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Borneo is the third largest island on Earth. It occupies a central position in SE Asia and has a Palaeozoic core to which material was accreted during the Mesozoic and early Cenozoic. It is overlain and surrounded by considerable thicknesses of Neogene sedimentary rocks which can only have come from Borneo itself. The amount of sediment around Borneo, and in SE Asia generally, has been largely overlooked, partly because the mountains of the region are not high, but the volume of sediment around Borneo indicates that at least of 6 km of crust has been removed by erosion during the Neogene, corresponding to an average rate of erosion of c.850 tonnes/km2/a. The thickness of crust removed is probably an underestimate. Early-Middle Miocene erosion rates may have approached c.2500 t/km2/a, although this figure is very uncertain. Uranium series dating implies Quaternary erosion rates of c.500 t/km2/a in Sarawak. There are problems accounting for the huge volume of Neogene sediment around Borneo. Many published assertions about geomorphological and tectonic controls on sediment removal rates in the geological literature are questionable in their relevance to SE Asia. Most of the data were not obtained from SE Asia, those that were come from areas significantly modified by man, and conclusions are largely based on studies of much smaller, climatically different, regions of much younger uplift such as Taiwan and New Zealand. Estimates of present erosion rates are lower. Natural erosion rates are typically less than 500 t/km2/a although in areas disturbed by fires or forestry they may be much higher, up to 1,000-2000 t/km2/a. Hydrological studies also illustrate the importance of extreme events, for example, in one year-long study 40% of the suspended-sediment flux was generated in a single day. The long-term estimates cited above are therefore higher than 'natural erosion' in Borneo but comparable to man-induced 'accelerated erosion'. Erosion rates are influenced by rainfall, relief, rock-type and climate, and these interact with tectonic processes. All of these need to be considered to understand the evolution of tropical mountain belts. Currently it is not possible to assess adequately the importance of rainfall, elevation, relief, area, suspended/bed-load sediment, and extreme events in the short and long-term. However, whatever the causes, in Borneo the high rate of erosion influenced the structural development of the orogenic belt. It prevented tectonic denudation by thrusting and instead, the orogenic belt was denuded by erosion. There was no lithospheric flexure due to thrust loading and no true foreland basins developed. Furthermore, the average thickness of crust removed is similar to that removed from the Himalayas during the same period and the total sediment volume is at least one third of that removed from the Himalayas. If areas such as New Guinea and other large land-masses are included, the SE Asian basins could contain a eogene sediment volume at least equal to that removed from the Himalayas with implications for climate-tectonic links and ocean composition over time. It is usual to find that short-term studies overestimate features such as sediment accumulation rates because of incompleteness of geological record. In the case of tropical erosion the reverse is the case. What is the significance of this? Borneo was ever-wet throughout the Neogene whereas many other parts of SE Asia developed a monsoonal, highly seasonal climate by the Pliocene. During the Quaternary sea levels and vegetation throughout SE Asia varied dramatically with glacially-induced climate change. How have these changes influenced erosion rates? Are present rates comparable to the past? Logging, building and deforestation are activities which affect erosion rates. Equally, climate change, forest fires and sea level changes are natural causes of variations. We require good estimates of long-term erosion rates to assess anthropogenic effects and evaluate their impact. Indonesia is the region from which almost all this information must come.