Stratovolcanoes pose the greatest hazards to populations living on or near their slopes because they typically erupt explosively, and frequently without warning. Molten lava is a threat to the surrounding area, as are the large amounts of volcanic ash and gas that stratovolcanoes spew. Large, explosive eruptions of stratovolcanoes can throw volcanic ash high into the atmosphere, posing a significant engine-clogging hazard for jet aircraft that fly into the ash cloud. Volcanic gases, ejected into the atmosphere can also form a cloud of acid droplets. Such a cloud can lead to acid rain, which causes damage to property and the environment.

The summits of many stratovolcanoes are covered by snow and ice during the winter, and the tallest of these mountains are capped by snow and glaciers throughout the year. During an eruption, the snow and ice can melt and cause an enormous mudflow to travel down the mountain, destroying towns in its path.

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