Field guides for excursions to the Nevado del Ruiz Volcano and to the Romeral Fault System (Colombia), in the frame of the Neotectonics of arc-continent collision concepts

central cordillera of colombia near to the nevado del ruiz volcano, is a seismically active area above the subducting slab ofthe nazca plate and deforming upper crust of the andes. buildings in the region require strengthening against the effects of both types of hazards: earthquakes and volcanoes. during these trips, we will discuss the 13 november, 1985, nevado del ruiz volcano eruption that destroyed the armero city with about 22,000 deceases, as well the 25 january, 1999, armenia earthquake (m 6.2) that killed about 2000 people and injured 4000 largely as the result of older, poorly constructed buildings. the economic impact ofthe quake on the region was significant with about 8000 coffee farms either completely or partially destroyed and over 13,000 structures either partially damaged or completely destroyed. both phenomena are associated to a large-transversal structure termed caldas tear, which is controlling strong motion earthquakes and the quaternary volcanism of the northern andes.