Geomorphology - EOLSS Chapters/C01/E6-14-02-01.pdf · Geomorphology, the study of landforms, is an integrative science since it includes soils, country rock, climate, water, and vegetation

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GEOGRAPHY – Geomorphology - Hanna Bremer

GEOMORPHOLOGY Hanna Bremer Geographisches Institut, Universität Köln, Germany Keywords: Geomorphology, landform, relief, klimagenetische geomorphologie, process geomorphology, structural geomorphology, geoecology, paleoclimatology, weathering Contents 1. Introduction 2. Development of Geomorphology 3. Main Concepts, Research Lines, and Methods 4. Structural Geomorphology 5. Weathering and Soils 6. Morphoclimatic Zones and Special Landform Associations 7. Process Domains 8. Environmental and Global Change Glossary Bibliography Biographical Sketch To cite this chapter Summary Geomorphology, the study of landforms, is an integrative science since it includes soils, country rock, climate, water, and vegetation as controlling factors. It is therefore a good basis for geoecological research on a medium and large scale. A morphogenetic analysis in particular allows a better evaluation of many detailed paleoclimatic studies. Advances will come from correlation of landforms with soils and sediments inclusive of laboratory analyses and absolute datings. Increasingly, applied geomorphology is helping with questions of land degradation (soil erosion and desertification) and engineering (flood, landslide damage, and coastal erosion). Geomorphology is helpful for many geoecological problems, such as underground water movement, soil distribution, and vegetation patterns. 1. Introduction Geomorphology is the study of landforms and of the processes shaping them. Exogenic forces act from above the surfaces (i.e. are climate controlled) and endogenic forces, mainly tectonic movements, are considered relevant for shaping landforms. They change in quality and quantity in space and time. Rock resistance or lithology is the third component. As all three cover a wide field of individual constituents, investigations that apply all three components in detail are possible only for a limited area. Often single landforms are studied, such as a lakeshore, where the three components can be isolated. Obviously which constituents and to what extent they are

©Encyclopedia of Life Support Systems(EOLSS)

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incorporated varies, so that a distinction is made between micro- (weathering of a bloc), meso- (evolution of a valley), and megageomorphology (subcontinental fault scarps). But it is not only the spatial scale that characterizes geomorphological investigations. They differ rather more in the extent to which they take into account other geoecological sciences like climatology, hydrology, soil science, and biology; geology is always borne in mind. This results in a comprehensive approach, which seems to be less determinable than the measurement of, for example, erosion rates. But increasingly, the interdependence of geoecological factors is realized and the isolation of single factors is considered incomplete. The surface of the earth, or landforms, is not only the basis for all processes in ecology, the evolution of landforms is also responsible for the depth of weathering and the sediment cover, for example, and therefore for hydrological pathways, the distribution of soils, and the availability of nutrients. This in turn forms the vegetation pattern and the natural resource for land use. Landform evolution is the best control for geoecological budgets on a medium scale, especially to distinguish between natural and human-induced processes. 2. Development of Geomorphology

2.1. Early History

Living with nature has always meant dependence not only on weather but on geomorphological processes as well. The management of water began with the very early civilizations: floods and natural fertilization by river sediments were acknowledged, as when Herodotus said: “Egypt is the gift of the river.” Aristotle noted the rapid change of a coastline by sedimentation in delta areas. Earthquakes and volcanoes, so relevant in the Mediterranean, were a subject of speculation. Early descriptions of landforms are to be found in the itineraries of ancient explorers and soldiers. In the medieval age, dogmatic views left little room for questions on the evolution of the earth. The Arab Avicenna, however, was aware of uplift and slow erosion. Only with the Renaissance, when the cosmic position of the earth became known and with this the timescale of a few millennia for creation was extended, was the way opened for the perception of the long-term slow processes of geomorphology and geology. The description of landforms still prevailed and it was only in the second half of the eighteenth century that investigations on the origin of landforms began. This period of description and speculation saw a debate between Neptunists (Abraham Werner 1750–1817), who thought the earth was shaped by running water, and Plutonists (Leopold von Buch 1774–1853), who believed tectonic movements controlled from the interior were the major causes. In the nineteenth century, geomorphology evolved mainly from two roots. During geological exploration and surveys, strange sediments such as till in Central Europe or large gravel deposits in the western United States were discovered. The question of their origin led to the study of processes. Sediments were probed in areas where they were young and the results were transferred to ancient areas (known as “actualism” or “uniformitarianism”). The second root was the exploration of then little-known countries by earth scientists and their records of strange landforms and processes.


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Mainly it was research devoted to the special landscape investigated. Observation of phenomena was the basis. Explanations were derived from combining the occurrence of processes or deducing them from fresh sediments or erosional features. Eventually general rules developed. This might be called the period of inventory exploration. As landscapes differ from country to country, or even inside large states, methods were manifold. It is hardly possible to attribute the start of systematic geomorphology or even of special fields to one person; rather, there was a more or less national development. Exchange began slowly, but two main streams may be distinguished: the American–British line and the European continent geomorphologists. However, from the late twentieth century, there has clearly been independent development in other countries.

2.2. Evolution of the Main Concepts

The first part of the twentieth century was dominated in the English-speaking world by W.M. Davis’s model of landform development. This proposed an initial uplift, incision of narrow valleys, their broadening, and, as an end stage, a surface without marked relief—a peneplain. This brought different landforms into an evolutionary order, a cycle of erosion, a concept that has been given up partly because its rigidity left no room for detailed research. Some geomorphologists in the English-speaking world are still suspicious of investigations of landform evolution. However, the tide is turning, albeit on a different level. Though the only textbooks of Davis were published in German, they had little influence in continental Europe. This was also true for the Morphologische Analyse by the geologist Walter Penck, son of the geographer Albrecht Penck, who tried to deduce differentiated tectonic movements from landforms. Neither theory was much discussed on the continent, as there were known to be substantial contradictions in landform evolution. British geomorphology historians stated that: “Towards the end of the nineteenth century, German geomorphology was unique in the heavy concentration which was placed on the study of process.” Before World War I, research on the continent broadened in range and, instead of a model, provided more plausible answers for the wealth of landforms. Processes were investigated directly or deduced from the analysis of landforms. The main methods were comparison of sequences with the same or with similar ones in other areas, especially in different climates under divergent conditions. Rock resistance and observed tectonic movements were incorporated. After World War II, there was a revolution in the English-speaking world sparked by hydrologists. This led to a phase of measuring and modeling, followed by field experiments and theoretical considerations like dynamic equilibrium. More recently, the latter has become less important than case studies of rivers, beaches, and slopes, where detailed investigations of processes are often used for applied geomorphology. On the continent, climatic geomorphology was extended to climatogenetic geomorphology. The mutual relationship with paleoclimatic research became increasingly important. This brought about a close connection with soil science and hydrology. The study of the evolution of landforms developed into research on the history of landscapes, which led to a better understanding of many geoecological correlations. This was one reason for increasing interest in measurement of dynamic components in the landscape. Another might have been the influence of English-speaking colleagues, while a third was the


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wish to get absolute data on evolution. Another line, especially in Eastern countries, was mapping geomorphological and geoecological features, mainly as a basis for planning. Still, terminology is quite often not compatible and is rarely unified. This is because of the different approaches and interpretations, and might ease with increasing international cooperation. In recent years, there has been a rapprochement between the English-speaking and the continental branches of geomorphology as the applied aspects of geomorphological or geoecological research has become more important worldwide. The second reason is the increasing knowledge of absolute dates. Some dates are very old, so that evolutionary questions become more important. In general, differences should not be stressed because there always have been exceptions to the Davisian school as many geomorphologists studied processes in detail. On the other hand, numerical geomorphology has a tradition on the continent. New aspects and methods are applied in all fields of geomorphological research. In general, there is a large range of laboratory analyses and dating methods. Global positioning systems (GPS) help in areas where small-scale maps are not available. Geographical information systems (GIS) give a better oversight of geoecological parameters in relation to landforms. Larger areas can be more easily connected to detailed field investigations.

2.3. Organizations and Journals

The exchange of ideas evolved only slowly and geomorphology took a long time to get internationally organized. Geomorphologists met at geographical or geological congresses, where they were heavily outnumbered. There were few sessions devoted to geomorphology. Contacts at first were mainly on a personal basis, as was the exchange between Davis and A. Penck for the whole winter term of 1908/09. Mortensen devoted a great deal of effort to getting an international board for the Zeitschrift für Geomorphologie, which he revived in 1957 after the national Zeitschrift had collapsed in 1938. From 1960 to 2002, there were 46 normal and 128 supplementary volumes. There was some international cooperation, however, which increased over the years in commissions on geomorphology in the International Geographical Union. The first was the commission on periglacial geomorphology (1949–1972) followed by periglacial phenomena (1980–1988), frost action environments (1988–1996), and climatic change and periglacial environments (1996–2000). Coastal geomorphology (1952–1972) became coastal environment (1976–1992), and finally coastal systems (1992–2000). The commission for the evolution of slopes (1952–1968) evolved to geomorphological processes (1968–1976), then field experiments (1976–1984), measurement, theory and application (1984–1992), and geomorphological response to environmental change (1992–2000). A commission on applied geomorphology was active from 1956 to 1968. Karst phenomena were a topic from 1956 to 1964, and there was a later study group on environmental changes in karst areas. The commission on geomorphological survey and mapping (1968–1980) became a working group (1980–1988). Other groups investigated the geomorphology of river and coastal plains, or morphotectonics. A study group was concerned with rapid geomorphological hazards (1988–1992), out of which evolved the commission on natural hazard studies (1992–2000). A new commission was started on


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land degradation and desertification (1996–2000). By the first years of the twenty-first century there were five commissions. The first national organization was the British Geomorphological Research Group (BGRG), started in 1960, and the Deutsche Arbeitskreis für Geomorphologie had its first meeting in April 1974. In September 1979, there was a very successful British–German meeting at Würzburg, followed three years later by a visit of members of the German group to Scotland. The BGRG was very active in establishing international relations. In 1978, the second international geomorphological journal, Earth Surface Processes, was launched; it was later expanded to include landforms, in the title as well. There were several conferences with international participation as, for example, that on megageomorphology in London in 1981. The BGRG organized the first international congress on geomorphology in Manchester, which attracted 675 participants from 51 countries, confirming the demand for the exchange of ideas. The next congresses at four-yearly intervals, at Frankfurt, Hamilton, Bologna, and Tokyo had about the same number of participants. The International Association of Geomorphologists was formally founded at Frankfurt in 1989 in response to the formation of many national organizations. The 28th Binghamton Symposium was included at Bologna, the symposium being an American institution established in 1970 and usually consisting of two days of lectures, mainly by American colleagues from the State University of New York. Out of this grew the journal Geomorphology that started in 1988. More specialized journals begun since 1979 are Studia Geomorphologica Carpatho-Balcanica and Transactions of the Japanese Geomorphological Union. Geoabstracts, which originated as Geomorphological Abstracts in 1960, is extremely useful. 3. Main Concepts, Research Lines, and Methods

3.1. Klimatische Geomorphologie and Climatic Geomorphology

Geomorphological processes occur predominantly in loose material, in the regolith and its upper parts, the soil, whose properties are largely controlled by moisture and temperature. The movement of material is regulated by water and only in exceptional cases by wind. Gravity—altered by tectonic uplift—is a factor for the magnitude of transport, but even in this regard, water plays an important role, either directly or indirectly, via weathering in determining friction. The term coined for the complex interaction of the different forces was climatic geomorphology, a term widely misunderstood. The title of this section is intended to draw attention to the different conceptions in continental and English literature. Of course, the influence of exogene forces has long been known and there have been many attempts to classify morphoclimatic zones or regions to relate climatic data to specified processes. Peltier’s often repeated and sometimes enlarged diagram, like Davis’s model, could not deal with details and had little influence on further research. Climatic geomorphology in the English literature still classifies regions and processes according to climatic zones. This was not an important issue on the continent. A first systematic approach was the conference “Geomorphologie der Klimazonen” held at Düsseldorf in 1926. Each author compared observations of geomorphological


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processes from overseas with those at home. When Büdel proposed the System der klimatischen Geomorphologie in 1948 he summarized the forming processes then known and described what he called morphoclimatic zones. Three important steps resulted from this comparison: the relative significance of different processes for landscape shaping in a specified zone was delineated, the interaction of processes became clearer (Formungsmechanismus is the interaction and sum of forming processes), and a basis was found not only for the designation of single paleoforms but for their systematic derivation. The comparison was mainly done for landform assemblages, stressing the most important processes. It is possible to compare single processes in different climatic zones, but this has rarely been done. Perhaps this is because single processes are studied in detail, making it difficult to get an overview for a whole zone. Secondly, knowledge of rivers in the temperate zones, for instance, is much better than of those in the tropics. Therefore, it has been said that climatic geomorphology is good for megageomorphology but does not help with the detailed investigation of processes. In the early 1950s it was shown that bloc fields in the Harz Mountains started by weathering in the Tertiary because the quarzite blocs have a thick red rind of hematite iron like that in paleosoils. This is missing on sharp indentations, which were due to frost splitting and where a small white rind developed in the Pleistocene. Transport of the blocs occurred in a solifluction layer during the cold ages, the removal of the entrenched fine material and thus the exposing of the blocs occurring in recent times. This example demonstrates that it is not possible to investigate even small features without seeking the history of an area, which in the case of the Harz Mountains is also indicated by relics of tertiary soils, etchplains, the glacial and periglacial forms nested into them, and the recent soil cover. The search for paleoforms was well established in glacial geomorphology. At the beginning of the twentieth century A. Penck and Brückner made a model after many initial observations of the glaciation of the Alps and the foreland. They then searched systematically each valley for evidence of glaciation and in the foreland of the glacial series: the relation of end moraines, the fan in front, and the outwash plain or fluvioglacial terraces. This succession enabled them to bring order into the en echelon formation of these landform elements and thus establish four ice ages. Model and observation were constantly developed, checked and altered. After World War II, glacial and periglacial forms, recent and relic, were systematically sought overseas, and snowlines and periglacial limits were derived. This paleoclimatic research was the first step for many geomorphologists to look for relic features overseas. It was already known before the war that inselbergs and red loams had been formed in the Central Europe plains in a warm, humid climate in the Tertiary. The widespread cover of solifluction soils and loess is considered a relic of the cold periods of the Pleistocene. The systematic discrimination of landform generations, the klimagenetische Geomorphologie, outside Central Europe was done first in 1955 in the central Sahara. Initially, recent processes and landforms were matched. Similar forms in other areas were sought for those that could not be explained, leading to the conclusion that they were formed under a climate like the one there. Only then was the paleoclimatic data sought that might have been derived from, for example, paleobotany. In the meantime,


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it is acknowledged that all climatic zones have relic features in landforms, usually also in the regolith. Therefore, a systematic approach to the evolution of the landforms is possible and necessary. Continental geomorphologists consider investigations as incomplete that do not discuss this. The scene where the processes of today are acting is rarely the scene they formed: for example, a riverbed in present-day Central Europe armored in stretches by periglacial cobbles and gravels. The investigations of landform generations have regional as well as general connotations as, for instance, a comparison of Central Australia with other desert areas might show. This is due to their different climatic and tectonic history. The methods for klimatische and klimagenetische Geomorphologie are observation, comparison, evaluating sequences and interlocking or nesting of landforms, connections with recent and paleosoils, and correlative sediments. Wherever possible this is supported by absolute dating, laboratory and field analyses of soils and sediments. Klimatische Geomorphologie does not aim to link geomorphology with climatic data, either for landform assemblages or for single processes. While there was an intensive discussion about the importance of certain processes, the forming mechanisms, and controlling agents like discharge and mode of water movement, there has been almost no discussion about classification and limits of morphoclimatic zones, demonstrating that this has not been of foremost interest in continental geomorphology. It is much more than simply adding geomorphology to arid, humid, etc. regions. Klimagenetische Geomorphologie is based on the results of klimatische Geomorphologie, and is thus equally founded on the analysis of processes. This is its fundamental difference from the classical denudation chronology. The research for landform generations may be called climatogenetic geomorphology. It should be distinguished from a “morphogenetic region,” which British geomorphologists define as “large areal units within which distinctive associations of geomorphic processes . . . are assumed to operate, tending towards a state of morphoclimatic equilibrium.” Such an areal unit would be called a klimamorphologische zone in German terminology. A morphogenetic region in German understanding has an individual character, as it comprises an area for which the processes of land forming in different climates, recent and in the past, and the tectonic history are the same. This is not only a difference in wording it is another approach. The concept of a morphoclimatic equilibrium is not real in nature as this would mean the elimination of all paleoforms. Klimatische and klimagenetische Geomorphologie are at a stage where arguments will not afford much progress. Progress will be achieved, rather, by detailed investigations. Further advances may come from the analyses of soils and weathering crusts, increasing numbers of absolute data (including new dating methods). The connection with tectonic and palaeoclimatic research will be mutually beneficial. It is the great advantage of klimatische and klimagenetische Geomorphologie that they are open to change, they will accept additions, they have no preconceptions, and they work on all scales.

3.2. Process Geomorphology, Field Experiments, Simulation, and Modeling

In these lines of research one tries to get numerical results and apply physical and statistical rules. So far, there has been very little replication or reproduction of


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experiments or measurements, a basic requisite for natural science. One problem is the high variability in nature. Absolute data should therefore be taken with a rather large range. The second problem is the large number of interrelated factors, and usually it is not easy to isolate a few in the field. Despite these reservations, one must say that orders of magnitude are now better known than ever before. The American hydrologist Horton started before World War II to register geometrical attributes of rivers, an endeavor that was later expanded. The hydrological branch of the U.S. Geological Survey not only measured discharge and sediment load but also added morphological investigations. This gave a strong incentive to the research community. Once equilibrium of process and form had been postulated, the stage was set for investigations of single forms and processes, and thus detachment from the Davis model. Equilibrium has since been defined in many ways and subdivided, but has rarely been proved in the field. A third line was the introduction by Chorley of systems theory impregnated with the ideas of the botanist von Bertalanffy. Functional relationships have been seen as essential for geomorphology, and attempts have been made to apply fractal and chaos theory to geomorphology. Probably the most important function of these approaches was the breakup of conventional thinking. Observation gained in prestige. Soon a large number of measurement programs and field experiments developed. Slaymaker defined three different types of field experiments: (1) Controlled interference to simulate landform evolution. This is rare in field

geomorphology because it usually requires a change of the natural conditions: for instance, an artificial rainstorm on a plot with fixed boundaries or a reduction of factors in time and space. True experiments as in physics are rarely possible in nature.

(2) In hybrid experiments, special landforms are selected and the changes are monitored in relation to climatic, hydrologic, or anthropogenic inputs. An example would be the mass movement on a periglacial solifluction slope in relation to freeze and thaw cycles.

(3) For a spatial unit or several of them (e.g. a cascade from small to large watersheds), energy and mass inputs as well as morphological changes are monitored. An example is the measurement of erosion rates at different points of a river in relation to discharge.

Measurements of erosion may be done in different ways. The lowering of a surface can be directly measured with erosion pins (e.g. 60 cm long and maximal 5 mm diameter). These must be introduced deeply enough into the soil that their position is not changed by frost, bioturbation, etc. On slopes or in very small valleys washed material may be measured by recovering it from troughs or bottles. The velocity of slow mass movement can be measured by putting marks into the soil, preferably with fixed points on outcrops. In the walls of pits, marking sticks have been installed in different positions to show the differential movement in the soil. The pits are filled in and opened up after ten or more years. Movement of blocs may be detected by painting them and mapping their position before and after events. In rivers, this was not very successful. Small magnets or even little transmitters have been inserted into pebbles, the better to follow them.


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Erosion rates of catchments are measured in rivers, where dissolved and suspended material is rather easily obtained from a boat, but movements of the bottom gravel or sand are difficult to record. Erosion measurements of plots on slopes to establish relationships with gradient, length of slope, material properties, or land use have greatly contributed to field experiments. Most important are the surveys to document anthropogenic interference by agriculture or devastation of vegetation. The second large group is the measurement of load in rivers, to get an understanding of the erosion rates in different areas. In both fields of interest, especially in the second, there is rarely a precise distinction between natural and human-induced erosion. It has been found in savanna areas in Tanzania that land use increases the rate of erosion more than 100-fold and that up to 35% of the sediments come from tracks and paths. Experiments in laboratories like the simulations at the well-known Mississippi River Station have a very long tradition with engineering institutes, especially for rivers and coasts. In geomorphology, there have been laboratories with experimental design at Uppsala (river work), Leuven, and Debrecen (fluvial erosion and denudation). In laboratories, time, space, and material properties must be reduced as factors, and at least one factor cannot be simulated in proportion. Many laboratories attached to geographical institutes are concerned with analyses of weathering products, dating procedures, and measurement of geoecological parameters. With research in river morphology and coasts and with field experiments, there came a discussion on general rules and concepts. The earliest considerations about physics in geomorphology were mainly concerned with river meanders and slope models. Rhythmic phenomena were described in 1929, and a comprehensive treatment of physical rules and mathematics in geomorphology was made in 1961. This latter considered exogene processes as essentially random and therefore able to be treated by stochastic models, the reason being the turbulence often involved. Erosional processes caused by tectonic stresses should be more homogeneous. For detailed investigations the following principles are generally discussed: • Thresholds must be surpassed before landforms are changed. They may be internal,

like lithological characteristics, or external, like climatic factors or change in elevation. There are thresholds for processes and thresholds for landforms. They are of different size and/or form. Fairbridge’s definition is: “A threshold is a boundary condition that separates two distinct but interconnected processes, fed by an identical energy source.”

• Feedback: negative feedback may also be called self-regulation. This means the diminishing or absorbing of changes by opposite processes. With positive feedback, the process changes and sparks new processes. Both positive and negative are limited in time and space, negative feedback becoming negligible, positive collapsing after a threshold is surpassed or turning into negative feedback.

• Equilibrium: if the state or the output of a system is adjusted to the input it is said to be in equilibrium. Dynamic equilibrium applies to processes. If forms remain unchanged, this may be called steady state. Dynamic equilibrium has been described as unstable because individual features change and the direction of change is away from uniformity. An increase of relief for the last 60–100 ma has been


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shown. Relic forms, even if they remain unchanged, have nothing to do with equilibrium, rather a threshold given by friction is not surpassed, and this may change in time and space.

• Relaxation time is the time needed before a system changes. • Recurrence interval is the time between two events of the same or similar

characteristics. • Recovery time is the time needed for a form changed by a catastrophic event to

return, usually slowly, to the original state or a similar one. For example, a river meander may be cut off during an extreme flood, but the straight reach will slowly develop into a meander again.

• Persistence of landforms: many forms persist for a longer time than it took to create them.

• Resistance and resilience: a system resists changes and recovers after disturbances. • Sensitivity is a measure of how fast landforms or landscapes will change due to

forces acting on them (recurrence interval/relaxation time). • Ergodic principle (ergon = energy or work, hodos = way): small forms will

develop in time into large ones. This means that space and time are exchangeable in evaluation of process–form relation. This applies only in some cases and is not universally appropriate.

• Systems may be distinguished as static systems, process systems, and, most importantly for geomorphology, process–response systems. Static systems are time-independent (e.g. the velocity of river flow in relation to pebble size). In process systems, processes are regularly linked (e.g. mass movements or solifluction influences the river load and therefore the transport processes). In process–response systems, the reaction of forms or material on one or several processes is investigated. They are often combined with negative feedback, that is, a decrease of intensity.

• Magnitude and frequency of processes responsible for shaping landforms are parameters for extrapolation.

• Event geomorphology considers especially high magnitude events and the sequences of events.

• SOC (self-organized criticality): the interrelated components of a system may evolve into a critical state, where a small change leads to a catastrophic event. An example is a landslide, where a rainfall triggers the process.

• Geologic, modern, and present times have been distinguished for the status of river variables and cyclic, graded, and steady time for drainage basin variables. Cyclic time is conceived of as 104, graded time as 102, and steady time as 10–1 years.

Thus there is a large range of conceptual models, mainly deductive and starting with plausible assumptions, that are carried to conclusions by argument. Somewhere in that process, field observations come into play. However, there is uncertainty about where to apply the model or the derived rule. This might be the reason why some scholars plead for intensification of field research with as few concepts as possible and drawing only careful conclusions. The application of physical laws in geomorphology should not neglect friction because relic forms will only be destroyed when a threshold of friction is surpassed. Changes in friction or inertia or entropy are responsible for the discontinuity of processes in time and space. Klimatische and klimagenetische


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Geomorphologie concepts evolved from case studies (e.g. relaxation time can be distinguished from relic forms). The term “model” is widely used, but sometimes just for a simple abstraction. In a narrower sense, it denotes a numerical evaluation of interrelated parameters. A succession of processes in a system is simulated until the landform feature evolves. This may be done by entering physical parameters like gradients, runoff, and thickness of the regolith whose changes are iterated. A large range of slope forms have been achieved by different combinations. They are then checked with nature and if there is conformity of the forms, an explanation for the evolution of slopes is offered. Earlier trials were carried out or theories offered for the development of slopes, but only with computer technology was the iteration good enough to come close to nature. Field evidence should probably be provided at several stages. Modeling should include: 1) morphological models, or morphometry (numerical values of landform elements), 2) morphological evolutionary models, especially the investigation of sediment storage, 3) in cascading models a sediment cascade approach based on budgets, 4) process–response models in different timescales. 4. Structural Geomorphology

4.1. Petrovariance

Structural geomorphology is concerned with landforms shaped by differences in rock hardness (petrovariance). The relation cannot be the same in diverse climates (e.g. granite under physical weathering conditions in polar countries may be quite resistant, while in the tropics with intense weathering it is more easily decomposed than sandstone). Sedimentary rocks with nearly horizontal layers of alternating resistance may develop to cuesta landscapes with wide plains and escarpments topped by the harder rock, best seen in arid countries. In Central Europe with the same structural conditions, the forms differ from this simple picture as the plains extend on hard and soft rock; sometimes the scarps are even missing on divides. Neighboring crystalline mountains have remnants of etchplains and relics of intensely weathered soils, thus planation is explained by hot and wet conditions, prevailing in the cuesta landscapes, too. Additional evidence comes from fossils, and nested periglacial features. These investigations that intensified in the 1950s and 1960s were one incentive for the development of climatogenetic geomorphology. Another landform quite often explained by petrovariance is inselbergs and waterfalls in the tropics. This might be true in several cases, but usually it is quite difficult to prove, as the surrounding deep weathering covers the neighboring rock necessary for comparison. If the geomorphological position, especially moisture conditions during development, is considered, the explanation for these landforms is more comprehensive. This is not the opposite of petrovariance but can easily include it.

4.2. Tectonic Geomorphology

In tectonic morphology, one field of study is morphostructures, looking for landforms following tectonic lines, and vice versa. Air photos and satellite imagery are widely


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used for these investigations. Three-dimensional digital landform models are especially expressive. Landforms predominantly shaped by tectonics are grabens, like the large systems in East Africa, fault scarps or, if altered by erosion, fault line scarps, and block mountains. With plate tectonics came a new understanding of the position of mountains, shields, and volcanoes. This makes it easier to delineate tectonic units for which similar tectonic behavior is projected. An example is continental margins, both active and passive. Most of them have a steeper side to the sea and a more gentle dip to the inland, on which the more important streams develop. Another tectonic unit for which there is so far no stringent explanation in plate tectonics is large intracontinental basins like the Amazon or Congo. Tectonic movements are either slow and relatively steady—the epeirogenesis—or fast—the orogeny. The young sediments in tectonic basins in front or in the orogens, like the Alps, the Andes, or the Himalayas allow conclusions about the exposure of a special rock at a certain time and about the transport path, and therefore about the uplift history. The transport mechanism is controlled by climate, relief energy, and distance in the mountains as well as in the sedimentary environment, questions that the geomorphologist is equipped to address. To estimate the uplift history of continental areas by evaluating the sediments of the shelf, or looking at erosion and sediment budgets on land is a field of study done in cooperation with geologists. A local deformation of plane surfaces like river or coastal terraces or planation surfaces may be evaluated for differential tectonic movements, but a change of river gradient may be due also to climatic change. Knickpoints in longitudinal profiles of rivers have different causes: rock hardness, glacial overdeepening, tropical landform evolution. They are therefore hard to interpret for tectonic movements. The worldwide tectonic picture that was developed from planation remnants of different height requires confirmation by absolute dates. W. Pencks’s concept designed to deduce tectonic movements from concave or convex slopes has been abandoned. The most detailed geomorphological analyses of tectonic movements come from coastal terraces. There are three possibilities for their origin: a) a coastal platform due to marine abrasion, b) a build up in a coral reef, c) in the tropics a planation surface adapted to sea level. A flight of coastal terraces may have two main causes: a) a decline of sea level due to water storage in inland ice (glacial eustasy), b) continental drift with high velocity retards sinking of the ocean floor, which results in high sea level (tectono-eustasy). Analysis of uplift or sinking of the land, regionally and locally and especially in marsh areas, may be complicated by compaction. Translocations of irregularities of the geoid of several tens of meters (up to 170 m?) may cause a change of sea level (geoidal eustasy). The uplift of Scandinavia and northern Canada around Hudson Bay has been determined from terraces and sediments. It is an isostatic rebound after the melting of a thick ice sheet. Coral terraces are very valuable for deducing tectonic movements as they are built up rather fast and allow absolute dating. At the Huon Peninsula in East New Guinea, a step-like co-seismic (connected with earthquakes) uplift was derived. An early discussion of uplift rates versus erosion rates was based on recent measurements and did not consider the episodic or even spasmodic nature of tectonic movements that are followed by long periods of quietness. Little is known about


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changing velocities of epeirogenic movements. A flight of etchplains, a Rumpftreppe, may indicate quietness or reduced uplift for the planation surfaces and accelerated movement for the scarps. But the latter might also evolve with continuous uplift by divergent weathering at the distal end of the plain. A new approach for tectonic geomorphology may come from a better knowledge of planational processes. The amount of erosion of the overburden may be estimated from the stratigraphy in sedimentary rocks, in crystalline rocks containing uranium from the cooling depth. The apatite fission track method may yield an age as well, which would be the maximum age for the beginning of the uplift. Further advances in tectonic geomorphology will probably come from intense cooperation with geologists, geophysicists, and geochronologists. The task of geomorphologists may primarily be in three fields: 1) analyses of landform evolution in considering climatic and tectonic control—a step in this direction would be the investigation of landforms and geomorphological processes after known tectonic movements or earthquakes; 2) modeling of erosion rates and landforms in relation to uplift rates; 3) evaluation of sediments for the transport modus.

4.3. Volcanic Geomorphology

Volcanic landforms are largely controlled by volcanic activity and material. Processes triggered by an outbreak, earthquake, or heavy rains are often catastrophic events, such as lava flows, lahars, or mudflows. Japanese geomorphologists are leading this research. In widespread tephra cover, new landforms develop at different speeds due to permeability. Tephra layers are excellent marker horizons if dated. 5. Weathering and Soils Rocks are disintegrated or decomposed by weathering. The term “weathering” indicates that this occurs under the influence of temperature and water often enriched by organic or anorganic acids or bases. Mainly rocks near the surface are involved, but weathering features have been found down to 100 m and more; permafrost goes down to 1000 m. Studies of weathering belong to several disciplines: mineralogy, pedology, and engineering sciences (especially for rock hardness). Geomorphologists study weathering from field observations of small (millimeters) to large (up to several tens of meters) forms. The main considerations are the geoecological conditions at the site and the comparison in the control of weathering. In explanations, chemical, physical, and biological forces are distinguished. The role of microorganism may have been underestimated so far. There are seven main fields of investigations: a) weathering features in hard rock, b) experimental weathering, c) influence of rock properties, d) deep weathering, e) rinds, crusts, and precipitates, f) soils and geomorphological processes, g) relation of landforms and soils. (a) Landforms shaped predominantly by weathering are to be seen mainly in hard rocks

and in precipitates. Those in hard rock can be classified according to morphoclimatic zones due to the atmosphaerilias shaping them. Forms of frost shattering in polar and high mountain regions are widely distributed. Thermal stress might produce similar forms in deserts, but most likely moisture and often salts are


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also involved. A combined chemical and physical weathering mainly in semihumid regions that produces small holes and caverns of different sizes (tafoni), with small-scale ones called honeycomb weathering. Base level caverns, shelters, or abris are due to solution and/or undercutting by intense soil formation followed by washout. These forms show a stability of the slope. Solutional features are best developed in limestones, and are known as karst.

(b) Experimental research in rock weathering consists of field observations, laboratory analyses, and simulations. Building stones and tombstones provide good dating, different exposures and lithology. The applied aspect of this is obvious. Hardness of the rock may be tested with a Schmidt hammer. Microenvironmental conditions are examined to understand the complex interactions of atmosphaerilias and rock properties. In the laboratory, the consistency of the material and the weathering changes, especially at the surface, are probed in detail using sophisticated methods such as micro-erosionmeters, microscopy (light, electron, laser), spectrometry, and mapping with digital, mechanical, and imaging techniques. In simulation experiments, rock tablets or boulders are exposed to the atmosphere or buried in the soil. In laboratories, weathering processes such as frost and thaw are simulated in climate chambers.

(c) Of rock properties, it is mainly the mineral composition but also the density, porosity, and water absorption capacity, that control the velocity of decay and alteration. This might be investigated at the micro-scale with minerals, where a stability series may be deduced. For rocks, a lithological hardness scale from acid (hard) to basic rocks may be established. For landforms and geomorphological processes, the structure of the rocks, the layering and fracturing, is important, as these are the pathways for the weathering agents. Especially in granite, the bloc weathering (wollsack, corestones) is predetermined by fractures and joints. For crystalline rocks, which originated at some depth, unloading of the overburden has been proposed as releasing residual stress. Sheeting of rock slabs and exfoliation of smaller rock parts has been ascribed to this. In nature, however, the planes are rather irregular and not parallel to the projected surface of the overburden, sometimes even being vertical to it. In artificial tunnels, the release of stress may be responsible for arched fractures.

(d) Deep weathering usually occurs as several to tens of meters of kaolin or grus. The latter consists of rock particles mainly below half a centimeter in size with sharp edges, cutting across mineral boundaries. Deep weathering exists only in patches, often connected to old landform elements. A hydrothermal origin has been suggested, but in many cases there are no indications for this. More likely is a weathering within reach of the groundwater.

(e) Rinds may cover outcrops and isolated stones as well as pebbles. They consist mostly of microorganisms and minerals like iron, silica, manganese, and titanium. As deserts varnish, they cover stones in large areas, indicating their immobility. The size of lichens on moraine blocs was used for dating. Rinds on building stones are often signs of air pollution. Iron crusts (ferricrete, plinthite, laterite) and calcrete (kunkar, caliche) may attain several meters in thickness. Silcrete, a silica enriched crust, is common in Australia on the surface, while in other continents it may be found as flint in cretaceous or even older sediments. Crusts are mainly paleofeatures of more intense weathering than today. Iron, silica, and calcium carbonate may occur in concretionary form, too, mainly with diameters around one centimeter.


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Precipitates of geomorphological interest are travertine, calcareous crust, and tufa, a more amorphous deposit. They are building landforms, sometimes several terraces of large extent and different age. Even small waterfalls may evolve. Sinter deposits of hot springs are usually less extensive. By intrusion in pores mainly of calcium carbonate, dune sands become eolianites or eolian calcarenites, especially in semiarid regions. Beach rock is a cemented coastal sand in tropical regions, and organisms may be involved.

(f) Decapitated soil profiles generally show erosion by water (e.g. sheet wash), wind, or mass movement, with paleosoils pointing to a stable surface. For processes on slopes, one can deduce the following. 1) An equal soil profile with the same thickness proves similar velocity of weathering and denudation in the area. A climax soil is a sign for a minimum of denudation (temperate zone) or of subterraneous removal of material and further weathering (tropical zone). 2) A reduced soil profile on higher gradients of the slope shows accelerated denudation. 3) An increased thickness of the weathering mantle, especially a doubling of horizons (colluvial layers), reveals accumulation. A soil catena is a regular pattern of soils from the divide to the lowest point. It may be due to weathering, particularly to the different moisture conditions. A catena may evolve by erosion on and near the divide with sedimentation in the lower part. Many catenas in the semihumid tropics consist of a red paleosoil on the divide, a recent, well-aerated, brown soil on the slope, and a gray soil in the colluvial material at the bottom. Another spatial pattern is given by paleosoils and/or changes in moisture conditions, for instance near an escarpment or an incised river. An overprinting of an old soil can be detected by micromorphology, concluding that there is a stable surface. Transport processes like wash on the surface or bioturbation in the soil profile may be detected by searching for Cs137 after atomic fallout. Cosmogenic isotopes can give an exposure date. Mode of transport, for instance deflation or river work, can be seen by electron microscopy of quartz grains.

(g) Soil scientists in Russia developed the concept of zonal soils in the early twentieth century. This matches the concept developed much later of morphoclimatic zones. In independent regional research, paleosoils and recent soils may be detected as well as older and younger landforms. There is positive feedback between both approaches. The main criterion for paleosoils is their spot-like occurrence. However, in semihumid and semiarid areas like Central Australia they can occupy large areas. In these cases, profile analyses in the field like decapitation or features like calcretes formed later in a semiarid climate in a humid red loam will help. Laboratory analyses support this: for instance, in micromorphology several weathering forms may be seen that can be evaluated for weathering intensity and thus indirectly for climatic conditions.

6. Morphoclimatic Zones and Special Landform Associations

6.1. Introduction

Only those zones are extensively described here where relief forming is very distinctive. Prominent forms are traceable as paleofeatures in other zones. In the temperate humid zone, geomorphological processes are relatively weak. Exceptions are areas with strong tectonic movements, coastal attacks, and river work in formerly glaciated areas. Many


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of the extratropical semihumid areas (Mediterranean) regions have been densely settled for a long time and they are tectonically very active. Therefore, it is difficult to distinguish between natural and human-induced processes. Soil erosion seems to be most severe in this zone, especially in regions with soft sedimentary or heavily weathered rock. Steppe and savannah regions are characterized by reworking of inherited relief. Incision in mountainous areas and areal denudation in low relief predominate. Weathering occurs at low intensity.

6.2. Glacial Geomorphology

Glacial forms and processes are studied mainly for three reasons:

(1) To understand their interrelation and the influence of other components such as the preexisting landform on glacial movement. The quantity of glacial erosion differs in time and space, and the mechanisms are not completely known. The geometry of the glacier, the landform, the consistence of the basal layer, especially the gravel content, and the sediment entrainment are the main components, and these are entered into models, including physical and chemical parameters (isotopes, mineral content, gases, phase changes, flow dynamics).

(2) To compare movements of several recent glaciers and deduce the controlling climatic parameters, and probable climatic change. In the Alps, with its long historic record of the advance and retreat of glaciers, climatic phases have been derived. Dated stadial moraines and fossil trees allow an extension for the whole Holocene, which was for the most part warmer than today. In less investigated high mountains, terminal moraines and rock avalanches are sometimes not easily distinguished. Not all glaciers of a mountain chain behave in the same way, mainly due to the configuration of the snow accumulation area.

(3) To evaluate glacial and fluvioglacial sediments for applied purposes. These are a very rich groundwater reservoir of the temperate zone and are valuable for engineering and building.

6.3. Periglacial Geomorphology

The term “periglacial” was originally used for the area or zone around glaciers or ice sheets. Now it is used primarily for the zone or alpine levels where permafrost is present. Patterned ground in the arctic zone gave an early incentive for periglacial geomorphology and measurements of mass movements by solifluction started rather early. In the periglacial zone, geomorphological processes are very active. Rocks are shattered by freeze and thaw into large and fine, sharp-edged particles. Clay minerals, however, are mainly relics of warm-period weathering. Denudation on slopes occurs in the form of solifluction (gelifluction), when the seasonally thawed active layer glides on top of the permafrost. Large debris cones or terraces develop at the foot of the slopes as accumulation forms. Especially in early spring, wash from snow melt and rain is very strong, as there is almost no percolation into the underground. At the end of the summer, interflow can remove fines. Fluvial erosion may be very strong where incision prevails, as freezing shatters stones and rock surfaces, so that the pickup is easy. In less


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steep terrain, rivers are braided but even so they may erode. Many rivers are able to transport the heavy load coming from the slopes, but accumulations can occur in valleys as well as in wide plain areas. Some rivers shift considerably as permafrost features like ice wedges in the banks thaw, which causes slumps. In the tundra, all these processes are reduced since denudation on slopes is lessened by the vegetation and thus there is less load for the rivers. Special features are: 1) string bogs (Aapamoore), which consist of ridges of peat and depressions, often with ponds; 2) pingos (hydrolaccoliths), which are large (up to 70 m high and 600 m in diameter) circular or oval ice-cored mounds; 3) palsas, which are mounds 1–7 m high, 10–30 m wide, and 15–150 m long, with ice lenses in the peat or soil; 4) rock glaciers, which are tongues of angular blocks with subsurface ice lenses or layers; 5) in the northern hemisphere there are large areas of thermokarst, depressions due to thawing of ground ice. They may be elongated, especially where constant winds force the thawing edge in one direction (oriented lakes). Round depressions evolve when pingos collapse. Alases, a Yakutian term, are up to several kilometers long and wide. They are grass-covered depressions, some containing a lake. Progressive melting of permafrost features, especially ice wedges, is followed by slumping and wash. They are widely distributed in the southern part of the Siberian permafrost. Engineering in the periglacial zone is very difficult since buildings and pipelines must be isolated from the permafrost, which would otherwise start thawing and subside differentially. Wooden houses of the early settlers have either collapsed or been distorted. In summertime, roads are softened, and pavements may have a wooden grating. Tarred streets get frost heaves in spring. Periglacial features are to be found in the temperate zones as paleoforms. Where the relict solifluction cover is still present, the postglacial erosion has been negligible. In contrast to the present arctic zone, wind action was very important in the cold periods, picking up fines from the zone of frost rubble and wide dry river beds and leaving it as a deposit, the loess, in areas that then had tundra or steppe vegetation. Towards the end of the cold periods, dunes were deposited at the upper edges of the outwash plains and on river terraces.

6.4. Tropical Geomorphology

Land forming in the perhumid tropics is the most effective as weathering and planational processes proceed very fast. Planation surfaces with or without inselbergs are distinct features that cannot be explained by “normal erosion.” The plains often cut across rocks of different hardness, which can by understood as intensive weathering producing uniform products. No other explanation has been proposed. Uniform weathering requires rather homogeneous moisture conditions, which pertain only close to base level of erosion, ultimately to sea level. As this has changed in the immediate geological past, recent plains are not very extensive or may even show accumulations. With the incision of rivers, the weathering front becomes irregular due to the differentiation in the movement of the underground water. Protruding rock areals, tors, and shield inselbergs grow relatively and evolve eventually to inselbergs. Pockets of deep weathering may show enrichment in commercial minerals. Once a rock area is


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exposed at the surface, the water runs off very fast and further weathering is negligible, especially in comparison to the surrounding area, which is continually weathered and lowered. This has been called divergent weathering and erosion. Inselbergs occur in special morphological positions, as on top and in front of scarps. For these positions, a differentiation of moisture during development is plausible. Inselbergs may be up to 300–400 m high, like Ayers Rock, and the tepuis of the Gran Sabana are up to 1000 m high. This is a minimum amount for planational lowering. River incision proceeds along prevalent lines, where weathering has been and is more intensive and the rock is disintegrated. The fine material is then washed out instead of breaking loose as in extratropical rivers. Therefore, many river nets show inherited plans (antecedence) or follow tectonic lines. Divergent weathering influences river work as well. If rock is exposed on the sides, the valley slopes become resistant. There are many old gorges in the tropics like Katherine Gorge in Australia’s Northern Territory. Even in the riverbed, rock outcrops may be resistant. Many waterfalls, such as the Angel Falls, are very old. Rapids and waterfalls in the tropics are not generally an indication of recent tectonics. Young tectonic areas are very different from this development on shields. Weathering is intensive and fast, too, but not so uniform. Rivers are incised, mainly in V-shaped valleys. Even steep slopes are covered by vegetation, and still there are many landslides. Close to sea level, where relief energy is not very strong, plains may develop as in shield areas.

6.5. Arid Geomorphology

The study of dunes remains the field of geomorphologists. Spatial distribution, grain size, and heavy minerals of the sands can elucidate origin and motion. Special features of arid geomorphology are paleolakes and paleodrainage, salt weathering, and pediments. Desertification has a geomorphological component, since erosion is accelerated with the devastation of vegetation, and even seeds may be blown away. Many landforms are inherited and are only slightly reworked. At the foot of mountains, extensive plains, called pediments (glacis, pediplain), are developed. As an erosional form, country rock is outcropping, but most are covered with a thick gravel layer, as in wide areas of the Basin and Range Province of the United States.

6.6. Karst

Karst is characterized by solutional forms. Other erosional processes are particularly active when waterways are blocked, for example by frost or by a thick loamy weathering cover. Very often, the water soaks in rapidly and moves fast underground. The danger of pollution is larger than in other landform types. Underground caverns may be connected for over several hundred kilometers. Frequently, karst rivers flow at their bottom, and in the deeper underground they are a possible water resource. Most of these caverns are picturesque due to dripstones. Karren are solution features on limestone surfaces. Exposed ones are bare karst, while those developed under a soil cover are subterranean karst. Karren in the temperate zone range from a centimeter to half a meter, and in the tropics in well-developed grikes, pinnacles or spitzkarren may


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attain several meters. Solutional features in other rocks are often called pseudokarst; they occur mainly in the tropics. Karst forms are especially well developed in pure limestone with low angle bedding. In extratropical zones, this is characterized by depressions (doline, uvala, polje, this last often being a paleoform) comprising 20%–30% of the area. In the warm and humid climates, there are areas where the rises (tower karsts) take up less than 20%, but in the famous tower karst of China they comprise up to 80%. In cockpit country, there is a close spacing of dolines. Mountains may be characterized by a regularity of the river net following tectonic lines, some valleys being exceptionally wide. Here the lower parts of the landscape may occupy only 10% of the area.

6.7. Coasts

There are many classifications for coasts. The most important are rising, stable, or subsiding coasts according to tectonic movements. Prograding coasts are seaward moving due to rising, or to accumulation, like deltas. Retrograding coasts are erosional forms. Rising sea levels (eustasy) drowned many coasts, and estuaries are V-shaped river mouths of varying width. Cliffs are worked by undercutting and slumping, lowland areas may be drowned by extreme floods. Coastal geomorphology includes the shelf and geomorphologists may consider coasts under three headings: 1) accumulation forms, the influence of transport from the land (e.g. deltas), or the reworking of marine sediments (e.g. coastal dunes), or submarine bars; 2) erosion, the reaction of the landform to undercutting by waves and processes controlled by subaerial forces; 3) tectonic and structural outlay.

6.8. Lakes

There are a great many lakes of different sizes in some periglacial regions; these are thaw-out features. Formerly glaciated country has many lakes from overdeepening by glacial erosion, by moraines, or by thaw-out of sediment-buried dead ice (kettle holes). These kinds of lakes occur as relic features in temperate zones or in high mountains. Tectonic depressions are the cause of many lakes in all morphoclimatic zones. The deepest lakes, over 1000 m, are to be found in graben, as in East Africa. Gentle tectonic depressions may have very large lakes, which in the arid zone have had a recent, or more probably an ice-age, change of area of more than double in size, like Lake Chad. Small lakes exist in cut-off meanders; oxbow lakes or, in the arid zone, groundwater pools may occur in dry riverbeds. Caldera lakes lie in volcanoes. Sometimes volcanic flows, landslides, or moraines may dam up a lake, which can be a serious hazard. Some lakes behind depositional coasts have fresh water, but lagoons are still in contact with the sea. There are composite forms (e.g. of tectonic and glacial origin, of periglacial and wind-blown origin). 7. Process Domains 7.1. Introduction


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While morphoclimatic zones and lithological provinces are concerned with integrated research based on analyses, in process fields there are more detailed investigations. Only the main fields of current research are mentioned here.

7.2. Mass Movements

There is a large range of mass movements, including free fall of stones, avalanches, soil creep, mudflows, and large landslides. In all cases, gravity is a major force. Controlling factors are parent material, geometry of slopes, soil moisture, physical properties, and mechanics of movement. Three factors make regions especially prone to landslides: tectonic activity, since earthquakes often trigger landslides, an alternating bedding of clayish and sandy, not well-consolidated sedimentary rocks, and episodic or periodic heavy rainfall. An international group has undertaken an inventory that will allow better conclusions to be drawn about geoecological conditions, volume of erosion, and human-induced processes. Cooperation with soil mechanics engineers and geologists is well developed in the English-speaking world. 7.3. Fluvial Geomorphology A major topic of recent research is erosion rates. Cascading measurement systems give results not only for the amount of erosion but also for sedimentation in the investigated discharge area since the load in a large river is less than the sum of the load in its tributaries. This can be checked by estimating the volume of deposits. Critical approaches to extrapolation and distinction of natural and human-induced erosion may evolve, and become a basis for medium-scale geoecological budgets, together with landform analyses. Values may be compared and thus the vulnerability to erosion of an area may be established, an important tool for land use or reservoir planning. There is a broad range of other topics that partly fall into evolutionary geomorphology such as recent changes of river plan, bank erosion, especially the influence of riparian vegetation, and development of older terraces and valleys. Partly there is an overlapping with engineering sciences, as with the modeling of flow dynamics and transport or the investigation of bedload movement. 7.4. Slope Runoff Processes Slow erosion on slopes is indicated by soil profiles. The processes involved are wash by overland flow, largely acting step by step, creep, rainsplash, rill erosion, and interflow. There are few areas with uniform slopes and a straight profile. Because lithology, climate inclusive aspect, incision, soil, and vegetation are boundary conditions, and because the processes act slowly, evolution and further development are not easy to deduce. Erosion on slopes may produce decreasing gradients, especially if there is accumulation at the foot. In the tropics, slopes may become steeper by extension of the plain at their foot. They quite often have irregular elements, especially if the country rock is exposed in parts. Stability of slopes, mainly against mass movements, is better known than slower evolution. This can be deduced from spatial comparison and from sediments. Little is known, however, about the recurrence interval and whether the next landslide will occur at the same place. Parallel slope retreat or decline associated with W. Penck, L.C. King, or W.M. Davis was a debate on theory, but is no longer a general


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issue. Parallel slope retreat is still suggested for steep slopes, the assumption seeming to be that gravity is the predominant force that keeps the slope angle constant. 7.5. Planational Processes Plains are produced by several processes. Coastal abrasion was the first named. Lateral erosion of rivers or sheet floods was claimed for arid areas and the development of footplains (pediment, glacis, panplain). River terraces may be several kilometers wide and accumulations in basins with an overall flat surface can extend over tens of kilometers. If parallel slope retreat continues for a long time, a plain is left behind. None of these processes can explain an erosional planation surface, be extrapolated in extension, or explain the lowering of divides. An exception might be marine abrasion, but large plains occur in Central Australia, for example, where it is impossible to imagine these processes. Furthermore, inselbergs, often connected with plains, are not accounted for unless they are ascribed to hard rock. A further characteristic of a planation surface is the lack of relief differences due to rock hardness (Rumpffläche). This led Büdel to the model of double planation surfaces: the plain and the weathering front. The weathering is so intensive that a similar or even an equal amount of erosional material evolves, and this is transported by surface wash. Equally important is the subterranean removal of material, either by solution or as fines through macropores. The latter may lead in extreme cases to depressions, even in granite country, that carry lakes or that are filled with pure white sand or quartz split. Plains are very conservative forms and they provoke an areal denudation. This led in many regions of the savannah zone to slightly incised wide valleys, or to dambos. These and similar forms are planational processes following traditional lines. This may be connected with sedimentation in certain localities. 7.6. Wind Action Wind action is relevant in deserts and along sandy coasts. The large dune fields (ergs) are mostly developed in tectonic basins. Loess is the most important wind deposit because of its great fertility, due to good structure and rich mineral content. Indicators for wind erosion are ventifacts; wind-shaped erosional forms are rare. 8. Environment and Global Change 8.1. Paleoclimatic Research There are two types of paleoforms: inherited forms on the surface are the concern of geomorphologists, and geologists investigate the buried ones. Inherited landforms are paleofeatures, which are rarely preserved in their full size, so that they are more or less relics. There may be younger forms incised into them or they may be reworked, mainly from the edges. The oldest ones are of cretaceous age and have survived at the surface, an amazing proof of stability. They are to be distinguished from buried landforms, which may be of any age, and their length and extent of exposure is often uncertain. If they consist of harder rock than the surrounding landscape, they may be called a structural landform.


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The earliest indications of a paleoclimate to be discovered were erratic: huge glacial-transported boulders. The large advances of glaciers and inland ice originated the subdivision of the Pleistocene ice age. In Central Europe, the question as to why there are four main advances from the Alps and only three in the north remains unsolved. Cold and warm periods of the Pleistocene are now mainly distinguished from ocean sediments. For paleoclimatic research in Antarctica, the distinction between ice-rafted sediments and glacial moraine surface deposits in ocean cores is difficult. A further rise of snow lines (e.g. in the Alps) might surpass thresholds, and there is thus no linear relation between glacial retreat and warming. A rise in temperature in Antarctica might even increase the ice volume since the higher absolute humidity brings more snow. An increasing knowledge of paleoweathering and inherited landforms will allow deductions to be made about paleoclimates. There are three fields for geomorphologists in this. 1) The spatial component of analyses allows a distinction between macro- and microclimatic influences. 2) The analyses are often possible where other methods are not applicable. 3) Distinctions need to be drawn between human and natural influences on climatic change. The disadvantage is a relatively low resolution since landform changes often have a long relaxation time. Traditionally, geomorphology has contributed to paleoclimatic research in the following fields: recent, Holocene, and Pleistocene snowlines or moraines, sea level changes, lake levels in the arid zone, paleodunes, paleorunoff, paleoweathering, periglacial indicators, and loess. Paleogeographic investigations (i.e. the position and outline of continents) are studied by geologists and geophysicists. Their results have rarely been considered by geomorphologists in regional studies except in the concept of wide planation surfaces under warm and wet climate in the upper Cretaceous and early Tertiary. The differences between deserts in the western United States, North Africa, and Central Australia might well be due to plate movement causing a different climatic history and tectonics. As paleoforms and paleoweathering occur all over the world, the hypotheses that, given enough time, the same landforms will develop everywhere is wrong. At a high morphological position, there are similar forms and this is due to the relics of the rather uniform Cretaceous/Tertiary landforms caused by similar climate and pre-main drift lack of collision, active continental margins, and other uplifts. The evolution that followed caused the differentiation in morphoclimatic zones, where the humid tropical one resembles the condition of the old-age plains. 8.2. Environmental Change The most important change is due to land use, and the most severe form is accelerated erosion. Soil erosion is in many countries the concern mainly of soil scientists and agriculturalists. Geomorphologists can contribute to basic research in evaluating the spatial distribution of erosional features and analyzing the correlated colluvium. Environmental impact assessment is quite often done by geomorphologists.


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8.3. Anthropogenic Geomorphology With human-made landforms one can distinguish between 1) completely human-made forms such as mining dumps and artificial lakes, and 2) forms where a construction changes the former flow conditions (e.g. a river after correction and bank stabilization often reacts with considerable incision).

8.4. Hazards

Hazards are potential risks for people and for settlements. Geomorphological hazards are 1) an outbreak of a lake ponded by a large landslide or a stadial moraine; 2) a volcanic outbreak and the associated flows; 3) large landslides; and 4) large flooding due to break of an artificial or natural dam (e.g. along the River Po). By careful analysis of former events and geomorphological comparison, a prediction of catastrophic events is possible in some cases. Long-term hazards are flooding due to subsidence (e.g. in delta areas). Thermokarst and desertification are often sparked by human interference.

8.5. Global Change

Most geomorphological processes and landforms have a long relaxation time. Therefore, the effect of global warming might be difficult to detect. In predictions, however, threshold values should be considered. With increased knowledge about Holocene oscillations, better predictions will be possible. Glossary Accumulation: The process of deposition of loose material and resulting mass

and form of large or small volume. Erosion: When rock material is loosened, broken up, or dissolved and

removed. In German, this is only applied to river work. Erosion rates: These are measures for the intensity of geomorphological

processes determined in different ways. Eustasy: Change of sea level. Denudation: Similar to erosion but applied to a larger area like a watershed. Geoecology: Sytems that consider the interrelation of all physical landscape

factors : landforms, country rock, climate, soils, water, vegetation.

Inselberg: An isolated rise of solid rock that may be of a very different size. Landform assemblage:

An arrangement of typical landforms shaped by processes of one morphoclimatic zone.

Morphoclimatic zone:

A zone with similar geomorphological processes controlled by climate.

Paleoforms: Landforms of a former time, mainly from a different climate, later reworked or reduced by nested younger forms.

Periglacial zone: A morphoclimatic zone or area with permafrost. Also used for fossil features of the former, more extensive, zone during the Ice Age.

Planation surface: A neutral term for a flat erosional surface of extending several


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kilometers; peneplain is a planation surface as the final stage of an erosion cycle; pediment is a planation surface evolved by parallel slope retreat; etchplain is a planation surface where intensive weathering precedes wash processes; Rumpffläche is the German term for a planation surface that cuts rocks of varying resistance.

Process: In geomorphology this is mainly applied to the movement of material.

Relief: The difference in height over a certain distance; in German it is a synonym for landforms.

Sediment: Deposited material; used also for transported material in rivers. Wash or sheet wash:

Transport of fine grains by water on larger surfaces.

Weathering: The physical breakup or chemical alterations of rocks or loose materials often assisted by vegetation, especially by organic acids.

Bibliography

Beckinsale R.P. and Chorley R.J. (1991). Historical and regional geomorphology 1890–1950. The History of the Study of Landforms; or, The Development of Geomorphology, Vol. 3 (ed. R.J. Chorley, A.J. Dunn, and R.P. Beckinsale). London: Methuen.

Bremer H. (1989). Allgemeine Geomorphologie. Methodik—Grundvorstellungen—Ausblick auf den Landschaftshaushalt, 450 pp. Berlin: Borntraeger.

Brunsden D. (1990). Tablets of stone: towards the ten commandments of geomorphology. Zeitschrift für Geomorphologie, Suppl.Bd. 79, 2–37.

Büdel J. (1982). Climatic Geomorphology (trans. L. Fischer and D. Busche). Princeton: Princeton University Press. [Originally published as Klima-Geomorphologie. Berlin, 1977.]

Chorley R.J., Schumm S.A., and Sugden, D.E. (1984). Geomorphology, 605 pp. London: Methuen.

Fairbridge R.W., ed. (1968). The Encyclopedia of Geomorphology, 1295 pp. New York: Reinhold.

McCann S.B. and Ford D.C., eds. (1996). Geomorphology Sans Frontières, 245 pp. Chichester: Wiley.

Slaymaker O., ed. (1991). Field Experiments and Measurement Programs in Geomorphology, 224 pp. Rotterdam: Balkema.

Walker H.J. and Grabau W.E., eds. (1993). The Evolution of Geomorphology: A Nation-by-Nation Summary of Development, 539 pp. Chichester: Wiley.

Yatsu E. (1988). The Nature of Weathering: An Introduction, 624 pp. Tokyo: Sozosha. Biographical Sketch Hanna Bremer was born in Bremerhaven, Germany, on July 15, 1928. She undertook university studies in geography, geology, and physics at Universität Göttingen. Her dissertation Flusserosion an der oberen Weser was presented for her Dr. rer. nat Göttingen. In 1958 she was an assistant at Geographisches Institut der Universität, and this was followed by nine months fieldwork in Central and North Australia, then appointment as a research scholar at Deutsche Forschungsgemeinschaft, and assistant and lecturer at Geographisches Institut der Universität, Heidelberg (1963–1972). She carried out eight months of fieldwork in Nigeria, Amazonia, habilitation. 1966 Zur Geomorphologie von Zentralaustralien. 1972


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Ordentlicher Professor und Direktor Geographisches Institut der Universität zu Köln; 1993 Emerita. Between 1973 and 1992 Dr. Bremer carried out 20 months of fieldwork in Amazonia, Mali, Kenya, India, Sri Lanka, and Australia. Editor: Zeitschrift für Geomorphologie. In 1993 she became an Honorary Fellow of the International Association of Geomorphologists; in 1994 an Honorary Corresponding Member of the Royal Geographical Society, London; in 1996 she was awarded the Gold Medal, City of Veszprém, Hungary; and in 2000 Ehrenmitglied der Ungarischen Geographischen Gesellschaft. Her monographies include Flüsse, Flächen- und Stufenbildung in den feuchten Tropen (1971), Reliefformen und reliefbildende Prozesse in Sri Lanka (1981), Allgemeine Geomorphologie (1989), Boden und Relief in den Tropen (1995), and Die Tropen (1999), and she has authored 66 contributions to scientific journals. To cite this chapter Hanna Bremer, (2003), GEOMORPHOLOGY, in geography, [Ed. Maria Sala], in Encyclopedia of Life Support Systems (EOLSS), Developed under the Auspices of the UNESCO, Eolss Publishers, Oxford ,UK, [http://www.eolss.net]


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Geomorphology - EOLSS Chapters/C01/E6-14-02-01.pdf · Geomorphology, the study of landforms, is an integrative science since it includes soils, country rock, climate, water, and vegetation