C. A. Carvajal 1990 <p>Because of the reactivation of Nevado del Ruiz volcano in the last days of 1984, we began studies whose purpose was directed toward the identification of hte risks that accompanied such volcanic activity. As a result of these investigations there appeared a preliminary map of volcanic risk in Octoer 7, 1985, the first map of its kind in Colombia &nbsp;</p> application/pdf en U.S Geological Survey Present state of studies of volcanic risk in Colombia article