The Effects of Persistently Degassing Volcanoes on the Natural Environment as Exemplified by Kilauea, Masaya and Poás Volcanoes.

While the effects on the global environment of large volcanic eruptions have been frequently studied, there has been little work on the impact of lower tropospheric emissions from persistently degassing volcanoes. In contrast to large volcanic eruptions which may have a short term but hemispheric/global effect (through injection of gas and ash into the stratosphere), persistently degassing volcanoes can have significant long-term (years to decades), local and regional effects. To examine these effects, we consider 3 persistently active degassing systems: Kilauea (USA), Poás (Costa Rica) and Masaya (Nicaragua). These volcanoes are characterized by SO₂ emission rates ranging from 100s to 1000s metric tonnes per day, and have emitted acid gases into the troposphere for extended periods of time. Masaya, for example, has degassed approximately the same amount of SO₂ (21 Tg) over a period of ~140 years as the 1991 eruption of Mount Pinatubo injected into the atmosphere in just a few hours. The extended degassing at Kilauea, Masaya and Poás impacts on commercial agriculture and has led to attempts to mechanically mitigate the hazard through capping of the active crater at Masaya and flooding to reinstate the acid crater lake at Poás. In order to investigate the environmental effects of persistent degassing, we use remote sensing data (Landsat ETM+, IKONOS) with NDVI band ratio algorithms to delineate poorly vegetated areas downwind of each volcano. These data are incorporated, through a GIS, with DEM and various ground truth data (soil pH, dry deposition rates, precipitation acidity, etc). Extremely distinct zones of vegetation "kill off" are noted that correlate with changes in topography. It appears that sharp topographic changes allow the gas plume to decouple or couple with the ground, hence lessening or increasing its impact at any down wind location. This integrated study of degassing at persistently active volcanoes may aide in limiting the effects on human populations and agriculture downwind of such systems through improved land use management.