The loess plateau has loose soil, so why can we build caves?

Loess is loose and easy to be eroded when washed by water, but it is firm after drying and compaction. Today, there are still many places that use compacted clods as walls to build houses. The cave is selected on a thick facade, which is relatively solid due to long-term gravity. There is no need to cover the top of the cave, because the thickness of loess at the top is still quite large. In addition, if the top of the cave is relatively flat, the erosion rate is also very slow!