Mit Hilfe eines neu entwickelten experimentellen Aufbaus sollen die Entstehungsmechanismen hydromagmatischer Aschen näher untersucht werden
Final Report Abstract
Traditional experimental studies of hydromagmatism produced clasts via fuel-coolant interaction (e.g., vapour explosions or thermal detonation) by utilizing the maximum explosive potential of ideal water/melt mixing ratios. This was accomplished by bringing melt into direct contact with water by either having a water source contact the (?) melt from beneath or by injecting water into melt. The hydromagmatic products of such experiments are small (<180 μm), blocky pyroclasts. However, some violent hydromagmatic eruptions that generate fine ash clearly involve mixing of water and magma in the atmosphere. A series of experiments has been conceived using a new experimental design to imitate the interaction between magma and water in the atmosphere by producing a jet of melt that is sprayed with water. The experiments will investigate whether "turbulent shedding" is a viable mechanism for the production of fine ash particles. This project was conducted as part of a larger ongoing study of hydromagmatic interaction in close collaboration with Dr. Larry Mastin (USGS). A second series of experiments was devoted to peperite formation. Two methods of magma-sediment contact were chosen: (a) Explosive upward injection of melt into sediment-water mixture, (b) Melt was poured in a sediment-water mixture (effusive style). The influence of water to sediment ratio and sediment grain size was evaluated. Remobilization of the sediments (as in coastal areas) was mimicked by a shaking table and compared to non-moving sediment. A part of this project was dedicated to the advancement of the setup for upward ejection of silicate melt into sediments aiming at cost- and time-efficient testing of explosive magma sediment mixture. Several improvements could be established, as better furnace design and material, improved sealing of furnace wiring, thermocouples and pressure line connections. Melt was successfully explosively ejected into water and wet sediments. However the goal of developing a user-friendly, time-and costefficient device could not be reached during the duration of this project. On the other side a valuable knowledge concerning technical and experimental constraints was gained during advancement of the device; this will significantly facilitate the construction of new experiments to investigate the various still unsolved aspects of magma-water interaction.
Publications
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Experimentaly generated peperitic textures and hydromagmatic ash fragments using SMILE (2008). Geophysical Research Abstracts, Vol. 10, EGU2008-A-08189
Downey W.S., Spieler O., Kunzmann T., Mastin L.G., Dingwell D.B., Shaw C.S.
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An experimental study of hydromagmatic fragmentation through energetic, non-explosive magma-water mixing (2009). Journal of Volcanology and Geothermal Research, Vol. 180, Issues 2-4, pp. 161-170
Mastin L.G., Spieler O., Downey W.S.
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The sensitivity of mixing conditions on non-explosive hydromagmatic fragmentation, as illustrated in a series of simple laboratory experiments (2009). Geological Society of America Abstracts with Programs, Vol. 41, No. 7, p. 231
Mastin L.G., Downey W.S., Scheu B., Taddeucci J.
