Two quakes turn hills into deadly cascades of mud

The photos of the landslides show large amounts of soil and clay, which wouldn't happen if there were only one foot of soil on solid rock. I doubt you'd get a bridge being washed away that cleanly had it been anchored to solid rock.

Thin soil on solid rock is quite common in Ireland and the Scottish Highlands. You get mostly bare slopes with grass and heather, and not much else. Trees do not grow. The slopes in Kyushu were covered in trees, mostly planted sugis.

I know little about this subject, but isn't water a major factor in landslides? Mud is soil mixed with a lot of water. Planting the right sort of vegetation would help, and I'd have thought that, if possible, channellng of water away from areas of soil - normally on an incline - which could potentially liquefy and slide down onto areas of human habitation or activity might help? Only trouble is that there are thousands of locations around the country which must be at risk. Travelling extensively around Japan, I've seen many, many examples of poor land and resource management. Those who suffer tend to be people living in the smaller rural and mountain communities. The problems Japan has to deal with as a result of its geology/topology Japan have been compounded by successive corrupt governments and misguided, ineffective policies.

Both gogogo and klausdorth, As a resident of Kyushu, I can tell you both that the problem is that there is very little topsoil here at least in the more mountainous areas. At my own house I can only dig about a foot deep before I am hitting solid rock. Deep rooted trees would not help in these situations nor it this a man made problem. It is simple geology.

I had a look on Google Earth and the slope that failed above the Aso Ohashi bridge isn't actually that steep, even at the top. It will have been the angle, but it looked much steeper on some of the tv images.

I'm not a geologist, but perhaps there was a weak layer or a weak interface between different layers of subsoil.

About quakes, there are not very much that we can do but I am wondering why people are allowed to build house on what seems to be pretty easy to identify as potentially dangerous areas of "landslide, hills and mud" combined factors.

Ever since the earthquake/tsunami that occurred in 2011, the nature of earthquakes have changed in Japan. Having an earthquake of this magnitude has never been felt in this region before, and building constructed to withstand such tremors, have failed to meet up to those standards. All of this is occurring in an active volcanic area. The bigger question is what is happening to the island of Japan?

I'm wondering if planting different deep rooted trees would help to reduce these slides? I understand Japan is a mountainous area but something needs to be done.