Geoscience Reference
In-Depth Information
20
SPANISH FANS
10
5
2
1
0.5
0.2
Dissected fans (Base-level related)
Dissected fans (Mid-fan dissection)
Aggrading/prograding fans
0.1
0.05
0.2
0.1
0.05
0.02
0.01
0.1
0.2
0.5
1
2
5
10
20
50
100
200
Drainage area (km
2
)
Figure 14.11
Morphometric regression relationships between drainage area and fan area and gradient for 67 Spanish Quaternary
fans (modified from Harvey, 2002a), differentiating between dissected and aggading/prograding fans. Open symbols are for
multiapex fans, not used in the regression analysis (see text for details).
sediments, using the morphometric properties of modern
fans (Mather, Harvey and Stokes, 2000).
The morphometric approach has proven to be an im-
portant tool in the analysis of the controls of fan morphol-
ogy, but it has its limitations in that it tends to generalise
rather than focus on the depositional processes themselves
(Whipple and Dunne, 1992; Whipple
et al
., 1998).
control, past tectonics may determine the position and
overall relief of mountain-front environments and hence
the settings of alluvial fans. Cessation of tectonic activity
tends to result in the backfilling of fans into the moun-
tain catchments and to translate a former linear mountain
front into an irregular and recessed mountain front (Bull,
1978), on which fan sediments lap unconformably onto
the underlying bedrock.
As an active control, ongoing tectonic activity during
the existence of the fan directly affects the fan itself, sig-
nificantly altering the processes or morphology, or acts by
modifying regional base levels, which in turn affect the
fan environment as base-level change propagates through
14.3.2
Dynamic controls
14.3.2.1
Ongoing tectonics