sub basin scale dust source geomorphology detected using modis 1 the spatial and temporal variability of dust emissions from different surfaces in the lake eyre basin australia is determined using modis data for 2003 6 the sources of 529 dust plumes were classified overall 37 of plumes originated in areas of aeolian deposits 30 from alluvial deposits and floodplains and 29 from ephemeral lakes or playas at this sub basin scale the relative importance of different dust source geomorphologies varied primarily in response to sediment supply and availability and was not related to aeolian transport capacity suggesting the lake eyre basin is a supply limited system

sand dunes as a major proximal dust source for late pleistocene loess in the negev desert israel grain size analyses of three hilltop primary eolian loess sequences in the negev desert southern israel show a bimodal grain size distribution at 50 60 m and 3 8 m using analyses of mineralogy and osl ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time suggesting an enhancement of a time transgressive proximal dust source compared to a distal saharan fine grain dust the only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into sinai and the negev concurrently with the loess accretion during the late pleistocene as a result of the exposure of the mediterranean shelf we therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea this relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as northern africa china and australia

the 1930s dust bowl geoarchaeological lessons from a 20th century environmental crisis the dust bowl of the 1930s was an environmental crisis of epic proportions characterized by unprecedented soil erosion population redistribution and profound transformation of the landscape in th

aeolian abrasion and modes of fine particle production from natural red dune sands an experimental study a series of experiments was conducted to determine the potential for aeolian abrasion of natural dune sands to produce fine particles 125 m by 1 the release of resident fines 2 spalling chipping and breakage of particles and 3 the removal of grain surface coatings parent samples were obtained from the surfaces of four active continental dunes and abraded using a glass test tube chamber for up to 120h the fine particles produced by this abrasion process were trapped at varying time intervals and subject to detailed particle size analyses using a coulter multisizer the abrasion of untreated parent samples produced fine particles in one of two main size classes 50 m but when the parent sample was sieved to exclude particles 250 m relatively more material in the range 10 50 m was produced for unsieved parent samples the size range associated with the dominant mode varied according to the length of the abrasion time the coarsest mode 63 m was dominant during the first 16 h of abrasion then became less significant and is thought to be associated with the release of resident fines into suspension the finest mode 10 m was absent or very weak during the first 16h of abrasion then became more significant and in some instances dominated the distribution as abrasion continued removal of grain surface coatings is the main source of fine material 10 m and this may be a significant source of fine material in areas where sands are dominated by subrounded and rounded particles by comparison with previous studies of aeolian particle abrasion these natural dune sands produced very low quantities of fine material by weight but their spatial extent makes them potentially a significant source of dust sized particles at the global scale

temporally and spatially uniform rates of erosion in the southern appalachian great smoky mountains we measured 1 0 be in fluvial sediment samples n 27 from eight great smoky mountain drainages 1 330 km 2 results suggest spatially homogeneous sediment generation on the 10 4 10 5 yr time scale and 100 km 2 spatial scale at 73 11 t km 2 yr 1 equivalent to 27 4 m m y of bedrock erosion this rate is consistent with rates derived from fission track long term sediment budget and sediment yield data all of which indicate that the great smoky mountains and the southern appalachians eroded during the mesozoic and cenozoic at 30 m m y in contrast unroofing rates during the paleozoic orogenic events that formed the appalachian mountains were higher 10 2 m m y erosion rates decreased after termination of tectonically driven uplift enabling the survival of this ancient mountain belt with its deep crustal root as an isostatically maintained feature in the contemporary landscape

eolian processes and heterogeneous dust emissivity during the 1930s dust bowl drought and implications for projected 21st century megadroughts the 1930s dust bowl drought on the us great plains was an environmental crisis with failure of agricultural systems landscape denudation and elevated atmospheric dust loads poor agricultural practices were implicated for triggering widespread eolian erosion and heightened dust emissions but this assumption is called into question this study classified land surface changes in southwest kansas from aerial images taken in 1936 and 1939 to infer surficial processes dust sources and associated emissivity in total seven distinctive surface classes were identified from an arcgis analysis of spectral reflectance values connected to surface vegetation cover and eolian activity demonstrating a strikingly heterogeneous landscape response to the drought stratigraphic studies indicate accumulation of up to 4 m of eolian sand in places with erosion of a subjacent silty pre 1930s soil surface potential dust emissivity estimates for particulate matter were derived from the distribution of classified land surf

constraining lithologic variability along the alleghanian detachment in the southern appalachians using passive source seismology polarities and amplitudes of intracrustal p sv conversions p waves converted to vertically polarized shear waves in receiver functions from the southeastern suture of the appalachian margin experiment array and usarray transportable array provide new constraints on the origin of seismic reflectivity delineating the alleghanian detachment in the southern appalachians eastern united states forward modeling of receiver functions is consistent with a 3 5 km thick high shear wave velocity vs 3 9 km s section of deformed paleozoic platform metasedimentary rocks beneath the blue ridge at 3 6 5 km depth in the inner piedmont conversions from the top and base of a low vs zone 3 1 km s at depths of 5 9 km are interpreted as a package of metasedimentary rocks or a shear zone characterized by radial anisotropy the detachment continues to the southeast beneath the carolina terrane where high amplitude negative conversions at 10 13 km depth are consistent with arc rocks vs 4 0 km s overlying sheared rocks with lower vs 3 2 km s southeast dipping conversions at 5 10 km depth mark the boundary between the inner piedmont and carolina terrane this study demonstrates that relatively high frequency receiver functions up to 3 hz though still lower in frequency than p wave energy analyzed for reflection profiling 20 hz can provide important links between surface geology and active source experiments to better constrain models of crustal structure

cocorp seismic profiling of the appalachian orogen beneath the coastal plain of georgia a southeastward extension onto the coastal plain of an earlier cocorp traverse which confirmed large scale thin skinned thrusting of crystalline rocks of the southern appalachians has provided some of the most spectacular reflections yet seen in crustal seismic data most of the reflectors can be interpreted as either fault surfaces or as metamorphosed strata of late precambrian early paleozoic age they are consistent with the hypothesis that a major detachment extends eastward beneath this part of the orogen although other interpretations with a more complex pattern of detachments or sutures are also possible large scale overthrusting provides a mechanism for incorporating sedimentary rocks into the lower crust and may help to explain many of the layered features on crustal seismic data reflections from deep beneath the coastal plain indicate that the structural configuration of the rocks is complex and that the remains of a collision zone are being observed several east dipping horizons which bear strong similarities to thrust faults in valley and ridge sedimentary rocks are seen in the basement at shallow and mid crustal levels beneath the coastal plain the augusta fault for example displays a reflection which extends at a low angle some 80 km or more southeast of its surface position in conjunction with surface geologic information these new data demonstrate that late paleozoic compressive deformation was pervasive and resulted in lateral movements in the upper crust extending from the valley and ridge to the crystalline rocks beneath the coastal plain a distance of 400 km or more a large antiform cresting at about 2 3 sec or about 6 km below the surface and other structures beneath the coastal plain of georgia deserve further consideration for petroleum exploration although metamorphism may have eliminated petroleum from these rocks refracted arrivals and fault geometries indicate two triassic rift basins beneath coastal plain sedimentary rocks one of which has apparently not been recognized previously

reprocessing and reinterpretation of cocorp southern appalachian profiles abstract reprocessing of cocorp southern appalachian data was focused on basic seismic evidence for continuation of sediments beneath a master decollement the most important evidence is a nearly continuous series of subhorizontal reflections extending from the valley and ridge province into the piedmont province continuity of subhorizontal reflections becomes tenuous in the inner piedmont careful reprocessing has yielded evidence for termination of strong reflections beneath the allochthon and the beginning of a relatively weak and complex series of events termination of sedimentary rocks beneath the piedmont is interpreted from true amplitude seismic data a zone of detachment continues southeast of the sediment termination as far as the master decollement root zone research on stacking velocities has indicated that complex velocity structures could create apparent low stacking velocities this phenomenon may occur in the charlotte belt of georgia bouguer gravity can be modeled as a former craton of normal density with an accreted margin of very slightly higher density variation in crustal thickness also contributes to the bouguer gravity gradient no continuous large scale overthrust is needed southeast of the interpreted master decollement root zone located beneath the kings mountain belt and charlotte belt

influence of vegetation on aeolian sand transport rate from a backshore to a foredune at hasaki japan the influence of vegetation on aeolian sediment transport rate in the region from a backshore to a foredune was investigated at the hasaki coast in japan where an onshore wind was predominant and the creeping beach grasses carex kobomugi and calystegia soldanella were major species the comparison of cross shore distributions of the cross shore component of aeolian sand transport rate with and without vegetation which were estimated on the basis of the beach profile changes and a mass conservation equation showed that the creeping grasses influenced the aeolian sand transport rate the landward aeolian sand transport rate rapidly decreased landward from the seaward limit of vegetation when the grasses grew the aeolian sand transport rate reduced by 95 with a vegetation cover of 28 on the other hand when the grasses were absent the landward aeolian sand transport rate did not decrease near the seaward vegetation limit but near the foot of the foredune

factors affecting the nature and rate of dust production from natural dune sands this paper evaluates the influence of natural sand particle characteristics on the amount and particle size distributions of dust produced by aeolian abrasion it contrasts with previous studies of aeolian abrasion by conducting experiments using i whole sand samples as opposed to selected size fractions ii natural mature dune sands rather than artificial or freshly crushed material and iii weathered sands that have acquired a superficial clay coating instead of grains with clean surfaces whilst previous research has found clear positive relationships between particle size sorting roundness and the amount of dust produced by aeolian abrasion the relationships determined in this study show some variation according to the geomorphological context from which the original samples were obtained the most important factor affecting the amount and particle size characteristics of the dust produced was the presence of a clay coating on the grain surface that is removed by the abrasion process the dust produced by this mechanism had a modal size of 2 5 m and material 10 m comprised up to 90 of the particles produced

satellite traces an ionogram signature for large scale wave structure and a precursor for equatorial spread f 1 although the source that controls day to day variability in the occurrence of equatorial plasma structure i e equatorial spread f or esf remains to be identified progress is being made there is evidence that the appearance of large scale wave structure lsws in the bottomside f layer around the time of its post sunset rise pssr is a more direct precursor of esf than the pssr itself the bulk of the evidence however is in the form of satellite f traces in ionograms which may be viewed as less than convincing because these signatures have not been shown to be causally related to lsws in this paper incoherent scatter radar and ionosonde data both collected on 24 july 1979 from the kwajalein atoll marshall islands are used to show that this is indeed the case

multiple dust sources in the sahara desert the importance of sand dunes 1 we determine the current sources of dust in the sahara desert using quantitative correlation between the number of days with dust storms nds derived from remote sensing data of high temporal resolution with the distribution of the soil types and geomorphic units during 2006 8 the source of over 90 of the nds was found to be sand dunes leptosols calcisols arenosols and rock debris in contrast to previous studies only few dust storms originated from playas and dry lake beds land erodibility was estimated by regressing the nds to the number of days with high speed wind events and was found to be high for sand dunes clay and fine silt grains and aggregates are scarce in sand dunes which most likely produce dust particles through aeolian abrasion of sand grains thus saltating sand grains impacting clay aggregates on playa surfaces cannot be the sole process for generating dust in the sahara

dust production and the release of iron oxides resulting from the aeolian abrasion of natural dune sands global dust trajectories indicate that significant quantities of aeolian transported iron oxides originate in contemporary dryland areas one potential source is the iron rich clay coatings that characterize many sand sized particles in desert dunefields this paper uses laboratory experiments to determine the rate at which these coatings can be removed from dune sands by aeolian abrasion the coatings impart a red colour to the grains to which previous researchers have assigned variable geomorphological significance the quantities or iron removed during a 120 hour abrasion experiment are small 99 mg kg 1 and difficult to detect by eye however high resolution spectroscopy clearly indicates that ferric oxides are released during abrasion and the reflectance of the particles alters one of the products of aeolian abrasion is fine particles 10 mum diameter with the potential for long distance transport copyright c 2004 john wiley sons ltd

a 10 000 year record of dune activity dust storms and severe drought in the central great plains dune fi elds and loess deposits of the great plains of north america contain stratigraphic records of eolian activity that can be used to extend the short observational record of drought we present a 10 000 yr reconstruction of dune activity and dust production in the central great plains region based on 95 optically stimulated luminescence ages the integration of data from both eolian sand and loess is an important new aspect of this record clusters of ages defi ne episodes of extensive eolian activity which we interpret as a response to frequent severe drought at 1 0 0 7 ka and 2 3 4 5 ka with peaks centered on 2 5 and 3 8 ka sustained eolian activity occurred from 9 6 to 6 5 ka parts of this record may be consistent with hypotheses linking holocene drought to sea surface temperature anomalies in the pacifi c or atlantic oceans or to the el nino southern oscillation phenomenon but the record as a whole is diffi cult to reconcile with any of these hypotheses

wide angle seismic imaging of the elberton granite georgia a pilot study using instantaneous blasts at dimension stone quarries abstractwide angle recordings of small multiple hole blasts at dimension stone quarries in the elberton granite show coherent reflections at offsets between 7 and 15 km in contrast with much larger blasts at crushed stone quarries this type of blast is fired without delays between holes the data were recorded with an array of twenty portable seismographs using three component 4 5 hz geophones migration of source gathers for two of the blasts shows a number of subhorizontal interfaces at depths between 2 and 4 km that may represent a layered complex near the base of the granite other reflectors include southeast dipping interfaces at depths between 6 and 9 3 km and a more gently southeast dipping complex at 9 5 11 km that may represent the master decollement the results of the pilot study show that this type of quarry blast can be useful for imaging structure within the upper crust although preliminary the wide angle results support the interpretation that the elberton granite is a tabular body l

modern and late holocene wind regimes over the great plains central u s a the great plains of the central united states contain numerous presently stabilized dune fields that were active during the late holocene the most recent period of reactivation occurred about 700 1000 years ago during the medieval climatic anomaly a period of frequent severe drought recognized throughout the north american west dune orientations and internal bedding preserve information about paleowinds from this time period we compared paleowind information with modern winds and potential sand transport analyzed from meteorological data while both reconstructed paleowinds and modern winds include a strong northwesterly component over the northern to central portions of the great plains a significant difference exists to the south during the late holocene southwesterly winds had a strong influence on dune forms over the central and southern great plains while modern potential sand transport is dominated by southerly to southeasterly winds that bring moisture to the region from the gulf of mexico hypothetical dune types forming under modern winds would be different and have different crestal orientations than those preserved from the late holocene in order for such a shift in southerly winds to take place it is likely that 1 the typical position of the bermuda high in summer was shifted either to the east or to the south resulting in weaker low level winds from the south and southeast and greater extent of southwesterly winds on the great plains and or 2 drought likely enhanced by evapotranspiration and soil moisture feedbacks brought the normally higher level southwesterly flow down to the land surface given our understanding of megadroughts over the great plains as well as recent climate predictions for increased warmth and drought over this area future reactivation of the dunes seems likely

possible deposit of soil dust from the 1930 s u s dust bowl identified in greenland ice 1 we have identified a dust storm deposit in the gisp2 ice core that most likely originated from the great plains region of the united states during the 1930 s dust bowl era these results indicate that the central u s can be a significant source of dust to the greenland ice sheet especially when the source area is affected by intense drought conditions

geophysical data reveal the crustal structure of the alaska range orogen within the aftershock zone of the mw 7 9 denali fault earthquake geophysical information including deep crustal seismic reflection magnetotelluric mt gravity and magnetic data cross the aftershock zone of the 3 november 2002 mw 7 9 denali fault earthquake these data and aftershock seis micity jointly interpreted reveal the crustal structure of the right lateral slip denali fault and the eastern alaska range orogen as well as the relationship between this structure and seismicity north of the denali fault strong seismic reflections from within the alaska range orogen show features that dip as steeply as 25 north and extend downward to depths between 20 and 25 km these reflections reveal crustal structures probably ductile shear zones that most likely formed during the late cretaceous but these structures appear to be inactive having produced little seis micity during the past 20 years furthermore seismic reflections mainly dip north whereas alignments in aftershock hypocenters dip south the denali fault is nonre flective but modeling of mt gravity and magnetic data suggests that the denali fault dips steeply to vertically however in an alternative structural model the denali fault is defined by one of the reflection bands that dips to the north and flattens into the middle crust of the alaska range orogen modeling of mt data indicates a rock body having low electrical resistivity 10 xm that lies mainly at depths greater than 10 km directly beneath aftershocks of the denali fault earthquake the maxi mum depth of aftershocks along the denali fault is 10 km this shallow depth may arise from a higher than normal geothermal gradient alternatively the low electrical resistivity of deep rocks along the denali fault may be associated with fluids that have weakened the lower crust and helped determine the depth extent of the after shock zone

remote sensing and spatial analysis of aeolian sand dunes a review and outlook abstract for more than four decades remote sensing images have been used to document and understand the evolution of aeolian sand dunes early studies focused on mapping and classifying dunes recent advances in sensor technology and software have allowed investigators to move towards quantitative investigation of dune form evolution and pattern development these advances have taken place alongside progress in numerical models which are capable of simulating the multitude of dune patterns observed in nature the potential to integrate remote sensing rs spatial analysis sa and modeling to predict the future changes of real world dune systems is steadily becoming a reality here we present a comprehensive review of significant recent advances involving rs and sa our objective is to demonstrate the capacity of these technologies to provide new insight on three important research domains 1 dune activity 2 dune patterns and hierarchies and 3 extra terrestrial dunes we outline how several recent advances have capitalized on the improved spatial and spectral resolution of rs data the availability of topographic data and new sa methods and software we also discuss some of the key research challenges and opportunities in the application of rs and sa dune field including the integration of rs data with field based measurements of vegetation cover structure and aeolian transport rate in order to develop predictive models of dune field activity expanding the observational evidence of dune form evolution at temporal and spatial scales that can be used to validate and refine simulation models the development and application of objective and reproducible sa methods for characterizing dune field pattern and expanding efforts to quantify three dimensional topographic changes of dune fields in order to develop improved understanding of spatio temporal patterns of erosion and deposition overall our review indicates a progressive evolution in the way sand dunes are studied whereas traditional field studies of airflow and sand transport can clarify event based process form interactions investigators are realizing a synoptic perspective is required to address the response of dune systems to major forcings the integration and evolution of the technologies discussed in this review are likely to form a foundation for future advances in aeolian study

tectonic implications of subthrust structures revealed by seismic profiling of appalachian ouachita orogenic belt a growing body of deep seismic reflection profiles across the appalachian ouachita orogenic belt reveals subthrust structures which have been previously interpreted as products of continental rifting of later thrusting or of some combination of rifting and thrusting the subthrust features can be placed into three general categories 1 small normal faults which offset lower plate shelf sequences and basement in the foreland and have been attributed to thrust loading perhaps reactivating earlier rifting faults 2 moderately dipping seismic events which lie entirely below lower plate shelf sediments in the foreland interpreted in part as strata deposited during the earlier rifting and 3 hinterland dipping reflection sequences beneath more interior portions of the mountain belt previously interpreted as thrust faults which imbricate sediments and basement related to the earlier rifted margin these interpretations are evaluated through a comparison of reflection profiles across the orogenic belt to previously interpreted seismic lines across modern extensional and compressional settings the comparisons suggest that although some normal fault offsets of lower plate shelf sequences may be original or reactivated rifting faults the dipping events entirely beneath the shelf sequence are more diagnostic of the rifting process these dipping sequences are therefore consistent with previous interpretations that large portions of the earlier rifted margin are preserved in an undeformed state beneath thrust sheets in the appalachian foreland the comparisons also suggest an alternative to interpretations of the hinterland dipping sequences as thrust related in that the sequences are similar in seismic appearance to that of volcanic wedges commonly observed in the narrow zone separating continental from oceanic basement on modern passive margins the implication of this new interpretation is that the actual continent ocean boundary related to the earlier rifted margin may be preserved on the lower thrust plate beneath interior portions of the appalachians and ouachitas

mapping erodibility in dust source regions based on geomorphology meteorology and remote sensing mineral dust in the atmosphere has implications for earth s radiation budget biogeochemical cycles hydrological cycles human health and visibility currently the simulated vertical mass flux of dust differs greatly among the existing dust models while most of the models utilize an erodibility factor to characterize dust sources this factor is assumed to be static without sufficient characterization of the highly heterogeneous and dynamic nature of dust source regions we present a high resolution land cover map of the middle east and north africa mena in which the terrain is classified by visually examining satellite images obtained from google earth professional and environmental systems research institute basemap we show that the correlation between surface wind speed and moderate resolution imaging spectroradiometer deep blue aerosol optical depth aod can be used as a proxy for erodibility which satisfactorily represents the spatiotemporal distribution of soil derived dust sources this method also identifies agricultural dust sources and eliminates the satellite observed dust component that arises from long range transport pollution and biomass burning the erodible land cover of the mena region is grouped into nine categories 1 bedrock with sediment 2 sand deposit 3 sand deposit on bedrock 4 sand deposit stabilized 5 agricultural and urban area 6 fluvial system 7 stony surface 8 playa sabkha and 9 savanna grassland our results indicate that erodibility is linked to the land cover type and has regional variation an improved land cover map which explicitly accounts for sediment supply availability and transport capacity may be necessary to represent the highly dynamic nature of dust sources in climate models

constraints from deep crustal structure on long term landform development of the british isles and eastern united states abstract it is assumed that some major landforms not easily explained by surface geology could be controlled by deep crustal properties the concept was first applied in the british isles and then to the u s atlantic provinces both regions were affected by similar orogenies in late precambrian paleozoic times and presently belong to the passive margins of the north atlantic ocean in both areas the pattern of rifting was greatly influenced by preexisting tectonic fabric of the continental crust in the british isles pre mesozoic structures are cut obliquely by the atlantic margin while in the u s border the present margin is nearly parallel to the paleozoic sutures the british isles were affected by differential block tectonics during the tertiary examples are given of regional scale landforms linked with crustal hinges recent data confirm the great heterogeneity of the crust beneath the british isles each crustal unit has its own isostatic response according to the state of stress and its own dynamic equilibrium between rock resistance erosion processes and uplift rate in the atlantic provinces of the united states the regional physiographic framework is simpler but allochthonous terranes thrust westward over the grenville basement and shelf sediments have buried some major discontinuities in the deep crust reverse faults associated with the nw se compressional stressfield are numerous but cannot explain regional scale landforms like the blue ridge escarpment above the piedmont rock control is not the direct cause of the escarpment the blue ridge from reaches its highest relief where discontinuities in the deep crust interfere with surficial geological features ocean to continent creep processes are suggested to explain the sustained uplift of the appalachian highlands and the relatively stable position of the mountainous front since middle mesozoic times

shear zone between the inner piedmont and kings mountain belts in the carolinas the kings mountain shear zone which marks the boundary between the inner piedmont and kings mountain belts near the north carolina south carolina state line is a northeast striking steeply to moderately dipping zone of ductile mylonitic deformation and late stage semibrittle deformation the zone is at least 60 km long and is no more than a few hundred metres wide it truncates rock units of both belts the juxtaposition of two lithologically different terranes suggests that displacement may be considerable probably on the order of kilometres inconclusive evidence suggests that the northwest inner piedmont side is upthrown the kings mountain zone is one of several in the southern appalachian piedmont that were active during a middle to late devonian acadian deformational event and it may be part of a regional fault system extending from alabama to virginia the kings mountain lowndesville and towaliga zones may be a single zone more than 550 km long

erosion of an ancient mountain range the great smoky mountains north carolina and tennessee analysis of 10be and 26al in bedrock n 10 colluvium n 5 including grain size splits and alluvial sediments n 59 including grain size splits coupled with field observations and gis analysis suggest that erosion rates in the great smoky mountains are controlled by subsurface bedrock erosion and diffusive slope processes the results indicate rapid alluvial transport minimal alluvial storage and suggest that most of the cosmogenic nuclide inventory in sediments is accumulated while they are eroding from bedrock and traveling down hill slopes spatially homogeneous erosion rates of 25 30 mm ky 1 are calculated throughout the great smoky mountains using measured concentrations of cosmogenic 10be and 26al in quartz separated from alluvial sediment 10be and 26al concentrations in sediments collected from headwater tributaries that have no upstream samples n 18 are consistent with an average erosion rate of 28 8 mm ky 1 similar to that of the outlet rivers n 16 24 6 mm ky 1 which carry most of the sediment out of the mountain range grain size specific analysis of 6 alluvial sediment samples shows higher nuclide concentrations in smaller grain sizes than in larger ones the difference in concentrations arises from the large elevation distribution of the source of the smaller grains compared with the narrow and relatively low source elevation of the large grains large sandstone clasts disaggregate into sand size grains rapidly during weathering and downslope transport thus only clasts from the lower parts of slopes reach the streams 26al 10be ratios do not suggest significant burial periods for our samples however alluvial samples have lower 26al 10be ratios than bedrock and colluvial samples a trend consistent with a longer integrated cosmic ray exposure history that includes periods of burial during down slope transport the results confirm some of the basic ideas embedded in davis geographic cycle model such as the reduction of relief through slope processes and of hack s dynamic equilibrium model such as the similarity of erosion rates across different lithologies comparing cosmogenic nuclide data with other measured and calculated erosion rates for the appalachians we conclude that rates of erosion integrated over varying time periods from decades to a hundred million years are similar the result of equilibrium between erosion and isostatic uplift in the southern appalachian mountains

limitations of quantitative analysis of deep crustal seismic reflection data examples from glimpce amplitude preservation in seismic reflection data can be obtained by a relative true amplitude rta processing technique in which the relative strength of reflection amplitudes is preserved vertically as well as horizontally after compensating for amplitude distortion by near surface effects and propagation effects quantitative analysis of relative true amplitudes of the great lakes international multidisciplinary program on crustal evolution seismic data is hampered by large uncertainties in estimates of the water bottom reflection coefficient and the vertical amplitude correction and by inadequate noise suppression processing techniques such as deconvolution f k filtering and migration significantly change the overall shape of amplitude curves and hence calculation of reflection coefficients and average reflectance thus lithological interpretation of deep crustal seismic data based on the absolute value of estimated reflection strength alone is meaningless the relative strength of individual events however is preserved on curves generated at different stages in the processing we suggest that qualitative comparisons of relative strength if used carefully provide a meaningful measure of variations in reflectivity simple theoretical models indicate that peg leg multiples rather than water bottom multiples are the most severe source of noise contamination these multiples are extremely difficult to remove when the water bottom reflection coefficient is large 0 6 a condition that exists beneath parts of lake superior and most of lake huron

mechanism of continental crust subsidence in fold belts the urals appalachians and scandinavian caledonides abstract formation of deep basins on continental crust is usually explained by lithospheric stretching stretching produces the large deformations in the upper brittle part of the crust that have been found in many rift valleys the sedimentary cover of deep basins on continental crust is exposed at the surface in fold belts in many places some undeformed basins have been covered by detailed seismic profiling and drilling the sedimentary cover structure in the urals appalachians and in the scandinavian caledonides has been analysed no deformations typical of stretching were found in the greater part of the basins on continental crust high magnitude subsidence without stretching can be produced by thrust loading or by a large density increase in the crust or mantle paleotectonic conditions exclude thrust loading as a cause of formation of the major basins in the above fold belts most of them were formed in cool cratonic areas by rapid subsidence in a few m y their initial depth was 1 3 km subsidence of this type cannot be produced by thermal relaxation without significant stretching gabbro eclogite transformation in the lower crust is proposed as a possible mechanism intense shortening of continental crust is observed only where rapid subsidence of a large magnitude took place before the folding not one cratonic block was strongly compressed in the fold belts considered

evaluation of southern eastern overthrust belt beneath blue ridge piedmont thrust seismic reflection surveys in the southern part of the eastern overthrust reveal that crystalline rocks of the blue ridge and piedmont were thrust westward burying a large segment of sedimentary rocks of the valley and ridge surface and subsurface data suggest that the buried segment includes cambrian and lower ordovician shallow shelf clastic and carbonate rocks overlain by middle ordovician foredeep black shale because eastward increasing regional thermal patterns existed prior to thrusting westward movement of thrust sheets disrupted and telescoped that pattern by placing more thermally mature eastern rocks over less mature western rocks the original thermal pattern can be reconstructed by restoring the thrust sheets to their prethrust position the reconstruction mphasizes that rocks less metamorphosed than greenschist facies are contained in only two thrust sheets all of the saltville and part of the pulaski because subgreenschist rocks of the saltville and pulaski thrust sheets appear to be confined to the subsurface of the blue ridge and westward it is most likely that rocks with commercial gas potential will not be present in the subsurface of the piedmont east of the brevard fault nevertheless the concealed area of the southern eastern overthrust with possible gas potential is about as wide as its exposed part thus the combined surface and subsurface area for future exploration in the southern appalachians is about doubled in size

on the formation of desert loess sequences of quartz rich coarse 20 63 m silt occur in many low and midlatitude unglaciated arid and semiarid areas and have been termed desert loess the processes by which these deposits are generated have been debated for decades all hypotheses to explain their origin seek to provide mechanisms for the generation of silt sized material without glacial grinding which is the main process involved in the production of coarse silt at high latitudes possible mechanisms for the formation of coarse silt in arid regions include derivation from preexisting siltstones mechanical weathering of silicate rocks and abrasion of sand grains in active dune environments during intense transport events examination of the characteristics of desert loess and field and laboratory experiments to assess the role of dune areas as a source of coarse silt by abrasion and or resuspension of residual fines suggests that many loess sequences are dominated by locally derived coarse silt improvements in the characterization of desert loess particle size mineralogy and geochemistry are needed however to identify sources and sinks of coarse silt especially when combined with climatic back trajectory analysis properly scaled experiments and modeling of particle collisions will also help to better quantify the effectiveness of abrasion in the generation of coarse silt in support of field observations

intensification of north american megadroughts through surface and dust aerosol forcing abstracttree ring based reconstructions of the palmer drought severity index pdsi indicate that during the medieval climate anomaly mca the central plains of north america experienced recurrent periods of drought spanning decades or longer these megadroughts had exceptional persistence compared to more recent events but the causes remain uncertain the authors conducted a suite of general circulation model experiments to test the impact of sea surface temperature sst and land surface forcing on the mca megadroughts over the central plains the land surface forcing is represented as a set of dune mobilization boundary conditions derived from available geomorphological evidence and modeled as increased bare soil area and a dust aerosol source 32 44 n 105 95 w in the experiments cold tropical pacific sst forcing suppresses precipitation over the central plains but cannot reproduce the overall drying or persistence seen in the pdsi reconstruction droughts in the scenario with dust aerosols

seismic velocity and anisotropy in mylonites and the reflectivity of deep crystal fault zones compressional wave velocity anisotropy has been measured to 1 kb confining pressure in several mylonites in one cataclasite and in their protoliths no significant difference in the velocity or density was found between the protolith and the tectonically altered rock at 1 kb strong seismic anisotropy greater than 10 was present in only two of nine mylonites measured the anisotropy was due to their aphanitic texture high content of layered silicates and pervasive foliation most mylonitic rocks studied were not strongly anisotropic despite a well developed macroscopic foliation where anisotropy was present velocities usually were slowest perpendicular to the foliation and fastest parallel to both foliation and lineation these preliminary results suggest that ductile fault zones in the crust are not strong seismic reflectors unless mylonites in the fault zone are aphanitic and contain large amounts of foliated phyllosilicates it is also possible that anomalous environmental conditions such as high pore pressure in the fault zone in situ may explain observed seismic reflectivity

relationship between observed upper mantle structures and recent tectonic activity across the southeastern united states the lithospheric structure of the southeastern united states is a product of earlier episodes of continental collision and breakup the region is located in the interior of the north american plate away from active plate margins however there is ongoing tectonism in the region with multiple zones of seismicity uplifting arches and cenozoic intraplate volcanism the mechanisms controlling this activity and the state of stress remain enigmatic two important factors are plate strength and preexisting inherited structures here we present new tomographic images of the upper mantle beneath the southeastern united states revealing large scale structural variations in the upper mantle examples include the relatively thick lithospheric mantle of stable north america that abruptly thins beneath the paleozoic appalachian orogeny and the slow upper mantle of the proterozoic reelfoot rift our results also indicate fast seismic velocity patterns that can be interpreted as ongoing lithospheric foundering this provides a viable explanation for seismicity uplifting and young intraplate volcanism we postulate that not only tectonic inheritance but also continuing lithospheric foundering may control the ongoing activity of the region long after it became a passive margin based on distinct variations in the geometry and thickness of the lithospheric mantle and foundered lithosphere we propose that piecemeal delamination has occurred beneath the region throughout the cenozoic removing a significant amount of reworked deformed mantle lithosphere ongoing lithospheric foundering beneath the eastern margin of stable north america explains significant variations in thickness of lithospheric mantle across the former grenville deformation front

the alleghanian southern appalachian piedmont a transpressional model alleghanian dextral transpression produced multiple strike slip shear zones forming a contractional mega duplex in the central and southern appalachian piedmont structural upwelling along the zones is identifiable as crustal arching on seismic reflection profiles that roughly corresponds to the piedmont gravity high the structural upwelling coincides both temporally and spatially with areas of peak alleghanian plutonism and metamorphism the compositionally bimodal plutons generally occur in or around the fault zones and are isotopically primitive geobarometry of cognate xenocryst inclusions of coexisting plagioclase and pyroxene from a granitoid indicates 8 11 kbar or 31 to 42 5 km depth to proposed source region this depth roughly corresponds to the pre erosional location of multiple reflections beneath the arches on seismic profiles that are interpreted as the moho the granitoids are proposed to have formed by partial melting of the lowermost crust through heat from mafic intrusions and decompression resulting from crustal arching beneath the strike slip faults the granitoids ascended along the strike slip faults and were emplaced in or near them the crustal arching and melting processes appear to be important mechanisms in the development of strike slip orogens

late quaternary eolian sand depositional record for southwestern kansas landscape sensitivity to droughts abstract eolian deposits and landforms are ubiquitous in western kansas particularly south of the arkansas river with the presence of a stabilized dune field stratigraphic studies and associated optical dating reveal a complex depositional history for this dune field spanning the late quaternary the oldest eolian deposits from ca 16 to 12 ka completely or partially bury high terraces with ages of ca 16 and 33 ka it is unknown whether these eolian deposits reflect regional aridity and or a change in sediment availability with the transition of the arkansas river from a single channel to a braided system there is pervasive evidence for episodic eolian erosion and deposition ca 9 8 to 6 3 ka generally coincident with loess deposition on upland surfaces olson c g nettleton w d porter d a brasher b r 1997 middle holocene aeolian activity on the high plains of west central kansas holocene 7 3 255 261 and thus it is inferred to reflect regional aridity sites within the dune field show a sequence of eolian sands and weak buried soils reflecting either dune migration or sand sheet accretion at ca 1490 430 380 320 180 and 70 yr ago which correspond well with continental scale droughts in the tree ring record eolian sand in the arkansas river dune field may be derived principally with variability in fluvial activity and in climate during the late pleistocene to the middle holocene with substantial reactivation of eolian systems during decadal scale drought variability in the past 2000 yr

paleozoic and grenvillian structures in the southern appalachians extended interpretation of seismic reflection data interpretive reprocessing of seismic reflection data has elucidated paleozoic and grenvillian structures in the southern appalachians the seismic data include a 7500 km grid of adcoh seisdata and cocorp reflection profiles that traverse the blue ridge and inner picdmont geologic provinces of north carolina south carolina and georgia surface geology and potential field data were used to constrain the interpretation the reprocessed seismic reflection data have delineated the internal and external geometry of the crystalline blue ridge inner piedmont allochthon including the locations of the blue ridge master decollement haycsville fault and brevard fault zone on the basis of the reprocessed data all of the major faults within the allochthonous upper crust sole in the blue ridge master decollement reflections extending to the southeast from beneath the surface location of the hayesville fault to the blue ridge thrust might be the seismic signature of a high strain zone this implies that internal deformation of the blue ridge allochthon associated with the alleghanian orogeny might have occurred farther to the west than has been previously documented from field studies relative amplitude seismic data enabled the discrimination between blue ridge inner piedmont crystalline rocks and underlying lower paleozoic shelf strata thereby delineating the blue ridge thrust the interpreted geometry constrains the top of the shelf sequence beneath the blue ridge to depths of less than 3 km this relatively shallow depth of the shelf strata together with the presence of duplex structures and bright spots that are imaged within the sequence might imply favorable conditions for hydrocarbon exploration beneath the blue ridge midcrustal reflections from within the upper to iower crust are interpreted to originate from preserved grenvillian structures that were reactivated at the basement surface during late proterozoic early cambrian extension reflection continuity is occasionally disrupted by interpreted post grenvillian pre early cambrian low density intrusions topography at the basement surface possibly caused by the intrusions is interpreted to have controlled the formation of some of the structures within the overlying allochthon including blue ridge and brevard fault zone ramps correlation of seismic time structure contour maps with available gravity data and two dimensional gravity modeling suggest that anomalies in the gravity field can be attributed to low density sources within the autochthonous crust discontinuous reflection packages from depths of 36 42 km are interpreted to originate from the mohorovi i discontinuity the reflectors trend about n15 e with a true dip of approximately 15 nw

on the occurrence of postmidnight equatorial f region irregularities during the june solstice 1 postmidnight equatorial f region irregularities efis are known to develop mainly during the solstitial months however it is not well understood whether they occur at all longitudes and what process causes their occurrence at different longitude sectors in this study we use the gps total electron content tec fluctuations obtained from a global gps network and spread f in ionograms from jicamarca 283 e 12 s dip 1 n in the american longitude sector and kwajalein 167 e 9 n dip 4 n bac lieu 106 e 9 n dip 2 n and chumphon 99 e 11 n dip 3 n in the pacific and asian longitude sectors during 2000 2009 to investigate the efi characteristics during june solstice results from global tec fluctuations show that at solar maximum the occurrence rate of postmidnight efis is high in african and pacific regions moderate in the southeast asian region and low in the peruvian region and that most postmidnight efis are the continuation of postsunset efis during solar minimum the postmidnight efis were rarely observed in tec but were very frequent in ionograms the latter had more frequent postmidnight onsets over peru whereas they were initiated during late postsunset hours in pacific and southeast asian longitudes in both longitudes the postsunset layer rise occurred with some delay the layer rise was more prominent on spread f nights over jicamarca and less so over pacific longitudes the results showing different degrees of association at the different longitudes between the postsunset postmidnight efis and f layer heights highlight the influence of other factors in the late night efi development perturbation seeds and plasma drifts neutral winds in particular are discussed as strong candidates for causing these irregularities in the june solstitial months of solar minimum years

master decollement root zone beneath the southern appalachians and crystal balance a root zone of the southern appalachian master decollement is postulated to exist beneath kings mountain belt on the basis of an alternative interpretation of cocorp seismic profiles palin spastic restoration of the entire crust and earlier geological and geophysical interpretations mildly deformed cambrian metased imentary rocks beneath the decollement end beneath the piedmont in the vicinity of danielsville georgia reflections farther southeast are probably from ultramylonites weak subhorizontal reflections continue southeasterly to the kings mountain belt where a series of east dipping 30 reflections dominate the section to a depth of 20 km beneath the charlotte belt reflections southeast of the root zone are possibly all related to the structure in an accreted island arc

high resolution proxy record of holocene climate from a loess section in southwestern nebraska usa abstract multi proxy analysis was used to produce a high resolution paleoclimatic record from an exceptionally thick section of the holocene bignell loess near wauneta southwestern nebraska in the central great plains the wauneta section has excellent age control based on optically stimulated luminescence osl and radiocarbon dating and records multiple episodes of rapid loess deposition alternating with slower deposition and soil formation the lowermost and uppermost osl ages obtained from the bignell loess are 10 250 610 years 5 9 m depth and 100 10 years 0 1 m depth respectively as a result the holocene has been temporally confined stratigraphically the bignell loess overlies the late pleistocene peoria loess deposited 21 14 ka and the two units are separated by the brady soil which is distinguished by its color and other pedogenic features l a b color parameters and organic carbon content of bignell loess are sensitive proxies to differentiate drought induced aeolian sediment layers from the intercalated soil horizons soil organic carbon derived 13 c data suggest that the c 3 dominated floral environment during peoria loess deposition shifted dramatically to a c 4 dominated environment during brady soil formation in response to a warming trend even greater c 4 abundance characterized the late holocene high resolution 13 c data support the contention that c 3 vs c 4 vegetation change in the holocene reflects ecosystem response to frequent vegetation disturbance under arid conditions time series analysis reveals that 13 c and color parameters display high frequency variation with periodicities of 103 118 years and 103 years respectively similar periodicities were also reported in studies of north dakota lakes though the physical mechanism responsible is uncertain comparison of bignell loess color and tropical pacific sea surface temperatures ssts allows evaluation of a proposed teleconnection between drought in the great plains and la nina like conditions in the tropical pacific the loess color index and eastern tropical pacific sst display broad similarities through the late pleistocene and holocene that are consistent with this teleconnection on the other hand drought centered at 3800 years ago is not consistent with the teleconnection and the end of early holocene aridity at the wauneta section around 6500 years ago is much earlier than the corresponding rise in sst and increase in el nino frequency in the eastern tropical pacific

optically stimulated luminescence dating of young sediments a review optically stimulated luminescence osl dating of young 1000 years sediments is used increasingly in a wide variety of late holocene studies as a mean of establishing contemporary sedimentation rates or the timing of sediment deposition this paper provides a summary of the basic principles of osl dating outlines the problems specific to the dating of young material and then uses recent applications to young sediments to illustrate the greatly increased scope and potential of the method in geomorphology and the geology of recent deposits the overall reliability of this new generation of osl ages is examined by comparing where possible osl ages with independent age control it is concluded that the osl ages are accurate in that there is no evidence for systematic over or under estimation it is our conclusion that osl dating should be regarded as a reliable chronological tool for determining the time of deposition of water lain sediments from the coastal zone and aeolian deposits from both coastal and inland environments our conclusion is supported by the growing popularity of osl dating in geomorphology and geology

eolian sand sheet deposition in the san luis paleodune field western argentina as an indicator of a semi arid environment through the holocene abstract eolian deposits are common in the western pampas of argentina and most are assumed to be associated with glacial conditions stratigraphic and sedimentologic studies coupled with osl dating in san luis province document for the first time a nearly continuous sequence of eolian sand sheet deposits that span most of the holocene petrology and geochemical analyses indicate that the source of the sand is from pre existing pleistocene eolian sediments sand sheet deposition between ca 12 and 1 ka is associated with sparse monte type vegetation that occurs with drier conditions map 450 100 mm than the late 20th century 700 mm this paleoenvironmental inference is consistent with nearby pollen and lake level records a persistent semi arid environment in western argentina during the holocene may reflect sustained warm ssts in the western equatorial atlantic ocean which may have suppressed the pressure gradient between the south atlantic anticyclone and chaco low and thus the flux of summer moisture to western argentina there appears to be a paleoclimatic dipole response between a dry western argentina and a wet southeastern brazil which is consistent with the increasing strength of the south american monsoon through the holocene sand sheet accretion appears to cease by 800 to 200 years ago with wetter conditions and succession to espinal vegetation prior to european contact

gross erosion net erosion and gross deposition of dust by wind field data from 17 desert surfaces wind erosion measurements were carried out in nellis dunes recreation area southern nevada usa gross erosion the total mass of sediment effectively blown away from a surface gross deposition the total mass of sediment effectively depositing on a surface and net erosion the difference in sediment mass before and after an event were measured for 1 year on 17 different types of surfaces developed on loose dune sand compacted sand loose silt compacted and or aggregated silt rock covered sands and silts mixtures of sand silt and clay exposed petrocalcic horizons gravelly substrata and bedrock results showed that net erosion which is the type of erosion measured in field and laboratory experiments strongly differs from gross erosion activity on a surface is much higher than classic net erosion measurements suggest future studies on wind erosion should better acknowledge the distinction between the two types of process also a grain diameter of maximum susceptibility to wind erosion optimum deflation diameter near 70 m as proposed by the aeolian literature only exists for net wind erosion no such optimum diameter was found for gross wind erosion within the particle range 0 100 m delineating the transport modes of suspension and modified saltation in addition desert surfaces predominantly composed of sand did not show an optimum deflation diameter for net erosion around 70 m instead there was a preferential grain size around 15 m at which particles were most vulnerable to net emission desert surfaces poor in sand showed the classic value of 70 m this suggests that interactions exist between the type of surface and the susceptibility of particles to wind erosion this study is solely based on field data although results are supported by two previous wind tunnel studies more wind tunnel experiments documenting the interactions between gross erosion and gross deposition are necessary copyright 2010 john wiley sons ltd

evidence of active dune sand on the great plains in the 19th century from accounts of early explorers eolian sand is extensive over the great plains of north america but is at present mostly stabilized by vegetation accounts published by early explorers however indicate that at least parts of dune fields in nebraska colorado kansas new mexico and texas were active in the 19th century based on an index of dune mobility and a regional tree ring record the probable causes for these periods of greater eolian activity are droughts accompanied by higher temperatures which greatly lowered the precipitation to evapotranspiration ratio and diminished the cover of stabilizing vegetation in addition observations by several explorers and previous historical studies indicate that rivers upwind of great plains dune fields had shallow braided sandy channels as well as intermittent flow in the 19th century wide braided sandy rivers that were frequently dry would have increased sand supplies to active dune fields we conclude that dune fields in the great plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high with or without greenhouse warming

a kinematic model for the collision and complete suturing between gondwanaland and laurussia in the carboniferous maps of middle to late carboniferous strike slip faults in western europe northern africa and eastern north america have been compiled from geological gravity and magnetic onshore and offshore data a large majority of these faults can be interpreted in terms of a logical syn to post collisional pattern superimposed on the initial suture between the african i e gondwana and north american european laurussian continental margins the pre collision positions of the major continents are derived from paleomagnetic data and when combined with the general distribution of the strike slip faults lead to a kinematic model of the complex middle late carboniferous collision in this model the west african precambrian craton acted as a rigid promontory or die with respect to the partially rigid plastic zones between it and the large north american craton these partially rigid plastic zones comprise the external appalachian and canadian maritime margins the mauritanide and hercynian margins of north

structural analysis of the carolina inner piedmont terrane boundary implications for the age and kinematics of the central piedmont suture a terrane boundary that records paleozoic laurentia gondwana interactions new field mapping along the carolina inner piedmont terrane boundary in south carolina and eastern georgia reveals preaccretionary synaccretionary and postaccretionary faults the dextral strike slip lowndesville shear zone is adjacent to a 50 km long segment of the terrane boundary however the lowndesville shear zone is correlated eastward with the dextral strike slip beaver creek shear zone which is within the carolina terrane and predates 415 ma the lowndesville shear zone is overprinted by a dextral strike slip phyllonite zone named the deal creek shear zone the deal creek shear zone is correlated eastward with the gold hill silver hill shear zone which is also within the carolina terrane and records dextral strike slip motion between 400 and 325 ma the cross anchor and mulberry creek faults both truncate the lowndesville and the deal creek shear zones and form the terrane boundary the mulberry creek fault probably of triassic jurassic age juxtaposes the lowndesville shear zone adjacent to the carolina inner piedmont terrane boundary west of waterloo south carolina the cross anchor fault is the terrane boundary east of waterloo south carolina and forms the southeastern boundary of the whitmire reentrant crosscutting relationships indicate that the cross anchor fault is the oldest fault which juxtaposes the carolina and inner piedmont terranes in the study area these structural interpretations and available geochronological data indicate that the cross anchor fault is a 325 ma thrust fault and may be the central piedmont suture an early alleghanian suture resolves the problem of inserting the carolina terrane into the western iapetus ocean

quantifying dust emissions from desert landforms eastern mojave desert usa abstract the measurement of natural dust emissions from desert landforms is crucial in environmental hazard assessment and field checking the accuracy of global dust models more than 500 individual dust measurements from eight common desert landforms in southern california were collected using the pi swerl portable in situ wind erosion lab the largest emitters of dust are dry washes 13 787 to 0 007 mg m 2 s 1 dunes playa margins distal alluvial fans and lacustrine beaches low emitters include salt crusted playas 0 692 to 0 002 mg m 2 s 1 silt clay crusted playas and desert pavements high emissions are a function of saltating sand that bombards the surface liberating dust sized particles for entrainment low dust emissions are primarily a function of surface crusting gravel armoring and vegetation density pi swerl measurements reveal that emission rates can vary by at least three orders of magnitude reflecting local variability in soil texture and continuity of surface crusts shear stress partitioning models can be applied to dust data measured by the pi swerl to account for large surface roughness features such as vegetation the results presented here give an approximation of the contributions to atmospheric dust loading by landforms in the mojave desert and can potentially be used to improve atmospheric dust models

probing the structure of the deep continental crust old buried deformed crystalline rocks apparently make up most of the 40 kilometer thick continental crust this part of the earth is poorly explored and constitutes a major frontier of modern earth science two techniques seismic reflection profiling and drilling which were developed by industry for other purposes offer special potential for such exploration seismic profiling of the deep crust by cocorp the consortium for continental reflection profiling has already produced important information including evidence for extensive thin skinned thrusting of older rocks over a continental margin as the corresponding ocean basin closed deep drilling of crystalline rocks of the continents for scientific purposes is so far relatively unexploited in the united states but is already being carried on elsewhere in general big science is likely to become more important in basic geology as this frontier is explored

estimating crustal thickness using sspmp in regions covered by low velocity sediments imaging the moho beneath the southeastern suture of the appalachian margin experiment sesame array se atlantic coastal plain

digisonde spread f and gps phase fluctuations in the equatorial ionosphere during solar maximum 1 the jicamarca 11 95 s 76 87 w digisonde and the arequipa 16 47 s 71 49 w gps receiver observed the equatorial f region irregularities on the western south america from april 1999 to march 2000 the spread f measured by the digisonde were classified into four types and the gps phase fluctuations derived from the temporal variation of total electron content were divided into three levels to represent the irregularity strength the observation shows that the occurrences of all four types of spread f are higher in the d months january february november and december than in the e months march april september and october for the gps phase fluctuations both seasonal and nighttime variations show that the occurrences of strong level irregularities are higher than moderate level irregularities in the e months but the situation is reversed in the d months moreover the occurrence sequences of four types of spread f and three levels of gps phase fluctuations all can be explained by the e b drift variations and the generalized rayleigh taylor instability for the comparisons between the gps phase fluctuations and the digisonde spread f plasma bubbles results show that the gps phase fluctuations can represent the appearances of the digisonde spread f and the strong level of gps phase fluctuations are associated with the occurrence of topside plasma bubbles these results imply that the greater gps phase fluctuation is related to the larger altitudinal range distribution of irregularities