Yangling (ᬉ)
Just west of Xi'an in Shaanxi is the relatively new town of Yangling. It was our second stop, where we visited the Institute of Soil and Water Conservation to learn more about the Loess Plateau in particular before continuing on to see the region ourselves. The Institute boasts the nation's highest concentration of specialists from a variety of fields related to desertification, though much of the research there is focused on the Loess Plateau.
Loess is formed when glacial activity grinds rocks into powder; the light, powdery loess is loosely structured and highly susceptible to wind erosion, thus the Loess Plateau is the result of ages of loess-bearing northwesterly winds funneled into western China through corridors formed by numerous mountain ranges.
China's Loess Plateau spans 367,000 sq km (comprising 9% of "three norths" area I mentioned earlier). Loess covers 240,000 sq km of that, forming a layer that is on average about 100 m thick, or nearly 200 m in some places.
Unfortunately, human activity has removed much of the natural vegetation, paving the way for the most serious wind and water erosion in the world. We saw (and you will see) some pretty amazing vistas complete with deep gullies as far as you can see.
More than 10,000 tons of soil is eroded from every square kilometer of the Loess Plateau each year, equivalent to losing 1 cm of the land surface.
Of course, all that soil has to go somewhere. Every year 1.6 billion tons of mud and sand rush through the Yellow River's Sanmen Gorge, causing an annual buildup of 400 million cu m of sediment downstream and raising the riverbed by 10 cm per year. In some downstream areas of the river, the riverbed is now 10 meters above the ground.
At the Institute, we met with the director and other head scientists. They briefed us on the overall situation and various prevention methods, methods which we saw put into practice during our later travels. Frequently used techniques include terracing; "fish-scale pits," which are mini-terraces that accommodate just one tree each on a mountain slope; aerial seeding of bushes and grass; reforestation using pine, poplar, cypress, and locust trees where appropriate; and sediment dams to catch eroding soil and reclaim new land for planting trees or crops (usually the latter).
Diversion: For lunch one of the scientists took us to have his favorite: zhanshui noodles (ÅÙ¤ôÄÑ), or "noodles dipped in water." The name may not sound very appetizing, but they are a great Shaanxi speciality. You actually order by the noodle (as in "I would like 2 noodles"), because each 1-in wide noodle noodle is a meter long! The noodles come in a large water-filled basin placed at the center of the table, and each person edges their own bowl, filled with a spicy broth, over near the larger one and gradually pulls one noodle into their bowl (because that's all that will fit at one time). Each noodle is 100 grams, so two noodles makes a meal.
Within the Institute is the State Key Lab of Soil Erosion and Dryland Farming on the Loess Plateau. There we met the lab director and other scientists, after which we saw a demonstration of their Precipitation Lab.
In the 1,200 sq m facility, an adjustable amount of rain (up to 200 mm/hr) falls on a model of a tiny loess gully. In a somewhat amusing touch, the rain was accompanied by a soundtrack which featured sounds of thunder, timed to match sudden flashes of light... (In this picture I'm actually standing around the middle of the facility; behind me is another area where they can elevate and tilt the ground to simulate different slopes)
The lab is an especially effective tool for measuring soil runoff when compared to the alternative: waiting for it to rain.
Of course there needs to be something to be washed away in the experiments. Just outside the lab were women crushing earth and tossing it through screens to create fine loess soil.
Here you can see the building exterior, along with many piles of dirt representing different stages of the soil preparation process.
That's the extent of our time in Yangling. We were only there for one full day, but a very full day it was.