Biogeomorphology: From Darwin to future evolution

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A Review and Reassessment of Travertine Classification

This paper provides a review of the classification of travertines with emphasis on their morphology. Three criteria are used to describe them: geochemistry, microfabric and morphology. Geochemically, travertines may be divided into two groups, the meteogene travertines, where the carrier carbon dioxide originates in the soil and epigean atmosphere, and the thermal (thermogene) travertines where the carbon dioxide comes from thermally generated sources. Many travertine fabrics are influenced by bacteria and plants. These include 'stromatolitic' forms, many oncoids, shrubs, tufts, mats and moss travertines. Morphologically, travertines are conveniently divided into autochthonous (spring mounds and ridges, cascades, barrages, fluvial and lacustrine crusts, paludal deposits and cemented rudites) and the allochthonous or clastic travertines (valley-fills, back-barrage deposits, alluvial cones). Travertine deposits often include a wide range of fabrics and morphologies in one system. They are influenced locally by discharge, slope, vegetation, climate and human activity. Intergradations occur, both within travertine types but also with other freshwater deposits, e.g. calcrete and lake chalk. The influence of travertine deposition on the local hydrology and geomorphology is also discussed. The review emphasises the significance of scale and hydrology and aims to provide a unified scheme of travertine classification.Cette revue met l'accent sur la morphologie des travertins. Leur description repose sur trois critères : la géochimie, la microfabrique et la morphologie. Du point de vue de la géochimie, les travertins peuvent être divisés en deux groupes : les travertins d'eau météorique, où le dioxide de carbone provient du sol ou de la surface, et les travertins d'eau thermale, où le dioxide de carbone provient de sources thermales. La fabrique des travertins est souvent influencée par la présence des bactéries et des plantes, ce qui comprend des stromatolithes, de nombreux oncolithes et diverses formes caractéristiques. Du point de vue de la morphologie, les travertins sont autochtones (monticules, cascades, barrages, encroûtements fluviatiles ou lacustres, dépôts palustres et rudites cimentées) ou allochtones (dépôts de remblaiement de vallée, de remplissage amont de barrage, de cônes alluviaux). Les dépôts travertineux comprennent souvent un assortiment de fabriques et de morphologies comprises dans un seul ensemble selon le débit, la pente, la végétation, le climat et les activités humaines. On discute également de l'effet de la mise en place du travertin sur l'hydrologie locale et la géomorphologie. Cette revue fait ressortir l'importance de l'échelle et de l'hydrologie et tente de faire ressortir une vision intégrée de la classification des travertins.Dieser Aufsatz gibt einen ûberblick ùber die Klassifizierung der Travertine unter Hervorhebung ihrer Morphologie. Bei ihrer Beschreibung werden drei Kriterien benutzt: Geochemie, Mikrostruktur und Morphologie. Geochemisch kann man die Travertine in zwei Gruppen aufteilen: die Verwitterungs-Travertine, wo das Trâger-Kohlendioxyd aus dem Boden und der epigenetischen Atmosphâre stammt, und die thermischen Travertine, wo das Kohlendioxyd aus thermisch erzeugten Quellen kommt. Viele Travertin-Strukturen sind durch Bakterien und Pflanzen beeinfluBt. Dies umfaBt "stromatolithische" Formen, zahlreiche Onkoide, Straucher, Bûschel, Matten und Moos-Travertine. Morphologisch teilt man am besten die Travertine in autochthone (Bodenerhebungen und Rùcken Wasserfàlle, Dàmme, FIuR- und Seeverkrustungen, Sumpfablagerungen und verkittete Rudite) und in allochthone oder klastische Travertine (Tal-Auffùllungen, Ablagerungen hinter Dâmmen, alluviale Kegel). Die Travertin-Ablagerungen enthalten oft eine groBe Auswahl von Strukturen und Morphologien in einem einzigen System. Sie sind ôrtlich beeinfluBt durch Wasserfùhrung, Bôschung, Vegetation, Klima und menschliche Aktivitâten. Intergradation kommt vor, sowohl innerhalb der Travertin-Typen aber auch mit anderen Frischwasser-Ablagerungen, z.B. Kalkkrusten und See-Kreide. Auch wird der EinfluB der Travertin-Ablagerung auf die ôrtliche Hydrologie und Géomorphologie diskutiert. Der ûberblick hebt die Bedeutung von MaBstab und Hydrologie hervor und suent ein vereinheillichtes Schema der Travertin-Klassifikation zu geben

A Comparative Evaluation of Methods to Monitor Moisture in Historic Porous Masonry Materials

The project aimed to develop a methodology to compare the performance of a range of invasive and non-invasive moisture measurement methods used to assess moisture in porous masonry. This methodology was laboratory-based and used test blocks of common traditional building materials (limestone, sandstone, brick and lime mortar) under controlled conditions of drying and wetting. The performance of each method tested was compared against weight measurements, which give absolute measurements of moisture content – often called the gravimetric method. Experiments were also carried out to evaluate the influence of drying conditions and block size on the test results. A variety of non-invasive handheld moisture measurement devices were tested, including commonly available resistance, capacitance and microwave moisture meters. Also tested was a range of invasive methods, including wooden and ceramic dowels, relative humidity sensors and time domain reflectometry (TDR) probes. For some of the non-invasive methods, further experiments were designed and carried out to evaluate the depths to which they could measure saturated parts of otherwise dry blocks of sandstone and limestone. A simple experiment was also designed to measure the depth to which some of the non-invasive methods could sense metal objects in otherwise dry materials. This was used to evaluate whether the presence of metal in historic walls could affect the moisture measurements obtained. Finally, a short field monitoring exercise was carried out to explore the usefulness of both non-invasive and invasive microwave moisture measurements in comparison with conventional wooden dowel surveys

Seasonality in Moisture Dynamics in the Walls of the rock-cut Churches in Lalibela, Ethiopia: Implications for Weathering

Moisture plays a key role in rock decay in the built and natural environments. Rock-cut sites are particularly vulnerable to moisture-related weathering as they are carved into rock outcrops and do not have impermeable foundations or roofs to retard the flow of moisture. To characterise the moisture dynamics and its influence on weathering of rock-cut sites, we undertook a moisture monitoring campaign using a non-destructive Microwave Moisture Measurement System (MMMS) at two monolithic rock-cut churches in Lalibela, Ethiopia. The results showed that the walls were more saturated at depth than on the surface during the wet season. This suggests that low surface temperature and higher moisture content at depth will lead to constant-rate drying and accumulation of salts on the surface of the walls during the wet season. In the dry season, there was higher saturation near the surface than at depth (falling-rate drying). High rock surface temperature during the dry season contributes to subsurface drying and accumulation of salts below the surface. This seasonally shifting moisture dynamics will lead to a complex and dynamic damage profile. This study highlights the significant wetting facilitated by a lack of impermeable roofs and foundations at rock-cut structures during rainy periods

Investigating the effect of nanolime treatment on the drying kinetics of Clipsham limestone

Climate change poses an ever-increasing risk to our stone built heritage. Among conservation actions, the use of consolidant products is considered a possible response to this challenge, and the adoption of nanolimes has been widely studied showing promising results. However, while the effectiveness and method of application has been assessed, few studies have probed the changes in drying kinetics following treatment. In fact, a drastic alteration of the water transport might lead to further anomalies. This study investigates the influence of nanolimes dispersed in ethanol on the drying kinetics of Clipsham limestone using cavity ring-down spectroscopy. The degree of treatment was assessed by gravimetry, Raman spectroscopy, optical microscopy, colorimetry, optical profilometry and thin section analysis. Results showed an increase in the dry mass, observable colour changes and decrease in surface roughness. Small but reproducible increases were observed in the evaporation flux for phase I behaviour following treatment, however, no changes were observed in the total mass of water released or the phase II diffusivity. Determination of the activation energy associated with phase II drying was unchanged following treatment . These results indicate that following treatment there has been little-to-no change in the internal surfaces and structure of the stone to affect vapour transport

The global transformation of geomorphology

This chapter reviews the various developments in geomorphology in terms of institutions, journals, textbooks, research stations, etc. Among the institutions discussed are the Binghamton Geomorphology Symposium, the Geological Society of America Quaternary Geology and Geomorphology Division, the Association of American Geographers Geomorphology Specialty Group, the British Geomorphological Research Group, the IGU Commission on Measurements, Theory and Application in Geomorphology (COMTAG), the International Association of Geomorphologists, the European Geosciences Union (EGU), the American Geophysical Union (AGU), the International Quaternary Association, and the International Conference on Aeolian Research. Many countries established their own national bodies. A number of new journals appeared, including Catena, Earth Surface Processes and Landforms, Géomorphologie, and Geomorphology. In addition, during the closing decades of the twentieth century there was a proliferation of textbooks in geomorphology. One development was that geomorphological research was promoted by the establishment of research stations. These permitted long-term monitoring and provided bases for sustained investigations. The study of fluvial processes was much encouraged in the United States at USDA Forest Service research basins (known as ‘watersheds’ in the USA) such as the Hubbard Brook Experimental Forest (New Hampshire), Coweeta Hydrologic Laboratory (North Carolina) and the H.J. Andrews Experimental Forest (Oregon). The Royal Geographical Society (with the Institute of British Geographers) organized ambitious research projects in collaboration with host nations. Various US government departments supported much geomorphological research in various parts of the world. Some European countries fostered overseas geomorphological research and created missions. Notable was the work of ORSTOM (Office de la Recherche Scientifique et Technique Outre-mer) in former francophone colonies. In the post-war years, and as independence approached and then occurred, new universities were established in Africa. These employed expatriate geomorphologists and also trained up a new generation of indigenous scholars. The decades since the 1960s have been a period of space exploration and the development of remote sensing. This has had important implications for geomorphology. The period also saw the onset of the digital age and the beginning of the World Wide Web's influence on teaching and research. Applied research became increasingly important. A major cause for international and cross-disciplinary co-operation during the period was the emergence of geoarchaeology. Finally, since the 1950s, an increasing number of women have made important contributions to the discipline