Surtseyan Volcanic Eruptions: An Experimental Perspective

Abstract:

Submarine volcanic eruptions take place in the “mysterious world” hidden from land-based view. One type of submarine volcanic activity is a surtseyan eruption, in which rising magma comes into contact with a volume of water, generating explosive interactions at relatively shallow water depths. Such eruptions can begin breaching the water surface before an island forms, and continue to build a volcanic edifice that may reach hundreds of meters above the sea level (e.g. Surtsey, Iceland). The focus of the bench-scale underwater experiments here is on the submerged stage of these eruptions. The experimental apparatus is a container filled with water (32cm x 32cm), into which different types of particles are forced by release of compressed argon gas. All runs were performed at the same driving pressures and recorded at 1000 fps and 1 Mpx/frame. Three run types were carried out: 1) water-saturated particles forced into water, similar to motion of slurry particles being driven upward by an explosion; 2) dry particles driven into water, similar to motion of particles produced and entrained in an explosion; 3) dry particles released into air [=subaerial]. For the first two settings, a clear repeatable sequence was observed: (i) initial doming; (ii) expansion of the three-phase mixture (water, gas and particles); and (iii) collapse of the jet. For the subaerial runs, only the doming and expansion were observed. A key result is that water-saturated particles couple more effectively with water, once in the tank, than do dry particles. Second order variations observed are related to the different features of the material (particle mass, particle density, and particle-population homogeneity). Finally, many runs showed specific behaviours after the collapse phase: particle shedding, re-entrainment of particles into the plume, and generation of vertical density currents.