Geoscience Reference
In-Depth Information
characterize the environmental sedimentology
of all mountain areas. The aim is, therefore, to
highlight the general functioning of active sedi-
mentary processes in mountain environments
and, using case studies and examples, show how
these processes are affected by climate change
and human actions and how adjustments to sed-
iment systems have an impact on human use of
mountain regions. The chapter begins by con-
sidering the main characteristics of mountain
environments (section 2.1.2) that are most relev-
ant to environmental sedimentology. This forms
a basis for classifying mountain environments
(section 2.1.3). The bulk of the chapter that
follows is divided into five main sections: sedi-
ment sources and transfer processes (section 2.2);
processes and impacts - events related to natural
disturbance (section 2.3); processes and impacts
- anthropogenic influences (section 2.4); manage-
ment and remediation (section 2.5); and future
issues (section 2.6). Inevitably some topics, such
as climate change, depositional processes (i.e.
alluvial-fan and glacial-lake sedimentation) and
some slow geomorphological processes (e.g.
creep), are not covered in great depth.
onments. High levels of gravitational stress result
in rapid sediment movements both in terms of
slope instability and channel sediment transport
(Jones 1992).
4
There is considerable variability in the spatial
and temporal rates of sediment transfer and this
has important environmental and social con-
sequences for mountain environment develop-
ment (Butler et al. 2003).
5
Mountain environments are sensitive to dis-
turbance both from climate change and anthro-
pogenic impacts (Ives & Messerli 1989).
6
The incidence of geomorphological hazards
tends to be high in mountainous, high-energy
environments where narrow valley floors are
juxtaposed with steep unstable side slopes.
Infrastructure and population are always at
risk and this risk increases as expansion of
roads and settlements continue. These issues
are often greatest in mountainous terrain where
population and infrastructure have developed
along upland river valleys. There is, however,
growing recognition that heavy engineering
approaches designed to manage such active
geomorphological settings are unsustainable. A
greater understanding of catchment-wide sedi-
ment budget dynamics can provide the neces-
sary knowledge to better manage such systems
(Gerrard 1990).
7
Mountain sediment systems are often only a
part of a larger drainage basin structure. There-
fore, sediment delivery from the headwaters
will have an impact downstream on floodplain
processes. The degree of coupling needs to be
established so that floodplains can be managed
effectively (Brizga & Finlayson 1994; Piégay
et al. 2004) and hazards at the mountain front
reduced (White et al. 1997).
2.1.2 Characteristics of mountain environments
relevant to environmental sedimentology
There are seven general themes that need to be
considered when dealing with the environmental
sedimentology of mountainous areas.
1
Mountains are generally regions of abundant
sediment supply and high erosion potential.
Typically erosion rates and sediment yields are
globally some of the highest recorded (Milliman
& Syvitski 1992).
2
High rates of sediment production translate
into elevated rates of sediment transfer and
increased sediment deposition. However, sedi-
ment delivery in tectonically stable and tectonic-
ally active regions differs markedly depending
on the nature and rate of the different geomor-
phological processes that operate (Marutani
et al. 2001).
3
The importance of steep slopes is fundamental
to many processes operating in mountain envir-
2.1.3 Definition and classification of
mountain environments
Mountains occur in virtually all geographical
and climate settings on Earth. Mountain areas
vary significantly from small isolated moun-
tains to huge mountain chains stretching for
many hundreds of kilometres across continents.
