Laki Eruptions: the science

The volume of basaltic lava extruded was approximately 3.5 cubic miles (14.7 km3) and the pyroclastic fall deposit was 0.1 cubic mile (0.4 km3).

What made the Laki eruptions especially dangerous was the high sulphur content of the gases that were ejected and its northern location, where the tropopause (the boundary between the troposphere and stratosphere) was shallow. This margin in the polar regions of the planet is several kilometres lower than at the equator, so aerosols from major eruptions can more easily escape the troposphere allowing them to travel thousands of miles until brought to earth by descending air masses.

There were ten eruption episodes over five months. Gases released are calculated to have been sulphur dioxide – 122 million tons (MT); water – 235 MT; chlorine – 18 MT; and fluorine - 7 MT. Water combined with the Sulphur dioxide and Oxygen in the atmosphere to form sulphuric acid (potentially 100 to 200 MT) as the plume moved to the east and south (Figure 3).

Figure 3 – left: simplified cross section from Iceland to mainland Europe showing the dispersal and development of the Laki plumes in the first three to four weeks of the eruption. Eruption columns produced by explosive activity at the Laki fissures (L) carried ash, sulphur dioxide and other gases to altitudes of 9 to 12 km (yellow) to be dispersed southeastward over Europe by the polar jet stream. Due to convergence of airflow at the tropopause level, the Laki aerosol cloud was sucked into a large quasi-stationary high-pressure cell (H) located over Europe at the time and reintroduced into the lower atmosphere by the subsiding air masses, spreading in a spiral-like fashion across the continent. The arrows indicate subsiding air within the core of the anticyclone from mid or upper tropospheric levels. (source: Thordarson & Self, 2003; used with permission of author); right: main path of plume flow.