Geography
Geography is a science that studies the relationship between human beings and their environment, as well as the distribution and differentiation of events and phenomena within geographic space, and their individualization and locational analysis. Geographic space is locatable, dynamic, evolving, distinguishable, homogeneous, and fragile. It possesses both magnitude and scale.
The study of geography is approached from two main perspectives:
physical geography and human geography.
Physical geography
Strahler (1989) defines physical geography as “the set of basic principles of the natural sciences that deal with the contact and interrelationship of the elements of the physical environment and humankind.” The sciences considered within physical geography deal with specific spheres of the Earth system, the most fundamental being geodesy, which studies the shape of the Earth; climatology and meteorology, which study the atmosphere; oceanography, which studies the oceans, their waves, currents, and tides; hydrology, hydrogeology, and limnology, which study continental waters, such as groundwater and surface runoff; geology, which studies the varieties and structures of rocks below the surface; geomorphology, which studies the origin and development of landforms; edaphology and pedology, which study the soil; and biogeography, which studies the structure and distribution of organisms.
Geology
James Hutton (Theory of the Earth, 1795) and Charles Lyell (Principles of Geology, 1830, 1833) can be considered as the fathers of modern geology.
Hutton proposed the principle of uniformitarianism, which refers to the permanence of the Earth's current causes throughout its evolution; that is, he postulated that the geological changes that occurred in the past are the same as those at work in the present. These ideas were later consolidated by the work of Playfair (Illustrations of the Huttonian Theory of Earth, 1802), making an important contribution to a sequential (gradualist) perspective of the Earth, challenging the earlier catastrophist paradigm of Cuvier (1769-1832), which posited that the Earth's geological changes had occurred suddenly and abruptly.
Sedimentary rocks
Sedimentary rocks form through the precipitation and accumulation of minerals from a solution (originating from liquids) or through the compaction of the remains of living organisms (both animal and plant) that compact until they solidify into hard rocks. This sedimentation process consists of several major general phases.
Erosion : Whether biological, chemical, or mechanical, this phase of the sedimentary process is characterized by the destruction of pre-existing solid rock, breaking it down into smaller fragments. The destructive agents can be wind, water, or ice.
Transport: In this phase, water in its different states or wind transport the fragments produced by erosion.
Geomorphology
Geomorphology studies landforms (geoforms) and the processes that gave rise to them. Geoforms refer to geographical features present on the Earth's surface, such as rivers, hills, plains, beaches, dunes, among others. However, some also consider underwater geoforms, or even those on other planets and satellites in the solar system—Mars, the Moon, Venus—to be within the scope of geomorphology. Its study is carried out at different spatial and temporal scales, from small particles to mountains and tectonic plates, and from days to eons (Fig. 1.1) (Huggett, 2007).
The first to wonder how mountains and other landforms were formed were the ancient Greek and Roman philosophers, such as Aristotle, Herodotus, Seneca, Strabo, and Xenophanes, who hypothesized about the origin of river valleys and the presence of marine remains in the mountains (Hugget, 2007).
The study of geomorphology can be approached from three main aspects: form, processes, and history. The first two are considered within the scope of functional or process geomorphology, while the latter is called historical geomorphology (Chorley, 1978). Process geomorphology studies the relationships between landforms and the processes that act on them. Historical geomorphology, on the other hand, studies the temporal dynamics of these processes, which refer to vestiges of the last glaciations as well as long-standing processes dating back millions and hundreds of millions of years.
Historical geomorphology
“The present is the key to the past” refers to the fact that the effects of geomorphic processes observed in the present can be used to infer the causes of landscape changes that occurred in the past.
The first theory on landscape evolution was proposed by W.M. Davis (1889), who proposed the “geographic cycle” by which forms evolve through the stages of youth, maturity, and old age (Fig. 2). According to this theory, the topography gradually wears away, starting with an initial rapid uplift, culminating in an extensive flat region close to the base level, with occasional hills corresponding to remnants of local erosion. Although this theory was later widely questioned, it was an important contribution as it was the first properly geomorphological paradigm and the first evolutionary interpretation of relief.
Later, Walther Penck postulated that uplift and denudation—the process that leads to the degradation and lowering of the terrain—can occur simultaneously, and not just alternately as Davis suggested. In this way, landforms evolve with different combinations of uplift and denudation rates, with the individual evolution of each slope determining the evolution of the entire landscape (Penck, 1924, 1953). Penck proposes that there are three main slope forms: convex slope profiles, which result from upward development (aufsteigende Entwicklung), when the rate of uplift exceeds the rate of denudation; straight slopes, which result from stationary development (gleichförmige Entwicklung), when the rates of uplift and denudation coincide; and concave slopes, which result from declining development (absteigende Entwicklung), when the rate of uplift is less than the rate of denudation.
Subsequent work has shown that landforms and their slopes depend not only on the interaction between uplift and denudation processes, but also on the nature of their materials and erosion processes, giving way to a phase of regionalization.
For their part, other historical geomorphologists sought to interpret events that occurred in the Pleistocene based on geologically young sediments. The first insights into the effects of Pleistocene glaciations on the relief were provided by Eduard Brückner and Albretcht Penck—father of W. Penck—(Penck and Brückner, 1901–1909), giving rise to the branch of geomorphology known as Quaternary geomorphology. Brückner and Penck proposed a river-terrace sequence that gave its name to the main glacial stages: Donau, Gunz, Mindel, Riss, and Würm.
Modern historical geomorphology is no longer based on Davis's geographical cycle, but on various chronological analyses, such as stratigraphic studies of Quaternary sediments. Relative chronologies can be established from observed stratigraphic relationships, or absolute chronologies can be established using sequences dated by radiocarbon analysis, dendrochronology, luminescence, paleomagnetism, among others.
Process geomorphology
Process geomorphology studies the processes that give rise to landforms or geoforms. Grove K. Gilbert was the first process geomorphologist, with the publication of his treatise on the Henry Mountains of Utah, USA (Gilbert, 1877), where he discussed the mechanics of fluvial processes and, later, the transport of debris by running water (Gilbert, 1914).
Other notable authors in process geomorphology include Ralph A. Bagnold, Filip Hujlstrøm, Arthur N. Strahler, and John T. Hack. Strahler made a fundamental contribution through his work Dynamic Bases of Geomorphology (Dinamic
Figure 2. W.M. Davis' geographical cycle (Source: Huggett, 2007)
basis of geomorphology) (Strahler, 1952). Hack, developing Gilbert's ideas, established the concept of dynamic equilibrium in the landscape, where the landscape tends toward a steady state, even though material is added by tectonic uplift and removed by a constant set of geomorphic processes (Hugget, 2007). In the field of fluvial geomorphology—the study of interactions between river channel forms and processes—notable contributions were made by Leopold and Wolman (Leopold et al., 1964). Schumm, for his part, integrated concepts such as thresholds and dynamically metastable states into notions of landscape stability. During the 1960s and 1970s, process geomorphology focused largely on model building to predict changes in landforms in the short term, i.e., on human time scales. The models were based mainly on notions from soil engineering (slope stability) and hydraulic engineering (flow, transport, and deposition of sediments in rivers).
Process geomorphologists made significant contributions to the development of this science, especially in the creation of a database of process rates in different regions of the world, in the construction of predictive models of short-term changes, and in the proposal of some concepts about stability and instability in geomorphic systems.
Structural geomorphology
Structural geomorphology studies the internal structure of the Earth and its lithology. Internal or endogenous morphogenetic agents, such as tectonics, diastrophism, volcanism, and seismology.
Figura 1. Estructura interna de la Tierra, según composición física y química
Dynamic geomorphology
Dynamic geomorphology studies external or exogenous morphogenetic agents, such as morphodynamic processes, the morphogenetic system, and the morphoclimatic system (inherited landforms).
It studies the nature and modes of action of exogenous forces. That is, the incorporation or transport of material by a dynamic agent, such as water and wind. Strahler (1952) proposes the existence of two main forces:
Wind erosion
This is a selective agent that transports fine materials (<2 mm). Its action is significant in coastal areas and deserts.
Deflation
Abrasion of rock exposed to wind
Water erosion
Fluvial (rivers)
Glacial (ice): stripping, abrasion, cryoclasty.
Glacial erosion
