Stratovolcanoes form when a conduit grows out from a pocket of magma and eventually reaches the surface. Over millions of years and countless eruptions, the magma and ash cool and settle, forming the large, summit-like volcano. Stratovolcanoes grow larger than any of the other types of volcano and some reach more than a mile in height.
Stratovolcanoes feature gently sloped lower elevations, steep upper elevations and a small vent at the top. Part of the reason that stratovolcanoes grow so large is that their magma has an exceptionally high viscosity and percentage of dissolved gases. This thick lava does not spread out like it does in shield volcanoes, which form low, flat structures.
Stratovolcanoes differ from both shield volcanoes and scoria volcanoes, the other two major types of volcano, in their rate of eruptions. Stratovolcanoes take a long time to develop enough magma to cause an eruption. Unfortunately, this means that stratovolcanoes are the most deadly of the three types. Some stratovolcano explosions are so violent that they change the entire planet’s climate for a period of time.
Many of the world’s most notable and picturesque volcanoes are stratovolcanoes. Examples of stratovolcanoes include Mount Mayon, Mount Agua, Mount Fuji and Mount Rainier.