Andesitic and rhyolitic Magmas Andesitic magmas are about 10 percent of the total magma Magma from Mount St Helens in Washington State and Krakatau in Indonesia is usually andesitic. Rhyolitic magmas are about 10 percent of the total magma Magmas erupted from volcanoes that once were active at Yellowstone Park are mostly rhyoliticAndesitic and Rhyolitic Magmas ◼ Andesitic magmas are about 10 percent of the total magma. ◼ Magma from Mount St. Helens in Washington State and Krakatau in Indonesia is usually andesitic. ◼ Rhyolitic magmas are about 10 percent of the total magma. ◼ Magmas erupted from volcanoes that once were active at Yellowstone Park are mostly rhyolitic