Long piles of basaltic lava pods that have the general appearance of a stack, often many hundreds of metres thick, of discrete stone pillows, each ‘pillow’ rarely being more than 1 m in diameter. The morphology indicates that the ‘pillows’ continued to behave as fluid bodies after the chilled carapace had formed. This provides good evidence of submarine eruption: lava entering water acquires a glassy outer skin as heat is conducted rapidly from the surface. Because water absorbs heat more readily than air, with little increase in its own temperature, the rapid surface cooling allows the molten plastic state of the pillow interior to be maintained longer than it would be in air. Pillows have been observed forming under water from lava entering the sea off Hawaii.
Subjects: Earth Sciences and Geography — Ecology and Conservation.