Eroded loess terrain.
The loess plateau consists of a thick layer of wind-blown deposit,
several hundred meters deep, formed during the last
ice age when precipitation was nearly absent.
Before water erosion started to take its toll,
it was a flat land as shown here on the top picture.
Erosion proceeds when a slight slope in the terrain is created
channeling running water to scour into the soil, and
magnifies as the gradient increases, so much so that
sharp drops at the edges of the flat ground are formed,
which gradually converge to reduce the flat top to ridges
(middle picture), and then to mounds (bottom picture).
The flat form is called yuan
The ridge form is called liang
The mound is called mao
Erosion further reduces mounds to take
the shape of stalagmites
Picture source: YRCC, Huanghe Feng,
Yellow River Pub House, 1996.
