170
11 Detecting Fingerprints of Gravity Erosion Drivers …
mass failure is the principal cause of long-term productivity losses (Luckman et al.
1999; Dregne 1995). In fact, mass failure processes essentially feature catastrophic
removal or displacement by the gravity of the whole soil body from a slope. Hence, it
frequently causes serious on-site and off-site damages. Local hazards, such as serious
soil degradation, are led by the mass failure, because the mass failure often removes
the entire soil profile in one event. Even if mass failure removes only part of the
soil profile, that part almost always includes the organic matter and nutrient-rich A
and upper B horizons (Blaschke et al. 2000). Mass failure also brings about off-site
damages by sediment, such as transport route damage (Zieli´ nski et al. 2016), building
damage (Hungr et al. 2016), fluvial sediment deposition (West et al. 2014), reservoir
sedimentation (Tsai et al. 2013), and channel silting (Sayed and González 2014). In
addition, gravity erosion can cause fatalities. For example, a heavy rainfall-induced
landslide in Xi’an on 17 September, 2011 caused 32 Fatalities (Zhuang and Peng
2014). The above-mentioned damages correlate with the pattern of the scar, because
the failure scar (i.e., fingerprint) mirrors the size of the gravity erosion (Lucas et al.
2011).
The physics of fingerprinting has been embraced in studies of mass failure. For
example, Convertino et al. (2013) argued that landslide size distribution is a fingerprint of the geomorphic effectiveness of rainfall as a function of climate change;
Densmore and Hovius (2000) used the topographic fingerprints of bedrock landslides
to distinguish triggers of earthquake and rainfall processes. Indeed, the application
of the scars is the best way to explore the triggering mechanisms of mass failure
since each hill slope generally produces a distinct geometry of scar, or fingerprint,
during the process of mass failure. Previous studies have indicated that mass failures
occurred in a natural slope with distinctly different morphologies of the scar. Skepton and Hutchinson (1969) showed that the ratio between depth and length of the
failure scar (D r /L r ) is generally between 0.15 and 0.33 when the mass slides along
the upward concave scar. Meanwhile, the ratio of the scar is less than 0.1 when the
mass slides along the translational face (Lu and Godt 2013). In addition, different
morphologies of the scars are introduced in the stability analysis of the hillslope,
such as planar, concave, convex, and terraced surfaces (Yin et al. 2009; Highland
and Bobrowsky 2008; Leshchinsky et al. 1985). However, the lack of normative
data tests has hampered the vital research in this area. Furthermore, varying failure
surfaces were applied to the slope movement model, but all of them suffered from
a significant lack of experimental validation and thus possibly led to an inaccurate
prediction. Hence, it is necessary to correctly determine the scar morphology during
the process of mass failure.
Several studies (e.g., Jeong et al. 2003; Lee et al. 1995) based on simplified scars
reveal the mechanism of mass failure. However, applying the hypothetical scar, i.e.,
simplified scar shape, to study the triggering mechanism of gravity erosion might
have inevitable limitations and flaws. Osman and Thorne (1988) assumed that steep
slopes fail along an almost planar failure surface. The major limitation is that the
failure plane is constrained to pass through the toe of the slope, which is unrealistic
(Darby and Thorne 1996). Simon et al. (1991) also observed that the scar may, in
fact, intersect the slope profile at other points. Moreover, the classical methods of
11 Detecting Fingerprints of Gravity Erosion Drivers …
mass failure is the principal cause of long-term productivity losses (Luckman et al.
1999; Dregne 1995). In fact, mass failure processes essentially feature catastrophic
removal or displacement by the gravity of the whole soil body from a slope. Hence, it
frequently causes serious on-site and off-site damages. Local hazards, such as serious
soil degradation, are led by the mass failure, because the mass failure often removes
the entire soil profile in one event. Even if mass failure removes only part of the
soil profile, that part almost always includes the organic matter and nutrient-rich A
and upper B horizons (Blaschke et al. 2000). Mass failure also brings about off-site
damages by sediment, such as transport route damage (Zieli´ nski et al. 2016), building
damage (Hungr et al. 2016), fluvial sediment deposition (West et al. 2014), reservoir
sedimentation (Tsai et al. 2013), and channel silting (Sayed and González 2014). In
addition, gravity erosion can cause fatalities. For example, a heavy rainfall-induced
landslide in Xi’an on 17 September, 2011 caused 32 Fatalities (Zhuang and Peng
2014). The above-mentioned damages correlate with the pattern of the scar, because
the failure scar (i.e., fingerprint) mirrors the size of the gravity erosion (Lucas et al.
2011).
The physics of fingerprinting has been embraced in studies of mass failure. For
example, Convertino et al. (2013) argued that landslide size distribution is a fingerprint of the geomorphic effectiveness of rainfall as a function of climate change;
Densmore and Hovius (2000) used the topographic fingerprints of bedrock landslides
to distinguish triggers of earthquake and rainfall processes. Indeed, the application
of the scars is the best way to explore the triggering mechanisms of mass failure
since each hill slope generally produces a distinct geometry of scar, or fingerprint,
during the process of mass failure. Previous studies have indicated that mass failures
occurred in a natural slope with distinctly different morphologies of the scar. Skepton and Hutchinson (1969) showed that the ratio between depth and length of the
failure scar (D r /L r ) is generally between 0.15 and 0.33 when the mass slides along
the upward concave scar. Meanwhile, the ratio of the scar is less than 0.1 when the
mass slides along the translational face (Lu and Godt 2013). In addition, different
morphologies of the scars are introduced in the stability analysis of the hillslope,
such as planar, concave, convex, and terraced surfaces (Yin et al. 2009; Highland
and Bobrowsky 2008; Leshchinsky et al. 1985). However, the lack of normative
data tests has hampered the vital research in this area. Furthermore, varying failure
surfaces were applied to the slope movement model, but all of them suffered from
a significant lack of experimental validation and thus possibly led to an inaccurate
prediction. Hence, it is necessary to correctly determine the scar morphology during
the process of mass failure.
Several studies (e.g., Jeong et al. 2003; Lee et al. 1995) based on simplified scars
reveal the mechanism of mass failure. However, applying the hypothetical scar, i.e.,
simplified scar shape, to study the triggering mechanism of gravity erosion might
have inevitable limitations and flaws. Osman and Thorne (1988) assumed that steep
slopes fail along an almost planar failure surface. The major limitation is that the
failure plane is constrained to pass through the toe of the slope, which is unrealistic
(Darby and Thorne 1996). Simon et al. (1991) also observed that the scar may, in
fact, intersect the slope profile at other points. Moreover, the classical methods of