Anthropogeomorphology

Anthropogeomorphology, the alteration of the Earth’s surface by human activity, has profound effects on the environment, including land, air, and water, and has the potential to alter local climates as well.

Background

Human civilizations alter natural landscapes, both land and water. They partially remove or scrape away natural landforms (subtractive processes), and they build up new topographic features (additive processes). Humans have long reshaped existing bodies of water, created new bodies of water, redirected water in canals or aqueducts, changed the paths of existing rivers, scraped away surfaces, and reclaimed land from seas or marshes behind dikes and seawalls. There is some evidence that these modifications of the landscape affect local climates.

Anthropogenic changes in the landscape easily surpass the scope of natural erosional processes globally. Overconsumption of water resources in such places as the Jordan Valley in the Levant causes bodies of water such as the Sea of Galilee and the Dead Sea to shrink. It also increases by changing the and reducing evaporation with increased land temperature. Replanting trees in arid zones can mitigate surface temperatures and increase orographic precipitation at lower elevations, where evaporation is reduced with and is reached more easily. This has occurred, for example, in Israel’s Judaean Hills, where rainfall increased dramatically over thirty documented years after reforestation.

Anthropogeomorphology and Climate Change

One subtractive process has been documented for millennia. Plato noted that severe soil erosion in fourth century B.C.E. Greece was causing much lost topsoil. Ancient observers were sometimes able to determine causes of topsoil loss, such as aggressive deforestation to clear farmland or destruction of native plant roots by animal grazing. Sheep and goat herds were particularly destructive, because they consumed root systems as well as surface plants, effectively killing the plant cover.

Once there were no longer roots to hold the soil, erosion often removed devastating volumes of surface soil. As soil cover moved downward, the resulting filled river bottoms, lakes, and harbors, which were eventually silted up, changing surface landscapes. Coastlines also changed when alluviated river deltas encroached into bodies of water, as, for example, the Rhone River encroached into the Mediterranean Sea. Erosion is normally a subtle, gradual process, but it can be accelerated by extreme through human agency. Erosion was exacerbated in the late Roman Empire and afterward in North Africa, where Atlas Mountain deforestation by humans resulted in alluviated coastal watersheds and silted up harbors. This erosion combined with rising land temperatures when rainfall ceased, partly as a result of deforestation, to render the climate much less hospitable. Ultimately, once great North African cities such as Sabratha and Leptis Magna were abandoned as a result of these climate changes.

Alteration of Seacoasts

Another example of ancient anthropogenic land change along seacoasts occurred at Tyre (now in Lebanon), beginning in 332 B.C.E., when Alexander the Great built a stone causeway out to the then-island city in a siege. Over millennia, the causeway trapped enough marine-transported sandy alluvium that the land bridge—originally around 7 meters across—widened into today’s peninsula, which is so much broader that a casual observer would not guess that there was once an open water channel of almost 400 meters between the mainland and island. Prevailing currents from the north built up far more seaborne sandy alluvium on the curved northern side of the peninsula, whereas the southern side of the artificial peninsula remains more contiguous to the original causeway. The volume of sand and eventual structures added over time now approximate about 200 hectares and millions of metric tons of alluvium. This land extension has changed local water and air circulation patterns along and over the coast of Lebanon.

Dams and Reservoirs

Humans have also created many artificial, interior bodies of water, such as reservoirs and artificial lakes. Water storage in artificial lakes fills millions of hectares of land surface on every continent, with concomitant climatic impacts ranging from temperature changes to increased evaporation. Additional anthropogenic aquatic change includes the construction of major canals, such as the Suez Canal linking the Mediterranean and Red Seas and the Panama Canal linking the Pacific Ocean and the Caribbean Sea. Construction of such canals includes the creation or exploitation of connecting lakes and locks to accommodate sea-level differences.

One dramatic human engineering project, China’s Three Gorges Dam, is already threatening to offset potential hydroelectric economic gains. Water has seeped into steep lands along the dam’s perimeter, causing more than 35 kilometers of banks to cave in, resulting in more than 20 million cubic meters of rockslide since 2003. In addition, there is mounting evidence that regional rainfall has been decreased, leading to drought and loss of biodiversity, while fault activity has increased where the dammed lake sits across two major, active fault lines.

Land Reclamation

Conversely, the Zuider Zee’s extensive dikes in the Netherlands reclaimed from the North Sea millions of hectares of land slightly below or just at sea level. The reclaimed land was used extensively for farming. The major dike (Afsluitdijk) created new land that gradually reduced the former early twentieth century Zuider Zee by about 38 percent.

A similar phenomenon exists around urbanNew Orleans, where former swamps and Mississippi River delta wetlands were drained, and dense human settlements were generally protected by extensive levees. Hurricane Katrina’s surge in summer, 2005, however, emphasized the fragility of such and urbanization. failure caused devastating flooding of 80 percent of New Orleans at great local, regional, and national cost.

Channeling former coastal rivers into stone or concrete storm drains is a major surface change, mostly aimed at reducing flooding. Precedents for such projects can be found in pre-Columbian Inca Peru, along the Urubamba River in the Yucay Valley. Around 1400, Inca engineers not only took out natural oxbows and straightened the river but also created farmland from the natural floodplain, where there had been no prior extensive agriculture, thus humidifying the air in the Yucay Valley.

Anthropogeomorphology and the Mining Industry

Perhaps the most extensive modern anthropogeomorphologic surface change in North America has been produced by the Canadian oil sands industry, which engages in open pit mining of the Athabaska River Valley in Alberta. Boreal forest and earth are scraped away to depths of about 30 meters in many places over a 390-square-kilometer area. This mining is creating vast, toxic, mine-tailing sludge lakes and growing pollutant containment problems. Naphthenic acid and polycyclic aromatic hydrocarbons, which are not easily degradable for centuries, leak from the mines into water tables, as well as the Athabaska River.

The oil sands industry extracts enormous quantities of bitumen-laced sands, heats them, and cleans them using hot water and other agents. This process has resulted in a huge spike in aerosol CO₂ emissions over northern Canada, at a much higher rate than the emission rate of conventional oil production. Oil produced in Alberta’s oil sands is mostly consumed by the United States; this single source supplies 10 percent of total U.S. foreign oil.

It takes 3.6 metric tons of earth to produce one barrel of oil, and 4.53 million barrels of crude oil were produced per diem in Alberta in 2023. This requires considerable energy, much of which was generated from natural gas, and yields a vast landscape of stored toxic waste. Environmental scientists are beginning to link accelerated Arctic ice-cover loss with the northern Canadian oil sand industry. The industry may raise local temperatures through deforestation, as well as adding steam to the air.

Context

Anthropogeomorphology as a by-product of human activity is a growing concern, as evidenced by a burgeoning global environmental response. Quantitative analyses of climatic changes resulting from have yet to be produced, but growing attention to the subject will render such analyses of great scientific and political interest. Once the phenomenon is better understood, it may be possible not only to prevent further projects from creating negative climatic effects, but also to launch projects to mitigate local and global climate trends.

Key Concepts

• additive processes: processes that enhance surface topography
• alluviation: soil erosion that results in the filling of watercourses or harbors
• dew point: the temperature at which water vapor condenses into liquid water
• orographic precipitation: precipitation caused by changes in topography that drive air higher, where it cools and condenses
• polders: Dutch land areas reclaimed from sea or marsh
• subtractive processes: processes that reduce surface topography

Bibliography

Adu-Boahen, Kofi, et al. "Human-Environment Nexus: Evaluating the Anthropo-Geomorphology and Urban Expansion of the Wieja Gbawe Municipality, Ghana." Discover Environment, 4 Dec. 2023, doi.org/10.1007/s44274-023-00022-0. Accessed 21 Dec. 2024.

Atlas of Israel: Cartography, Physical and Human Geography. New York: Macmillan, 1985.

Hvistendahl, Mara. “China’s Three Gorges Dam: An Environmental Catastrophe?” Scientific American, March 25, 2008.

Kunzig, Robert. “Scraping Bottom: The Canadian Oil Boom.” National Geographic, March 2009.

LaFreniere, Gilbert. The Decline of Nature: Environmental History and the Western Worldview. Bethesda, Md.: Academica Press, 2008.

Nikiforuk, Andrew. Tar Sands: Dirty Oil and the Future of a Continent. Berkeley, Calif.: Greystone Books, 2008.