high resolution studies of rainfall on norfolk island part iii a model for rainfall redistribution abstract a dense network of high resolution rain gauges has provided data on spatial scales of about 1 5 km and time scales of 15 sec on norfolk island where the topography is dominated by a 300 m hill that is found to modify the spatial distribution of rainfall depending on wind direction a correlation method is used to track coherent storm motion so as to identify the dominant wind direction and speed transects are selected across the island in the wind direction and the rainfall interpolated along each transect it is found that there is often a decrease in rainfall upwind of the hill followed by an increase downwind of the peak the ratio of downwind to upwind catches increases linearly with wind speed these observations do not accord with the often accepted explanation using a seeder feeder mechanism a simple wind drift model is proposed in which raindrops follow trajectories modified by the perturbed wind flow over the hill the transects are approximated by bell shaped hill profiles analytic solutions for potential flow over a cylinder are then used to find a streamline with a bell shape similar to a topography transect through the hill and aligned with the wind direction this streamline is used as the solid surface boundary thereby giving a direct analytic flow field for the bell shaped hill a streamfunction is found for drop motion allowing rainfall variations to be predicted a parameterisation is developed that explains the shape and magnitude of the observed rainfall variations along a transect agreement between the rudimentary model and observations is found possible to within a few percent this indicates that the wind drift process is viable as the dominating mechanism for determining rainfall distribution in the presence of low hills when low level moisture is absent

rain shadow hydrology influences on river flows and flood magnitudes across the central massif divide of la grande terre island new caledonia summary within the tropical south pacific islands meaningful examination of how mountain barriers influence river flow characteristics has not previously been attempted owing principally to the lack of reliable long term data from an adequate number of basins that are geographically spread across opposing sides of a major topographic divide the island of la grande terre in new caledonia provides an exception since robust flow records with effective durations between 15 and 52 years are available for 22 monitored rivers draining both sides of a massif dividing range cross island differences in several fundamental hydrological parameters were statistically analysed including runoff coefficients median daily discharges and specific flood flows results identify that significant flow contrasts exist between windward versus leeward basins which are not necessarily revealed by observing patterns of rainfall distribution over the island power relationships are derived using both empirical and theoretically based models for maximum decadal q 10y and centennial q 100y flood size against catchment area with basins grouped according to windward or leeward location on la grande terre a key finding is that the rain shadow influence ri is essentially constant and therefore quantifiable across the central massif divide flood magnitudes for both q 10y and q 100y events are between 35 and 80 greater for windward versus leeward basins of equivalent size depending on whether empirical or accepted theoretical models are applied the term rain shadow hydrology is proposed for the generalised concept of windward vs leeward divergence in hydrological patterns in spite of being developed for the la grande terre situation the theme has relevance for neighbouring high islands in the tropical south pacific and therefore contributes to understanding tropical island hydrological characteristics in the trade wind belt however the transferability of estimated ratios of the rain shadow influence ri ratios requires validation with flow data from other islands especially to establish windward vs leeward differences in flood magnitude basin area relationships

beginning of foreland subsidence in the columbian sevier belts southern canada and northwest montana subsidence analysis and geometry of jurassic cretaceous foreland strata in northwestern montana and southern alberta and british columbia suggest that loading by the fold thrust belt in canada began as much as 40 m y earlier than in montana in canada early foreland basin deposits are late jurassic age thicken rapidly westward and are restricted to a narrow belt within 30 km of the thrust belt in western montana contemporaneous deposits are widespread and do not increase markedly in thickness toward the thrust belt the unconformity overlying these deposits also changes from canada where it is angular to a disconformity in western montana near great falls between these two areas foreland geometry is transitional over a distance of 250 km beyond the transition zone early foreland basin geometries are broadly consistent showing late jurassic foreland subsidence in southern canada and early cretaceous initial subsidence in the united states

an interpretation of the variscan structures in sw england the variscan structures in sw england apart from the high level structures in the culm synclinorium of n devon are recumbent with an overall gentle southward dip of cleavages thrusts and recumbent folds translation was towards the nnw the structures are interpreted on a thin skinned model with a basal decollement dipping gently s related to a s dipping subduction zone s of the lizard the granites are thought to have been generated to the s of their present position and injected northwards above the decollement zone

foreland basin subsidence driven by topographic growth versus plate subduction the subsidence of foreland basins is classically thought to accelerate with time however a synthesis of data from numerous foreland basins recognizes a wide range of signals and rates our analysis investigates the influence of two broadly ubiquitous controlling factors 1 the upward and outward growth of mountain topography and 2 the subduction velocity of the underthrust lithosphere these two factors have contrasting subsidence signals the former tends to be slow and decelerates while the latter is more rapid and accelerates the geodynamic setting of a foreland basin determines the degrees to which these components dominate the final signal of tectonically induced subsidence in small collisional mountain ranges the common asymmetry of subduction defines a pro and a retro foreland basin based on model experiments and the synthesized data we demonstrate that pro foreland basins exhibit short lived usually 0 05 km m y 1 accelerating subsidence histories recording only a portion of the orogenic history of the mountain range type examples are the carpathian foredeep and the north alpine foreland basin in contrast retro foreland basins are characterized by relatively slow 0 05 km m y 1 protracted usually 40 m y subsidence that records the majority of the orogenic history a good example is the aquitaine foreland basin retro arc foreland basins such as the alberta basin appear comparable to collisional retro foreland basins examples where there is more protracted subsidence appear to record greater evidence of episodic loading and unloading as the topography of the range grows or shrinks in response to the balance between crustal thickening and erosion rates

jurassic onset of foreland basin deposition in northwestern montana usa implications for along strike synchroneity of cordilleran orogenic activity stratigraphic provenance and subsidence analyses suggest that by the middle to late jurassic a foreland basin system was active in northwestern montana united states u pb ages of detrital zircons and detrital modes of sandstones indicate provenance from accreted terranes and deformed miogeoclinal rocks to the west subsidence commenced ca 170 ma and followed a sigmoidal pattern characteristic of foreland basin systems thin jurassic deposits of the ellis group and morrison formation accumulated in a backbulge depozone a regional unconformity and or paleosol zone separates the morrison from early cretaceous foredeep deposits of the kootenai formation the model presented here is consistent with regional deformation events registered in hinterland regions and challenges previous interpretations of a strongly diachronous onset of cordilleran foreland basin deposition from northwestern montana to southern canada

rainfall redistribution over low hills due to flow perturbation abstract a simple potential flow model is developed for airflow over low hills the model readily allows incorporation of simple rain microphysics so that drop trajectories can be traced in the region of a hill complex rainfall intensity variations are found in the horizontal and in the vertical and a straightforward modification to the model allows for time dependence to be studied the model is shown to serve as a useful diagnostic tool to describe rain drop redistribution due to perturbed airflow in particular increased rainfall is predicted in the lee of hill peaks and depleted rainfall is predicted on ridges the redistribution effects dominate at low levels in contrast to predictions based on seeder feeder enhancement comparison with field measurements shows good qualitative agreement over low hills and in some cases close quantitative agreement redistribution of rain appears to be a significant process that should be considered in rainfall interpolation and prediction schemes involving hilly terrain

application of lu hf garnet dating to unravel the relationships between deformation metamorphism and plutonism an example from the prince rupert area british columbia abstract the tectonic history of the prince rupert area is marked by profound crustal thickening from thrusting that produced inverted metamorphic field gradients and transpression in crustal scale shear zones syn tectonic garnet in the prince rupert area has lu hf ages of 102 6 3 7 ma and 108 3 4 1 ma 2 porphyroblast matrix relationships in these samples and samples from the same outcrops indicate syn tectonic garnet growth these relationships imply that the garnet ages directly date the development of the metamorphic foliations a third sample of migmatitic garnet amphibolite from the contact aureole of the 94 90 ma ecstall pluton had complex isotope systematics interpreted to indicate a garnet growth episode 105 ma similar to the ages obtained from the other samples and a growth or equilibration event at 94 ma during pluton emplacement the data show that the older lu hf garnet ages date prograde metamorphism during foliation development and modification during pluton emplacement the ecstall pluton was emplaced 10 to 15 m y after regional metamorphism and thrust stacking in the prince rupert area in order to place our samples in a regional tectonic context we compare our results to patterns of regional deformation metamorphism and plutonism throughout the north american cordillera in the time period between 110 and 85 ma contractional and transpressional deformation occurred throughout much of the north american cordillera at this time from southeastern alaska to the baja peninsula in mexico left lateral transpression dominated the canadian cordillera whereas right lateral transpression affected areas south of the idaho salmon river suture zone including the sierra nevada batholith this reversal in kinematics in the northern and southern cordillera within coeval magmatic belts appears to be a first order feature of the geology of the north american cordillera during the cretaceous

the evolution of the hercynides of central sw england towards the end of lower carboniferous times sedimentation accompanied by widespread igneous activity proceeded in a tectonically active unstable and constricted basinal zone visean flysch and olistostromic sequences were generated in front of an advancing deformation front which caused erosion of submarine rises and heralded the beginning of the hercynian orogeny in this region between dartmoor and bodmin moor upper devonian basin and rise facies sediments were thrust northwards over both upper devonian and lower carboniferous northern equivalents which were themselves incorporated onto the allochthon the tectonic deformation history began in the late visean and early namurian with the gravity sliding dl of the bulk of the lower carboniferous northwards to form the greystone nappe subsequently the main thrusting event d2 from late lower namurian times onwards led to the successive overthrusting and emplacement of the heathfield petherwin and tredorn nappes towards the end of the namurian and in the westphalian the intrusion of the granite batholith caused the fold belt to tighten which resulted in the formation of numerous low angle normal faults d3 offsetting earlier thrusts to the n overall the regime is one of very thin skinned thrust and nappe tectonics with the allochthon probably not exceeding 1 km in thickness

plate tectonics and basin subsidence history tectonic setting exerts fi rst order control on basin formation as refl ected in basin subsidence history while our approach ignores the effects of fl exural loading and eustatic sea level change consistency of backstripped subsidence histories i e with local loading effects of sediment removed suggests consistent tectonic driving mechanisms in each tectonic setting with the possible exception of forearc basins based on published subsidence curves and open fi le stratigraphic data we show the subsidence characteristics of passive margins strike slip basins intracontinental basins foreland basins and forearc basins passive margin subsidence is characterized by two stages rapid initial synrift subsidence and slow post rift thermal subsidence with increasing subsidence rates toward the adjacent ocean basin subsidence of intracontinental basins is similar in magnitude to that seen in passive margin settings but the former is generally slower longer lived and lacks initial subsidence long lived subsidence for many intracontinental basins is consistent with cooling following thermal perturbation of thick lithosphere found beneath old parts of continents basins associated with strike slip faults are usually short lived with very rapid subsidence changes in local stress regimes as strike slip faults evolve and migrate over time coupled with three dimensional heat loss in these small basins likely explain this subsidence pattern foreland basin subsidence rates refl ect the fl exural response to episodic thrust loading resultant subsidence curves are punctuated by convex up accelerating segments forearc basins have the least consistent subsidence patterns subsidence histories of these basins are complex and may refl ect multiple driving mechanisms of subsidence in forearc settings second order deviations in subsidence suggest reactivation or superimposed tectonic events in many basin settings the effects of eustatic sea level change may also explain some deviations in curves for many of these settings subsidence histories are suffi ciently distinctive to be used to help determine tectonic setting of ancient basin deposits

aerial observations of hawaii s wake abstract under the influence of the east northeasterly trade winds the island of hawaii generates a wake that extends about 200 km to the west southwest during the harp project in july and august 1990 five wake surveys were carried out by the ncar electra the patterns of wind and aerosol concentration revealed by these flights suggest that hawaii s wake consists of two large quasi steady counterrotating eddies the southern clockwise rotating eddy carries a heavy aerosol load due to input from the k volcano at the eastern end of the wake the eddies are potentially warmer and more humid than the surrounding trade wind air several other features are discussed sharp shear lines near the northern and southern tips of the island dry and warm air bands along the shear lines a small embedded wake behind the kohala peninsula wake centerline clouds hydraulic jumps to the north and south of the island a descending inversion connected with accelerating trade winds and evidence for side to side wake mo

synoptic reconstruction of a major ancient lake system eocene green river formation western united states numerous 40ar 39ar experiments on sanidine and biotite from 22 ash beds and 3 volcaniclastic sand beds from the greater green river piceance creek and uinta basins of wyoming colorado and utah constrain 8 m y of the eocene epoch multiple analyses were conducted per sample using laser fusion and incremental heating techniques to differentiate inheritance 40ar loss and 39ar recoil when considered in conjunction with existing radioisotopic ages and lithostratigraphy biostratigraphy and magnetostratigraphy these new age determinations facilitate temporal correlation of linked eocene lake basins in the laramide rocky mountain region at a significantly increased level of precision to compare our results to the geomagnetic polarity time scale and the regional volcanic record the ages of eocene magnetic anomalies c24 through c20 were recalibrated using seven 40ar 39ar ages overall the ages obtained for this study are consistent with the isochroneity of north american land mammal ages throughout the study area and provide precise radioisotopic constraints on several important biostratigraphic boundaries applying these new ages average sediment accumulation rates in the greater green river basin wyoming were approximately three times faster at the center of the basin versus its ramp like northern margin during deposition of the underfilled wilkins peak member in contrast sediment accumulation occurred faster at the edge of the basin during deposition of the balanced filled to overfilled tipton and laney members sediment accumulation patterns thus reflect basin center focused accumulation rates when the basin was underfilled and supply limited accumulation when the basin was balanced filled to overfilled sediment accumulation in the uinta basin at indian canyon utah was relatively constant at 150 mm k y during deposition of over 5 m y of both evaporative and fluctuating profundal facies which likely reflects the basin margin position of the measured section the most rapid sediment accumulation for the entire system 1 m k y occurred between 49 0 and 47 5 ma when volcaniclastic materials from the absaroka and or challis volcanic fields entered the green river formation lakes from the north our new ages combined with existing paleomagnetic and biostratigraphic control permit the first detailed synoptic comparison of lacustrine depositional environments in all the green river formation basins coupled with previously published paleocurrent observations our detailed correlations show that relatively freshwater lakes commonly drained into more saline downstream lakes the overall character of eocene lake deposits was therefore governed in part by the geomorphic evolution of drainage patterns in the surrounding laramide landscape freshwater overfilled lakes were initially dominant 53 5 52 0 ma possibly related to high erosion rates of remnant cretaceous strata on adjacent uplifts expansion of balanced fill lakes first occurred in all green river formation basins at 52 0 51 3 ma and again between 49 6 and 48 5 ma evaporative underfilled lakes occurred in various basins between 51 3 and 45 1 ma coincident with the end of the early eocene climatic optima and subsequent onset of global cooling defined from marine record however evaporite intervals in the different depocenters were deposited at different times rather than being confined to a single episode of arid climate evaporative terminal sinks were initially located in the greater green river and piceance creek basins 51 3 48 9 ma then gradually migrated southward to the uinta basin 47 1 45 2 ma this history is likely related to progressive southward construction of the absaroka volcanic province which constituted a major topographic and thermal anomaly that contributed to a regional north to south hydrologic gradient the greater green river and piceance creek basins were eventually filled from north to south with absarokaderived detritus at sedimentation rates 1 2 orders of magnitude greater than the underlying lake deposits

geochemistry geochronology and fluid inclusion study of the late cretaceous newton epithermal gold deposit british columbia newton is an intermediate sulfidation epithermal gold deposit related to late cretaceous continental arc magmatism in south central british columbia disseminated gold mineralization occurs in quartz sericite altered late cretaceous felsic volcanic rocks and feldspar quartz hornblende porphyry and quartz feldspar porphyry intrusions the mineralization can be divided into three stages 1 disseminated pyrite with microscopic gold inclusions and sparse quartz pyrite molybdenite veins 2 disseminated marcasite with microscopic gold inclusions and minor base metal sulfides and 3 polymetallic veins of pyrite chalcopyrite sphalerite arsenopyrite re os dating of molybdenite from a stage 1 vein yielded an age of 72 1 0 3 ma published by mcclenaghan in 2013 the age of the host rocks has been constrained by u pb dating of zircon late cretaceous felsic volcanic rocks 72 1 0 6 ma amarc resources ltd unpublished data reported by mcclenaghan in 2013 feldspar quartz hornblende porphyry 72 1

extensional fault arrays in strike slip and transtension abstract sedimentary basins developed under conditions of strike slip or transtension are subject to significant rotational strains yet faults developed in such regimes are commonly explained using simplified models that ignore rotation the heaves of extensional faults developed provide a means of quantifying this rotation for ideal strike slip simple shear the apparent stretch due to fault heaves can be related simply to shear strain at shear strains above 1 0 previously formed extensional faults begin to show inversion as reverse faults becoming fully inverted at 2 0 in transtensional basins the apparent stretch is related in addition to the initial orientation of the faults which may itself be related to the incremental strain in the stellarton basin of nova scotia canada fault heaves and orientations can be measured from subsurface mine plans measurements of these quantities indicate that strain was only mildly transtensional with a small the measurement of fault heaves potentially provides detailed information on strain wherever strike slip or transtensional basins have been explored in detail by seismic or other subsurface methods

thermal history of michigan basin the elevated organic maturity observed in shallowly buried units from the michigan basin implies that higher temperatures and thicker overburdens once existed in the basin evidence from sediment accumulation rates regional dips and maturity of pennsylvanian age coals suggests that up to 1 000 m 3 280 ft of sediment were removed by erosion prior to the late jurassic when the basin became stable geothermal gradients during paleozoic basin subsidence probably ranged from 35 to 45 c km 19 to 25 f 1 000 ft in contrast to the average present value of 25 c km 14 f 1 000 ft depths to the top of the oil window ranged from 1 900 to 2 300 m 6 230 to 7 540 ft during the paleozoic post pennsylvanian erosional uplift and further thermal m turation of the basin have combined to raise the top of the oil window to its present level of 500 m 1 640 ft

subsidence of the paris basin and its bearing on the late variscan lithosphere evolution a comparison between plate and chablis models abstract in this study two different models for the lithospheric thermal evolution are used to predict the long term subsidence of the paris basin the plate or chablis models have a constant temperature or constant heat flow at the base of the lithosphere these boundary conditions yield a different thermal relaxation time for a given equilibrium lithospheric thickness the final thermal steady state does not depend on the boundary condition fixed at the base of the lithosphere the thermal evolution of the lithosphere is computed taking into account temperature and pressure dependent thermal characteristics metamorphism in the crust top crustal erosion and phase transition in the mantle spinel garnet the long term tectonic subsidence of the paris basin constrains the mesozoic thermal evolution of the lithosphere and the amplitude of the initial thermal anomaly the chablis model including the effects of spinel garnet phase transition predicts present day lithospheric thickness in better agreement with observation than the plate model the chablis model involves a basal heat transfer of 37 mw m2 similar to the value beneath oceanic plates the long term subsidence of the paris basin obviously results from the decay of a thermal anomaly initiated during late variscan times we first assume that at 300 ma the lithosphere was less than 150 km thick and the thickened crust started returning to its present thickness 35 km by uniform lithospheric extension the subsidence data can be explained by short stephano autunian as well as long stephano triassic lasting extension these hypotheses both implicitly refer to extensional collapse of the variscan belt however the evolution of the variscan belt from 350 to 300 ma may have involved almost no crustal thickening but an anomalously thin lithosphere ca 55 km the corresponding thermal evolution of the lithosphere is computed using the chablis model with an initially high heat transfer of 61 mw m2 at the base of the base of the lithosphere at 280 ma this heat transfer is tuned to 40 mw m2 leading to lithospheric cooling from 280 to 30 ma which can also explain the paris basin subsidence for the short lasting extension hypothesis the late variscan lithospheric evolution predicted with the chablis model yields paleogeography magmatism and retrograde p t t paths in good agreement with those reported from areas around the paris basin conversely the plate model does not allow mantle melting during the end of carboniferous and permian times the long lasting extension hypothesis does not explain the paleogeographic evolution the timing of magmatism and retrograde p t paths showing isothermal decompression the hypothesis with a strong lithospheric delamination cannot be ruled out however it is less plausible than the extensional collapse hypothesis

orographic effects during a severe wintertime rainstorm in the appalachian mountains abstract the evolution of precipitation features during a severe wintertime rainfall and flooding event associated with a cold front that crossed the central appalachians on 19 january 1996 is illustrated through the analysis of radiosonde rainfall and streamflow gauge data and wsr 88d images striking evidence of the linkage between heavy precipitation cells and orography was obtained by tracking the movement of the center of mass of storm precipitation which closely followed the contours of regional orographic features higher intensity precipitation cells were consistently located windward of the orographic crest and the trajectory described by the center of mass of precipitation was also consistent with the spatial arrangement of the river basins where hazardous flooding occurred persistent low intensity 5 mm h 1 rainfall was registered in these basins during the 12 h period that preceded the arrival of frontal storm activity it is argued that this prefrontal precipitation had a critical im

the subsidence of the williston basin a detailed comparison between the pre cretaceous stratigraphic record in the williston basin and the available information about phanerozoic sea level changes indicates that most stratigraphic breaks in the basin reflect eustatic control the basin appears to have been subsiding continuously and steadily about the same centre for most of the phanerozoic above a thick 55 km continental crust deposition kept up with subsidence and most of the sedimentary record was laid down close to sea level erosional breaks in the stratigraphic record may represent periods of removal of strata during episodes of low sea level a possible explanation of this essentially steady nonexponential subsidence record is that a mafic subcrustal body is undergoing transformation to eclogite

book review the variscan fold belt in the british isles hancock p l editor 1983 adam hilger 217 pp price hardcover 34 00

fault slip and exhumation history of the willard thrust sheet sevier fold thrust belt utah relations to wedge propagation hinterland uplift and foreland basin sedimentation

spatial rainfall distribution at a storm event in mountainous regions estimated by orography and wind direction in this paper the orographical effect for rainfall distribution at a storm event is discussed the main effect is represented by the ground forced ascending current of air a three dimensional numerical model of the hydrostatic atmosphere including basin orography is used to estimate the ascending current area for any wind direction the authors also propose a new concept named directional probability of storm event dipose a severe storm is more likely to occur when the wind blows from a high dipose direction rather than from a low dipose direction the wind direction at a storm event is determined from a dipose analysis and is used in the numerical model the calculated ascending air region is regarded as a severe rainfall area in mountainous river basins the results are examined and compared with observations

regionalization of extreme precipitation distribution using the principal components of the topographical environment this paper deals with the regionalization of the extreme rainfall intensities in the volcanic island of tahiti french polynesia and focuses how the method automatically takes into account the topographical relief features principal component analysis of a digital elevation model supplies a limited set of variables describing the topographical environment these synthetic descriptors are linked to the parameters of the rainfall intensity gumbel distribution by using a stepwise regression adjusted on 20 point rainfall records the model is then applied on a regular 300 points grid node and interpolated using a spline function to provide an approximation of the pluviometric risk all over the island in the case of the island of tahiti the relationship between the rainfall parameter distributions and the topographical descriptors is very strong and the method supplies a direct estimation in space of the rainfall statistics through the regression model validation of the results and comparison with simple kriging interpolation show the relevance of the approach however more data are needed for a better confidence in the parameter estimation in some areas of the island this automatic and objective method could be applied in any mountainous area where topography has a major influence on the precipitation features to characterize the non stationarity of point rainfall statistics in space