The magmas that have created the Cascade volcanoes generally have a different consistency. As they make their way to the surface of the earth from the subducting oceanic plate, they often lose iron- and magnesium-rich crystals and gain silica from the melting of continental rocks. By the time the magma erupts, it has a consistency more like road tar than honey. This kind of magma can form stiff, sticky plugs in volcanic vents that bottle up the gases and pressure in a volcano. When the blockage gives way, explosive eruptions can result. The Hawaiian volcanologists had studied other kinds of
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