The Hudson volcano eruption and its effects on the agriculture of the XI Region

Eduardo Besoain M.1, Rafael Ruiz S.1 y Christian Hepp K.2

The eruption of the Hudson volcano (08.09.91) in Aysen, South of Chile (XI Region) is the most intense one occurred in the country after that of the Quizapú volcano in 1932. The first eruptive phase was moderate, with deposition of pyroclastics and lahars in the direction NNE. The second phase was paroxistic, of high magnitude (about 6 km3), reaching the Falkland Islands distant about 1,200 km SE. The eruption caused damages in the agriculturallands around the General Carrera Lake, cattle mortality, forest deterioration and threated the lives of the residents. In order to evaluate its effects on the soil productivity, the mineralogical, chemical and nutritional value of the covering ashes was invstigated. The ashes were. pumiceous, vitric andf andesitic-basaltic, with about 60% of SlO2. The available nutrients (N, P, K, Ca, Mg, Fe, Mn) were moderate but sulphur as gypsum (CaSO42H2O) or bassanite (CaSO41/2H2O) reached contents from 14 to 2,500 kg ha-1 of S according to S density is ashes. Toxic effects due to heavy metals (Pb, Zn, Cd, Cu, As...) were not detected and fluoride contamination was minimal: 14.4 mg kg-1 of F in ashes; 0.16 to 0.68 mg kg-1 of F in water and 35 to 114 mg kg-1 of F in forage. It is presumed that the recovery of agricultural lands in the affected areas where the ash deposits were not deeper than 10 to 15 cm, could occur in a period of years. In other places, covered with thick depositions of pyroclastics, recuperation will be very slow over a period of hundred or thousand years.

Keywords: eruption, gypsum, bassanite, nutrients, Chile.
1 Centro Regional de Investigación La Platina (INIA), Casilla 439, Correo 3, Santiago.
2 Centro Regional de Investigación Tamel Aike, Casilla 296, Coihaique, Chile.