326
Climatic Geomorphology
limestones. The cementation degree of the rock is also essential to its resistance. To
lithology has to be added the structure. If the free slope is formed by finely stratified or
jointed rocks, debris slopes show good development; on the other hand, blocks of a large
size will cover the slope.
It has been indicated that debris slopes come from the breaking of the resistant rock that
constitutes the free slope. This is what supplies most of the cover of a debris slope,
although other parts can come from the underlying substrate. Despite the great
development that they can undergo in most deserts, studies of them are scarce compared
with the ones carried out in Alpine areas (Oberlander, 1997b).
Schumm and Chorley (1966) indicated that the difference between one slope and others
could be explained quantitatively by the relation of weathering (W). The existence or
absence of debris at the foot of the scarp depends on the velocity of fragment generation in
the free slope (p) before the destruction at the foot of it (d). If this relation is higher than 1
it generates slope accumulation, alluvial fans and a great amount of debris in general. If W
is equal to 1, there is a balance between p and d. If W is less than 1, blocks when falling
disintegrate upon impact and the remainder is weathered before the next fall. This last is
common in the Colorado Plateaus.
This debris can totally or partially cover the slope and, at the same time, be affected by
rilling and gullying that gradually work down to a major extension of the rock substrate.
The extreme case results from the practical disappearance of the slope cover and, if clays
are the outcropping material a badland landform generates. In some cases, hard and weak
layers constitute the materials of the substrate; in this case a stepped form originates from
composite microslopes (free slope and debris slopes) along the main slope (Figure 14.7).
These are the characteristics of the complex slopes.
The fragments of the debris slope show a poor sorting. They are affected by sheet
erosion, which exports the fine particles to a lower part of the slope, with the bigger
fragments standing out. These also can show an important weathering, with development
of alveoles and tafoni in their walls. Finally, in some cases small mass movements can
occur that affect to the debris slope.
3. Talus flatirons
These landforms were originally referred to as talus flatirons (Koons, 1955), flatirons
(Everard, 1963), dreieckshiinge (Wirthmann, 1964; Btidel, 1970), versants tripartites
(Gossmann, 1976), tripartites slopes and triangular slope facets (Btidel, 1982), and talus
relicts (Gerson, 1982). It should be noted, however, that the term "flatiron" has been
previously designated only for upfolded, hard sedimentary rock, and "triangular facets"
for eroded fault scarps, so considerable care must be utilized to avoid sloppy terminology.
These talus flatirons are characteristic forms of arid and semi-arid environments, although
they have been also recognized, as seen before, in periglacial areas. They have been
studied in the Sahara-Arabian Desert, southwestern United States and in some
Mediterranean semi-arid zones.
Their origin initially corresponds to a composite slope, which afterwards is incised by
water erosion (rilling, gullies, piping), of the remaining portions of individualized relict
slopes (Koons, 1955) (Figure 14.12). These paleoslopes have a triangular form with their
Climatic Geomorphology
limestones. The cementation degree of the rock is also essential to its resistance. To
lithology has to be added the structure. If the free slope is formed by finely stratified or
jointed rocks, debris slopes show good development; on the other hand, blocks of a large
size will cover the slope.
It has been indicated that debris slopes come from the breaking of the resistant rock that
constitutes the free slope. This is what supplies most of the cover of a debris slope,
although other parts can come from the underlying substrate. Despite the great
development that they can undergo in most deserts, studies of them are scarce compared
with the ones carried out in Alpine areas (Oberlander, 1997b).
Schumm and Chorley (1966) indicated that the difference between one slope and others
could be explained quantitatively by the relation of weathering (W). The existence or
absence of debris at the foot of the scarp depends on the velocity of fragment generation in
the free slope (p) before the destruction at the foot of it (d). If this relation is higher than 1
it generates slope accumulation, alluvial fans and a great amount of debris in general. If W
is equal to 1, there is a balance between p and d. If W is less than 1, blocks when falling
disintegrate upon impact and the remainder is weathered before the next fall. This last is
common in the Colorado Plateaus.
This debris can totally or partially cover the slope and, at the same time, be affected by
rilling and gullying that gradually work down to a major extension of the rock substrate.
The extreme case results from the practical disappearance of the slope cover and, if clays
are the outcropping material a badland landform generates. In some cases, hard and weak
layers constitute the materials of the substrate; in this case a stepped form originates from
composite microslopes (free slope and debris slopes) along the main slope (Figure 14.7).
These are the characteristics of the complex slopes.
The fragments of the debris slope show a poor sorting. They are affected by sheet
erosion, which exports the fine particles to a lower part of the slope, with the bigger
fragments standing out. These also can show an important weathering, with development
of alveoles and tafoni in their walls. Finally, in some cases small mass movements can
occur that affect to the debris slope.
3. Talus flatirons
These landforms were originally referred to as talus flatirons (Koons, 1955), flatirons
(Everard, 1963), dreieckshiinge (Wirthmann, 1964; Btidel, 1970), versants tripartites
(Gossmann, 1976), tripartites slopes and triangular slope facets (Btidel, 1982), and talus
relicts (Gerson, 1982). It should be noted, however, that the term "flatiron" has been
previously designated only for upfolded, hard sedimentary rock, and "triangular facets"
for eroded fault scarps, so considerable care must be utilized to avoid sloppy terminology.
These talus flatirons are characteristic forms of arid and semi-arid environments, although
they have been also recognized, as seen before, in periglacial areas. They have been
studied in the Sahara-Arabian Desert, southwestern United States and in some
Mediterranean semi-arid zones.
Their origin initially corresponds to a composite slope, which afterwards is incised by
water erosion (rilling, gullies, piping), of the remaining portions of individualized relict
slopes (Koons, 1955) (Figure 14.12). These paleoslopes have a triangular form with their