Geoscience Reference
In-Depth Information
100
80
60
40
Length
Depth
Area
Volume
20
0
0
0.2
0.4
0.6
2
4
10
20
50
100
% of gully's lifetime
Figure 10.10
Gully evolution based on the experimental data of Kosov
et al
. (1978) cited in Sidorchuk (1999), showing the
relative rates of evolution of the different morphological characteristics relative to the lifetime of the gully. Note the different
extents at 5 % of the gully lifetime.
thus reducing their stability and leading to the triggering
of large mass movements. At a smaller scale, Collison
(1996) demonstrated that this mechanism can also be
important in the collapse and retreat of gully headwalls.
As well as the small translational mass movements
noted above, badlands can produce large-scale landslides
as well. The best-studied case is that of Super Sauze
at Barcelonette in the
Terres Noires
of the French Alps
(Maquaire
et al
., 2003). This style of landslide is typ-
ically triggered by extended periods of rain (Flageollet
et al
., 1999) and so is typically restricted to the more hu-
mid end of the badland spectrum. Initially triggered as a
series of large block falls and translational slides in the
1960s, it has continued to develop as a series of earthflows
(Flageollet, Malet and Maquaire, 2000; Maquaire
et al
.,
2003). The chaotic surfaces produced by the block falls
have been smoothed by the flows and subsequent rainfall
events have superimposed a new dendritic gully drainage
on the surface. Flageollet
et al
. (1999) demonstrated the
importance of older gully systems in producing disconti-
nuities that promoted the initial instability and Maquaire
et al
. (2003) showed that the material strength may take up
to 150 years to recover. This evidence suggests a cyclicity
in dominant processes in this setting, which is not in-
consistent with that interpreted for the much drier Henry
Mountains badlands by Howard (1997). Mass movements
have been noted on large scales in badlands in Alberta (De
Lugt and Campbell, 1992), Italy (Piccarreta
et al
., 2006;
Ciccacci
et al
., 2008) and Spain (Griffiths
et al
., 2005).
As well as contributing to large-scale evolution, mud-
flows have also been demonstrated in extreme events on a
1998; Ciccacci
et al
., 2008; Godfrey, Everitt and Martın
Duque, 2008).
While not a dominant process in most badlands, God-
frey (1997) has demonstrated the local importance of wind
erosion in the Mancos Shale badlands in Utah. Near ridge
crests, he found that local acceleration was able to provide
sufficient lift force to entrain surface crusts. This 'vacu-
uming' of the crust could further develop microcirques
up to 1 m tall and 3 m wide along ridges, and in some
exposed cases cliffs of up to 10 m tall.
In summary, despite their superficial simplicity, slope
systems in badlands evolve according to a complex set of
interrelated processes over a range of timescales. Com-
parison of Figures 10.1 and 10.3 suggest that the slope
forms that evolve lead to various interactions in terms
of boundary conditions set up between the dominant
slopes and processes operating on different slope units.
For this reason, a holistic approach, including modelling
(Howard, 1997), is important for understanding badland
evolution. As noted in Chapter 11, there is an increas-
ing focus on ideas of connectivity for understanding the
large-scale behaviour and evolution of hydrologic and ge-
omorphic systems, and badlands are no different in this
respect. Faulkner (2008) has developed these ideas most
fully, differentiating between meso-scale, closed-system
and macro-scale, in open-system explanations. In the for-
mer, connectivity first increases as erosional links between
parts of the system increase, and then decreases again as
slope angles decrease and depositional processes become
more important. However, as noted above, connectivity
between landscape elements (e.g. through pipe devel-
