William Morris Davis & His Concept of Landscape Development

William Morris Davis, the father of geomorphology, introduced a fascinating theory—the Geographical Cycle of Erosion, also called the Cycle of Erosion.

According to Davis landforms undergo sequential changes through time (passing through three stages of youth, mature and old).

• The earth’s surface is affected by two types of forces i.e. Endogenetic forces and exogenetic forces.
• Endogenetic forces create vertical irregularities on the earth’s surface by forming several types of relief features whereas
• Exogenetic forces such as wind, rivers, glaciers etc. try to remove the vertical irregularities and ultimately become successful in bringing down the reliefs to low featureless plain, called as a peneplain.

Over time, the battle between these two forces leads to a systematic transformation of landforms through three distinct stages—Youth, Maturity, and Old Age—just like a human life cycle!

The Three Pillars of Davis’ Model

According to Davis three factors i.e. structure, process and time play important roles in the origin & development of landforms of a particular place where,

• structure means lithological and Structural characteristics of rocks.
• Time was not only used in temporal context by Davis but it was also used as a process itself.
• Process means an agent of denudation including both weathering & erosion.

Assumption of Davisian Model:

The basic premises of Davisian model of ‘geographical cycle’ included assumptions —

• Landforms are the evolved products of the interactions of endogenetic forces originating from within the earth & the exogenetic forces such as winds, rivers, glaciers etc. originating from the atmosphere.
• The evolution of landforms takes place in an orderly manner in such a way that a systematic sequence of landforms is developed through time.
• Streams erode their valleys rapidly downward until the graded condition is achieved.
• There is a short period rapid rate of upliftment in landmass.
• Erosion does not start until the upliftment is complete.

Therefore first Endogenetic forces come into play and after that exogenetic forces.

The Three Stages of Landscape Evolution

Youthful Stage

Think of this stage as a fresh, newly uplifted landmass, full of energy but not yet sculpted by erosion. Imagine a rough, untouched terrain where rivers are just starting to carve their paths.

• Since the land has just been uplifted, erosion is in its infancy. The highest parts (summits) of the landscape remain untouched because the rivers are too small and too far apart to reach them.
• The rivers, though small, are ambitious. They work hard, extending their lengths through headward erosion—meaning they erode backward toward their source, trying to stretch as far as possible.
• The rivers flow rapidly down steep slopes, cutting deep into the ground through vertical erosion. As a result, valleys start forming, but they are narrow, deep, and shaped like a “V” because the river mainly cuts downward rather than sideways. So, basically, Valleys are of V shape characterized by convex valley side slopes
• The difference between the highest point (summits) and the deepest valleys (relative relief) keeps increasing, though the absolute height of the landscape remains unchanged.
• If you could fly over this stage, you’d see a rugged landscape with deep, V-shaped valleys separated by high, untouched ridges.
• The lower curve (B) falls rapidly because of valley deepening but the upper curve (A) remains almost parallel to the horizontal axis because summits are not affected because of erosion, thus absolute relief remains constant & relative relief continues to increase till the end of youthful stage.

Note: Absolute Relief never increases in Davis Theory in any stage

Mature Stage

Now, imagine the land has aged a little—it’s not as wild and extreme as in its youth. The rivers have grown larger and more organized, forming a well-connected drainage system.

• The rivers, now stronger and more stable, shift their focus from cutting downward (vertical erosion) to cutting sideways (lateral erosion).
• This sideways cutting makes valleys broader, transforming the sharp V-shape of the youthful stage into a more gentle U-shape.
• The once untouched summits of the water divides are now getting eroded, lowering the overall elevation.
• The absolute and relative relief (the height difference between peaks and valleys) both start to decrease.
• By the end of this stage, the landscape is well-integrated with smoothly flowing rivers and widening valleys

Old stage

At this point, the landscape has become old and mature—just like an experienced elder who has settled into a peaceful life. The rivers no longer cut deep into the land but instead focus on expanding the landscape sideways.

• There is almost no more vertical erosion—the rivers have lost their aggressive cutting power. Instead, they continue their lateral erosion, widening valleys even more.
• The highlands and divides keep eroding down, making the entire landscape much flatter.
• The valleys are now broad and flat, with gentle concave slopes instead of sharp, rugged edges.
• The landscape is dominated by large floodplains, meandering rivers, and occasional isolated hills (called monadnocks), which are the last remnants of the once towering peaks.
• Eventually, the entire land flattens into a peneplain—a nearly level surface with minimal elevation differences.

Absolute Relief (AR) and Relative Relief (RR) in Davis’ Cycle of Erosion

Absolute Relief (AR):

• Absolute relief refers to the total elevation of a landmass above sea level.
• It indicates the maximum height of the landscape, typically measured from the highest summit to the base level (sea level).
• In Davis’ model, absolute relief never increases; it either remains constant (in the youthful stage) or decreases (in maturity and old age) due to erosion.

Relative Relief (RR):

• Relative relief is the difference in elevation between the highest and lowest points of a given area (e.g., the height difference between summits and valley floors).
• It indicates how rugged or uneven the terrain is.
• In Davis’ model, relative relief increases in the youthful stage (as valleys deepen) and decreases in the mature and old stages (as lateral erosion reduces elevation differences).

Evaluation of Davis’ Theory: Strengths & Weaknesses

William Morris Davis’ Cycle of Erosion was one of the earliest and most influential theories in geomorphology. However, like any scientific model, it has its strengths and limitations. Let’s analyze both sides logically.

Pros: Why Davis’ Theory Was Revolutionary

1. Simplicity & Applicability – The theory provided a simple and structured explanation of how landscapes evolve over time. It was easy to understand and widely applicable.
2. Empirical Basis – Unlike purely theoretical models, Davis’ concept was based on extensive field observations, making it an empirical study rooted in real-world examples.
3. Predictive & Historical Relevance – The model not only helped in interpreting past landform evolution but also had the potential to predict future changes, making it a useful tool for geographers.
4. Synthesis of Evolutionary Ideas –
   • Davis successfully combined Charles Darwin’s theory of biological evolution (young → mature → old) with James Hutton’s uniformitarianism (geological changes happen gradually over time).
   • Just like species evolve through different life stages, Davis’ landforms also followed a similar progression.

Cons: The Limitations of Davis’ Model

While Davis’ model was groundbreaking, modern geomorphologists have identified several flaws:

1. Unrealistic Assumption of Rapid Upliftment

• Davis assumed that upliftment happens quickly over a short period, followed by a long, stable period of erosion.
• However, plate tectonics (discovered later) proved that upliftment is actually slow and continuous, rather than sudden.

2. Overemphasis on Rivers & Erosion

• His model focused only on fluvial (river) processes and neglected other important erosional agents like glaciers, wind, and coastal processes.
• This oversimplification led to criticisms that his model was too narrow and incomplete.

3. The ‘Time’ Factor Dominated Over ‘Structure & Process’

• Davis identified structure, process, and time as key factors shaping landscapes, but in practice, his model gave too much importance to time (cyclical stages).
• This created a stage-based framework, which ignored the complex and simultaneous action of multiple processes.

4. Ignoring Continuous Tectonic Activity

• The model assumes that erosion starts only after upliftment is complete.
• However, modern science shows that erosion and upliftment happen simultaneously—as soon as land starts rising, erosion begins.
• Davis’ model also assumes long tectonically stable periods, which is unrealistic because earthquakes, faults, and crustal movements constantly shape landscapes.

5. Forced Expansion to Other Erosional Agents

• Davis later introduced Glacial and Marine Cycles of Erosion under pressure from critics.
• However, he called them “climatic accidents”, implying that fluvial erosion was the norm, and other processes were just exceptions.
• This weakened the universality of his model, as landscapes are typically shaped by multiple processes acting together (polygenetic nature) rather than a single agent.

6. Lack of Acknowledgment for Endogenetic Forces

• While Davis recognized upliftment as a starting point, his model did not account for the continuous role of internal (endogenetic) forces like volcanism, faulting, and folding.
• Landscapes are shaped not just by erosion but also by forces from within the Earth.

Peneplain

Imagine you are standing atop a vast, endless plain, where the land stretches out in every direction, almost featureless except for a few scattered hills that stubbornly rise above the surface. The rivers meander lazily, their once-mighty currents now tamed, carving only gentle curves into the earth. This is a peneplain, the near-final stage of a landscape’s life—a silent testament to millions of years of erosion.

The Making of a Peneplain

Every landform has a life cycle, just like a human being. It starts as a rugged, youthful terrain with towering mountains, deep valleys, and fast-flowing rivers—full of energy and movement. But as time passes, erosion acts like an invisible sculptor, wearing down the peaks, widening valleys, and flattening the land.

W.M. Davis, often called the father of geomorphology, introduced the concept of peneplanation—a slow but relentless process where landforms lose their dramatic heights and sharp features, gradually turning into low-lying, almost level plains.

Key Features of a Peneplain

1. The Final Stage of Erosion
   • In the last stages of a landscape’s evolution, deep valleys stop forming. Instead, rivers begin to erode sideways (lateral erosion) rather than downward, cutting into the surrounding land.
   • The result? Interstream areas (regions between rivers) shrink as erosion smooths out the rough edges of the terrain.
2. The Vanishing Act of Water Divides
   • Water divides—those ridges that separate river valleys—become lower and lower until they are barely noticeable.
   • Valleys lose their depth and adopt a flatter, concave shape, making the land appear more uniform.
3. A Land Without Sharp Features
   • Eventually, the land becomes so eroded that absolute relief (height differences between peaks and valleys) is greatly reduced.
   • The rivers, now at their base level (the lowest point they can erode to), become slow and meandering, no longer powerful enough to carve deep gorges.
4. The Rise of Monadnocks: Last Survivors of a Once-Mighty Landscape
   • Even in the most level peneplain, some isolated hills remain, refusing to be eroded completely.
   • Davis called these leftover landforms Monadnocks, named after Mt. Monadnock in New Hampshire, USA.
   • These are like wise old sages of the landscape, standing tall amidst the flattened land, telling the story of a terrain that once was.
5. A Landscape That Never Reaches Perfection
   • Davis himself acknowledged that a true peneplain—where the land is perfectly level—doesn’t really exist.
   • The process of erosion never fully erases a landmass, nor does the Earth remain still for long enough to complete this transformation.

Types of Peneplain

Not all peneplains are created equal. Some are still forming, some have merged, and others have been lifted up again by tectonic forces. Let’s look at the different types:

1. Local Peneplain – A small section of land that has undergone peneplanation while the rest of the region is still eroding. Think of this as a few students finishing an exam while the rest of the class is still writing.
2. Regional Peneplain – When multiple local peneplains merge together, forming an almost continuous featureless plain over a vast area.
3. Uplifted Peneplain – The story doesn’t always end in a quiet, level plain. Sometimes, tectonic forces push up an already flattened peneplain, giving it a new lease of life.
   • Example: The Appalachian Mountains in the USA have three uplifted peneplains:
     • Schooling Peneplain
     • Harrisburg Peneplain
     • Sommerville Peneplain
4. Resurrected Peneplain – Imagine a peneplain getting buried under sediments or submerged under the sea. Later, due to erosion or tectonic uplift, it is exposed again.
   • These are called “resurrected” because they are like ancient ruins being uncovered after centuries.

Criticism of the Peneplain Concept

While Davis’ peneplain model was revolutionary, later scientists pointed out several flaws:

• Peneplains are rare in reality – If Davis’ model was universal, we should see more fully developed peneplains, but very few places fit his description.
• Most remnants of peneplains are incomplete – Many supposed peneplains are found in fragments, suggesting other processes shaped them.
• No landscape reaches a perfect base level – Even where land is heavily eroded, some height variations always remain.
• Earth is always changing – Tectonic movements, climate variations, and erosion never let a landform stay undisturbed long enough for a perfect peneplain to form.

SAMPLE QUESTION

Q. What do you understand by downwasting and backwasting? Explain their role in landscape evolution and identify which process is responsible for the formation of a peneplain. (150 words)

ANSWER:

Downwasting and Backwasting

Downwasting refers to the uniform lowering of a landscape due to widespread erosion. It occurs through sheet erosion, deflation (wind erosion), and chemical weathering, gradually reducing the elevation of the land while maintaining relative relief.

Backwasting, on the other hand, involves the lateral retreat of slopes while maintaining their steepness. This occurs due to weathering, landslides, and erosional processes acting on escarpments, mesas, and cliffs.

Role in Landscape Evolution

• Backwasting is common in arid and semi-arid regions, leading to the shrinking of landforms like mesas and buttes.
• Downwasting occurs in humid regions, gradually reducing surface elevation over time.

Formation of Peneplain

Downwasting is responsible for peneplain formation as it uniformly lowers the landscape over an extended period, creating a near-flat surface with minimal relief. This represents the final stage of landscape evolution in humid regions.

Conclusion

While both processes contribute to landscape evolution, downwasting dominates in long-term landform reduction, leading to the development of peneplains.