In November 1985, volcanic activity once again increased as magma neared the surface. The volcano began releasing increasing quantities of gases rich in sulfur dioxide and elementary sulfur. The water content of the fumaroles' gases decreased, and water springs in the vicinity of Nevado del Ruiz became enriched in magnesium, calcium and potassium, which were leached from the magma. The thermodynamic equilibration (stationary heat energy) temperatures, corresponding to the chemical composition of the discharged gases, were from to . The extensive degassing of the magma caused pressure to build up inside the volcano, which eventually resulted in the explosive eruption.