The 2018 eruption at Hawaii's Kīlauea volcano was as spectacular as it was destructive. Over a quarter of a cubic mile of lava poured out at the eastern edge of the big island, burying multiple towns and filling in an entire bay. It was an eruption that was unexpected in many ways: the massive volume of lava erupted, the location that the many vents formed far from the summit and the collapse that happened at the distant top of Kīlauea. So, what might have triggered this eruption in the first place?
That is a tough question to answer. What exactly causes volcanoes to erupt is an open question in volcanology. There are definitely a few geologic events we can point to as something that can push a volcano to erupt. New intrusions of magma into the volcano is the big one. The new magma mixes with older magma inside the volcano. All that new heat, gas and molten rock can overpressure the system that holds all that magma, causing some to erupt.
We can also point to gases dissolved in magma. As magma rises and cools, it will release these gases like water and sulfur dioxide in the form of bubbles. Adding all those bubbles can cause similar overpressure leading to a big boom.
