1.92. Badland Erosion. In semi-arid, sandy or clayey areas where there is not enough moisture and time available between cloudbursts to allow vegetation to grow profusely, the water washes gulleys and valleys into otherwise undisturbed, flat strata. Due to the lack of vegetation, the sides of the gulleys remain bare of plant growth although the more level parts show some cover with such low-lying plants as prairie grass and cactus. The whole area thus takes on a bleak appearance; the type of landscape it represents is therefore referred to as "badlands".
Since erosion in badlands does not proceed at the same pace in all localities, characteristic and sometimes fantastic features result. At times, strata are encountered which present slightly more resistance to ablation and dissolution by water than others so that "islands" are formed around which erosion takes place at a faster pace. The water now collects even more in the deeper places and the more resistive top of the developing feature acts as a protection. Thus, a series of features will eventually stand out in an area which all around has been eroded to a lower level. In general, the features thus created are pyramidal structures and are referred to as mesas or buttes.
In addition to the pyramidal structures just mentioned, one occasionally finds clusters of more unusual structures which have a strange, mushroom-shaped form. Instead of being pyramidal, they have an overhanging "hat" so that they have the general appearance of giant mushrooms. Such structures are called hoodoos.
The writer1 took measurements on three hoodoos in the Alberta Badlands (near Drumheller); the result is shown in Table 5. On inspecting this table, it will be noted that in some instances, there are two numbers given. These indicate the maximum and minimum values for various cross-sections of the hoodoo in question. The most striking feature of hoodoos is the overhanging hat; the overhang may reach up to 50 cm.
The occurrence of hoodoos in badlands requires an explanation. It is obvious that they are erosional features; - but so are mesas and buttes which have a pyramidal structure. The reasons for the different appearance of hoodoos are not at all a priori evident.
1. SCHEIDEGGER, A.E.: Geofis. Pura e Appl. 41, 101 (1958).