Geology Reference
In-Depth Information
the measurement of rates and in the understanding
of the physical basis of tectonic and geomorphic pro-
cesses have revitalized it as a field of enquiry. It is
a stimulating and highly integrative field that uses
techniques and data drawn from studies of geomor-
phology, seismology, geochronology, structure, geodesy,
and
FORM
The two main approaches to form in geomorphol-
ogy are description (field description and morphological
mapping) and mathematical representation (geomor-
phometry).
Quaternary
climate
change
(e.g.
Burbank
and
Anderson 2001).
Submarine geomorphology
deals with the form,
origin, and development of features of the sea floor.
Submarine landforms cover about 71 per cent of the
Earth's surface, but are mostly less well studied than
their terrestrial counterparts. In shallow marine envi-
ronments, landforms include ripples, dunes, sand waves,
sand ridges, shorelines, and subsurface channels. In the
continental slope transition zone are submarine canyons
and gullies, inter-canyon areas, intraslope basins, and
slump and slide scars. The deep marine environment con-
tains varied landforms, including trench and basin plains,
trench fans, sediment wedges, abyssal plains, distributary
channels, and submarine canyons.
Planetary geomorphology
is the study of landforms
on planets and large moons with a solid crust, for exam-
ple Venus, Mars, and some moons of Jupiter and Saturn.
It is a thriving branch of geomorphology (e.g. Howard
1978; Baker 1981; Grant 2000; Irwin
et al
. 2005).
Surface processes on other planets and their satellites
depend materially on their mean distance from the Sun,
which dictates the annual receipt of solar energy, on
their rotational period, and on the nature of the plane-
tary atmosphere. Observed processes include weathering,
aeolian activity, fluvial activity, glacial activity, and mass
wasting.
Climatic geomorphology
rests on the not uni-
versally accepted observation that each climatic zone
(tropical, arid, temperate for example) engenders a dis-
tinctive suite of landforms (e.g. Tricart and Cailleux
1972; Büdel 1982). Climate does strongly influence geo-
morphic processes, but it is doubtful that the set of
geomorphic processes within each climatic zone creates
characteristic landforms. The current consensus is that,
owing to climatic and tectonic change, the climatic fac-
tor in landform development is more complicated than
climatic geomorphologists have on occasions suggested
(cf. p. 389-90).
Field description and morphological
mapping
The only way fully to appreciate landforms is to go
into the field and see them. Much can be learnt from
the now seemingly old-fashioned techniques of field
description, field sketching, and map reading and map
making.
The mapping of landforms is an art (see Dackombe
and Gardiner 1983, 13-20, 28-41; Evans 1994).
Landforms vary enormously in shape and size. Some,
such as karst depressions and volcanoes, may be rep-
resented as points. Others, such as faults and rivers,
are linear features that are best depicted as lines. In
other cases, areal properties may be of prime concern
and suitable means of spatial representation must be
employed. Morphological maps capture areal properties.
Morphological mapping
attempts to identify basic
landform units in the field, on aerial photographs, or
on maps. It sees the ground surface as an assemblage of
landform elements.
Landform elements
are recognized
as simply curved geometric surfaces lacking inflections
(complicated kinks) and are considered in relation to
upslope, downslope, and lateral elements. They go by a
plethora of names - facets, sites, land elements, terrain
components, and facies. The 'site' (Linton 1951) was
an elaboration of the 'facet' (Wooldridge 1932), and
involved altitude, extent, slope, curvature, ruggedness,
and relation to the water table. The other terms were
coined in the 1960s (see Speight 1974). Figure 1.6
shows the land surface of Longdendale in the Pennines,
England, represented as a morphological map. The map
combines landform elements derived from a nine-unit
land-surface model (p. 169) with depictions of deep-
seated mass movements and superficial mass movements.
Digital elevation models lie within the ambits of land-
form morphometry and are dealt with below. They have
greatly extended, but by no means replaced, the classic
