Google this site:

Region > South American Volcanoes

Volcanoes of the Central Andes
by S.L. De Silva , Springer-Verlag, 1991, 216 pages
No Apparent Danger: The True Story of Volcanic Disaster at Galeras and Nevado Del Ruiz
by V. Bruce, Harper Perennial, 2002, 256 pages
Surviving Galeras
by S.N. Williams & F. Montaigne, Houghton Mifflin Co, 2001, 320 pages
Eruption of Nevado Del Ruiz Volcano Colombia, South America November 13, 1985
by D.S. Mileti (Editor), National Academy Press, 1991, 128 pages