What characteristic defines a stratovolcano?

A stratovolcano, also known as a composite volcano, is characterized by its conical shape with steep slopes. This shape is primarily the result of a combination of explosive volcanic activity and the accumulation of viscous lava flows, which create a layered structure. Stratovolcanoes tend to produce more explosive eruptions compared to other types of volcanoes, such as shield volcanoes, which have broad, gentle slopes and a flatter profile.

The steep sides of stratovolcanoes are formed by the layering of ash, pumice, and hardened lava, which solidify into rock. This accumulation results in a distinctive, tall, and conical appearance that is easily recognizable. Such volcanoes are often found at convergent plate boundaries, where an oceanic plate is subducted beneath a continental plate, contributing to their explosive potential.

In contrast, the other options describe different volcanic features. A flat, shield-like shape is typical of shield volcanoes, which are built by the flow of low-viscosity lava that travels long distances. A large caldera represents a different volcanic structure formed by the collapse of a volcano after a major eruption. Extensive lava tubes are usually associated with the flow of low-viscosity lava and are not a defining feature