Denudation rate

Rivers transport suspended sediments derived from the disintegration of basin surface layers. With reduced velocity, sediment is deposited in the river channel. The finest material is carried to the sea. It has been estimated that the average mechanical denudation rate for continents is 0.056 mm year (35). This is based on a total suspended load of 13.5 x 10 metric tons year (S). Presently, about two-thirds of the world s total suspended sediment load derives from Southern Asia and large Pacific Islands. Berner has estimated the increase in sediment loss in the U.S. and world since prehuman times to be approximately 200% (35). Current estimated erosion rate from the major land forms is provided in Table I. The relatively recent construction of large sediment trapping dams that normally caused sediment to be deposited in river valleys or transported to the ocean has drastically reduced sediment yields in great rivers. 

Ruxton, B. P. and McDougall, I. (1967) Denudation rates in northeast Papua from potassium-argon dating of lavas. Am. ]. Sci. 265,545-561. 

Soil water flow is decidedly episodic. During dry times the water solutions in the soil are probably fairly concentrated and not very reactive. Time-averaged reaction rates should be roughly proportional to the fraction of time reacting minerals are in contact with thermodynamically imdersaturated (and reactive) water. In a study of the relationship between denudation rate and runoff for rivers draining igneous and metamorphic rock in Kenya, Dunne (1978) obtains the relationship of (denudation rate in tons/km per year) = 0.28 (runoff in mm/ year)°. ... 

Paolini, 1986 Stallard, 1980). Comparison with Fig. 9-7 shows a reasonable match between denudation rates and uplift rates for a particular type of terrain. The most concentrated water samples and highest denudation rates are observed in river basins in tectonically active areas. 

Fig. 9-8 Histogram of dissolved solids of samples from the Orinoco and Amazon River basins and corresponding denudation rates for morpho-tectonic regions in the humid tropics of South America (Stal-lard, 1985). The approximate denudation scale is calculated as the product of dissolved solids concentrations, mean armual runoff (1 m/yr), and a correction factor to account for large ratios of suspended load in rivers that drain mountain belts and for the greater than average annual precipitation in the lowlands close to the equator. The correction factor was treated as a linear function of dissolved solids and ranged from 2 for the most dilute rivers (dissolved solids less than lOmg/L) to 4 for the most concentrated rivers (dissolved solids more than 1000 mg/L). Bedrock density is assumed to be 2.65 g/cm. (Reproduced with permission from R. F. Stallard (1988). Weathering and erosion in the humid tropics. In A. Lerman and M. Meybeck, Physical and Chemical Weathering in Geochemical Cycles," pp. 225-246, Kluwer Academic Publishers, Dordrecht, The Netherlands.)...

Earth (Li, 1976). The high denudation rate is a reflection of the poorly lithifled, highly tecton-ized nature of the sedimentary rocks that compose the island. Sediment-yield data compiled by Milliman and Meade (1983) and Milliman and Syvitski (1992) indicate that island arcs and mountain belts in the tropical and subtropical west Pacific may contribute as more than 22% of all solid material discharged by rivers into the ocean. Furthermore, the tropical mountainous areas in southeast Asia and India may contribute another 33%. 

Mountain building usually involves compres-sional deformation of the crust. Studies of the physics of orogeny suggest that there is a feedback between the nature of the building process and denudation rates. Suppe (1981), Davis et al. (1983), and Dahlen et al. (1984) have modeled the effects of brittle deformation in accretionary fold-thrust mountain belts such as Taiwan and the Andes. The basis of their model is the hypothesis that rock deformation is governed... 

This is in part because denudation rates are very low and because sea-level fluctuation may be important to the erosion process. Cratons seem to undergo major episodes of erosion following drops of sea level. When the level drops to a stable stand of several million years, much of the landscape is eroded down to the new level and an erosion surface or a planation surface forms. 

Edmond, J. M., Palmer, M. R., Measures, C. I. Grant, B., and Stallard, R. F. (1995). The fluvial geochemistry and denudation rate of the Guayana Shield in Venezuela, Colombia, and Brazil. Geochim. Cosmochim. Acta 59,3301-3325. 

Louvat P, Allegre CJ (1997) Present denudation rates on the island of Reunion determined by river geochemistry Basalt weathering and mass budget between chemical and mechanical erosions. Geochim Cosmochim Acta 61(17) 3645-3669... 

Historical rates of anthropogenic erosion (open diamonds). Solid black diamonds are volumes of several large volcanic eruptions (dates in parentheses) heavy black line Is the mean deep-time denudation rate of 24m/10 y. Source From Wilkinson, B. H. (2005). Geology 33(3), 161-164. 

Figure 4 Steady-state temperature structure beneath a periodic topography as calculated using the algorithms of Mancktelow and Grasemann (1997). This simulation assumes a topographic relief of 1.5 km, a topographic wavelength of 20 km, and a uniform denudation rate of 1 mm yr. The topmost sinusoidal line indicates the land surface (defined as having a temperature of 0 °C). Shaded contours are steady-state isotherms from 50 °C to 350 °C at 50 °C intervals. The red contours represent nominal bulk closure isotherms for the muscovite Rb/Sr, apatite fission track, and apatite and titanite (U-Th)/He thermochronometers. Positions A and B and their dashed unroofing paths...

Moore M. A. and England P. C. (2001) On the inference of denudation rates from cooling ages of minerals. Earth Planet. Sci. Lett. 185, 265-284. 

A number of studies have observed a linear correlation between precipitation or runoff and solute fluxes or chemical denudation rates (Dunne, 1978 Dethier, 1986 Stewart et ai, 2001). The relationship between solute silicon fluxes and runoff of the large watershed data set plotted in Figure 20 shows comparable relationships for granitic and basaltic rock types (Bluth and Kump, 1994). 

Basin Specific runoff (myr-3 Catchment area km (and % ice cover) Total solute flux (kgkm yr 6 ( X lOh Cationic denudation rate (meq m ) Lithology Source... 

Eyles N., Sasseville D. R., Slatt R. M., and Rogerson R. J. (1982) Geochemical denudation rates and solute transport mechanisms in a maritime temperate glacier basin. Can. J. Earth Sci. 19, 1570-1581. 

Schaller, M., von Blanckenburg, F., Kubik, P. Kramers, J. D. 1999. Catchment-wide denudation rates from cosmogenic nuclides in river sediment. Jourrml of Conference Abstracts, 4, 444. 

Gunnell, Y. (2003) Radiometric ages of laterites and constraints on long-term denudation rates in West Africa Geology 31, 131-134. 

Physical denudation rates of 80-800 mm ka 1 would cause erosion of the land mass to the present-day mean elevation of continents, 840 m, in a period of 106-107 years if there were no crustal uplift compensating for, or exceeding, the rates of erosion. 

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