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Quantification of the development of solution dolines provides important information for understanding the long-term evolution of karst landscapes. This study reports the initial results of an investigation of the long-term denudation rates along the side slopes of a solution doline based on analyses of cosmogenic [sup.36]Cl in calcite. The denudation rates increase in proportion with increasing size of the topographic contributing area, thereby supporting the hypothesis that the rate of surface lowering in carbonate terrains is controlled by water convergence in the epikarst. A simple model based on the empirical correlation between denudation rate and contributing area is successful in explaining the form of several solution dolines located close to the analyzed doline. The model reveals that these solution dolines, which have varying diameters, developed over similar time scales of the order of [l0.sup.5] yr. doi: 10.1130/G31302.1

To study the rate and mechanism of granitic rock weathering, field weathering experiments using granodiorite tablets (diameter 3.5 cm, height 1.1 cm, weight 30 g) were conducted at a catchment over 10 yr. The tablets were exposed at three positions having different weathering conditions: ground surface, above aquifer, and in aquifer. The weight of the tablets decreased linearly with time: 0.022 wt% [yr.sup.-1] for the ground surface, 0.013 wt% [yr.sup.-1] above the aquifer, and 0.42 wt% [yr.sup.-1] in the aquifer. Only minor changes of the tablet surface were observed after 10 yr of weathering at the ground surface and above the aquifer. In contrast, the tablets in the aquifer were remarkably weathered, and weathering of biotite was particularly noticeable, whereas that of plagioclase, K-feldspar, quartz, and hornblende was minor or moderate. The weathering of granodiorite is inferred to proceed by initial dissolution of mineral grain boundary (chemical process) and subsequent detachment of the mineral grain (physical process). To evaluate the amount of weathering caused only by the chemical process, a laboratory dissolution experiment was conducted on the granodiorite tablet using a flow-through reactor at 20 [degrees]C and pH 6-7. The obtained rates, 0.0078-0.010 wt% [yr.sup.-1], were ~50 times slower than the field rate in the aquifer. This result shows that the contribution of the physical process to granodiorite weathering in the aquifer is very large compared to that of the chemical process, and the relative intensities of the two processes during the 10 yr weathering are estimated to be chemical:physical = 1:~50. Keywords: chemical weathering, physical weathering, weathering rate, granodiorite, grain boundary, dissolution.