Stratovolcanoes (or composite volcanoes)
Stratovolcanoes are characterized by their cone shape,
which is shaped so evenly due to the alternating layers of magma and pyroclastic flows (Keller, 2005). These volcanoes are
distinguishable by their explosive nature, due in part to their high SiO2 content, but
also due to the fact that they are so gaseous. These gases are trapped in the viscous lava flow and often just erupt (sort
of like bubbles) randomly throughout the flow, making this sort of lava stream particularly dangerous to its surroundings.
When these gaseous magmas erupt however, creates a pyroclastic rain of minerals and ash that covers the dome of the mountain
(Montgomery, 2000). These pyroclastic eruptions, followed by the regular lava flow, create the layered characteristic mentioned
above. Bernard (2000) also suggests that a third layer could also be considered: a layer of deposits from the lahars that
are particularly characteristic of Mt. Kelud, whose crater lake causes devastating mudslides.
The dangerous nature of composite volcanoes can be
further reinforced by the fact that they are the most responsible for the volcano-related deaths that have been documented
throughout history (Keller, 2005).
The most common form of rock produced by eruptions
from composite volcanoes is andesite, which is a fine-grained igneous rock that is partly feldspar, iron and magnesium (Plummer
et. al., 2007).
Some famous stratovolcanoes include Mt. St. Helens
and Mt. Rainier (both in Washington, DC).