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Topographic Prominence

Topographic Prominence - A New Way of Measuring Mountain Height

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A picture of Mt. Everest.

Mt. Everest has significant topographic prominence.

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We are all familiar with the concept of elevation, the measure of vertical space between sea level and any particular point. Sea level is chosen because ignoring tides and wind-driven waves we can assume that no part of the sea is any higher than any other. Yet this standard has limitations – it completely ignores a mountain's surroundings and offers no indication of the quality of its panorama. It downplays the stunning vista on the summit of Massachusetts' Mt. Greylock yet rewards higher peaks from which almost nothing is visible besides taller neighbors. What an outrage!

A New Perspective - Topographic Prominence

An idea that developed fairly recently is topographic prominence, a quality derived from elevation yet often more useful, particularly for mountaineers. It refers to the height of a summit's peak relative to its surroundings rather than a fixed point. Peaks with high prominences often have impressive summit views even if their elevations are relatively modest. In effect, prominence provides an objective rating system for a subjective quality.

Prominence measures a summit’s vertical distance from the lowest contour line that encircles it and no higher peak. It can also be described as the least vertical distance you would have to descend before beginning the ascent of a something higher. Pretend you are standing on the summit Mt. Katahdin, the highest point in Maine. You would have to go down at least 4,292 feet before you begin to climb a higher mountain. In this situation the higher peak is New Hampshire’s Mt. Madison. In reality, you would probably descend more than 4,292 feet if you walked from Katahdin to Madison, but what’s important is that you could not descend any less. Mt. Katahdin, then, has a prominence of 4,292 feet even though its total elevation above sea level is greater (5,267 feet).

Additional Examples of Topographic Prominence

Consider Mt. Massive, a rounded, 14,421-foot mountain in central Colorado's Sawatch range. Despite its impressive elevation, its prominence is a mere 1,961 feet due to its closeness to the higher peak Mt. Elbert. The highest point that connects these two peaks must be 1,961 feet beneath the summit of Mt. Massive. Massive is thus "prominent" over at least 1,961 vertical feet of its surrounding terrain independent of any higher peak.

Mt. Elbert, at an elevation of 14,440 feet, is Colorado’s highest point above sea level. Despite this title, it is prominent by just 9,073 feet, which is calculated by finding the lowest point along the highest ridge that connects Elbert to its parent peak (the nearest higher peak), California’s Mt. Whitney. The highest point of the lowest contour that encircles Whitney but not its parent peak, volcano Pico De Orizaba, is located in New Mexico at 4,420 feet above sea level. If you take this amount and subtract it from Whitney’s total elevation you will arrive at its prominence of 10,080 feet for that mountain. You can also say that the least amount of vertical distance you would have to traverse if you were to travel from Mt. Whitney to the nearest higher peak is 10,080 feet, equivalent to Whitney’s prominence.

Can Prominence Equal Elevation?

So far we’ve defined a peak’s prominence based on its relation to a higher peak. Then what of Mt. Epomeo, the highest point on the small volcanic island of Ischia? There is no higher point – at least not without crossing the Gulf of Naples into mainland Italy. The most you can possibly descend from its summit would bring you to sea level. Mt. Epemeo typifies the unusual situation where elevation and prominence are identical.

While these island peaks make up the bulk of mountains with equivalent prominence and elevation, there are a handful of others. Mount Everest is the highest point on Earth so it doesn’t have a parent peak. Mt. Aconcagua in Argentina, Mt. Kilomanjaro in Africa, and Vinson Massif in Antarctica also lack parent peaks within their landmasses. All of these mountains have prominences that are equal to their elevations and the view from their summits its pure, unobstructed perfection.

Using Prominence in Mountain Rankings

Prominence also plays a role as a qualifier for “mountain status” and inclusion in lists of high peaks. It is used to determine whether a peak constitutes an independent mountain or a sub-peak of something else. For the Rockies, there is a general rule that a mountain must have at least 300 feet of prominence in order to qualify as a mountain. Otherwise, it is not considered a true mountain and cannot be included in mountain ranking lists regardless of its elevation.

A list of Colorado’s fourteeners (or 14ers, mountains above 14,000 feet in elevation) can be found here. Looking at the list, notice that 300 feet of prominence was used as a cut-off for mountain status, but keep in mind that other locations have different prominence standards. The summits of Wales, due to their modest elevations, require cut-offs that are much lower. Prominence can also be used as a rating system by itself. Here is a list of the most prominent peaks in Europe, ordered by prominence, or “primary factor” as it appears here.

Topographic Prominence is thus a measure of a peak’s height above its surroundings. Useful as an accompaniment to elevation, it provides a more detailed and balanced description of a mountain than can be understood with elevation alone. It can also be used as an alternative to elevation as a method to rank, compare, and define mountains. A great resource for further reading can be found here.

Rob London is a graduate student at the University of Denver. He is enrolled in the Geographic Information Systems certificate program.

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