Comment on " Volume of magma accumulation or withdrawal estimated from surface uplift or subsidence, with application to the 1960 collapse of Kīlauea volcano" by P. T. Delaney and D. F. McTigue

Abstract

In volcanoes that store a significant quantity of magma within a subsurface summit reservoir, such as Kīlauea, bulk compression of stored magma is an important mode of deformation. Accumulation of magma is also accompanied by crustal deformation, usually manifested at the surface as uplift. These two modes of deformation -bulk compression of resident magma and deformation of the volcanic edifice -act in concert to accommodate the volume of newly added magma. During deflation, the processes reverse and reservoir magma undergoes bulk decompression, the chamber contracts, and the ground surface subsides. Because magma compression plays a role in creating subsurface volume to accommodate magma, magma budget estimates that are derived from surface uplift observations without consideration of magma compression will underestimate actual magma volume changes.

Estimation of Pre-eruptive Magma Ascent Using a Hydrokinetic Model of Magma Plumbing System

“…The optimum bulk moduli of the deeper reservoir for the permeable and Poiseuille models are 1 and 15 GPa, which are consistent with the typical values of magma with and without gas, respectively 6,8) .…”

“…We accordingly try to reproduce the phenomena to quantitatively demonstrate the pre-eruptive magma migration. 8) . For the evaluation of ch V , the volume transfer from the deeper to the shallower have to be calculated by numerical flow simulations in the conduit.…”

Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode

“…Furthermore, if the magma remaining in the chamber contains exsolved gases, it will expand when the pressure drops. The volume change of the magma chamber in these circumstances has previously been estimated to be as much as 4-5 times smaller than the volume of magma withdrawn from the chamber 20,21 . We cannot therefore rule out the shallow chambers as being the source for all of the magma intruded into the dyke.…”

Strain accommodation by slow slip and dyking in a youthful continental rift, East Africa

“…Volume-change calculations depend strongly on Poisson's ratio (a constant value of 0.25 is used here), the shape of the magma chamber (here a point source) and magma degassing and expansion as pressure drops (not accounted for here) 26,27 . This later process may result in a volume increase by a factor of up to five 28 .…”