Page 86 - Fundamentals of Physical Volcanology

9780632054435_4_004.qxd 12/10/2007 12:19PM Page 63

MAGMA STORAGE 63

West, M., Menke, W., Tolstoy, M., Webb, S. & Sohn, R. 3 What differences are there between the patterns
(2001) Magma storage beneath Axial volcano on the of activity of basaltic volcanoes as a function of
Juan de Fuca mid-ocean ridge. Nature 413, 833–6. their tectonic setting? What effect does this have
Yamamoto, M., Kawakatsu, H., Yomogida, K. & on the chemistry of the magma erupted?
Koyama, J. (2002) Long-period (12 sec) volcanic 4 For each of the eruptions described in Table 4.1,
tremor observed at Usu 2000 eruption: seismic work out the area of the caldera (treating it as
detection of a deep magma plumbing system. a circle or ellipse, as appropriate). Next divide
Geophys. Res. Lett. 29, 43-1-4. the erupted volume by the caldera area to get
the equivalent vertical depth of magma that
was erupted from the shallow magma reservoir,
4.7 Questions to think about assuming one exists. Finally assume that, as
implied by the data in Table 4.2, most magma re-
1 Describe four kinds of evidence that might be servoirs extend vertically for ∼5 km and work
used to suggest that a currently active volcano out what percentage of all the magma originally
has a region of magma storage at shallow depth in the reservoir is represented by the erupted
below its summit. magma volume. Recalling that theory suggests
2 What kinds of features would you look for in that caldera collapse will occur if more than 0.1
rocks now exposed at the Earth’s surface by to 1% of the magma in a reservoir is erupted,
uplift and erosion as evidence for the presence would you have expected collapse to occur in all
of an ancient volcano? of these eruptions?