  Mechanical relaxation behaviour of various natural volcanic glasses have been
investigated in the temperature range RT-1200K using special low frequency
flexure (f~0.63Hz) pendulum experiments. The rheological properties complex
Young's modulus M* and internal friction 1/Q have been studied from a pure
elastic solid at room temperature to pure viscous melt at log(eta[Pas])=8.
Several relaxation processes are assumed to act: the primary alpha-relaxation
(viscoelastic process, E_a=(344...554)kJ/mol) above the glass transition
temperature T_g=(935...1105)K and secondary anelastic beta', beta and
gamma-relaxation processes below T_g. With a simple fractional Maxwell model
with asymmetrical relaxation time distribution, phenomenological the mechanical
relaxation behaviour, is described. This establish a basis of realistic
concepts for modelling of volcanic or magmatic processes.
