Interruptions in the Cycle of Erosion

Imagine you are standing atop a vast plateau, looking at rivers carving their way through valleys, shaping the land ever so gradually. Now, visualize this transformation as a slow but continuous process, much like an artist chiselling a sculpture over centuries. This is the essence of the Davisian Cycle of Erosion, a concept that describes how landscapes evolve through three distinct stages—youth, maturity, and old age—ultimately resulting in a nearly featureless plain called a peneplain.

However, the Earth is not a static canvas. It is alive, dynamic, and constantly changing. Forces like tectonic movements and climate variations disrupt this seemingly smooth cycle, introducing interruptions that alter the course of landscape evolution. Let’s embark on a journey to understand these interruptions and their impact on the landforms around us.

1. Understanding Interruptions in the Cycle of Erosion

Think of a river that begins its journey in the mountains, young and energetic, cutting deep valleys. Over time, as erosion continues, the land flattens, and the river slows down. If left undisturbed, this process would eventually result in a peneplain. But nature seldom allows such uninterrupted progression.

Any hindrance in this orderly cycle is called an interruption. These interruptions occur due to two main reasons:

1. Tectonic Activity – The land may rise (uplift) or sink (subsidence), changing the base level of erosion.
2. Climate Changes – A rise or fall in sea level, often linked to glaciation, can alter the rate at which landscapes erode.

These interruptions cause the cycle to either advance forward (accelerated erosion) or go backward (rejuvenation), creating landscapes that have seen multiple cycles of erosion.

2. How Interruptions Affect the Cycle of Erosion

(a) Positive Change in Base Level – A Leap Forward

Imagine a floodplain where the sea level rises or the land subsides. This means that rivers will slow down their erosion, and sediment deposition will increase, leading to a faster completion of the erosion cycle.

For instance:

• If a region is in its youth stage, it might suddenly shift to maturity.
• If it is in its mature stage, it might quickly reach old age, becoming a lowland.

📌 Example: During an interglacial period (when glaciers melt), the sea level rises, reducing erosion and leading to the faster development of peneplains.

(b) Negative Change in Base Level – A Reset Button

Now, imagine the opposite scenario—land uplifts or the sea level falls. This is like hitting a reset button on landscape evolution. Rivers that were once slow and meandering suddenly regain their energy and start cutting into the land with renewed vigor. This rejuvenation leads to deep, narrow valleys and striking landscapes.

📌 Example: During an Ice Age, when glaciers expand, water gets locked in ice, causing a drop in sea level. This exposes new land and forces rivers to carve deeper valleys, resetting the erosion cycle to a youthful stage.

🔹 Real-World Examples:

• Damodar Valley (Jharkhand) and Narmada River (Madhya Pradesh) show signs of rejuvenation with paired terraces and deep valleys.
• Dhuandhar Falls (Jabalpur)—where the Narmada River has cut deep into the rock—illustrates how rejuvenation creates spectacular landscapes.

3. Interrupted Cycles and Polycyclic Landscapes

When interruptions occur repeatedly over time, multiple erosion cycles take place, creating polycyclic landscapes. These regions have seen land rise and fall multiple times, resulting in complex topography.

📌 Examples of Polycyclic Landscapes:

• Appalachian Mountains (USA) – Rejuvenated multiple times due to tectonic uplift.
• Chottanagpur Plateau (India) – Has undergone several erosion cycles, leading to diverse landforms.

Think of these landscapes as books with multiple chapters—each interruption adds a new chapter to the story of landform evolution.

4. Two Types of Interruptions

We categorize these interruptions into two types:

• Interruptions that modify the existing cycle (Base Level Change Interruption)
• Interruptions that completely end a cycle and start a new one (Accidents)

A. Interruptions Due to Vulcanicity and Climatic Changes (Accidents)

This is like a hard reset for the landscape! If a volcanic eruption covers a region with lava or extreme climate changes alter the landform drastically, the ongoing erosion cycle is permanently closed, and a new cycle begins after a long gap.

• Imagine a river shaping a valley peacefully, cutting deeper over time. Suddenly, a volcanic eruption pours lava all over the valley, completely burying it.
• The original landscape is obliterated—rivers disappear, valleys are gone, and everything is covered by hardened basalt.
• Only after the lava cools and solidifies does erosion resume, but now on a completely new surface, marking the beginning of a fresh erosion cycle.

Example: Deccan Lava Flows (Cretaceous Period, India)

• This happened in India during the Cretaceous period when the Deccan Plateau experienced massive lava flows, covering regions like Chotanagpur Plateau and Vindhyan Uplands.
• This closed the Jurassic cycle and only when the lava cooled and monsoon climate set in did the Tertiary cycle of erosion begin.

So, volcanic eruptions and climatic shifts are like erasing a drawing on a board and starting fresh—a total reset!

B. Interruptions Due to Base Level Changes

Now, imagine a place where a river is trying to reach the ocean. The sea level (base level) determines how much energy the river has to cut through the land. If the sea level rises or falls, the rules of the game change!

How Does This Work?

• Positive base level change (Sea level rise / Land subsidence):
  • If the sea level rises or land subsides, rivers slow down, and deposition (alluviation) increases instead of erosion.
  • This shortens the erosion cycle because sediment fills the valleys faster.
• Negative base level change (Sea level fall / Land upliftment):
  • If the sea level falls or land uplifts, rivers gain more energy and start cutting deeper, leading to rejuvenation.
  • This extends the erosion cycle, making the landscape young again, even if it was mature before!

Conclusion

The cycle of erosion is not a one-way journey; it is a dynamic process influenced by tectonic forces and climatic shifts. Interruptions ensure that no two landscapes evolve in exactly the same way. From the rejuvenated valleys of the Narmada to the ancient, worn-down hills of Appalachia, the Earth’s surface is a testament to the power of these disruptions