It had been over two years since Kīlauea on Hawaii last erupted. For a volcano that had been erupting continuously for almost 35 years prior to that, two years of quiet is a long time. The summit Halema'uma'u Crater collapsed during the massive 2018 eruption at the lower east rift zone and the bottom of that pit had filled with a small lake. However, in a few fitful minutes early in the morning of December 21, that lake was changed from a lake of water to a lake of lava.
Earlier last week, the scientists at the Hawaiian Volcano Observatory (HVO) had noted that the summit area was inflating and feeling numerous small earthquakes. This is something that hadn't happened since the end of the 2018 eruption. These were all signs that magma was intruding into the summit area of the volcano. Although they couldn't say that an eruption was going to happen, it was enough activity to at least let that thought creep into your head if you were monitoring the volcano's rumbling.
