Rivers deliver substantial amounts of sediment to coasts, and their mouths are a dynamic assemblage of landforms. Large Asian rivers and those on the tectonically active islands of Oceania supply more than 70% of the sediment reaching the oceans. Estuaries occur where preexisting topography has been incompletely infilled, whereas deltas protrude from the coast. A prominent triangular delta has formed at the mouth of the River Nile, bifurcating into distributaries before discharging into the sea. Detailed studies of the Mississippi Delta provide chronological and stratigraphic frameworks for river-dominated systems. Most deltas are also influenced to differing degrees by waves and tides, and delta morphology can be classified in relation to the relative dominance of river, wave, and tide influences. However, these processes can vary spatially and temporally within both active and abandoned delta plains deposited during former phases of delta progradation. This is particularly clearly demonstrated by the mega deltas of Asia, but can also be recognized in smaller coastal waterways around Australia. Human activities have impacted many rivers, increasing sediment load on some, and decreasing the flux in others through damming and diversion. Such catchment impacts, together with rapid urbanization on delta plains, accentuate the threats posed by natural hazards and climate change
This record is in the process of being updated. Please contact us for more information.