observational evidence of slantwise convective adjustment abstract attempts were made during two field experiments to fly instrumented aircraft along absolute momentum m surfaces as a means of accurately determining slantwise convective stability the application of this technique appears to have been quite successful we present the results of four such efforts conducted in the ascent regions of midlatitude cyclones observed during the new england winter storms and genesis of atlantic lows experiments in three of the four cases the atmosphere was almost exactly neutral to slantwise ascent while being quite stable to vertical displacements in the fourth case the atmosphere departed from neutrality but was also substantially drier evidently due to subsidence we find excellent agreement between assessments of stability based on the m surface flights and on cross sections constructed from rawinsonde observations on the basis of these results i hypothesize that slantwise convective neutrality is characteristic of the ascent regions of baroclinic cyclones and

modeling forced pool riffle hydraulics in a boulder bed stream southern california the mechanisms which control the formation and maintenance of pool riffles are fundamental aspects of channel form and process most of the previous investigations on pool riffle sequences have focused on alluvial rivers and relatively few exist on the maintenance of these bedforms in boulder bed channels here we use a high resolution two dimensional flow model to investigate the interactions among large roughness elements channel hydraulics and the maintenance of a forced pool riffle sequence in a boulder bed stream model output indicates that at low discharge a peak zone of shear stress and velocity occurs over the riffle at or near bankfull discharge the peak in velocity and shear stress is found at the pool head because of strong flow convergence created by large roughness elements the strength of flow convergence is enhanced during model simulations of bankfull flow resulting in a narrow high velocity core that is translated through the pool head and pool center the jet is strengthened by a backwater effect upstream of the constriction and the development of an eddy zone on the lee side of the boulder the extent of flow convergence and divergence is quantified by identifying the effective width defined here as the width which conveys 90 of the highest modeled velocities at low flow the ratio of effective width between the pool and riffle is roughly 1 1 indicating little flow convergence or divergence at bankfull discharge the ratio of effective width is approximately 1 3 between the pool and downstream riffle illustrating the strong flow convergence at the pool head the effective width tends to equalize again with a ratio of 1 1 between the pool and riffle during a modeled discharge of a five year flood as the large roughness elements above the pool become drowned out results suggest that forced pool riffle sequences in boulder bed streams are maintained by flows at or near bankfull discharge because of stage dependent variability in depth averaged velocity and tractive force

enhanced sediment delivery in a changing climate in semi arid mountain basins implications for water resource management and aquatic habitat in the northern rocky mountains the delivery and transport of sediment through mountain rivers affects aquatic habitat and water resource infrastructure while climate change is widely expected to produce significant changes in hydrology and stream temperature the effects of climate change on sediment yield have received less attention in the northern rocky mountains we expect climate change to increase sediment yield primarily through changes in temperature and hydrology that promote vegetation disturbances i e wildfire insect pathogen outbreak drought related die off here we synthesize existing data from central idaho to explore 1 how sediment yields are likely to respond to climate change in semi arid basins influenced by wildfire 2 the potential consequences for aquatic habitat and water resource infrastructure and 3 prospects for mitigating sediment yields in forest basins recent climate driven increases in the severity and extent of wildfire suggest that basin scale sediment yields within the next few years to decades could be greater than the long term average rate of 146 t km 2 year 1 observed for central idaho these elevated sediment yields will likely impact downstream reservoirs which were designed under conditions of historically lower sediment yield episodic erosional events massive debris flows that dominate post fire sediment yields are impractical to mitigate leaving road restoration as the most viable management opportunity for offsetting climate related increases in sediment yield however short term sediment yields from experimental basins with roads are three orders of magnitude smaller than those from individual fire related events on the order of 101 t km 2 year 1 compared to 104 t km 2 year 1 respectively for similar contributing areas suggesting that road restoration would provide a relatively minor reduction in sediment loads at the basin scale nevertheless the ecologically damaging effects of fine sediment material

crustal velocity structure associated with the eastern tennessee seismic zone vp and vs images based upon local earthquake tomography we present three dimensional p and s wave velocity models for the active eastern tennessee seismic zone etsz using arrival time data from more than 1000 local earthquakes a nonlinear tomography method is used that involves sequential inversion for model and hypocenter parameters we image several velocity anomalies that persist through most of the inversion volume some anomalies support the presence of known features such as an ancient rift zone in northern tennessee other anomalies reveal the presence of basement features that can be correlated with regional gravity and magnetic anomalies we image a narrow ne sw trending steeply dipping zone of low velocities that extends to a depth of at least 24 km and is associated with the vertical projection of the prominent new york alabama magnetic lineament the low velocity zone may have an apparent dip to the se at depths exceeding 15 km the low velocity zone is interpreted as a major basement fault juxtaposing granite rhyolite basement to the nw from grenville southern appalachian basement to the se relocated hypocenters align in near vertical segments suggesting reactivation of a distributed zone of deformation associated with a major strike slip fault we suggest that the etsz represents reactivation of an ancient shear zone established during formation of the super continent rodinia

sediment transport by dry ravel 1 dry ravel is a general term that describes the rolling bouncing and sliding of individual particles down a slope and is a dominant hillslope sediment transport process in steep arid and semiarid landscapes during fires particles can be mobilized by the collapse of sediment wedges that have accumulated behind vegetation on a daily basis particles may be mobilized by bioturbation and by small landslides experiments on a dry ravel flume indicate that a basic expression of the momentum equation predicts the distance traveled by particles propelled down a rough surface this equation is further elaborated to produce a nonlinear slope dependent transport equation for dry ravel that represents the rate at which sediment crosses a contour width of slope sediment traps installed on two hillslope transects near santa barbara california measured the flux from dry ravel initiated by bioturbation and the data support the form of the equation additionally a physical model based on the infinite slope stability analysis is proposed for the initiation of dry ravel by landsliding the analytical result from this model is supported by experiments and field data reported by others

holocene valley floor deposition and incision in a small drainage basin in western colorado usa the valley floor of a 33 9 km 2 watershed in western colorado experienced gradual sedimentation from before 6765 to 500 cal yr bp followed by deep incision renewed aggradation and secondary incision in contrast at least four terraces and widespread cut and fill architecture in the valley floor downstream indicate multiple episodes of incision and deposition occurred during the same time interval the upper valley fill history is atypical compared to other drainages in the colorado plateau one possible reason for these differences is that a bedrock canyon between the upper and lower valley prevented headward erosion from reaching the upper valley fill another possibility is that widespread sand rich clay poor lithologies in the upper drainage limited surface runoff and generally favored alluviation whereas more clay rich lithologies in the lower drainage resulted in increased surface runoff and more frequent incision twenty two dates from valley fill charcoal indicate an approximate forest fire recurrence interval of several hundred years similar to that from other studies in juniper pinon woodlands results show that closely spaced vertical sampling of alluvium in headwater valleys where linkages between hillslope processes and fluvial activity are relatively direct can provide insight about the role of fires in alluvial chronologies of semi arid watersheds

crustal modeling from spectrally correlated free air and terrain gravity data a case study of ohio we investigate the use of spectral correlation theory to analyze terrain gravity effects and free air gravity anomalies of ohio for possible constraints on the thickness variations and neotectonics of the crust terrain gravity effects are computed from the topography by gauss legendre quadrature integration and are compared against independent free air gravity anomaly observations for their wavenumber correlation spectrum spectral correlation filters are designed accordingly to extract terrain correlated free air gravity anomalies that are subtracted from the terrain gravity effects for estimates of the compensated terrain gravity effects these effects are used to model the moho by inversion assuming they predominantly reflect crustal thickness variations our results characterize the middle third of ohio as a broad zone of thickened precambrian crust which also may include rifted regions where the thickness of the prerift crust has been reduced greatly furthermore we find that about 83 of the ins

the 1 1 ga midcontinent rift system central north america sedimentology of two deep boreholes lake superior region abstract the midcontinent rift system mrs of central north america is a 1 1 ga 2500 km long structural feature that has been interpreted as a triple junction rift developed over a mantle plume as much as 20 km of subaerial lava flows mainly flood basalts are overlain by as much as 10 km of sedimentary rocks that are mostly continental fluvial red beds this rock sequence known as the keweenawan supergroup has been penetrated by a few deep boreholes in the search for petroleum in this paper two deep boreholes in the upper peninsula of michigan are described in detail for the first time both the amoco production 1 29r test herein referred to as the st amour well and the nearby hickey creek well drilled by cleveland cliffs mining services were 100 cored the former is 7238 ft 2410 m deep and the latter is 5345 ft 1780 m deep the entirety of the stratigraphic succession of the hickey creek core correlates very well with the upper portion of the st amour core as determined by core description and point counting of 43 thin sections selected out of 100 studied thin sections two lower paleozoic units and two keweenawan red bed units the jacobsville sandstone and the underlying freda sandstone are described the jacobsville is largely a feldspatholithic sandstone and the freda is largely a lithofeldspathic sandstone below the freda the remaining footage of the st amour core consists of a thick quartzose sandstone unit that overlies a heterogenous unit of intercalated red bed units of conglomerate sandstone siltstone and shale black shale individual basalt flows and a basal ignimbritic rhyolite this lower portion of the st amour core presents an enigma as it correlates very poorly with other key boreholes located to the west and southwest while a black shale sequence is similar to the petroleum bearing nonesuch formation farther west there is no conglomerate unit to correlate with the copper harbor conglomerate other key boreholes are distributed over a 1300 km distance along the better known southwest arm of the triple junction mrs and can be correlated rather well with the units that are exposed in the lake superior region however a definitive explanation of the anomalous deeper st amour stratigraphy is elusive and any explanation is tenuous a possible explanation for this anomalous stratigraphy may be the geographic proximity of the st amour borehole to the keweenawan hot spot mantle plume the suggested thermal force behind the development of the mrs similarly a drastic change in structural architecture may be explained by this geographic relationship thus within the locale of this rifting center complexities of expansion tectonics may well be responsible for igneous and sedimentary sequences that differ considerably from those found farther west along the rift arm

fluvial sediment transport in response to moderate storm flows following chaparral wildfire ventura county southern california chaparral wildfire has a profound effect on erosion and sedimentation in southern california the wheeler fire in july 1985 burned the entire basin of a tributary drainage area 2 14 km 2 of the north fork of matilija creek near ventura california after the fire fine gravel was delivered to the channel by the process of dry ravel dry particle by particle sliding of debris under the force of gravity at a rate of 0 29 m 3 km 2 month the first winter flow 2 1 m 3 s following the fire deposited 550 m 3 of fine gravel in the 270 m study reach near the mouth of the tributary at least 90 of this fine gravel was derived from colluvium delivered by dry ravel processes from hillslopes near the channel the second winter flow 2 5 m 3 s eroded the channel to the pre fire thalweg a reduction in particle size and critical shear stress associated with deposition of small gravel following the fire allowed these moderate magnitude flows to transport large volumes of sediment deposits of two debris flows were identified in the tributary basin radiocarbon dating of these deposits gives dates of 1045 95 yr b p for the older deposit and between 295 35 and 385 84 yr b p for the younger deposit these dates indicate that the recurrence interval of large debris flows in the study basin is at least an order of magnitude greater than the recurrence interval of fire in the area

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones xiii structure of a warm front abstract mesoscale measurement from radars aircraft and rawinsondes and synoptic and satellite data are used to provide a detailed description of a warm front as it approached the washington coast in many respects the warm front was consistent with the classical model temperature rises were concentrated within a forward sloping frontal zone winds veered with height and lapse rates were more stable within the frontal zone clouds and precipitation were produced by upglide over the warm frontal surface and as the warm front approached clouds lowered and precipitation generally increased however in several important respects the warm front differed from the classical picture air flowed through the warm front and the warm frontal zone also the warm frontal zone had a staircase profile with some segments nearly horizontal and other segments with steep slopes finally precipitation was by no means uniformly distributed instead it occurred in both irregular and banded shaped mesoscale features

authigenic k feldspar in the precambrian basement of ohio and its effect on tectonic discrimination of the granitic rocks authigenic k feldspar of apparent low temperature origin is widespread in the uppermost part of the two main precambrian basement terranes of ohio the subsurface extension of the grenville province of canada and the anorogenic granite rhyolite terrane of the transcontinental proterozoic province of the united states the authigenic k feldspar occurs mainly as a replacement of both primary k feldspar and albitic plagioclase in a variety of igneous and metamorphic rocks and can be identified by a salmon color in plane or ordinary light moderate to low optic angle monoclinic or triclinic symmetry and or rich composition its origin has been ascribed to alkali exchange by potassic brines in early paleozoic time the k feldspar authigenesis has changed whole rock major elemental compositions by increasing k2o decreasing na2o and cao and in general modifying sio2 and al2o3 these changes rule out using chemical parameters such as alkalis alkaline earths alumina and silica as tectonic or petrologic disc

the effects of log erosion barriers on post fire hydrologic response and sediment yield in small forested watersheds southern california wildfire usually promotes flooding and accelerated erosion in upland watersheds in the summer of 1999 a high severity wildfire burned a series of mixed pine oak headwater catchments in the san jacinto mountains of southern california log erosion barriers lebs were constructed across much of the burned area as an erosion control measure we built debris basins in two watersheds each about 1 ha in area one with lebs the other without to measure post fire hydrologic response and sediment yield and to evaluate the effectiveness of the lebs the watersheds are underlain by granitic bedrock producing a loamy sand soil above large extents of weathered bedrock and exposed core stones tors on the surface measured soil water repellency was similar over the two catchments rain gauges measured 348 mm of precipitation in the first post fire year the ephemeral stream channels experienced surface flow after major rainstorms and the source of the water was throughflow exfiltration at the slope channel interface post fire overland flow produced some rilling but hillslope erosion measured in silt fences away from any lebs was minor as was sediment accumulation behind the lebs stream channels in the catchments exhibited minor net scour water yield was much greater in the leb treated watershed this resulted in 14 times more sediment yield by weight than the untreated watershed average soil depths determined by augering were nearly double in the catchment without the lebs compared with the treated watershed this suggests that differences in water and sediment yield between the two catchments are due to the twofold difference in the estimated soil water holding capacity in the untreated watershed it appears that the deeper soils in the untreated watershed were able to retain most of the precipitation releasing less water to the channels and thereby reducing erosion and sediment yield thus the test of leb effectiveness was inconclusive in this study because soil depth and soil water holding capacity may have masked their performance

a wide cold frontal rainband and its relationship to frontal topography a wide cold frontal rainband associated with a vigorous surface cold front was investigated using conventional meteorological data and the velocity and reflectivity data from high resolution doppler radar it was found that the movement of the rainband was closely related to the velocity of the frontal surface and that the substructural features of the rainband corresponded closely with the topographical features of that surface the evolution of the topography of the frontal surface is described and some processes that might affect frontal topography and therefore the structure and movement of rainbands are examined

reviewing the configuration and extent of the midcontinent rift system abstract uncertainty exists in the configuration and extent of the midcontinent rift system mrs because of deficiencies in geophysical data and limited information from outcrops and basement drill holes additional ambiguity is caused by misunderstanding the definition of continental rifts six principal problematic regions in mapping the mrs are described gravity and magnetic data supported by drill hole and seismic reflection data show that the eastern lake superior rift segment of the mrs continues south from lake superior and connects to a much narrower rift in northern lake michigan the eastern margin of this transition is ill defined because of the lack of definitive anomalies and supporting seismic and drill hole data but is interpreted to occur near the u s canada border the rift segment in southeastern michigan intersects the grenville front and likely continues eastwards in modified form to near the boundary with canada cross cutting gravity and magnetic signatures may reflect grenvillian overthrusts near the terminus of the mrs in michigan the proposed southerly extensions of both branches of the rift system into oklahoma and ohio are based primarily on positive gravity anomalies but neither postulated extension appears to be associated with rifted troughs rather the gravity anomalies of the western branch are related to intrusive mafic rocks and those of the eastern branch are most likely related to deep crustal metamorphic rocks thrust into juxtaposition with less dense crust by grenville orogenesis recent paleomagnetic investigations in conjunction with high resolution radiometric dating imply that the mrs developed during the rapid southward movement of laurentia during a quiescent period along its eastern continental margin massive magmatic activity accompanying the rifting was likely due to rising mantle material that was displaced by subducted lithosphere along the southern margin the heated crust was made more ductile fostering rifting due to extensional stresses the nipigon embayment remains as a possible candidate for an early third branch of the mrs but current evidence is insufficient to include the fort wayne rift as part of the mrs future studies of the mrs would be well served by new age dating and high resolution seismic studies of the lithosphere

a morphometric analysis of gullies scoured by post fire progressively bulked debris flows in southwest montana usa in the fall of 2001 an intense thunderstorm in southwest montana triggered many debris flows in the burned area of sleeping child creek in most instances the debris flows cut deep gullies into previously unchannelized colluvial hollows and deposited large volumes of sediment onto the valley floor the presence of rill networks above the gullies as well as the absence of landslide features indicate that the gullies were scoured by progressively bulked debris flows a process in which dilute surface runoff becomes increasingly more laden with sediment until it transforms into a debris flow in this contribution we present a morphometric analysis of six of the gullies to better understand this relatively understudied process we find that the locations of the rill heads and gully heads conform to slope area thresholds that are characteristic of erosion by overland flow our data also suggest that the volumes of the debris flows increase exponentially with normalized drainage area thus lending support to an assumption used in a recently proposed debris flow incision law finally the debris flow fans have been relatively unaltered since deposition suggesting that the valley may be currently aggrading while the hillslopes are being denuded

a cocorp deep reflection profile across the buried reelfoot rift south central united states abstract a cocorp deep reflection survey across the northern mississippi embayment reveals essential features of the late precambrian early paleozoic reelfoot rift stratified reflections delineating the sedimentary fill of the rift basin are of variable thickness the base ranging from 2 0 to a maximum of 3 5 s twt 4 to 8 km depth in contrast the base of phanerozoic the sedimentary section immediately east of the rift is at 1 4 s 2 8 km depth correlation with a basement penetrating well indicates that the base of the upper cretaceous holocene mississippi embayment supergroup base of the cambrian ordovician knox group and the lower upper cambrian bonneterre formation are basin wide seismic stratigraphic markers clastic sedimentary strata of the lamotte formation which immediately overlie precambrian basement show clear angular discordance with the overlying subhorizontal bonneterre formation indicating that the base of the bonneterre marks the transition from active extension to passive subsidence within the reelfoot rift palinspastic restoration of the basement suggests relatively modest extension associated with rift formation 17 the blytheville arch an axial antiformal feature as well as a number of lesser structures indicative of multiple episodes of fault reactivation are also evident on the cocorp profile the crystalline basement beneath the reelfoot rift is relatively devoid of reflections down to 5 0 s 12 15 km depth beyond which it passes gradationally into a complexly reflective diffractive middle and lower crust the lower crust however does not exhibit the distinctly laminated character commonly observed in mesozoic cenozoic extensional provinces the crust mantle transition beneath the rift is characterized by a gradational downward cessation of crustal reflectivity at 12 13 s 40 km depth followed by an unreflective zone which in turn is followed by a distinct horizontal reflection at 14 5 s the latter is not observed on existing profiles outside the rift at present it is not possible to determine strictly whether the deep horizon represents moho or alternatively a discrete feature sill within the uppermost mantle however its spatial association with the reelfoot rift suggests that the two are genetically related regional relations together with the existence of dipping fabric in the deep crust beneath the rift suggest the possibility that the reelfoot rift formed along the southern extension of the circa 1 ga grenville front

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones xi comparisons between observational and theoretical aspects of rainbands abstract comparisons are made between the characteristics of several types of rainbands observed in an extratropical cyclone and dynamical mechanisms relevant on the mesoscale the warm sector flow ahead of the cold front and above the cold frontal zone aloft was unstable to conditional symmetric instability and theoretical predictions for this mechanism am consistent with several aspects of the warm sector and wide cold frontal rainbands in the case of the warm sector rainbands other mechanisms e g wave cisk and mixed dynamic convective instabilities may have also played a role the core structure of the narrow cold frontal rainbands appeared to be affected by an instability that derived its energy from the horizontal shear across the surface front also many aspects of the narrow cold frontal rainband were similar to a density current shear induced gravity waves appeared to be responsible for the wavelike rainbands observed in the vicinity of the cold frontal zone aloft the orientation of the

effect of storms during drought on post wildfire recovery of channel sediment dynamics and habitat in the southern california chaparral usa author s florsheim joan l chin anne kinoshita alicia m nourbakhshbeidokhti samira abstract current global warming projections suggest a possible increase in wildfire and drought augmenting the need to understand how drought following wildfire affects the recovery of stream channels in relation to sediment dynamics we investigated post wildfire geomorphic responses caused by storms during a prolonged drought following the 2013 springs fire in southern california usa using multi temporal terrestrial laser scanning and detailed field measurements after the fire a dry season dry ravel sediment pulse contributed sand and small gravel to hillslope channel margins in big sycamore creek and its tributaries a small storm in wy 2014 generated sufficient flow to mobilize a portion of the sediment derived from the dry ravel pulse and deposited the fine sediment in the channel totaling 0 60 m3 m of volume per unit length of channel the sediment deposit buried step pool habitat structure and reduced roughness by over 90 these changes altered sediment transport characteristics of the bed material present before and after the storm the ratio of available to critical shear stress t o t c increased by five times storms during wy 2015 contributed additional fine sediment from tributaries and lower hillslopes and hyperconcentrated flow transported and deposited additional sediment in the channel together these sources delivered sediment on the order of six times that in 2014 further increasing t o t c these storms during multi year drought following wildfire transformed channel dynamics the increased sediment transport capacity persisted during the drought period characterized by the longer residence time of relatively fine grained post fire channel sedimentation this contrasts with wetter years when post fire sediment is transported from the fluvial system during the same season as the post fire sediment pulse results of this short term study highlight the complex and substantial effects of multi year drought on geomorphic responses following wildfire these responses influence pool habitat that is critical to longer term post wildfire riparian ecosystem recovery

sediment yield from the tectonically active semiarid western transverse ranges of california sediment yields from the world s rivers are generally highest from steep drainage basins with weak lithology active tectonics or severe land use impacts here we evaluate sediment yields from the western transverse ranges of california in an attempt to explain why they are two to tenfold greater than the surrounding areas of california we found that suspended sediment yields across the gauged basins of the western transverse range during 1969 1999 varied by approximately an order of magnitude 740 5300 t km2 yr similarly fine sediment concentrations for normalized discharge rates varied by almost two orders of magnitude e g 1 3 110 g l for the mean annual flood for 11 previously unmonitored drainages of the santa ynez mountains areas with high sediment yields consistently have weakly consolidated bedrock quaternary pliocene marine formations and are associated with the highest rates of tectonic uplift of the region 5 mm yr these regions are important to the sediment discharge budgets because 50 of the total suspended sediment discharge from the western transverse range is estimated to be generated within these regions even though they represent only 10 of the total watershed area previous estimates of suspended sediment discharge from the ventura river have likely been underestimated by 50 because the gauging station is located immediately upstream of a high sediment yield region we also found a significant and positive correlation between sediment yield and the percentage of a watershed with grassland and agricultural land use these results suggest that there is adequate variation within the lithology tectonics and land use of the broader western transverse range geologic province to induce large variations in sediment yield at the local scale

slope grain size and roughness controls on dry sediment transport and storage on steep hillslopes existing hillslope sediment transport models developed for low relief soil mantled landscapes are poorly suited to explain the coupling between steep rocky hillslopes and headwater channels here we address this knowledge gap using a series of field and numerical experiments to inform a particle based model of sediment transport by dry ravel a mechanism of granular transport characteristic of steep hillslopes we find that particle travel distance increases as a function of the ratio of particle diameter to fine scale 1 m topographic variability associated with rocky landscapes applying a 2 d dry ravel routing model to lidar derived surface topography we show how spatial patterns of local and nonlocal transport control connectivity between hillslopes and steep headwater channels that generate debris flows through failure of ravel filled channels following wildfire our results corroborate field observations of a patchy transition from soil mantled to bedrock landscapes and suggest that there is a dynamic interplay between sediment storage roughness grain sorting and transport even on hillslopes that well exceed the angle of repose

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones part xv a numerical modeling study of frontogenesis and cold frontal rainbands abstract a two dimensional hydrostatic primitive equation model is used to investigate the dynamics of frontogenesis in a moist atmosphere the development of a cold front is simulated through shear deformation associated with the non linear evolution of an eady wave simulations are performed with 5 10 40 and 80 km horizontal resolutions and 14 levels in the vertical four in the boundary layer compared to the dry case the inclusion of moisture in the model produces a stronger low level jet ahead of the front and a stronger upper level jet moisture also produces a stronger ageostrophic circulation across the front and a more concentrated updraft just ahead of the surface front the updraft develops a banded structure above and behind the surface front with a wavelength of about 70 km bands form near the back edge of the cloud shield and move toward the surface front with a relative velocity of 1 m s 1 these characteristics agree with observations of wide cold frontal rainbands the banded str

geomorphic complexity and sensitivity in channels to fire and floods in mountain catchments abstract fires and floods are important drivers of geomorphic change while the hydrologic and geomorphic effects of fires have been studied at the hillslope scale we have much more limited data on post fire runoff channel changes and inferred or measured sediment storage and delivery at larger scales in this study we intensively documented channel changes over four years in two very similar 15 km2 catchments in the northern colorado front range skin gulch and hill gulch that were burned primarily at high and moderate severity in june 2012 ten and 11 cross sections and longitudinal profiles along the lower channel network were repeatedly surveyed in skin gulch and hill gulch respectively summer thunderstorms generally caused deposition in the valley bottoms while incision resulted from the intervening baseflows and spring snowmelt but a very high intensity summer thunderstorm in skin gulch just one week after burning caused much more deposition than in hill gulch fifteen months after burning both watersheds experienced an exceptional long duration flood resulting from a multi day rainstorm with a several hundred year recurrence interval this removed nearly all of the deposited post fire sediment along with some of the older valley bottom deposits the expansion and coarsening of the channel has greatly decreased the geomorphic sensitivity of both watersheds to future floods and eliminated the more typical and persistent post fire depositional signature the channel changes in skin gulch after the fire and long duration flood were much greater than in hill gulch and this can be attributed to the much greater sediment deposition in skin gulch shortly after the fire reduced geomorphic sensitivity in hill gulch resulting from a large erosional flood in 1976 and the spatial distribution of burn severity and storm rainfalls leading to lower peak flows in hill gulch these results suggest that fires in the rocky mountains can trigger significant and dynamic hillslope and channel changes over sub decadal timescales but unusually long or intense rainstorms can cause larger and more persistent changes regardless of whether a catchment has recently burned

structure and tectonic evolution of the transitional region between the central appalachian foreland and interior cratonic basins abstract the transitional region between the central appalachian foreland basin and michigan and illinois interior cratonic basins is characterized by first and second order structures related to plate convergent processes at the laurentian plate margin the first order structures are the waverly and cincinnati arches believed to be forebulges associated with the taconic and alleghanian orogenies respectively the second order structures are basement faults that exhibit a protracted history of recurrent displacements first and second order structures are linked in that the basement faults have had a major effect in controlling the location and uplift history of the arches the waverly and cincinnati arches share many similarities that suggest a common process of arch development the waverly arch developed over the low density rocks in the central metasedimentary belt of the grenville province near its structural contact with the central gneiss belt uplift on the arch commenced during passive margin development in the cambrian but reached its maximum development at the end of the middle ordovician taconic orogeny reactivation of faults along the arch continued as late as the pennsylvanian the cincinnati arch as expressed in the precambrian basement surface is coincident with the underlying grenville front on a regional scale the front is a major crustal suture which served to localize and control the history of the cincinnati arch local deviations between the location of the arch and front are explained by the presence of proterozoic rift basins filled with low density sedimentary rocks by interactions between the developing appalachian michigan and illinois basins and by a northward decrease in alleghanian tectonic loading in a pattern similar to the waverly arch the cincinnati arch began its history with a period of regional uplift as early as the middle to late ordovician followed by maximum arch development in the pennsylvanian in response to the alleghanian orogeny neither arch showed significant migration following initial development as predicted by general models of forebulge development we attribute this to the effect of preexisting basement anisotropies such as lithotectonic boundaries which served to control the initial location of the forebulge and affect its subsequent history a third major arch the kankakee arch occurs in the western part of the transitional region and is oriented at right angles to the other arches unlike the waverly and cincinnati arches this arch owes its development to subsidence in the adjacent michigan and illinois basins rather than orogenic activity in the appalachians

a possible southeastern extension of the midcontinent rift system located in ohio in 1988 a stratigraphic test core drilled in southwestern ohio penetrated a previously unknown structure and sedimentologic unit core analyses disclosed a sequence of lithic arenite and siltstone of probable pre phanerozoic age deposited within an alluvial fluvial environment a seismic reflection profile across the core site shows a sequence of strong horizontal paleozoic reflectors unconformably overlying eastward dipping layered units of poor reflectivity beyond the core hole total depth a regime of excellent reflectors is seen the pre mount simon upper cambrian sedimentary sequence encountered has been defined as the type section of the middle run formation point counter analyses of typical middle run formation samples indicate that this sequence is similar in composition to middle proterozoic units associated with the midcontinent rift system in the lake superior region the newly discovered structure in ohio is also similar to half graben structures composing the lake superior basin portion of the midcontinent rift on the basis of similarities in lithology stratigraphy structure and proximity to regional gravity anomalies the middle run formation and its apparent half graben basin is proposed as evidence for the probable extension of the midcontinent rift system southward from its normally accepted termination in southeastern michigan into southwestern ohio

crustal structure interpreted from magnetic anomalies this review discusses publications during the last quadrennium 1987 1990 that used aeromagnetic data marine magnetic data satellite magnetic data and rock magnetic and petrologic data to provide information on the sources of magnetic anomalies the publications reviewed reflect increased integration of rock magnetic property and petrologic studies with magnetic anomaly interpretation studies particularly in deep crustal magnetization exploration for hydrocarbons and inversion of marine magnetic anomalies interpretations of aeromagnetic data featuring image display techniques and using the horizontal gradient method for locating magnetization boundaries became standard

short term post wildfire dry ravel processes in a chaparral fluvial system abstract dry ravel the transport of sediment by gravity transfers material from steep hillslopes to valley bottoms during dry conditions following wildfire dry ravel greatly increases in the absence of vegetation on hillslopes thereby contributing to sediment supply at the landscape scale dry ravel has been documented as a dominant hillslope erosion mechanism following wildfire in chaparral environments in southern california however alteration after initial deposition is not well understood making prediction of post fire flood hazards challenging the majority of big sycamore canyon burned during the may 2013 springs fire leaving ash and a charred layer that covered hillslopes and ephemeral channels dry ravel processes following the fire produced numerous deposits in the hillslope channel transition zone field data focus on 1 deposition from an initial post wildfire dry ravel pulse and 2 subsequent alteration of dry ravel deposits over a seven month period between september 2013 and april 2014 we quantify geomorphic responses in dry ravel deposits including responses during the one small winter storm that generated runoff following the fire field measurements document volumetric changes after initial post wildfire deposition of sediment derived from dry ravel erosion and deposition mechanisms that occurred within dry ravel deposits situated in the hillslope channel transition zone included 1 mobilization and transport of a portion or the entire deposit by fluvial erosion 2 rilling on the surface of the unconsolidated deposits 3 deposition on deposits via continued hillslope sediment supply and 4 mass wasting that transfers sediment within deposits where surface profiles are near the angle of repose terrestrial lidar scanning point clouds were analyzed to generate profiles quantifying depth of sediment erosion or deposition over remaining dry ravel deposits after the first storm season this study contributes to the understanding of potential effects of wildfire on fine sediment delivery to fluvial systems in chaparral ecosystems

post fire geomorphic response in steep forested landscapes oregon coast range usa abstract the role of fire in shaping steep forested landscapes depends on a suite of hydrologic biologic and geological characteristics including the propensity for hydrophobic soil layers to promote runoff erosion during subsequent rainfall events in the oregon coast range several studies postulate that fire primarily modulates sediment production via root reinforcement and shallow landslide susceptibility although few studies have documented post fire geomorphic response here we describe field observations and topographic analyses for three sites in the central oregon coast range that burned in 1999 2002 and 2003 the fires generated strongly hydrophobic soil layers that did not promote runoff erosion because the continuity of the layers was interrupted by pervasive discontinuities that facilitated rapid infiltration at each of our sites fire generated significant colluvial transport via dry ravel consistent with other field based studies in the western united states fire driven dry ravel accumulation in low order valleys of our sulphur creek site equated to a slope averaged landscape lowering of 2 5 mm given holocene estimates of fire frequency these results suggest that fire may contribute 10 20 of total denudation across steep dissected portions of the oregon coast range in addition we documented more rapid decline of root strength at our sites than has been observed after timber harvest suggesting that root strength was compromised prior to fire or that intense heat damaged roots in the shallow subsurface given that fire frequencies in the pacific northwest are predicted to increase with continued climate change our findings highlight the importance of fire induced dry ravel and post fire debris flow activity in controlling sediment delivery to channels

logging effects on sediment flux observed in a pollen based record of overbank deposition in a northern california catchment a palynological approach was used to estimate overbank deposition rates in a forested catchment affected by logging the palynological approach uses downcore variations in total fossil pollen and fossil pollen assemblage to calculate rates of overbank deposition and has a distinct advantage over radioisotopic approaches in that it is not limited by radioactive decay using this approach we determined that overbank deposition rates increased over 400 per cent within years of logging events and that the increased rates persisted for less than 4 years after logging induced deposition peaked overbank deposition decreased over 60 per cent relative to the pre logging background values the decreased deposition rates persisted for over 40 years the immediate effect of logging in this catchment was to induce mass wasting events in hollows that produced rapidly travelling sediment pulses in the subsequent recovery period reduced sediment loading occurred as a result of a reduction in the volume of sediment available for transport the reduction in sediment load led to a reduction in overbank deposition rates until subsequent logging disturbances destabilized and emptied other hollows

the lagrangian parcel dynamics of moist symmetric instability abstract a simple model describing the slantwise ascent of a two dimensional horizontal air tube subject to moist symmetric instability is developed under the assumptions that the froude number is small and that mixing is absent it is shown that in general the horizontal velocities attained by the tube are comparable to those of the mean flow and that vertical velocities of up to a few meters per second are possible the tube ascends slantwise in such a way that its buoyancy remains nearly zero unless the environment is my very nearly moist adiabatic in which case ascent at an angle of 45 to the vertical is preferred results of the analysis support the contentions of bennetts and hoskins and emanual that moist symmetric instability is the cause of some mesoscale rainbands in a companion paper it is demonstrated that the stability of the moist baroclinic atmosphere to two dimensional slantwise displacements of arbitrary magnitude can be approximately assessed by reversibly lifting parcel along sur

channel and woody debris characteristics in adjacent burned and unburned watersheds a decade after wildfire park county wyoming abstract large variability in responses of stream sediment and large woody debris lwd to severe fire has limited the accurate prediction of the magnitude and duration of fire effects on streams conditions in one absaroka range stream that was severely burned in 1988 were compared to those in an adjacent undisturbed stream to improve understanding of fire effects on channel and lwd characteristics beyond the first few years ten reaches of each stream were sampled during summer 1999 average bankfull channel width was greater in burned jones creek than in unburned crow creek lwd frequency and overall frequency of lwd accumulations were greater in crow creek than jones creek debris jam frequency was greater in jones creek after accounting for differences in the frequency of pieces with length greater than channel width larger piece size and better anchoring contributed to more frequent small accumulations of lwd in crow creek differences between streams in lwd frequency are consistent with greater mobility of debris in burned jones creek lwd associated fine sediment deposits were thicker but less frequent along jones creek than crow creek

wildfire related debris flow initiation processes storm king mountain colorado a torrential rainstorm on september 1 1994 at the recently burned hillslopes of storm king mountain co resulted in the generation of debris flows from every burned drainage basin maps 1 5000 scale of bedrock and surficial materials and of the debris flow paths coupled with a 10 m digital elevation model dem of topography are used to evaluate the processes that generated fire related debris flows in this setting these evaluations form the basis for a descriptive model for fire related debris flow initiation the prominent paths left by the debris flows originated in 0 and 1st order hollows or channels discrete soil slip scars do not occur at the heads of these paths although 58 soil slip scars were mapped on hillslopes in the burned basins material derived from these soil slips accounted for only about 7 of the total volume of material deposited at canyon mouths this fact combined with observations of significant erosion of hillslope materials suggests that a runoff dominated process of progressive sediment entrainment by surface runoff rather than infiltration triggered failure of discrete soil slips was the primary mechanism of debris flow initiation a paucity of channel incision along with observations of extensive hillslope erosion indicates that a significant proportion of material in the debris flows was derived from the hillslopes with a smaller contribution from the channels because of the importance of runoff dominated rather than infiltration dominated processes in the generation of these fire related debris flows the runoff contributing area that extends upslope from the point of debris flow initiation to the drainage divide and its gradient becomes a critical constraint in debris flow initiation slope area thresholds for fire related debris flow initiation from storm king mountain are defined by functions of the form acr tan 3 s where acr is the critical area extending upslope from the initiation location to the drainage divide and tan is its gradient the thresholds vary with different materials

post wildfire landscape change and erosional processes from repeat terrestrial lidar in a steep headwater catchment chiricahua mountains arizona usa abstract flooding and erosion after wildfires present increasing hazard as climate warms semi arid lands become drier population increases and the urban interface encroaches farther into wildlands we quantify post wildfire erosion in a steep initially unchannelized 7 5 ha headwater catchment following the 2011 horseshoe 2 fire in the chiricahua mountains of southeastern arizona using time lapse cameras rain gauges and repeat surveys by terrestrial laser scanner we quantify the response of a burned landscape to subsequent precipitation events repeat surveys provide detailed pre and post rainfall measurements of landscape form associated with a range of weather events the first post fire precipitation led to sediment delivery equivalent to 0 017 m of erosion from hillslopes and 0 12 m of erosion from colluvial hollows volumetrically 69 of sediment yield was generated from hillslope erosion and 31 was generated from gully channel establishment in colluvial hollows processes on hillslopes included erosion by extensive shallow overland flow formation of rills and gullies and generation of sediment laden flows and possibly debris flows subsequent smaller rain events caused ongoing hillslope erosion and local deposition and erosion in gullies winter freeze thaw led to soil expansion likely related to frost heaving causing a net centimeter scale elevation increase across soil mantled slopes by characterizing landscape form the properties of near surface materials and measuring both precipitation and landscape change we can improve our empirical understanding of landscape response to environmental forcing this detailed approach to studying landscape response to wildfires may be useful in the improvement of predictive models of flood debris flow and sedimentation hazards used in post wildfire response assessments and land management and may help improve process based models of landscape evolution

secondary frontal waves in the north atlantic region a dynamical perspective of current ideas the current understanding of the dynamics of secondary cyclogenesis on frontal systems in the north atlantic region is reviewed these secondary cyclones are often poorly forecast and in extreme cases can have damaging consequences but because of their small scales and potential for rapid growth detailed observations and analyses are limited in this paper recent work is described and compared it is argued that on the synoptic scale the development of primary baroclinic waves is well understood but on the subscales of these systems where the secondaries develop there is a wider variety of mechanisms which may cause or modify cyclone growth this variety may be reflected in a wider range of resulting systems various dynamical models have been postulated secondary frontal waves are seen as the instability of a low level potential vorticity strip or warm band at a front with possible finite amplitude triggering by upper level features latent heating is thought to provide a suitable unstable potential vorticity strip but the degree to which the latent heating contributes to the instability itself is a matter of dissent secondary systems are often shallow so boundary layer processes are important but the influence of these is not well understood laboratory experiments have suggested that the boundary layer will act to suppress instability in general frontogenetic strain flow while acting to intensify the basic state front suppresses wave development in contrast recent work suggests that a frontolytic strain flow may be important in enhancing the development of one class of waves the fastex experiment an international field study of north atlantic secondary cyclogensis has recently attempted to observe these systems in detail it is hoped that the data which have been obtained will help to resolve some of the outstanding issues in this field

sediment storage by vegetation in steep bedrock landscapes theory experiments and implications for postfire sediment yield 1 mechanistic models for sediment transport on hillslopes are needed for applications ranging from landscape evolution to debris flow hazards progress has been made for soil mantled landscapes however little is known about sediment production and transport in bedrock landscapes that often maintain a patchy soil mantle even though slopes exceed the angle of repose herein we investigate the hypothesis that patchy soil cover is stable on steep slopes due to local roughness such as vegetation dams that trap sediment upslope to quantify local sediment storage we developed a new theory and tested it against tilt table experiments results show that trapped sediment volume scales with the cube of dam width where the dam width is less than about fifty grain diameters particle force chains appear to enhance stability resulting in greater trapped volumes and sediment pile slopes that exceed the angle of repose trapped volumes are greatest for hillslopes that just exceed the friction slope and are independent of hillslope gradient for gradients greater than about twice the friction slope for neighboring dams spaced less than about five grain diameters apart grain bridging results in a single sediment pile that is larger than the sum of individual piles this work provides a mass conserving framework for quantifying sediment storage and nonlocal transport in bedrock landscapes results may explain the rapid increase in sediment yield following wildfire in steep terrain in the absence of rainfall as sediment dams are incinerated particles become gravitationally unstable and move rapidly downslope as dry ravel

mesoscale dynamics of cold fronts structures described by dropsoundings in fronts 87 the fronts 87 project was a european experiment to make mesoscale observations to deduce the dynamics of active cold fronts approaching north west europe with a minimum of orographic influences in this paper data from dropsoundings made by the meteorological office s c 130 research aircraft are analysed the aircraft flew a pattern with 4 or 5 runs oriented approximately at right angles to the front but with each run displaced in the along front direction by about 100 km the dropsondes gave soundings to a height of approximately 7 km with a cross frontal spacing of 20 km at best and 60 km on average between 30 and 50 soundings were made in each event over an area of 500 500 km2 these data are unique in their mesoscale resolution over a synoptic scale region this was made possible by the ability to track up to 5 sondes in the air at any time several new aspects of cold front dynamics have been identified from these data the approach here is to treat each run as an instantaneous cross frontal section the discussion is centred on the hypotheses postulated before the experiment these were intended to allow verification or refutation of aspects of models of frontal dynamics such as those embodied in semi geostrophic theory a minimal and purely objective analysis has been performed on the data presented here but the high resolution of the dropsonde observations permits evaluation of differentiated quantities such as potential vorticity pv with some confidence issues raised here include the degree of thermal wind balance the structure of conserved variables such as equivalent potential temperature and absolute momentum the cross frontal circulation and the role of diabatic processes such as the evaporation of snow and the potential vorticity structure on the mesoscale and its interpretation the intention is to present an integrated view of the dynamical structure of fronts in the light of theoretical rather than conceptual or airflow models

middle late holocene river terraces in the erhjen river basin southwestern taiwan implications of river response to climate change and active tectonic uplift abstract we reconstruct the holocene river history of the erhjen river area 140 km 2 by correlating river terraces aided by 28 radiocarbon dates multiple terraces developed in the lower erhjen river since the middle holocene they converge downstream to the coastal plain the rates of channel incision into bedrock calculated from these terraces at yuehshihchieh are 7 8 mm year during ca 5 7 2 5 ka 5 cm year during 1 5 1 3 ka and 1 cm year since 1 ka the last is close to the average incision rate since middle holocene meanwhile only a single but wide middle late holocene paleo floodplain was developed in the upper erhjen river it was completely abandoned only after 0 8 ka likely following an episode of base level fall starting from the coastal plain based on the apparent downstream and upstream convergence of these dated terraces we identify a doming structure or anticline within the basin which results in a tilt rate of 10 6 to 10 7 per year in the lower erhjen river valley the major terraces here had different initial long profiles which implies that a critical graded long profile may not be a prerequisite for formation of a wide erosional terrace surface instead we propose that these terraces were initiated by a series of catastrophic rainfall events probably climatic related which brought a large amount of bedload from hillslopes to prevent the channel from incising when valley widening was facilitated by high discharge runoff we find that not only terrace surface formation but also channel incision can be strongly controlled by climatic driven discharge and bedload conditions as suggested by the contrast of bedrock incision rates we observe at yuehshihchieh apparently the climate and its effects on the landscape cannot be regarded as constant during the holocene even in a humid tropical area like taiwan however such a fluctuation of climate could only be recorded in a setting where rivers have a high tendency to incise so that multiple terraces can be created the lower erhjen river that is characterized by active tectonic tilting is an example of this setting

a holocene frozen accident sediments of extreme paleofloods and fires in the bedrock confined upper huis river western cape south africa wildfires and flooding events are common and are forceful intrinsic controls over landscape evolution biodiversity and preserved sediment architecture in dryland environments charcoal bearing holocene flood sediments of the upper huis river provide a rare perspective on the powerful and episodic sedimentary processes in a bedrock confined fluvial setting in the tectonically stable sw cape fold belt in south africa the sediments described in this paper are associated with high magnitude debris flow dominated paleofloods and their charcoal content is linked to a series of radiocarbon dated holocene paleofires that occurred from 2165 37 bp to 653 35 bp the five sedimentary facies associations are documented as products of a noncohesive pseudoplastic debris flows b transitional high matrix strength debris flows with heterogeneous fluid content and flow behavior c low cohesion debris flows d hyperconcentrated flows and e fluvial channel flow in the upper huis river the last is interpreted mainly from massive subrounded to subangular boulder bars which provide key evidence for the dramatic scouring of the upper huis valley the paleofloods which not only filled the valley with debris flow sediments up to 12 m thick but also subsequently flushed it out nearly to the bedrock had estimated extreme discharges of few thousands of m3 s in summary the upper huis river sediments are exceptional because they preserve the geological record of recurring fires and at least three extreme paleofloods i e massive sedimentation events over a period of 1500 years in an area typified by the fire prone and fire dependent fynbos biome furthermore this study provides insights into what the gaps in the commonly fragmented bedrock confined alluvial stratigraphic record would be like should there be more record than gap

organization and structure of clouds and precipitation on the mid atlantic coast of the united states part vi the synoptic evolution of a deep tropospheric frontal circulation and attendant cyclogenesis abstract interactions between an upper level frontal system and an initially weak surface cold front resulted in the production of a deep precipitating frontal structure over the south atlantic states on 26 27 january 1986 attendant with the intensification of the frontal circulation was the development of an intense marine cyclone off the delmarva peninsula the increase in frontal circulation strength is attributed to a favorable vertical superposition of the surface frontal trough and the upper level frontogenetic horizontal deformation field that resulted in a deep column of divergence over the surface frontal trough the surface cyclone developed partly and indirectly in response to the increase in warm air advection in the lower stratosphere which was directly related to an increase in the slope of the dynamic tropopause the increase in the slope of the tropopause is hypothesized to have been the result of the combined effect of adiabatic advection of low tropopause height in the cold air of t

a model for fire induced sediment yield by dry ravel in steep landscapes sediment flux from hillslopes to channels commonly increases following wildfires with implications for the carbon cycle river habitats and debris flow hazards although much of this material is transported via dry ravel existing ravel models are not applicable to hillslopes with gradients greater than the angle of repose which can constitute the majority of mountainous terrain to fill this knowledge gap we develop a continuity model for sediment storage by vegetation dams on steep hillslopes to predict sediment yields following wildfire the maximum volume of sediment stored prior to wildfire is set to be a function of vegetation density the capacity of plants to impound sediment and the contributing hillslope area time is required after fire to establish vegetation and replenish hillslope sediment storage which introduces vegetation regrowth rate soil production rate and fire recurrence interval as important variables that affect ravel yield model results for the san gabriel mountains california predict that sediment yield can increase by several orders of magnitude following fire these results are consistent with field data of ravel yield 30 mm per contributing area of hillslope in 5 months we collected following the 2009 station fire as well as postfire sediment flux recorded by 93 debris basins in contrast to previous work our model shows that heightened postfire sediment yields can be explained by a change in hillslope sediment storage independent of major changes in the soil production rate and landscape form over geomorphic timescales

vegetation and wildfire controls on sediment yield in bedrock landscapes steep rocky landscapes commonly exhibit high sediment yields and are especially sensitive to climate tectonics and wildfire predicting landscape response to these perturbations demands a quantitative understanding of erosion processes however existing models for hillslope sediment production and transport do not apply to landscapes with patchy soil and slopes that exceed the angle for sediment stability here we present field measurements in southern california usa which indicate that sediment storage on steep slopes is enabled by vegetation that traps sediment upslope we find that the storage capacity of unburned vegetation dams follows a geometric scaling model with a cubic dependence on effective plant width and an inverse dependence on local slope measured sediment volumes behind burned vegetation dams indicate a loss of at least 75 relative to unburned dams and when expanded to the catchment scale our measurements match records of postfire sediment yield from nearby retention basins contrary to existing models our observations indicate that wildfire induced sediment yield is driven by transient storage and release of sediment by vegetation dams rather than increased bedrock to soil conversion rates without a feedback between soil production and wildfire fire may play little role in long term landscape evolution and increasing fire frequency in response to climate change may not result in heightened sedimentation hazards due to supply limitations

fluvial geomorphology of a boulder bed debris flow dominated channel in an active tectonic environment abstract numerous streams with a drainage area of a few square kilometers draining the south flank of the santa ynez range in southern california are characterized by steep boulder bed debris flow dominated channels rattlesnake creek is a good example approximately 90 of the stored sediment in the stream valley is stable debris flow deposits found in debris flow terraces and levees adjacent to the channel the remaining 10 of stored sediment resides in the active channel where the channel morphology is dominated by large boulders 1 to 4 m in diameter derived from debris flows or rock fall that along with bedrock outcrops form rock or boulder transverse ribs with frequent step pools the dominant channel pool morphology is the step pool which accounts for most of the pools and approximately 30 of relief drop in elevation through the study reaches less common pool types identified in the study reaches include forced pools that result from convergence of flow with scour between lbres large boulder roughness elements and bedrock outcrop along the channel at near bankfull discharge the lbres and boulders in step pools armor the channel and are primary controls on channel morphology and gradient rock strength is a secondary control on channel morphology location and abundance of pools we hypothesize that step pools when inundated with sand and fine gravel from a disturbance such as wildfire during a flow event fill near bankfull stage and scour on falling stage below bankfull when unit stream power is a maximum over the step thus as with forced pools step pool maintenance depends on a specific pattern of discharge and process the process of scour during falling stage reestablishes step pools during moderate flows following disturbance

mesoscale structure in the megalopolitan snowstorm of 11 12 february 1983 part i frontogenetical forcing and symmetric instability abstract a cyclone moving northeastward off the coast of the northeastern united states on 11 12 february 1983 was accompanied by a band of heavy snow across all the major cities of this region from washington to boston frontegenetical forcing and symmetric instability are discussed as possible explanations of the intense precipitation rawinsonde data were analyzed to investigate the roles of these effects in this case we found that intense ascent was part of a thermally direct transverse circulation to be expected in response to frontogenetical forcing when the symmetric stability in the warmer air is small symmetric instability per se in the saturated major cloud mass may have been responsible for pulselike oscillations in its top these were men in satellite imagery elongated in the direction of the tropospheric thermal wind

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

post wildfire erosion response in two geologic terrains in the western usa abstract volumes of eroded sediment after wildfires vary substantially throughout different geologic terrains across the western united states these volumes are difficult to compare because they represent the response to rainstorms and runoff with different characteristics however by measuring the erosion response as the erodibility efficiency of water to detach and transport sediment on hillslopes and in channels the erosion response from different geologic terrains can be compared specifically the erodibility efficiency is the percentage of the total available stream power expended to detach remobilize or transport a mass of sediment erodibility efficiencies were calculated for the i initial detachment and for the ii remobilization and transport of sediment on the hillslopes and in the channels after wildfire in two different geological terrains the initial detachment efficiencies for the main channel and tributary channel in the granitic terrain were 10 9 and 5 4 and were similar to those for the volcanic terrain which were 5 5 and 1 1 no initial detachment efficiency could be measured for the hillslopes in the granitic terrain because hillslope measurements were started after the first major rainstorm the initial detachment efficiency in the volcanic terrain was 1 3 0 41 the average remobilization and transport efficiencies associated with flash floods in the channels also were similar in the granitic 0 18 0 57 and volcanic 0 11 0 41 terrains on the hillslope the remobilization and transport efficiency was greater in the volcanic terrain 2 4 than in the granitic terrain 0 65 however this may reflect the reduced sediment availability after the first major rainstorm 30 min maximum rainfall intensity 90 mm h 1 in the granitic terrain while easily erodible fine colluvium remained on the hillslope after the first rainstorm 30 min maximum rainfall intensity 7 2 mm h 1 in the volcanic terrain the erosion response in channels and on hillslopes of the granitic and volcanic terrains was similar when compared using erodibility efficiencies

a 9000 year flood history for southern california a revised stratigraphy of varved sediments in santa barbara basin abstract the center of santa barbara basin sbb preserves annual laminations through most of the holocene providing an important locality for high resolution late quaternary paleoclimate and paleoceanography reconstructions an accurate chronology is necessary for these sediment based records and enables comparisons with more distal data time series of similar quality here we present an improved high resolution radiocarbon chronology for the last 9000 yrs based on 89 accelerator mass spectrometric ams 14c dates of mixed planktonic foraminiferal carbonate from three sediment cores collected in sbb mv0811 14jc spr0901 06kc and odp hole 893a accurate core to core correlation is demonstrated using prominent gray flood and olive turbidite layers identified in sbb and dated in multiple cores gray layer deposits were found more frequently in wetter intervals as determined by multi proxy hydroclimate records in southern california e g lake deposits and tree rings mass accumulation rates mars calculated for the sbb depocenter using the improved radiocarbon age model indicate high mars are associated with these gray layers that have been associated with floods thus sediment accumulation in sbb is largely controlled by sediment delivery via river runoff following precipitation events although mars may also be influenced by other factors that enhance erosion in river catchments folded sediment is observed within the basal core section of mv0811 14jc which stratigraphically correlates with 14c age reversals in odp hole 893a we associate this sediment slump feature with the large goleta submarine slide complex in santa barbara channel and estimate the submarine slide event occurred at 9000 200 yrs bp furthermore small olive turbidite layers identified and dated in sbb can be temporally linked with large earthquakes along san andreas fault and can therefore potentially reconstruct earthquake history in southern california

widespread buried precambrian layered sequences in the u s mid continent evidence for large proterozoic depositional basins large regions of the north american mid continent are underlain by precambrian layered rocks buried beneath phanerozoic sedimentary strata south of the wichita mountains published seismic reflection profiles show a precambrian layered assemblage extending for at least 40 km in both the north south and east west directions and industry data show that it may continue 150 km to the southeast seismic reflection data in the illinois region show a precambrian layered assemblage extending 320 km in an east west direction and 200 km in a north south direction in both cases the layered rocks are as much as 12 km thick apparent sequence boundaries onlap downlap within these assemblages suggest they are parts of large depositional basins with diffractions and dipping strat due to faulting the layered sequences correlate with regions of relatively long wavelength and low amplitude magnetic anomalies the extent of this magnetic signature suggests that about 200 000 km 2 of illinois indiana and western ohio about 50 000 km 2 of southernmost oklahoma and north central texas and about 32 000 km 2 of southern missouri and northern arkansas may be underlain by similar precambrian strata drill holes indicate that the top of the mid continent precambrian basement is composed largely of silicic igneous rocks such material may comprise a large part of the layered sequences alternatively these igneous rocks could be intermixed with or underlain by nonvolcanic meta sedimentary strata the strong reflectivity of some layers suggest that minor mafic flows and or sills may also be present analysis of u pb and nd sm isotopes within the granites and rhyolites imply that the layered sequences postdate crustal formation at 1 7 2 0 ga and predate or are contemporaneous with the 1 3 1 5 ga crystallization ages of the granites and rhyolites though these layered rocks have a spatial association with igneous rocks and thus have likely been metamorphosed the possibility tha they contain precambrian hydrocarbons that escaped heating is as yet untested

frontogenesis in the presence of small stability to slantwise convection abstract it is often observed that despite the existence of near neutrality to slantwise convection rainbands and snowbands can persist for long periods with narrow intense updrafts producing large quantities of precipitation in many cases this is probably due to the presence of active frontogenesis which as shown here maintains such structures in order to investigate this process we use two dimensional semigeostrophic theory to solve the deformation forced frontogenesis problem for a circumstance in which the stability to moist slantwise convection is small but positive in this case numerical simulation is necessary to determine the evolution of the front several previous studies have described the role of diabatic forcing in modifying the cross frontal circulation by use of the sawyer eliassen equation in particular analytic solutions of that equation for the case of small moist symmetric stability show that a narrow updraft should occur ahead of the maximum geostrophic frontogenesis numeri

gravity waves generated during frontogenesis abstract gravity waves forced by nonhydrostatic and nongeostrophic processes within a frontal zone are discussed in particular stationary waves immediately above and below the surface front are considered the waves that appear above the front are horizontally stationary with respect to the front but are vertically propagating the vertical wavelength here is given by 2 n since the waves are nearly hydrostatic the horizontal wavelength of the waves above the front is determined by standing waves that set up below the front these waves corrugate the frontal surface and these corrugations in turn determine the horizontal scale of the waves above the front the waves under the front are standing and are trapped between the earth s surface and the frontal zone which due to its conditions of flow reversal and small ri is assumed to be a reflector of gravity waves the horizontal scale of the standing waves is determined by their vertical wavelength and the slope of the frontal surface these waves

possible extension of the midcontinent rift in west texas and eastern new mexico the midcontinent rift system forms one of the most prominent gravity features in north america the recognized geophysical anomaly extends in an arc from southern oklahoma to lake superior and then into southern michigan the midcontinent rift system was active between 1185 1010 ma as indicated in the lake superior region by age determinations on intrusive igneous rocks we suggest that the period of formation of the midcontinent rift was also a time of extensive igneous activity in texas and new mexico this activity is represented by intrusions beneath the central basin platform texas and new mexico intrusions which crop out at the pajarito mountain in the sacramento mountains new mexico a basaltic debris flow in the franklin mountains texas basalt flows at van horn texas and the crosbyton geophysical anomaly east of lubbock texas these bodies and other bodies located by geophysical anomalies and wells drilled into mafic precambrian rocks may be related to the midcontinent rift system

functional and structural connectivity within a recently burned drainage basin abstract studies examining post wildfire sediment transport have often focused on changes to individual landscape compartments planar slopes rills gullies channels or alluvial fans or have captured coarse scale hydrologic and sediment transport events at the drainage basin scale we advance the understanding of functional and structural connectivity by quantifying changes of the morphodynamics of and sediment transport along seven rill gully threads rgts after two low intensity rainstorms in a burned basin from the 2008 gap fire near goleta ca usa tls surveys conducted within two months of the initial fire and three days after the rainfall events provide point clouds for high resolution digital terrain models dtms dtm differencing techniques and morphological sediment budgets from the rgts showed discontinuous sediment transport along the extent of these two landscape compartments immediately after the rainfall surface runoff was unable to remove dry ravel deposits within the rgts and implied a high degree of structural disconnectivity there dry ravel and runoff erosion from the contributing areas to the rgts indicated functional and structural connectivity at this scale of analysis the results provide clear evidence that small amounts of rainfall and gravity induced erosion are interacting at different scales within the recently burned watershed to produce structural and functional disconnectivity along the rgts while the current system was transport limited during the analyzed event higher magnitude rainstorms may produce enhanced connectivity resulting in the ability of surface runoff to remove the stored sediments and perhaps produce debris flows

particle motion on burned and vegetated hillslopes climate change is causing increasingly widespread frequent and intense wildfires across the western united states many geomorphic effects of wildfire are relatively well studied yet sediment transport models remain unable to account for the rapid transport of sediment released from behind incinerated vegetation which can fuel catastrophic debris flows this oversight reflects the fundamental inability of local continuum based models to capture the long distance particle motions characteristic of steeplands probabilistic particle based nonlocal models may address this deficiency but empirical data are needed to constrain their representation of particle motion in real landscapes here we present data from field experiments validating a generalized lomax model for particle travel distance distributions the model parameters provide a physically intuitive mathematical framework for describing the transition from light to heavy tailed distributions along a continuum of behavior as particle size increases and slopes get steeper and or smoother we show that burned slopes are measurably smoother than vegetated slopes leading to 1 lower rates of experimental particle disentrainment and 2 runaway motion that produces the heavy tailed travel distances often associated with nonlocal transport our results reveal that surface roughness is a key control on steepland sediment transport particularly after wildfire when smoother surfaces may result in the preferential delivery of coarse material to channel networks that initiate debris flows by providing a first order framework relating the statistics of particle motion to measurable surface characteristics the lomax model both advances the development of nonlocal sediment transport theory and reveals insights on hillslope transport mechanics

conditions for generation of fire related debris flows capulin canyon new mexico comparisonoftheresponsesofthreedrainagebasinsburnedbythedomefireof1996innewmexicoisusedtoidentifythe hillslope channelandfirecharacteristicsthatindicateasusceptibilityspecificallytowildfire relateddebrisflow summer thunderstorms generated three distinct erosive responses from each of three basins the capulin canyon basin showed widespreaderosivesheetwashandrillingfromhillslopes andseverefloodingoccurredinthechannel thenorthtributary basin exhibited extensive erosion of the mineral soil to a depth of 5 cm and downslope movement of up to boulder sized material andatleastonedebrisflowoccurredinthechannel negligiblesurfacerunoffwasobservedinthesouthtributary basin thenegligiblesurfacerunoffobservedinthesouthtributarybasinisattributedtothelimitedextent andseverityof the fire in that basin the factors that best distinguish between debris flow producing and flood producing drainages are drainage basin morphology and lithology a rugged drainage basin morphology an average 12 per cent channel gradient andsteep roughhillslopescoupledwithcolluviumandsoilweatheredfromvolcaniclasticandvolcanicrockspromotedthe generation of debris flows a less rugged basin morphology an average gradient of 5 per cent and long smooth slopes mantled with pumice promoted flooding flood and debris flow responses were produced without the presence of waterrepellentsoils thecontinuityandseverityoftheburnmosaic theconditionoftheriparianvegetation theconditionofthe fibrous root mat accumulations of dry ravel and colluvial material in the channel and on hillslopes and past debris flow activity appearedtohavelittlebearingonthedistinctiveresponsesofthebasins publishedin2000byjohnwiley sons ltd

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

aeromagnetic and gravity anomaly constraints on the crustal geology of ohio the u s geological survey and the ohio geological survey recently compiled aero magnetic anomaly maps and revised gravity anomaly data for crustal studies of ohio updated structural and lithologic maps of the precambrian basement surface provide additional constraints to limit interpretational ambiguities of the geopotential anomaly data the combined modeling of five east west gravity and magnetic anomaly profiles supports a generalized crustal model for ohio involving a lower zone of intermediate composition a more felsic and relatively homogeneous middle zone and an upper zone consisting of intrusive and extrusive igneous rock in the western third of the state and medium grade grenville metamorphic rocks to the east modeling of the geopotential field anomalies indicates the presence of large dense lower crustal bodies in western and south central ohio that may be related to a paleo rift system large possibly anorthositic masses in southern ohio post tectonic granitization in northwestern ohio and a volcanic source for igneous rocks in southwestern ohio may also be interpreted from the combined anomaly analysis

prediction of spatially explicit rainfall intensity duration thresholds for post fire debris flow generation in the western united states abstract early warning of post fire debris flow occurrence during intense rainfall has traditionally relied upon a library of regionally specific empirical rainfall intensity duration thresholds development of this library and the calculation of rainfall intensity duration thresholds often require several years of monitoring local rainfall and hydrologic response to rainstorms a time consuming approach where results are often only applicable to the specific region where data were collected here we present a new fully predictive approach that utilizes rainfall hydrologic response and readily available geospatial data to predict rainfall intensity duration thresholds for debris flow generation in recently burned locations in the western united states unlike the traditional approach to defining regional thresholds from historical data the proposed methodology permits the direct calculation of rainfall intensity duration thresholds for areas where no such data exist the thresholds calculated by this method are demonstrated to provide predictions that are of similar accuracy and in some cases outperform previously published regional intensity duration thresholds the method also provides improved predictions of debris flow likelihood which can be incorporated into existing approaches for post fire debris flow hazard assessment our results also provide guidance for the operational expansion of post fire debris flow early warning systems in areas where empirically defined regional rainfall intensity duration thresholds do not currently exist

characterizing the primary material sources and dominant erosional processes for post fire debris flow initiation in a headwater basin using multi temporal terrestrial laser scanning data abstract wildfire dramatically alters the hydrologic response of a watershed such that even modest rainstorms can produce hazardous debris flows relative to shallow landslides the primary sources of material and dominant erosional processes that contribute to post fire debris flow initiation are poorly constrained improving our understanding of how and where material is eroded from a watershed during a post fire debris flow requires 1 precise measurements of topographic change to calculate volumetric measurements of erosion and deposition and 2 the identification of relevant morphometrically defined process domains to spatially constrain these measurements of erosion and deposition in this study we combine the morphometric analysis of a steep small 0 01 km 2 headwater drainage basin with measurements of topographic change using high resolution 2 5 cm multi temporal terrestrial laser scanning data made before and after a post fire debris flow the results of the morphometric analysis are used to define four process domains hillslope divergent hillslope convergent transitional and channelized incision we determine that hillslope divergent and hillslope convergent process domains represent the primary sources of material over the period of analysis in the study basin from these results we conclude that raindrop impact induced erosion ravel surface wash and rilling are the primary erosional processes contributing to post fire debris flow initiation in the small steep headwater basin further work is needed to determine 1 how these results vary with increasing drainage basin size 2 how these data might scale upward for use with coarser resolution measurements of topography and 3 how these results change with evolving sediment supply conditions and vegetation recovery