Stratovolcano Stratovolcano A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava, tephra, pumice and ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions and effusive eruptions, although some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and hardens before spreading far due to high viscosity. The magma forming this lava is often felsic, having high-to-intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less-viscous mafic magma. Extensive
Ringing rocks that retained the olivine and pyroxene crystals (OPM) is extremely resistant to weathering and is the material which forms the tors. The altered rock (AM) conversely is very weak and readily breaks down to a coarse soil. The inner felsic core is a medium grained quartz monzonite that gradually grades into granite at the center. The transitional unit between the mafic zone and the felsic core units is completely obscured, and is represented by distinctive low-lying swales. A series of radial dikes punctured the mafic units, beginning in the felsic zone and terminating at the outer border of the intrusion.