School of Geography and the Environment

Back to Nature

Jennifer Booth, Prof. Heather Viles and Dr Philip Fletcher.

The British Museum has a large collection of stone artefacts from a range of geographical and historical sources, many of which are deteriorating and exhibit structural decay and friable or delaminating surfaces. The conservation of these artefacts is essential if they are to survive for future generations. 'Back to Nature' is a collaborative doctoral award between the University of Oxford and the British Museum. Funded by the AHRC, it is investigating two newly developed conservation techniques that mimic natural rock hardening and strengthening processes, to assess the feasibility of their use within the field of heritage stone conservation.

Damp towers: Understanding and controlling the ingress of driven rain through exposed walls.

Chris Wood, Prof. Heather Viles, Dr Mona Edwards and Dr Troy Sternberg

We are working with English Heritage in collaboration with Dr Liz Laycock, Sheffield Hallam University on this 3-year project to improve understanding of dampness within church towers and similar tall structures in order to devise more effective solutions. Driving rain poses a severe problem for many such structures, especially in the south west of England. Large scale testing is being carried out in the climatic chamber at Sheffield Hallam University, whilst smaller scale testing and field monitoring are being carried out by our laboratory.

Ivy on walls - biodeterioration or bioprotection?

Prof. Heather Viles, Dr Troy Sternberg and Alan Cathersides.

Funded by English Heritage.

This is a 3-year project that aims to investigate whether ivy covering historical walls and buildings is a deteriorative or protective practice. Different types of ivy are considered, specifically Common ivy (Hedera helix) as well as other types such as Canary Island ivy (Hedera canariensis). The spatial span of the study covers England, with up to 5 field sites located in the North (Yorkshire), Southeast (Kent), Southwest (near Bristol), and Centre (Oxford). Various methods will be used in the field and laboratory. Field investigations shall include detailed mapping, the construction of a test wall, 2D resistivity surveys to measure moisture content, and dataloggers to assess temperature and relative humidity above vs. below the ivy canopy. Laboratory work will consist of surveys of the stone surface at the micro-scale, including scanning electron microscopy (SEM), as well as experiments into the physical breakdown of stone surfaces by penetration of ivy growth, possibly aided by use of high-resolution ground penetrating radar (GPR). Chemical analyses will also be executed; for example, examining calcium oxalate deposits on stone surfaces. In a scoping project, Carter and Viles (2006) found less extreme microclimatic fluctuations below the ivy canopy than above it in a winter session of monitoring. For this reason, there is some indication of the bioprotective role of ivy on the surface of historical walls as an agent of thermal and moisture regulation. Findings are expected to contribute to a lengthy debate on the topic and should influence future practice, management, and policy of ivy on walls.

More information can be obtained about this project by visiting the project website.

Microbial communities associated with Arctic crustose lichens: Diversity, function and weathering impact.

Dominique Chaput, Prof. Heather Viles, and Prof. Andrew Whiteley (Centre for Ecology and Hydrology, Oxford).

Across vast areas of the Arctic, where exposed bedrock is highly resistant to physical weathering, biological processes appear to be important in rock breakdown. Most studies of lithobionts and their weathering impacts have focused on single organism types, usually lichens; however, in natural systems, these organisms belong to complex assemblages that can also include free-living fungi, algae, bacteria and archaea. We are adopting a community-level approach, using tools from molecular biology to address the following questions: 1) What is the extent of microbial diversity in crustose lichen-dominated communities? 2) What role do the other organisms play in community function, notably carbon and nitrogen cycling? 3) How might community structure affect the weathering impact? Results will help forge a link between microbial ecology and geomorphology of polar areas.

Rapid, catastrophic decay of building limestones.

Hong Zhang and Prof. Heather Viles.

This EPSRC-funded project is being carried out in collaboration with Prof. Bernie Smith and Prof. Muhammed Basheer of Queen's University Belfast and Prof. Ken Grattan and Dr Tong Sun from City University, London. Stone is a sustainable construction material used in many cultural heritage buildings and monuments, but one which can decay rapidly when faced with aggressive conditions such as those found in polluted urban environments. In particular, many building limestones experience seemingly unpredictable, episodic and sometimes catastrophic breakdown. Our project aims to investigate the nature of this rapid decay, using state-of-the-art fibre optic sensor technology embedded within stone structures in Oxford and nearby areas, alongside laboratory experimentation. Results will be used, in discussion with end-users, to develop protocols for limestone conservation and the selection of new and replacement stone matched to specific environmental conditions.

More information on this project is available on the project website at Queen's University Belfast.

Rock breakdown and landscape evolution in Northern Namibia.

Prof. Heather Viles and Dr Mary Bourke.

Thanks to funding from the Peter Fleming Award of the RGS-IBG we have begun studying the interplay of geomorphology and ecology in landscape evolution in Northern Namibia on the eastern fringes of the largely unexplored Cunene Sandsea. One of our ongoing projects in this area focuses on the mica schists which break down as a result of the interplay of salt, fog and heating and cooling and contribute to sediment production. Sand dunes, fed by the Cunene Sandsea, form along valley-side slopes of the perennial Cunene River and become covered episodically by mica schist debris from rockfalls. We are studying the interplay between sand deposition and in situ breakdown of this debris in order to better understand process regimes within this hyper arid area.

Salt weathering of historic sandstone: Impact of consolidation on migration, crystallization and decay mechanisms.

Satish Pandey, Mark Pollard (Research Laboratory for Archaeology and the History of Art), and Prof. Heather Viles.

Soluble salts are major agents of decay of porous building materials and a major concern to those involved in the conservation of historic buildings. Crystallization, hydration and differential thermal expansion of salts within the pores of stones can generate sufficient stresses to cause cracking, powdering and crumbling of the surface. The resistance of any porous material to salt damage is dependent on the pore size distribution, with stones which have a higher proportion of fine pores being less resistant. Surface treatments such as consolidation or water proofing significantly reduce the porosity and permeability of stone and can encourage salts to grow inside the stone. This research focuses on studying the impact of consolidation of sandstones on the migration and crystallization of water-soluble salts, and on salt-induced decay. It also attempts to explore suitable materials and methods for the treatment and preservation of decayed stone prone to salt attack.

Testing the role of soft wall capping in the conservation of ruined monuments (Phase 2)

Prof. Heather Viles, Alan Cathersides and Chris Wood.

The conservation of ruined monuments is important for heritage preservation yet it can be a time-consuming, expensive and often difficult task. This is the second phase of a detailed investigation into the use of soft capping as a method for conserving ruined historic masonry walls. English Heritage are the clients and are actively participating in the research. Four test walls have been commissioned at our Wytham Woods site. A long term field experiment is running here investigating how a turf soft cap changes moisture patterns and run off in the wall. Data is being collected using a monthly dowel measurement of 64 400mm x 6mm wooden dowels, monthly protimeter surveys down a central transect of each wall, three monthly high resolution protimeter surveys and three monthly geoelectrics surveys.

The second aim of the project is to investigate different methods of soft capping as alternatives to using turf. This is being studied at a second field site, on a long section of uncapped wall at Godstow Nunnery. Here we have installed four different types of soft capping; a seeded mat, a sedum mat, commercial turf and local turf and are conducting a long term photographic survey to monitor how each of them establish and survive on a wall top environment.

More information on this project is available on the project website.

The breakdown of basaltic rocks on Earth and Mars.

Bethany Ehlmann, Prof. Heather Viles, Dr Mary Bourke and Dr Mona Edwards.

Funded by the NASA Planetary Geology and Geophysics Program.

Boulders record environmental processes such as erosion, transport, and weathering. By examining rock breakdown signatures, we can unravel the environmental history of landscapes. However, interpreting these signatures is complex. Some signatures require thousands of years to form while others take minutes. The creation of one type of weathering signature may erase others. This project catalogues the diversity and characteristics of rock breakdown signatures and studies their persistence over time. We are presently focusing on fluvial and flood transport features on basalt in the Channeled Scablands of Washington State and in the Sonoran Desert of Arizona. In addition to advancing terrestrial geomorphology, results will aid in interpreting datasets from robotic missions to Mars and help to answer critical questions in Mars geology: When did water last flow on the surface? How were boulders transported to their current locations? How long does it take aeolian and cratering processes to completely mask evidence for past water?

More information on this project is available on the project website at the Planetary Science Institute.

The role of moisture in lichen weathering in Antarctica.

Christopher Stearn, Prof. Heather Viles, and Roger Worland (British Antarctic Survey).

Water availability is a key issue in geomorphology because moisture fuels the vast majority of weathering and erosional processes. Rock moisture changes over space and time are important controls on both weathering and the lithobiontic (rock dwelling) communities which are often dominated by lichens and cyanobacteria. In harsh, arid and cold environments such as Antarctica, links between lithobiontic communities and rock weathering are poorly understood. This project, which focuses on the Antarctic Peninsula, aims to assess and increase our understanding of (a) the distribution of moisture within the near-surface zone of rocks using a range of innovative monitoring techniques, and (b) the impact of moisture variations on weathering and lithobiontic communities.

Climate change, 'greening' of masonry and implications for the decay of built heritage and new build.

Prof. Heather Viles, Prof. Andrew Whiteley (Centre for Ecology and Hydrology), Dr Nick Cutler and Samin Ahmad.

This EPSRC-funded project is being carried out in collaboration with Prof. Bernie Smith, Prof. Muhammed Basheer, Dr Nick Betts and Dr John McAlister of Queen's University Belfast.

Recent observations have shown an increase in algal 'greening' of external sandstone walls in many places in the north west UK. As well as being unsightly, algal greening contributes to the deterioration of sandstone, both biochemically (through the exudation of organic acids) and biophysically (by expansion and contraction associated with wetting and drying). Algal patches also change rock surface porosity and permeability, leading to altered sub-surface moisture regimes, a crucial factor in stone decay. Algal growth is controlled in large part by climatic conditions (particularly precipitation regimes) and air quality. Predicting and mitigating the impacts of future environmental change on sandstone buildings will therefore require an understanding of the controls on algal colonization and growth. The research carried out at the School will investigate the colonization of sandstone surfaces by algae and the impact that algal greening has on moisture regimes and stone deterioration. Surface and sub-surface moisture will be monitored using geoelectrical techniques (electrical resistivity tomography, or ERT). Algal colonization under different environmental conditions will be simulated in the laboratory. State-of-the-art molecular techniques will be used to study algal community assembly. Ultimately, the research will lead to the development of practical guidance for the future use and management of sandstone masonry in the north west UK and beyond.

More information on this project and video is available from the project website.

Canal heritage conservation and urban revitalization in Zhenjiang, Jiangsu, China.

Shuaishuai He and Prof. Heather Viles.

The Beijing-Hangzhou Grand Canal has a history of 2,400 years and a length of 1,800 km. Lying in the Eastern China, the canal connects more than 20 cities. Since the end of 2005, the World Heritage listing application for the canal has been in preparation for the submission in 2013. Facilitated by this on-going application, special attention has been drawn to "canal cities" and "canal heritage". As one of the 20 "canal cities", Zhenjiang is rich in the resource of "canal heritage". This project explores the issues of identifying and conserving "canal heritage" in the built environment of Zhenjiang with the dual purpose of preparing the World Heritage listing application and aiding the revitalization of the city.

The role of soil as a method for conserving cultural stone ruins: effects of physical and chemical characteristics on stone weathering.

Noreen Zaman and Prof. Heather Viles.

Ruins pose many challenges for conservation because they are highly prone to deterioration. Full or partial burial of ruins in soil, and soft capping the tops of ruin walls, have all been proposed as possible conservation solutions. They require further research and evaluation if they are to be implemented effectively as conservation strategies. Thus, the overall aim of this research is to evaluate whether soils used to help conserve stone heritage (through full / partial burial and soft wall capping) are benign or whether they can cause deterioration. If deterioration does occur, then to what extent and in what conditions? The research projects explores this through a combination of laboratory and field-based experiments that examine chemical and physical changes in the soil environment over time, and the weathering affects this has on buried cultural stone.