A scarp is a fundamental geological feature identified as a steep, linear slope or cliff-like structure that breaks the general continuity of the land. Derived from the Italian word scarpa meaning “shoe,” a scarp is essentially a sharp, abrupt change in elevation. Scarps are topographic expressions that reveal the dynamic processes continually reshaping the Earth’s surface, offering insight into the planet’s tectonic activity and long-term erosional history.
Defining the Scarp
A scarp is formally defined as a relatively straight, cliff-like face or slope of considerable linear extent, separating two surfaces that lie at different levels. This landform represents a vertical offset or displacement of the Earth’s crust, marking a distinct boundary between higher and lower terrain. The steep surface of the feature is referred to as the scarp face.
The characteristic linearity of a scarp results from the underlying geological structure that controls its formation. It is a sharp break in the angle of the slope, distinguishing it from a gradual incline. Scarps can range in height from a few centimeters to many hundreds of meters, depending on the scale and age of the geological event that created them.
Formation Mechanisms
Scarps generally form through two distinct geological processes: movement along a fault or differential erosion of rock layers. These two mechanisms result in features with different characteristics, but both create the signature steep slope. The underlying cause determines whether the feature is a product of rapid tectonic forces or slower surficial processes.
Tectonic Scarps
Tectonic scarps, also known as fault scarps, are created directly by seismic activity where one block of the Earth’s crust moves vertically relative to another along a fault plane. During an earthquake, the sudden displacement of the ground surface results in a freshly exposed, steep, step-like offset. The height of the scarp corresponds to the vertical displacement that occurred during one or multiple faulting events.
These features are sharp and geologically young, as the steep face is immediately exposed to weathering and erosion. The dramatic topography of the Teton Range in Wyoming is caused by recent activity on the Teton Fault, creating a prominent fault scarp at the mountain front. Fault scarps are indicators of active seismic zones, as their presence suggests rapid tectonic displacement that outpaces the rate of degradation.
Erosional Scarps
Erosional scarps are formed by the long-term process of differential erosion acting on layered sedimentary rocks. This occurs where alternating layers of hard, resistant rock and softer, less resistant rock are exposed at the surface. Water, wind, and ice erode the softer layers more quickly, undercutting the harder caprock above.
The harder layer eventually breaks away, maintaining a steep face as erosion continues laterally and vertically into the landscape. This process is common in regions with gently tilted rock strata, often resulting in large-scale features that persist over millions of years. Erosional scarps are associated with landforms called cuestas, which have a steep scarp face on one side and a gentle slope on the other.
Key Distinctions and Examples
The terms “scarp” and “escarpment” are frequently used interchangeably, though geologists often use them to denote a difference in scale or origin. A scarp is applied to the steeper, cliff-like slope itself, especially smaller features or those resulting directly from faulting. An escarpment, by contrast, is used for a long, continuous line of cliffs or a margin between two major landforms, often implying a larger-scale erosional feature.
The Great Rift Valley in East Africa offers a significant example of tectonic scarps, where vast blocks of the Earth’s crust have separated. This separation creates vertical drops along the fault lines, exposing the underlying geology and revealing the active rifting process. Vertical displacement in such active regions can involve multiple episodic movements over time.
In contrast, the Niagara Escarpment, which stretches across parts of the United States and Canada, is a classic example of a large-scale erosional feature. This escarpment is characterized by a resistant caprock of dolomite over softer shales and sandstones, which has maintained the steep face as the underlying rock has eroded.