Cliffs and ramparts: Persistent steep slopes in the landscape

• Published in: Geomorphology (Amsterdam, Netherlands) Netherlands), 2023-09, Vol.436, p.108776, Article 108776
• Main Author: Kirkby, Michael J.
• Format: Article
• Language: English
• Subjects: Cliff; Coast; Gorge; Mesa; Talus
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2023.108776

The gross morphology of a free face and talus rampart occurs in a range of landscape settings. Semi-arid mesas, river gorges and coastal cliffs all share this geometry, but differ in how the components respond to their respective environments, to each other and to the capacity to export material from the talus rampart. Differences are reflected in the rates and processes of cliff retreat, and in the boundary conditions for rampart growth and removal. For mesas and buttes, export from the talus is controlled by the rate at which coarse material weathers to a size that can be readily washed away, leading to a stable proportional height for the rampart, which then consists of a boulder controlled slope at the angle of repose. For river gorges, a high incremental increase in fluvial sediment transport allows incision to accompany cliff retreat, while low rates lead to valley widening and rampart formation. Coastal cliffs may either lack ramparts, with supply limited development controlled by wave attack on cliffs; or be limited by the transport capacity of transverse offshore sediment processes, allowing development of a persistent rampart. In all contexts, the transport term should not be ignored in understanding both the rates of retreat and the morphology of cliffed landforms. [Display omitted] •Cliffs with a talus rampart occur in diverse settings.•Mesas, river gorges and steep coasts.•Boundary conditions depend on the process setting and geometry.•Evolution may be driven by supply- or transport-limited removal.•The rate of material transport from rampart base is always important.