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COMMENTARY
Decoupling Process from Form in Landscape

Evolution Studies

D.W. Hedding, Dept. of Geography, University of South Africa, volumes of debris. Thus, conflation of process and form in terminology
Florida 1710, South Africa, heddidw@unisa.ac.za used across the disciplines encompassed by the geosciences (e.g., geol-
ogy, geochemistry, geomorphology, and sedimentology) may lead to a
According to Cruden (2003), the term “landslide” was first recorded limited understanding of the processes responsible for landscape evolu-
in 1838 by J.D. Dana. Varnes (1958) used “landslide” in the title of his tion and denudation, particularly where English may be the second lan-
well-known paper but subsequently abandoned the term in favor of guage of the researcher and a literal or direct interpretation is utilized.
“slope” in the updated iteration (see Varnes, 1978). Varnes (1978, p. 11) To resolve the potential confusion, the term “landsliding” should be
states that the reason for the change is that “improvements in technical abandoned and replaced with the term “mass wasting,” an established
communication require a deliberate and sustained effort to increase the term in geomorphology, to decouple process(es) from form(s) in
precision associated with the meaning of words, and therefore the term research on landscape evolution and in other geosciences. Mass wasting
slide will not be used to refer to movements that do not include sliding.” is an encompassing term that refers specifically to the processes respon-
Later, Cruden (1991, p. 28) suggested that a landslide is “the movement sible for the movement of material downslope. In addition, “deep-seated
of a mass of rock, earth or debris down a slope” and is intended for mass wasting” should be used to replace “bedrock-landsliding” in the
informal, non-technical use. Several other definitions have been sug- lexicon of landscape evolution. To avoid further confusion, it is perti-
gested; however, Shanmugam (2015) notes that the term “landslide” nent to highlight that “mass movements” is a term used to describe the
lacks conceptual clarity. Nevertheless, the term “landslide” remains resultant landforms generated through the processes of mass wasting.
entrenched in the literature and, with each scientific discipline using its
own nomenclatural scheme, it means different things to different REFERENCES CITED
groups (Shanmugam, 2015). Cendrero, A., and Dramis, F., 1996, The contribution of landslides to landscape evolu-
In the study of landscape evolution, the transfer of considerable vol- tion in Europe: Geomorphology, v. 15, p. 191–211, https://doi.org/10.1016/0169
-555X(95)00070-L.
umes of material downslope under the influence of gravity plays a sig- Cruden, D.M., 1991, A simple definition of a landslide: Bulletin of the International
nificant role in shaping landscapes (Cendrero and Dramis, 1996). As Association of Engineering Geology, v. 43, p. 27–29, https://doi.org/10.1007/
such, various papers assess the role and significance of slope processes BF02590167.
and resultant mass movements in landscape evolution, typically within Cruden, D.M., 2003, The first classification of landslides?: Environmental & Engi-
neering Geoscience, v. 9, p. 197–200, https://doi.org/10.2113/9.3.197.
the context of quantifying erosion rates (Roda-Boluda et al., 2019) and/ Egholm, D.L., Knudsen, M.F., and Sandiford, M., 2013, Lifespan of mountain rang-
or the roles of tectonic and climatic factors in weathering (Emberson et es scaled by feedbacks between landsliding and erosion by rivers: Nature, v. 498,
al., 2016). Often the terms “landsliding” or “bedrock landsliding” are p. 475, https://doi.org/10.1038/nature12218.
used to describe the process by which material moves downslope Emberson, R., Hovius, N., Galy, A., and Marc, O., 2016, Chemical weathering in
(Egholm et al., 2013; Roering et al., 2001, 2005). However, their usage active mountain belts controlled by stochastic bedrock landsliding: Nature Geo-
science, v. 9, p. 42–45, https://doi.org/10.1038/ngeo2600.
demonstrates a poor appreciation of the difference between process and Hedding, D.W., 2016, Pronival ramparts: Origin and development of terminology:
form in geomorphology since these terms are intrinsically linked to Erdkunde, v. 70, p. 141–151, https://doi.org/10.3112/erdkunde.2016.02.03.
landslides that are a discrete geomorphological landform and not to the Hedding, D.W., Brook, M.S., and Winkler, S., 2018, Old landscape, new eyes: Re-
range of process(es) that are responsible for the movement of material visiting geomorphological research in the Southern Alps of New Zealand: New
downslope in landscape evolution. In addition, form-convergence Zealand Geographer, v. 74, p. 109–112, https://doi.org/10.1111/nzg.12189.
(equifinality) suggests that morphologically similar landforms can be Roda-Boluda, D.C., D’Arcy, M., Whittaker, A.C., Gheorghiu, D.M., and Rodés, A.,
2019, Be erosion rates controlled by transient response to normal faulting
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generated by different processes, on their own or in combination, which through incision and landsliding: Earth and Planetary Science Letters, v. 507,
complicates the correct identification of the process-origin of landforms p. 140–153, https://doi.org/10.1016/j.epsl.2018.11.032.
(Hedding, 2016; Hedding et al., 2018). Still, the term “landsliding” is Roering, J.J., Kirchner, J.W., Sklar, L.S., and Dietrich, W.E., 2001, Hillslope evolution
often described as the process responsible for the movement of material by nonlinear creep and landsliding: An experimental study: Geology, v. 29,
p. 143–146, https://doi.org/10.1130/0091-7613(2001)029 <0143:HEBNCA> 2.0.CO;2.
downslope and has received a level of credence (see Roering et al., 2001) Roering, J.J., Kirchner, J.W., and Dietrich, W.E., 2005, Characterizing structural and
through repetition and subsequent acceptance in the literature, rather lithologic controls on deep-seated landsliding: Implications for topographic relief
than recognition of the actual process-form relationships. Not- and landscape evolution in the Oregon Coast Range, USA: Geological Society of
withstanding the poor phrasing, the term “landsliding” is sometimes America Bulletin, v. 117, no. 5–6, p. 654–668, https://doi.org/10.1130/B25567.1.
used as a synonym for “mass wasting.” However, the movement of Shanmugam, G., 2015, The landslide problem: Journal of Palaeogeography, v. 4,
no. 2, p. 109–166, https://doi.org/10.3724/SP.J.1261.2015.00071.
material downslope in landscape evolution can be generated through a Varnes, D.J., 1958, Landslide types and processes, in Eckel, E.B., ed., Landslide and
suite of mass wasting (movement) processes resulting in landforms Engineering Practice: Highway Research Board Special Report, v. 29, p. 20–47.
(e.g., catastrophic mudflows and rockfalls) and not solely from move- Varnes, D.J., 1978, Slope movement types and processes, in Schuster, R.L., and
ment of material along a plane of weakness resulting in various types of Krizek, R.J., eds., Landslides: Analysis and Control: Washington, D.C., Nation-
landslides. In particular, the relative contribution of material through al Academies of Science, Special Report 176, p. 11–33.
rockfall activity may be critical, specifically in seismically active Manuscript received 19 Sept. 2019
regions where topographic amplification of seismic waves along ridge- Revised manuscript received 11 Nov. 2019
lines, which are not supported laterally, can produce significant Manuscript accepted 16 Nov. 2019

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