Laboratory Manual for Introductory Geology 4e

FIGURE 5.11 The four major types of volcanoes.
(a) Shield volcano (fluid lava), Mauna Loa, Hawaii.
(b) Lava dome (viscous lava) in the crater of Mt. Kelud volcano,
Indonesia.
(c) Cinder cone (pyroclastic material), Sunset Crater, Arizona.
(d) Stratovolcano (pyroclastic material plus lava), Mt. Mayon,
Philippines.
two kinds of material. Two types are made almost entirely of lava. Shield volcanoes
(FIG. 5.11a) are formed by eruptions of highly fluid lava. The lava’s fluidity produces
broad structures with gentle slopes—the largest volcanoes on the Earth (and Mars)
are shield volcanoes. Because ketchup or maple syrup has a consistency similar to
that of highly fluid lava, you can simulate the formation of a shield volcano by pouring
one of them onto a flat surface.
Lava domes (FIG. 5.11b) are much smaller than shield volcanoes, often forming
in the craters of other types of volcanoes. As their name implies, they too are
made of lava, but in this case the lava is extremely viscous, more like pizza or cookie
dough than ketchup. As a result, the lava can pile up to form steeper slopes than
those of shield volcanoes. To simulate formation of a lava dome, squeeze a blob of
toothpaste onto a flat surface.
Eruptions of lava domes and shield volcanoes are the least violent of all volcanic
eruptions, but even so can pose serious hazards. Lava from Hawaiian shield volcanoes
has buried homes, forests, and fields, displacing people and blocking roads at
a cost of millions of dollars.
Cinder cones (FIG. 5.11c) are made mostly from relatively fine-grained pyroclastic
material. Unlike other volcanoes, they are formed partly from above, when ash
erupted from the volcano’s vent falls to the ground, like sugar being poured into
a pile on a plate. Eruptions that build cinder cones are relatively peaceful, and the
resulting volcanoes are much smaller than shield volcanoes, with moderate slopes.
5.6 VOLCANOES AND VOLCANIC HAZARDS
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