Loess in west Zhengzhou

I decided to go somewhere a little different in the city, so on Golden Week, I took the subway out to the civic centre.

Correction: I took the subway to the station that was called Civic Centre. It seemed reasonable at the time to assume the civic centre was there. Since it was a national holiday, I thought it possible that there would be some kind of public event in the space.

The subway system was built very rapidly over the past few years, and is in the midst of an enormous expansion. The subway appears to be built to support the growth model designed by the local urban planners, so that there are portions of it built through areas that are as yet undeveloped.

Such as the 'Civic Centre' station.

Inside the station was a map of the surrounding area. There were three exits, and the third exit appeared (from the map) to be near an amphitheatre, with a winding path through a forest leading to the main road. This was the exit I chose. But when I reached the surface, all that was there was a chewed up field, with a couple of collapsing buildings with a farming family squatting inside. Nearby, a dirt track led to a dilapidated village.

In the distance were several high-rise apartments under construction. So my conclusion is that this area will host the civic centre one day. But not quite yet.
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South and a little east of the civic centre is a broad ravine with steep sides. Near the subway line there is no easy access, but as one approaches Zhongyuan Road, the ravine becomes a park, and there are a number of easy access points. This park is called Xiliuhugongyuan, or West Six Lake Park (it isn't clear to me if this means there are six lakes, or it refers to lake number six).

 

Zhongyuan Bridge crossing the ravine

Given the density of population and commerce, Zhongyuan Rd. looks like a better choice for the subway than where it actually is. But then it would have to cross this bridge, which isn't strong enough.

What struck me is the thick accumulations of loess that are exposed at the sides of the park.

The cliffs range from about 5-10 m high, and consist of nearly vertical, fractured faces of silt. Presumably, they resulted from fracturing and successive block failures from the loess faces

When the loess faces collapse, they break into blocks, which themselves 
may further break down over time.

Henan province mainly lies within the great loess plain of China, where loess covers over 630 000 sq km of central China. Loess is composed of windblown silt particles in central China, but is coarser in the west, where it consists of windblown sand. In places along Huang He, the loess terraces rise above the river terrace level by up to 100 m. So the terraces in western Zhengzhou are not spectacular, but they are the only place within the city where I have seen them.

 

Fractures in the unconsolidated loess in Xiliuhugongyuan. 

Loess tends to be occur in dry climates, as moisture encourages plant growth which will bind the sediment together and prevent it from being transported by wind. Central China is fairly dry most of the year, with annual evaporation exceeding precipitation (Derbyshire, 1998). The majority of rain falls from July to September (it lasted well into October this year), and up to 40% of annual rainfall can happen in one day (which I can attest to, having experienced such days twice). 

Artisanal gold mining on the Loess Plateau (updated)

On the bullet train the other day, I caught a glimpse of an artisanal mining operation. I snapped several pictures of it as it flew past--not great pictures, as it is hard to capture something so close to the train when you are whipping by at 300 km/h.

I didn't know for sure that it was a gold mining operation, but there aren't too many other kinds of artisanal operations. However, this paper (pdf) confirms that artisanal gold mining is common in the Loess Plateau, at least near the border between Shaanxi and Henan provinces, which the route map confirms as the location of these photos.

The crew are just left of centre in this picture. They appear to be sucking up loess interbedded with gravels from the old river bed.

(Update: Now that I look more carefully, I think the concentrator has to be in that shack near the top of this photo. It makes more sense looking at its position relative to the tailings.)

"Tailings" pile (discarded fines from gravity recovery or just screening) of loess, which is composed of wind-borne silt-sized particles.

Gravel beds in the river channel--this river flows north, feeding the Yellow River. There are gold mines upstream on the river, according to the report in the above link. The equipment at the bottom is probably a concentrator, but the image isn't very clear.

Looks like there's been a lot of work down here too. All these photos overlap to an extent, but in some of them I am looking forward and in others I am looking back, so they are not easy to stitch together.

Xi'an is flat, yes

Xi'an sits on the great loess plateau of China and is mostly pretty flat. I've seen loess before--mainly in Alaska, but that is nothing compared to the loess plateau here. Criss-crossing it by high-speed train in the past week has been a revelation.

Loess plain near Luo Yang

Loess has been a long-time interest of mine, as it is the "medium" which records the variations of the Himalayan monsoon strength, which I have used to look at the dynamics of Neogene climate variations.

While touring around Xi'an, one local told me that the area was so flat, every time you see a mound or hill, it always turns out to be somebody's tomb . . .

. . . like this one.

Like all cities in China, Xi'an is growing monstrously. The photo below can't capture the scale of the construction, but the area covered by this new apartment development must have covered a square mile, composed of dozens of towers.

What kind of mound will they leave in the future, I wonder?