The summit lava lake within Halemaʻumaʻu Crater on Sunday Jan. 15, 2017 was about 50.5 m (166 ft) below the crater floor (vent rim). One of the most interesting things exposed by the lower lake level was the clear view of the thick, dark veneer of lava on the eastern vent wall (close-up shown below). This veneer formed when the lava lake level was high; lava next to the vent wall cooled and solidified, leaving “bathtub rings” as the lake level rose and fell.
The black rock on the crater floor around the vent was created when the lava lake rose to the point of overflowing in April-May 2015 and October 2016.
Telephoto image of the lava veneer on the 50.5 m (166 ft) tall eastern vent wall; the lava lake surface is visible at lower left. The solidified lava coating the vent wall is quite thick. Parts of it have bathtub rings, but much of it is composed of lumpy protuberances that might have been small ledges at the lake margin or ramparts that formed around spattering sources.
In places, the dark-colored veneer of lava, or bathtub rings, have already collapsed into the lava lake, exposing older, light- or rusty-colored rocks in the vent wall. The lava lake surface is visible in the foreground.