the influence of paleofloods on archaeological settlement patterns during a d 1050 1170 along the colorado river in the grand canyon arizona usa abstract excavations at four archaeological sites consisting of the material remains of a d 1050 1170 era farmers along the colorado river in grand canyon national park yield geomorphic information used to address questions related to settlement patterns archaeological excavation units test pits feature fill and natural exposures contain sediments used to interpret geomorphic history that can in turn shed light on archaeological site selection in a challenging environment the grand canyon experiences dramatic geomorphic events such as catastrophic floods and destructive debris flows that are preserved in the stratigraphic record and can be used to understand cultural landscape interactions by combining new geomorphic stratigraphic and archaeological data collected during recent excavations with results from previous geomorphic and sediment transport studies observed trends can be interpreted regarding the possible influence of paleofloods on past settlement patterns for example at each of the four sites reconstructed paleoflood elevations from existing hec ras virtual shorelines flood recurrence intervals site layout and site stratigraphy geomorphic setting suggests a temporal trend in site location the two early sites early pueblo ii period a d 1050 1080 contain habitation features located above the approximately 6 8 year high flood 3500 cubic meters per second cms recurrence interval larger floods 4800 to 5900 cms of a longer recurrence interval between 40 and 80 years inundate these features the two later sites in the sample late pueblo ii a d 1080 1170 contain habitation features located well above the 40 80 year recurrence high flows we suggest that early farmers early pueblo ii period a d 1050 1080 may not have had adequate experience with flood magnitudes and frequencies and therefore their habitation structures were located in risk prone areas relatively close to the river later habitations late pueblo ii a d 1080 1170 were positioned in more protected areas further from the river perhaps reflecting an acquired knowledge of river dynamics these trends although currently based on a limited data set provide insights into site selection decisions and settlement patterns of early farmers along the colorado river through grand canyon

monument creek debris flow 1984 implications for formation of rapids on the colorado river in grand canyon national park a recent debris flow in monument creek illustrates the nature of debris flows in small tributaries and their hydrologic effects on the colorado river in grand canyon national park a debris avalanche originated in the permian esplanade sandstone of the supai group during intense rainfall on july 27 1984 and fell 600 m into monument creek forming a 7 m high barrier across the channel the subsequent debris flow traveled 4 5 km to the colorado river and achieved velocities of 3 4 to 4 0 m s and a peak discharge of 100 to 120 m 3 s the flow consisted of a main pulse followed by subsequent pulses of debris flow or hyperconcentrated flow the main pulse moved boulders as large as 2 7 m in diameter and deposition at the mouth of monument creek enlarged the fan surface and significantly constricted the colorado river most of the major rapids on the colorado river in grand canyon national park appear to be maintained by episodic debris flows

impact of the 2008 wenchuan earthquake in china on subsequent long term debris flow activities in the epicentral area abstract the 2008 wenchuan earthquake triggered the largest number of landslides among the recent strong earthquake events around the world the loose landslide materials were retained on steep terrains and deep gullies in the period from 2008 to 2015 numerous debris flows occurred during rainstorms along the provincial road 303 pr303 near the epicentre of the earthquake causing serious damage to the reconstructed highway approximately 5 24 10 6 m 3 of debris flow sediment was deposited shortly after the earthquake this paper evaluates the evolution of the debris flows that occurred after the wenchuan earthquake which helps understand long term landscape evolution and cascading effects in regions impacted by mega earthquakes with the aid of a gis platform combined with field investigations we continuously tracked movements of the loose deposit materials in all the debris flow gullies along an 18 km reach of pr303 and the characteristics of the regional debris flows during several storms in the past seven years this paper presents five important aspects of the evolution of debris flows 1 supply of debris flow materials 2 triggering rainfall 3 initiation mechanisms and types of debris flows 4 runout characteristics and 5 elevated riverbed due to the deposited materials from the debris flows the hillslope soil deposits gradually evolved into channel deposits and the solid materials in the channels moved towards the ravine mouth accordingly channelized debris flows became dominant gradually due to the decreasing source material volume and changes in debris flow characteristics the triggering rainfall tends to increase from 30 mm h 1 in 2008 to 64 mm h 1 in 2013 and the runout distance tends to decrease over time the runout materials blocked the river and elevated the riverbed by at least 30 m in parts of the study area the changes in the post seismic debris flow activity can be categorized into three stages i e active unstable and recession

enrichment of trace elements in garnet amphibolites from a paleo subduction zone catalina schist southern california the abundance p t stability solubility and element partitioning behavior of minerals such as rutile garnet sphene apatite zircon zoisite and allanite are critical variables in models for mass transfer from the slab to the mantle wedge in deep regions of subduction zones the influence of these minerals on the composition of subduction related magmas has been inferred and disputed from inverse modelling of the geochemistry of island arc basalt or by experiment although direct samples of the dehydration partial melting region of a mature subduction zone have not been reported from subduction complexes garnet amphibolites from melanges of circumpacific and caribbean blueschist terranes reflect high t 600 c conditions in shallower regions such rocks record geochemical processes that affected deep seated high t portions of paleo subduction zones in the catalina schist a subduction zone metamorphic terrane of southern california metasomatized and migmatitic garnet amphibolites occur as blocks in a matrix of meta ultramafic rocks this mafic and ultramafic complex may represent either slab derived material accreted to the mantle wedge of a nascent subduction zone or a portion of a shear zone closely related to the slab mantle wedge contact or both the trace element geochemistry of the complex and the distribution of trace elements among the minerals of garnet amphibolites were studied by inaa xrf electron microprobe and sem in order of increasing alteration from a probable metabasalt protolith three common types of garnet amphibolite blocks in the catalina schist are 1 non migmatitic clinopyroxene bearing blocks which are compositionally similar to morb that has lost an albite component 2 garnet amphibolite blocks which have rinds that reflect local interaction between metabasite metaperidotite and fluid and 3 migmatites that are extremely enriched in th hfse lree and other trace elements these trace element enrichments are mineralogically controlled by rutile garnet sphene apatite zircon zoisite and allanite alkali and alkaline earth elements are much less enriched in the solid assemblage and thus appear to be decoupled from the other elements in the inferred metasomatic process es the compositions of migmatitic garnet amphibolite blocks seem to complement that of average island arc tholeiite trace element metasomatism reflects fluid solid rather than melt solid interaction the metasomatic effects indicate that h2o rich fluid perhaps with a significant component of na al silicate and alkalis carried th u sr ree and hfse fractionations of lree in migmatites resemble those of migmatitic metasedimentary rocks underlying the mafic and ultramafic complex exotic lree deposited in allanite in migmatites could have been derived from fluids in equilibrium with subducted sediment if the paleo subduction zone represented by the mafic and ultramafic complex of the catalina schist had continued its thermal and fluid evolution a selvage of similarly enriched rocks might have been generated along the slab mantle wedge contact between 30 and 85 km depth rocks affected by subduction zone metasomatism although rarely recognized at the surface could be volumetrically significant products of the initiation of subduction and may prove to be geochemical probes of convergent margins that approach the significance of xenoliths in the study of other magmatic environments

geochronology of the pre andean metamorphism and magmatism in the andean cordillera between latitudes 30 and 36 s abstract in the 30 36 s section of the andean cordillera the pre andean basement is composed by metamorphic igneous and sedimentary rocks of precambrian paleozoic and lower triassic ages they crop out in the morphostructural units named from east to west sierras pampeanas precordillera cordillera frontal and bloque de san rafael in argentina and cordillera de la costa in chile isotopic age determinations of the metamorphic rocks indicate a migration of the metamorphic events from east to west such as precambrian to lower paleozoic ages 900 m y and 650 400 m y in the sierras pampeanas lower paleozoic ages about 500 m y in the precordillera and cordillera frontal and upper paleozoic to lower triassic ages 340 210 m y in the cordillera de la costa these metamorphic belts contain a large variety of mafic and ultramafic rocks the distribution of the pre andean granitoids show no apparent chronological zonation however the plutonic activity persisted until the lower carboniferous in the sierras pampeanas to the lower triassic in the cordillera frontal and precordillera associated with an important vulcanism which also develops in the bloque de san rafael and until the jurassic in the cordillera de la costa

frequency and initiation of debris flows in grand canyon arizona 1 debris flows from 740 tributaries transport sediment into the colorado river in grand canyon arizona creating rapids that control its longitudinal profile debris flows mostly occur when runoff triggers failures in colluvium by a process termed the fire hose effect debris flows originate from a limited number of geologic strata almost exclusively shales or other clay rich fine grained formations observations from 1984 through 2003 provide a 20 year record of all debris flows that reached the colorado river in grand canyon and repeat photography provides a 100 year record of debris flows from 147 tributaries observed frequencies are 5 1 events year from 1984 to 2003 and historic frequencies are 5 0 events year from 1890 to 1983 logistic regression is used to model historic frequencies based on drainage basin parameters observed to control debris flow initiation and transport from 5 to 7 of the 16 parameters evaluated are statistically significant including drainage area basin relief and the height of and gradient below debris flow source areas variables which reflect transport distance and potential energy the aspect of the river channel which at least partially reflects storm movement within the canyon is also significant model results are used to calculate the probability of debris flow occurrence at the river over a century for all 740 tributaries owing to the variability of underlying geomorphic controls the distribution of this probability is not uniform among tributaries of the colorado river in grand canyon

tributary confluences and discontinuities in channel form and sediment texture rio chama nm numerous morphological changes can occur where two channels of distinct sediment and flow regimes meet including abrupt shifts in channel slope cross sectional area planform style and bed sediment size along the receiving channel along the rio chama between el vado and abiquiu dams northern new mexico arroyo tributaries intermittently deliver sediment from erodible sandstone and shale canyon walls to the mainstem channel much of the tributary activity occurs in flash floods and debris flows during summer thunderstorms which often load the channel with sand and deposit coarser material at the mainstem confluence in contrast mainstem channel flow is dominated by snowmelt runoff to examine tributary controls we systematically collected cross section elevation and bed sediment data upstream and downstream of 26 tributary confluences along a 17 km reach data from 203 cross sections were used to build a one dimensional hydraulic model for comparing estimated channel parameters at bankfull and low flow conditions at these sites as compared to intermediate reaches confluences primarily impact gradient and bed sediment size reducing both parameters upstream of confluences and increasing them downstream cross section area is also slightly elevated above tributary confluences and reduced below major shifts in slope and bed sediment size at confluences appear to drive variations in sediment entrainment and transport capacity and the relative storage of sand along the channel bed the data were analyzed and compared to models of channel organization based on lateral inputs such as the network variance model and the sediment link concept at a larger scale hillslope channel coupling increases in the downstream third of the study reach where the canyon narrows resulting in steeper slopes and more continuous coarse bed material along the mainstem and thus limiting the contrast with tributary confluences however channel form and sediment characteristics are highly variable along the study reach reflecting variations in the size and volume of sediment inputs related to the surface geology in tributary watersheds morphology of the rio chama at the junction i e bends confinement and the relative magnitude and location of past depositional events copyright 2014 john wiley sons ltd

peak discharge of a pleistocene lava dam outburst flood in grand canyon arizona usa abstract the failure of a lava dam 165 000 yr ago produced the largest known flood on the colorado river in grand canyon the hyaloclastite dam was up to 366 m high and geochemical evidence linked this structure to outburst flood deposits that occurred for 32 km downstream using the hyaloclastite outburst flood deposits as paleostage indicators we used dam failure and unsteady flow modeling to estimate a peak discharge and flow hydrograph failure of the hyaloclastite dam released a maximum 11 109 m3 of water in 31 h peak discharges estimated from uncertainty in channel geometry dam height and hydraulic characteristics ranged from 2 3 to 5 3 105 m3 s 1 for the hyaloclastite outburst flood this discharge is an order of magnitude greater than the largest known discharge on the colorado river 1 4 104 m3 s 1 and the largest peak discharge resulting from failure of a constructed dam in the usa 6 5 104 m3 s 1 moreover the hyaloclastite outburst flood is the oldest documented quaternary flood and one of the largest to have occurred in the continental usa the peak discharge for this flood ranks in the top 30 floods 105 m3 s 1 known worldwide and in the top ten largest floods in north america

geologic versus wildfire controls on hillslope processes and debris flow initiation in the green river canyons of dinosaur national monument abstract as in many areas of high relief debris flows are an important process linkage between hillslopes and the green river in the canyons of the eastern uinta mountains yet the physical conditions that lead to debris flow initiation are unknown a recent episode of enhanced debris flow and wildfire activity provided an opportunity to examine the geomorphic impact of fire and the processes by which weathered bedrock is transported to the green river field investigations and analysis of elevation and precipitation data were undertaken in 15 catchments with recent debris flows to determine how surficial geology wildfire topography bedrock strength and meteorology influence hillslope processes the recent debris flows were triggered by intense summer rainstorms the dominant debris flow initiation mechanism the firehose effect occurred when overland flow generated on bedrock hillslopes cascaded down steep cliffs onto colluvium causing failure sixty percent of the debris flows occurred in unburned catchments however 15 of the burned catchments in the study area produced debris flows over the study period whereas only 7 of the unburned catchments did thus fire was not the primary driver of debris flows but fire related events did contribute to the increased debris flow activity the geomorphic impact of wildfire in the eastern uinta mountains is not as great as in transport limited settings with regolith mantled hillslopes the strong rocks and dry climate of the study area cause hillslopes to be very steep and weathering limited with high runoff ratios and a dearth of regolith as a result there is little vegetation and thus we hypothesize that burning does little to change hillslope processes the suite of hillslope processes in the eastern uintas are like those documented in the similarly dry grand canyon but differ from other locations in the western u s where wildfire is a primary control on debris flow processes

sediment transport through self adjusting bedrock walled waterfall plunge pools many waterfalls have deep plunge pools that are often partially or fully filled with sediment sediment fill may control plunge pool bedrock erosion rates partially determine habitat availability for aquatic organisms and affect sediment routing and debris flow initiation currently there exists no mechanistic model to describe sediment transport through waterfall plunge pools here we develop an analytical model to predict steady state plunge pool depth and sediment transport capacity by combining existing jet theory with sediment transport mechanics our model predicts plunge pool sediment transport capacity increases with increasing river discharge flow velocity and waterfall drop height and decreases with increasing plunge pool depth radius and grain size we tested the model using flume experiments under varying waterfall and plunge pool geometries flow hydraulics and sediment size the model and experiments show that through morphodynamic feedbacks plunge pools aggrade to reach shallower equilibrium pool depths in response to increases in imposed sediment supply our theory for steady state pool depth matches the experiments with an r 2 value of 0 8 with discrepancies likely due to model simplifications of the hydraulics and sediment transport analysis of 75 waterfalls suggests that the water depths in natural plunge pools are strongly influenced by upstream sediment supply and our model provides a mass conserving framework to predict sediment and water storage in waterfall plunge pools for sediment routing habitat assessment and bedrock erosion modeling

nd sr isotopic and ree constraints on the genesis of hydrothermal manganese crusts in the galapagos manganese oxide crusts from the galapagos spreading centre interpreted to be of hydrothermal origin have nd isotopic compositions and rare earth element ree concentrations that approach seawater values as the age increases numerous authors1 2 have cited hydrothermal processes along the mid oceanic ridges to explain the composition of metalliferous sediments other authors believe that these sediments whether now located on a ridge axis or in some deep were derived from hydrothermal activity near ridges and were modified during removal from these ridges3 6 nd and sr isotopic compositions as well as concentrations of ree and cu ni and co in hydrothermal mn crusts of different ages from the galapagos spreading area were determined to provide new information regarding the problem of the alteration behaviour with time of oceanic sediments our data suggest that hydrothermal crusts react with seawater and ultimately acquire the trace element characteristics of hydrogeneous crusts

debris flow release processes investigated through the analysis of multi temporal lidar datasets in north western iceland debris flows are fast moving gravity flows of poorly sorted rock and soil mixed and saturated with water debris flow initiation has been studied using empirical and experimental modelling but the geomorphic changes indicative of different triggering processes are difficult to constrain with field observations only we identify signatures to distinguish two different debris flow release styles by integrating high resolution multi temporal remote sensing datasets and morphometric analysis we analyse debris flows sourced above the town of isafjor ur iceland two debris flow triggering processes were previously hypothesized for this site i slope failure characterised by landslides evolving into debris flows and ii the fire hose effect in which debris accumulated in pre existing steep sided bedrock passages is transported by a surge of water it is unknown which process dominates and determines the local risk to investigate this question we compare airborne lidar elevation models and aerial photographs collected in 2007 with similar data from 2013 we find that two new debris flow tracks were created by slope failures these are characterised by steep sliding surfaces and lateral leveed channels slope failure also occurred in two large recently active tracks creating the preparatory conditions for the fire hose effect to mobilise existing debris these tracks show alternating zones of fill and scour along their length and debris stored below the source area at rest angles 35 our approach allows us to identify and quantify the morphological changes produced by slope failure release process which generated the preparatory conditions for the fire hose effect as debris flows are rarely observed in action and morphological changes induced by them are difficult to detect and monitor the same approach could be applied to other landscapes to understand debris flow initiation in absence of other monitoring information and can improve the identification of zones at risk in inhabited areas near hillslopes with potential for debris flows

mineralogy geochemistry and genesis of the ferromanganese ores from hazara area nw himalayas northern pakistan abstract ferromanganese ores occur in hazara area near abbottabad within the hazira formation of the kalachitta margala thrust belt of the nw himalayas of the indo pakistan plate in pakistan the hazira formation of cambrian age is a relatively thin unit up to 150 m thick which consists of either thin ferruginous siltstone with variable amounts of clay shale ferromanganese ores phosphorite and barite or thicker evenly bedded reddish brown siltstone it has a conformable lower contact with the abbottabad formation cambrian and an unconformable upper contact with the samana suk limestone jurassic the ferromanganese ores of the hazara area were studied in terms of their mineral and geochemical composition mineralogically a variety of mn and fe phases have been noticed in kakul galdanian and chura gali ferromanganese ores bixbyite is the principal mn phase while pyrolusite hollandite partridgeite and braunite occur in lesser amounts hematite however is the only fe phase in these ores gangue minerals include carbonates cryptocrystalline quartz iron clay and variable amounts of apatite plumbogummite and barite glauconite occurs in traces textural features suggest remobilization and subsequent precipitation of early diagenetic mn and fe phases along the fractures and interstices of the gangue minerals during later metamorphism chemical analyses show that the mn fe ratio in the ores is highly variable and ranges from 0 46 to 5 25 these ores exhibit a line of descent from lree to hree with a small positive ce anomaly their ree is higher than the hydrothermal mn deposits and lower than the hydrogenous crust the petrochemical characteristics suggest a mixed hydrothermal hydrogenetic source for the ferromanganese ores which have formed in shallow water or continental shelf environment due to the upwelling of anoxic deep seated water

geochemistry and origin of mn deposits in the waziristan ophiolite complex north waziristan pakistan the waziristan ophiolite complex is located along the western margin of the indian plate in northwestern pakistan the mn deposits in the saidgi and shuidar areas are part of this ophiolite complex these deposits both banded and massive in nature are hosted by metachert and are generally overlying metavolcanics braunite and cryptocrystalline quartz are the main constituents of the manganese ores in both areas hematite occurs in the shuidar deposits as a minor phase metacherts are microcrystalline aggregates of microcrystalline quartz chalcedony and lesser hematite chemically the studied mn deposits and associated metacherts are very similar to those formed by submarine hydrothermal effusive processes the deposits originated along sea floor spreading centers mid ocean ridges within the neo tethys ocean and were later obducted as part of the waziristan ophiolite complex

analyzing debris flows with the statistically calibrated empirical model laharz in southeastern arizona usa abstract hazard zone delineation for extreme events is essential for floodplain management near mountain fronts in arid and semiarid regions on 31 july 2006 unprecedented debris flows occurred in the santa catalina mountains of southeastern arizona following extreme multiday precipitation recurrence interval 1000 years for 4 day precipitation most mobilized sediment contributing to debris flows was derived from shallow seated failures of colluvium on steep slopes a total of 435 slope failures in the southern santa catalina mountains released 1 34 million mg of sediment into the channels of 10 drainage basins five drainages produced debris flows that moved to the apices of alluvial fans on the southern edge of the mountain front damaging infrastructure and aggrading channels to reduce future flood conveyance using the statistically calibrated empirical debris flow model laharz and modified model coefficients developed to better match conditions in southeastern arizona we predicted the approximate area of deposition and travel distance in comparison to observed depositional areas and travel distance for seven debris flows two of the modeled debris flows represented single slope failures that terminated downslope with no additive influence of other debris flows or streamflow flooding five of the simulated debris flows represented the aggregation of multiple slope failures and streamflow flooding into multiple debris flow pulses because laharz is a debris flow hazard zone delineation tool the complexity of alternating transport and deposition zones in channels with abrupt expansions and contractions reduces the applicability of the model in some drainage basins

holocene landscape response to seasonality of storms in the mojave desert abstract new optically stimulated and radiocarbon ages for alluvial fan and lake deposits in the mojave desert are presented which greatly improves the temporal resolution of surface processes the new mojave desert climate landscape record is particularly detailed for the late holocene evidence from ephemeral lake deposits and landforms indicates times of sustained stream flow during a wet interval of the latter part of the medieval warm period at ca ad 1290 and during the little ice age at ca ad 1650 the former lakes postdate megadroughts of the medieval warm period whereas the latter match the maunder minimum of the little ice age periods of alluvial fan aggradation across the mojave desert are 14 9 cal ka and 6 3 cal ka this timing largely correlates to times of increased sea surface temperatures in the gulf of california and enhanced warm season monsoons this correlation suggests that sustained alluvial fan aggradation may be driven by intense summer season storms these data suggest that the close proximity of the mojave desert to the pacific ocean and the gulf of california promotes a partitioning of landscape process responses to climate forcings that vary with seasonality of the dominant storms cool season pacific frontal storms cause river flow ephemeral lakes and fan incision whereas periods of intense warm season storms cause hillslope erosion and alluvial fan aggradation the proposed landscape process partitioning has important implications for hazard mitigation given that climate change may increase sea surface temperatures in the gulf of california which indirectly could increase future alluvial fan aggradation

debris flow deposition and reworking by the colorado river in grand canyon arizona 1 flow regulation by large dams affects downstream flow competence and channel maintenance debris flows from 740 tributaries in grand canyon arizona transport coarse grained sediment onto debris fans adjacent to the colorado river these debris fans constrict the river to form rapids and are reworked during river flows that entrain particles and transport them downstream beginning in 1963 flood control operations of glen canyon dam limited the potential for reworking of aggraded debris fans we analyzed change in debris fans at the mouths of 75 mile and monument creeks using photogrammetry of aerial photography taken from 1965 to 2000 and supplemented with ground surveys performed from 1987 to 2005 our results quantify the debris fan aggradation that resulted from debris flows from 1984 to 2003 volume area and river constriction increased at both debris fans profiles of the two debris fans show that net aggradation occurred in the middle of debris fans at stages above maximum dam releases and surface shape shifted from concave to convex dam releases above power plant capacity partially reworked both debris fans although reworking removed much less sediment than what was added by debris flow deposition large dam releases would be required to create additional reworking to limit the rate of debris fan aggradation in grand canyon

predicting the probability and volume of postwildfire debris flows in the intermountain western united states empirical models to estimate the probability of occurrence and volume of postwildfire debris flows can be quickly implemented in a geographic information system gis to generate debris flow hazard maps either before or immediately following wildfires models that can be used to calculate the probability of debris flow production from individual drainage basins in response to a given storm were developed using logistic regression analyses of a database from 388 basins located in 15 burned areas located throughout the u s intermountain west the models describe debris flow probability as a function of readily obtained measures of areal burned extent soil properties basin morphology and rainfall from short duration and low recurrence interval convective rainstorms a model for estimating the volume of material that may issue from a basin mouth in response to a given storm was developed using multiple linear regression analysis of a database from 56 basins burned by eight fires this model describes debris flow volume as a function of the basin gradient aerial burned extent and storm rainfall applications of a probability model and the volume model for hazard assessments are illustrated using information from the 2003 hot creek fire in central idaho the predictive strength of the approach in this setting is evaluated using information on the response of this fire to a localized thunderstorm in august 2003 the mapping approach presented here identifies those basins that are most prone to the largest debris flow events and thus provides information necessary to prioritize areas for postfire erosion mitigation warnings and prefire management efforts throughout the intermountain west

composition and origin of hydrothermal ironstones from central pacific seamounts abstract ironstones recovered from five late cretaceous seamounts in the central pacific region probably formed during late stage edifice building volcanism ironstones are dense and compact with the appearance of brown chert the ironstones are characterized by a goethite mineralogy with feooh contents up to 88 extreme fractionation of fe and mn low trace element and rare earth element abundances low co zn ratios and isotopic equilibration temperatures of about 20 45 c these characteristics indicate that the ironstones formed from hydrothermal fluids ironstones probably formed below the seawater seafloor interface as indicated by their occurrence as a proximal hydrothermal deposit presence of primary goethite cement pervasive replacement of rocks by goethite and absence of interbedded pyro clastic beds

late quaternary climate and seismicity in the katrol hill range kachchh western india abstract a channel fill sequence in the upper catchment of the khari river in the south of the katrol hill fault khf has been investigated to understand the role of climate and tectonics in the evolution of fluvial landforms detailed sedimentology and limited optical chronology suggest that the channel incision occurred during weak summer monsoon prior to 19 9 ka and is attributed to the activity along the khf and its subsidiary faults the post glacial to early holocene was a phase of landscape stability subdued tectonics which persisted until around 7 1 ka particularly between 9 4 ka and 7 1 ka an enhanced monsoon activity is inferred a renewed phase of uplift is suggested after 7 1 ka that probably continues till present

chronology of rock falls and slides in a desert mountain range case study from the sonoran desert in south central arizona abstract in order to respond to the general paucity of information on the chronology of ubiquitous small rock falls and slides that litter the slopes of desert mountain ranges a case study in the sonoran desert reveals new insight into the desert geomorphology of mountain slopes rock falls and rock slides in the mcdowell mountains that abut metropolitan phoenix usa fall in three chronometric groupings dated by conventional radiocarbon and rock varnish microlamination methods first the oldest events are 74 ka and take the form of stable colluvial boulder fields positive relief features that are tens of meters long and a few meters wide second randomly sampled slides and falls of various sizes and positions wasted during wetter periods of the terminal pleistocene and holocene third an anomalous clustering of slides and falls occurred during the late medieval warm period medieval climatic anomaly when an extreme storm was a possible but unlikely trigger one speculative hypothesis for the cluster of medieval warm period events is that a small to moderate sized earthquake shook heavily shattered bedrock close to failure just enough to cause a spate of rock falls and slides a second speculative hypothesis is that this dry period enhanced physical weathering processes such as dirt cracking however the reasons for the recent clustering of rock falls remain enigmatic while the temporal distribution of slides and falls suggests a minimal hazard potential for homes and roads on the margins of the mcdowell mountains this finding may not necessary match other desert ranges in metropolitan phoenix or mountains with different rock types and structures that abut other arid urban centers

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

geochemistry and depositional environment of mn oxide deposits in the tokoro belt northeastern hokkaido japan numerous early cretaceous mn oxide and mn fe deposits are distributed in the tokoro belt northeastern hokkaido japan the mn oxide deposits usually occur in the southwestern part of the belt and within bedded cherts whereas the mn fe deposits are restricted to the northeastern part of the belt and occur between bedded cherts and underlying basaltic pillow lava the mn oxide ores are characterized by low fe mn ratios and the trace element concentrations and rare earth element ree patterns are similar to those of the submarine hydrothermal mn deposits distribution patterns of trace elements co ni cu and zn and ree in the mn oxide ores determine two types of deposits hydrogenous deposits which have relatively high concentrations and submarine hydrothermal deposits which have low concentrations these compositional trends and geologic evidences of the tokoro mn deposits suggest that the fe phases precipitated first closer to their source whereas the mn phases deposited later at a distance from their source some hydrogenous effects on the mn oxide deposits are due to the adsorption of trace elements from seawater trace element concentrations of tokoro mn oxide deposits show that they formed within 40 km from their source

late quaternary fluvial aggradation and incision in the monsoon dominated alaknanda valley central himalaya uttrakhand india the present study aims to explain the spatial and temporal variability in phases of aggradation incision in response to changes in climate and seismicity during the late quaternary in the alaknanda river valley a major tributary of the river ganges or ganga geomorphology stratigraphy and optical dating of the fluvial sediment reveal that the oldest fluvial landforms preserved in the south of the main central thrust are debris flow terraces developed during the early part of pluvial marine isotopic stage 3 following this a period of accelerated incision erosion owing to an increase in uplift rate and more intense rainfall occurred in the lesser himalaya three phases of valley fill aggradation around 26 3 ka 18 2 ka and 15 1 ka and 8 1 ka occurred in response to changes in monsoon intensity and sediment flux the last phase was regionally extensive and corresponds to a strengthening of the early holocene indian summer monsoon a gradual decline in the monsoon strength after 8 1 ka resulted in reduced fluvial discharge and lower sediment transport capacity of the alaknanda river leading to valley fill incision and the development of terraces the study suggests that fluvial dynamics in the alaknanda valley were modulated by monsoon variability and the role of tectonics was subordinate limited to providing accommodation space and post deposition modification of the fluvial landforms copyright 2010 john wiley sons ltd

late diagenetic changes in manganese ores of the upper proterozoic penganga group india sedimentary manganese oxide ores occur interstratified with chert and minor calcareous shale and enclosed in limestone in the transgressive upper proterozoic marine sequence of the penganga group andhra pradesh india this sequence shows no evidence of volcanism or hydrothermal activity and is not metamorphosed the manganeseoxide ores show unusual coexistence of the primary sedimentary minerals todorokite and birnessite with their diagenetic conversion products manganite braunite and bixbyite the mineralogical characters and chemical compositions of the important phases as well as their texture are discussed braunite occurs in two generations one earlier or contemporaneous with bixbyite and the other later than bixbyite the different stages of conversion of todorokite and birnessite to braunite and todorokite to manganite are preserved the general observations suggest that bixbyite was also produced by conversion of todorokite birnessite pyrolusite and cryptomelane conventionally considered as diagenetic products of mn oxide hydroxide precursors deposited as primary sediments are here rarely present and then only as supergene derivatives this documentation of diagenetic transformation of primary todorokite and birnessite directly to braunite and bixbyite should be considered while extrapolating the progenitor mineralogy of the metamorphosed manganese oxide ores that abound in the precambrian

changes in the water surface profile of the colorado river in grand canyon arizona between 1923 and 2000 1 in 1923 a u s geological survey expedition surveyed the water surface profile of the colorado river through grand canyon with theodolite and stadia rod in 2000 lidar overflights collected topographic data centered on the river corridor allowing construction of a new water surface profile and detection of change in the profile since 1923 by registering the surveys with respect to each other on the basis of 11 locations that were independently determined to have been unchanged between 1923 and 2000 80 rapids were directly compared for change between 1923 and 2000 the average change for all measured rapids was 0 26 m indicating net aggradation of the coarse grained alluvium forming the rapids throughout grand canyon in addition comparison of the two water surface profiles showed enhanced pool and rapid morphology while 50 of the total drop of the river occurred in just 9 of the river distance in 1923 that value increased to 66 by 2000

a reply to the discussion of our paper on the structure of the precambrian and lower paleozoic basement of the central andes between 22 and 32 s lat as presented by a p willner and h miller

comparing models of debris flow susceptibility in the alpine environment abstract debris flows are widespread in val di fassa trento province eastern italian alps where they constitute one of the most dangerous gravity induced surface processes from a large set of environmental characteristics and a detailed inventory of debris flows we developed five models to predict location of debris flow source areas the models differ in approach statistical vs physically based and type of terrain unit of reference slope unit vs grid cell in the statistical models a mix of several environmental factors classified areas with different debris flow susceptibility however the factors that exert a strong discriminant power reduce to conditions of high slope gradient pasture or no vegetation cover availability of detrital material and active erosional processes since slope and land use are also used in the physically based approach all model results are largely controlled by the same leading variables overlaying susceptibility maps produced by the different methods statistical vs physically based for the same terrain unit of reference grid cell reveals a large difference nearly 25 spatial mismatch the spatial discrepancy exceeds 30 for susceptibility maps generated by the same method discriminant analysis but different terrain units slope unit vs grid cell the size of the terrain unit also led to different susceptibility maps almost 20 spatial mismatch maps based on different statistical tools discriminant analysis vs logistic regression differed least less than 10 hence method and terrain unit proved to be equally important in mapping susceptibility model performance was evaluated from the percentages of terrain units that each model correctly classifies the number of debris flow falling within the area classified as unstable by each model and through the metric of roc curves although all techniques implemented yielded results essentially comparable the discriminant model based on the partition of the study area into small slope units may constitute the most suitable approach to regional debris flow assessment in the alpine environment

initiation conditions for debris flows generated by runoff at chalk cliffs central colorado abstract we have monitored initiation conditions for six debris flows between may 2004 and july 2006 in a 0 3 km 2 drainage basin at chalk cliffs a band of hydrothermally altered quartz monzonite in central colorado debris flows were initiated by water runoff from colluvium and bedrock that entrained sediment from rills and channels with slopes ranging from about 14 to 45 the availability of channel material is essentially unlimited because of thick channel fill and refilling following debris flows by rock fall and dry ravel processes rainfall exceeding i 6 61 d 0 77 where i is rainfall intensity mm h and d is duration h was required for the initiation of debris flows in the drainage basin the approximate minimum runoff discharge from the surface of bedrock required to initiate debris flows in the channels was 0 15 m 3 s colluvium in the basin was unsaturated immediately prior to antecedent and during debris flows antecedent volumetric moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 4 9 and 4 7 respectively during debris flows peak moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 10 20 and 4 12 respectively channel sediment at a depth of 45 cm was unsaturated before and during debris flows antecedent moisture ranged from 20 22 and peak moisture ranged from 24 38 although we have no measurements from shallow rill or channel sediment we infer that it was unsaturated before debris flows and saturated by surface water runoff during debris flows our results allow us to make the following general statements with regard to debris flows generated by runoff in semi arid to arid mountainous regions 1 high antecedent moisture levels in hillslope and channel sediment are not required for the initiation of debris flows by runoff 2 locations of entrainment of sediment by successive runoff events can vary within a basin as a function of variations in the thickness of existing channel fill and the rate of replenishment of channel fill by rock fall and dry ravel processes following debris flows and 3 rainfall and simulated surface water discharge thresholds can be useful in understanding and predicting debris flows generated by runoff and sediment entrainment

paleoceanographic model of neogene phosphorite deposition u s atlantic continental margin the neogene stratigraphic section of the southeastern u s continental shelf coastal plain system is characterized by i a series of major regional phosphogenic episodes ii a strong spatial relationship between the structural or topographic framework and phosphate deposition and iii distinct cyclical and regional patterns of deposition of the terrigenous carbonate and phosphate lithofacies the complex depositional patterns are explained by a paleoceanographic model based upon the interaction of glacial eustatic sea level fluctuations associated changes in climate and the dynamics of the gulf stream in response to the bathymetric configurations of the continental margin during the past 20 million years

debris flows from small catchments of the ma ha tuak range metropolitan phoenix arizona abstract debris flows debauch from tiny but steep mountain catchments throughout metropolitan phoenix arizona usa urban growth in the past half decade has led to home construction directly underneath hundreds of debris flow channels but debris flows are not recognized as a potential hazard at present one of the first steps in a hazard assessment is to determine occurrence rates the north flank of the ma ha tuak range just 10 km from downtown phoenix was selected to determine the feasibility of using the varnish microlaminations vml method to date every debris flow levee from 127 catchment areas only 152 of the 780 debris flow levees yielded vml ages in a first round of sampling this high failure rate is due to erosion of vml by microcolonial fungi the temporal pattern of preserved debris flow levees indicates anomalously high production of debris flows at about 8 1 ka and about 2 8 ka corresponding to northern hemisphere climatic anomalies because many prior debris flows are obliterated by newer events the minimum overall occurrence rates of 1 3 debris flows per century for the last 60 ka 2 2 flows century for the latest pleistocene and 5 flows century for the last 8 1 ka has little meaning in assessment of a contemporary hazard this is because newer debris flows have obliterated an unknown number of past deposits more meaningful to a hazards analysis is the estimate that 56 flows have occurred in the last 100 years on the north side of the range an estimate that is consistent with direct observations of three small debris flows resulting events from a january 18 22 2010 storm producing 70 mm of precipitation in the ma ha tuak range and a 500 m long debris flow in a northern metropolitan phoenix location that received over 150 mm of precipitation in this same storm these findings support the need for a more extensive hazard assessment of debris flows in metropolitan phoenix

braunite mineralogy and paragenesis from the kajlidongri mine madhya pradesh india the kajlidongri manganese deposit madhya pradesh india contains braunite belonging to at least two different parageneses i e a fine grained metamorphic type and a younger coarser grained hydrothermal type microanalyses of braunite from these paragenetic types indicate considerable variations in iron content from zero to 32 7 fe3o3 which the writers consider is due to varying proportions of braunite i and bixbyite modules in polysomatic braunite

geomorphology of the colorado river in the grand canyon sediment supplied to the colorado river within the grand canyon has been sorted into distinct deposits of three grain size ranges the major rapids are formed by boulder deposits from side canyon tributaries as a result of a fourfold reduction in peak discharge when glen canyon dam was closed in 1963 new fan debris may increase the gradient through some of the rapids by a factor of 1 8 cobbles and gravel transported only during flood stages are preferentially deposited in the wider sections of the river as bars and riffles and are for the most part inactive during post dam discharges fine grain largely sandy terraces occur throughout the canyon especially along the banks of the large reverse eddies above and below the rapids the lower terraces are being reworked into beach like shores by diurnally varying post dam discharges a slight net lateral erosion of the terraces has resulted prior to construction of the dam sandy bed deposits underwent scour averaging about 1 m during spring floods

initiation process of debris flows on different slopes due to surface flow and trigger specific strategies for mitigating post earthquake in old beichuan county china the 12 may 2008 wenchuan earthquake ms 8 0 in china produced an estimated volume of 28 108 m3 loosened material which led to debris flows after the earthquake debris flows are the dominant mountain hazards and serious threat to lives properties buildings traffic and post earthquake reconstruction in the earthquake hit areas it is very important to understand the debris flow initiation processes and characteristics for designing debris flow mitigation the main objective of this article is to examine the different debris flow initiation processes in order to identify suitable mitigation strategies three types of debris flow initiation processes were identified designated as types a b and c by field survey and experiments in a type initiation the debris flow forms as a result of dam failure in the process of rill erosion slope failure landslide dam or dam failure this type of debris flow occurs at the slope of 10 2 with a high bulk density and several surges following dam failure b type initiation is the result of a gradual increase in headward down cutting bank and lateral erosion and then large amount of loose material interfusion into water flow which increases the bulk density and forms the debris flow this type of debris flow occurs mainly on slopes of 15 3 without surges c type debris flow results from slope failures by surface flow infiltration loose material crack slope failure and fluidization this type of debris flow occurs mainly on slopes of 21 4 and has several surges of debris flow following slope failure and a high bulk density to minimize the hazards from debris flows in areas affected by the wenchuan earthquake the erosion control measures such as the construction of grid dams slope failure control measures the construction of storage sediment dams and the drainage measures such as construction of drainage ditches are proposed based on our results it is recommend that the control measures should be chosen based on the debris flow initiation type which affects the peak discharge bulk density and the discharge process the mitigation strategies discussed in this paper are based on experimental simulations of the debris flows in the weijia huashiban and xijia gullies of old beichuan city the results are useful for post disaster reconstruction and recovery as well as for preventing similar geohazards in the future

fluvial landforms and their implication towards understanding the past climate and seismicity in the northern katrol hill range western india abstract the tectonically active kachchh peninsula in western india lies in the southwest monsoon trajectory and hence provides a rare opportunity to decipher the temporal changes in climate tectonics interaction in the evolution of the fluvial landforms reconstructions based on geomorphology sedimentology and geochemistry supported by optical chronology suggest that the fluvial aggradation in the region was initiated during the onset of the indian summer monsoon ism after the last glacial maximum lgm the sedimentary characteristics and major elemental concentrations suggest that the sediments are dominated by fluvially reworked miliolites with subordinate contribution from the mesozoic sandstones and shales and were deposited with the initiation of the ism after the lgm temporal changes in facies architecture and major element concentrations suggest a progressive strengthening of the monsoon between 17 and 12 ka this was succeeded by an overall strengthened ism phase with fluctuations after 12 ka and based on the morphology of the fluvial landforms two major events of enhanced uplift can be suggested the geomorphic expression of the older uplift event dated to 17 ka is represented by the beveled mesozoic bedrock surfaces which accommodated the post lgm valley fill aggradation the younger event of enhanced uplift which is assigned to

the formation of runoff generated debris flow in southwestern of china take gangou as an example in the mountain area of southwestern china there are large quantities of runoff generated debris flows that are threatening the local people and facilities seriously gangou is a typical runoff generated debris flow its source is old deposit from floods and the debris flows downstream of the channel on june 30 2005 gangou occurred debris flow the debris flow destroying the road the communications facilities and the farmland at the gully mouth unlike the formation mechanisms of other debris flows the formation of 2005 debris flow in gangou has its distinctive characteristics as follows 1 the supply of the loose sources is intensive and distribute near the mouth of the gully it is rare to see any debris flow initiate at such a lower location 2 the debris flow finishes its initiation flow and deposition around the 700 m long channel accompanied with the blocking process in the gully when the debris flow ran out however 10 min later it releases and amplifies the peak flow about three times 3 the topographic condition of the basin does not contribute much to the formation of the 2005 debris flow instead its formation is the result of the co effort of continuous rainfall and a short time heavy rainfall in other words the previous cumulative precipitation enables the moisture content of the soil on the right bank of the gully to reach saturation then the soil slides into the channel under the action of the heavy rainfall at a later time meanwhile the heavy rainfall accelerates the formation of gully run off and initiates the loose mass in the channel from slide thus forming the debris flow

the structure of the precambrian and lower paleozoic basement of the central andes between 22 and 32 s lat three major diastrophic cycles defined by their structural style and their spatial distribution are recognized in the andean basement of this region the oldest structures are related to the panamerican orogeny 500 to 700 m a which produced in the central craton multiply deformed complexes of schists gneisses and granites that are covered discordantly by unmetamorphosed cambrian and ordovician beds west of the central craton ordovician sedimentary beds are folded with a simple structural style and intruded by granites both the sedimentry beds and the granites are covered discordantly by undeformed devonian sequences the folding of the ordovician is attributed to the ocloyic phase of the caledonian movements west of the ocloyic belt is another foldbelt consisting of strongly folded devonian beds attributed to the chanic phase hercynian the chanic belt is intruded by carboniferous and permian granites and covered discordantly by carboniferous and permian sequences

effects of tributary debris on the longitudinal profile of the colorado river in grand canyon 1 the colorado river in grand canyon has long been known as a rapids and pools river with the rapids owing their existence primarily to tributary debris flows the debris flows deposit subaerial debris fans that constrict the channel laterally and when they enter the river raise the bed elevation the rapids are short wavelength 0 1 to 1 km small amplitude 5 m convexities in the river s longitudinal profile arising from the shallow gradient in the upstream pool and the steep gradient through the rapid itself analysis of the entire longitudinal profile through grand canyon reveals two long wavelength 100 km large amplitude 15 30 m river profile convexities the eastern canyon convexity between river mile rm 30 and rm 80 and the western canyon convexity between rm 150 and rm 250 convexities of intermediate scale are also identified in the longitudinal profile these longer wavelength larger amplitude convexities have strong spatial correlations with high rates of debris flow occurrence high densities of holocene debris fans the largest debris fans along the river and alluvial thicknesses of 10 m or more river profile convexities are unstable and require an active and powerful geologic process to maintain them in this case the abundant frequent and voluminous holocene debris flow activity in grand canyon at all wavelengths the most likely cause for these river profile convexities is holocene aggradation of the riverbed beneath them driven by the coarse particles of tributary debris flows large enough debris flows will slow river flow for kilometers upstream causing it to drop much of its suspended load integrated over time and all of the tributary point source contributions this process will build short wavelength convexities into long wavelength convexities for most if not all of the holocene the colorado river has been dissipating most of its energy in the rapids and expending the remainder in transporting fine sediment through grand canyon with little or no regional incision of bedrock

engineering measures for debris flow hazard mitigation in the wenchuan earthquake area avalanches and landslides caused by the wenchuan earthquake in the longmen mountains area provide abundant loose solids for debris flows and a large number of debris flows have occurred during the period 2008 2012 the engineering measures in certain gullies failed causing serious damage and loss of life judging from the debris flow characteristics in the wenchuan earthquake area engineering measures should be better constructed after the active period of debris flows in severely affected areas to reduce debris flow disasters this paper proposes a mitigation method and design principle based on the transport capacity of the main river a series of check dams with various opening sizes was designed by investigating and analyzing existing cases furthermore a new type of drainage channel with prefabricated reinforced concrete boxes is proposed finally a case study of the xiaogangjian gully which is a typical debris flow gully in the wenchuan earthquake area is presented this system of engineering measures is based on the main river s transport capacity and consists of five check dams with various opening sizes a drainage channel with sidewalls constructed of prefabricated reinforced concrete boxes and a debris flow basin at the base of the main gully the debris flow mitigation measures constructed in the xiaogang jian gully effectively resisted a debris flow with a 50 year return period that was triggered by rainfall on july 26 2012 specifically these measures effectively protected a highway and minimized debris flow damage thus the layout and engineered structures involved in this new engineering technique can provide a reference design for debris flow hazard mitigation c 2014 elsevier b v all rights reserved

rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments abstract analyses have been made of ree contents of a well characterized suite of deep sea 4000 m principally todorokite bearing ferromanganese nodules and associated sediments from the pacific ocean ree in nodules and their sediments are closely related nodules with the largest positive ce anomalies are found on sediments with the smallest negative ce anomalies in contrast nodules with the highest contents of other rare earths 3 ree are found on sediments with the lowest 3 ree contents and vice versa 143 nd 144 nd ratios in the nodules 0 51244 point to an original seawater source but an identical ratio for sediments in combination with the ree patterns suggests that diagenetic reactions may transfer elements into the nodules analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to ree contents of nodules and sediments is negligible inter element relationships and leaching tests suggest that ree contents are controlled by a p rich phase with a ree pattern similar to that for biogenous apatite and an fe rich phase with a pattern the mirror image of that for sea water it is proposed that 3 ree concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate processes which favour the enrichment of transition metals in equatorial pacific nodules favour the depletion of 3 ree in nodules and enrichment of 3 ree in associated sediments in contrast ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions

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

a ground water mixing model for the origin of the imini manganese deposit cretaceous of morocco the imini deposit just south of the atlas mountains of morocco consists of three beds of manganese oxide ore in a slightly deformed dolomite unit about 10 m thick of cenomanian turonian late cretaceous age the dolomite host is sugary textured massive and permeable dolomite occurs as nearly euhedral rhombs each ore bed is about a meter thick and consists almost entirely of intergrowths of pyrolusite and hollandite family minerals bao up to 11 and pbo up to 28 with a flattened geode structure overlying the ore beds are solution collapse breccias with dolomite clasts janggunite mn fe oxide and dolomite matrix and pyrolusite hollandite calcite cement the ore solution collapse breccia and coarsely recrystallized pure dolomite are coextensive a zone only 400 to 1 000 m wide but 25 km long and elongate east northeast west southwest diagenetic features of the deposit are recrystallized texture of the dolomite flattened geode structure of the ore solution collapse breccia and associated draped laminae of the insoluble residues fossil replacement by mn oxides and zoned chert nodules with inclusions a mineralogic paragenesis shown independently in each of these features from older to younger is 1 precursor carbonates 2 dolomite janggunite and 3 hollandite pyrolusite chert calcite diagenesis probably occurred during the late cretaceous in a mixing zone of fresh and saline ground water as similar diagenetic sequences without manganese deposits are widely reported to have formed in such environments carbon and oxygen isotope compositions of carbonates and oxygen isotope compositions of chert show that an increasing component of fresh meteoric ground water was present as diagenesis proceeded falling sea level allowed the mixing zone to occupy various positions within the carbonate unit and convert the primary calcareous carbonate rocks to dolomite with chert nodules anoxic seawater is known both worldwide and from the local depositional basin atlas gulf in the cenomanian turonian this is believed to be the key to manganese deposition because anoxic conditions greatly enhance manganese solubility two specific versions of the mixing zone model are presented for manganese deposition one in which a primary sedimentary manganese precipitate formed along margins of the anoxic basin and was recrystallized during diagenesis in the mixing zone and the other in which anoxic saline ground water brought manganese into the mixing zone where it precipitated

environments and processes of manganese deposition concentration of manganese in solution and its deposition takes place by redox controlled processes in a variety of modern and ancient geologic and geochemical environments modern mn deposition occurs predominantly in deep sea areas rather than shallow water domains although deep sea sedimentary deposits dominate hydrothermal contribution of mn to the ocean system may be substantial mn deposition from hydrothermal solutions at or near sea floor spreading centers and less commonly in island arc areas is known in addition near and far field dispersion of mn from vent sites is also substantial such distributions are controlled by the flow rate and egress temperature of the solution and the residence time of mn in seawater thus even in sedimentary deposit domains at least partial derivation of mn from a hydrothermal source is possible sedimentary fe mn crusts on older volcanic substrates on seamounts form by hydrogenous deposition of metal concentrated from terrigenous sources in the mid water column oxygen minimum zones thus the presence or absence of volcanic rocks is not a clear indication of whether sedimentary mn deposits particularly in the ancient geologic record are the result of a totally terrigenous or a totally volcanogenic source abyssal fe mn nodules are considered to form from a basin water hydrogenous and or pore water early diagenetic supply of metals but in most cases the extent of supply from either of the sources is unknown the metal incorporation mechanisms of free moving nodules is little understood and it is possible that in most cases both sources contribute to the nodule composition therefore no nodule should be considered as totally hydrogenous or totally early diagenetic based only on its bulk composition the determined growth rate giving only an average value cannot by itself reveal the growth history of the nodules biological participation directly or indirectly controls mn deposition the stratified black sea demonstrates the concentration of mn in solution in an anoxic zone its advection toward the redox interface and its precipitation in an oxygenated condition similar stratified basins are contemplated for ancient mn deposition in shallow water basin margin areas geologic and geochemical signatures indicate that during sea level highstands stratified basins formed in which mn was concentrated in solution in the anoxic part corresponding transgression led to the impingement of the redox interface on the continental shelf and precipitation of mn oxides could take place across the interface during transgression regression cycles offshore in anoxic or dysaerobic conditions mn carbonate could form by early diagenetic reaction of mn super 2 with co 2 or hco 3 super produced by organic carbon oxidation critical mn deposits occurring in transgressive glaciogenic and black shale bearing ancient sequences support this paleoenvironmental model for mn deposition

transition from foreland to piggyback basin deposition plio pleistocene upper siwalik group shinghar range nw pakistan plio pleistocene synorogenic deposits of the upper siwalik group in the shinghar range trans indus salt ranges of north western pakistan record the transition from foreland basin to piggyback basin deposition on the hangingwall of the salt range thrust the siwalik and upper siwalik groups are over 4 km thick in the shinghar range the lower 3 km consists of the miocene siwalik group which was deposited by a south flowing foreland trunk stream the palaeo indus river the upper 1 5 km consists of the upper siwalik group which is herein divided into three members the lowest member includes deposits of the south flowing palaeo indus river and is distinguished from the underlying siwalik group by the first appearance of conglomerate the transition from the lower member to the middle member is interpreted as recording uplift on the salt range thrust as the salt range thrust was active the palaeo indus river was bifurcated to the east and west around the embryonic shinghar range and overbank and lacustrine deposition occurred represented by the middle member when the shinghar range achieved significant topography the upper member was deposited by streams transporting gravel and sand that flowed north and west out of the range and into a piggyback basin that formed on the hangingwall of the salt range thrust new and previously published palaeomagnetic stratigraphy and fission track ages from volcaniclastic deposits within the upper siwalik group provide tight constraints on the chronology of sedimentary facies transitions and timing of uplift of the shinghar range the integration of sedimentological and geochronological data indicates that motion on the salt range thrust and repositioning of the indus river began at 1 0 ma

a new hierarchical bayesian approach to analyse environmental and climatic influences on debris flow occurrence abstract how can debris flow occurrences be modelled at regional scale and take both environmental and climatic conditions into account and of the two which has the most influence on debris flow activity in this paper we try to answer these questions with an innovative bayesian hierarchical probabilistic model that simultaneously accounts for how debris flows respond to environmental and climatic variables in it full decomposition of space and time effects in occurrence probabilities is assumed revealing an environmental and a climatic trend shared by all years catchments respectively clearly distinguished from residual random effects the resulting regional and annual occurrence probabilities evaluated as functions of the covariates make it possible to weight the respective contribution of the different terms and more generally to check the model performances at different spatio temporal scales after suitable validation the model can be used to make predictions at undocumented sites and could be used in further studies for predictions under future climate conditions also the bayesian paradigm easily copes with missing data thus making it possible to account for events that may have been missed during surveys as a case study we extract 124 debris flow event triggered between 1970 and 2005 in 27 catchments located in the french alps from the french national natural hazard survey and model their variability of occurrence considering environmental and climatic predictors at the same time we document the environmental characteristics of each debris flow catchment morphometry lithology land cover and the presence of permafrost we also compute 15 climate variables including mean temperature and precipitation between may and october and the number of rainy days with daily cumulative rainfall greater than 10 15 20 25 30 40 mm day 1 application of our model shows that the combination of environmental and climatic predictors explained 77 of the overall variability of debris flow occurrences in this data set occurrence probabilities depend mainly on climatic variables which explain 44 of the overall variability through the number of rainy days and maximum daily temperature this important time component in the variability of overall debris flow occurrence is shown to be responsible for a significant increase in debris flow activity between 1970 and 2005 at regional scale environmental variables which account for 33 of the overall variability includes mostly the morphometric variables of the debris flow catchments