Geology Reference
In-Depth Information
Figure 3.8. Viscosities of common magma compositions at their
typical eruption temperatures, showing increasing viscosities at
lower temperatures and for increasing silica content ranging from
komatiite (rocks with very high ma
c content) to rhyolite (this
gure
was published in Encyclopedia of Volcanoes, ed. H. Sigurdsson, B. F.
Houghton, S. R. McNutt, H. Rymer and J. Stix, in the article Physical
properties of magma, by F. J. Spera, pp. 171
Figure 3.9. Glass Mountain is in the Medicine Lake highlands of
northern California. It is composed of rhyolitic obsidian lava
ows
that drape amoeba-like over the topography.
-
190, copyright Academic
Press, 2000).
Figure 3.11. Mauna Loa shield volcano (left side on horizon) formed
from the eruption of abundant basaltic lava
flows; the volcano on
the right is Mauna Kea, the summit of which is marked by numerous
cinder cones, the re
ecting mildly explosive eruptions which
followed its primary shield-building phase (US Navy photograph
0066, November 1954).
Figure 3.10. Lava domes, as seen in this digital elevation image of
Mt. Elden in northern Arizona, form from the extrusion of thick,
pasty lavas that
flow only short distances from their vents or from
intrusion of magma. Although typical of silica-rich lavas, they can
form in lavas of any composition, including (rarely) basalts. The
highways (white lines) visible in this image indicate the general scale
(courtesy of the US Geological Survey).
