The difference between a mountain and a hill appears simple, relating to size and steepness. However, this distinction is not universally standardized across geography or geology. While both are natural landforms that rise above the surrounding terrain, the exact point where a hill becomes a mountain is often a matter of local convention rather than a single scientific definition. Many organizations have adopted differing criteria, meaning the classification of any given peak depends on local standards.
Height as the Defining Factor
The most common way to distinguish between the two landforms is by absolute elevation. Historically, a feature exceeding 1,000 feet (about 305 meters) above sea level was often considered a mountain, especially in early American cartography. Today, a widely referenced informal global threshold is 2,000 feet (approximately 610 meters). Landforms falling below this height are typically labeled as hills, while those exceeding it are classified as mountains.
The United Kingdom, for example, traditionally uses the 2,000-foot mark to define a mountain. The UK government’s Countryside and Rights of Way Act 2000 used a similar elevation of 600 meters (1,969 feet) to define mountainous areas for public access legislation. Conversely, the United States Geological Survey does not maintain any official height-based rule for distinguishing hills from mountains. These differing national standards demonstrate that height is a flexible metric, reflecting a local perception of a significant vertical rise.
Slope, Prominence, and Relief
While absolute height offers a simple metric, the shape and context of a landform are often more definitive in its classification. Mountains generally possess a steeper slope, which is the angle of ascent from the base to the summit. Hills, in contrast, are characterized by gentle, rounded gradients, making them easier to ascend.
Topographic prominence quantifies a peak’s independence from higher landforms. It is the vertical distance between a summit and the lowest point on the ridge connecting it to any higher peak, known as the key col. Mountains typically exhibit greater prominence than hills, meaning they rise more distinctly from the surrounding terrain. This difference in local relief—the height difference between the summit and its immediate base—often gives mountains their rugged, sharp appearance compared to the smoother profile of a hill.
Differences in Geological Origin
The forces that create these landforms offer another scientific distinction. Mountains are generally the result of intense geological processes acting over millions of years. This includes orogenesis, where tectonic plate collisions cause massive folding and faulting of the Earth’s crust, leading to large-scale uplift. Volcanism, involving the accumulation of erupted material, is also a mountain-building process.
Hills are often the product of less dramatic geological activity or the long-term effects of surface processes. Many hills are formed through extensive erosion and weathering, which gradually break down and round the peaks of ancient, larger mountain ranges. Other hills may result from localized uplift or the deposition of glacial till and sediment. Geologists recognize that mountains represent the power of crustal forces while hills often represent the remnants of those forces shaped by time.
Regional Variability in Terminology
Ultimately, the distinction between a hill and a mountain is complicated by local tradition and geographical context. Names given to landforms frequently predate modern scientific measurement, leading to inconsistencies. For example, the Black Hills in South Dakota are named as hills but contain peaks rising over 7,000 feet (2,100 meters) above sea level, making them taller than many features called mountains elsewhere. Conversely, some peaks in Scotland meet the 2,000-foot elevation criterion for a mountain but are still commonly referred to as “hills,” such as the Cuillin Hills. In the United States, what is locally known as a mountain in the flatter Midwest may be considered merely a large hill in the more rugged Western states. This regional variation demonstrates that the label applied to a landform often reflects its perceived significance relative to the immediate surroundings.