Log10 of 1931-1998 Mississippi River streamflow in meters3/second measured daily at Vicksburg MS, represented by a yellow-red color scale. Each row represents 2 years of data but is one year later than the one above it; this redundancy avoids arbitrary temporal divisions. The graphic shows 1) seasonal precipitation and snowmelt, 2) a near-decadal cycle (perhaps reflecting a solar cycle, and 3) such major events as droughts in 1940 and 1988 (which brought saltwater over 100 miles upriver) and the 1973 and 1993 floods (which damaged levees and caused hypoxic zones in the Gulf of Mexico).