Scientists at the Hawaiian Volcano Observatory have created a thermal image video of the lava lake in Hale­mau­mau Crater that shows lava upwelling in the lake and spreading out like sheets of ice on the ocean.

The lake is about 520 feet wide in the video, which spans about 12 minutes but is shown at 30 times normal speed. The crust migrates toward the south, where it sinks back into the magmatic system along the south and southeast margins of the lake. The surface moves at roughly 1 mph in real time.

The lake surface consists of numerous thin plates of crust separated by hot cracks, the scientists say. As the lake surface migrates, these plates split, merge and change shape.

The video can be seen at hvo.wr.usgs.gov/multimedia/uploads/multimedia-File-555.mov.

The lava lake level has been fluctuating a small amount but was still at 148 feet below the floor of crater Wednesday morning.

At the middle east rift zone, meanwhile, the Kahau­alea 2 lava flow was active, with small scattered breakouts burning forest north of Puu Oo. The so-called Peace Day flow southeast of Puu Oo may no longer be active, the observatory’s website says.