Halemaʻumaʻu is a pit crater within the much larger Kīlauea Caldera at the summit of Kīlauea volcano on island of Hawaiʻi. The roughly circular crater was 770 meters x 900 m before collapses that roughly doubled the size of the crater after May 3, 2018. Following the collapses of 2018, the bottom of Halemaʻumaʻu was roughly 600 m below the caldera floor. Halemaʻumaʻu is home to Pele, goddess of fire and volcanoes, according to the traditions of Hawaiian religion. Halemaʻumaʻu means "house of the ʻāmaʻu fern".
Halemaʻumaʻu contained an active lava lake for much of the time before 1924, and was the site of several eruptions during the 20th century. The crater again contained an active lava lake between 2008 and 2018, with the level of the lava usually fluctuating between 20 and 150 meters below Halemaʻumaʻu's crater floor, though at times the lava lake rose high enough to spill onto crater floor. The lava lake drained away in May 2018 as new volcanic vents opened in lower Puna. The subsidence of the lava lake was accompanied by a period of explosions, earthquakes, large clouds of ash and toxic gas, and finally a gradual collapse of the summit caldera around Halemaʻumaʻu.