While each volcano is unique they can largely be divided into red volcanoes and grey volcanoes.
Red volcanoes typically have effusive eruptions dominated by the classic red-glowing lava flow or lava lake. The constant mild eruptions of lava let gases escape reducing the chances of gas build-up and larger explosions. A classic red volcano is Kīlauea in Hawaii.
Grey volcanoes are known for explosive eruptions. Trapped gases and heat can build up within the volcano releasing explosive eruptions that can shoot ashes and rock high into the sky and cause fast-moving pyroclastic flows of solidified lava and ash. Grey volcanoes are typically much more destructive than red volcanoes and can exhibit some behaviours like their red counterparts. A classic grey volcano is Mt St Helens.
I learned this distinction from the remarkable film Fire of love.
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