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MAGMA STORAGE 57

Kilauea Pacific
caldera
Ocean

0 3 km
0

5

10
Depth (km)

15

20
25
30
0 3 km
35
40

Fig. 4.18 The magmatic system thought to underlie Kilauea volcano in Hawai’I as derived mainly from seismic data. Not all of
the shaded region is occupied by completely molten rock at any one time. Note the frequently-used pathway leading up from
the mantle and the extension of the summit chamber into the volcano’s two lateral rift zones. (Adapted from fig. 12 in Ryan,
M.P. (1988) The mechanics and three-dimensional internal structure of active magmatic systems: Kilauea Volcano, Hawai’I.
J. Geophys. Res., 93, 4213–4248.)

Once a deep plumbing system has become estab- chamber walls and to grow outwards from them.
lished, the magma chamber it feeds may progres- These offshoots from the main chamber may
sively evolve in shape and size by a range of pro- increase the complexity of the chamber shape.
cesses. At Skaergaard (Fig. 4.12), for example, They also facilitate the stoping process in which
the intrusion developed from a sill into a more blocks of wall rock or roof rock break away and
laccolithic shape by the updoming of the overlying sink into the magma to be melted, thus increasing
layers. Deformation of the surrounding rocks is the chamber volume at the expense of reducing
therefore one method by which the chamber shape its temperature.
may change and its volume expand. As chambers A final issue here concerns the lifetimes of
inflate and the pressure inside them increases it magma chambers. The application of deformation
becomes possible for fractures to develop in the and seismic techniques shows that the volcano