Chalk flows from the coastal cliffs of northwest Europe
Published:January 01, 2002
Chalk flows are flow slides that develop under certain circumstances from falls in chalk slopes. They are characterized chiefly by the mobility of the debris, which can run out over near-horizontal surfaces for as much as five to six times the slope height.
After a brief account of the stratigraphy and extent of the Upper Cretaceous exposures of northwest Europe, chalk flows are described in outline, classified, and set in context with other types of flow slides. The relevant morphological parameters are defined. The incidence of chalk flows on the coasts of northwest Europe is outlined. Such failures occur in England, to a small extent in Sussex but predominantly in southeast Kent, in France from just north of Cap de la Hève to Ault in Haute-Normandie, in Denmark at Møns Klint, and in north Germany at Jasmund, in the northeast of the Isle of Rügen.
It is shown that these flows occur only in soft chalks of high porosity (>~40%), in cliffs higher than ~30 m. Their mobility is inferred to derive principally from high excess pore-water pressures generated by a process of impact collapse in the saturated or near-saturated metastable soft chalk as it impacts onto the shore platform. Where earlier saturated colluvium is present on this platform, its undrained loading by the falling debris probably also plays a role, as does the presence or absence of seawater. Desirable further research is outlined, and the hazards posed by chalk flows are described.
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>This volume documents further advances in our knowledge of catastrophic landslides since the pioneering compilations of the late 1970s by Barry Voight. It provides a worldwide survey of catastrophic landslide events written by leading authorities. Catastrophic Landslides begins by drawing upon South America to dramatically illustrate the impact of these phenomena on human populations. The occurrence of catastrophic landslides, including site-specific insights, is shown through six events of the past 20 years. Several other chapters focus on the mechanisms involved with catastrophic landsides both in relation to geologic factors in a particular geographic area as well as to specific geologic processes.