Fig. 4. Surface activity on four linear dune cross-profiles near Gobabeb. Profiles for (a) Narabeb, (b) Flodden Moor and (c) Rooibank
are redrawn from data provided by Nick Lancaster, originally plotted in Lancaster (1989, Fig. 59). Profile for (d) Visitors’ Dune is
redrawn from data originally plotted in Livingstone (1989, Fig. 6). Ordinate scale is the modulus of change (value regardless of
whether it is positive (deposition) or negative (erosion)). For Lancaster’s data, values are the sum of changes measured every two
weeks for a year. For Livingstone’s data, values are average change over a four-week period based on four years’ data.