Airborne measurements of particle and gas emissions from the 1990 volcanic eruptions of Mount Redoubt

Airborne in situ and remote sensing (lidar and correlation spectrometer) measurements are described for the volcanic emissions from Mount Redoubt, Alaska, in January and June 1990. The lidar provided excellent real-time information on the distribution of the volcanic effluents. In postanalysis the lidar observations were used to determine cross-sectional areas of the plumes of emissions which, together with the airborne in situ measurements, were used to derive the fluxes of particles and gases from the volcano. For the intraeruptive emissions the ranges of the derived fluxes were for water vapor, ∼160-9440 kg s^-1; for CO₂, ∼30-1710 kg s^-1; for SO₂, ∼1-140 kg s^-1; for particles (<48 μm diameter), ∼1-6 kg s^-1; for SO₄⁼, <0.1-2 kg s^-1; for HCl, <0.01-2 kg s^-1; and for NO_x, <0.1-2 kg s^-1;. Independent measurements of SO₂ from a correlation spectrometer during the period of active dome growth between late March and early June 1990 gave fluxes from 12 to 75 kg s^-1;. The particles in the intraeruptive emissions consisted primarily of silicate rock and mineral fragments devoid of any sulfuric acid coating. Very little of the SO₂ (∼0.1%) was oxidized to sulfate in the cold, dark conditions of the Arctic atmosphere. During a large eruption of Mount Redoubt on January 8, 1990, the particle (<48 μm diameter) emission flux averaged ∼10⁴ kg s^-1. During posteruptive emissions on June 11, 1990, the fluxes of both particles and gases were either close to or less than our lower detection limits (except for water vapor, which had a flux of ∼6×10³ kg s^-1).