Lava lakes are large volumes of molten lava, usually basaltic, contained in a volcanic vent, crater, or broad depression. The term is used to describe both lava lakes that are wholly or partly molten and those that are solidified (sometimes referred to as frozen lava lakes). Formation Lava lakes can form in three ways: from one or more vents in a crater that erupts enough lava to partially fill the crater; or when lava pours into a crater or broad depression and partially fills the crater; or atop a new vent that erupts lava continuously for a period of several weeks or more and slowly builds a crater progressively higher than the surrounding ground. Behaviors Lava lakes occur in a variety of volcanic systems, ranging from the basaltic Erta Ale lake in Ethiopia and the basaltic andesite volcano of Villarrica, Chile, to the unique phonolitic lava lake at Mt. Erebus, Antarctica. Lava lakes have been observed to exhibit a range of behaviours. A "constantly circulating, apparently steady-state" lava lake was observed during the 1969–1971 Mauna Ulu eruption of Kīlauea, Hawaii. By contrast, a lava lake at the 1983–1984 Puʻu ʻŌʻō eruption of Kilauea displayed cyclic behaviour with a period of 5–20 minutes; gas "pierced the surface" of the lake, and the lava rapidly drained back down the conduit before the onset of a new phase of lake activity. The behaviour observed is influenced by the combined effects of pressure within the reservoir, exsolution and decompression of gas bubbles within the conduit and, potentially, exsolution of bubbles within the magma reservoir. Superimposed upon this is the effect of bubbles rising through the liquid, and coalescence of bubbles within the conduit. The interactions of these effects can create either a steady-state recirculating lake, or a lake level that periodically rises and then falls.<ref>Witham and Llewellin (2006). "Stability of Lava Lakes". '+Journal of Volcanology and Geothermal Research vol. 158 p.321–332</ref> Notable examples Persistent lava lakes are a rare phenomenon. Only a few volcanoes have hosted persistent or near-persistent lava lakes during recent decades: Ambrym, Vanuatu Mount Erebus, Ross Island, Antarctica Erta Ale, Ethiopia Kīlauea, Big Island, Hawaii Masaya volcano, Nicaragua Mount Michael, Saunders Island, South Sandwich Islands Mount Nyiragongo, Democratic Republic of the Congo Mount Yasur, Vanuatu The lava lakes at Ambrym volcano disappeared after a large eruption in December 2018. For many years, Kīlauea had two persistent lava lakes: one in the