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ERUPTION STYLES, SCALES, AND FREQUENCIES 149

0.001 0.01 0.1 1 10
100 100
(a)
Coalescence
10 30 10
Bubble diameter (m) 0.1 1 300 100 0.1
1

0.01
0.01
0.001 0.001
No Coalescence
0.0001 0.0001
0.001 0.01 0.1 1 10
–1
Rise speed (m s )

0.001 0.01 0.1 1 10
100 100
Coalescence (b)
10 1 10
Bubble diameter (m) 0.1 1 0.25 0.5 0.1
1

0.01
0.01
0.001 0.001
No Coalescence
0.0001 0.0001
Fig. 10.3 Variation of the size of the largest gas
0.001 0.01 0.1 1 10
bubble that can form in a rising magma as a function
–1
Rise speed (m s )
of the rise speed for various combinations of magma
viscosity and volatile content. (a) The volatile
content is kept constant and the curves are labeled 0.001 0.01 0.1 1 10
with the magma viscosity in Pa s; increasing the 100 100
viscosity makes coalescence more difﬁcult. (b) The Coalescence (c)
viscosity is held constant and the curves are labeled 10 10
with the exsolved volatile content of the magma; (0.25, 30)
decreasing the gas content makes coalescence more 1 1
difﬁcult. (c) The viscosity and volatile content vary (1, 300)
together, and the inﬂuence of the viscosity is seen Bubble diameter (m) 0.1 0.1
to outweigh the inﬂuence of the volatile content. 0.01 (0.5, 100) 0.01
(The ﬁgure is based on ﬁgs 2 & 3 in Parﬁtt, E.A. &
Wilson, L. (1995) Explosive volcanic eruptions – 0.001 0.001
IX: the transition between Hawaiian-style lava No Coalescence
fountaining and Strombolian explosive activity. 0.0001 0.0001
0.001 0.01 0.1 1 10
Geophys. J. Internat., 121, 226–232. Copyright
–1
Wiley-Blackwell Publishing Ltd.) Rise speed (m s )

in which coalescence increases with increasing gas the combined effect that coalescence becomes
content for a given rise speed. Figure 10.3c shows progressively less likely for a given rise speed, i.e.,
one example of the combined effects of composi- the effect of increasing viscosity is dominant.
tion on the likelihood of bubble coalescence. Here Magma viscosity varies so greatly between differ-
viscosity and gas content increase together, with ent magmas (Fig. 10.2), compared with the relative

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