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Burger et al. (2001) also made a link between
river morphology and glaciation-related sea-level
changes. They suggested that the dendritic channel
pattern (and related fluvial incision) in the Eel
River Basin, California formed during glacio-
eustatic lowstands and periods of continental shelf
exposure, but also pointed out that local tectonic
uplift may have also played a role. In fact, many
other studies (e.g. Veldkamp & Van Dijke 1998)
have demonstrated the complex links between
tectonic, climatic and sea-level changes and their
combined effects on river morphology and sedi-
mentation. Although Harvey et al. (2003) showed
that sedimentary sequences and the morpho-
logical evolution of late Quaternary alluvial fans
in the Tabernas basin of south-east Spain were
mainly controlled by climatic change, the de-
positional environment of toes of the fans was
created in response to tectonic uplift. Bridg-
land (2000) and Bridgland & Maddy (2002)
suggested that sedimentation-incision cycles of
the Middle-Late Pleistocene that correspond
to the low-frequency, high-amplitude 100 kyr
eccentricity-driven climate cycle resulted from
the overprinting of long-term fluvial responses
to tectonic uplift driven by climate changes in
sediment supply.
extent and severity of the fire, the rate of recovery
of vegetation and the fluvial geomorphology.
It has been suggested that the most important
factor is the percentage of burned area, because
this causes a range of fluvial adjustments through-
out the whole basin (Legleiter et al. 2003).
Following a fire, the width, depth, planimetric
geometry and longitudinal profile of the river
will be modified to accommodate the elevated
sediment loads arising from the increased flow
magnitude and frequency. Channels are reported
to respond to fire-related change by aggrada-
tion, active braiding, enlargement and lateral
migration, entrenchment and narrowing (Laird
& Harvey 1986; Legleiter et al. 2003). The time
needed for basins to return to pre-fire surface
erosion and fluvial sediment delivery rates has
been reported to be relatively short, in the order
of 2 to 10 years (Morris & Moses 1987; Legleiter
et al. 2003). This normally follows exhaustion
of available fine-grained sediment, vegetative
recovery and the development of coarse surface
lags (Morris & Moses 1987).
It is important to note that, although forest
fires are often 'natural' events, they can equally
be classified as 'anthropogenic disturbances',
because many forest fires are started deliberately
by humans. This is not only a contemporary
phenomenon; late Mesolithic to early Neolithic
charcoal finds in the North Yorkshire Moors,
UK, suggest that fires were started deliberately
to control vegetation or drive out game for
hunting, or both (Simmons & Innes 1996).
3.3.3 Forest fires
Forest fires result in the removal of vegetation,
reduction of ground cover and alteration of
soil properties (e.g. decreased infiltration rates,
formation of water-repellent layers by vaporiza-
tion of forest organic compounds). All of these
processes can cause significant increases in run-
off and fine sediment production in the fire-
affected basins (Morris & Moses 1987; Inbar
et al. 1998). In Australia, for example, hydrogeo-
morphological changes resulted in widespread
erosion and alluvial deposition of remobilized
topsoil in river systems following the Christmas
2001 bushfires near Sydney (Shakesby et al.
2003). Many other studies have demonstrated
similar widespread post-fire sediment delivery
to rivers (e.g. Inbar et al. 1998) (Fig. 3.12).
The fluvial response to forest fire is complex
(Schumm & Lichty 1965), and depends on the
3.3.4 Volcanic eruptions
Explosive volcanic eruptions can dramatically
affect sedimentary processes in rivers, both dur-
ing the eruption itself and for years or decades
after the eruption has ceased. The sediment
loads of rivers draining volcanoes are among the
highest documented, and have been compared
with those of rivers in arid climates impacted
by flash floods (Hayes et al. 2002). The effects
of high rainfall in volcanic areas (particularly
tropical volcanic belts) compound the sediment-
carrying capacity of associated rivers compared
with arid rivers. During eruptions, river valleys
