Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers Find Evidence of Geological ‘Facelift’ in the Appalachians

01.02.2013
How does a mountain range maintain its youthful, rugged appearance after 200 million years without tectonic activity? Try a geological facelift – courtesy of the earth’s mantle.

Researchers from North Carolina State University noticed that a portion of the Appalachian Mountains in western North Carolina near the Cullasaja River basin was topographically quite different from its surroundings.

They found two distinct landscapes in the basin: an upper portion with gentle, rounded hills, where the average distance from valley to mountain top was about 500 feet; and a lower portion where the valley bottom to ridgeline elevation difference was 2,500 feet, hills were steep, and there was an abundance of waterfalls. The researchers believed they could use this unique topography to decipher the more recent geologic history of the region.

The Appalachian mountain range was formed between 325 to 260 million years ago by tectonic activity – when tectonic plates underneath the earth’s surface collided and pushed the mountains up. Around 230 million years ago, the Atlantic Ocean basin began to open, and this also affected the regional topography. But geologists knew that there hadn’t been any significant tectonic activity in the region since then.

“Conventional wisdom holds that in the absence of tectonic activity, mountainous terrain gets eroded and beveled down, so the terrain isn’t as dramatic,” says Sean Gallen, NC State graduate student in marine, earth and atmospheric sciences. “When we noticed that this area looked more like younger mountain ranges instead of the older, rounded, rolling topography around it, we wanted to figure out what was going on.”

Gallen and Karl Wegmann, an assistant professor of marine, earth and atmospheric sciences at NC State, decided to look at the waterfalls in the area, because they would have formed as the topography changed. By measuring the rate of erosion for the falls they could extrapolate their age, and therefore calculate how long ago this particular region was “rejuvenated” or lifted up. They found that these particular waterfalls were about 8 million years old, which indicated that the landscape must have been raised up around the same time.

But without tectonic activity, how did the uplift occur? Gallen and Wegmann point to the earth’s mantle as the most likely culprit. “The earth’s outer shell is the crust, but the next layer down – the mantle – is essentially a very viscous fluid,” Wegmann says. “When it’s warm it can well up, pushing the crust up like a big blister. If a heavy portion of the crust underneath the Appalachians ‘broke off,’ so to speak, this area floated upward on top of the blister. In this case, our best hypothesis is that mantle dynamics rejuvenated the landscape.”

The researchers’ findings appear in Geological Society of America Today. Del Bohnenstiehl, NC State associate professor of marine, earth and atmospheric sciences, contributed to the work.

Note to editors: Abstract follows.

“Miocene rejuvenation of topographic relief in the southern Appalachians”

Authors: Sean F. Gallen, Karl W. Wegmann, and DelWayne R. Bohnenstiehl, North Carolina State University

Published: Geological Society of America Today

Abstract:
Conventional wisdom holds that the southern Appalachian Mountains have not experienced a significant phase of tectonic forcing for > 200 m.y.; yet, they share many characteristics with tectonically active settings, including locally high topographic relief, steep slopes, incised river gorges and frequent mass-wasting events. Two competing hypotheses are commonly used to explain their modern topographic expression. One suggests that relief is largely controlled by variable lithologic resistance to weathering and that their modern form has long persisted in a dynamic equilibrium. The second postulates that their relief is a product of recent rejuvenation, driven either by climate change or the epeirogenic uplift of the land surface driven by mantle forcing. Within portions of the Cullasaja River Basin of the southern Appalachians, we show that relief has increased by > 150% since the Miocene. Evident within the basin are a set of retreating knickpoints that delineate a rugged actively incising landscape from lower-relief relict topography. Constraints on the timing of knickpoint entry into the basin suggest that the process of landscape rejuvenation began well prior to the late Cenozoic (

Tracey Peake | EurekAlert!
Further information:
http://www.ncsu.edu

More articles from Earth Sciences:

nachricht First Eurasians left Africa up to 130,000 years ago
22.04.2014 | Eberhard Karls Universität Tübingen

nachricht Lab researcher discovers the green in Greenland
18.04.2014 | Lawrence Livermore National Laboratory

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Anzeige

Anzeige

Event News

Siemens at the 2014 UIC ERTMS World Conference in Istanbul

01.04.2014 | Event News

AERA Meeting: German and US-American educational researchers in dialogue

28.03.2014 | Event News

WHS Regional Meeting: International experts address health challenges in Latin America

24.03.2014 | Event News

 
Latest News

High-Calorie and Low-Nutrient Foods in Kids' TV

23.04.2014 | Studies and Analyses

A three dimensional biodegradable hydrogel for treating gum diseases

23.04.2014 | Materials Sciences

Malaysian and Taiwanese researchers make major advances in dye sensitized solar cells

23.04.2014 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>