(smaller area but higher yields). If the average river draining the western sides of the mountains is 15,000 km2, then the average sediment yield would be about 1200 t/km2/yr (Figure 5.6c), equaling a sediment discharge of 2.4 bt/yr (1200 multiplied by an area of 2 x 106 km2). This calculated sediment flux may be unrealistically high, as the arid parts of the western slope may contribute little sediment to the sea; nevertheless, the total sediment discharge from western South American rivers probably is much higher than the 168 mt estimated by Milliman and Meade (1983). At present we can cite only one west coast river, the Chira (Peru), and the data represent only two years of measurement, for one of which, however, the load was 75 mt (yield 3700 t/km2, Burz, 1977).
Europe is generally regarded as having the lowest sediment flux to the sea (e.g., Holeman, 1968; Milliman and Meade, 1983). However, the Alps (a collision orogen) are a major sediment source, and the short rivers draining south into the Mediterranean have high to very high yields, generally 500 to >1000 t/km2/yr (Table 2, Milliman and Syvitski, 1992). For example, the little known Semani River (Albania) has more than twice the annual discharge (22 mt) of the collective sediment discharges of the well-known north-flowing rivers Garonne, Loire, Seine, Rhine, Weser, Elbe, Oder, and Vistula, most of which drain upland or lowland terrain. Many rivers draining north from