John Webb

La Trobe University, Environmental Geosciences, Faculty Member

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John Webb (PhD UQ 1982) is Professor of Environmental Geoscience at La Trobe University. The bulk of his research and teaching is on groundwater and contaminated site management, with on-going research projects on the influence of climate and land-use change on groundwater, and improving treatment procedures for acid mine drainage. He also carries out research on karst and tectonic geomorphology, and has utilised his geological background in a variety of archaeological projects.

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Eocene paleobotanical altimetry of Victoria's Eastern Uplands

Australian Journal of Earth Sciences, May 16, 2017

Climatic range data for modern plant taxa used for the bioclimatic analysis of the fossil macrofl... more

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The Magnetic Sludge

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title: Salt accumulation and groundwater recharge on granite slopes in Southeastern Australia

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Springs of the Arabian Desert: Hydrogeology and Hydrochemistry of Abu Jir Springs, Central Iraq

by Jaafar Jotheri, John Webb, and Rod Fensham

Water, 2024

The Arabian Desert is characterised by very low rainfall and high evaporation, yet over 210 sprin... more The Arabian Desert is characterised by very low rainfall and high evaporation, yet over 210 springs are on its northeastern edge in central Iraq along the Abu Jir lineament, which represents the western depositional margin of a foreland basin infilled by the floodplain sediments of the Tigris and Euphrates Rivers; there is little evidence of faulting. The springs discharge from gently east-dipping Paleocene–Eocene limestones, either where groundwater flowpaths intersect the ground surface or where groundwater flow is forced to the surface by confining aquitards. Calculated annual recharge to the aquifer system across the Arabian Desert plateau (130–500 million m3) is significant, largely due to rapid infiltration through karst dolines, such that karst porosity is the primary enabler of groundwater recharge. The recharge is enough to maintain flow at the Abu Jir springs, but active management of groundwater extraction for agriculture is required for their long-term sustainability. The hydrochemistry of the springs is determined by evaporation, rainfall composition (high SO4 concentrations are due to the dissolution of wind-blown gypsum in rainfall), and plant uptake of Ca and K (despite the sparse vegetation). Limestone dissolution has relatively little impact; many of the springs are undersaturated with respect to calcite and lack tufa/travertine deposits. The springs at Hit-Kubaysa contain tar and high levels of H2S that probably seeped upwards along subvertical faults from underlying oil reservoirs; this is the only location along the Abu Jir lineament where deep-seated faults penetrate to the surface. The presence of hydrocarbons reduces the Hit-Kubaysa spring water and converts the dissolved SO4 to H2S.

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Quantifying the Amorphous Content of Acid Rock Drainage (ARD) Treatment Sludge using XRD and XRF

The Effect of Neutralization Method and Reagent on the Rate of Cu and Zn Release from Acid Rock Drainage Treatment Sludges

Journal American Society of Mining and Reclamation, 2006

Neutralisation of Acid Rock Drainage (ARD) by adding an alkaline reagent produces sludges general... more Neutralisation of Acid Rock Drainage (ARD) by adding an alkaline reagent produces sludges generally dominated by amorphous ferrihydrite, often with high levels of adsorbed heavy metals. The effect of neutralisation method and reagent on the long-term chemical stability of these treatment sludges was investigated experimentally using a relatively oxidised synthetic ARD (containing Fe[~70% Fe +3 ], Al, Cu and Zn) with a variety of reagents and processes, and two reduced synthetic ARD compositions (Fe +2 , Al, Cu and Zn; Fe +2 , Cu and Zn) treated with hydrated lime. The sludges were all subjected to kinetic testing to determine the rate of Cu and Zn release at pH 4, simulating disposal in a moderately acidic pit lake. All sludges precipitated from the oxidised ARD by standard ARD neutralisation procedures and reagents (lime, limestone, Bauxsol, KB-1 and HDS lime) showed similar chemical stability, with an initial rapid rate of release of Cu and Zn (~50% of leaching in the first 5 minutes) that reduced over time, apparently exponentially. The Cu and Zn are adsorbed onto the surface of the amorphous ferrihydrite present. Sludges initially precipitated as ferrous hydroxide and then oxidised may contain a finely crystalline goethite component; if the ARD was Al-free the crystalline content is greater and coarser-grained and may consist of magnetite as well as goethite. Leaching of zinc from these crystalline sludges can be as much as an order of magnitude less than from sludges precipitated as ferric hydroxide, due to the incorporation of Zn within the mineral structure. Copper is more readily released from the sludges with a higher goethite/magnetite content, because it is adsorbed on the crystallite surfaces. However, it appears that Al-rich goethite can incorporate Cu, reducing its leachability. Thus, modifications to the ARD treatment procedure, in particular control of oxidation state and Al levels, can substantially increase the crystallinity and improve the chemical stability of the sludge precipitated, and have a much greater influence on sludge leachability than the neutralisation agent used. These modifications are probably applicable to any water treatment sludges formed by pH adjustment.

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A two-part Seabed Geomorphology classification scheme (v.2); Part 1: Morphology Features Glossary

This report updates the 'Two-part Seabed Geomorphology classification scheme' of Dove et ... more This report updates the 'Two-part Seabed Geomorphology classification scheme' of Dove et al. (2016) and presents a new glossary (<em>Part 1</em>) of Seabed Morphology features. This Morphology glossary is intended to provide marine scientists with a robust and consistent way to characterise the seabed. Each glossary entry includes a feature definition and a representative schematic diagram to support clear and accurate classification.

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Energy, water and carbon flux responses to meteorological and edaphic drivers in agricultural ecosystems of Australia and New Zealand

Despite occupying one-third of the terrestrial surface and being highly sensitive to changes in h... more Despite occupying one-third of the terrestrial surface and being highly sensitive to changes in hydrology, agricultural ecosystems are under-represented in flux studies of water and carbon cycles across the globe. Australia and New Zealand are no different, where only 16% of OzFlux sites are located in predominately agricultural landscapes. Consequently, the primary objective of this study was to investigate and compare the responses of agricultural fluxes of surface energy (sensible heat flux), water (evapotranspiration, ET) and carbon (net ecosystem exchange, NEE) to eight meteorological and edaphic drivers (net radiation, atmospheric specific humidity, vapour pressure deficit, net radiation, air temperature, ground heat flux, soil temperature and soil water content). Three levels of management intensity were considered, including minimal management (e.g. grazed rangelands); moderate management (e.g. dryland agriculture and pasturelands); and irrigated or other intensively managed...

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The Exploitation of Acorn and Rice in Early Holocene Lower Yangzi River, China

Acta Anthropologica …, 2010

Recent excavations at Shangshan and Xiaohuangshan (11,400-8000 cal BP) in Zhejiang Province have ... more

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Landsat Image Based Temporal and Spatial Analysis of Farm Dams in Western Victoria

With the continuing pressure on Australia’s water resources and interand intra-annual rainfall va... more With the continuing pressure on Australia’s water resources and interand intra-annual rainfall variability, farmers, especially in rainfed agricultural and pastoral zones, have been developing farm dams as a mean of providing additional water sources for irrigation and stock. The density of farm dams has increased over time, and an accurate knowledge of the spatial distribution of farm dams is essential for water resource management at the catchment level. There are more than 2 million farm dams across Australia, most with a storage area of <5-10 ha. These small dams are frequently unlicensed. In Victoria stock and domestic dams do not require a license, so more than 90% of farm dams, contributing 85% to the total storage capacity, are not documented, despite their significant impact on water resources and stream flow. To document farm dam distribution and historical trends in their development, an approach has been developed using medium resolution Landsat images coupled with Go...

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Calibrated pXRF data for: Sourcing hornfels artefacts in eastern Tasmania: understanding Aboriginal mobility in a lithic-rich landscape

Late Pleistocene to Early Holocene Faulting, Surface Rupture and Liquefaction Near Montagu, Northwest Tasmania

GSA Annual Meeting in Denver, Colorado, USA - 2016, 2016

Response to Parker: Rebuttal: ENGE-D-13-00994R2 ‘‘Modelling of lake level under climate change conditions: Lake Purrumbete in southeastern Australia’’ by Yihdego et al. (2015)

Environmental Earth Sciences, Dec 19, 2015

Parker (2015) criticises the modelling by Yihdego et al. (2015) of future fluctuations in the lev... more Parker (2015) criticises the modelling by Yihdego et al. (2015) of future fluctuations in the level of Lake Purrumbete because we used climate change predictions that include global warming due to anthropogenic carbon dioxide emissions. Parker (2015) analysed Bureau of Meteorology data for weather stations in the area around Lake Purrumbete and states that measured rainfall in this region has been generally stable while exhibiting interannual and multi-decadal oscillations, and recently there has been a small increase. Parker appears to believe that there was no drought in southeastern Australia in the period 1997-2009, because he criticises Yihdego et al. for claiming that there was a drought induced by global warming and that the drought period started in 2010, when there is clear evidence for abundant rainfall and high lake levels at this time. He goes on to analyse monthly maximum temperatures for the Lake Purrumbete region and states that temperature has been ''reducing rather than increasing from 1864 to 2015''. Parker then deduces that because temperatures are not warming and there is no consistent rainfall pattern, ''anthropogenic carbon dioxide concentration in the atmosphere (cannot) be the issue''.

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Liquefaction along Late Pleistocene to early Holocene Faults as Revealed by Lidar in Northwest Tasmania, Australia

AGU Fall Meeting Abstracts, Dec 1, 2016

Origin, geomorphology and geoheritage potential of Australia’s longest coastal cliff lines

Australian Journal of Earth Sciences, Apr 2, 2020

Two spectacular cliff lines occur along Australia's south and west coasts: the Great Southern Sca... more Two spectacular cliff lines occur along Australia's south and west coasts: the Great Southern Scarp (new name) and the Zuytdorp Cliffs. Detailed measurements of their length show that they are exceptionally long and unusually continuous. The Great Southern Scarp is the southern edge of the Nullarbor Plain's Bunda Plateau; it is cut into shallow marine sediments and extends for 820 km. Once a continuous sea-cliff, local uplift has isolated two sections from the ocean, so it now comprises the Bunda Cliffs (210 km of coastal cliff, 180 km of which is uninterrupted cliff line), Hampton Range (inland; 300 km), Baxter Cliffs (160 km of coastal cliff) and Wylie Scarp (inland; 160 km). The Zuytdorp Cliffs are coastal cliffs cut into eolianite, and extend for 210 km with an uninterrupted section of 120 km. The length of the Great Southern Scarp and the Zuytdorp Cliffs results from an unusual combination of circumstances. They are both composed of poorly jointed, relatively homogenous biogenic calcarenites, presented to high-energy ocean waves by regional uplift. The carbonates are sufficiently well cemented to maintain a steep vertical cliff face, but susceptible to disintegration under direct wave attack. Cliff retreat has been fairly uniform because of the broad spatial scale of both lithology and erosion. The arid climate, absence of nearby nonkarstic catchments and karstic nature of the cliffs' hinterlands has discouraged integrated drainage development, so no significant fluvial systems dissect the cliffs; this is a key factor in cliff edge preservation. In the case of the Great Southern Scarp, these processes have formed the longest continuous cliff line in Australia and probably the world. Referenced against criteria from Australia's National Heritage List, the cliffs have potentially international/national levels of significance for the rarity of their scale, their demonstration of landscape evolution, and their spectacular beauty. KEY POINTS 1. Australia's longest coastal cliffs, the Bunda (SA) and Zuytdorp (WA) cliffs, are equal in length (210 km, within defined confidence levels). 2. The Bunda Cliffs are part of the Great Southern Scarp (new name), an 820 km-long feature of the Nullarbor Plain that also includes the coastal Baxter Cliffs (160 km in length) and two paleocoastal scarps. 3. The unusual continuity of the cliff lines results from a landscape history specific to the Australian continent, and the Great Southern Scarp is likely to be unusual on a global scale. 4. The Great Southern Scarp and the Zuytdorp Cliffs have potentially national and/or international levels significance for geoheritage values in the criteria of events and processes, rarity and aesthetics.

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[Special section on the Yiluo project] INFLUENCES ON SELECTION OF LITHIC RAW MATERIAL SOURCES AT HUIZUI, A NEOLITHIC/EARLY BRONZE AGE SITE IN NORTHERN CHINA

Bulletin of the Indo-Pacific Prehistory Association, Sep 5, 2007

At Huizui, a major centre of ground stone tool manufacture, five main lithologies were used, each... more At Huizui, a major centre of ground stone tool manufacture, five main lithologies were used, each for a particular purpose: oolitic dolomite for spades; diabase for axes, adzes and chisels; fine micaceous sandstone for knives and sickles; other sandstone for grinding slabs; and fine limestone for lime. This reflects the functional properties of these lithologies. Diabase, oolitic dolomite and fine micaceous sandstone are tough and take sharp edges, which for diabase are particularly sharp and easily resharpened. All five rock types are probably available within 8 km of the site. Ground stone tool production may have been located at Huizui because of its proximity to the adjacent sandstone hills, which provided abundant abrasive material. Overall, raw materials are dominated by oolitic dolomite, which was quarried from a single thin-bedded layer that outcrops as flat pavements. Diabase was sourced from river cobbles, and micaceous sandstone was quarried. All three of these lithologies were extracted as raw material that required minimal shaping to make tools. This factor was probably responsible for the choice of oolitic dolomite over fine-grained dolomite, which is more common and occurs closer to Huizui, but cannot be easily quarried. The small amounts of probably exotic lithologies (including red rhyolite, marble, turquoise, ?jade) may have been used for elite items.

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Megafans of the Northern Victorian Riverine Plains, SE Australia

Cambridge University Press eBooks, May 18, 2023

6.31 Karst in Deserts

Elsevier eBooks, 2013

Hot deserts are characterized by low mean annual rainfall (<250 mm, <10″) and very high eva... more Hot deserts are characterized by low mean annual rainfall (<250 mm, <10″) and very high evapotranspiration, so karst processes are inhibited. However, karst features are abundant and well developed in many deserts around the world. Salt caves occur predominantly in this environment and develop rapidly despite the arid climate, because they are formed mainly by rare, but intense, rain events. Deserts also preserve, relatively unaltered, gypsum and carbonate karst that formed in prior wetter climates or by hypogene processes. Carbonate karst, which is the most common karst in hot deserts, is modified very slowly by desert processes, including dissolution and salt crystallization, which fragments bedrock and speleothems.

Denudational Isostatic Rebound of Intraplate Highlands - the Lachlan River Valley, Australia - Discussion

Earth Surface Processes and Landforms, 1993

A range of evidence from the Lachlan valley in the southeast Australian highlands is consistent w... more A range of evidence from the Lachlan valley in the southeast Australian highlands is consistent with Neogene isostatic rebound in response to denudational unloading. This evidence is found along the inland edge of the highlands in the transition zone between the highlands proper and the Lachlan's inland alluviated valley and the intracratonic Murray Basin. The amounts and rates of uplift indicated by offsets of suballuvium bedrock profiles and the long profiles of Tertiary valley-filling basalts are consistent with modelling of denudational rebound using known rates of highland denudation and basinal sedimentation, and reasonable crustal properties. The modelling shows that weak to moderately strong lithosphere (effective elastic thickness, T, = 1-25 km) and strong lithosphere (T. = 100 km) are all consistent with the observed amounts of rebound. Strong lithosphere must be broken, however, to be consistent with the field data. Even in the Australian setting, which is characterized by very low rates of denudation, isostatic rebound in response to denudational unloading must be a significant factor in maintaining highland elevation and must be incorporated in models of long-term landscape evolution. It would be expected that denudational isostatic rebound would be an even more significant component of long-term landscape evolution in areas of higher denudation rates. KEY WORDS Isostatic rebound Denudation Australia Southeast Australian highlands Intraplate highlands Lithosphere Effective elastic thickness

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Effect of surface weathering on portable X‐Ray fluorescence analysis of artefacts: Evidence from Tasmanian hornfels

Geoarchaeology-an International Journal, Oct 21, 2021

Hornfels was commonly utilised by Aboriginal people in southeastern Tasmania for stone artefact m... more Hornfels was commonly utilised by Aboriginal people in southeastern Tasmania for stone artefact manufacture. Sourcing of hornfels artefacts in this region using pXRF analysis is potentially compromised by the weathering patina generally present on this lithology. To understand the impact of weathering on hornfels composition, the mineralogy and chemical composition of weathered and unweathered hornfels were analysed, and weathering was simulated in column experiments. The results demonstrate that the cordierite and, to a lesser extent, plagioclase present in the hornfels transform very rapidly into kaolinite, which is the dominant component of the pale, porous weathering patina. Weathering simulation experiments and isocon comparisons of major and trace element analyses show that this alteration is accompanied by a substantial loss of Mg, Na and Ca (≥50%). For the trace elements, 25%–35% are removed (except Zr, which is relatively immobile), with the remainder retained in unaltered minerals or adsorbed to the neoformed kaolinite. Rb and Nb are more stable than Sr, which demonstrates the highest absolute mobility, but even this element shows relatively little loss, provided that the weathering patina is &lt;1 mm thick. For Rb, Sr, Y, Zn and Nb, the percentage loss during weathering is similar (25%–35%), so bivariate plots of these trace elements show a spread due to weathering, but with a more or less constant ratio. As a result, pXRF analyses of these elements can be used to successfully differentiate hornfels artefacts from different sites in southeastern Tasmania. This study showed that Rb, Sr, Y and Nb, which are commonly used to source igneous artefacts, are also effective in sourcing hornfels, even though they are mobile during weathering. This study also demonstrated the importance of isocon plots in identifying the trace elements best suited to artefact sourcing using pXRF, if the analyses are affected by chemical weathering.

John Webb

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