Modelling Esker Formation on Mars

Introduction:&#160; Eskers are sinuous sedimentary ridges that are widespread across formerly glaciated landscapes on Earth. They form when sediment in subglacial tunnels is deposited by meltwater. Some sinuous ridges on Mars have been identified as eskers; whilst some are thought to have formed early in Mars&#8217; history beneath extensive ice sheets, smaller, younger systems associated with extant glaciers in Mars&#8217; mid latitudes have also been identified. Elevated geothermal heating and formation during periods with more extensive glaciation have been suggested as possible prerequisites for recent Martian esker deposition.Here, we adapt a model of esker formation with g and other constants altered to Martian values, using it initially to investigate the impact of Martian conditions on subglacial tunnel systems, before investigating the effect of varying water discharge on esker deposition.Methods: To investigate the effect of these values on the operation of subglacial tunnel systems we first conduct a series of model experiments with steady water discharge, varying the assumed liquid density (rw) from 1000 kgm-3 to 1980 kgm-3 (the density of saturated perchlorate brine) and ice hardness (A) from 2.4x10-24 Pa-3s-1 to 5x10-27 Pa-3s-1 (a temperature range of 0&#176;C to -50&#176;C). We then investigate the impact of variable water discharge on esker formation to simulate very simply a possible release of meltwater from an assumed geothermal event beneath a Martian glacier or ice cap.Results and Discussion:&#160; A key aspect of model behaviour is the decrease in sediment carrying capacity towards the ice margin due to increased tunnel size as ice thins. Our results suggest that Martian parameters emphasise this effect, making deposition more likely over a greater length of the conduit. Lower gravity has the largest impact; it reduces the modeled closure rate of subglacial tunnels markedly as this varies with overburden stress (and hence g) cubed. Frictional heating from flowing water also drops, but much less sensitively. Thus, for a given discharge, the tunnels tend to be larger, leading to lower water pressure and a reduction in flow power. This effect is amplified for harder ice. Higher inferred fluid density raises the flow power, but by a smaller amount.These effects are clearly seen in the variable discharge experiments. Sediment is deposited on the falling limb of the hydrograph, when the tunnels are larger than the equivalent steady-state water discharge would produce. Sediment deposition occurs much further upglacier from the glacier snout, and occurs earlier on the falling limb leading to longer periods in which deposition occurs.Conclusions: Our results suggest that esker formation within a subglacial meltwater tunnel would be&#160;more likely on Mars than Earth, primarily because subglacial tunnels tend to be larger for equivalent water discharges, with consequent lower water flow velocities. This allows sediment deposition over longer lengths of tunnel, and to greater depths, than for terrestrial systems. Future work will use measured bed topography of a mid-latitude esker to assess the impact of topography on deposition patterns and esker morphology, and we will expand the range of discharges and sediment supply regimes investigated.

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Middle Holocene environmental reconstruction and climatic inferences through multi-proxy records from Seymareh lake sediments (Zagros Mts., Iran)

10.5194/egusphere-egu21-12511 ◽

2021 ◽

Author(s):

Michele Delchiaro ◽

Giulia Iacobucci ◽

Francesco Troiani ◽

Marta Della Seta ◽

Paolo Ballato ◽

...

Keyword(s):

Sedimentation Rate ◽

Water Discharge ◽

Sediment Supply ◽

Grain Size Analysis ◽

Size Analysis ◽

The Holocene ◽

Middle Holocene ◽

Lake System ◽

Proxy Records ◽

The Impact

The Seymareh landslide is the largest rock slope failure (44&#8201;Gm3) ever recorded on the exposed Earth surface. It detached &#8764;10&#8201;ka BP from the northeastern flank of the Kabir-Kuh anticline (Zagros Mts., Iran) originating the natural dam responsible for the formation of a three-lake system (Seymareh, Jaidar, and Balmak lakes, with an area of 259, 46, and 5 km2, respectively). The lake system persisted for &#8764;3000 yr during the Holocene before its emptying phase due to overflow. A sedimentation rate of 21&#8201;mm&#8201;yr&#8722;1 was estimated for the Seymareh lacustrine deposits, which increased during the early stage of lake emptying because of enhanced sediment yield from the lake tributaries.&#160;To reconstruct the climatic and environmental impact on the lake infilling, we reviewed the geomorphology of the basins and combined the results with multi-proxy records from a 30 m thick lacustrine sequence in Seymareh Lake. Major analyses comprise grain size analysis, carbon and oxygen stable isotopes of carbonate-bearing sediments, and X-ray diffraction analysis of clay minerals.Lake overflowing is largely accepted as the main response to variations in water discharge and sediment supply since the alternation from dry to wet phases enhances sediment mobilization along hillslopes decreasing the accommodation space in the downstream sedimentary basins. In this regard, during the early-middle Holocene, the Seymareh area, as well as the entire Middle East, was affected by short-term climate changes at the millennial-scale, as testified by both paleoecological and archaeological evidence. Indeed, several records from Iranian lakes (i.e., Mirabad, Zeribar, Urmia) well documented the temperature and the moisture conditions of the western Zagros Mountains during the Holocene. During the early Holocene, the precipitation remained low up to 6 ka BP, reaching the driest condition around 8-8.2 ka BP. The impact of this abrupt climate change is evident across West Asia, where the first large villages with domesticated cereals and sheeps disappeared, converting to small hamlets and starting habitat-tracking. As regards the Seymareh area, a more irregular distribution of rainfalls and their increasing seasonality may support rhexistasy conditions, during which the scarce vegetation cover enhances both the hillslope erosion and sedimentation rate in the basins, most likely contributing to the overflow of Seymareh Lake.&#160;

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Efficacy of bedrock erosion by subglacial water flow

Earth Surface Dynamics Discussions ◽

10.5194/esurfd-3-849-2015 ◽

2015 ◽

Vol 3 (3) ◽

pp. 849-908 ◽

Cited By ~ 2

Author(s):

F. Beaud ◽

G. E. Flowers ◽

J. G. Venditti

Keyword(s):

Water Flow ◽

Water Pressure ◽

Water Discharge ◽

Sediment Supply ◽

Fluvial Systems ◽

Glacial Meltwater ◽

Erosion Rates ◽

Subglacial Environment ◽

Basin Scale ◽

Bedrock Erosion

Abstract. Bedrock erosion by sediment-bearing subglacial water remains little-studied, however the process is thought to contribute to bedrock erosion rates in glaciated landscapes and is implicated in the excavation of tunnel valleys and the incision of inner gorges. We adapt physics-based models of fluvial abrasion to the subglacial environment, assembling the first model designed to quantify bedrock erosion caused by transient subglacial water flow. The subglacial drainage model consists of a one-dimensional network of cavities dynamically coupled to one or several Röthlisberger channels (R-channels). The bedrock erosion model is based on the tools and cover effect, whereby particles entrained by the flow impact exposed bedrock. We explore the dependency of glacial meltwater erosion on the structure and magnitude of water input to the system, the ice geometry and the sediment supply. We find that erosion is not a function of water discharge alone, but also depends on channel size, water pressure and on sediment supply, as in fluvial systems. Modelled glacial meltwater erosion rates are one to two orders of magnitude lower than the expected rates of total glacial erosion required to produce the sediment supply rates we impose, suggesting that glacial meltwater erosion is negligible at the basin scale. Nevertheless, due to the extreme localization of glacial meltwater erosion (at the base of R-channels), this process can carve bedrock (Nye) channels. In fact, our simulations suggest that the incision of bedrock channels several centimetres deep and a few meters wide can occur in a single year. Modelled incision rates indicate that subglacial water flow can gradually carve a tunnel valley and enhance the relief or even initiate the carving of an inner gorge.

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Reconstructions of past sediment and water discharges from fluvial-fill terraces in the southern Central Andes of NW Argentina

10.5194/egusphere-egu2020-4887 ◽

2020 ◽

Author(s):

Stefanie Tofelde ◽

Taylor Schildgen ◽

Andrew Wickert ◽

Manfred Strecker ◽

Ricardo Alonso

Keyword(s):

Water Discharge ◽

Central Andes ◽

Climatic Conditions ◽

Sediment Supply ◽

Fluvial Terraces ◽

Sediment Routing ◽

Pleistocene Climate ◽

Combining Data ◽

Southern Central ◽

The Impact

Alluvial river long profiles continually adjust to their water discharge (Qw) and sediment supply (Qs). Qw and Qs are in turn functions of local climatic and tectonic conditions. Hence, changes in the prevailing tectonic or climatic conditions will trigger adjustments to channel long profiles, either by channel incision into previously deposited sediments or by sediment deposition. Because fluvial terraces are abandoned floodplains that preserve ancient river elevation profiles formed from past Qs and Qw, they store information on past climatic or tectonic conditions.&#160;In NW Argentina, reconstructions of Pleistocene climate are sparse due to the limited availability of paleo-climatic records, such as stable isotope data from speleothems or lake cores. However, many intermontane basins within the Southern Central Andes of NW Argentina are characterized by multiple generations of fluvial-fill terraces, some of which date back several tens to hundreds of thousands of years. Here, we show that these geomorphic units provide an opportunity to extract information about paleo-climatic conditions.&#160;A combination of several geochronological techniques has revealed the history of a >200-m-thick fluvial-fill terrace sequence within the Quebrada del Toro. The terrace sequence experienced alternating episodes of incision and aggradation since at least 500 ka. Subsequent terrace surfaces appear to have formed following a cyclicity of ca. 100 kyr. From detrital sediment within those fill terraces, past Qs could be reconstructed for times of sediment aggradation based on cosmogenic 10Be concentrations. The analyses revealed that over the last ~500 kyr Qs has varied at most by a factor of 4, but overall has been relatively constant. As the slope of a river channel (and likewise, the slope of a well preserved terrace surface) is a function of incoming Qs and Qw, combining data of terrace slope and past Qs allowed us to reconstruct past Qw for the times represented by the ages of the terrace surfaces, which mark the onset of river incision. The analyses revealed that during these times, Qw was 10 to 80% higher than today. The results are in line with the few existing quantitative estimates of past precipitation changes in the Central Andes, but have the advantage of extending further back in time. Moreover, the widespread occurrence of fluvial-fill terraces throughout the Central Andes offers the opportunity to reconstruct past Qw with high spatial resolution, offering a new perspective regarding the impact of past climate changes on the sediment-routing system through space and time.

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Efficacy of bedrock erosion by subglacial water flow

Earth Surface Dynamics ◽

10.5194/esurf-4-125-2016 ◽

2016 ◽

Vol 4 (1) ◽

pp. 125-145 ◽

Cited By ~ 15

Author(s):

F. Beaud ◽

G. E. Flowers ◽

J. G. Venditti

Keyword(s):

Water Flow ◽

Water Pressure ◽

Water Discharge ◽

Sediment Supply ◽

Fluvial Systems ◽

Glacial Meltwater ◽

Erosion Rates ◽

Subglacial Environment ◽

Basin Scale ◽

Bedrock Erosion

Abstract. Bedrock erosion by sediment-bearing subglacial water remains little-studied; however, the process is thought to contribute to bedrock erosion rates in glaciated landscapes and is implicated in the excavation of tunnel valleys and the incision of inner gorges. We adapt physics-based models of fluvial abrasion to the subglacial environment, assembling the first model designed to quantify bedrock erosion caused by transient subglacial water flow. The subglacial drainage model consists of a one-dimensional network of cavities dynamically coupled to one or several Röthlisberger channels (R-channels). The bedrock erosion model is based on the tools and cover effect, whereby particles entrained by the flow impact exposed bedrock. We explore the dependency of glacial meltwater erosion on the structure and magnitude of water input to the system, the ice geometry, and the sediment supply. We find that erosion is not a function of water discharge alone, but also depends on channel size, water pressure, and sediment supply, as in fluvial systems. Modelled glacial meltwater erosion rates are 1 to 2 orders of magnitude lower than the expected rates of total glacial erosion required to produce the sediment supply rates we impose, suggesting that glacial meltwater erosion is negligible at the basin scale. Nevertheless, due to the extreme localization of glacial meltwater erosion (at the base of R-channels), this process can carve bedrock (Nye) channels. In fact, our simulations suggest that the incision of bedrock channels several centimetres deep and a few metres wide can occur in a single year. Modelled incision rates indicate that subglacial water flow can gradually carve a tunnel valley and enhance the relief or even initiate the carving of an inner gorge.

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Metal Contamination of Stream Waters under the Impact of Tanneries

Pesquisas em Geociências ◽

10.22456/1807-9806.19514 ◽

2006 ◽

Vol 33 (2) ◽

pp. 55 ◽

Cited By ~ 1

Author(s):

MARIA LUCIA KOLOWSKI RODRIGUES ◽

MILTON LUIZ LAQUINTINIE FORMOSO

Keyword(s):

Water Quality ◽

Water Discharge ◽

Solid Material ◽

Total Variance ◽

Oxygen Conductivity ◽

Contamination Degree ◽

Iron Aluminum ◽

Relevant Variables ◽

Stream Waters ◽

The Impact

This study evaluated the contamination of water samples from Cadeia and Feitoria rivers (Rio Grande do Sul State, Brazil), affected by tannery activities. From July 1999 to April 2000, four sampling campaigns were performed at ten sites in order to evaluate selected metals and ancillary physicochemical variables. Sample preservation and analyses followed recommendations of the Standard Methods. Factor analysis was used to obtain statistical indexes representing the contamination degree of waters evaluated. The information was summarized in two principal components. The first, which accounted for 50% of the total variance, was associated to a tannery contribution and generated a contamination index. Total, Suspended and Dissolved Solids, Dissolved Oxygen, Conductivity, Chromium, Manganese, Copper, Nickel, Sodium, Calcium, Potassium, and Magnesium were the well-correlated variables with this first component. The water quality decreased from headwaters up to mouth along both streams, but the most contaminated sites were located at the lower reach of Feitoria river (Ivoti and Lindolfo Collor cities), where tanneries are concentrated. After the entrainment of Feitoria waters (São Sebastião do Caí municipality), Cadeia river also presented an increased contamination degree. The application of statistical randomization tests highlighted these same sites as significantly distinct from the others. Water contamination also showed association to flow variations, and a poorer water quality was observed during the dry period (January). The second component, in which Iron, Aluminum, and Suspended Solids were the relevant variables, was loaded with 15% of the total variance. It was linked to natural events, since higher factor scores in this component were obtained during a period of increased water discharge (October), which caused resuspension and entrainment of solid material to the rivers bed. As a final result of the study, sampling stations were classified according to the contamination degree, and graphically represented on a basin map, which synthesized the environmental diagnosis.

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A general theory of glacier surges

Journal of Glaciology ◽

10.1017/jog.2019.62 ◽

2019 ◽

Vol 65 (253) ◽

pp. 701-716 ◽

Cited By ~ 15

Author(s):

D. I. Benn ◽

A. C. Fowler ◽

I. Hewitt ◽

H. Sevestre

Keyword(s):

General Theory ◽

Frictional Heating ◽

Element Model ◽

Geothermal Heating ◽

Lumped Element ◽

Systems Model ◽

Flow Speeds ◽

Glacier Surges ◽

Lumped Element Model ◽

Polythermal Glacier

AbstractWe present the first general theory of glacier surging that includes both temperate and polythermal glacier surges, based on coupled mass and enthalpy budgets. Enthalpy (in the form of thermal energy and water) is gained at the glacier bed from geothermal heating plus frictional heating (expenditure of potential energy) as a consequence of ice flow. Enthalpy losses occur by conduction and loss of meltwater from the system. Because enthalpy directly impacts flow speeds, mass and enthalpy budgets must simultaneously balance if a glacier is to maintain a steady flow. If not, glaciers undergo out-of-phase mass and enthalpy cycles, manifest as quiescent and surge phases. We illustrate the theory using a lumped element model, which parameterizes key thermodynamic and hydrological processes, including surface-to-bed drainage and distributed and channelized drainage systems. Model output exhibits many of the observed characteristics of polythermal and temperate glacier surges, including the association of surging behaviour with particular combinations of climate (precipitation, temperature), geometry (length, slope) and bed properties (hydraulic conductivity). Enthalpy balance theory explains a broad spectrum of observed surging behaviour in a single framework, and offers an answer to the wider question of why the majority of glaciers do not surge.

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Greenland land-terminating glaciers velocity trends during the last two decades

10.5194/egusphere-egu21-2084 ◽

2021 ◽

Author(s):

Paul Halas ◽

Jeremie Mouginot ◽

Basile de Fleurian ◽

Petra Langebroek

Keyword(s):

Water Pressure ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Melting ◽

Limited Area ◽

Ice Dynamics ◽

Basal Sliding ◽

Surface Melt ◽

Ice Sheet Dynamics ◽

The Impact

<div> Ice losses from the Greenland Ice Sheet have been increasing in the last two decades, leading to a larger contribution to the global sea level rise.&#160;Roughly 40% of the contribution comes from ice-sheet dynamics, mainly regulated by basal sliding.&#160;The sliding component&#160;of glaciers has been observed to be strongly related to surface melting, as water&#160;can eventually&#160;reach the bed and impact&#160;the subglacial water pressure, affecting the basal sliding.&#160;&#160; </div><div> The link between ice velocities and surface melt on multi-annual time scale is still not totally understood&#160;even though it&#160;is of major importance with expected increasing surface melting.&#160;Several studies showed&#160;some&#160;correlation between an increase in surface melt and a slowdown in&#160;velocities, but&#160;there is no&#160;consensus&#160;on those trends.&#160;Moreover&#160;those&#160;investigations&#160;only&#160;presented results&#160;in a limited area over&#160;Southwest&#160;Greenland.&#160;&#160; </div><div> Here we present the ice motion over many land-terminating glaciers on the Greenland Ice Sheet for the period 2000 - 2020. This type of glacier is ideal for studying processes at the interface between the bed and the ice since they are exempted from interactions with the sea while still being relevant for all glaciers since they share the same basal friction laws. The velocity data was obtained using optical Landsat 7 & 8 imagery and feature-tracking algorithm. We attached importance keeping the starting date of our image pairs similar, and avoided stacking pairs starting before and after melt seasons, resulting in multiple velocity products for each year.&#160;&#160; </div><div> Our results show similar velocity trends for previously studied areas with a slowdown until 2012 followed by an acceleration.&#160;This trend however does not seem to be observed on the whole ice sheet and is probably&#160;specific&#160;to&#160;this region&#8217;s&#160;climate forcing.&#160; </div><div> Moreover comparison between ice velocities from different parts of Greenland allows us to observe the impact of different climatic trends on ice dynamics. </div>

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Feasibility of sedimentation strategies for the Mekong delta to counterbalance relative sea-level rise

10.5194/egusphere-egu21-5140 ◽

2021 ◽

Author(s):

Frances E. Dunn ◽

Philip S. J. Minderhoud

Keyword(s):

Land Use ◽

Sea Level Rise ◽

Sea Level ◽

Mekong Delta ◽

Sediment Deposition ◽

Sediment Supply ◽

Sediment Flux ◽

Relative Sea Level ◽

Fluvial Sediment ◽

Relative Sea Level Rise

As one of the largest deltas in the world, the Mekong delta is home to over 17 million people and supports internationally important agriculture. Recently deposited sediment compacts and causes subsidence in deltas, so they require regular sediment input to maintain elevation relative to sea level. These processes are complicated by human activities, which prevent sediment deposition indirectly through reducing fluvial sediment supply and directly through the construction of flood defence infrastructure on deltas, impeding floods which deliver sediment to the land. Additionally, anthropogenic activities increase the rate of subsidence through the extraction of groundwater and other land-use practices.This research shows the potential for fluvial sediment delivery to compensate for sea-level rise and subsidence in the Mekong delta over the 21st century. We use detailed elevation data and subsidence scenarios in combination with regional sea-level rise and fluvial sediment flux projections to quantify the potential for maintaining elevation relative to sea level in the Mekong delta. We present four examples of localised sedimentation scenarios in specific areas, for which we quantified the potential effectiveness of fluvial sediment deposition for offsetting relative sea-level rise. The presented sediment-based adaptation strategies are complicated by existing land use, therefore a change in water and sediment management is required to effectively use natural resources and employ these adaptation methods. The presented approach could be an exemplar to assess sedimentation strategy feasibility in other delta systems worldwide that are under threat from sea-level rise.

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THM analysIs of natural and engineered barriers for large excavations in deep nuclear waste repository

10.5194/egusphere-egu21-7588 ◽

2021 ◽

Author(s):

Matias Alonso ◽

Jean Vaunat ◽

Minh-Ngoc Vu ◽

Antonio Gens

Keyword(s):

Nuclear Waste ◽

Host Rock ◽

Thermal Load ◽

Water Pressure ◽

Large Diameter ◽

Coupled Processes ◽

Nuclear Waste Repository ◽

Damaged Zone ◽

Waste Repository ◽

The Impact

Argillaceous rocks have great potential as possible geological host medium to store radioactive waste. &#160;Andra is leading the design of a deep geological nuclear waste repository to be located in the Callovo-Oxfordian formation. In the framework of this project, excavations of large diameter galleries are contemplated to access and to store intermediate-level long-lived nuclear waste at repository main level. The closure of the repository will be realized by building sealing structures of expansive material.The response of such structures is affected by several thermo-hydro-mechanical coupled processes taking place in the near and far field of the argillaceous formations. They include the formation of an excavation induced damaged zone around the galleries, the impact of the thermal load on host rock pressures and deformations, the long-term interaction with support concrete structural elements and the hydration and swelling of sealing materials. As a result, the study of their performance requires to perform simulation works of increasing complexity in terms of coupling equations, problem geometry and material behaviour. As well, challenging computational aspects, as the ones related to fractures creation and propagation, have to be considered for a representative analysis of the problem.This work presents advanced large scale THM numerical models to provide keys about the response of the host rock around large diameter galleries during excavation and further thermal load as well as to analyse the performance of large diameter sealing structures. Particular features of the models include on one hand advanced constitutive laws to capture the development of the fractured zone around excavations, the behaviour of host rock/gallery support interfaces and the multi-scale response of bentonitic backfill. On the other hand, simulations consider geometries including constructive details of interest at decimetre scale within large discretization domain covering the whole formation stratigraphic column.These challenging simulations provided qualitative and quantitative results on key aspects for natural and engineered barrier integrity, like extension of the damaged zone, impact of the thermal load and water pressure variations in the surrounding geological layers, duration of natural hydration phase, swelling pressure development and seals global stability.

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Functional trait responses to sediment deposition reduce macrofauna-mediated ecosystem functioning in an estuarine mudflat

Biogeosciences ◽

10.5194/bg-15-2587-2018 ◽

2018 ◽

Vol 15 (9) ◽

pp. 2587-2599 ◽

Cited By ~ 9

Author(s):

Sebastiaan Mestdagh ◽

Leila Bagaço ◽

Ulrike Braeckman ◽

Tom Ysebaert ◽

Bart De Smet ◽

...

Keyword(s):

Oxygen Consumption ◽

Ecosystem Functioning ◽

River Estuary ◽

Functional Trait ◽

Sediment Deposition ◽

Sediment Chemistry ◽

Sediment Layer ◽

Sediment Reworking ◽

Macrobenthic Communities ◽

The Impact

Abstract. Human activities, among which dredging and land use change in river basins, are altering estuarine ecosystems. These activities may result in changes in sedimentary processes, affecting biodiversity of sediment macrofauna. As macrofauna controls sediment chemistry and fluxes of energy and matter between water column and sediment, changes in the structure of macrobenthic communities could affect the functioning of an entire ecosystem. We assessed the impact of sediment deposition on intertidal macrobenthic communities and on rates of an important ecosystem function, i.e. sediment community oxygen consumption (SCOC). An experiment was performed with undisturbed sediment samples from the Scheldt river estuary (SW Netherlands). The samples were subjected to four sedimentation regimes: one control and three with a deposited sediment layer of 1, 2 or 5 cm. Oxygen consumption was measured during incubation at ambient temperature. Luminophores applied at the surface, and a seawater–bromide mixture, served as tracers for bioturbation and bio-irrigation, respectively. After incubation, the macrofauna was extracted, identified, and counted and then classified into functional groups based on motility and sediment reworking capacity. Total macrofaunal densities dropped already under the thinnest deposits. The most affected fauna were surficial and low-motility animals, occurring at high densities in the control. Their mortality resulted in a drop in SCOC, which decreased steadily with increasing deposit thickness, while bio-irrigation and bioturbation activity showed increases in the lower sediment deposition regimes but decreases in the more extreme treatments. The initial increased activity likely counteracted the effects of the drop in low-motility, surficial fauna densities, resulting in a steady rather than sudden fall in oxygen consumption. We conclude that the functional identity in terms of motility and sediment reworking can be crucial in our understanding of the regulation of ecosystem functioning and the impact of habitat alterations such as sediment deposition.

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