Original paper
The origin of Bornhardts
King, Lester
Zeitschrift für Geomorphologie Volume 10 Issue 1 (1966), p. 97 - 98
5 references
published: Apr 13, 1966
ArtNo. ESP022001001007, Price: 29.00 €
Abstract
Two papers recently appearing in the Zeitschrift explain the origin of bornhardts as due primarily to deep-seated weathering beneath the smooth planation of a previous prolonged erosion cycle, coupled with excavation of “residual core” features under surface lowering in a second landscape cycle. Emphasis is heavily upon the dominant rôle of pre-weathering which is deemed to produce bornhardts as residual masses within the body of the earth, later becoming nascent at the arrival of a new geomorphic cycle. Bornhardts are therein not regarded as normal landscape features developed beneath the sun and wind of the open sky. These views, though expressed in several papers of recent years, are open to question. A two-cycle origin is not only plausible, it has been long accepted (Jessen 1936), but deep weathering as a pre-requisite is neither necessary nor in most cases likely. On the contrary, apart from a few minor features such as perched summit blocks and rocking stones, the landforms in the major bornhardt fields of Central Africa and Brazil are determined not by deep weathering from a former summit plain, but by stream incision along joint lines between walls of impressively solid rock sometimes narrowly pedimented across rock at the base. Air photos show how remarkably the pattern of dissection by streams follows the joint system in the bed rock. In the field the relevant joints show in stream beds across bare rock, without pre-weathering.
Keywords
bornhardt • weathering