The Earth’s surface is sculpted by forces that produce geological features ranging from gentle slopes to dramatic, abrupt drops. Cliffs represent the latter, standing as spectacular, near-vertical rock exposures. These formations occur in diverse environments worldwide, from rugged coastlines pounded by the sea to high mountain ranges shaped by ice and faulting. They are found along rivers, on the edges of plateaus, and even beneath the ocean’s surface. The sheer scale of these rock walls makes them some of the most recognizable landforms on the planet.
Defining the Geological Feature
A cliff is defined as a steep slope of rock or earth material that is nearly vertical or, in some cases, overhanging. Its high angle distinguishes it from a typical steep hill or slope, known geologically as an escarpment. Cliffs maintain this verticality because they are composed of rock highly resistant to breakdown and removal, such as durable sedimentary rocks like sandstone and limestone, or hard igneous rocks like granite and basalt. The elevation difference between the top and the base must be significant relative to the surrounding terrain. Loose rock debris, known as talus or scree, often forms a slope at the base due to gravity and weathering.
Processes of Cliff Creation
The formation of a cliff requires the removal of material, driven by the combined actions of weathering and erosion. Weathering is the breakdown of rock by atmospheric and biological agents. Physical processes, such as the freeze-thaw cycle, pry apart rock fragments when water expands in cracks. Chemical weathering, such as carbonation in limestone, also weakens the rock structure. Erosion is the subsequent transport of this broken-down material by agents like water, wind, or ice.
Many cliffs are created through differential erosion, where softer rock layers are worn away faster than the harder layers above them. This undercutting causes the resistant caprock to eventually collapse under its own weight, leading to the vertical face. In coastal environments, marine erosion is a powerful force, where waves use hydraulic action and abrasion to carve a wave-cut notch at the cliff’s base. The collapse of the unsupported rock above this notch causes the cliff face to retreat inland. Inland cliffs are often formed by fluvial erosion, as rivers cut downward through rock strata, or by glacial ice, which carves massive, steep-sided valleys known as U-shaped valleys.
Major Classifications of Cliffs
Cliffs are categorized based on the dominant environment or geological process that created them, which helps to explain their unique morphology.
Sea Cliffs
Sea Cliffs are the most recognized type, found along coastlines and shaped primarily by the erosive power of ocean waves. Their rate of retreat depends on the rock type; hard rock cliffs, like those made of granite, recede slowly, while soft cliffs, composed of materials like shale or boulder clay, can retreat several meters per year.
Inland Cliffs
Inland Cliffs are separated into categories based on their formative agent, such as fluvial cliffs created by river action or glacial cliffs formed by the movement of ice. Fluvial cliffs, or bluffs, form when a river’s meander erodes one bank while depositing on the other, creating a steep slope.
Fault Scarps
A distinct category is the Fault Scarp, a type of cliff formed directly by tectonic activity. These features result from the vertical movement of Earth’s crust along a geological fault line, leaving one block of land uplifted relative to the other, creating an immediate, non-erosional cliff face.