ionian lava lakes are depressions partially filled with molten lava covered by a thin solidified crust. these lava lakes are directly connected to a magma reservoir lying below. observations of thermal emission at several ionian lava lakes reveal glowing molten rock along the patera margin, caused by the lake's crust breaking up along the edge of the patera. over time, because the solidified lava is denser than the still-molten magma below, this crust can founder, triggering an increase in thermal emission at the volcano. for some lava lakes, like the one at pele, this occurs continuously, making pele one of the brightest emitters of heat in the near-infrared spectrum on io. at other sites, such as at loki patera, this can occur episodically. during an overturning episode at these more quiescent lava lakes, a wave of foundering crust spreads out across the patera at the rate of about per day, with new crust forming behind it until the entire lake has been resurfaced. another eruption would only begin once the new crust has cooled and thickened enough for it to no longer be buoyant over the molten lava. during an overturning episode, loki can emit up to ten times more heat than when its crust is stable.