late stage water eruptions from ascraeus mons volcano mars implications for its structure and history abstract ascraeus mons was one of the first of the martian volcanoes to be imaged by the high resolution stereo camera hrsc experiment onboard the esa mars express spacecraft these images show much of the volcano at a higher resolution than previously and details of its lava flows sinuous rilles flank vents and tectonic features indicate an unexpected origin for some of these features we establish the time stratigraphic sequence for these features and use a numerical model on hrsc stereo dtms of the sinuous rilles and conclude that they were formed by water erosion terrestrial analogues for such features are found at reunion island and other volcanoes we then examine the overall structure of the volcano which is dissimilar to that of large terrestrial volcanoes in important respects and perform laboratory analogue experiments of its deformation concluding that the tectonic features were formed by sinking of the volcano into a substratum that was much weaker than the volcanic edifice an ice rich substratum melted by a combination of pressure melting and magmatic heating seems the most likely mechanism analogous water escape structures in a similar volcanic situation have been identified at mt haddington in the antarctic the possible role of a hydrological cycle and a hydrothermal system within the volcano are discussed based on field evidence we propose that much of the broad aprons of lobate flows issuing from the ne and ssw foot of ascraeus mons are composed of mudflows rather than lava flows these different approaches are linked into a coherent history of this volcano the similarity of ascraeus mons to pavonis mons and arsia mons though ascraeus is younger suggests that some of our conclusions may apply to these volcanoes too

ejecta deposits of bakhuysen crater mars abstract bakhuysen crater is a late noachian to early hesperian age 150 km diameter impact structure located in the heavily cratered southern highlands of mars it is one of the largest craters on mars with well preserved ejecta deposits impact ejecta deposits allow an understanding of crustal composition volatile content and evolution of terrestrial planets yet the emplacement of ejecta deposits on bodies throughout the solar system is still debated here we present the first detailed geomorphologic map of bakhuysen crater we distinguish two distinct ejecta units 1 a largely hummocky ejecta unit be1 that comprises the continuous ejecta blanket and 2 an uppermost discontinuous unit be2 with a distinct ponded morphology pitted texture and previously unreported lobate and flow deposits pitted materials are present in the crater interior deposits as well as the ejecta bakhuysen is the largest martian crater thus far identified with crater related pitted material which has been suggested previously to represent volatile rich primary impact melt bearing deposits unit be1 is interpreted as the continuous ejecta blanket emplaced through ballistic sedimentation and radial flow unit be2 shares many attributes with impact melt rich ejecta seen on other planetary bodies e g earth moon and mercury and is interpreted as having been emplaced as ground hugging flows during the later modification stage of crater formation channels are observed as having emanated from bakhuysen impactites and represents a clear example of the role of volatiles in the impact cratering process on mars bakhuysen ejecta deposits and its associated features suggests that if indeed a substantial volatile source is sampled by martian impact events then the formation of ejecta associated channels on mars are likely genetically linked to the formation of pitted materials where present the preservation and exposure of the impact deposits of bakhuysen present a unique opportunity to study these features and their relationship to the impact process on mars

a shear instability seeding mechanism for quasiperiodic radar echoes the quasiperiodic echoes with periods in the range of 1 10 minutes originally discovered at the middle and upper atmosphere mu radar in japan in the early 1990s are now known to be a common feature of midlatitude sporadic e a possible role of shear instabilities and the associated kelvin helmholtz structure in seeding the plasma instabilities that produce the radar echoes is suggested in this paper the proposed mechanism has the advantage that the seed structure is generated in situ as part of the same neutral wind structure that serves to initiate the generation of the sporadic e layer in addition the range of observed periods can easily be explained since the kelvin helmholtz structure is embedded in the shear flow and moves with the mean flow in the shear layer the period observed in the ground based frame is simply a product of the horizontal wavelength and the mean flow velocity at the center of the disturbance finally a typical feature of the radar observations has been that the quasiperiodic structure often ebbs and wanes in intensity over a period of 30 to perhaps 60 min recent simulations of unstable neutral shears show that the timescale for the build up and eventual restabilization of the shear flow is 30 40 min comparable to the timescale found in the observations

radar investigations of low altitude quasi periodic echoes in chung li 1 quasi periodic qp radar echoes from the sporadic e layers are also found at altitudes below 100 km which we call low altitude quasi periodic echoes lqp we have used the chung li vhf radar to study correct locations of these echoes creating irregularities which are confined to the height range between 90 km and 100 km have a thickness of 2 4 km and are only slowly descending in altitude they occur with periods of some tens of seconds to maximum three minutes since chung li is close to the equatorial region we can prove that these lqp occur in this temperate region as well the particular progress reported here is that interferometry allows us to determine the position of the scattering irregularities in three dimensions which provides new information about the motion of the scatterers we concur with the assumption that the lqp echoes are created in a strong wind shear below 100 km altitude

heavy metal concentrations in shallow marine sediments affected by submarine tailings disposal and artisanal gold mining buyat ratototok district north sulawesi indonesia trace element concentrations in shallow marine sediments of the buyat ratototok district of north sulawesi indonesia are affected by sub marine disposal of industrial gold mine tailings and unregulated dumping of tailings and wastewater from small scale gold mining using mercury amalgamation industrial mine tailings contained 590 690 ppm arsenic 490 580 ppm antimony and 0 8 5 8 ppm mercury tailings affected sediment as and sb concentrations were 20 30 times higher than in muddy sediments not contaminated with tailings and 50 60 times higher than pre mining average highest mercury concentrations were observed in sediments affected by small scale mining using mercury amalgamation 5 29 ppm concentrations of most other trace elements were comparable in sediments affected by both types of mining and were slightly higher than regional averages for sediments collected before the onset of industrial mining elevated concentrations of both as and sb in approximately equal proportions suggest tailings dispersal of at least 3 5 km mercury released from artisanal gold mining dispersed up to 4 km from river mouths slight increases in concentrations of non mer cury trace elements in areas affected by artisanal mining over pre industrial mining concentrations were proba bly caused by increased rates of erosion

aqueous processes at gusev crater inferred from physical properties of rocks and soils along the spirit traverse 1 gusev crater was selected as the landing site for spirit on the basis of morphological evidence of long lasting water activity including possibly fluvial and lacustrine episodes from the columbia memorial station to the columbia hills spirit s traverse provides a journey back in time from relatively recent volcanic plains showing little evidence for aqueous processes up to the older hills where rock and soil composition are drastically different for the first 156 sols the only evidence of water action was weathering rinds vein fillings and soil crust cementation by salts the trenches of sols 112 145 marked the first significant findings of increased concentrations of sulfur and magnesium varying in parallel suggesting that they be paired as magnesium sulfate spirit s arrival at west spur coincided with a shift in rock and soil composition with observations hinting at substantial amounts of water in gusev s past we used the microscopic imager data up to sol 431 to analyze rock and soil properties and infer plausible types and magnitude of aqueous processes through time we show the role played early by topography and structure the morphology texture and deep alteration shown by the rocks in west spur and the columbia hills formation chf suggest conditions that are not met in present day mars and required a wetter environment which could have included transport of sulfur chlorine and bromine in water vapor in volcanic gases hydrothermal circulation or saturation in a briny fluid containing the same elements changing conditions that might have affected flow circulation are suggested by different textural and morphological characteristics between the rocks in the chf and those of the plains with higher porosity proxy higher void ratio and higher water storage potential in the chf soils were used to assess aqueous processes and water pathways in the top layers of modern soils we conclude that infiltration might have become more difficult with time

volcanism on mars more than 15 years of planetary exploration of mars have given insight into the geologic processes that have shaped its surface the newly acquired viking data have shown that volcanism is one of the most important geologic processes operating on mars throughout its history in situ chemical analyses of martian soil by the viking lander spacecraft indicate mafic to ultramafic source rocks this is consistent both with available remote sensing data which indicate the presence of mafic minerals such as pyroxene and olivine and with petrologic modeling based on available geophysical data which suggest that martian lavas are probably iron rich and ultramafic these data strongly suggest that basaltic volcanism is widespread on mars and much of the photogeological data may be studied in this context photogeological analysis of the martian surface has shown two main types of volcanic morphologies the first type is central volcanoes which are volcanic landforms developed by continued and prolonged eruption from a point source vent this category includes 1 shields the classic low profile volcanic mountains of which olympus mons is the most spectacular example 2 domes steep sided constructs such as tharsis tholus that may represent lower rates of eruption than the shields or possibly more silicic lava compositions 3 highland patera radially textured low profile volcanoes that occur in the cratered terrain and are interpreted as ash shields 4 alba patera an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree and 5 various small features such as cinder cones the second major category is volcanic plains which are units recognized by several criteria of which the presence of mare ridges and flow lobes are the most useful volcanic plains are subdivided into four main groups 1 simple flows broad smooth to rolling plains that contain numerous mare type ridges but no flow lobes interpreted as being composed of thick single cooling units 2 complex flows displaying multiple overlapping flow lobes interpreted to be indicative of thin multiple cooling units 3 undifierentiated flows plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers and 4 questionable plains volcanic units heavily modified by other processes erosion tectonism etc so that their origins are uncertain when these categories of volcanic morphologies are combined with relative age data provided by crater statistics a volcanic history for mars can be derived as follows early heavy bombardment of mars was accompanied and followed by small scale fluvial channeling extensive flood volcanism the plateau plains and ash shield volcanism in the cratered terrain shortly after this time less extensive flood volcanism continued to resurface the planet during formation of the northern southern hemisphere dichotomy central volcanism became more prominent with the development of the alba patera center as well as the older shields and domes of the northern hemisphere early tharsis and elysium regions the development of the tharsis and elysium uplifts may have triggered the release of large scale catastrophic floods producing large channels continued uplift and lithospheric thinning concentrated volcanic activity in the tharsis region producing large shield volcanoes and extensive lava plains both central vent and plains volcanism have been active throughout martian history but the volumes of extrusion have gradually decreased with time this is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time gradually turning off the volcanism although many questions remain regarding martian volcanism the viking data have provided a remarkable detailed overview of the probable nature of the volcanic history of mars

the martian hemispheric dichotomy may be due to a giant impact mars is divided into two fundamentally different geological provinces of approximately hemispherical extent1 3 the more southerly province is heavily cratered contains relatively old geological units and superficially resembles the lunar and mercurian highlands the northern province is relatively lightly cratered and contains younger geological units including extensive plains volcanic edifices and volcanic calderas except for the tharsis and elysium regions and other large volcanoes most of the younger northern province consists of lowlands which lie an average of 3 km below the highlands lowlands occupy about one third of mars they are separated from the highlands by a distinct scarp or by a sloping transitional zone as much as 700km wide in which highland materials have been disrupted and partly replaced by lowland deposits fig 1 the transition is characterized by a variety of landforms unknown on other planets the highlands and lowlands are in isostatic equilibrium across the transitional zone4 no generally accepted explanation for the cause of the highland lowland dichotomy has been proposed although thinning of the lithosph re in the northern hemisphere by internal processes has been suggested5 large impacts which were a feature of early solar system history have also been suggested as an important cause of such early planetary surface heterogeneities3 6 7 subcircular lowlands such as argyre chryse hellas and isidis planitia and the plains south of tharsis occupy previously recognized impact basins8 10 we propose here that the largest expanse of lowlands also results from formation of a large impact basin early in mars history that has profoundly shaped the planet s surface

paleohydrology of eberswalde crater mars abstract eberswalde crater mars contains a well preserved fluvial distributary network in a likely deltaic setting the meandering inverted paleochannels and closed drainage basin of this deposit support relatively well constrained estimates of channel forming discharge over an individual event flood timescale runoff production event and annual timescales and longevity of deposition geologic timescale during the late hesperian to early amazonian epochs the width and meander dimensions of two inverted paleochannels reflect the channel forming discharge from event floods 200 to 400 m 3 s the deposit surface indicates the level 1400 to 1350 m and surface area 410 to 810 km 2 of the likely paleolake and the topography and mapped extent of tributaries constrain the watershed area 5000 to 17 000 km 2 based on these results and terrestrial empirical constraints on evaporation and sediment concentration we evaluated three hypothetical water sources meltwater liberated by the nearby holden crater impact continuous deposition over 10 1 10 2 years intermittent rainfall or snowmelt during finite periods controlled by orbital evolution deposition over 10 4 10 6 years and highly infrequent runoff or melting of accumulated snowpacks following distant impacts or secular changes in orbital parameters local impact generated runoff and highly infrequent rainfall or snowmelt require unreasonably high and low rates of evaporation respectively to maintain the paleolake level the local impact hypothesis alternatively depends on one flooding episode with very high concentrations of fluvial sediment that are inconsistent with morphologic considerations multiple primary impact craters in the area postdate holden ejecta but were later dissected indicating fluvial erosion long after the holden impact intermittent rainfall of 1 cm day and seasonal snowmelt are both consistent with our results over a deposition timescale totaling 10 4 10 6 years

hf radar observations of quasiperiodic e layer echoes over north america midlatitude e region plasma irregularities have been observed with a new low power hf coherent scatter radar at clemson south carolina the observations reveal a high incidence of quasiperiodic striations like those first observed at the middle and upper atmosphere mu radar in shigaraki japan quasiperiodic echoes were seen on approximately 70 of the evenings in august 1998 on which observations were made they occurred mainly at altitudes above 100 km had range rates usually between 100 and 150 m s implying propagation toward the radar downward and southward but typically exhibited doppler velocities indicating rapid phase propagation away from the radar upward and northward the quasiperiodic echoes sometimes had periods comparable to the brunt vaisala period but more often had significantly shorter periods closer to 1 min the doppler shifts of the strongest echoes oscillated with a period of just under 1 hour and the phase of this oscillation seemed to control the occurrence of the radar echoes

geology of the gusev cratered plains from the spirit rover transverse 1 the cratered plains of gusev traversed by spirit are generally low relief rocky plains dominated by impact and eolian processes ubiquitous shallow soil filled circular depressions called hollows are modified impact craters rocks are dark fine grained basalts and the upper 10 m of the cratered plains appears to be an impact generated regolith developed over intact basalt flows systematic field observations across the cratered plains identified vesicular clasts and rare scoria similar to original lava flow tops consistent with an upper inflated surface of lava flows with adjacent collapse depressions crater and hollow morphometry are consistent with most being secondaries the size frequency distribution of rocks 0 1 m diameter generally follows exponential functions similar to other landing sites for total rock abundances of 5 35 systematic clast counts show that areas with higher rock abundance and more large rocks have higher thermal inertia plains with lower thermal inertia have fewer rocks and substantially more pebbles that are well sorted and evenly spaced similar to a desert pavement or lag eolian bed forms ripples and wind tails have coarse surface lags and many are dust covered and thus likely inactive deflation of the surface 5 25 cm likely exposed two toned rocks and elevated ventifacts and transported fines into craters creating the hollows this observed redistribution yields extremely slow average erosion rates of 0 03 nm yr and argues for very little long term net change of the surface and a dry and desiccating environment similar to today s since the hesperian or 3 ga

origin and development of theater headed valleys in the atacama desert northern chile morphological analogs to martian valley networks abstract understanding planetary landforms including the theater headed valleys box canyons of mars usually depends on interpreting geological processes from remote sensing data without ground based corroboration here we investigate the origin and development of two mars analog theater headed valleys in the hyperarid atacama desert of northern chile previous workers attributed these valleys to groundwater sapping based on remote imaging topography and publications on the local geology we evaluate groundwater sapping and alternative hypotheses using field observations of characteristic features strength measurements of strata exposed in headscarps and estimates of ephemeral flood discharges within the valleys the headscarps lack evidence of recent or active seepage weathering such as spring discharge salt weathering alcoves or vegetation their welded tuff caprocks have compressive strengths multiple times those of the underlying epiclastic strata flood discharge estimates of cubic meters to tens of cubic meters per second derived using the manning equation are consistent with the size of transported clasts and show that the ephemeral streams are geomorphically effective even in the modern hyperarid climate we interpret that headscarp retreat in the quebrada de quisma is due to ephemeral flood erosion of weak miocene epiclastic strata beneath a strong welded tuff with erosion of the tuff facilitated by vertical jointing the quebrada de humayani headscarp is interpreted as the scar of a giant landslide maintained against substantial later degradation by similar strong over weak stratigraphy this work suggests that theater headed valleys on earth and mars should not be attributed by default to groundwater sapping as other processes with lithologic and structural influences can form theater headscarps

low altitude quasi periodic echoes studied using a large database of gadanki radar observations 1 in this paper we present studies on low altitude quasiperiodic lqp echoes based on a large database of gadanki radar observations lqp echoes have been observed 33 of the time during daytime and 39 during nighttime their occurrence is found to be maximum in the summer daytime 58 nighttime 57 followed by the september equinox daytime 32 nighttime 48 the march equinox daytime 26 nighttime 36 and minimum in the winter daytime 25 nighttime 26 height time occurrence of lqp echoes shows two local time maxima one in the morning 0700 1100 lt and another in the evening 1900 0000 lt the most significant results not reported earlier are the large occurrence rate of lqp echoes and the height time occurrence maps showing a descending pattern with close resemblance to tidal wind behavior the doppler velocities are upward northward downward southward for positive negative sloped lqp echoes also we find the doppler spread as high as 200 m s 1 at times underlining the presence of strong plasma turbulence in the collision dominated lower e region these results are discussed in the light of the current understanding of the lqp echoes

the origin of fluvial valleys and early geologic history aeolis quadrangle mars in southern aeolis quadrangle in eastern mars parallel slope valleys flat floored branching valleys v shaped branching valleys and flat floored straight canyons dissect the heavily cratered plateau sequence associated knife like ridges are interpreted as fissure eruption vents and thin dark stratiform outcrops are interpreted as exhumed igneous sills or lava flows ridged lava plains are also common but are not themselves modified by fluvial processes i mapped 56 asymmetric scarps or ridges that are probable thrust faults these faults exhibit an orientation vector mean of n63 w 11 95 confidence interval and they transect the lava plains and the older plateau sequence units by comparison the vector mean for the 264 valleys mapped is n48 w 12 with a larger dispersion about the mean the similar orientations displayed by thrust fault and valley axes suggest that valley locations are partly controlled by preexisting thrust faults and related fracture systems most valleys are also arranged orthogonally to and along the perimeter of the ridged plains a possible model for valley development is 1 freshly outgassed water became entombed as frost snow and ice within the cratered terrains during heavy bombardment and the accompanying deposition of impact ejecta volcanic ash and eolian materials 2 effusive volcanism and lava sill emplacement heated subsurface ice in the vicinity of the ridged plains and faults and fractures provided zones of increased permeability for water transport to the surface and 3 headward sapping at thermal springs thermokarst subsidence and limited downvalley fluid flows then carved and modified the valleys

tes and themis study of proposed paleolake basins within the aeolis quadrangle of mars 1 several studies have described photogeologic evidence for paleolacustrine basins on mars mostly within impact craters if these basins contained persistent standing water subsequently lost through evaporation they may have contained deposits of evaporite minerals if still present and sufficiently exposed these evaporites would be detectable in orbital thermal infrared spectra using data from mars orbiter thermal emission imaging system mo themis and mars global surveyor thermal emission spectrometer mgs tes we examined proposed paleolake basins within aeolis quadrangle including gusev and gale craters gusev crater is dominated by units with a spectrally intermediate to thick layer of dust mantling the surface tes linear deconvolutions of the low albedo deposits which have a thinner dust mantling include surface type 1 basalt materials when sulfates are included in the end member library otherwise the linear deconvolution uses surface type 2 andesite or weathered basalt themis surface emissivity spectra for the low albedo deposits do not display sufficient contrast to distinguish between surface types gale crater is relatively dust free except for the mound variably covered in a spectrally intermediate to thick layer of dust tes linear deconvolutions of crater floor and less dusty portion of the mound are consistent with a mixture of surface types 1 and 2 themis surface emissivity spectra are consistent with surface type 1 or a mixture of surface types 1 and 2 for the crater floor and surface dust for the mound these results do not discriminate between several previously suggested origins fluvial lacustrine aeolian or volcanic deposition for the mound layers we find no spectral evidence for evaporite deposits that might substantiate paleolakes existed in these craters

a case for ancient evaporite basins on mars observations indicate that a martian analog to the earth s salt pans and saline lakes of arid regions may have existed in crater basins during mars early noachian epoch terraced and channelized crater basins point to ponding of surface water as well as possible prolonged and evolving base levels in addition supportive evaporite basin analogs are offered for three other morphologic features of martian crater basins an evaporite basin model for crater basins on mars has major implications for the mechanical chemical and even biological processes that potentially have operated in mars past and represent a spectrum of potential mineral resources

new martian paradigms several interrelated paradigms concerning the nature and the evolution of mars are discussed these include an impact origin of the northern lowland mars as a water rich planet former oceans in the northern lowlands a warm wet climate on early mars and the possibility of ancient life on mars locations on mars suggested for the search of possible ancient life include the heavily cratered terrain dissected by valley networks possible lacustrine deposits in valles marineris the oxidizing layer below the surface sites along the fringes of the hypothetical northern circumpolar ocean and in evaporite deposits

plasma structures of 3 meter type 1 and type 2 irregularities in nighttime midlatitude sporadic e region 1 although the plausible mechanisms involved in the generation of midlatitude type 1 sporadic e es irregularities have been suggested rare observational evidence is provided to validate the proposed plasma structure associated with the midlatitude type 1 es irregularities in this article the type 1 echoes observed by the chung li vhf radar located in the equatorial anomalous region are interferometrically analyzed and the corresponding plasma structure of the type 1 irregularities is reconstructed we find that the plasma structure has sharp lateral and top and bottom boundaries with thickness of about 1 2 km and horizontal extent of about 3 5 km in e w direction its dimension in n s direction cannot be resolved by using interferometry technique because of considerably narrow width of expected echoing region in elevation the observed doppler velocity of the type 1 echoes can be as low as 220 m s substantially smaller than nominal ion acoustic wave speed about 360 m s in es region the spatial structure of the concurrent type 2 irregularities is also reconstructed the result strongly suggests that it be a well defined thin layer with thickness of 1 2 km and horizontal extent of 9 17 km in e w direction very different from that of the type 1 irregularities the whole structure of type 1 irregularities moves bodily toward east at speed of about 31 m s and no vertical displacement of the structure is observed although the movement of the layer structure of the type 2 irregularities in e w direction is indistinct it descends remarkably at a rate of 10 3 m s these features imply that for the present case the factors governing the dynamic behavior of the type 1 and type 2 irregularities are different and independent irrespective of the fact that the clump of the type 1 irregularities separates from that of concurrent type 2 irregularities only by about 4 km in distance

evidence of intermediate layer characteristics in the gadanki radar observations of the upper e region field aligned irregularities 1 the gadanki vhf radar observations of the upper e region field aligned irregularities are presented these are the first observations of low latitude upper e region irregularities that resemble the characteristics of intermediate layers observed over arecibo the most interesting aspect of these observations is their occurrence at altitudes as high as 160 km which requires an interpretation in terms of their source mechanism these irregularities were found to trigger about 21 lt first at higher altitude 140 160 km and propagate downward with time the signal intensities are found to be lower by about 12 db and the doppler spectra narrower by more than a factor of two compared to that of the normal e region echoes the doppler velocities are found to be both upward and downward with values less than 40 m s 1

low latitude quasiperiodic echoes observed with the piura vhf radar in the e region we present the first quasiperiodic qp echoes from 3 m e region field aligned irregularities observed in the southamerican sector just outside the magnetic equator 7 5 n geomagnetic these qp echoes occur only at night and between 105 and 120 km in general piura qp echoes present periods close to the brunt vaisala period 5 to 10 min striations with positive slopes and altitude rates of 20 25 m s 1 upward northward striations spacings of 3 to 10 km and downward southward doppler velocities these results are compared to midlatitude qp echoes from 3 and 6 m irregularities observed between 13 3 n and 46 7 n geomagnetic we found that the general characteristics that are common to our observations and other qp observations are the nighttime occurrence and the periods close to the brunt vaisala period on the other hand the discrepancies with some of the qp echoes observed at mid latitudes are found in the slope and spacing of the striations the mean phase velocities and the mean altitude location of the e layer containing the striations

ma adim vallis evolution geometry and models of discharge rate abstract episodes of confined flows in ma adim vallis are reconstructed by surveying the terraces in the valley three major levels and their associated tributary systems are identified and mapped this study points out the evidence of the cessation of the valley activity between the formation of levels 1 and 2 characterized by degraded and large perched valleys which floor are not adjusted to the following flow episode level a strong asymmetry in the tributary distribution points toward a groundwater supplied water origin of the valley potential source areas are demonstrated to be in volcano tectonic regions implying a hydrothermal origin of the water that may include melted permafrost calculation of hydraulic radii valley sections and models of discharge rates associated with the morphologic and geologic survey shows that ma adim vallis was an episodic channel the lifetime of which spanned between the noachian and amazonian

three dimensional spatial structures of midlatitude type 1 es irregularities 1 concurrent type 1 and type 2 radar returns from sporadic e es irregularities detected by the chung li vhf radar are analyzed and discussed in this paper for the present case the mean doppler velocities of the type 1 echoes lasting 8 min are between 250 and 302 m s smaller than those observed in equatorial and auroral regions the backscatter from type 1 irregularities is greater than that from type 2 irregularities by 6 8 db interferometry analysis indicates that the echo patterns of the type 1 and type 2 irregularities projected in mutually orthogonal planes are striation like strongly suggesting that the plasma structure associated with the irregularities is in a form of thin slab the plasma slab with thickness of 1 2 5 km locates in the height range from 104 to 107 km the horizontal extents of the type 1 irregularities in the striation like echoing region range from 12 7 to 6 8 km in the east west direction and from at least 7 2 to 5 1 km in the north south direction the observational evidences that the slab structure has sharp edges in lateral edges and the type 1 irregularities drift in the meridional direction favor the slab model proposed by haldoupis et al 1996 to account for the excitation of the midlatitude type 1 irregularities however the other observations including considerably large zonal extent of type 1 irregularities in the plasma slab and wide coverage of zonal polarization electric field are unfavorable to the slab model in addition we present conclusive evidence in this article to show that the range variation of backscatter from es irregularities may result directly from the zonal bulk movement of the es irregularities in the echoing region rather than from the height variation of the irregularities therefore great caution should be taken in analyzing the dynamic behavior of es irregularities from range time intensity plot

50 mhz radar observations of mid latitude e region irregularities at camp santiago puerto rico a 50 mhz radar interferometer was used near salinas puerto rico to probe the meter scale e region plasma density irregularities during two campaigns conducted in 1998 during the february april period e region echoing layers were primarily observed between 90 and 100 km heights the layers were typically thin 1 km and unstructured although in several cases short period 90 s layer oscillations were observed during the june july period e region echoes showed more varied characteristics in addition to low altitude layers quasi periodic structures with descending echoing layers were observed at altitudes above 100 km zonal motions detected during descending layer events were at times variable and oscillated between westward and eastward directions while the layer descent rates remained fixed

mineralogy and trace element relative solubility patterns of shallow marine sediments affected by submarine tailings disposal and artisanal gold mining buyat ratototok district north sulawesi indonesia shallow marine sediments of the buyat ratototok district of north sulawesi indonesia are affected by submarine disposal of industrial gold mine tailings and small scale gold mining using mercury amalgamation industrial mine tailings contained 590 660 ppm arsenic 490 580 ppm antimony and 0 8 5 8 ppm mercury electron microprobe survey found both colloidal iron arsenic phases without sulphur and arsenian pyrite in tailings and sites to which tailings had dispersed but only arsenopyrite in sediments affected by artisanal mining antimony in tailings was present as antimony oxides colloidal iron antimony phases colloidal iron antimony phases and stibnite in sediments affected by both types of mining a sequential extraction found that 2 of arsenic held in tailings and tailings contaminated sediments was exchangeable 20 30 was labile including weakly adsorbed carbonate and arsenate bound 20 30 was metastable probably incorporated into iron or manganese oxyhydroxides or strongly adsorbed to silicate minerals and 40 48 was relatively insoluble probably incorporated into sulphides or silicates arsenic in sediments affected by artisanal gold mining was 75 95 relatively insoluble antimony in all sediments was 90 relatively insoluble relative solubility patterns of most other metals did not differ between industrial tailings affected artisanal mining affected areas and fluvial sediments results suggest that submarine tailings disposal is not suitable for refractory carlin like gold deposits because ore processing converts arsenic to forms unstable in anoxic marine sediments

geomorphology of ma adim vallis mars and associated paleolake basins 1 ma adim vallis one of the largest valleys in the martian highlands appears to have originated by catastrophic overflow of a large paleolake located south of the valley heads ma adim vallis debouched to gusev crater 900 km to the north the landing site for the spirit mars exploration rover support for the paleolake overflow hypothesis comes from the following characteristics 1 with a channel width of 3 km at its head ma adim vallis originates at two eastern and western gaps incised into the divide of the 1 1 m km2 enclosed eridania head basin which suggests a lake as the water source 2 the sinuous course of ma adim vallis is consistent with overland flow controlled by preexisting surface topography and structural control is not evident or required to explain the valley course 3 the nearly constant 5 km width of the inner channel through crater rim breaches the anastomosing course of the wide western tributary the migration of the inner channel to the outer margins of bends in the valley s lower reach a medial sedimentary bar 200 m in height and a step pool sequence are consistent with modeled flows of 1 5 106 m3 s peak discharges were likely higher but are poorly constrained by the relict channel geometry 4 small direct tributary valleys to ma adim vallis have convex up longitudinal profiles suggesting a hanging relationship to a valley that was incised quickly relative to the timescales of tributary development 5 the eridania basin had adequate volume between the initial divide and the incised gap elevations to carve ma adim vallis during a single flood 6 the eridania basin is composed of many overlapping highly degraded and deeply buried impact craters the floor materials of the six largest craters have an unusually high internal relief 1 km and slope 0 5 1 5 among degraded martian craters which are usually flat floored long term fluvial sediment transport appears to have been inhibited within these craters and the topography is inconsistent with basaltic infilling 7 fluvial valleys do not dissect the slopes of these deeper crater floor depressions unlike similar slopes that are dissected at higher levels in the watershed these characteristics 6 7 suggest that water mantled at least the lower parts of the eridania basin floor throughout the period of relatively intense erosion early in martian history the lake level increased and an overflow occurred near the close of the noachian age determined using 5 km crater counts initially the eridania basin debouched northward at two locations into the intermediate basin a highly degraded impact crater 500 km in diameter as this intermediate basin was temporarily filled with water erosion took place first along the lower northern reach of ma adim vallis debouching to gusev crater the western overflow point was later abandoned and erosion of the intermediate basin interior was concentrated along the eastern pathway subsequent air fall deposition impact gardening tectonism and limited fluvial erosion modified the eridania basin region so evidence for a paleolake is restricted to larger landforms that could survive post noachian degradation processes

morphometric analysis of martian valley network basins using a circularity function 1 this paper employs a circularity function to quantify the internal morphology of martian watershed basins in margaritifer sinus region and to infer the primary erosional processes that led to their current geomorphologic characteristics and possible climatic conditions under which these processes operated the circularity function describes the elongation of a watershed basin at different elevations we have used the circularity functions of terrestrial basins that were interpreted as having been modified by 1 erosion related to primarily groundwater sapping and 2 erosion related to primarily rainfall and surface run off as well as the circularity functions of cratering basins on the moon in order to formulate discriminant functions that are able to separate the three types of landforms the spatial pattern of the classification of martian basins based on discriminant functions shows that basins that look morphologically similar to terrestrial fluvial basins are mostly clustered near the mainstream at low elevation while those that look morphologically similar to terrestrial basins interpreted as groundwater sapping origin are located near the tributaries and at higher elevation there are more of the latter than the former this spatial distribution is inconsistent with a continuous earth like warm and wet climate for early mars instead it is more aligned with an overall early dry climate punctuated with episodic wet periods alternatively the concentrated erosion in the mainstream could also be caused by a change of water source from rainfall to snowfall or erosion cut through a duricrust layer

character of the alleghanian orogeny in the southern appalachians part iii regional tectonic relations geological and geochronological studies in the eastern piedmont of the southern appalachians have documented a polyphase late paleozoic deformational chronology d 2 d 4 that is contemporaneous with the alleghanian orogeny recorded in the western appalachian foreland the scale and vergence of d 3 anticlinoria in the eastern piedmont are similar to those of anticlinoria in the western appalachians which are related to ramping of underlying thrust surfaces we suggest that the appalachian decollement extends southeastward beneath the entire piedmont province and that all of the piedmont rocks were displaced at least 175 km northwestward relative to north america during the alleghanian orogeny late paleozoic deformational effects in the eastern piedmont thus are considered cogenetic with alleghanian foreland deformation we interpret the alleghanian orogeny to be the result of oblique dextral convergence and collision of gondwana and laurentia

statistical study of midlatitude e region echoes observed by the hokkaido superdarn hf radar statistical characteristics of short range coherent echoes observed by the hokkaido super dual auroral radar network superdarn high frequency hf radar geographic geomagnetic latitude 43 5 n 37 3 n at midlatitudes are investigated we show that the echo occurrence is increased during nighttime and especially strongly during winter and summer during summer the occurrence rates are still large during morning prenoon hours for these periods strong sporadic e layers are observed by the wakkanai ionosonde geographic geomagnetic latitude 45 2 n 39 1 n located in the vicinity of the radar field of view echo occurrence rate does not increase with the planetary magnetic activity characterized by the kp and dst magnetic indices and seasonally anticorrelates with variations of the ap index with respect to the magnetic l shells echoes are seen more frequently in beams oriented almost perpendicular to l shells during summer in beams at intermediate angles during equinoxes and winter and sometimes in beams at the smallest available angles 45 during winter midlatitude echoes are of about the same power as at high latitudes but narrower by a factor of 5 power and spectral width of nighttime echoes increases with doppler velocity consistent with high latitude observations the doppler velocity shows a clear semidiurnal variation the local time of these maxima changes with season it is hypothesised that many hokkaido echoes are received at high magnetic aspect angles of several degrees and they are coming from the lower part of the e region where the irregularity phase velocity is affected by both e b plasma drifts and neutral winds

water or ice in the martian regolith clues from rampart craters seen at very high resolution abstract very high resolution viking orbiter images 8 17 m per pixel have been used to investigate the morphology of martian rampart crater ejecta blankets and the crater interiors with the objective of identifying the fluidizing medium for the ejecta and the physical properties of the target rock the occurrence of well preserved small scale pressure ridges and scour marks evidence for subsidence around isolated buried blocks in partially eroded ejecta lobes and the stability of crater walls and distal ramparts argue for ground ice being the dominant state for volatiles within the target rocks at the time of impact rare examples of channels 190 650 m wide on the surfaces of ejecta blankets and on the inner walls of the crater cerulli indicate that in some instances liquid water was incorporated into the ejecta during its emplacement no morphological evidence has been found to discount the idea that atmospheric effects were partially responsible for ejecta fluidization but it is clear that these effects were not the sole reason for the characteristic lobate deposits surrounding at least some rampart craters on mars

topography of valley networks on mars from mars express high resolution stereo camera digital elevation models 1 martian valley networks have been identified mainly in the noachian heavily cratered uplands the geometry of valley networks can be studied using mars orbiter laser altimeter mola altimetry which is sufficient to map large valleys without a detailed 3 d shape of valley networks imaging from the mars express high resolution stereo camera hrsc is used to generate digital elevation models dems with resolution 50 m and vertical accuracy 60 m we studied valleys near huygens crater and in the aeolis region both in the noachian bedrock and on the west echus plateau in hesperian bedrock hrsc dems in these areas show that 1 drainage density is 3 times higher than is observed in mola data 2 degree of ramification is 1 order more than with mola 3 transverse valley profiles show a v shape more accurately and a minimum depth of 20 m and 4 higher drainage density shows greater headward extension that is not correlated to greater valley depth the deepest valleys 400 m are found in the huygens region where the density in the dem is 0 1 km 1 compared to shallow valleys 100 m of the echus region where the density is higher 0 3 km 1 these regional differences are due to spatially variable preservation and bedrock lithology longitudinal profiles suggest variations in duration of activity profile concavity is only developed in some noachian terrains valleys visible in hrsc images correspond to topographic features in dems showing the same geometry as terrestrial valleys thought to be formed by overland flows and seepage

possible precipitation of ice at low latitudes of mars during periods of high obliquity most of the old cratered highlands of mars are dissected by branching river valleys that appear to have been cut by running water1 2 yet liquid water is unstable everywhere on the martian surface in the equatorial region where most of the valleys are observed even ice is unstable3 4 it has been suggested therefore that mars had an early denser atmosphere with sufficient greenhouse warming to allow the existence of liquid water5 here we suggest instead that during periods of very high obliquities ice could accumulate at low latitudes as a result of sustained sublimation of ice from the poles and transport of the water vapour equatorwards at low latitudes the water vapour would saturate the atmosphere and condense onto the surface where it would accumulate until lower obliquities prevailed the mechanism is efficient only at the very high obliquities that occurred before formation of tharsis very early in the planet s history but limited equatorial ice accumulation could also have occurred at the highest obliquities during the rest of the planet s history partial melting of the ice could have provided runoff to form the channels or replenish the groundwater system

origin of the valley networks on mars a hydrological perspective abstract the geomorphology of the martian valley networks is examined from a hydrological perspective for the compatibility with an origin by rainfall globally higher heat flow and localized hydrothermal systems comparison of morphology and spatial distribution of valleys on geologic surfaces with terrestrial fluvial valleys suggests that most martian valleys are probably not indicative of a rainfall origin nor are they indicative of formation by an early global uniformly higher heat flow in general valleys are not uniformly distributed within geologic surface materials as are terrestrial fluvial valleys valleys tend to form either as isolated systems or in clusters on a geologic surface unit leaving large expanses of the unit virtually untouched by erosion with the exception of fluvial valleys on some volcanoes most martian valleys exhibit a sapping morphology and do not appear to have formed along with those that exhibit runoff morphology in contrast terrestrial sapping valleys form from and along with runoff valleys the isolated or clustered distribution of valleys suggests localized water sources were important in drainage development persistent groundwater outflow driven by localized but vigorous hydrothermal circulation associated with magmatism volcanism impacts or tectonism is however consistent with valley morphology and distribution snowfall from sublimating ice covered lakes or seas may have provided an atmospheric source of water for the formation of some valleys in regions where the surface is easily eroded and where localized geothermal hydrothermal activity is sufficient to melt accumulated snowpacks

vertical accumulation of potential toxic elements in a semiarid system that is influenced by an abandoned gold mine abstract the mining zone at el triunfo baja california sur mexico was exploited for gold extraction for 200 years this area includes more than 100 abandoned mining sites these sites contain mine tailings that are highly contaminated with potential toxic elements pte such as as cd pb sb zn and other associated elements over time these wastes have contaminated the sediments in the adjacent fluvial systems our aim was to assess the vertical pte variations in the abandoned mining zone and in the discharge of the main arroyo into a small lagoon at the pacific ocean sediments were collected from the two following locations in the mining zone near the arroyo basin tailings 1 an old alluvial terrace overbank and a test pit tp and 2 two sediment cores locations at the arroyo discharge into a hypersaline small lagoon samples were analyzed by icp ms icp oes and inaa and the methods were validated the overbank was the most contaminated and had as cd pb sb and zn concentrations of 8690 226 84 700 17 400 and 42 600 mg kg 1 respectively which decreased with depth in addition the tp contained elevated as cd pb sb and zn concentrations of 694 18 8 5001 39 2 and 4170 mg kg 1 respectively the sediment cores were less contaminated however the as cd pb sb and zn concentrations were greater than the concentrations that are generally found in the earth s crust the normalized enrichment factors nefs which were calculated from the background concentrations of these elements in the system showed that extremely severe as cd pb sb and zn nef 50 enrichment occurred at the overbank the tp was severe to very severely enriched with as cd pb sb and zn nef 10 50 the sediment cores had a severe enrichment of as pb and zn nef 10 25 their vertical profiles showed that anthropogenic influences occurred in the historic sediment deposition at the overbank and tp and in the sediment cores in addition the as pb and zn concentrations in the sediment cores were related to the deposition of fine sediments and organic carbon

the structure and evolution of ancient impact basins on mars the number of martian impact basins once thought deficient owing to a low number of impactors has been significantly increased through the identification of structural imprints that remain even after nearly complete erasure of basin massifs five ancient multiringed impact basins were selected for detailed study and exhibit a systematic pattern of rejuvenation of the multiring plan through endogenic modification concentric zones of unstable terrain are believed to reflect deep seated impact related fractures that have localized regional igneous processes in a manner analogous with the basin controlled distribution of basalts on the moon most martian outflow channels were found to originate along the unstable ring zones hydrothermal melting and temporary confinement of channel source materials at sites analogous to lunar sinuous rille source regions are proposed to play an important role in the distribution of martian outflow channels ancient basins also can be delineated by the concentric pattern of topographically and structurally controlled narrow valley networks that are particularly abundant along the outer rings where basin ejecta deposits occur remnant massifs and scarps commonly exhibit extensive furrowing by narrow valley networks perhaps due to a different paleoclimate or sapping during a period of geothermal melting of trapped ices the systematic patterns of valley networks stable and unstable annuli scarps and massifs provide bases for interpreting impact structure in general and for recognizing multiringed structures elsewhere the chryse basin in particular is proposed to represent a major multiringed structure that controlled the formation and distribution of eastern valles marineris and the chaotic terrains of margaritifer sinus in response to volcanism tectonism related to tharsis we conclude that 1 mars is probably not deficient in large body impactors 2 the multiring patterns of basins represent deep seated fracture zones that can be reexposed through subsequent volcanism hydrothermal activity sapping and differential erosion 3 many martian terrains and features e g chaotic terrains and outflow channels are controlled by ancient basins and 4 the resurrection and destruction of impact basins reveal an important third dimension depth for interpreting impact basin formation

origin of planetary wrinkle ridges based on the study of terrestrial analogs wrinkle ridges linear asymmetric topographic highs are common physiographic features on the moon mars and mercury we describe here some terrestrial features of similar morphology and scale that have formed under compressional stress systems similar to planetary wrinkle ridges all of the terrestrial analogs are produced by the anticlinal folding of rocks above reverse faults that shallow and typically break the surface characteristics common to both terrestrial and planetary ridges include 1 a linear asymmetric antiformal shape 2 tension cracks and grabens along the hinges of the antiform 3 overlapping en echelon lobes 4 reversals of the sense of asymmetry along strike 5 occurrence in compressional environments and 6 similarity to features produced during compression of various materials in laboratory scale models these similarities strongly suggest that planetary wrinkle ridges result from deformation associated with shallow thrust faults that either break or come close to the surface kinematic models capable of explaining the development of wrinkle ridges include 1 anticlinal folding of rocks over a buried thrust fault that may subsequently propagate to the surface and 2 fault bend folding of upper plate rocks over the surface flattening bend of a thrust fault

joint observations of sodium enhancements and field aligned ionospheric irregularities resonance lidar observations of neutral sodium and vhf coherent scatter radar observations of field aligned 3 meter irregularities were obtained during the coqui ii rocket campaign in puerto rico the lidar a facility instrument at the arecibo observatory 18 3 n 66 8 w and the university of illinois radar located near salinas on the south of the island both monitored volumes near where the uplegs of the nominal rocket trajectories intersected the e region the observatory s incoherent scatter radar was also used to characterize the plasma layers preliminary investigation of the data sets has shown a potential correspondence between vhf backscatter from plasma layers and a new class of characteristic enhancements in the neutral sodium

analysis of a mid latitude e region lqp event observed during the coqui 2 campaign 1 arecibo isr observations and vhf coherent backscatter data collected with a radar situated in southern puerto rico are examined to understand the causes of quasi periodic variations in vhf returns from lower e region heights 93 km it is found that bragg scale density irregularities causing the observed vhf backscatter are formed and propagated horizontally in a density perturbation field localized at the upper boundary of a tidal ion layer the density perturbation has a 7 km horizontal wavelength propagates in southwest direction and it is not aligned with the geomagnetic field thus the production mechanism of the observed density perturbation cannot be the gradient drift instability often invoked to account for the generation of mid latitude sporadic e radar echoes nevertheless secondary gradient drift instability operating on the gradients of the southwest propagating perturbation remains the most likely cause of bragg scale electron density waves responsible for the vhf returns

low altitude quasi periodic radar echoes observed by the gadanki vhf radar 1 we report here on the low altitude quasi periodic lqp radar echoes from low latitude sporadic e layer es observed by the gadanki 13 5 n 79 2 e geomagnetic latitude 6 3 n vhf radar the lqp echoes occurred both during daytime and nighttime and are confined to a slowly descending layer with a thickness of about 2 4 km in the height range of 90 100 km the periods are found to range from tens of seconds to less than about 3 minutes the doppler velocities vary over a range of 20 to 20 m s during daytime and 0 to 10 m s during nighttime and are known to be sensitive to the layer height being dominated by the effect of zonal electric field above and meridional neutral wind below a height of 97 km for the type 2 irregularities krishna murthy et al 1998 the spectral widths are found to be of the order of 50 to 75 m s during daytime and 30 to 60 m s during nighttime the lqp echoes reported here are similar to that observed recently over midlatitudes rao et al 2000 urbina et al 2000 but distinctly different from the widely reported quasi periodic qp echoes occurring at higher altitudes 100 km the observations are discussed briefly in terms of the potential source mechanisms

mars a water rich planet abstract mars had outgassed at least 0 5 to 1 km of water 10 to 20 bar of co2 and 0 1 to 0 3 bar of n2 the volatiles that have been retained are mostly in the cratered uplands terrain softening fretted channels debris flows and closed depressions indicate that at least the upper 2 km of the cratered uplands at high latitudes 30 contain ice in amounts that exceed the porosity estimated to be 10 20 theoretical studies and lack of these features in the cratered uplands at low latitudes suggest that the upper 1 km of the uplands at low latitudes is ice poor however valley networks indicate that water was present near the surface early in the planet s history although in amounts smaller than at high latitudes the entire upper 1 km planetwide is estimated to have contained 75 125 m of water at the end of heavy bombardment the largest sink for water is the megaregolith below 1 km episodic eruption of water from the deep megaregolith cut many of the large outflow channels from the volume of water needed to cut the circum chryse channels and assuming uniform planetwide distribution of water the deep megaregolith is estimated to have contained at least 350 m of water at the end of heavy bombardment thereby giving a total minimum inventory of 424 475 m planetwide most of the water lost from the low latitude uplands by diffusion and in cutting the valley networks is now believed to be in the polar layered terrains most of the water involved in cutting the outflow channels is in the low lying northern plains where a variety of features that have been attributed to ground ice is present a large fraction of the planet s surface has been overplated with water poor volcanics of which we have samples in the snc meteorites the younger volcanics have reacted extensively with the old volatile rich basement some of the co2 and n2 outgassed was lost during heavy bombardment by impact erosion of the atmosphere and other processes the remaining was fixed carbonates and folded deep into the megaregolith during heavy bombardment

crater size frequency distributions and a revised martian relative chronology a revised martian relative chronology is determined which dates geologic units with respect to the end of the period of heavy bombardment this analysis differs from previous studies by using viking 1 2m photomosaics to map all 25 826 craters 8km diameter which postdate the lithologic units making up the martian surface the relative plotting technique is used because it shows changes in the shape and density of the crater size frequency distribution curves more clearly than cumulative plots the changes in shapes of the distribution curves are interpreted to be due to two different impacting populations one dominating during the heavy bombardment period and the other emplaced during the post heavy bombardment period the 8 km diameter limit was chosen to exclude the majority of secondary craters and to minimize obliteration effects acting over the age of the planet the results obtained are average ages valid for units with typical thicknesses between about 1 and 3 km and extending over an area of about 105 km2 the shapes and densities of the crater distribution curves indicate that approximately 60 of the martian lithologic units in which these craters occur formed during the period of heavy bombardment many of the small volcanoes those generally less than 200 km diameter including most in the tharsis and elysium regions date from this period the hellas and argyre impacts bracket the average age of the intercrater plains in the highlands the ridged plains distribution curves indicate formation during the period of heavy bombardment but their lower crater density indicates that they are the last geologic unit to retain the scars from this population of impactors they therefore likely formed near the end of heavy bombardment the remaining 40 of martian terrain units show distribution curves indicative of emplacement since the end of heavy bombardment the wide range in crater densities among different regions of plains indicate a range in formation ages although the general view of martian geologic evolution does not differ significantly from previous studies the present analysis explicitly states the relationship of numerous geologic units to the period of heavy bombardment and has revised the relative ages of localized regions across mars

heavy metal concentrations in marine sediments impacted by a mine tailings spill marinduque island philippines a mine tailings spill occurred on the island of marinduque philippines on 24 march 1996 originating from the marcopper mine tailings sludge flowed down the boac river abruptly and during subsequent storm events most of the tailings material has since accumulated in the nearshore environment along the western coast of the island nineteen sediment cores were collected from this site and analyzed for heavy metals elevated concentrations of cu 706 3 080 ppm mn 445 1 060 ppm pb 43 56 ppm and zn 131 276 ppm are present in the tailings two horizons of high metal concentrations in the marine sediment profile are interpreted to correspond to two distinct tailings input events the lower horizon corresponds to the original 1996 spill whereas the spike near the surface is thought to be a combination of input due to dredging of the river in 1997 and reworking of sediments a previous history of contamination is also deduced from the metal profiles the volume of tailings material released into the marine environment due to the spill is estimated to be 180 000 to 260 000 m3

small martian valleys pristine and degraded morphology the equatorial heavily cratered uplands of mars are dissected by two classes of small valleys that are intimately associated in compound networks pristine valleys with steep valley walls preferentially occupy downstream portions of compound basins degraded valleys with eroded walls are laterally more extensive and have higher drainage densities than pristine valleys morphometric and crater counting studies indicate that relatively dense drainage networks were emplaced on mars during the heavy bombardment about 4 0 b y ago over a period of approximately 10 sup 8 years these networks were degraded and subsequently invaded by headwardly extending pristine valleys the pristine valleys locally reactivated the compound networks probably through sapping processes dependent upon high water tables fluvial activity in the heavily cratered uplands generally ceased approximately 3 8 3 9 b y ago coincident with the rapid decline in cratering rates the relict compound valleys on mars are morphometrically distinct from most terrestrial drainage systems the differences might be caused by a martian valley formation episode characterized by hyperaridity by inadequate time for network growth by very permeable rock types or by a combination of factors

mid latitude e region field aligned irregularities observed with the mu radar fine structures e region field aligned irregularities were observed on june 24 25 1989 with the mu radar at shigaraki japan 34 9 n 136 1 e geomagnetic latitude 25 0 n the 3 2 m scale irregularities were observed with the mu radar in five main beam directions each of which was nearly perpendicular to the geomagnetic field at 100 km altitude doppler spectra were obtained every 20 s with a range resolution of 600 m field perpendicular echoes appeared from 2130 to 2330 lt and from 0400 to 1100 lt times that correspond to postsunset and postsunrise period in the e region a preliminary examination of the doppler spectra indicates spectral widths of 50 120 m s 1 and the mean doppler velocities are well below the ion acoustic speed these spectral characteristics are consistent with those obtained in the equatorial and auroral electrojets and have been attributed to the gradient drift instability the echoes observed during the postsunset and postsunrise periods showed quite different morphologies in the time height distribution for this reason they are classified into two types continuous and quasi periodic the appearance of the continuous echoes was mainly continuous in time and situated between 90 and 100 km altitude during the postsunrise period the appearance of the quasi periodic echoes was intermittent with periods of 5 10 min and situated above 100 km altitude during the postsunset period the quasi periodic echoes showed phase propagation toward the radar while the averaged mean doppler velocity was away from the radar by measuring the time delays in echo regions from five directions an apparent westward motion approximately 120 m s 1 of the irregularity regions was estimated

lava flows on mars analysis of small surface features and comparisons with terrestrial analogs small scale surface features on lava flows provide information on the eruption parameters and the volcanic history of the flows in which they occur high resolution images of four sites on mars reveal lava flows with a different type or combination of features including pressure ridges tumuli festoon ridges and ring ridges pressure ridges tumuli and pressure plateaus are spaced irregularly and tend to be oriented parallel to flow they are formed by inflation of small flow lobes and are indicative of compound flows emplaced by sporadic eruptions with low effusion rates festoon ridges are oriented transverse to flow direction mimic the flow margin and have a regular spacing using a model by fink and fletcher 1978 and fink 1980 a interior viscosity values of approximately 108 pa s were calculated for festoon ridges tens to hundreds of meters apart and a few meters high on two basalt flows in iceland and a flow on mars this viscosity is comparable to results from similar studies of more silicic flows and suggests that high viscosities are necessary to form large festoon ridges by analogy to the icelandic flows martian flows containing festoon ridges are considered to be large single unit basalt flows emplaced through flood style eruptions high viscosity of the basaltic flows may result from cooling a high crystal content or low effusion temperatures disruption of the surface of some of these large sheet flows possibly by lava water interaction is suggested by the presence of ring ridges and rugged terrain consisting of mesa like mounds and channel like troughs

martian cratering revisited implications for early geologic evolution improved crater statistics from varied martian terrains are compared to lunar crater populations the distribution functions for the average martian cratered terrain and the average lunar highlands over the diameter range 8 2000 km are quite similar the martian population is less dense by approximately 0 70 from 8 to 256 km diameter and diverges to proportionally lower densities at greater diameters crater densities on martian pure terra give a lower limit to the mars moon integrated crater flux of 0 75 since the last stabilization of the respective planetary crusts the crater population 8 km diameter postdating the martian northern plains is statistically indistinguishable from that population postdating the lunar maria monte carlo simulations were performed to constrain plausible mechanisms of crater obliteration the models demonstrate that if the crater density difference between the lunar and martian terra has been due to resurfacing processes random intercrater plains formation cannot be the sole process if plains preferentially form in and obliterate larger craters then the observed martian distribution retains its shape as the crater density decreases this result is consistent with the morphology of martian intercrater plains