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

Focus: Microscopic Theory for Peeling Tape
Mechanics

Focus: Microscopic Theory for Peeling Tape

Extensive experiments lead to a theory that describes the microscale, jerky process involved in the seemingly smooth peeling of tape from a surface. Read More »

Synopsis: Sorting Blood Cells via Their Stiffness
Biological Physics

Synopsis: Sorting Blood Cells via Their Stiffness

A proposed modification to a microfluidic cell-sorting device could separate cells by their deformability, an important marker for several diseases. Read More »

Focus: <i>Video</i>—Slow-Motion Footage Captures Rubber Band Ripples
Mechanics

Focus: Video—Slow-Motion Footage Captures Rubber Band Ripples

Videos of a moving rubber band show that the band takes on previously unpredicted wavy shapes when it is shot through the air. Read More »

More Articles