Page 27 - Fundamentals of Geomorphology

10 INTRODUCING LANDFORMS AND LANDSCAPES

a product of phases of erosion during the later Roman (e.g. Leopold et al. 1964). Stanley A. Schumm, another
Imperialtimes,throughtheDarkAges,andtotheMiddle fluvial geomorphologist, refined notions of landscape sta-
Ages. Vita-Finzi believed it to be the result of increased bility to include thresholds and dynamically metastable
erosion associated with the climate of the MedievalWarm states and made an important contribution to the under-
Period or the Little Ice Age, a view supported by John standing of timescales (p. 27). StanleyW.Trimble worked
Bintliff (1976, 2002). Other geomorphologists, includ- on historical and modern sediment budgets in small
ing Karl Butzer (1980, 2005) and Tjierd van Andel and catchments (e.g. Trimble 1983). Richard J. Chorley
his co-workers (1986), favoured human activity as the brought process geomorphology to the UK and demon-
chief cause, pointing to post-medieval deforestation and strated the power of a systems approach to the subject.
agricultural expansion into marginal environments. The Process geomorphologists have done their subject at
matter is still open to debate (see p. 363). least three great services. First, they have built up a
database of process rates in various parts of the globe.
Second, they have built increasingly refined models for
Process geomorphology
predicting the short-term (and in some cases long-term)
Process geomorphology is the study of the processes changes in landforms. Third, they have generated some
responsible for landform development. In the modern enormously powerful ideas about stability and instability
era, the first process geomorphologist, carrying on the in geomorphic systems (see pp. 19–21).
tradition started by Leonardo da Vinci (p. 5), was Grove
Karl Gilbert. In his treatise on the Henry Mountains Measuring geomorphic processes
of Utah, USA, Gilbert discussed the mechanics of flu-
vial processes (Gilbert 1877), and later he investigated Some geomorphic processes have a long record of mea-
the transport of debris by running water (Gilbert 1914). surement. The oldest year-by-year record is the flood
Up to about 1950, when the subject grew apace, impor- levels of the River Nile in lower Egypt. Yearly readings
tant contributors to process geomorphology included at Cairo are available from the time of Muhammad,
Ralph Alger Bagnold (p. 85), who considered the physics and some stone-inscribed records date from the first
of blown sand and desert dunes, and Filip Hjulstrøm dynasty of the pharaohs, around 3100 BC. The amount
(p. 73), who investigated fluvial processes. After 1950, of sediment annually carried down the Mississippi River
several ‘big players’ emerged that set process geomorphol- was gauged during the 1840s, and the rates of modern
ogy moving apace. Arthur N. Strahler was instrumental denudation in some of the world’s major rivers were
in establishing process geomorphology, his 1952 paper estimated in the 1860s. The first efforts to measure
called ‘Dynamic basis of geomorphology’ being a land- weathering rates were made in the late nineteenth cen-
mark publication. John T. Hack, developing Gilbert’s tury.Measurementsofthedissolvedloadofriversenabled
ideas, prosecuted the notions of dynamic equilibrium estimates of chemical denudation rates to be made in
and steady state, arguing that a landscape should attain the first half of the twentieth century, and patchy efforts
a steady state, a condition in which land-surface form were made to widen the range of processes measured
does not change despite material being added by tec- in the field. But it was the quantitative revolution in
tonic uplift and removed by a constant set of geomorphic geomorphology, started in the 1940s, that was largely
processes. And he contended that, in an erosional land- responsible for the measuring of process rates in differ-
scape, dynamic equilibrium prevails where all slopes, ent environments. Since about 1950, the attempts to
both hillslopes and river slopes, are adjusted to each other quantify geomorphic processes in the field have grown
(cf. Gilbert 1877, 123–4; Hack 1960, 81), and ‘the forms fast. An early example is the work of Anders Rapp
and processes are in a steady state of balance and may (1960), who tried to quantify all the processes active
be considered as time independent’ (Hack 1960, 85). in a subarctic environment and assess their compara-
Luna B. Leopold and M. Gordon Wolman made notable tive significance. His studies enabled him to conclude
contributions to the field of fluvial geomorphology that the most powerful agent of removal from the