HONEYCOMB patterns, like the one pictured below, plaster the surface of rocks around the world, but how they form has long been a mystery. Now it seems they may be created by the action of water and salt.
Ji艡铆 Bruthans at Charles University in Prague, Czech Republic, and his colleagues investigated why the 鈥渞idges鈥� get preserved while the hollows they surround get eroded.
Advertisement
They focused on an area just below the rock鈥檚 surface called the 鈥渆vaporation front鈥�. Here, water in the rock escapes into the air, leaving behind any salt it was carrying. Salt crystals then form. These expand when heated, causing cracks in the rock and helping it erode.
The evaporation front is invisible to the naked eye, says Bruthans. So his team added a fluorescent dye to the surface of the honeycombs. The evaporation front quickly popped out, marked bright red.
When the rock had only a little water in it, any slight protrusions jutted above the evaporation front. That meant water was evaporating from some patches of the surface but not others. Areas of evaporation accumulated salt crystals and were eroded, becoming hollows (Geomorphology, ).
Bruthans says uneven surfaces of only a few millimetres between hollows and protrusions is enough to spur honeycombs to develop.
This article appeared in print under the headline 鈥淢ystery rock formation solved鈥�