Jökull - 01.12.2003, Page 33

The 1783–1785 Laki-Grímsvötn eruptions
3m
10 m
tumulus ridge
b)
lava-rise plateau inflation cleft
inflated flow front
d)
5 m
a)
lava-rise
plateau
lava-rise pit
500 m
c)
tumulus
Figure 7. Flow structures in the Laki lava flow field indicative of insulated lava transport and flow inflation (i.e.,
endogenous growth). Location of each photograph is shown on Figure 2: (a) tumuli, formedwhen flow inflation
locally exceeds that of the surrounding lava, for example above a pool in a subsurface lava pathway (Walker,
1991; Hon et al., 1994). (b) A tumulus ridge, which are the surface manifestation of an inflating pathway (e.g.,
Thordarson, 2000). The hornito (arrowed) was formed by a rootless eruption through the central cleft; (c) lava
rise plateaus and lava rise pits (aerial view). The plateaus are formed by uniform inflation of broad pahoehoe
sheet lobes, whereas the pits are localized areas where the rate of inflation was lower than in adjacent parts of
the flow (Walker, 1991), and (d) inflated margin of a lava rise plateau, the cracks are inflation clefts.
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