Tectonic stress feedback loop explains U-shaped glacial valleys

Mar 13, 2014

In the shadow of the Matterhorn, the broad form of the Matter Valley—like so many throughout the Alps—is interrupted by a deep U-shaped glacial trough. Carved into a landscape reflecting millennia of tectonic uplift and river erosion, growing evidence suggests the 100-meter-deep (328-foot-deep) U-shaped groove was produced shortly after a shift toward major cycles of Alpine glaciation almost a million years ago. Subsequent glaciations may have therefore had little effect on the landscape.

The Matter Valley and other Alpine valleys' U-shaped incisions were carved by glaciers, but the power of ice alone is not enough to explain the location or apparent timing of the troughs' formation. If glacial forces were the sole driver, the valleys would be three times as wide, and would grow consistently deeper during each period of glaciation.

In previous research, Leith et al. proposed a new mechanism to explain characteristic fracturing in beneath glaciers, and in the present study, they find that this may have driven a one-off period of amplified glacial erosion in the Matter Valley. In the authors' model, bedrock stresses left over from mountain formation are focused beneath the surface at the center of V-shaped valleys. Early periods of glacial erosion carved through the upper bedrock layers, exposing the stressed rock. Thinning glaciers allowed the stressed bedrock to fracture, and broken rock was easily carried away by flowing ice. As the valleys deepened, stresses were further focused at the valley floor, creating more fractured bedrock and making it easier for the glaciers to dig in. Their model suggests that bedrock stresses were relieved once the valley glacier retreated, and that subsequent periods of glaciation may not have encountered similar conditions.

The authors' model shows how glacial erosion promotes the formation of U-shaped valleys of a particular size and with a particular frequency, results which align with their observations in the Matter Valley.

Explore further: Scientists discover giant trench under Antarctic Ice

More information: Subglacial extensional fracture development and implications for Alpine valley evolution, Journal of Geophysical Research-Earth Surface, DOI: 10.1002/2012JF002691, 2013 http://onlinelibrary.wiley.com/doi/10.1002/2012JF002691/abstract

add to favorites email to friend print save as pdf

Related Stories

Measuring the forces generated by erosive debris flows

Apr 16, 2013

Like water flows, debris flows can carve out steep valleys and change landscapes. By studying the mechanics of bedrock incision caused by flowing debris, scientists are better able to understand patterns and rates of landscape ...

Mountain erosion accelerates under a cooling climate

Dec 19, 2013

The Earth's continental topography reflects the balance between tectonics, climate, and their interaction through erosion. However, understanding the impact of individual factors on Earth's topography remains ...

Alberta's hidden valleys offer both resources and danger

Nov 12, 2009

Alberta is crisscrossed with hidden glacial valleys that hold both resource treasures and potential danger. University of Alberta researcher Doug Schmitt discovered a 300 metre deep, valley hidden beneath the surface of the ...

Recommended for you

Scientists make strides in tsunami warning since 2004

Dec 19, 2014

The 2004 tsunami led to greater global cooperation and improved techniques for detecting waves that could reach faraway shores, even though scientists still cannot predict when an earthquake will strike.

Trade winds ventilate the tropical oceans

Dec 19, 2014

Long-term observations indicate that the oxygen minimum zones in the tropical oceans have expanded in recent decades. The reason is still unknown. Now scientists at the GEOMAR Helmholtz Centre for Ocean Research ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.