Tensional Forces

Imagine you are pulling apart a chocolate bar slowly with both hands. At first, tiny cracks appear, and then—snap!—it breaks along a jagged line. Now, replace the chocolate with the Earth’s crust, and what you have just witnessed is a process called crustal fracture.

Deep within the Earth, tremendous forces are always at play, shaping the land we live on. Among these, tensional forces play a key role in pulling apart large sections of the crust, creating fractures, faults, and even reshaping entire landscapes over millions of years.

Crustal Fracture

The Earth’s crust is not a single unbroken shell; instead, it’s made of large rock masses that are continuously stressed by internal forces. When these forces pull apart (tensional forces) or push together (compressional forces) beyond the rock’s ability to bend, something dramatic happens—the crust breaks.

This breaking and displacement of rock along a plane is called a crustal fracture.

• If there is no significant movement along the break, it is simply a fracture or a joint.
• If the rocks actually move along the fracture, it is called a fault.

Faults and Their Types

When the crustal rocks are displaced, due to tensional movement caused by the Endogenetic forces along a plane is called fault & that plane is called fault plane.

These movements define the different types of faults.

1. Normal Fault

This occurs when tensional forces stretch the crust apart, causing one block of rock to drop downward relative to the other.

Effect: The area between the fault lines extends (becomes wider).

📍 Example: The Great Rift Valley in Africa is a classic case of a normal fault where the land is literally being pulled apart.

2. Reverse Fault

Here, if you see at the figure it seems compressional forces push two blocks towards each other, forcing one to rise over the other.

🚨 But wait! Shouldn’t compression create folds instead of faults?

Good question! Normally, compression bends rock layers into folds, but if the rocks are already fractured, they cannot bend anymore. Instead, one block thrusts over the other, creating a reverse fault.

Effect: The land shortens and becomes more compact.

📍 Example: The Himalayas were formed due to massive reverse faulting as the Indian Plate pushed into the Eurasian Plate.

3. Strike-Slip Fault (Lateral Fault)

Now, imagine two people walking side by side, but suddenly one moves ahead while the other lags behind. This sideways displacement is what happens in a strike-slip fault.

Here, the rock blocks move horizontally past each other instead of moving up or down.

Depending on the direction of movement, these faults can be:

• Left-lateral (Sinistral): If the block on the far side moves to the left.

• Right-lateral (Dextral): If the block on the far side moves to the right.

Real-World Analogy: Imagine placing your hands together and rubbing them in opposite directions—your hands remain level, but they slide past each other.

📍 Example: The San Andreas Fault in California, which is responsible for many earthquakes in the region, is a classic strike-slip fault.

Difference between compression and tensional Forces:

As we have already studied that in plate tectonics, forces acting on the Earth’s crust determine the formation of various landforms and the two of the most fundamental types of stress are compressional forces and tensional forces. These operate in opposite directions and lead to distinct geological features and processes. Let’s see the distinction between the two:

🔄 1. Basic Definition

Aspect	Compressional Forces	Tensional Forces
Meaning	Forces that push rocks towards each other	Forces that pull rocks away from each other
Direction of Force	Acting towards the center from both sides	Acting outwards in opposite directions

🗻 2. Effect on Earth’s Crust

Aspect	Compressional Forces	Tensional Forces
Crustal Response	Crust is shortened and thickened	Crust is stretched and thinned
Deformation Type	Leads to folding, faulting, and crustal uplift	Leads to fracturing, normal faulting, and crustal subsidence

🏔️ 3. Landforms Created

Aspect	Compressional Forces	Tensional Forces
Major Landforms	– Fold Mountains (e.g., Himalayas) – Reverse and Thrust Faults – Anticlines and Synclines	– Block Mountains (Horst) and Rift Valleys (Graben) – Fault Scarps – Linear valleys
Examples	Himalayas (India), Andes (South America), Alps (Europe)	East African Rift Valley, Rhine Rift Valley, Basin and Range Region (USA)

🧭 4. Plate Tectonic Setting

Aspect	Compressional Forces	Tensional Forces
Tectonic Plate Boundary	Convergent Boundaries (plates moving toward each other)	Divergent Boundaries (plates moving apart)
Process Involved	Subduction, Continental Collision	Sea-Floor Spreading, Rift Formation

📊 5. Associated Fault Types

Aspect	Compressional Forces	Tensional Forces
Type of Fault	Reverse Fault, Thrust Fault	Normal Fault
Stress Type	Compressional Stress	Tensional Stress

Let me elaborate this point a bit:

Crustal Deformation: Force Type vs. Resulting Landform

Force Type	Direction of Stress	Primary Deformation	Outcome if Rock is…
Compressional	➡️⬅️ Pushing together	Folding (if ductile)	Bends into folds like anticlines & synclines
		Faulting (if brittle)	Reverse/Thrust faults if rocks can’t bend
Tensional	⬅️➡️ Pulling apart	Fracturing & Faulting	Normal faults; crust stretches and fractures

🧱 Compression ➡️ Folding or Faulting?

• If rocks are ductile (plastic-like): They bend, forming folds.
• If rocks are brittle or already fractured: They break, forming reverse faults.

🔧 Tension ➡️ Fracturing

• Pulls crust apart → fractures → normal faults.
• Typical in divergent boundaries, where new crust is created.

📌 Summary in Simple Terms:

Compressional forces act like a vice, squeezing the Earth’s crust from both sides and forming mountains and folds.

Tensional forces act like a pulling rope, stretching the crust and causing it to break and sink, forming rifts and valleys.