Concept of System in geomorphology

Systems of all kinds are open, closed, or isolated according to how they interact, or do not interact, with their surroundings. Traditionally, an isolated system is a system that is completely cut off from its surroundings and that cannot therefore import or export matter or energy. A closed system has boundaries open to the passage of energy but not of matter. An open system has boundaries across which energy and materials may move.

Geomorphic Systems is the study of deep and shallow Earth processes that integrate through time to shape the landforms and landscapes that compose our physical environment.

All geomorphic systems, including hill slopes, are open systems as they exchange energy and matter with their surroundings. They are also dissipative systems, which mean that irreversible processes resulting in the dissipation of energy (generally in the form of friction or turbulence) govern them. Thus, to maintain itself, a geomorphic system dissipates energy from such external sources as solar energy, tectonic uplift, and precipitation. Four kinds of geomorphic system may be identified: form systems, process systems, form and process systems, and control systems.

Form systems

Form or morphological systems (fig. 1a) are sets of form variables deemed to interrelate in a meaningful way in terms of system origin or system function. Several measurements could be made to describe the form of a hill slope system. Form elements would include measurements of anything on a hill - slope that has size, shape, or physical properties.

A simple characterization of hill slope form is shown in figure, which depicts a cliff with a talus slope at its base. All that could be learnt from this ‘form system’ is that the talus lies below the cliff; no causal connections between the processes linking the cliff and talus slope are inferred. Sophisticated characterizations of hill slope and land surface forms may be made using digital terrain models.

Process systems

Process systems, which are also called cascading or flow systems (fig. 1b), are defined as ‘interconnected pathways of transport of energy or matter or both, together with such storages of energy and matter as may be required’. An example is a hill slope represented as a store of materials: weathering of bedrock and wind deposition add materials to the store, and erosion by wind and fluvial erosion at the slope base removes materials from the store. The materials pass through the system and in doing so link the morphological components. In the case of the cliff and talus slope, it could be assumed that rocks and debris fall from the cliff and deliver energy and rock debris to the talus below.

Form and process systems

Process–form systems (fig 1c) (also known as process–response systems) comprise an energy-flow system linked to a form system in such a way that system processes may alter the system form and, in turn, the changed system form alters the system processes. A hill slope may be viewed in this way with slope form variables and slope process variables interacting. In the cliff-and-talus example, rock falling off the cliff builds up the talus store. However, as the talus store increases in size, so it begins to bury the cliff face, reducing the area that supplies debris. In consequence, the rate of talus growth diminishes and the system changes at an ever-decreasing rate. The process described is an example of negative feedback, which is an important facet of many process–form systems.

Control systems

Control systems are process–form systems that interact with humans. They include managed rivers, coasts with some caves. Given the degree to which humans now affect the planet, it might be argued that many geomorphic systems – certainly all anthropo-geomorphic systems – are control systems.