Geology Reference
In-Depth Information
Figure 3.12. Channels often form in basaltic and some andesitic
ows,
and transport lavas to the advancing
ow front. Constructional levees,
seen along these lava channels in Hawaii, are common.
Figure 3.13. Lava tubes are conduits that develop in some basalt
flows, either within the body of the
ow, or by channels that become
roofed; in either case, lava tubes act as extensions of the vent,
reducing cooling of the magma, and feeding the
flow front. This
aerial photograph shows a nearly completely collapsed lava tube
indicated by the series of collapse holes on the left side of the image.
The lava tube originated from the large (~500m in diameter) circular
pit crater and
flowed toward the top of the image.
features result from mild explosions generated locally by
the interaction of the hot lava and water. The term
“
pseudo
”
(meaning false) simply refers to the fact that the features are
not directly linked to a vent over a magma chamber.
Figure 3.19
classi
es common volcanoes and their rela-
tion to some of the more important factors involved in vol-
canic eruptions. Unfortunately, because data are so limited,
the details of volcanic processes on other planets are poorly
known. Nonetheless, to some extent, the styles of eruption
can be inferred from the morphology of volcanic features.
3.3.4 Intrusive structures
Not all magma reaches the surface to produce volcanoes.
Some magma intrudes crustal rocks, cools, crystallizes
and may be exposed later through weathering and erosion.
Frequently, these intrusive structures are more resistant to
erosion than the host rock, and they stand out as topo-
graphic features.
Figure 3.20
shows Green Mountain in
Figure 3.14. Calderas are volcanic features that result fromexplosions,
collapse over magma chambers, erosion, or some combination of these
processes. This view is of the caldera at the summit of Kilauea volcano
in Hawaii; the area shown is about 3 km by 5 km.
