Page 182 - Fundamentals of Physical Volcanology

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ERUPTION STYLES, SCALES, AND FREQUENCIES 159

10 4 between events and the volume erupted. This sim-
ple picture mirrors the observed behavior of many
10 3 small basaltic systems. Figure 10.9 shows, for exam-
ple, part of the tilt record of Kilauea volcano for
Caldera area (km 2 ) 10 of the volcano continuously measures the slope
part of 1983 and 1984. A tiltmeter at the summit
2
10
or “tilt” of the ground surface. When the magma
chamber beneath the summit is inflating the
ground above it tilts upwards and outwards in re-
1
sponse. When an intrusion or eruption removes
magma from the magma chamber deflation occurs
0.1
and the ground tilt direction reverses. Figure 10.9
shows a series of inflation and deflation events
10 –2
10 –3 10 –2 0.1 1 10 10 2 10 3 10 4 10 5 which occurred at the summit of the volcano dur-
ing 1983 and 1984 in response to a series of erup-
Erupted volume (km )
3
tions occurring on the volcano’s flank. Forty-seven
Fig. 10.8 Illustration of the strong correlation between the such eruptions occurred between 1983 and 1986,
area of the caldera formed in a large-volume eruption and and Fig. 10.9 shows the tilt variations associated
the volume of magma erupted. Modified from fig. 2 in with eruptions 3 to 19 in this series. The tilt record
Smith, R.L. (1979) Ash-flow magmatism. Geol. Soc. Am.
shows the cyclic pattern of magma chamber infla-
Spec. Pap., 180, 5–27.
tion and deflation predicted by the simple elastic
magma chamber models just described. Prior to
chamber of a given size the model predicts a pat- each eruption the magma chamber fills with fresh
tern of behavior in which the chamber inflates as magma and the ground gradually tilts outwards.
magma is added to it, erupts a certain volume of Each eruption is associated with a rapid inward tilt-
magma when the failure point is reached, and then ing as the magma chamber deflates. The tilt re-
reinflates once eruption ceases, initiating a new cord in Fig. 10.9 also shows the variability in repose
cycle of activity. Variations in the exact failure con- times between each eruption and in the amount of
ditions (due to irregularities in the chamber wall, inflation and deflation associated with each erup-
for example) and of the magma supply rate to the tion. Compare, for instance, the different amounts

chamber will lead to variations in the repose time of deflation associated with eruptions 18 and 19.

Tilt (microradians) 3 4 5 6 7 8 9 10 11 12 1314 15 16 17 18 19 Inflation Deflation

Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May

Fig. 10.9 Summit tilt changes reflecting a series of inflation and deflation events in the summit magma chamber of Kilauea
volcano, Hawai’I, corresponding to a series of eruptive episodes in 1983 and 1984. Modified from fig. 1.2 in Wolfe, E.W., Neal,
C.A., Banks, N.G. & Duggan, T.J. (1988) Geological observations and chronology of eruptive events. pp. 1–97 in The Puu Oo
eruption of Kilauea volcano, Hawai’I: Episodes 1 through 20, January 3, 1983, through June 8, 1984. U.S.G.S. Prof. Pap. 1463.