And there were severe impacts on the river's ecosystem. The loose material throughout the valley is easily eroded, and can affect the river's ecosystem for many years following the eruption. Therefore, logarithms of the sediment yield are calculated and plotted. The data show a non-linear, almost monotonic decrease of sediment yield as a function of time, up until about 1994. An exponential model fits the data fairly well, however tends to underestimate the enormous sediment yields immediately following the eruption.
High precipitation means more erosion and transport of sediment.
Note also the spike of sediment flux associated with the 1990 wet year. In 1988, the Army Corps of Engineers built a sediment retention dam upstream from the data measuring point, to block sediment from reaching the lower part of the Toutle River valley. Since 1988, the dam has trapped about 80,000 Ggrams of sediment of suspended sediment. It would be interesting to use the sediment yield and precipitation values to create a series of best and worst case scenarios, to determine when the dam will be completely filled with sediment.