catastrophic failure of large land masses which generate landslides rockfalls and debris avalanches can have hazardous consequences extending far beyond the source observations show that the mobility of such events depends strongly on the volume for volumes larger than 10 6 m 3 with many different processes invoked to explain higher mobilities hypermobility for both terrestrial and extraterrestrial events although the mobility of large events has been extensively studied there is no generally accepted mechanism for predicting extreme travel distances because the underlying physical processes are poorly understood here we show using physical and rheological arguments that the wide scatter observed for very large mass wasting events in all environments collapses to a single relationship between event volume or inundation area and mobility hypermobility is defined to be the reciprocal of the effective friction coefficient e where the scale dependent e is derived analytically as a function of the mechanical volumetric and topographical parameters of the flow the dominant term in the coefficient is the degree of fluidization involved in the flow our results show that fluidization is limited in extraterrestrial events that significant fluidization occurs in non volcanic and volcanic events and fluidization dominates submarine events this analysis demonstrates that fluidization is associated with long run out distances and that the degree of fluidization can be predicted by the volume and physical and topographic parameters the methodology is simple physically based and validated with datasets of very large terrestrial and extraterrestrial avalanche events we demonstrate that the effective coulomb friction rheology and the hypermobility function are applicable to avalanche events of any size providing an opportunity to simulate past and or potential huge landslide and debris avalanche events run out distances destructive impact and assessment of risk the model can be used to estimate the overrun area and volume in terms of known mobility data

heavy rainfall triggered loess mudstone landslide and subsequent debris flow in tianshui china abstract continuous and heavy precipitation triggered a large loess landslide at the southern dagou village of mapaoquan town tianshui city gansu province of china on july 21 2013 the landslide debris rapidly turned into a debris flow that was deposited in the ravine mouth with the volume of 1 9 105 m3 detailed field mapping three dimensional laser scanning aerial photograph interpretation and laboratory tests were carried out to study the formation and moving characteristics of the landslide and subsequent debris flow the results showed that 1 the peak flow velocity and peak discharge of the debris flow were estimated to be approximately 7 2 m s and 730 m3 s respectively the velocity had a tendency to first increase and then decrease from the head to entrance in the dagou gully 2 the analysis of rainfall conditions showed that the effective antecedent rainfall within 7 days and hourly rainfall intensity which triggered the slide debris flows was 239 mm and 20 mm h respectively compared with the critical rainfall in this area the effective antecedent rainfall was found to be more significant in triggering this event 3 the mean and effective particle sizes were approximately 0 73 1 3 mm and 0 036 0 087 mm respectively and had the same distribution along the gully as the velocity which confirmed the process of the variation in the flow velocity 4 the scale amplification was very obvious in the formation and moving process of the slide debris flows

pore pressure generation and fluidization in a loess landslide triggered by the 1920 haiyuan earthquake china a case study abstract during the 1920 haiyuan earthquake numerous catastrophic landslides were triggered in the loess area in northwest china we investigated in detail a large example of these landslides referred to as dangjiacha landslide in this paper this landslide originated from a slope of about 20 and the displaced soil mass traveled about 3200 m damming a valley we performed a field survey and found that standing water existed in the landslide area and the loess had high porosity we infer that it was the liquefaction of the water saturated loess layer rather than the suspension of silt in the pore air in the loess that caused the great mobility of this landslide to test this inference we performed undrained triaxial compression and ring shear tests on loess samples to examine the shear behavior of loess saturated by either air or water the test results showed that the water saturated loess soil was highly susceptible to flow liquefaction failure fast shear tests on naturally air dried loess samples revealed that the generated pore air pressure was small under the undrained condition and no significant reduction in the shear resistance was observed implying that air entrapped in the loess was unlikely to be the main contributor to the high mobility of this large scale landslide