Mount Unzen is a stratovolcano, and is part of a chain of statovolcanos. The volcano is made out of layers of volcanic ash and blocks of cooled lava, granite and basalt (called tephra). Statovolcanos have steep sides which are not very strong. Magma builds up underground; when there is enough pressure, there is an eruption. Stratovolcanoes have eruptions that makle lava and lava tubes.

Strata - This is the makeup of the volcano which consists of volcanic ash, tephra and cooled lava.
Lahar - This is a mixture of rock and water. This is made when the lava melts snow on top of the mountain and combines with rock and this mixture can destroy anything as it goes down the side of the mountain.