Jim Rudolph writes me: "Just saw your comment about the mid slide at MP. Also just returned from a short trip to Cusco. The mudslide was in Aguas Calientes [closest town to Machu Picchu on the railway from Cusco], across the river from MP, and had little to do with overuse of the site, but rather, with the fact that AC is built in a quebrada -- where mudslides occur frequently and naturally toward the end of the rainy season. Similar to Chosica [up the Rimac Rivery valley from Lima]. They are talking about moving the whole town of Aguas Calientes -- something that would be a good idea, I believe."
Jim married into Peru, just as I did, and has stuck it out in the country through some really hard times. Nice to know that he still keeps an eye on this site. He wrote a book about the country: Peru: The Evolution of a Crisis (Politics in Latin America)