Collaboration with Amanda Keen-Zebert (Desert Research Institute) and Stephen Tooth (Aberystwyth University). Mixed bedrock-alluvial anabranching rivers form some of the world’s most spectacular fluvial scenery but their dynamics remain poorly documented. Previous conceptual models have outlined how alluvial islands form on the underlying bedrock template but timescales of island development are largely unknown owing to limited geochronology. This study uses optically stimulated luminescence (OSL) dating to establish the growth rates and stability of alluvial islands on the Vaal River at Parys, South Africa. The Vaal traverses the World Heritage-listed Vredefort Dome, an eroded, ancient meteorite impact site. The river enters and exits the dome as a 150-170 m wide single channel flanked by sedimentary rocks, but changes to a distinctive 1.5 km wide anabranching river with 10-15 channels and numerous islands as it flows across granitoid rocks exposed in the dome's core. The numerous islands are formed of rock and/or alluvium, and support extensive native riparian tree communities, providing habitat diversity that contrasts with the surrounding semi-arid, grass- and shrub-covered terrain. We measured the age and aggradation rates of 9 islands in the anabranching reach using OSL. Single grain measurements of quartz were made using the single aliquot regenerative dose (SAR) approach. Equivalent dose populations have up to 60% overdispersion, common for fluvial samples, and the minimum age model was used to calculate final ages. Results demonstrate that the complex of alluvial islands is relatively young, with all having formed in the past 1000 years. The alluvial islands grow rapidly (mean vertical aggradation >0.28 cm/yr) during low to moderate floods (Q <2500 m3/s) owing to interactions between sediment deposition in the lee of bedrock outcrop, tree colonisation, and island coalescence. Islands tend to erode during larger floods through lateral erosion, vertical stripping, and dissection by newly-forming anabranches. The ages demonstrate that the alluvial islands are essentially dynamic, short-lived features that develop on a bedrock template that is underlying slower, long-term erosion. Our goal is to expand this dataset to include bedrock cored islands and place the age of formation of the islands in the context of the age of the broader floodplain within which the island complex exists. These findings will contribute to geoheritage education and to ongoing development of sustainable management plans for the tree-covered islands, many of which are threatened by altered flow regimes, invasive species, and encroaching tourism developments.