What is Geomorphology?
Chapter – 1
Table of Contents
- Geomorphology derives from Greek words: γεω (Earth), μoρφη (form), and λογος (discourse).
- Coined in the 1870s and 1880s to describe the morphology of Earth’s surface (e.g. de Margerie 1886, 315).
- Defined as ‘the genetic study of topographic forms’ (McGee 1888, 547).
- Used in popular parlance by 1896.
- Today, geomorphology is the study of Earth’s physical land-surface features, its landforms – rivers, hills, plains, beaches, sand dunes, and myriad others.
- Some include submarine landforms and landforms of other terrestrial-type planets and satellites.
- Landforms are conspicuous features of the Earth and range in size from molehills to mountains to major tectonic plates.
- Lifespans of landforms range from days to millennia to aeons (Figure 1.1).
- David Mark and Barry Smith (2004) listed twenty-six broad landform types, many with subtypes: basin, catchment, cave, cirque, cliff, continent, crater, cut, earth surface, floodplain, gap, ground, ground surface, moraine, mount, mount range, peak, pinnacle, plain, plateau, ridge, ridge line, terrace, trough, and valley.
- Geomorphology investigates landforms and the processes that fashion them.
- Form, process, and interrelationships between them are central to understanding the origin and development of landforms.
- Form or morphology has three facets – constitution (chemical and physical properties), configuration (size and form), and mass flow (rates of flow) (Figure 1.2; Strahler 1980).
- Dynamic variables contrast with form variables and are associated with geomorphic processes: power, energy flux, force, stress, and momentum.
- Example of a beach: constitutional properties (sorting of grains, grain diameter, grain shape, moisture content), configurational properties (slope angle, beach profile form, water depth), mass-flow variables (rates of erosion, transport, deposition).
- Dynamic variables include drag stresses from water currents, possibly by channeled water flowing over the beach, wind, and forces from burrowing animals and humans.
- Geomorphic processes are chemical and physical means by which the Earth’s surface undergoes modification.
- Driven by endogenic (internal Earth) forces, exogenic (surface and atmospheric) forces, and extraterrestrial forces (e.g., asteroid impacts).
- Processes include transformation and transfer associated with weathering, gravity, water, wind, and ice.
- Mutual interactions between form and process are core to geomorphic investigation.
- Atmospheric, ecological, and geological processes influence and are influenced by geomorphic process–form interactions (Figure 1.2).
- The connection between Earth’s surface processes and forms is central to geomorphological discourse.
- Language expressing these connections has changed with cultural, social, and scientific contexts.
- Qualitative approach by Classical thinkers preceded a quantitative approach in the mid-20th century.
- Early writers linked surface features to assumed processes, such as catastrophic floods.
- Example: Nicolaus Steno’s six-stage sequence explaining Tuscan landscape (Steno 1916 edn) (Figure 1.4).
- First true geomorphologists, like William Morris Davis and Grove Karl Gilbert, inferred landforms’ fashioning by geomorphic processes.
- Four approaches in studying landforms (Slaymaker 2009): process–response (process–form) or functional approach, landform evolution approach, characterizing landforms approach, and environmentally sensitive approach.
- Process and historical approaches dominate modern geomorphology, with process studies predominating in Anglo-American and Japanese geomorphology.
- Process geomorphology focuses on mechanics of geomorphic processes and process–response relationships.
- Historical geomorphology focuses on histories or trajectories of landscape evolution.
- Historical and process geomorphology are complementary, often used together.
- George Gaylord Simpson (1963) distinguished between ‘immanence’ (timeless processes) and ‘configuration’ (historical states).
- Schumm’s idea: as landform size and age increase, explanations require more historical information.
- Understanding landforms requires a mix of process and historical geomorphology.
HISTORICAL GEOMORPHOLOGY
The foundations of historical geomorphology
- All landforms have a history, but short-lived features like ripples and terracettes tend to go unrecorded unless buried in sediments.
- Geomorphologists focusing on long-term changes study persistent landforms from coastal features to continental drainage systems.
- Small-scale sedimentary features that survive can offer clues to past processes and events.
- Historical geomorphology studies landform evolution over centuries, millennia, and millions of years.
- Relies on form of the land surface and sedimentary record for data.
- Traditionally, historical geomorphologists used morphological and sedimentary features to deduce landscape history.
- Principle of ‘the present is the key to the past’ assumed current processes reflect past changes.
- Early studies relied on educated guesswork due to lack of dating techniques.
- William Morris Davis formulated the ‘geographical cycle’ theory of landscape evolution (1889, 1899, 1909).
- Theory assumed quick uplift followed by gradual erosion to form extensive flat regions (peneplains).
- Monadnocks are local erosional remnants that stand above peneplains.
- Cycle stages: youth, maturity, old age (criticized as misleading terms).
- Theory applied to various landscapes: humid temperate, arid, glacial, periglacial, shore, and karst.
- Davis’s theory had significant theoretical influence despite being superseded (Figure 1.6).
- Influence extended to denudation chronology and understanding landscape evolution.
- Eduard Brückner and Albrecht Penck used young sediments to interpret Pleistocene events.
- Studied glacial effects on Bavarian Alps and forelands.
- River-terrace sequence named glacial stages: Donau, Gunz, Mindel, Riss, and Würm.
- Contributions led to Quaternary geomorphology and divisions of geological time.
Modern historical geomorphology
- Historical geomorphology has evolved beyond Davis’s geographical cycle, embracing diverse chronological analyses and a deeper understanding of geomorphic and tectonic processes.
- Stratigraphical studies of Quaternary sediments provide relative chronologies; absolute chronologies utilize historical records, radiocarbon analysis, dendrochronology, luminescence, and palaeomagnetism.
- Studies in historical geomorphology are categorized into Quaternary geomorphology and long-term geomorphology.
- Quaternary geomorphology examines environmental changes over the past couple of million years, impacted by climatic swings between glacial and interglacial periods.
- Climatic changes, influenced by orbital forcing, drive consistent patterns in landscape changes over 1,000 to 100,000 years.
- Initially focused on Holocene and Late Pleistocene, Quaternary geomorphologists now apply their knowledge to earlier times, collaborating for palaeogeographical reconstructions and predictive models.
- Long-term geomorphology studies landforms older than the Quaternary, including Cenozoic, Mesozoic, and sometimes Paleozoic periods.
- Davis’s geographical cycle laid foundations for long-term geomorphology, exploring baselevel surfaces and denudation chronology before the Quaternary.
- Recent advances in long-term geomorphology include numerical models integrating tectonic and surface processes, focusing on high-elevation passive continental margins and convergent zones.
- Analytical and geochronological techniques, such as apatite fission-track analysis, aid in determining rates of rock uplift and landscape evolution.
- Despite advancements, setting accurate ages to long-term landforms remains challenging due to subsequent processes altering or destroying them.
PROCESS GEOMORPHOLOGY
The history of process geomorphology
- Process geomorphology focuses on studying the processes responsible for landform development.
- Grove Karl Gilbert, influenced by Leonardo da Vinci, initiated modern process geomorphology with his work on fluvial processes in the Henry Mountains of Utah, USA.
- Ralph Alger Bagnold contributed by studying the physics of blown sand and desert dunes, while Filip Hjulström investigated fluvial processes up to about 1950.
- Arthur N. Strahler’s 1952 paper, ‘Dynamic basis of geomorphology’, was pivotal in establishing process geomorphology, proposing a system grounded in mechanics and fluid dynamics.
- Luna B. Leopold and M. Gordon Wolman contributed empirically to fluvial geomorphology, employing statistical treatments of form variables and their controls.
- William E. H. Culling and Michael J. Kirkby furthered the characterization of geomorphic processes in the 1960s and 1970s.
- William E. Dietrich and colleagues in the 1980s expanded on Strahler’s ideas, developing dynamic geomorphology and landscape evolution models (LEMs).
- Process geomorphology also explores landscape stability concepts, including thresholds and metastable states, pioneered by Stanley A. Schumm and Stanley W. Trimble.
- Richard J. Chorley introduced process geomorphology to the UK, emphasizing a systems approach to studying landscapes.
The legacy of process geomorphology
- Process geomorphologists have contributed significantly in three key areas: building a database of process rates globally, developing refined models for short-term and sometimes long-term landform changes, and generating powerful ideas on stability and instability in geomorphic systems.
- Geomorphic processes have been measured extensively over time, with records such as the annual flood levels of the River Nile dating back to 3100 BC and sediment transport rates in the Mississippi River measured since the 1840s.
- Quantitative revolution in geomorphology since the 1940s enabled systematic measurement of process rates, supported by advancements in field instrumentation and methodology.
- Anders Rapp’s work in the 1960s exemplified quantification efforts in subarctic environments, focusing on running water as a dominant geomorphic agent.
- Instrumented hillslopes and drainage basins have facilitated ongoing measurements, particularly valuable in climatically sensitive areas, despite geographical disparities in measurement coverage.
- Since the 1960s and 1970s, process geomorphologists have increasingly directed efforts towards constructing models predicting short-term landform changes, integrating principles from soil and hydraulic engineering.
- Pioneering efforts by Michael J. Kirkby and Jonathan D. Phillips expanded into long-term landscape evolution modelling, leveraging computational advancements and geomorphic transport laws.
- Landscape evolution models have become feasible with high-speed computers, allowing integration of multiple processes over complex topographies and extended timeframes.
- Process geomorphology intersects with global environmental change research, focusing on energy and mass fluxes, and understanding landform responses to climate, hydrology, tectonics, and land use.
- The field parallels developments in biogeoscience, an interdisciplinary study of interactions between biological, chemical, and physical processes in the biosphere and other Earth spheres.
OTHER GEOMORPHOLOGIES
- Structural geomorphologists historically emphasized geological structures as crucial for understanding landform origins.
- Modern geomorphology integrates process and historical studies alongside a wide range of specialized disciplines within Earth and life sciences.
- Reintegration of Earth and life sciences began with Arthur George Tansley’s ecosystem concept (1935), later expanding into Earth System Science, which broadens perspectives on Earth and its geological and cosmic contexts.
- The ‘new natural history’ approach considers interdependencies among life, air, water, rocks, and landforms, including processes from deep within the Earth to cosmic scales.
- Emerging ‘new’ geomorphologies include hydrogeomorphology, biogeomorphology (phytogeomorphology, zoogeomorphology), applied geomorphology, and anthropogeomorphology.
- Specialized sub-disciplines like tectonic geomorphology, submarine geomorphology, climatic geomorphology, and planetary geomorphology are integral to modern geomorphological research.
Hydrogeomorphology
- Hydrogeomorphology studies the interaction between hydrology and geomorphology.
- It explores how water movement through hillslopes, rivers, and landscapes influences geomorphic processes and forms.
- Geomorphic forms affect the distribution of shallow groundwater spatially and temporally.
- It is an interdisciplinary science integrating hydrologic processes with landforms and earth materials.
- Focuses on interactions between geomorphic processes and surface/subsurface water in both temporal and spatial dimensions.
- Helps identify hazards and understand impacts of land use and climate change.
- Japanese geologists have contributed significant research on surface and subsurface flow regimes’ roles in fluvial erosion and mass wasting.
- Ecologists utilize hydrogeomorphology to describe water-geomorphic conditions defining habitats in wetlands, rivers, and other environments.
Biogeomorphology and ecogeomorphology
- Plants, animals, and microorganisms influence landforms and geomorphic processes.
- Geomorphic processes, in turn, influence the distribution and development of life forms.
- Charles Darwin’s work on earthworms pioneeringly explored these interactions (Darwin 1881).
- Biogeomorphology and ecogeomorphology integrate geomorphology with ecological sciences.
- These terms encompass biomorphodynamics, phytogeomorphology, zoogeomorphology, among others.
- Biogeomorphology was termed by Heather Viles in 1988 to denote the influence of organisms on landforms and vice versa.
- It focuses on biotic feedbacks affecting chemical and physical weathering.
- Zoogeomorphology examines animals like beavers as geomorphic agents.
- Phytogeomorphology studies relationships between plants, landforms, and geomorphic processes.
- Ecogeomorphology and biogeomorphology both explore bidirectional influences between biota and landscapes.
- Biomorphodynamics studies biological-physical feedbacks influencing sediment transport and landform change.
- Evolutionary ecogeomorphology extends these concepts to include ecological and evolutionary processes influencing Earth-surface processes and landforms.
Applied geomorphology
- Applied geomorphology began as the application of geomorphological knowledge to societal issues.
- James Alfred Steers’s book “Applied Coastal Geomorphology” (1971) marked its initial formalization.
- Applied geomorphology now includes anthropogeomorphology, focusing on human impacts on geomorphic forms and processes.
- It addresses environmental management issues like resource evaluation and natural hazard prediction.
- Applications span coastal erosion, beach management, soil erosion, building weathering, landslide protection, river management, and landfill site planning.
- Books like “Geomorphology in Environmental Planning” (Hooke 1988) discuss geomorphology’s role in public policies.
- “Geomorphology in Environmental Management” (Cooke 1990) explores geomorphology’s role in environmental management.
- “Geomorphology and Land Management in a Changing Environment” (McGregor and Thompson 1995) focuses on managing land amid environmental changes.
- Applied geomorphologists are crucial in mitigating natural hazards exacerbated by global warming.
- They use techniques such as terrain mapping, remote sensing, and GIS for environmental management.
- They translate predictions of global warming into actionable insights for minimizing environmental impacts.
Anthropogeomorphology
- Anthropogeomorphology studies human interactions with geomorphic processes.
- Coined by Berl Golomb and Herbert M. Eder in 1964, it focuses on human-induced creation and modification of landforms.
- It encompasses weathering, erosion, transport, and deposition influenced by human activities.
- In its broadest sense, anthropogeomorphology examines all interactions between humans and landscapes.
- Recent developments include geodiversity and related concepts like geoheritage, geosites, and geoconservation.
- Geoconservation within anthropogeomorphology focuses on preserving geological and geomorphological features.
Tectonic geomorphology
- Studies the interaction between tectonic and geomorphic processes in actively deforming regions of Earth’s crust.
- Recent advances in measurement techniques and understanding of physical processes have revitalized the field.
- Highly integrative, drawing on geomorphology, seismology, geochronology, structure, geodesy, and Quaternary climate change.
- Focuses on measuring rates of tectonic and geomorphic processes.
- Examines how tectonic forces shape landforms and landscapes over various timescales.
Submarine geomorphology
- Deals with the form, origin, and development of features of the sea floor.
- Submarine or subsea landforms cover about 71 per cent of Earth’s surface.
- Less well studied compared to terrestrial landforms.
- Shallow marine environments feature landforms like ripples, dunes, sand waves, sand ridges, shorelines, and subsurface channels.
- Continental slope transition zone includes submarine canyons, gullies, inter-canyon areas, intraslope basins, slump and slide scars.
- Deep marine environment encompasses trench and basin plains.
- Features in deep marine environment include trench fans, sediment wedges, abyssal plains, distributary channels, and submarine canyons.
Planetary geomorphology
- Study of landforms on planets and large moons with solid crust.
- Includes planets like Venus, Mars, and moons of Jupiter and Saturn.
- Thriving branch of geomorphology.
- Key factors influencing surface processes are mean distance from the Sun, rotational period, and planetary atmosphere.
- Observed processes include weathering, aeolian activity (wind-related), fluvial activity (related to rivers), glacial activity, and mass movements.
Climatic geomorphology
- Chief proponents: French and German climatic geomorphologists.
- Their argument: Each climatic zone (tropical, arid, temperate) produces distinct landforms.
- Not universally accepted that each climatic zone generates characteristic landforms.
- Climate strongly influences geomorphic processes.
- Current consensus: Climatic factor in landform development is complex due to climatic and tectonic changes.
- Debate around whether specific geomorphic processes within climatic zones create characteristic landforms.
The two geomorphologies
- Mike Church (2010) identifies a widening rift in geomorphology approaches.
- Geophysical approach: Focuses on physical principles governing material breakdown and transport, viewing the land surface as integral to the Earth system.
- Example: Robert S. and Suzanne P. Anderson’s textbook “Geomorphology: The Mechanics and Chemistry of Landscapes.”
- Emphasizes rigorous physical principles and processes.
- Human-centered approach: Increasingly concerned with social and economic values, environmental change, human impact on the environment.
- Includes geoconservation, social justice, and equity issues.
- Referred to as neogeomorphology by Peter K. Haff (2002, 2003) and sociogeomorphology by Peter Ashmore (2015).
- Incorporates human social and economic dimensions into analyses.
- Views humans as integral parts of Earth’s systems, not just agents modifying the surface.
- Example: Dénes Lóczy and László Sütő’s chapter on “Human Activity and Geomorphology” highlights this approach.
- Both approaches (geophysical and human-centered) coexist in contemporary geomorphology, offering complementary perspectives.
GEOMORPHOLOGICAL ‘ISMS’: A NOTE ON METHODOLOGY
- Geomorphologists face methodological challenges rooted in scientific guidelines.
- Scientific rules guide all scientists, including geomorphologists, in conducting inquiries.
- Uniformity of law: Assumes natural laws are constant throughout Earth’s history (physics, chemistry, biology).
- Actualism (uniformity of process): Events in the past are outcomes of processes observed today.
- Challenges to actualism: Some argue past processes occurred under different circumstances.
- Views include non-actualism, suggesting past conditions differed significantly.
- Rate of Earth surface processes: Views range from gradualism (slow, steady change) to catastrophism (sudden, dramatic events).
- Changing state of Earth’s surface: Views include steady-statism (relatively constant state) and directionalism (ongoing changes).
- Uniformitarianism: Often conflated with actualism, originally Charles Lyell’s concept involving uniformity of law, process, rate, and state.
- Alternatives to uniformitarianism: Non-uniformity in process, rate, and state.
- Geomorphology’s shift towards neocatastrophism acknowledges modern versions of catastrophism.
- Concerns about future Earth system changes and tipping points challenge the maxim “the present is the key to the future.”
- Jasper Knight and Stefan Harrison (2014) argue against uniformitarianism’s applicability in the Anthropocene due to nonlinear system feedback.