Chemical Denudation Rates Research Articles

Promotion of chemical weathering by higher plants: field observations on Hawaiian basalts

An electron microprobe and petrographic microscope were used to study the biota-rock interface beneath higher-plant communities and lichens, as well as unvegetated surfaces, on Hawaiian basalt flows ranging from a few years to several thousand years in age and currently receiving moderate to extremely high annual rainfall. We find dramatic (order of magnitude minimum) acceleration of weathering rates beneath vascular plants on the youngest flows relative to adjacent non- or primitively-vegetated controls, notably rocks colonized by the common fruticose lichen Stereocaulon uulcani. Bulk dissolution of plagioclase accounts for most of the weathering observed beneath higher plants on these young basalts. Analysis of older flows under mature forests reveals that chemical weathering beneath vascular plant communities continues unabated for thousands of years after initial colonization. Moreover, such weathering is not limited to exterior basalt surfaces but is commonly found adjacent to joints and vesicles within the rock, where it is often associated with fine (sub-2 mm diameter) plant roots. Plagioclase dissolution was also observed on lichen-encrusted and unvegetated flows a few hundred to thousands of years in age, but it was typically much less advanced than beneath higher plants and rarely extended more than several millimeters from exterior rock surfaces. Chemical denudation rates on older flows with higher plants are at minimum ten times greater than those with only lichens or microbiota in the environments studied. If S. uulcani and associated microflora resemble the terrestrial precursors to vascular plant communities, then the results of studies such as this have implications for the history of atmospheric CO 2 and the Earth's climate.

Rates of erosion and sediment evacuation by glaciers: A review of field data and their implications

Diverse field data on glacial sediment yields are assembled in the context of the current interest in sedimentary basin development in glaciated regions, and in controversial linkages between global climate and topography. Attention herein is directed at sediment yields, including both overall bedrock erosion and evacuation of sediments stored in glaciated basins over several years or decades. These yields, expressed as effective rates of glacial erosion, vary by orders of magnitude from 0.01 mm yr −1 for polar glaciers and thin temperate plateau glaciers on crystalline bedrock, to 0.1 mm yr −1 for temperate valley glaciers also on resistant crystalline bedrock in Norway, to 1.0 mm yr −1 for small temperate glaciers on diverse bedrock in the Swiss Alps, and to 10–100 mm yr −1 for large and fast-moving temperate valley glaciers in the tectonically active ranges of southeast Alaska. In Alaska, current sediment yields generally increase with the extent of glacial ice cover, and are particularly high in the large heavily-glaciated basins of southern Alaska, where they exceed those of basins from other regions by about one order of magnitude. These results, supported by comparisons of sediment yields between glaciated and nonglaciated basins in Alaska, Norway and Iceland, suggest that climatic conditions favorable for the expansion of temperate valley glaciers tend to increase both mechanical and chemical denudation rates. The results are discussed in the broader context of linking erosion and climate during the ice ages of the Quaternary, and interpreting records of sedimentation from glaciated regions.

The Himalaya-Bengal Fan Denudation-Accumulation System during the past 20 Ma

Mass balances for both denudation in the Himalayas and sediment accumulation in the Subhimalayan basins, including the Bengal deep-sea fan but excluding the Indus fan, yield 7.1 × 106 km3 and 7.4 × 106 km3 (s ± 20%, rock of 2.75 g/cm3 density), respectively, for the past 20 million years. Coarsening and increased sediment accumulation rates in the foreland basin and in the Bengal foredeep indicate accentuated tectonic activity and unroofing in the Himalayas since that time. The sediment volume includes ≥1 × 106 km3 of Neogene Bengal fan sediment that was lost via the Nicobar fan to the Sunda accretionary wedge. In addition, the Indian peninsular rivers contributed about c. 0.6 × 106 km3 of solid load to the basins. Average denudation during the past 20 m.y., as derived from geothermobarometric data and restored cross sections, occurred most rapidly along the High Himalayan crystalline chain (vertical unroofing c. 1000 m/m.y.; northward lateral retreat of southern Himalayan slope, exposed to monsoonal rain, ≤3.5 km/m.y.) and much slower in the Tethyan sedimentary zone to the north (average 150 m/m.y.). The solute loads of the modern Himalayan rivers indicate a mean chemical denudation rate of 17 m/m.y. The distinct decrease in sediment accumulation on the outer Bengal fan between about 7 and 1 Ma (in contrast to the Indus fan) is probably caused by exogenic factors rather than by a significant decline in tectonic activity. Pre-20 Ma sediments in the Subhimalayan basins were derived mainly from the southern margin of the Tibet plateau or from sources outside the study area.

Natural and anthropogenic budgets of a small watershed in the massif central (France): Chemical and strontium isotopic characterization of water and sediments

A small watershed (160 km2) located in the Massif Central (France) has been chemically, isotopically and hydrologically studied through its dissolved load, bed sediments and soils. This watershed is underlain by basaltic bedrock and associated soils in which the vegetation is dominated mainly by meadows. Dissolved concentrations of major ions (Cl, SO4, NO3, HCO3, Ca, Na, Mg, K, Al and Si), trace elements (Rb and Sr) and strontium isotopes have been determined for two different hydrologic periods on the main stream of the Allanche river and its tributaries. The major objectives of this study were to characterize the chemical and isotopic signatures of each reservoir occurring in the watershed. Changes in chemical and isotopic signatures are interpreted in terms of fluctuations of the different components inputs: rainwater, weathering products, anthropogenic addition. Water quality may be influenced by natural inputs (rainwater, weathering processes) and anthropogenic additions (fertilizers, road salts, etc.). Precipitation serves as a major vehicle for dissolved chemical species in addition to the hydrosystem and, in order to constrain rain inputs, a systematic study of rainwaters is carried out over a one year period using an automatic collector. Corrections of rainwater addition using chloride as an atmospheric input reference were computed for selected elements and the “Sr/”Sr ratio. After such corrections, the geochemical budget of the watershed was determined and the role of anthropogenic additions evaluated through the relationship between strontium isotopes and major and trace element ratios. Thus, 10% of Ca and Na originate in rainwater input, 40 to 80% in fertilizer additions and 15 to 50% in rock weathering The cationic denudation rates for this watershed are around 0.3 g s−1 km2 during low water discharge and 0.6 g s−1 km2 in high water stage. This led to a chemical denudation rate of 5.3 mm/1000 years. For solid matter, the normalization of chemical species relative to parent rocks shows the depletion or enrichment in soils and sediments. The use of K and Ca as mobile reference illustrates the weathering state of soils and sediments relative to parent rocks. This weathering state for bed sediments range from 15 to 45% for the K normalization and from 2 to 50% for the Ca normalization. For the soils, the weathering state ranges from 15 to 57% for the K normalization and from 17 to 90% for the Ca normalization.

Rates of chemical denudation and CO drawdown in a glacier-covered alpine catchment

Research Article| January 01, 1995 Rates of chemical denudation and CO2 drawdown in a glacier-covered alpine catchment Martin Sharp; Martin Sharp 1Department of Geography, University of Alberta, Edmonton, Alberta T6G 2H4, Canada Search for other works by this author on: GSW Google Scholar Martyn Tranter; Martyn Tranter 2Department of Geography, University of Bristol, Bristol BS8 1SS, United Kingdom Search for other works by this author on: GSW Google Scholar Giles H. Brown; Giles H. Brown 3Institute of Earth Studies, University College of Wales, Aberystwyth, Dyfed SY23 3DB, United Kingdom Search for other works by this author on: GSW Google Scholar Mark Skidmore Mark Skidmore 1Department of Geography, University of Alberta, Edmonton, Alberta T6G 2H4, Canada Search for other works by this author on: GSW Google Scholar Geology (1995) 23 (1): 61–64. https://doi.org/10.1130/0091-7613(1995)023<0061:ROCDAC>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Martin Sharp, Martyn Tranter, Giles H. Brown, Mark Skidmore; Rates of chemical denudation and CO2 drawdown in a glacier-covered alpine catchment. Geology 1995;; 23 (1): 61–64. doi: https://doi.org/10.1130/0091-7613(1995)023<0061:ROCDAC>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Solute fluxes from a glacier-covered alpine catchment are partitioned into components derived from sea-salt, acid aerosol, dissolution of atmospheric CO2, and crustal weathering. The bulk of solute is crustally derived. Coupled sulfide oxidation and carbonate dissolution (SO-CD) and carbonation of carbonate minerals generate approximately equal amounts of solute. Chemical denudation constitutes <1.5% of solid denudation but is significantly higher than the continental average. CO2 drawdown by weathering reactions varies directly with discharge and suspended-sediment load and inversely with meltwater p(CO2). If it is generally true that flushing rates control CO2 drawdown in glacier-covered catchments, then glacially driven chemical weathering could be a significant factor in carbon cycling and climate change on glacial-interglacial time scales. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Natural controls of fluvial denudation rates in major world drainage basins

We present a new compilation of estimates of modern rates of mechanical and chemical denudation for externally drained basins exceeding 5×105 km2 in area. These estimates are based on sediment and solute load data selected in order to represent natural rates as far as possible. Chemical denudation rates have been calculated by deducting the nondenudational component of solute load. Mechanical denudation rates range from 1 mm kyr−1 for the St. Lawrence and Dnepr basins to 670 mm kyr−1 for the Brahmaputra basin. Chemical denudation rates vary from 1 mm kyr−1 (Kolyma, Niger, Nile and Rio Grande basins) to 27 mm kyr−1 (Chiang Jiang basin). The Kolyma basin has the lowest (4 mm kyr−1), and the Brahmaputra basin the highest, overall rate of denudation (688 mm kyr−1). Relationships between denudation rates and a range of morphometric, hydrologic, and climatic variables are investigated through correlation and regression analysis. Morphometric variables, such as mean local relief, are accurately calculated for large basins for the first time by using the National Geophysical Data Center 10‐minute topographic database. Variables expressing basin relief characteristics and runoff are found to be most strongly associated with both mechanical and chemical denudation rates, with more than 60% of the variance in total denudation being accounted for by basin relief ratio and runoff. Basin area, runoff variability, and mean temperature, however, are only weakly associated with rates of denudation. Although direct comparisons cannot be made, it appears that rates of basin denudation derived from present‐day mass flux estimates are not, overall, significantly different from estimates of long‐term rates based on sediment volume and thermochronologic data. It therefore appears that the key factors identified as controlling denudation rates here are also applicable to the geological time spans relevant to the interaction between tectonic and denudational processes.

Lithologic and climatologic controls of river chemistry

The chemistries of rivers draining a variety of lithologic and climatic regions have been surveyed for the purpose of quantifying the fluxes of bicarbonate and silica from rivers with respect to bedrock lithology and runoff. In all, 101 different rivers, each draining a primary lithology, were examined across the United States, Puerto Rico, and Iceland. To minimize seasonal effects, only rivers with at least two years of data were used. Basaltic catchments were examined in the greatest detail. In a survey of Hawaiian Island watersheds, the average river chemistries could be related to the distribution of soil associations within each catchment. An analysis of cation activity relationships among rivers draining basaltic catchments shows that the river compositions define slopes which are consistent with an equilibrium (ion exchange) control on cation ratios. Among different lithologies, unique weathering rate relationships were developed with yields at typical present-day runoff rates (1–100 cm/y) increasing in the order sandstones, granites, basalts, shales, and carbonates. The bicarbonate and silica fluxes for each of these lithologies have been quantified for use in global studies of chemical denudation. Our study confirms that the dissolved yield of a given drainage basin is determined by a balance between physical and chemical weathering; thus, a warm, wet climate, or the presence of abundant vegetation cannot guarantee high rates of chemical denudation unless accompanied by high rates of physical removal.

Present Chemical Weathering of Basalt in Iceland

Before the initiation of the water cycle on the 'early Earth' all the rocks were volcanogenic (e.g. Ronov, 1964). At present, volcanic rocks cover about 8 % of the land surface of the Earth and more than half of that is of basaltic composition (Meybeck, 1987). The present contribution of the weathering of volcanic rocks to the dissolved load of the world's rivers is less than 3%, the most important contribution comes from carbonate rocks (45%) and shale (20%; Meybeck, 1987). The high contribution of shale is primarily due to the weathering of small portions of the shale, i.e. calcareousand pyritic-shales. The chemical weathering of Ca-Mg silicate rocks is important for the atmospheric COz on a multimillion-year time scale and may therefore influence the temperature of the atmosphere (e.g. Berner, 1992). Thus, even to day, the weathering of basalt is an important factor in the net loss of CO2 from the atmosphere, and it's general importance increases with geological age because the ratio of basalt to sedimentary rocks increases with the age of the crust (e.g. Ronov, 1964). Iceland provides an opportunity to study the effects of the age of rocks, glaciation and vegetation on the nature and rate of chemical weathering of basalts. About 10% of the country is covered with glaciers, and one fourth is covered with vegetation. The interior of the country is unpopulated, providing pristine unpolluted catchment areas of uniform temperature and rock composition (basalt) with a variable glacier-and vegetation cover and variable runoff. The objective of this paper is to define and interpret, the source of supply for the dissolved constituents in Icelandic rivers, the relative mobility of the elements during weathering of basalt, the rate of chemical denudation in Iceland and the effect of age of rocks, and glacier/ vegetation cover on the chemical weathering of basalt.

Chemical denudation and weathering mechanisms in central Massachusetts, U.S.A.

Two small streams on opposite sides of the catchment of Quabbin Reservoir, in west-central Massachusetts, have very different chemical compositions (Table 1 ). Cadwell Creek, which is underlain primarily by gneissic rocks, has a thin surficial cover of sandy till (Yurerich et al., 1989). Shallow groundwater and interflow through the litter layer provide most runoff, depressing the pH during high discharge events. In Mundberry Brook, schists and amphibolites are more prevalent in the watershed, and the till contains a substantial volume of well-neutralized groundwater. Storm events tend to flush this water into the stream channel; consequently, pH depressions are muted. The Quabbin catchment is dominated by this latter type of stream, which apparently regulates the alkalinity in the reservoir. The rate of chemical denudation for each stream, as determined by mass export relative to precipitation input, also shows some nota-

Chemical denudation rates in SW-Iceland

Chemical denudation rates in SW-Iceland

Major ion chemistry of the Ganga-Brahmaputra river system: Weathering processes and fluxes to the Bay of Bengal

The Ganga-Brahmaputra, one of the world's largest river systems, is first in terms of sediment transport and fourth in terms of water discharge. A detailed and systematic study of the major ion chemistry of these rivers and their tributaries, as well as the clay mineral composition of the bed sediments has been conducted. The chemistry of the highland rivers (upper reaches of the Ganga, the Yamuna, the Brahmaputra, the Gandak and the Ghaghra) are all dominated by carbonate weathering; (Ca + Mg) and HCO 3 account for about 80% of the cations and anions. In the lowland rivers (the Chambal, the Betwa and the Ken), HCO 3 excess over (Ca + Mg) and a relatively high contribution of (Na + K) to the total cations indicate that silicate weathering and/or contributions from alkaline/saline soils and groundwaters could be important sources of major ions to these waters. The chemistry of the Ganga and the Yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions. Illite is the dominant clay mineral (about 80%) in the bedload sediments of the highland rivers. Kaolinite and chlorite together constitute the remaining 20% of the clays. In the Chambal, Betwa and Ken, smectite accounts for about 80% of the clays. This difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins. The highland rivers weather acidic rocks, whereas the others flow initially through basic effusives. The Ganga-Brahmaputra river system transports about 130 million tons of dissolved salts to the Bay of Bengal, which is nearly 3% of the global river flux to the oceans. The chemical denudation rates for the Ganga and the Brahmaputra basins are about 72 and 105 tons· km −· yr −1, respectively, which are factors of 2 to 3 higher than the global average. The high denudation rate, particularly in the Brahmaputra, is attributable to high relief and heavy rainfall.

Groundwater chemistry and cation budgets of tropical karst outcrops, Peninsular Malaysia, I. Calcium and magnesium

The discharge and chemical properties of 217 autogenic groundwaters were monitored over a 1-yr period in the tower karsts of central Selangor and the Kinta Valley, and in the Setul Boundary Range. Because of differences in soil P CO 2 , calcium concentrations are significantly higher in the Boundary Range (mean, 82.5 mg l −1) than in the tower karst terrain (44.6 mg l −1). Local differences in both source area P CO 2 and amounts of secondary deposition underground cause marked intersite variability, particularly in the tower karst. Dilution occurs during flood peaks in certain conduit and cave stream waters. Generally, however, calcium correlates positively with discharge, since the amount of secondary deposition per unit volume of water decreases at higher flows. Magnesium concentrations and Mg:Ca + Mg ratios of groundwaters are strongly influenced by bedrock composition, though bedrock heterogeneity and the kinetics and equilibria of carbonate dissolution reactions preclude extremely low or high Mg:Ca + Mg values. Net chemical denudation rates range from 56.6 to 70.9 m 3km 2yr −1. The results are considered in relation to cation fluxes in surface runoff, soil throughflow and nutrient cycling. Preliminary calcium and magnesium budgets show that (1) dissolutional activity is largely confined to the near-surface zone; and (2) the annual uptake of calcium and magnesium by tropical limestone forests is similar in magnitude to the net solute output in groundwaters.

Strontium isotope stratigraphy and geochemistry of the late Neogene ocean

A curve describing the variation of the strontium isotopic composition of seawater for the late Neogene (9 to 2 Ma) was constructed from 87Sr/ 86Sr analyses of marine carbonate in five Deep Sea Drilling Project (DSDP) sites: 502, 519, 588, 590, and 593. The strontium isotopic composition of the oceans increased between 9 and 2 Ma with several changes in slope. From 9 to 5.5 Ma, 87Sr/ 86Sr values were nearly constant at ∼ 0.708925. Between 5.5 and 4.5 Ma, 87Sr/ 86Sr ratios increased monotonically at a rate of ∼ 1 × 10 −4 per million years. The steep slope during this interval provides the potential for high resolution strontium isotope stratigraphy across the Miocene/Pliocene boundary. The rate of change of 87Sr/ 86Sr decreases to near zero again during the interval 4.5–2.5 Ma, and ratios average 0.709025. The relatively rapid increase of 87Sr/ 86Sr between 5.5 and 4.5 Ma must be related to changes in the flux or average 87Sr/ 86Sr ratios of the major inputs of Sr to the oceans. Quantitative modelling of these inputs suggests that the increase was most probably caused by an increase in the dissolved riverine flux of strontium to the oceans, an increase in the average 87Sr/ 86Sr composition of river water, or some combination of these parameters. Modelling of this period as a transient-state requires a pulse-like increase in the input of 87Sr to the oceans between 5.5 and 4.5 Ma. Alternatively, the 5.5–4.5 Ma period can be modelled as a simple transition from one steady-state to another if the oceanic residence time of strontium was eight times less than the currently accepted value of 4 Ma. During the time interval of steep 87Sr/ 86Sr increase, other geochemical and sedimentologic changes also occur including an increase in sediment accumulation rates, a drop in the calcite compensation depth (CCD), and a decrease in the δ 13C of dissolved bicarbonate (i.e., “carbon shift”). The simplest mechanism to explain 87Sr/ 86Sr variation and these related geochemical changes is to invoke an increase in the dissolved chemical fluxes carried by rivers to the oceans. This, in turn, implies increased chemical denudation rates of the continents and shelves during the late Neogene. The increase in chemical weathering rates is attributed to increased exposure of the continents by eustatic regression, intensified glacial/interglacial cycles, and accelerated rates of global tectonism beginning at 5.5 Ma during the latest Miocene.

Continental erosion and large‐scale relief

A worldwide investigation of continental erosion is carried out by the study of large drainage basins, on the basis of hydrological data, environmental factors, and basin relief distribution. Inside each basin, mean geochemical and mechanical denudation rates are defined. A multicorrelation analysis shows that the mechanical denudation rates Ds are uncorrelated with environmental factors and correlated with mean basin elevation H, while chemical denudation rates Dd are insensitive to relief but correlated with mean annual precipitation. Furthermore, two linear relationships between H and Ds are detected: (1) Ds (m/10³ yr) = 419×10−6 H (m) ‐ 0.245, with V (explained variance) = 95.1%; this law concerns basins related to orogenies younger than 250 Ma. The negative intercept is interpreted as a continental sedimentation rate of 245 m/m.y. An alternative model in which one invokes a critical elevation, separating erosion from sedimentation, is equally successful and leads to lower sedimentation rates (60–110 m/m.y.). For both models, one derives from the slope of the adjustments, erosion time constants on the order of 2.5 m.y. (2) Ds (m/10³ yr) = 61×10−6 H (m), with V = 86.5%; this law concerns basins related to older orogenies. The null intercept suggests the lack of continental storage. Because of the more important dispersion of the data, the erosion time constant is calculated separately for each basin; it ranges from 15 to 360 m.y. The tectonic implications of these results are discussed. In particular, the short time constant 2.5 m.y. agrees with orogenic uplift rates on the order of 1 mm/yr, observed in active mountain chains.

Magnesium and calcium in carbonate bedrock and groundwaters, Peninsular Malaysia

Groundwaters draining Kuala Lumpur Limestone, Kinta Limestone and limestones of the Setul Formation were monitored over a 1 yr period. The closeness of the mean Mg:Ca + Mg ratios of the groundwaters (12.8%) and bedrock (13.3%) indicates calcium and magnesium dissolution to be broadly congruent. Ratios < 2.5and> 35% are much less common in groundwaters than in bedrock because of: (i) heterogeneity in bedrock mineralogy within groundwater catchments; (ii) differential solubilities of calcium and magnesium in calcites, high magnesium calcites and dolomites; and (iii) preferential precipitation of calcium in secondary carbonate deposits. In groundwaters with variable discharges, Mg:Ca + Mg correlates negatively with discharge, as calcium deposition per unit volume of water diminishes at higher flows. Use of groundwater survey data to locate areas of dolomitization and make specific inferences about the mineralogy of limestone formations is discussed, and estimates of net chemical denudation rates (range, 56.6–70.9m 3/km 2/yr) are presented.

The impact of urbanization on major ion flux through catchments: A case study in Southern England

Although much is known about chemical denudation and nutrient cycling through catchments, little has been done to identify and explain changes in major ion flux upon urbanization. Fifty-two weekly samples of precipitation and stream waters were analyzed for 9 major ions totaling 95% of the total dissolved solids for a catchment in southern England. Net major ion export rates from the urban area are between 2 and 104 times those for the rural areas. This increase is attributed both to accelerated denudation and non-denudational anthropogenic sources. Estimates of both components indicate that between 50 and 60% of the dissolved ions removed from urban areas is non-denudational. This translates to possible increases in the chemical denudation rate of up to six-fold upon urbanization.

Processes and controls involved in the transfer of fluviatile sediments to the deep ocean

Sediment transport processes are described in relation to land surfaces, river systems, estuaries, deltas and continental shelves. Complex interrelationships between variables controlling transport, within each of the environments, are summarized. Extreme rates of mechanical denudation are presented and can be as high as 44 × 10 3 tonnes/km 2 /a (for Taiwan); they compare with mean European rates of around 30 tonnes/km 2 /a. Comparison is made between some representative rates of mechanical and chemical denudation. River inputs are examined, within the context of deltaic sedimentation patterns. It is suggested that fluviatile sediments can be transported over continental shelf areas and out into the oceans as hyperpycnal discharges. Organic material contained within the sediments is important geologically, in terms of its burial within marine sediments.

Erosional and chemical denudation rates in the Southwestern Idaho batholith

AbstractAnnual erosional denudation (ED) and chemical denudation (CD) rates are determined on four forested watersheds located in the Idaho batholith, Idaho, U.S.A. Bedrock in the study area is a coarse‐grained quartz monzonite. Annual sediment yields are computed from sediment collected in settling ponds at the watershed mouths and corrected for trapping efficiency. Solution loads for denudation components (Na, K, Ca, Mg, SiO2, A12O3 and FeO) are computed using equations relating concentration to flow and by integration of mean daily flow values. Eleven years of water chemistry data and 19 to 23 years of sediment yield data are used in the denudation estimates. Strong relationships exist between CD, ED and annual water yield, so probability distributions of annual water yield are used in Monte Carlo simulations to establish frequency distributions of annual CD and ED rates.Mean annual total denudation for the four watersheds (CD + ED) equals 235 kg ha −1 yr−1 or 8‐9 Bubnoffs. The 11 ‐year mean ED rates exceed CD rates for three of the four watersheds, although it is more probable in any given year that CD will exceed ED for three of the watersheds. ED is temporally more variable than CD for all watersheds. Simulations of denudation over 1000‐year periods indicate that the frequency of occurrence of ED is skewed toward higher denudation values, and the modal ED rate is substantially lower than the mean value. CD rates are less skewed, with mean and mode in the same class. Ninety‐seven per cent of CD is composed of Na, Ca and SiO2 fluxes. Episodic high ED rates are related to high peak flows from snowmelt runoff associated with winters of large snow accumulation. Perturbations such as fire or road construction would be expected to accelerate ED more than CD.

RATES OF SOIL FORMATION FROM BEDROCK OR CONSOLIDATED SEDIMENTS

Current rates for the conversion of bedrock or consolidated sediments to soil, or regolith, cart be determined by measuring the chemical composition of the bedrock or consolidated parent material, the composition of soil formed from it, and the efflux of dissolved constituents. Few studies have been designed for this purpose. The literature has been reviewed to find other studies that could be adapted for estimating rates of soil formation from lithic or paralithic materials. Rates of chemical denudation and soil formation increase with increases in temperature, precipitation, and runoff but decrease as soil depth increases from shallow or moderately deep to deep. The quantitative effects of temperature are obscured by the dominating effects of runoff volume. Soil formation from bedrock or consolidated sediments is on the order of 0.5 Mg ha-1 yr-1. Estimated values range from < 0.1 for plutonic rocks and limestone to 1.0 Mg ha-1 yr-1 or more for calcareous clastic sedimentary rocks.

Some estimates of denudation rates in karstic areas of the saltfjellet — Svartisen region, North Norway

Rates of chemical denudation were estimated for 8 karstic areas in the Saltfjellet-Svartisen region at the Arctic Circle in Northern Norway. The rates were derived from late-summer solute contents of autogenic springs in each area and from average specific runoff for the period 1930 – 1960 in the region. The rates were found to be in the range 8.2 – 64.2 m 3km −2a −1. Heavy winter snowfall does not permit continuous measurements, but spot sampling from several springs of exclusively exsurgence waters in each area make the results fairly representative as a preliminary estimate. The values are lower than most estimates of denudation reported from other arctic and alpine areas, but are in accord with recent figures from Swedish Lapland and Canada.