ORCID Profile
0000-0003-1386-0897
Current Organisation
Monash University
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Quaternary environments | Physical geography and environmental geoscience not elsewhere classified | Geomorphology and earth surface processes | Quaternary Environments | Archaeology | Biological (Physical) Anthropology | Physical geography and environmental geoscience | Aboriginal and Torres Strait Islander Archaeology |
Expanding Knowledge in the Environmental Sciences | Understanding Australia's Past | Expanding Knowledge in History and Archaeology
Publisher: Authorea, Inc.
Date: 22-12-2022
DOI: 10.22541/ESSOAR.167169649.93488411/V1
Abstract: In the absence of consistent meteorological data on Mars, the morphology of dunes can be employed to study its atmosphere. Specifically, barchan dunes, which form under approximately unimodal winds, are reliable proxies for the dominant wind direction. Here, we characterize near-surface winds on Mars from the morphology of barchans mapped globally on the planet by a convolutional neural network. Barchan migration is predominantly aligned with the global circulation: northerly at mid-latitudes and cyclonic near the north pole, with the addition of an anti-cyclonic north-polar component that likely originates from winds emerging from the ice cap. Locally, migration directions deviate from regional trends in areas with high topographic roughness. Notably, obstacles km such as impact craters are efficient at deflecting surface winds. Our database, which provides insights into planetary-scale aeolian processes on modern-day Mars, can be used to constrain global circulation models to assist with predictions for future missions.
Publisher: American Geophysical Union (AGU)
Date: 21-09-2023
DOI: 10.1029/2022GL102610
Publisher: Springer Science and Business Media LLC
Date: 03-05-2022
DOI: 10.1038/S41467-022-30031-1
Abstract: Wherever a loose bed of sand is subject to sufficiently strong winds, aeolian dunes form at predictable wavelengths and growth rates. As dunes mature and coarsen, however, their growth trajectories become more idiosyncratic nonlinear effects, sediment supply, wind variability and geologic constraints become increasingly relevant, resulting in complex and history-dependent dune amalgamations. Here we examine a fundamental question: do aeolian dunes stop growing and, if so, what determines their ultimate size? Earth’s major sand seas are populated by giant sand dunes, evolved over tens of thousands of years. We perform a global analysis of the topography of these giant dunes, and their associated atmospheric forcings and geologic constraints, and we perform numerical experiments to gain insight on temporal evolution of dune growth. We find no evidence of a previously proposed limit to dune size by atmospheric boundary layer height. Rather, our findings indicate that dunes may grow indefinitely in principle but growth depends on morphology, slows with increasing size, and may ultimately be limited by sand supply.
Publisher: Springer Science and Business Media LLC
Date: 19-05-2022
Publisher: California Digital Library (CDL)
Date: 23-05-2021
DOI: 10.31223/X5QG8S
Publisher: Geological Society of America
Date: 08-2023
DOI: 10.1130/G51264.1
Abstract: Windblown dunes are common features in our solar system, forming on planetary surfaces that span wide ranges in gravity and both atmospheric and sediment properties. The patterns formed by their crests, which are readily visible from orbital images, can record information about recent changes in boundary conditions, such as shifts in wind regime or varying sediment availability. Here, we demonstrate that the density of dune interactions (where neighboring crestlines are close to each other) within a dune field is an indicator of such changes. Using orbiter-based images of 46 dune fields on Earth and Mars, we compiled a database of pattern parameters including dune spacing, crestline orientation, and interaction density. Combined with sediment fluxes derived from ERA5-Land data and a martian global circulation model, we also compiled dune turnover time scales (the time it takes for a dune to migrate one dune length) for each investigated dune field. First, we show that dune fields undergoing changes in boundary conditions display higher than expected dimensionless interaction indices. Second, dune fields with longer turnover times display a wider range in interaction indices on both Earth and Mars because they are more likely to be observed while still adjusting to recent changes in boundary conditions. Thus, a dune field’s interaction index offers a novel tool to detect and possibly quantify recent environmental change on planetary surfaces.
Publisher: Springer Science and Business Media LLC
Date: 22-11-2022
DOI: 10.1038/S41467-022-34974-3
Abstract: Sand mobilized by wind forms decimeter-scale impact ripples and decameter-scale or larger dunes on Earth and Mars. In addition to those two bedform scales, orbital and in situ images revealed a third distinct class of larger meter-scale ripples on Mars. Since their discovery, two main hypotheses have been proposed to explain the formation of large martian ripples—that they originate from the growth in wavelength and height of decimeter-scale ripples or that they arise from the same hydrodynamic instability as windblown dunes or subaqueous bedforms instead. Here we provide evidence that large martian ripples form from the same hydrodynamic instability as windblown dunes and subaqueous ripples. Using an artificial neural network, we characterize the morphometrics of over a million isolated barchan dunes on Mars and analyze how their size and shape vary across Mars’ surface. We find that the size of Mars’ smallest dunes decreases with increasing atmospheric density with a power-law exponent predicted by hydrodynamic theory, similarly to meter-size ripples, tightly bounding a forbidden range in bedform sizes. Our results provide key evidence for a unifying model for the formation of subaqueous and windblown bedforms on planetary surfaces, offering a new quantitative tool to decipher Mars’ atmospheric evolution.
Publisher: Geological Society of America
Date: 12-05-2022
DOI: 10.1130/G49936.1
Abstract: Loose sand, blown away from source regions by winds, is transported across Mars's surface into sand sheets and dunes and accumulates within topographic sinks. In the absence of plate tectonics, impact craters constitute a dominant sink for windblown sediments on Mars today. We analyzed the volume of all mapped eolian sands in martian craters & km in diameter to reveal spatiotemporal patterns of sediment accumulation on the planet's surface. We combined our results with global climate simulations, maps of depth to the ice table and dust cover, as well as lithologic and age information of the underlying geologic units, to better understand the controls on intracrater sand accumulation rates. We find that crater age, latitude, and lithology influence the accumulation rate of windblown sand and, notably, that it is enhanced in mechanically weaker substrates, high-latitude craters (suggesting that modern cryogenic processes may enhance sand production), and in Late Noachian and Early Hesperian craters (possibly hinting at increased erosion rates at that time).
Publisher: American Geophysical Union (AGU)
Date: 14-09-2020
DOI: 10.1029/2020GL088773
Abstract: Aeolian dune fields are self‐organized patterns formed by wind‐blown sand. Dunes are topographic roughness elements that impose drag on the atmospheric boundary layer (ABL), creating a natural coupling between form and flow. While the steady‐state influence of drag on the ABL is well studied, nonequilibrium effects due to roughness transitions are less understood. Here we examine the large‐scale coupling between the ABL and an entire dune field. Field observations at White Sands, New Mexico, reveal a concomitant decline in wind speed and sand flux downwind of the transition from smooth playa to rough dunes at the upwind dune‐field margin, that affects the entire ∼ 10‐km ‐long dune field. Using a theory for the system that accounts for the observations, we generalize to other roughness scenarios. We find that, via transitional ABL dynamics, aeolian sediment aggradation can be influenced by roughness both inside and outside dune fields.
Publisher: California Digital Library (CDL)
Date: 05-10-2023
DOI: 10.31223/X5M09D
Publisher: California Digital Library (CDL)
Date: 06-12-2020
DOI: 10.31223/X5SC70
Publisher: American Geophysical Union (AGU)
Date: 03-2021
DOI: 10.1029/2020GL090924
Abstract: Wind‐blown sand dunes are both a consequence and a driver of climate dynamics they arise under persistently dry and windy conditions, and are sometimes a source for airborne dust. Dune fields experience extreme daily changes in temperature, yet the role of atmospheric stability in driving sand transport and dust emission has not been established. Here, we report on an unprecedented multiscale field experiment at the White Sands Dune Field (New Mexico, USA), where by measuring wind, humidity and temperature profiles in the atmosphere concurrently with sediment transport, we demonstrate that a daily rhythm of sand and dust transport arises from nonequilibrium atmospheric boundary layer convection. A global analysis of 45 dune fields confirms the connection found in situ between surface wind speed and diurnal temperature cycles, revealing an unrecognized climate feedback that may contribute to the growth of deserts on Earth and dune activity on Mars.
Publisher: Wiley
Date: 03-08-2023
DOI: 10.1111/SED.13121
Abstract: The recognition of meandering rivers in Earth's prevegetation stratigraphic record is hindered by an absence of depositional models specifically tailored to unvegetated single‐channel rivers. As a result, their abundance on the early Earth is currently unknown. Here, sedimentological studies of two modern meandering river reaches with unvegetated banks were conducted. Both reaches are located in arid basins of Nevada, USA. Stratigraphy was analysed in conjunction with satellite imagery and high‐resolution topographic data to understand how channels and floodplains record past flow conditions. Analyses of point‐bar and channel‐fill deposits showed that lateral accretion sets are not heterolithic but, rather, composed of mixed sand and sand‐sized mud aggregates (clumps of clay and silt) interpreted to have formed through flocculation. Levées are present but subdued. Notably, downstream‐migrating outer‐bank‐attached bars are prominent architectural features that may be common in unvegetated meandering rivers in arid landscapes elsewhere. The identification of such depositional elements in the stratigraphic record may enhance recognition of ancient unvegetated meandering rivers and improve reconstructions of palaeohydrology on early Earth and Mars.
Publisher: California Digital Library (CDL)
Date: 07-05-2020
Publisher: California Digital Library (CDL)
Date: 31-07-2022
DOI: 10.31223/X5V921
Abstract: Sand seas are vast expanses of Earth’s surface containing large areas of aeolian dunes—topographic patterns manifest from above-threshold winds and a supply of loose sand. Predictions of the role of future climate change for sand-sea activity are sparse and contradictory. Here we examine the impact of climate on all of Earth’s presently-unvegetated sand seas, using ensemble runs of an Earth System Model for historical and future Shared Socioeconomic Pathway (SSP) scenarios. We find that almost all of the sand seas decrease in activity relative to present-day and industrial-onset for all future SSP scenarios, largely due to more intermittent sand-transport events. An increase in event wait-times and decrease in sand transport is conducive to vegetation growth. We expect dune-forming winds will become more unimodal, and produce larger incipient wavelengths, due to weaker and more seasonal winds. Our results indicate that these qualitative changes in Earth’s deserts cannot be mitigated.
Publisher: California Digital Library (CDL)
Date: 24-09-2023
DOI: 10.31223/X56Q28
Abstract: To meet electricity demand using renewable energy supply, wind farm locations should be chosen to minimise variability in output, especially at night when solar photovoltaics cannot be relied upon. Wind farm location must balance grid-proximity, resource potential, and wind correlation between farms. A top-down planning approach for farm locations can mitigate demand unmet by wind supply, yet the present Australian wind energy market has bottom-up short-term planning. Here we show a computationally tractable method for optimising farm locations to maximise total supply. We find that Australia’s currently operational and planned wind farms produce less power with more variability than a hypothetical optimal set of farms with equivalent capacity within 100 km of the AEMO grid. Regardless of the superior output, this hypothetical set is still subject to variability due to large-scale weather correlated with climate modes (i.e., El Niño). We study multiple scenarios and highlight several internationally transferable planning implications.
Publisher: Geological Society of America
Date: 23-02-2023
DOI: 10.1130/G50837.1
Abstract: Landscapes created through sediment transport are shaped by the interaction of flow and form. In landscapes where wind is the agent of geomorphic work, this is clear at the small scale equilibrium dune morphology is linked to the wind climate and the supply of sediment. At larger scales, this linkage becomes ambiguous because the form of giant dunes and dune fields integrates long histories of varied wind and sand supply. Without a framework to assess aeolian landscape evolution at this scale, the time taken to form and reorganize dune fields has been largely unexplored quantitatively. We show that these time scales can be understood by linking modern wind and topographic data sets for one of the most expansive and morphologically erse unvegetated dune fields, the Rub’ al Khali (southern Arabian Peninsula). By linking sediment flux to the surface area and slope of dunes, and growth to the ergence in that flux, we fully couple form and flow at the dune field scale. Our results show quantitatively how dune field formation and reorganization are outpaced by climate change and the implications for stratigraphic interpretation.
Publisher: California Digital Library (CDL)
Date: 31-01-2022
DOI: 10.31223/X52P4F
Abstract: Mud forms the foundation of many coastal and tidal environments. Clay suspensions carried downstream from rivers encounter saline waters, which encourages aggregation and sedimentation by reducing electrostatic repulsion among particles. We perform experiments to examine the effects of surface charge on both the rate and style of sedimentation, using kaolinite particles as a model mud suspension and silica spheres with equivalent hydrodynamic radius as a control. Classic hindered settling theory reasonably describes sedimentation rate for repulsive clay particles and silica spheres, which form a highly concentrated jamming front. The hindered settling description breaks down for attractive clay particles, which aggregate to form clay gels that consolidate like a soft solid. Water flow form fracture-like channels in the bulk of the gel, which disappear as gel enters a creep regime. Results may help toward understanding the effect of surface charge and particle shape on the sedimentation and erodibility of natural mud.
Publisher: American Geophysical Union (AGU)
Date: 30-03-2021
DOI: 10.1029/2020GL091251
Abstract: Mud forms the foundation of many coastal and tidal environments. Clay suspensions carried downstream from rivers encounter saline waters, which encourages aggregation and sedimentation by reducing electrostatic repulsion among particles. We perform experiments to examine the effects of surface charge on both the rate and style of sedimentation, using kaolinite particles as a model mud suspension and silica spheres with equivalent hydrodynamic radius as a control. Classic hindered settling theory reasonably describes sedimentation rate for repulsive clay particles and silica spheres, which form a highly concentrated jamming front. The hindered settling description breaks down for attractive clay particles, which aggregate to form clay gels that consolidate like a soft solid. Water flow form fracture‐like channels in the bulk of the gel, which disappear as gel enters a creep regime. Results may help toward understanding the effect of surface charge and particle shape on the sedimentation and erodibility of natural mud.
Publisher: Springer Science and Business Media LLC
Date: 27-06-2022
DOI: 10.1038/S41467-022-31123-8
Abstract: Sand seas are vast expanses of Earth’s surface containing large areas of aeolian dunes—topographic patterns manifest from above-threshold winds and a supply of loose sand. Predictions of the role of future climate change for sand-sea activity are sparse and contradictory. Here we examine the impact of climate on all of Earth’s presently-unvegetated sand seas, using ensemble runs of an Earth System Model for historical and future Shared Socioeconomic Pathway (SSP) scenarios. We find that almost all of the sand seas decrease in activity relative to present-day and industrial-onset for all future SSP scenarios, largely due to more intermittent sand-transport events. An increase in event wait-times and decrease in sand transport is conducive to vegetation growth. We expect dune-forming winds will become more unimodal, and produce larger incipient wavelengths, due to weaker and more seasonal winds. Our results indicate that these qualitative changes in Earth’s deserts cannot be mitigated.
Publisher: American Geophysical Union (AGU)
Date: 24-08-2020
DOI: 10.1029/2020GL088919
Abstract: In zones of loose sand, wind‐blown sand dunes emerge due the linear instability of a flat sedimentary bed. This instability has been studied in experiments and numerical models but rarely in the field, due to the large time and length scales involved. We examine dune formation at the upwind margin of the White Sands Dune Field in New Mexico (USA), using 4 years of lidar topographic data to follow the spatial and temporal development of incipient dunes. Data quantify dune wavelength, growth rate, and propagation velocity and also the characteristic length scale associated with the growth process. We show that all these measurements are in quantitative agreement with predictions from linear stability analysis. This validation makes it possible to use the theory to reliably interpret dune‐pattern characteristics and provide quantitative constraints on associated wind regimes and sediment properties, where direct local measurements are not available or feasible.
Start Date: 12-2024
End Date: 12-2027
Amount: $414,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 03-2019
End Date: 03-2025
Amount: $607,330.00
Funder: Australian Research Council
View Funded Activity