You are walking through rough, unstable rock that looks like the jumbled ‘a‘ā lava you see elsewhere in the park. But this rock is not ‘a‘ā. It formed when welded spatter (blobs of molten lava fused together) broke apart as it slid down the cone, rolling and tumbling into coarse, jagged pieces of rock.

What is a a rock you ask? A'ā lava flows have irregular rough surfaces made of jagged, spiny and rough clasts of lava called clinkers. These lavas have surfaces that are either too viscous or are flowing too rapidly to flow plasticly like pāhoehoe. Instead they are ripped apart by shear strain forming a breccia at the top of the flow.

Every episode ended with lava draining back into the vent. The rock beneath your feet—slabs of the lake’s crust—stacked up as lava drained from the crater. These brittle layers broke and pulled apart as they slumped into the vent, creating the dangerous cracks and unstable rock layers in front of you. The rocks here weigh less than you might expect because they contain numerous holes left by gas bubbles in the frothy lava. If you pick up a rock, watch out for its razor-sharp edges.