ALTITUDE MATTERS: ASSESSMENT OF SO2 CLOUDS FROM THE 2006 ERUPTION OF NYAMURAGIRA VOLCANO (D.R. CONGO, AFRICA)

Nyamuragira volcano (D.R. Congo) is located in the western branch of the East African Rift, and emits low viscosity alkaline magma and large amounts of SO₂ (up to 1 Mt/day) during eruptions occurring every ~1-3 years. Basaltic effusive eruptions with a volcanic explosivity index of less than 3, as is often the case with Nyamuragira, are thought to contribute volcanic gas mainly to the lower-mid troposphere and are not capable of higher altitude plumes. The SO₂ plume from the November 2006 Nyamuragira eruption, however, was tracked with satellites as far as the west coast of the United States within the first few weeks of eruption, which suggests upper tropospheric emplacement. Determining the height and distribution of volcanic gas in the atmosphere is important because plume altitude will affect the lifetime and dispersion of SO₂ and sulfate aerosol, having significant implications for local and global climate.

We constrained the 2006 Nyamuragira plume height using Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT), Atmospheric Infrared Sounder (AIRS), Microwave Limb Sounder (MLS), Multi-Angle Imaging Spectroradiometer (MISR), and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) data. In addition, we aimed to refine the 2006 eruption SO₂ emission estimates using ultraviolet (UV) measurements from the Ozone Monitoring Instrument (OMI). Plume height and OMI data interpretation are closely linked since the change in atmospheric properties (T, P, H₂O content) with altitude affects the plume’s absorption of UV radiation. We found that the 2006 Nyamuragira eruption emitted 0.06 Mt of SO₂ and the plume reached 15 km; the tropopause begins at 16-17 km at equatorial latitudes. This adds to the idea that historical effusive basaltic eruptions (e.g., Laki 1783) were capable of similar plume heights, allowing SO₂ and resultant aerosols to remain longer in the atmosphere, travel farther around the globe, and affect global climate. The lower tropopause altitude (~9 km) at high latitudes indicates that less energetic basaltic eruptions are equally capable of injecting volcanic gas into the polar stratosphere.