Volcanic ash concentrations in the plume from Sakurajima volcano in Japan are observed from airplanes equipped with optical particle counters and GPS tracking devices. The volcano emits several puffs a day. The puffs are also recorded by the Sakurajima Volcanological Observatory. High concentrations are observed in the puffs and fallout driven by vertical air current, called streak fallout. Puffs dispersion is analyzed by the classical diffusion-advection method and a new gravitational dispersion method. The fluid mechanic of the gravitational dispersion, streak fallout, and classical diffusion-advection theory is described in three separate appendices together with methods to find the time gravitational dispersion constant and the diffusion coefficient from satellite photos. The diffusion-advection equation may be used to scale volcanic eruptions so the same eruption plumes can be scaled to constant flux and wind conditions or two eruptions can be scaled to each other. The dispersion analyses show that dispersion of volcanic plumes does not follow either theories completely. It is most likely diffusion in the interface of the plume and the ambient air, together with gravitational flattening of the plumes core. This means larger boundary concentration gradients and smaller diffusion coefficients than state of the art methods can predict.

ELIASSON, J., 2008. A glacial burst tsunami near Vestmannaeyjar, Iceland. Journal of Coastal Research, 24(1), 13- 20. West Palm Beach (Florida), ISSN 0749-0208. Violent glacial bursts (jokulhlaup) are huge floods produced by subglacial volcanic eruptions. They are well known in Iceland. The biggest jokulhlaups come from Katla and can discharge water masses on a scale of several cubic kilo- meters into the ocean in just a few hours. Subglacial volcanoes can melt the glacier fast enough to produce 100,000- 300,000 m3/s discharges for a long enough time to produce such floods. Geological evidence of such large floods exists, and it is concluded that historical floods like the one produced by the Katla eruption of 1918 have most likely been of this order of magnitude. Results from a computational fluid dynamics (CFD) simulation of a jokulhlaup down the Markarfljot valley in Iceland are shown. The flood is a translatory wave, and the existence of the translatory wave is established for an inclined plane in a prismatic channel and in a funneling channel as an initial value problem. Inherent instabilities of the wave tail are discussed. The energy and power emitted by the flood wave into the ocean is estimated, and transformation into a wave group suggested as a method to find the height of a tsunami-like wave hitting the Vestmannaeyjar Islands. Edge waves along the coast are discussed. Probabilities of jokulhlaups that might cause tsunami-like waves are reported.