April 22, 2021- Close-up view of Halema‘uma‘u lava lake crusting-over

This zoomed-in photo of the far southwest end of the active lava lake within Halema‘uma‘u at Kīlauea's summit was captured on Thursday, April 22, and it illustrates the process by which parts of the lava lake become inactive. This area, which had seen substantial lava circulation as recently as last week, now has a stagnant pāhoehoe crust that sits 2–3 m (7–10 ft) lower than the fluid lava surface just to the northeast (right). This crust overlies and possibly overhangs fluid lava underneath, as evidenced by the incandescence visible through a hole along the levee at left. The process starts when the circulation of surficial lava slows in a part of the lake—for reasons that are not entirely clear—allowing the pāhoehoe crust to form. At this point, the area is no longer replenished with new surface lava, and the underlying molten lava will actually contract due to degassing, compression, and cooling. The crust may remain attached to the levees, and as the lava underneath cools and contracts, voids can form below the crust. Eventually, deeper accumulation of molten lava may start lifting this area again, as has happened in the eastern end of the Halema‘uma‘u lava lake. USGS image.