Felsic lavas (rhyolite and andesite) are very thick and gummy, resisting flow. So, felsic lava doesn’t usually flow very far from the volcano’s event, building up steep slopes.
When the volcano erupts, ejected particles of different sizes, known collectively as tephra, fall on the area surrounding the crater, creating a cone shape.
The sluggish streams of felsic lava and layers of tephra produce a stratovolcano.
Its tall cone steepens toward the summit, where you find the crater—a bowl-shaped depression.
The crater is the principal volcano vent. Felsic lavas from stratovolcanoes hold large amounts of gas under high pressure, so they can produce explosive eruptions.
Sometimes the volcanic explosion is so violent that it destroys the entire central portion of the volcano. Vast quantities of ash and dust fill the atmosphere for many hundreds of square kilometers around the volcano.
The only thing remaining after the explosion is a great central depression, called a caldera. Although some of the upper part of the volcano is blown outward in fragments, most of it settles back into the new caldera. Explosive stratovolcanoes also emit glowing avalanches (glowing clouds) such as the Soufrière Hills eruption of 1997 on Montserrat.
These clouds of white-hot gases and fine ash travel rapidly down the flank of the volcanic cone, searing everything in their path. A glowing cloud from the 1902 eruption of Mount Pelée on Martinique issued without warning, sweeping down on the city of St. Pierre and killing all but two of its 30,000 inhabitants.
Most of the world’s active stratovolcanoes lie within the circum-Pacific mountain belt, where there is active subduction of the Pacific, Nazca, Cocos, and Juan de Fuca plates.
One good example is the volcanic arc of Sumatra and Java, which lies over thesubduction zone between the Australian plate and the Eurasian plate.
Over time, exogenic processes erode stratovolcanoes, creating new landscapes. Erosion strips away their conical forms, leaving masses of resistant volcanic rock that continue to wear down. Ultimately, a landscape of lava mesas and volcanic necks with dikes remains.