Surface Processes Weathering

Highly weathered basalt, northern Lesotho. Note onion skin weathering. 

Mechanicai or physicai weathering is particuiariy effective in ciimatic regions that experience significant diurnai changes of temperature. This does not necessariiy impiy a iarge range of temperature, as frost and thaw action can proceed where the range is iimited. 

The mechanical effects of weathering are well displayed in hot deserts, where wide diurnal ranges of temperature cause rocks to expand and contract. Because rocks are poor conductors of heat, these effects are mainly localized in their outer layers where alternate expansion 

There are three ways whereby salts within a rock can cause its mechanical breakdown by pressure of crystallization, by hydration pressure, and by differential thermal expansion. Under certain conditions, some salts may crystallize or recrystallize to different hydrates that occupy a larger space (being less dense) and exert additional pressure, that is, hydration pressure. The crystallization pressure depends on the temperature and degree of supersaturation of the solution, whereas the hydration pressure depends on the ambient temperature and relative humidity. Calculated crystallization pressures provide an indication of the potential pressures that may develop during crystallization in narrow closed channels (see Chapter 6). Crystallization of freely soluble salts such as sodium chloride, sodium sulphate or sodium 

Honeycomb weathering in sandstone of Jurassic age, Isle of Skye, Scotland. 

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Under natural conditions the rates of dissolution of most minerals are too slow to depend on mass transfer of the reactants or products in the aqueous phase. This restricts the case to one either of weathering reactions where the rate-controlling mechanism is the mass transfer of reactants and products in the soHd phase, or of reactions controlled by a surface process and the related detachment process of reactants. 

To highlight one example of a surface process of global significance, we repeat here (Chapter 5.1) a brief account on carbonate weathering and CaC03 precipitation ... 

Talma AS, Netterberg F (1983) Stable isotope abundances in calcretes. In Residual Deposits Surface Related Weathering Processes and Materials. Wilson, RCL (ed) Oxford Blackwell Scientific Publ., p 221-233 Tian L, Masson-Delmotte V, Stievenard M, Tao T, Jouzel J (2001) Tibetan Plateau summer monsoon northward extent revealed by measurements of water stable isotopes. J Geophys Res 106 28,081-28,088 Tian L, Yao T, White JWC, Yu W, Wang N (2005) Westerly moisture transport to the middle of Himalayas revealed from the high deuterium excess. Chinese Sci Bull 50 1026-130 Uba CE, Heubeck C, Hulka C (2006) Evolution of the late Cenozoic Chaco foreland basin, southern Bolivia. Basin Res 18 145-170... 

McCarroll, D. Viles, H. (1995). Rock-weathering by the lichen Lecidea auriculata in an Arctic alpine environment. Earth Surface Processes and Landforms, 20, 199-206. 

These include the effect of the processing conditions on the mechanical properties of synthetic and natural polymers, the characterization of ion-implanted polymer surfaces, the study of mechanical changes in polymer implants after wear, the influence of coatings on surface properties, weatherability characterization of polymers, etc. 

Carlisle, D. (1983) Concentration of uranium and vanadium in calcretes and gyp-cretes. In Wilson, R.C.L. (Ed.) Residual Deposits Surface Related Weathering Processes and Materials. Special Publication 11. London Geological Society, pp. 185-195. 

Martini, I.P. Chesworth, W. (Eds) (1992) Weathering, Soils andPalaeosols. Developments in Earth Surface Processes 2. Amsterdam Elsevier. 

Summerfield, M.A. (1984) Isovolumetric weathering and silcrete formation, Southern Cape Province, South Africa. Earth Surface Processes and Landforms 9, 135-141. 

Goudie, A.S. (1993) Salt weathering simulation using a single-immersion technique. Earth Surface Processes and Landforms 18, 369-376. 

Weathering, and subsequent deterioration of rock exposed to the environment, are slow processes. Weathering rates are influenced by temperature, the presence of moisture, the presence of organic acids, and the carbon dioxide partial pressure in the solution in contact with the rock surface. In contemporary industrial societies, natural weathering processes are accelerated by elevated pollutant concentrations. Acidic pollutants in particular, in both air and rainfall, are recognized as serious hazards to carbonate rock used in commerce and cultural resources... 

Klappa, C.F. (1983) A process-response model for the formation of pedogenic calcretes. In Residual Deposits Surface Related Weathering Processes and Materials. (Ed. Wilson, R.C.I.). Spec. Publ. Geol. Soc. London, 11, 221-233. 

The second common lanthanide abundance pattern which is uniform and which has widespread geochemical significance, is that observed in most post-Archean sedimentary rocks such as shales. This pattern, as discussed later, is generally taken to represent that of the upper continental crust exposed to weathering and erosion, so that it forms a suitable base for comparison of terrestrial surface processes affecting the lanthanides. Two different sets of shale abundances have been used for normalisation. The first is the North American Shale Composite (NASC, Haskin et... 

Many important sedimentary phosphate deposits owe their present character to surface or near-surface processes. For instance, the Florida deposits have been reworked in the past under surface conditions. Several cycles of deposition and reworking have concentrated the phosphate, and weathering has removed most of the carbonates from the upper (near the surface) portions of the deposits. --------... 

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