Synopsis: Cracking Up

A new model explains why cracks in cooling lava tend to form hexagonal patterns.

Cooling lava shrinks and cracks, often forming stunning structures, such as the hexagonal columns found in the volcanic remains at Ireland’s Giant’s Causeway. Although cracks spread from the top down, hexagonal columns can emerge from a crack pattern on the surface that is initially rectangular. Researchers now explain why, using a new model that tracks the cracks from the moment they form at the surface to the time when they have penetrated through the cooling lava. The model could be applicable to crack patterns that form in other materials, such as cooling ceramics.

The surface of cooling lava contracts more quickly than the still-warm liquid underneath, creating a stress that is relieved by the formation of cracks. Martin Hofmann from the Dresden University of Technology, Germany, and colleagues considered a uniform lava layer and calculated the energy released from different crack patterns. They found that, in the initial stages of cooling, when the cracks start to appear at random places on the surface, the energy release is greatest if the cracks intersect at 90-degree angles. But as the lava continues to cool and shrink, and the cracks collectively start to penetrate into the bulk, more energy is released per crack if they intersect at 120-degree angles. This transition from individual to collective growth of the cracks drives the pattern from rectangular to hexagonal. The hexagonal pattern is then maintained as the lava cools further, eventually leading to an array of hexagonal columns, similar to those seen in nature.

This research is published in Physical Review Letters.

–Katherine Wright


Features

More Features »

Announcements

More Announcements »

Subject Areas

GeophysicsMechanics

Previous Synopsis

Next Synopsis

Biological Physics

Noise Gives Biology a Hand

Read More »

Related Articles

Synopsis: The Geometry of Arctic Ponds
Geophysics

Synopsis: The Geometry of Arctic Ponds

A geometric model of meltwater ponds may help predict how the polar ice caps might evolve under future climate changes. Read More »

Synopsis: Silica’s High-Pressure Phase
Materials Science

Synopsis: Silica’s High-Pressure Phase

The rapid compression of silica to pressures of 36 GPa and higher transforms it from an amorphous material to a tetragonal crystal. Read More »

Viewpoint: Intermittent Turbulence in a Global Ocean Model
Geophysics

Viewpoint: Intermittent Turbulence in a Global Ocean Model

A large-scale model of ocean dynamics finds intermittent behavior that may have implications for how the ocean’s energy budget is assessed. Read More »

More Articles