The modern understanding is that the evolution of slopes is much more complex than the classical models of decline, replacement and retreat imply.
[1] Parallel slope and scarp retreat, albeit proposed by early geomorphologists, was notably championed by Lester Charles King.
[3] Slopes that are convex upslope and concave downslope and have no free face were held by King to be a form that became common in the late Tertiary.
Colin Hayter Crick, who coined the term, proposed that unequal activity may be regulated by removal of debris at the base of slopes.
Following this thought erosion by the sea and lateral stream migration are of prime importance as these processes are effective in removing debris.
[6] From this it is derived that landscapes and slopes with limited river erosion may in many cases be considered as stagnant in their evolution.
To address this reality the following model for high angle slopes can be applied:[7] Sc stands here for the critical gradient which at which erosion and sediment fluxes runs away.
[7] At low erosion rates increased stream or river incision may make gentle slopes evolve into convex forms.
[13] Numerical modelling indicate that in periglacial settings broad low-angle convex hilltops can form in no less than millions of years.