Asian mega-deltas were initiated at ca. 8.0 ka after a rapid sea-level rise at
8.4–8.5 ka, as well as deltas in islands. Outbuilding (progradation) of mega-deltas has occurred continuously seaward, related to huge sediment supply and relatively stable sea level since the middle Holocene. Particularly continental large rivers in Southeast and East Asia together supplied ~2.5 × 109 tons/y of suspended sediment 30–40 years ago, which is more than 10 % of global sediment discharge, and formed more than 40 km2 of new land annually as delta plains, resulting from increased sediment discharge by human activities (e.g., deforestation) on a millennial scale. However they are delivering less than 1 × 109 tons/y currently because of another human activities (e.g., the reduction of sediment supply and relative sea-level rise caused by human activities), which is close to a pristine level of sediment discharge on these rivers in the middle Holocene. New land formation has come to a standstill, and some deltas are even shrinking, currently. The mega-deltas of Asia are thus at risk of destruction at present after delta construction since the middle Holocene. References Wang, H.J., Saito, Y., Zhang, Y., Bi, N.S., Sun, X.X., Yang, Z.S. (2011) Recent changes
of sediment flux to the western Pacific Ocean from major rivers in East and
Southeast Asia. Earth-Science Reviews, vol. 108, no.1–2, pp. 80–100. Woodroffe, C.D., Nicholls, R.J., Saito, Y., Chen, Z., Goodbred, S.L. (2006) Landscape
variability and the response of Asian megadeltas to environmental change. In
Harvey, N. (ed.), Global Change and Integrated Coastal Management: the Asia-
Pacific Region. Coastal Systems and Continental Margins, Vol. 10. Springer, pp.
277–314.
59 59
GEOSEA 2012