slopes

Landslides are mass movements of rock, earth, or debris down a slope. They can be initiated by rainfall, snowmelt, changes in water level, erosion by streams, earthquakes, volcanic activity, or by various human activities. Most landslides we hear about are sudden events that can cause all sorts of calamities. But not all landslides are rapid occurrences. There are also slow-moving landslides.

A new study by the University of Potsdam in Germany has found that as urban centers in mountainous regions grow, more people are building homes on steeper slopes prone to slow-moving landslides. Slow-moving landslides can move as little as one millimeter a year and up to as much as three meters per year. Locations with slow-moving landslides can seem safe to settle on; in some cases, the movement itself can be inconspicuous or even completely undetected.

Slow slides can gradually produce damage in houses and other infrastructure and there can also be sudden acceleration from heavy rain or other influences.

The study compiled a new database of nearly 8,000 slow-moving landslides with areas of at least 25 acres located in regions classified as “mountain risk.” Of the landslides documented, 563 are inhabited by hundreds of thousands of people. The densest settlements on slow-moving landslides are in northwestern South America and southeastern Africa.

In all regions of the study, urban center expansion was associated with an increase in exposure to slow-moving landslides. As cities expand in mountainous areas, people are moving into unsafe areas, but poorer populations may have few other options.

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Slow-moving landslides a growing, but ignored, threat to mountain communities

Photo, posted March 4, 2015, courtesy of Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

According to a new study published in the Proceedings of the National Academy of Sciences, more than a third of the farmland in the U.S. Corn Belt has completely lost its carbon-rich topsoil due to erosion. The affected area is nearly 100 million acres and the amount of carbon loss is nearly 2 million tons.

The study, led by scientists at the University of Massachusetts, Amherst, found that the greatest loss of carbon-rich topsoil was on hilltops and ridgelines. This indicates that tillage – the repeated plowing of fields – was the primary cause of the erosion because loosened soils move downslope.

The loss of topsoil has reduced corn and soybean yields in the Midwest by 6%, resulting in a loss of nearly $3 billion a year for farmers. In addition, the loosening of the topsoil increases runoff of sediment and nutrients into nearly waterways, worsening water quality.

Previous studies have shown that no-till farming practices can have a significant impact on reducing erosion. A study published last November found that if farmers shifted entirely to no-till practices, it would reduce soil erosion from U.S. agricultural fields by more than 70%, as well as significantly reducing nutrient and sediment runoff.

No-till farming is the practice of planting crops without tilling the soil. Instead, seeds are planted through the remains of previous crops by planters or drills that cut seed furrows, place the seeds, and close the furrow. Currently less than 15% of farmland in the upper Mississippi River watershed is farmed with no-till practices.

Even partial changes in tilling practices could produce positive results for topsoil retention and for waterways.

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One-Third of Farmland in the U.S. Corn Belt Has Lost Its Topsoil

Photo, posted September 15, 2010, courtesy of the United Soybean Board / Soybean Checkoff via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.