Credit: NATHAN BENN/CORBIS

Paul Hudson and Richard Kesel have returned to the Mississippi River of Mark Twain to investigate the rates of movement (migration) of river meanders. The inspiration for their study was not literary, however, but old surveys of the 1,700-km lower stretch of the river from Cairo, Illinois, to the Gulf of Mexico. The surveys concerned were carried out between 1877 and 1924 — a time when the river was still largely unconstrained by human influence. The photograph here is a recent one of the river in the delta region.

Data from smaller river systems and from modelling point to a specific relationship between meander migration rate and the ratio between meander-bend radius and channel width. But as they describe in Geology (28, 531–534; 2000), Hudson and Kesel find that the lower Mississippi does not follow this relationship. The reason, they suggest, lies in the heterogeneity of the deposits through which the river flows. In particular, clay plugs limited the rate of meander migration — the incidence of these plugs is higher in the northern part of their study area (average meander migration 45.2 m yr−1) than in the delta (59.1 m yr−1).