What are steep-sided volcanoes made from?

Steep-sided volcanoes, or stratovolcanoes, are primarily made from multiple layers of cinders and ash that were laid down during past eruptions. According to Oregon State University, stratovolcanoes are distinct from shield volcanoes due to their high altitude and steeply graded sides.

Stratovolcanoes form differently from shield volcanoes, which are lower and wider, because the ejected material is different. A shield volcano ejects lava that oozes slowly downhill. Cinder cones, on the other hand, eject more viscous fluids and more ash, the combination of which can hold a steeper grade. Thus, the cone built up by these volcanoes tends to be much taller.