Challenges for 1D models - part 3

Unsteady source conditions

Almost all 1D models presume steady flow conditions at the source. Many small to medium-sized explosive eruptions, however, also show stages of pulsating behavior, which could be a potential source of error when applying steady 1D models.

Under unsteady source conditions, plumes are not fed by a constant stream of ash and gas, but by a sequence of ash "pulses". The depicted image sequence shows the contours of an analyzed ash pulse during the 2010 Eyjafjallajökull eruption [1]. (Courtesy of M. Rietze [2])

Pulsating source behaviours is assessed by the pulse analysis method, which was developed to derive the mass of individual pulses by video analysis and to quantify their contribution to the overall mass flux [1].

Within MAXI-Plume this tool will be applied in combination with a time-dependent 1D plume model [3] to a number of Icelandic case scenarios (including the eruptions of Grímsvötn 2004 and 2011).

Based on video analysis and geometrical considerations, the volume, mass and density of individual ash pulses can be reconstructed. With these data and by counting the frequency of ash pulses it is possible to estimate the mass flux. (For details about this principle, please see Dürig et al. [1]).

We hope that this will provide us new insights on the link between fragmentation and eruptive source conditions, on the predictive capabilities of the tested model and on the effects of pulsating source conditions on plume dynamics.

Pulse gun: the three conduits are fired with a temporal delay, simulating a pulsating source.

<- back to mass flux

References and annotations:

[1]: Dürig, T. et al: Mass eruption rates in pulsating eruptions estimated from video analysis of the gas thrust–buoyancy transition – a case study of the 2010 eruption of Eyjafjallajökull, Iceland. Earth Planets Space 67(1), 180 (2015).

[2]: www.mrietze.de

[3]: Woodhouse, M. J., Phillips, J. C. & Hogg A. J. Unsteady turbulent buoyant plumes. J. Fluid Mech., 794, 595-638 (2016)