Laura Westoby is currently in Indonesia, today she sent through some photos and descriptions of what she was seeing on the SE flank of the volcano, Mt Merapi...
"This series of photos all show river channels that suffer from lahars in the rainy season and so the government has been building barriers to try and control them The photo to the left is a good example. Luckily its the dry season at the moment.
The material deposited by the lahars also gets used though. The second image (below) shows lorries and diggers moving material, a lot of which is used in the construction industry. Many of the locals also do this but on a smaller scale.
The third image shows (below), from what I understand, a dam being built to try and contain the larger blocks that are carried within the lahar.
The final two images show them excavating the channel (below left), but we were stood at the height at which the lahar was originally deposited. The second image (below right) was taken from the same spot only looking in the other direction. The lahar wiped out the original bridge and the new one can be seen in the background. Somebody has also rebuilt their house in the foreground. Note the huge (!) boulder that has been carried within it."