GK Gilbert’s Geomorphic Theory
Grove Karl Gilbert, an American geologist looked at landscapes not as fixed entities but as living, breathing systems shaped by an ongoing battle between forces. His theory of dynamic equilibrium explains how landforms evolve—not through a rigid cycle, but through a constant balancing act between driving forces and resisting forces.
The Battle of Two Forces: Variability vs. Uniformity
Gilbert proposed that every landscape is the result of two competing tendencies:
- tendency towards variability (when driving force exceeds resisting force) and
- tendency towards uniformity (when driving force equals resisting force)”.
Let’s understand these two forces:
👉 Driving Force – The energy that tries to change the landform (like tectonic uplift, volcanic eruptions, flowing water, or wind).
👉 Resisting Force – The strength of the landscape that tries to resist change (like rock strength, soil composition, and gravitational pull).
These two forces are constantly at work. Sometimes, one dominates over the other, and sometimes, they reach a balance. This is the principle of least work—where landforms adjust themselves in such a way that the total sum of these forces becomes zero.
So, in short:
Gilbert’s concept of equilibrium, also known as the principle of least force, envisages that in the final form of any functional system “the sum of the forces acting on the final form equaled zero“.
The Formation of Laccoliths: A Volcanic Experiment in Equilibrium
To better illustrate his theory, Gilbert studied laccoliths—bulbous, dome-like rock formations formed by volcanic activity. Imagine a scenario deep beneath the Earth’s crust:
1️⃣ Magma begins to rise due to high pressure beneath the surface. This is the driving force, pushing upwards.
2️⃣ However, the overlying rock layers exert a downward force, resisting the magma’s movement. This is the resisting force(overlying pressure of super-incumbent load.
3️⃣ If the driving force of magma is greater, it continues to push upward, slowly lifting the overlying layers.
4️⃣ But if the resisting force becomes equal to the magma’s force, the uplift stops, and a laccolith is formed—a dome-shaped structure of hardened magma trapped beneath the surface.
Gilbert’s concept of equilibrium explains why laccoliths don’t keep growing indefinitely—growth stops when the forces acting on them cancel out.
This principle doesn’t just apply to laccoliths—it explains why mountains stop rising, why rivers stop deepening, and why landscapes stabilize over time.
