Taxonomy term

geomorphology

Stronger monsoon drove ancient Indus civilization into the hills

Roughly 4,000 years ago, the Indus River Valley was home to the advanced and thriving Harappa culture. But by 1800 B.C., the civilization’s sophisticated cities along the river, which drains into the Arabian Sea on the coast of what is now Pakistan, were abandoned for smaller villages in the Himalayan foothills. A new study suggests that widespread changes in the Indian winter monsoon may have resulted in flooding that forced people to resettle farther from the Indus.

07 Mar 2019

Humans accidentally created new rivers in Europe

Meandering rivers that flow through and transport sediment to deltas often split off from their main courses and flow in different directions. This process, called avulsion, happens naturally when a river overflows its banks and the floodwaters carve out a new course for the river to follow. But humans can also trigger avulsions by changing the shape of the landscape, and in a new study, scientists report that people have been doing this for a very long time.

15 Feb 2019

Mighty Mekong cut by monsoon, not tectonics

The rivers draining the Tibetan Plateau are some of the largest, longest and most deeply incised waterways in the world. For decades, most geologists assumed that these river canyons were cut as the plateau was uplifted following the initial collision of the Indian subcontinent with Asia. However, recent studies have found that the plateau was already elevated by 40 million years ago — roughly 20 million years before the deep canyons formed. 

06 Feb 2019

Spawning salmon engineer landscapes

All animals depend on their ecosystems for habitat. And, in turn, many animals impact their ecosystems by engineering the landscape to suit their needs. Beavers provide an iconic example of ecosystem engineering when they build dams, which influence streams and wetlands. The engineering efforts of salmon, meanwhile, can even shape the bedrock of the watersheds in which they live, according to a recent study that modeled the evolution of those watersheds over several million years.

23 Feb 2018

Searching for the ancestors of meandering rivers

It might be difficult to imagine Earth devoid of vegetation, but for billions of years the sun shone, winds blew and rivers flowed on a planet without any plants.

21 Jun 2016

Due diligence in river incision data

As great equalizers of topography, rivers and streams whittle down landscapes by alternately scouring away broad flat swaths of sediment and rock, and incising deeply through them. If a landscape — a mountain range, for example — is being uplifted by tectonic forces, this whittling occurs even faster. River incision rates in particular are thus often used to infer past rates of rock uplift. But determining incision rates themselves is not clear-cut. In a new study in Geology, scientists look at one complicating factor in such calculations, what the authors call the “unappreciated effects of streambed elevation variability” on measuring river incision rates.
 
21 Nov 2015

Wormholes may limit landslides

When Emma Harrison, a graduate student at the University of Pennsylvania, began digging trenches in the Luquillos Mountains of Puerto Rico to study how the soil mantle responds to rapid changes in erosion, she couldn’t help but notice that the thick soils were chock-full of wriggling worms. Intrigued by the worms’ abundance and prodigious activity at her field site, Harrison wondered whether their presence could be influencing weathering and erosion in the Luquillos. 

09 Nov 2015

Sculpting the Alps

Mountains typically get steeper the higher you climb. The European Alps are an exception: Beginning at altitudes between about 1,500 and 2,000 meters, most slopes in the range tend to become less steep with increased elevation. This is largely caused by ancient glaciers, which scoured away much of the rock from the tops of the Alps. However, the steepness of alpine slopes also decreases in areas beyond the reach of glaciers, although the reasons why have remained elusive. New research is revealing how tectonic and fluvial forces have also helped shape the Alps’ unusual topography.
 
04 Oct 2015

Sediment load shapes rivers

The amount of sediment carried in meandering rivers influences how quickly the bends in those rivers migrate back and forth, according to recent research in Nature Geoscience addressing a longstanding question regarding river evolution. Meanders form when flowing water erodes one riverbank while simultaneously depositing sediment on the opposite bank, gradually creating more and more pronounced U-shaped bends. Sometimes, the rivers cut new channels across the narrow necks of such bends, isolating the abandoned meanders to form distinctive oxbow lakes. 
 
04 Jul 2015

Pre-settlement erosion rates illuminated

Humans are one of the most powerful erosive agents on Earth, moving copious amounts of sediment to and fro, mainly through agriculture and development. But quantifying how much we actually move — often a necessary step for developing sustainable land management practices — hinges on determining erosion rates in an area before humans intervened. A new study using surface exposure dating to estimate pre-colonial erosion rates in the southeastern U.S. has now clarified the natural background rate in more detail than ever before, revealing the dramatic human impact on the regional landscape.

 
31 May 2015

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