『Abstract
　This study critically assesses the temporal sensitivity of the steady-state model of erosion that has been applied to chemical and mechanical weathering studies of volcanic islands and the continents, using only one sample from each catchment. The model assumes a geochemical mass balance between the initially unweathered rock of a drainage basin and the dissolved and solid loads of the river.
　Chemical composition of 178 samples of suspended and dissolved inorganic river constituents, collected in 1998-2002, were studied from five basaltic river catchments in NE Iceland. The Hydrological Service in Iceland has monitored the discharge and the total suspended inorganic matter concentration (SIM) of the glacial rivers for 〜four decades, making it possible to compare modelled and measured SIM fluxes.
　Concentration of SIM and grain size increased with discharge. As proportion of clay size particles in the SIM samples increased, concentrations of insoluble elements increased and of soluble decreased. The highest proportion of altered basaltic glass was in the clay size particles.
　The concentration ratio of insoluble elements in the SIM was used along with data on chemical composition of unweathered rocks (high-Mg basalts, tholeiites, rhyolites) to calculate the pristine composition of the original catchment rocks. The calculated rhyolite proportions compare nicely with area-weighted average proportions, from geological maps of these catchments.
　The calculated composition of the unweathered bedrock was used in the steady-state model, together with the chemical composition of the suspended and dissolved constituents of the river. Seasonal changes in dissolved constituent concentrations resulted in too low modelled concentration of SIMmod at high discharge (and too high SIMmod at low discharge). Samples collected at annual average river dissolved load yielded SIMmod concentrations close to the measured ones. According to the model, the studied rivers had specific mechanical denudation rates of 1.3-3.0 kg/m²/yr whereas the average measured rates were 0.8-3.5 kg/m²/yr which are among the highest on earth.
　This study validates the use of a steady-state model of erosion to estimate mechanical weathering rates at the scale of a river catchment when the collected riverine dissolved load represents the average chemical composition over a mean hydrological year.

Keywords: chemical weathering; basalt weathering; mechanical denudation rate; erosion rates; river suspended sediments』

1. Introduction
　1.1. Study area
　1.2. Mineralogy and grain size of the suspended sediment
2. Materials and methods
　2.1. Sampling methods
　2.2. Analyses of water and sediment samples
3. Results
　3.1. Chemical composition of the riverine sediments
　3.2. Chemical composition of bedrocks in the river catchments
　　3.2.1. Rock types of the river catchments
　　3.2.2. Geochemical method to define the local rock composition in each catchment
　3.3. Steady-state model of erosion
　　3.3.1. Dissolved elements
　　3.3.2. Suspended sediment concentration from the steady-state model of erosion
　　　3.3.2.1. Seasonal variations
　　　3.3.2.2. Annual averages
　3.4. Mechanical denudation rate in NE Iceland
4. Discussions and conclusions
Acknowledgements
Appendix A. Supplementary material
References