Topographic Prominence - Wet Prominence and Dry Prominence

Wet Prominence and Dry Prominence

There are two varieties of topographic prominence: wet prominence and dry prominence. Wet prominence is the topographic prominence discussed in this article. Wet prominence assumes that the surface of the earth includes all permanent water, snow, and ice features. Thus, the wet prominence of the highest summit of an ocean island or landmass is always equal to the summit's elevation.

Dry prominence, on the other hand, ignores water, snow, and ice features and assumes that the surface of the earth is defined by the solid bottom of those features. The dry prominence of a summit is equal to the wet prominence of that summit unless the summit is the highest point of a landmass or island, or a summit surrounded by snow or ice. If a summit is completely surrounded by a water, snow, or ice feature, the dry prominence of that summit is equal to the wet prominence plus the depth of the highest col.

The dry prominence of Mount Everest is, by convention, equal to its wet prominence (8848 m) plus the depth of the deepest hydrologic feature (the Challenger Deep at 10,911 m), or 19,761 m. The dry prominence of Mauna Kea is equal to its wet prominence (4205 m) plus the depth of its highest col (about 5125 m), or about 9330 m; this is the world's second greatest dry prominence after Mount Everest. The dry prominence of Aconcagua is equal to its wet prominence (6962 m) plus the depth of the highest col of the Bering Strait (about 50 m), or about 7012 m.

Dry prominence is also useful for measuring submerged seamounts. Submerged summits have both a dry topographic prominence and a topographic isolation.

The following mental exercise may illustrate the meaning of topographic prominence. Imagine you are standing at the top of a mountain peak. Let an imaginary sea level slowly rise to the top of your peak. As the imaginary sea level rises, the mountain will shrink into an ever smaller island until the island disappears at your feet. Now let the imaginary sea level slowly drop. The island will reappear with your peak as its highest point. As the sea level continues to drop, the island will grow and merge with adjacent islands. At some point, unless you are atop Mount Everest, your island will touch another island with a higher summit. This point is called your peak’s key col, and the elevation rise from its key col to your summit is called its topographic prominence.