When magma rises towards the surface gas bubbles start to form. Whether or not they can escape as the magma is rising affects how explosive the eruption will be.
The Kīlauea volcano on Hawai'i's big island is threatening to produce violent and energetic eruptions not seen since 1924.
The short answer is that while lava is hot, it's not hot enough to melt the rocks that make up the side of the volcano.
And will the aviation sector implement vital lessons learned from Icelandic disruption in 2010?