Jökull - 01.01.2012, Page 32

B. A. Óladóttir et al.
Figure 4. a) Cyclic evolution of the
plumbing system under the Katla vol-
cano during the Holocene. The inset
diagrams show the schematic changes
in K2O concentration with time (t).
Modified from Óladóttir et al., 2008.
– a) Þróun kvikuaðfærslukerfis Kötlu
á nútíma. Einfaldaðar styrkleika-
breytingar K2O með tíma (t) eru sýnd-
ar á litlu gröfunum, sjá frekari um-
fjöllun í Óladóttir o.fl., 2008.
Figure 4. b) Tephra layer frequency (TLF) of the dif-
ferent plumbing system periods normalised to 500
years. Modified from Óladóttir et al., 2008. – b)
Gostíðni á tímabilum með mismunandi kvikuaðfærslu-
kerfum, stöðluð við 500 ár. Lítillega endurteiknað frá
Óladóttur o.fl., 2008.
son et al., 2007). Carefully determined correlations
between the refractive index of volcanic glass and
SiO2 concentration allowed Thorarinsson (1967) to
discover a linear relationship between the length of
repose before historical eruptions from Hekla and the
SiO2 concentration of the first emitted tephra (Figure
5a), i.e. after longer repose period the composition
of the initial erupted material is more silicic and the
explosive phase more violent. A positive relationship
also exists between the length of previous repose and
the emitted tephra mass and, hence, the magnitude of
the opening phase (Figure 5b).
Eyjafjallajökull volcano, the 2010 tephra layer and
the dynamics of magma mixing
Injection of basaltic magmas into silicic crustal hold-
ing chambers and subsequent mixing of the two com-
ponents is a well-known magmatic process that fre-
quently provokes explosive eruptions (e.g. Sparks et
al., 1977; Eichelberger, 1980). Detailed reconstruc-
tion and assessment of the mixing process caused by
such intrusion is possible because of exceptional time-
sequence sample suite collected during the tephra fall-
out of the 2010 summit eruption at Eyjafjallajökull
volcano. The predominantly explosive eruption be-
gan 14 April and lasted 39 days (e.g. Gudmundsson et
30 JÖKULL No. 62, 2012