Stratovolcanoes are steep and conical with explosive eruptions. Sudden, violent blasts can send particles as far as twenty miles high and many miles away from the volcano. The erupted material can range in size from tiny particles of ash to boulders the size of houses. Commonly there is little, if any, lava extruded. Such eruptions can be very dangerous and even deadly. Because they erupt infrequently, unpredictably, and violently, and because they occur in populated areas, these explosive volcanoes pose the greatest danger to humans.

The eruption at Mount St. Helens in the state of Washington in 1980 caused a giant landslide. Once the side of the mountain was gone, the volcanic gases exploded out of the side of the volcano, producing a lateral blast. This blast, traveling at speeds of up to 670 miles per hour, quickly overtook the landslide and extended up to nineteen miles from the volcano. In the areas closest to the volcano and up to about eight miles away, the blast destroyed everything—trees, houses, wildlife, etc. This area was left barren as the moon. Most of the fifty-seven people killed in the eruption, including volcanologist David Johnston, were killed by asphyxiation from the lateral blast. The hot gases scorched their lungs.