This small explosive event in the summit lava lake of Kilauea volcano was produced by a rockfall from the south wall of Halemaʻumaʻu Crater at 11:59 a.m. on November 28, 2016.
The explosion threw fragments of molten lava onto the rim of the crater, mostly to the west of the former visitor overlook.
This area has been closed to the public since 2008 due to ongoing volcanic hazards, including explosive events like the one that happened Monday, November 28, 2016.
Here another video of the event by USGS:
That was just a small event. Now imagine what it would be if a large piece of rock collapses.