Landslide hazard induced by river undercutting along the Danube

Abstract

Since the 1964 landslide of a loess bluff affecting the iron and steel plants of Dunaújváros, several papers have been written on the parameters to be considered for short-term bluff stability. The aim of the present investigation is to reveal the relationship between landslides, undercutting, and other processes of bluff recession. Opinions agree that undercutting is due to the gradual westward shifting of the Danube from its Pleistocene alluvial fan on the Danube-Tisza Interfluve to its present valley. The approximately north to south course is not directly explained by a single, major fault line. A local subsidence south of Budapest is probably responsible for an initial change of course, and the undercutting of the margin of the Mezöföld loess-mantled plain has been maintained subsequently by river mechanisms and the weak Coriolis force. The most effective mechanisms of bluff retreat along undercut river bank sections are collapse of detached slabs, removal by runoff during periods of above-zero temperatures, frost shattering in winter, and occasional landslides. Before flood control measures, the Danube had regularly removed part of the toes of previous landslides and thus generated renewed instability. Increased infiltration due to human settlement aggravated the landslide hazard. Archaeological evidence suggests that the previously proposed bluff retreat of 3–5 meters per 100 years may be valid for periods of undercutting only, while human interference has reduced the recurrence interval of landslides and considerably accelerated recession along certain sections. Through bank revetment, the Danube is now prevented from undercutting the bluff, and consequently, groundwater conditions have become the primary control of the landslide hazard.