Fourteeners
JB: This is Earth and Sky. Hamish Gowan, who grew up in Colorado, asked about the more than 50 mountains there known as “fourteeners.”
DB: Each peaks at more than 14,000 feet – more than 4,000 meters. Hamish writes, “Why do they all level out at the same height? Why couldn’t we have just one fifteen or sixteener?”
JB: Hamish, mountains in Colorado aren’t unique in this way. Ridges in the Appalachians also have what are called “accordant summits.” The Colorado fourteeners all lie within a circle having a radius of about 200 kilometers – or 120 miles. With the exception of Pikes Peak and Longs Peak, they’re all in or near Colorado’s “mineral belt” – where most mining in the state took place – or on the flanks of what’s called the Rio Grande rift. The highest and most numerous Colorado fourteeners lie near the intersection of these two geologic features.
DB: Scientists disagree on the details of the process that carried these great mountains upward for the past 70 to 80 million years. The mountains are different rock types, but because they’re near each other, all were subject to the same forces of uplift – and the same forces of erosion or weathering. So, Hamish, the simple answer to your question is that the Colorado fourteeners are all about the same elevation because they share a common history.
JB: More details at earthsky.org. Thanks to the U.S> Forest Service and the National Fish and Wildlife Foundation. We’re Block and Byrd for Earth and Sky.
Links:
““The secret of the Colorado 14ers” by Jack Reed”:http://www.cmc.org/cmc/tnt/956/whycolo14ers.htm
Author’s Notes:
Dr. Eleanora I. Robbins, of the Dept. of Geological Sciences at San Diego State University, added:
The last major uplift of the region occurred 85 million years ago (the Laramide orogeny). This was followed in time by intense rainfall, intense erosion, glaciation, and erosion. The features that are now mountains are, in some places, remnants of all these processes. Earthquakes tell us that uplift is continuing, as is erosion. This geologic history tell me that the mountains have had the same general history for the past 85 million years. So my guess is that they are the same general elevation because of their shared history.
Dr. Rudy Slingerland of the Department of Geosciences at Penn State University added:
There are two possible explanations: 1) A previously low-relief landscape has been uplifted sometime in the Tertiary, and due to the renewed erosion created by the increased elevation, most of the block of uplifted rock underlying Colorado has been removed, leaving just these remnants of peaks all at about the same elevation; 2) the landscape is everywhere in dynamic equilibrium such that the rock everywhere is being eroded at just the rate of rock uplift, regardless of their hardness. Let’s say bedrock erosion rate is proportional to local slope (or maybe relief) of the land. We also can assume that harder rocks require steeper slopes to erode at the same rate as softer rocks. Then the peaks continue to move upwards relative to the valley floors until the relief is enough to create steep enough slopes to cause landsliding to erode them at the rate of rock uplift, and they stop growing. If the relief around granite peaks can be made greater than around sedimentary peaks, then their upward growth will be arrested at the same elevation.
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The following people were interviewed for today’s program. Our thanks to:
Rudy Slingerland
Department of Geosciences
Penn State University
Eleanora I. Robbins, Ph.D.
San Diego State University
Dept. Geological Sciences
Additional Teacher Resources
Colorado Fourteeners Initiative: 14ers.org
The Colorado Rockies are part of the North American Cordillera which stretches from Alaska through western Canada and the United States into northern Mexico. The centerpieces of this dramatic uplift are the 54 peaks over 14,000 feet, or “fourteeners” as they are affectionately referred to by climbers. Colorado’s fourteeners now see nearly 500,000 people each year, this increased recreational use has seriously impacted many peaks and their alpine basins. This site is home to the Colorado Fourteeners Initiative which is a partnership among nonprofit organizations and public agencies to protect and preserve the natural integrity of Colorado’s Fourteeners. The site contains information on several aspects of Colorado’s fourteeners and links to various sites with more information.
Hoffmeyer.com: Fourteener Pictures and Photography
This site provides great photographic imagery of various “fourteeners” in Colorado’s Rocky Mountains.
14ers.com: Colorado Fourteeners and High Peaks
This site contains an abundant amount of random information on Colorado’s fourteeners. Information ranges from climbing routes, photos, and maps, to weather, wildlife and alpine ecosystems.
