Volatile release from flood basalt eruptions: understanding the potential environmental effects - Volcanism and Global Environmental Change - page 168

18

16

14

Range of Izu-Oshima plume heights

12

10

8

6

Linear vent ( w =16 m)
Linear vent ( w =4 m)
Central vent ( d = 50 m)

4

2

0

80 60 40 20 0

Effective gas content (wt%)

Figure 11.3 Maximum predicted plume heights as a function of effective gas
content fire-fountain. Grey shading

indicates the range of observed buoyant ash plume heights (12

in buoyant ash and gas plume above a

16 km ASL)
during the explosive phase of the 1986 Izu-Oshima basaltic fissure eruption. All
cases assume eruption temperature of 1350 K and initial velocity of 100 m/s at the
buoyant plume source 1000 m above the

-

fissure vent (point of gas separation from

fire-fountain height). Curves indi-
cate buoyant plumes from a circular source with a diameter d

fire-fountain, approximately 2/3 of maximum

¼ 50 m (solid

circles), a linear source with width w ¼ 4 m (open diamonds), and a linear source

with w ¼ 16 m (solid line). Figure modi ed from Glaze et al . (in press).

~

active ssure

length supported ~ 36 explosive events/phases (Brown et al ., 2014 ). Fissure
segments could have had one to several vents, which later produced lava without
signi

fissure segments, this suggests that the 180 km of known Roza

cant fountaining for a longer period within a decades-long eruption (Brown
et al ., 2014 ).
To estimate the likely plume rise height for the Roza eruptions, Glaze et al .
(in press) assume parameters analogous to the Izu-Oshima eruption. Based on glass
inclusion data reported by Thordarson and Self ( 1996 ), a bulk Roza volatile
content of 2 wt% is assumed. The range of estimated maximum plume heights
for the Roza eruption is 13.1 - 17.4 km ASL for fissure widths of 4 - 16 m (Glaze

et al ., in press). At Roza ' s 45 ˚ N palaeo-latitude, the tropopause is between

10 and 13 km ASL, depending on season. Thus, a plume from a 16-m-wide linear
source, analogous to Izu-Oshima, can easily drive a plume into the stratosphere
( Figure 11.3 ), even for ash-poor cases, and this indicates that

~

flood basalt erup-
tions, such as Roza, were capable of repeatedly injecting large amounts of SO 2 into
the stratosphere over many years to tens of years. Based on the 9000 Mt of SO 2

estimated by Thordarson and Self ( 1996 ) to be released mainly with the explosive
phases, Glaze et al . (in press) estimate that each

~

fissure segment might have
injected 62 Mt/day of SO 2 into the stratosphere while actively fountaining, each