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An example is The Great Wall of China

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An example is Island and Mountain.

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THE DIFFERENCES AND SIMILIARITIES OF NATURAL AND CULTURAL LANDSCAPE

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THE DIFFERENCES AND SIMILIARITIES OF NATURAL AND CULTURAL LANDSCAPE

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World's Largest Collection of Essays! Published by Experts

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A natural landscape is one that is a result of the changes that have taken place naturally in the earth's crust. Such changes sculpted and designed the landscape into mountains and valleys, and effect of weather over centuries further brought about gradual changes in a way that did not disturb the delicate ecological balance.

Today, however all natural habitats are altered by man. Therefore, the delicate balance in the ecosystems like forests, valleys and sea coasts is not maintained. We will now study the way in which mankind has changed the physical appearance of the environment.
Natural landscapes of India:
India is bestowed with a variety of landscapes such as mountains, hills, rivers, vast agricultural stretches, coastal areas, hot and cold deserts, humid belts, mangroves, grazing lands, alpine pastures, etc. This variety not only adds to the biological diversity of landscapes, it also provides a means of livelihood for the people of India.

India's landscape comprises the forests, grasslands and semi-arid ecosystems. These include ecosystems like the hills with their cold deserts and alpine pastures, the hot deserts of Rajasthan, the mangroves of the coastal region, and the wet tropical and wet temperate forests of Eastern India and East Himalayas. The presence of both the cold deserts in Ladakh and hot deserts in Rajasthan is unique to the country.

Man-made landscape or built environment:

These include human activities, like construction of buildings, flyovers, dams and reservoirs. Landscapes, like mountain farming systems and national parks, new townships, deforestation and mining are some examples of man-made landscapes.

Man has altered the environment for his own interest to meet the demands of growing population. He has indiscriminately cleared forests or converted arable land into new townships, built roads, bridges and set up industries.

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Difference between Natural Landscape and Man-Made Landscape

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Natural landscape: A natural landscape is one that is a result of the changes that have taken place naturally in the earth's crust. Such changes sculpted and designed the landscape into mountains and valleys, and effect of weather over centuries further brought about gradual changes in a way that did not disturb the delicate ecological [...]

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Watch the video below for better understanding the concept about landscape archaeology. Happy viewing!!!

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Landscape Archaeology and Routes to the Past

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Read and comprehend the article. Enjoy!!!

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the branch of physical geography that deals with natural territorial complexes (or geographic complexes, geosystems) as structural parts of the earth's geographic mantle. Landscape science was founded in Russia at the beginning of the 20th century by L. S. Berg, G. N. Vysotskii, G. F. Morozov, and other followers of V. V. Dokuchaev. The founder of the science abroad was the German geographer S. Passarge.

The basis of landscape science is the theory that the geographic landscape is the primary element in the physicogeo-graphical differentiation of the earth. Landscape science deals with the origin, structure, and dynamics of landscapes, the laws of the development and arrangement of landscapes, and the transformation of landscapes by the economic activity of man. One of its tasks is to study the parts of the landscape (the lowest-level geosystems-localities, natural boundaries, and facies), their relative arrangement and interactions, the types of spatial structures formed by landscapes, and the transformations of landscapes with the passage of time (landscape morphology). Landscape science also includes the study of zones, sectors, regions, provinces, and other higher-ranking regional geosystems, insofar as these represent regular groupings of landscapes. In the higher-level territorial units landscapes are interconnected by atmospheric circulation, runoff, the migration of plants and animals, and other factors. Elucidation of the general laws of the territorial differentiation of the geographic mantle-an area of research in which both landscape science and geography are engaged-serves as a basis for discovering the origin of the higher-ranking landscapes and geosystems and, at the same time, as a theoretical foundation for physicogeographical regionaliza-tion.

Elementary geographic complexes are studied as parts of related, regularly structured territorial systems (landscapes). Such complexes develop because of processes of limited spheres of action that are typical either of individual landscapes or of groups of landscapes and that follow from the internal development of the latter (for example, the action of flowing water and the formation of morphosculptural elements of the relief; the competitive relationships between plant communities and their interaction with the environment). The regional differentiation of higher-ranking geosystems is subject to the uneven distribution of energy entering the geographic mantle. Landscape belts, zones, and subzones develop as a consequence of the latitudinal distribution of solar energy. The principal consequence of the complex manifestations of the earth's internal energy is the azonal contrast between the land and the world ocean. The resultant continental-oceanic circulation of air masses brings about the formation of maritime, continental, and transitional physico-geographical sectors on the continents. The development of physicogeographical lands, regions, and districts (and, in the mountains, high-altitude stages and belts) is related to the variety of the morphostructures of the earth's crust.

Field investigations by expeditions and research stations are the main source of factual material for landscape science. Expeditions usually map landscapes and make it possible to establish the boundaries of natural territorial complexes and to describe their basic and most stable features. Aerial photography is very helpful in mapping landscapes, and the possibility of using photographs taken from space is being considered. Studying the dynamics of geosystems requires the organization of long-term observations, including the investigation of the thermal balance, the moisture balance, the migration of chemical elements, and biological productivity.

Landscape geochemistry, which elaborates the principles of landscape physics (geophysics), is a special branch of geography that developed at the point where landscape science converges on related sciences. In its investigation of facies as the landscape's energy cells and as the initial link in the chain of geographic interdependence, landscape science overlaps with biogeocenology. Long-term studies of the seasonal dynamics of the landscape are a prerequisite for the development of landscape phenology.

The systematization of observations and the establishment of empirical relationships in landscape science are based primarily on the comparative methods of geography, in which cartographic analysis and the historical method are very important. The first attempts to use mathematical statistics and mathematical logic to study and classify the interrelationships among the components of geosystems were made in the 1960's. Attempts have been made to define landscapes as self-regulating systems, in order to make possible the application of a structural systems approach to landscape study. There have been quite a few attempts to construct graphic models of geosystems. The next problem will be to create mathematical models to express the principal interrelationships between the various landscape components and between the lower-order geosystems.

Landscape science has always been basically an applied science. As it developed, its practical applications became considerably broader. Several special fields have developed in contemporary applied landscape science: agricultural production, engineering, land reclamation, health use, architectural planning, and recreation. Research in applied landscape science deals with the specialized classification of natural territorial complexes, the evaluation of natural territorial complexes from the point of view of the suitability and advisability of practical utilization, the development of recommendations for the transformation and protection of the complexes, and the forecasting of changes. The principal materials offered by landscape scientists for use in the various sectors of the national economy are applied maps, landscape maps, and charts of regionalization with corresponding texts. The most important practical tasks of landscape science are the development of scientific principles for managing geosystems and the creation of cultivated landscapes. These tasks can only be fulfilled on the basis of a theory of the development of geosystems and their interaction with man's economic activity. Such a theory will make it possible to forecast the behavior of geosystems caused by natural and anthropogenic factors.

In terms of its methodological importance, landscape science in the USSR occupies a central position among the geographic sciences. Research in landscape science is being conducted in the German Democratic Republic, Poland, Rumania, Czechoslovakia, Hungary, and the Federal Republic of Germany. Landscape science has not developed as a theoretical discipline in the USA, Great Britain, and many other capitalist countries, but particular applied studies (primarily land classification) are similar to landscape surveying. Landscape science has a number of points in common with ecosystems theory.

REFERENCES

Isachenko, A. G. Osnovy landshaftovedeniia i fizikogeograficheskoe raionirovanie. Moscow, 1965.
Landshaftnyi sbornik. Moscow, 1970.
Landshaftovedenie. Moscow, 1963.
Metodika landshaftnykh issledovanii. Leningrad, 1971.
Metody landshaftnykh issledovanii. Moscow, 1969.
Mil'kov, F. N. Osnovnye problemy fizicheskoi geografii. Moscow, 1967.
Preobrazhenskii, V. S. Landshaftnye issledovaniia. Moscow, 1966.
Topologiia stepnykh geosistem. Leningrad, 1970.
Landshaftovedenie. Moscow, 1972.
Neef, E. Die theoretischen Grundlagen der Landschaftslehre. Gotha, 1967.
Troll, C. "Die geographische Landschaft und ihre Erforschung." Studium generale, 1950, vol. 3, fascs. 4-5.

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the branch of physical geography that deals with natural territorial complexes (or geographic complexes, geosystems) as structural parts of the earth's geographic mantle. Landscape science was founded in Russia at the beginning of the 20th century by L. S. Berg, G. N. Vysotskii, G. F. Morozov, and other followers of V.

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CHECK YOUR UNDERSTANDING BY ANSWERING THE GIVEN LINK BELOW!!!

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CHECK YOUR UNDERSTANDING BY ANSWERING THE GIVEN LINK BELOW!!!

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CULTURAL LANDSCAPE are landscapes that have been affected, influenced, or shaped by human involvement.

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Read an overview about landscape evolution. Have fun!!!

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6.13.5.1 Erosion and Isostasy

The isostatic response to erosional unloading represents the simplest form of erosion-tectonic feedback. It is a feedback with some fascinating consequences for landscape evolution. When erosional loading is focused in a particular area, such as a large river or glacier valley, the surrounding region will rise isostatically. Molnar and England (1990) hypothesized that this phenomenon could lead to the uplift of mountain peaks when the valleys between them are deeply eroded. Because valley deepening is one potential outcome of climate change, there exists a potential mechanism for climatically driven surface uplift of summits. The actual magnitude and occurrence of this effect are matters of debate (Brocklehurst and Whipple, 2002; Gilchrist et al., 1994a; Lane et al., 2008; Menéndez et al., 2008; Montgomery, 1994; Montgomery and Greenberg, 2000; Pelletier, 2004; Small and Anderson, 1995; Stern et al., 2005; Whipple et al., 1999), but there is little doubt that the incision of a major valley can lead to some degree of isostatic surface uplift of the surrounding terrain.

Rifted continental margins present a fascinating case study in erosion-isostasy feedback. Relatively young rifts, such as the Eastern Africa and Red Sea extensional regions, have asymmetrical rift shoulders that presumably reflect thermal isostatic uplift. Many older passive margins show a similar geometry, with a seaward-facing escarpment(s) and an inland plateau that slopes gently toward the interior (Ollier, 1985; Weissel and Karner, 1989). Thermochronology data from passive margins such as Southern Africa (Brown et al., 1990, 2002), southeastern Brazil (Gallagher et al., 1994, 1995), eastern Australia (Moore et al., 1986), Western India (Widdowson, 1997), and the Red Sea (Abbate et al., 2002; Bohannon et al., 1989) show a postrift phase of substantial erosion on the seaward side of the escarpment (Gallgher and Brown, 1997). This observation supports the hypothesis that upwarps and escarpments along ancient rifted margins arise from an erosion-isostasy feedback: erosion focused along the rift leads to isostatic uplift that is focused along the margin, such that the area inland of an escarpment is tilted toward the interior (Gilchrist and Summerfield, 1990; Ollier, 1985; Partridge and Maud, 1987; Stüwe, 1991; ten Brink and Stern, 1992; van der Beek et al., 1995). This tilting inhibits drainage capture from the interior and can therefore help sustain a drainage divide that parallels the margin (Gilchrist et al., 1994b; Kooi and Beaumont, 1994; Sacek et al., 2012; Tucker and Slingerland, 1994; van der Beek et al., 2002). It is widely assumed that margin-parallel drainage divides originate during the rift phase, though Sacek et al. (2012) proposed that passive-margin escarpments and drainage divides may actually be the legacy of an interior flexural bulge, rather than the initial rift shoulder itself.

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3.1.4.5 Erosion Modeling

Landscape evolution theories indicate that the topography inherently records the interaction between climatic, tectonic, and surface processes. Consequently, geological and topographic information can be used to assess erosion and topographic evolution. Rather than focusing on empirical relationships, landscape-evolution modeling attempts to formalize the understanding of process mechanics and systems coupling.

Clearly, a better understanding of process-form relationships is needed for developing improved erosion models. Depending on the climatic and tectonic setting, variations in weathering, fluvial, mass movement, and glacial processes make it difficult to accurately assess the magnitude and spatial distribution of erosion and denudation.

Erosion modeling facilitates the understanding of such complications, as models account for the conservation of mass and energy, and are based on a series of mass continuity equations to address the erosion and deposition of rock and sediment. Continuity assumes that the rate of change of altitude is proportional to the volumetric sediment flux.

Uplift should account for isostatic and tectonic forcing components. Tectonic forcing includes the advection of rock mass, given structural controls, and the alteration of rock strength, given topographic stress fields and far-field velocities. The tectonics component requires the integration of mechanical models, as feedbacks exist between the topographic stress field, rock strength, and erosion and uplift (Koons, 1995; Koons et al., 2002). The magnitude of denudation also influences the isostatic compensation, which is a function of the flexural rigidity of the crust and the wavelength of the topography (Gilchrist et al., 1994).

Most models use a flexible parameterization scheme that accounts for the depth of regolith production from weathering (Tucker and Hancock, 2010). Parameterization schemes should account for variations in lithology, precipitation, and surface temperature and moisture conditions. Remote sensing and terrain analysis of surface and atmospheric conditions can be used to generate maps that may be associated with weathering patterns. Key variables include surface irradiance, temperature variation, atmospheric water vapor content, and precipitation patterns. In mountain environments, temperature and precipitation variations may be considerable, given highly variable topography and forcing factors (Barros et al., 2006).

Hillslope sediment flux can be accounted for using a linear or a nonlinear relation with the hillslope gradient. Diffusivity coefficients are commonly used, with different values for different environments.

Bedrock river incision is important in many regions and investigators have utilized the stream-power bedrock river incision law to account for fluvial erosion. In general, the change in elevation is modeled as:

where K is bedrock erodability and A is the upstream catchment area that is used as a proxy for discharge. The exponents m and n are constants used to differentiate between the stream power and shear stress-based rules.

Simulations of glacier erosion have also been conducted where erosion is based on basal-sliding velocity and ice thickness (MacGregor et al., 2000; Tomkin and Braun, 2002; Pelletier et al., 2010). An abrasion model (Hallet, 1979) can be used such that the rate of erosion is

where u s is the basal sliding speed, and a and b are empirical coefficients usually set to 1 or 2. Basal sliding is primarily dependent on the basal shear stress, τ b, and a bed-friction parameter. Simulations of glacier erosion demonstrate the complexity associated with relating process to form as glacier erosion can enhance or reduce relief and controls valley spacing and slope variability (Harbor, 1992; Bishop et al., 2003; Tomkin and Braun, 2002; Pelletier et al., 2010).

Although such landscape-evolution modeling could be implemented in a GIS (numerous issues do exist), most models for orogen evolution simulations exist outside of GIS environments. Common GIS-based erosion models focus on soil erosion modeling, given relatively mild to moderate topographic conditions. Soil erosion and sediment transport studies are important in agriculture, water quality, and sediment budget modeling, and in determining the magnitude of anthropogenic forcing. Geospatial technologies are ideally suited for soil erosion modeling and numerous models exist that use different sediment transport equations. Mitasova and others in Chapter 3.9 describe different types of erosion models and provide a physical and mathematical foundation for understanding their ability to predict the magnitude and spatial distribution of soil erosion over the landscape. Special emphasis is on using existing GIS-based erosion models and the visualization of erosion patterns.

Ultimately, remote sensing and GIS can provide new information that can be used to develop more rigorous parameterization schemes for erosion modeling. Geomorphometric characterization is required at each time interval to drive process mechanics and process domain states, such that modeling allows parameters, processes, and system characteristics to be mapped. Further advances in GIS space-time representations and formal process-form linkages are urgently needed to facilitate improved GIS-based erosion modeling.

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13.10.5.2 Landscape, Surface Processes, and Hazards

Landscape evolution, geomorphic processes, and natural hazards as related to glacier changes are closely interconnected. A prominent phenomenon is the formation and growth of new lakes, commonly located at the terminus of the glacier or behind terminal moraines ( Figure 22). The phenomenon as such is not new, and hazards due to formation of glacier lakes have been recognized for quite a while (Evans and Clague, 1994). In fact, severe disasters were caused in the past by outbursts from glacial lakes in various high-mountain regions of the world, including the Andes (Reynolds, 1992; Carey, 2005; Hegglin and Huggel, 2008), Caucasus and Central Asia (Narama et al., 2006; Aizen et al., 2007), the Himalayas (Vuichard and Zimmermann, 1987; Richardson and Reynolds, 2000; Xin et al., 2008), North America (Clague and Evans, 2000; Kershaw et al., 2005), and the European Alps (Haeberli, 1983; Haeberli et al., 2001; Kääb et al., 2004). Glacial lakes can be classified into several types according to their position relative to the glacier and the damming mechanism (Richardson and Reynolds, 2000; Clague and Evans, 2000). The different lake types are more or less frequent in different regions of the world, depending on climatic, glaciological, topographic, geological, and other factors. In recent years, increasingly fast formation of lakes has been observed in several high-mountain regions. Rapid lake growth processes are due to positive feedback effects with the thermal energy of water enhancing the melting of ice (Kääb and Haeberli, 2001). In the European Alps, for instance, a number of rapid lake formations have been observed in recent years, including Belvedere Glacier (Macugnaga, Italy; Tamburini et al., 2003; Kääb et al., 2004), Trift, and Lower Grindelwald Glacier ( see Chapter 13.17; Huggel et al., 2010; Werder et al., 2010). At Grindelwald, future scenarios suggest a continuing rapid glacier retreat with the potential of a significant enlargement of the lake. In late 2008, authorities therefore started to drill a more than 2-km-long tunnel that should enable an artificial drainage of the lake and prevent a serious lake outburst with expected damages between Grindelwald and Interlaken, ∼2.5-20 km downstream. The tunnel started functioning in spring, 2010. From case studies like Grindelwald and previous ones, it has become clear that the increasing destabilization of slopes due to glacier retreat and also permafrost degradation leads to complex hazard situations with respect to high-mountain lakes, which necessarily call for an integrative assessment.

A concentration of pronounced slope stability effects related to glacier downwasting and debutressing of rock and moraine slopes, permafrost degradation, rock fall, and debris flow activity, all interacting with the formation and growth of glacier lakes and further glacier decay, characterize the environment around the newly formed lake at the surface of the tongue of Lower Grindelwald Glacier (Figure 23). This could be a model case for increasingly destabilized future high-mountain environments. Debuttressing effects of rock slopes due to glacier downwasting may result in large rock avalanches, large-scale, progressive, and slow rock mass deformation, and frequent rock fall events (Ballantyne, 2002). The three modes of response are all consequences of stress redistribution and release and may act in a combined way. Rock slope failure is thereby commonly a result of slope steepening by glacial erosion and unloading or debuttressing due to glacier retreat (Augustinus, 1995). Many ice-related rock avalanches were recently documented around the world (Huggel, 2009). Examples are the Brenva and Triolet rock avalanches in the Mont Blanc massif in the eighteenth and twentieth centuries (Deline, 2009), the Kolka-Karmadon ice/rock-avalanche in the Caucasus (Evans et al., 2009), the Sherman glacier rock avalanche in 1964 in Alaska (Shreve, 1966), a significant number of rock avalanches in the Karakorum (Hewitt, 1988, 1999, 2009), and in British Columbia, Canada (Geertsema et al., 2006), just to name a few. Such rock slope failures can occur in permafrost-free conditions or the destabilization processes can additionally be affected by permafrost degradation (Fischer et al., 2006). Furthermore, they act separately or in relation with glacier lakes (cf. Grindelwald), thus seriously enhancing the hazard potential due to impact waves resulting in lake outburst floods. Continued atmospheric temperature rise could imply enhanced meltwater percolation into cold firn with a widespread transformation of cold to polythermal or temperate ice on steep slopes and thus alter the potential source zones for ice avalanches ( see Chapter 13.17; Huggel et al., 2010), because cold ice masses are stable at steeper slopes than temperate ice (Haeberli et al., 1989; Huggel et al., 2004).

The retreat of glaciers implies an increasing sediment availability, which can enhance overall erosion rates by up to an order of magnitude (Hinderer, 2001) and the potential for mass movement hazards. Since the end of the Little Ice Age, new proglacial areas with marked moraines and large amounts of poorly consolidated sediments have been uncovered, which are now prone to slope failure and large debris flows. In the Alps, some of the largest debris flows that occurred in recent years originated from such formerly glacierized areas ( see Chapter 13.17; Huggel et al., 2010; Zimmermann and Haeberli, 1992; Chiarle et al., 2007). At the same time, the unraveled sediment is likely to have serious implications for the management of alpine reservoir lakes connected to hydropower schemes (Boillat et al., 2003). More rapid filling of lakes by sediment and especially enhanced input of sediment into turbines leads to extremely costly maintenance, which additionally affect the operation schedule of the power schemes. Potential countermeasures against Alpine reservoir sedimentation by modification and/or stopping of turbidity currents have been analyzed recently (Oehy and Schleiss, 2007). The methods developed to detect the future location and approximate timing of formation of glacier lakes (Frey et al., 2010) can help in anticipating the multiple effects of natural hazards, sediment budgets, and water reservoirs in relation with hydropower or tourism activities.

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6.7 Conclusion

The past few decades of martian exploration have shown the wonderfully and unexpectedly dynamic nature of Mars, especially at the poles. For example, extensive landscape changes related to the deposition and condensation of CO ₂ occur even today in both polar regions.

The observed landscape evolution highlights the importance of condensable species such as CO ₂ and H ₂O in affecting the martian surface. In this chapter only observed changes linked to CO ₂ have been considered. Being the main atmospheric constituent, CO ₂ influences the martian surface indirectly when changes in climate patterns happen. For example, changes of CO ₂ pressure on Mars are always equal to general atmospheric pressure changes. These directly influence global wind regimes that, in turn, shift dunes, erode crater rims, and carve sandstone. Variation of the surface pressure may accelerate and decelerate erosion or induce climate change leading to an atmosphere tolerant of stable liquid water. The attentive reader will have noticed that the geomorphological features discussed earlier are, in many aspects, puzzling. Many questions remain outstanding, for now:

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What is the age of araneiforms? Were they created under the current climate or are they remnants from previous climate epochs? Is the recycling of atmospheric dust their sole purpose?

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What is the governing property or condition behind the spatial association of the araneiforms and the SPLD? Why does the shape of the araneiforms vary depending on their location?

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Do the CO ₂ jet eruptions and particularly the amounts of dust lifted by them into the lower atmosphere influence the local weather?

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Is there interannual variability in polar activity and is it connected to the global climate cycles? Do global dust storms augment or reduce the seasonal polar activity?

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Are the processes and constraints responsible for the origin and development of polar gullies as variable as the location of the gullies? What is the dominant mechanism or mechanisms responsible for polar dune alcove creation?

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Is there a climate shift that currently reduces CO ₂ from the residual SPC via the observed "Swiss cheese" ablation? Does this CO ₂ accumulate at other location(s)?

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What is the nature and rate of martian residual polar cap flow? Does the rate of viscous relaxation efficiently compensate for the avalanche erosion of the NPLD?

Both martian poles show geological complexity and enigmatic development far beyond one's expectations, certainly making them worthy of further monitoring and investigation. High-resolution imagery and hyperspectral data collected over long time periods will continue to inform us about active martian processes that are, at times, completely exotic to terrestrial geology.

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7.21.4 Changing Slope Angles in Landscape Evolution Models

Several efforts are ongoing in landscape evolution modeling that are trying to include one or several of the processes causing changes in slope angle described above and combine these with landslide modeling. Champel et al. (2002), for example, used a numerical model combining uplift, hillslope diffusion, and landsliding to show the dynamics of fault-related fold propagation in western Nepal. Coulthard et al. (2000) applied a cellular model with approximations for mass movement, creep, vegetation, hydrology, erosion, and deposition to an upland catchment in the UK to disentangle the effects of land use and climate change on channel formation. Dadson and Church (2005) studied the evolution of an idealized glaciated valley during the period following retreat of ice using a numerical model (including landsliding and fluvial sediment transport) with a numerical landscape evolution model that combines a detailed tectonic displacement field with a set of physically based geomorphic rules (including bedrock landsliding). Densmore et al. (1998) generated synthetic landscapes that closely resembled mountainous topography observed in the western US Basin and Range geomorphic province. Van Der Beek and Braun (1999) employed a numerical surface process model that included long-range fluvial transport, hillslope diffusion, and landsliding in order to quantitatively assess the tectonic, lithological, and structural controls on the landscape evolution and denudation history of the southeastern Australian highlands. Their results indicated that the observed highland morphology requires that the drainage divide be established at its present location prior to opening of the Tasman Sea; that escarpment retreat does not appear to be the fundamental process eroding the highlands; and that the observed barbed river drainage may be imprinted as a result of lithological variation. The LAPSUS modeling framework (Schoorl et al., 2002; Claessens et al., 2007) hosts separate modules for simulating overland flow, creep, solifluction, tillage erosion, and landsliding, all of which have process-based algorithms that make changes in slope angles over time. The combination of several processes in a general landscape evolution model, taking into account interactions and feedback mechanisms, is currently under progress.

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2.13.3.2 Landscape Evolution Models

At their core, modern landscape evolution models calculate the (possibly combined) effects of geomorphic and tectonic processes on the landscape, driven by topography, lithology, and climate. In mathematical terms, they are sets of equations operating on a digital representation of a landscape. The model setup scheme in Figure 1 (adapted from Beven, 2001) helps to structure a short introduction to such models and related concepts and definitions.

In the scheme, the setup of landscape evolution model studies proceeds from choosing the objectives through making perceptual, conceptual, and procedural models to model calibration and model validation. For now, we focus on the first four steps - where the model is built - rather than on the last two steps - where the model is used.

The choice of objectives determines the spatial and temporal extents of a quantitative landscape evolution modeling study. It also determines the type of output that is required: a digital representation of a landscape or alternatively a landscape metric, such as mean elevation or drainage network configuration (e.g., Rinaldo et al., 1993). Models that simulate landscape metrics are sometimes called surrogate models (Pazzaglia, 2003) to distinguish them from more traditional landscape evolution models. The objectives of a study also determine whether it is procedural, descriptive, postdictive, or predictive.

In the perceptual model phase, choices are made about the processes included in the model. For our purposes here, two choices are particularly important because they strongly impact on model structure.

First, whether to use multiple processes or one process only? When it is decided that multiple processes are relevant for a study, decisions regarding their interaction must be made during the next steps in model setup that are otherwise not necessary. Such decisions include the use of homogeneous or heterogeneous spatial and temporal resolution for the processes (Temme et al., 2011).

Second, and more specifically, is whether or not to include tectonics. At timescales shorter than hundreds of thousands of years, tectonics are not usually included in landscape evolution models. Therefore, these models are sometimes called surface process models (e.g., Codilean et al., 2006).

In the conceptual model phase, decisions are made about the equations that describe each process in the model. Typically, choices are placed along an imaginary axis ranging from fully mechanistic (Newtonian) approaches to fully descriptive (regression-based) approaches (like the Universal Soil Loss Equation-type hillslope erosion models (Renard et al., 1991; Wishmeier and Smith, 1978). Mechanistic models need limited calibration at the expense of strong computing and data demands. As a result, (nearly) mechanistic models are used only at short timescales and for small study areas - for instance, to study evolution of reaches of large-boulder rivers (Hodge et al., 2007). Because of their lack of use in whole-landscape studies, we disregard them in this chapter.

Descriptive models offer ease of use at larger temporal and spatial extents at the expense of larger calibration needs. All landscape evolution models are descriptive to some extent, most of them strongly so (Brasington and Richards, 2007). Common simplifications of the mechanistic St. Venant equations in the modeling of running water are first the assumptions that flow has steady speed within a time step (quasi-steady state, the gradually varied flow approximation), then that inertia of water is negligible (the diffusion-wave approximation), and, finally, that water pressure effects on water flow are negligible (the popular kinematic-wave approximation), where flow is determined by topography only (Tucker and Hancock, 2010; Van De Wiel et al., 2011).

Note that descriptive models are not the same as descriptive studies. The former designation gives information about the type of formulas used in models; the latter designation gives information about the use of models in a particular study. Mechanistic models can be used in descriptive studies and descriptive models can be used in nondescriptive studies (in fact, many studies in this chapter use descriptive models for procedural and postdictive studies).

In the procedural model phase, decisions are made about the translation of equations into computer code. This is no trivial step, at least because decisions include a choice for the discretization of the landscape. The two most popular discretizations are the digital elevation model (DEM) and the triangulated irregular network (TIN). In DEMs, the landscape is represented as a regular grid of square cells with uniform altitude. In TINs, the landscape is built up of Delaunay triangles. This choice is generally followed by the choice for an algorithm for the flow of water over the surface, based on the kinematic-wave approximation - if the geomorphic processes under consideration are dependent on the amount of water. Many water flow algorithms are available, most of them reviewed and tested in Freeman (1991) and Murray and Paola (1997). In the resulting calculation framework, equations are translated into computer code (Pelletier, 2008).

From the setup scheme, it can be argued that every new landscape evolution modeling study (with new objectives) should lead to a new model formulation. However, existing models (and their set of underlying perceptual, conceptual, and procedural choices) are often reused in later research with minor or no changes. This reuse is defensible as long as the assumptions underlying the initial model are not violated, but making that assessment requires a more intimate knowledge of the model than is usually possible from studying the interface and the documentation alone. This leads to frequent doubts about model validity.

Models or model frameworks that allow individual users to choose among a range of perceptual, conceptual, and procedural choices minimize this problem. Some of such choices have been included in the interfaces of modern landscape evolution models (e.g., LAndscape ProcesS modelling at mUlti dimensions and scaleS (LAPSUS), Figure 2 and CAESAR) - although especially procedural choices remain unavailable to the model user. Recent projects, such as the Community Surface Dynamics Modeling System (CSDMS; Voinov et al., 2010), which offer advanced facilities to combine and adapt models, are instrumental in opening up the range of model setup options to the inexperienced modeler.

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7.10.1 Introduction

The recognition and characterization of landscape evolution processes are both timely and important. Careful conceptualization of surface/near-surface hydrologic processes is necessary to capture the variability in spatiotemporal geomorphic response. The idea that landscape evolution is governed in large part by hydrologic response is not new. One only needs to peruse the water theory espoused by Leonardo Da Vinci, carefully revealed in the stunningly good book by Pfizer et al. (2009), to concede a deep foundation for hydrogeomorphology. Process-based conceptualization has been well discussed in geomorphology (e.g., Gilbert, 1880; Lobeck, 1939; Horton, 1945; Langbein and Schumm, 1958; Leopold et al., 1964; Carson and Kirkby, 1972; Dunne, 1980; Dietrich et al., 1982; Dietrich and Dunne, 1993; Montgomery and Dietrich, 1988; Rodriguez-Iturbe and Rinaldo, 1997; Wilcock and Iverson, 2003; Dietrich and Perron, 2006; Pelletier, 2008; Anderson and Anderson, 2010).

Many methods are available for conceptualizing hydrologically driven landscape evolution, ranging from simple schematic illustrations, sparse to detailed measurement campaigns, physical models, analog models, empirical models, analytical solutions (employed as operating algorithms) for relatively simple partial-differential equations, through comprehensive nonlinear first-order-coupled partial-differential equations solved numerically. The hillslope, channel, and flume studies by Tom Dunne (e.g., Dunne and Black, 1970a, b), Bill Dietrich (e.g., Dietrich et al., 1979; Dietrich and Smith, 1983, 1984), and Dick Iverson (e.g., Iverson et al., 1992; Iverson, 1997; Logan and Iverson, 2007), respectively, are examples of stellar efforts designed to understand how systems work by way of detailed measurement and observation. The slope stability studies of Al Freeze (e.g., Hodge and Freeze, 1977; Rulon and Freeze, 1985), Dick Iverson (e.g., Denlinger and Iverson, 2001; Iverson and Denlinger, 2001), and Bill Dietrich (e.g., Dietrich et al., 1992, 1993) are examples of modeling efforts designed to capture (via simulation) landscape dynamics at a variety of spatial scales. Most conceptual models begin with a mental image of important processes and their spatiotemporal interaction. An example is the conceptualization of the ecological staircase and pygmy forest development in northern California put forth by Jenny (1980). The first author saw this model in its simplest form, as a flowchart hand drawn on a single sheet of paper. This seemingly basic diagram provided an elegant tool for understanding and communicating the components and nuances of a complicated system.

In the broadest sense, conceptualization has utility for interpreting existing data, guiding future field-data collection efforts and investigations, and developing models that simulate the system within and beyond the observed excitation states. In general, two approaches are used for conceptualization in hydrology/geomorphology: downward (i.e., top-down, systems, holistic) and upward (i.e., bottom-up, reductionist, mechanistic, physics-based). Interdisciplinary earth science research increasingly employs consideration for nontrivial hydrologic driving forces using both the downward (i.e., Beven, 2001; McDonnell, 2003; Sivapalan, 2003; Sivapalan et al., 2003) and upward approaches (i.e., Loague and VanderKwaak, 2004; Ebel and Loague, 2006, 2008; Loague et al., 2006, 2010). Tension between the proponents of the downward and upward approaches as employed in hydrology is unnecessary as both have utility depending upon the problem at hand and the scale of interest. It is worth noting that the approach focused upon in this article is an upward protocol, driven by a hydrologic model that purports to represent the state of the art in physics-based simulation, for identifying data and/or conceptual gaps that may reveal nuances in our understanding of the processes associated with hydrologically driven landscape evolution.

Computer-based simulation with mathematical models has considerable utility for developing and refining concepts in hydrogeomorphology (Paola et al., 2006), hydropedology (Lin et al., 2006), and hydroecology (Newman et al., 2006). The reason for the expanding simulation culture is straightforward: measuring everything is not possible without digging everything up (which in and of itself is problematic) and waiting, at the human (let alone geologic) timescale, to see what will happen versus estimating what could happen is too limiting. Of course not everyone is enamored with computers, nor believes that simulation is good for the hydrologic science (e.g., Snyder, 1973; Philip, 1992; Klemeš, 1997). Several excellent commentaries are related to conceptualization in hydrology (e.g., Klemeš, 1983, 1986; Grayson et al., 1992; Jakeman and Hornberger, 1993; Seibert and McDonnell, 2002; Dunn et al., 2008; Fenicia et al., 2008a, b; Siegel, 2008; Soulsby et al., 2008).

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5.16.2 Early Conceptual Models for Landscape Evolution

5.16.2.1 Davis Model: Cycle of Erosion

Probably the earliest conceptual model for landscape evolution was proposed by Davis (1889, 1899). His Cycle of Erosion incorporated within his Geographical Cycle was a theoretical, deductive construct that described a progressive sequence of stages in river development under a humid temperate climate initiated by rapid uplift. Davis (1889, 1899) saw landscapes as being a function of 'the trio of geographic controls': regional geological structure (the initial condition), geomorphic processes (sum of weathering and transport), and stage of landform evolution (representing time in the sense of landscape development relative to the completion of the entire cycle). The main framework was time (stage), thus, the model was time-dependent. Assuming tectonic stability, the river system gains in potential energy, incises into the landscape, and then erodes it while passing through 'youthful,' 'mature,' to 'old age' landforms/landscapes (Figures 1 and 2(a)). During this succession, surface gradients decline, and the cycle progresses from a high-relief to a low-relief landscape close to river base-level, the peneplain. The next uplift event initiates a new cycle passing through all three stages of the succession with time. The stage of evolution at any given time can be expressed in terms of its mean elevation above a base level. Whenever uplift occurs before the landscape cycled through the entire succession, the landscape was said to be rejuvenated, and youthful landforms coexist with older landforms and thereby create a polycyclic landscape. Davis' (1889, 1899) concept of peneplanation dominated Anglo-American geomorphology for several decades, but never gained wide acceptance by geomorphologists in mainland Europe.

5.16.2.2 Penck Model: Uplift and Denudation Related

The Davisian Cycle of Erosion maintained its popularity through the late nineteenth and early twentieth centuries until Penck (1924) proposed an alternative model for landscape evolution. Penck's deductive model gained much support in mainland Europe. Penck (1924) suggested that the Davisian Cycle of Erosion was flawed because it assumed that uplift is followed by erosion of a stable crust, but in fact active uplift - although episodic - could continue for a considerable time, and that various possible successions occur in the landscape controlled by different rates of uplift and erosion (Figure 2(b)). Penck's model was largely time-independent, it was based on tectonic history, and it emphasized geologic structure and rates of endogenetic and exogenetic processes. Moreover, Penck (1924) proposed that uplift rates initially increased slowly before reaching a maximum and then declined gradually. Whenever downcutting of rivers increases, for example, a waxing development stage occurs and slopes steepen progressively from the base upward to produce a convex profile. In contrast, a waning development stage occurs whenever downcutting decreases, and concave profiles develop. Penck's model described a succession of uplift of a primary surface (Primärrumpf), the formation of a series of benches (Piedmonttreppen), valley widening through slope replacement, the formation of large residual hills (Inselbergs) and pediments, and eventually the elimination of inselbergs and formation of an Endrumpf landscape. Although Penck's concept of uplift and denudation helped to integrate endogenetic processes into long-term landscape evolution, his model failed to acknowledge the importance of many other factors affecting landscape development such as changes in stream discharge as a result of climate change.

5.16.2.3 King Model: Pediplanation

Debate over the relative merits of the Davisian Cycle of Erosion and Penck's model for landscape evolution continued throughout the first half of the twentieth century, but was reexamined by King (1957) who proposed a model similar to Penck's but with a significant different explanation of slope development. King (1957) proposed that instead of a slope replacement, which takes place in balance with tectonic activity as described in Penck's concept, whole-slope parallel retreat was a characteristic of steep semi-arid landscapes. King (1957) divided the slope profile into four segments (waxing slope, free face, debris slope, and waning slope), of which one or more might be entirely absent. The resultant succession of landscape evolution would result in an expansion and coalescence of pediments, a process called pediplanation that would produce pediplains, as the free face retreats eliminating the higher surfaces (older pediments) to create isolated erosional remnants (Figure 2(c)). King, being trained in the Davisian school, emphasized the importance of time more in his model than Penck (1924) did.

5.16.2.4 Büdel Model: Etchplanation

An expansion of landscape models came with Büdel's (1957) morphogenetic concept of etchplanation. This gained considerable influence in mainland Europe, especially in Germany, and it led to the development of the subdiscipline of climatic geomorphology. The concept asserts that, under a particular climatic regime, certain geomorphic processes will dominate to produce a characteristic topographic expression (Figures 3 and 4). Büdel (1957) argued that climatic controls outweighed rock type as a landform factor because the resistance of a rock type to erosion is dependent on the climate to which it is subjected. One of Büdel's key notions was that of a double surface of leveling. Büdel (1957) proposed that in ancient, stable cratonic areas of the humid tropics, a subsurface landscape is essentially etched from the rock by deep weathering and subsequent removal of the weathered regolith - an etchplain developed. This process often results in the exposure of structurally defined compartments of resistant rock. Since in the humid tropics the controlling factors vary spatially, the weathering front is highly irregular in form and depth. Although during periods of tectonic and climatic stability, rates of weathering and denudation are roughly in a steady state, climatic or tectonic variations might lead to imbalance in the geomorphic system, and, for example, the stripping of the entire weathering zone. In the now lowered landscape, more water will increase weathering rates again.

5.16.2.5 Critique of Early Landscape Evolution Models

In the following decades, the early descriptive concepts were criticized, in the case of the Davisian model specifically for its assumptions of rates and occurrence of uplift and climatic stability. It soon became clear that stable landscapes are rather rare and that landscapes that follow a simple unidirectional sequence of forms probably do not exist. Instead, polycyclic landscapes are likely to be the norm. However, although the early models are essentially qualitative, they contain important concepts, which are also relevant in the context of quantitative models, particularly the ideas of slope decline, slope retreat, and equilibrium.

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5.19.3.4.2.2 Transient versus dynamic equilibrium landscapes

Both conceptual and numerical models of landscape evolution predict hat the distribution of erosion rates within a watershed depends strongly on the history of uplift or river incision. In landscapes where uplift or incision rates have recently changed, erosion rates will be variable as relief grows or shrinks. For example, if river incision has accelerated due to fault motion downstream, then a pulse of rapid incision may migrate upstream. Hillslopes will steepen, and erosion rates will increase first in the downstream part of the watershed and later in the upstream part. This transient response will persist until stream incision rates and erosion rates match uplift rates in all parts of the landscape. This latter condition may be referred to as dynamic equilibrium ( Hack, 1960), or erosional steady state.

Although equilibrium landscapes are a useful conceptual model, their existence has historically been difficult to confirm or deny. What is needed is a way to measure erosion rates at many points in a watershed to find out if erosion rates are spatially uniform, or if instead they vary systematically throughout a landscape. Cosmogenic nuclides offer just such a method, and can be used to compare erosion rates under various tectonic and climatic conditions.

We begin by contrasting erosion rates in two landscapes in the northern Sierra Nevada, California. Both catchments are in similar granitic rock. The first landscape is in the Diamond Mountains, near Adams Peak. Hillslope gradients there range from 0.2 to 0.7, with varying degrees of bare rock exposure depending on gradient (Granger et al., 2001). Miocene volcanic flows extend from mountaintops to valley bottoms, showing that the Diamond Mountains have maintained similar relief and hillslope gradients over the past 10 Myr (Grose and Mergner, 2000). Eleven samples were collected from different catchments, chosen to represent as wide a range in hillslope gradient as possible.

The second landscape is along the Fall River. Again, bedrock is granodiorite, and hillslope gradients span a range from 0.2 to 0.7, similar to the range at Adams Peak. At this second site, however, relief has locally increased due to incision of the Fall River Canyon. Steep slopes are generally found near the canyon, while more gentle slopes are found away from the canyon. Eight samples were collected from different catchments, again chosen to maximize the range of hillslope gradients (Riebe et al., 2000).

Erosion rates in the two landscapes show very different relationships to hillslope gradient (Figure 12). At the Diamond Mountains, where relief has persisted unchanged for at least 10 Myr, erosion rates are indistinguishable from place to place, regardless of gradient, soil depth, or any other factor (Granger Riebe et al., 2001). In contrast, at Fall River, where relief has increased due to more recent canyon incision, erosion rates show a strong relationship with gradient ( et al., 2000).

Similar results have been seen elsewhere (von Blanckenburg, 2005). In areas where recent tectonics or river incision has occurred, erosion rates are correlated with hillslope gradient. For example, erosion rates vary with distance from active faults at the Fort Sage Mountains study site (Granger Wobus Hewawasam Matmon Riebe et al., 1996), and in the Siwalik Range ( et al., 2005). In regions of tectonic stability, erosion rates are uniform across a wide range of hillslope gradient. Examples include the highlands of tropical Sri Lanka, where erosion rates are slow even on slopes up to 30° ( et al., 2003), and the Smoky Mountains in the Appalachians, where erosion rates are nearly constant over various lithologies and gradients ( et al., 2003). Cosmogenic nuclides thus provide a method for distinguishing landscapes in a transient state of relief, where erosion rates are spatially variable, from those in dynamic equilibrium where erosion rates are spatially uniform ( et al., 2000; von Blanckenburg, 2005).

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The isostatic response to erosional unloading represents the simplest form of erosion-tectonic feedback. It is a feedback with some fascinating consequences for landscape evolution. When erosional loading is focused in a particular area, such as a large river or glacier valley, the surrounding region will rise isostatically.

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-the study of the physical features of the surface of the earth and their relation to its geological structures.

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Identifying each earth landforms.

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-is the study of the causes and ecological consequences of spatial pattern in landscapes.

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