If high-silica lavas contain little trapped gas, they may ooze slowly onto the surface to pile up as steep-sided lava domes. Andesite, dacite, and rhyolite lavas are progressively higher in silica and more viscous, so gases cannot escape gradually.Repeated fire-fountain and lava flow eruptions over long time periods form gently sloping shield volcanoes like Anahim Peak in central British Columbia, and the volcanoes of the Hawaiian Islands. When runny lava contains less gas, however, it erupts in outpouring lava flows. Small fire-fountain eruptions produce cinder cones (like Eve Cone in northern British Columbia). A low viscosity (runny) lava, like basalt that contains lots of gas, forms fire-fountains, spewing spectacularly into the air and breaking into globs that solidify as they fall to the ground.
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