What is the term for a plane along which rock masses slide horizontally past one another?

• A. Transform Fault
• B. Conduction
• C. Asthenosphere
• D. Buoyancy

Answer: (A)

In plate tectonics, horizontal sliding of rock masses along a plane is described by a transform fault. This is a fault plane where two tectonic plates move side by side, producing shear movement and earthquakes with little vertical displacement. It’s the opposite of spreading or subduction, where rocks move apart or one plate sinks beneath another. The other terms don't describe this horizontal shear boundary: conduction is heat transfer, the asthenosphere is the deformable mantle layer beneath the lithosphere, and buoyancy is the upward force that helps objects float. A well-known example is the San Andreas Fault, where two plates slide past each other.