Honeycombs like the one pictured above 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.
Honeycombs have been found on rocks at many places on Earth, and . of Charles University in Prague has studied them in the Czech Republic, where honeycombs on exposed sandstones create 鈥渘atural 鈥榬ock cities鈥� with cliffs and pinnacles鈥�.
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Over the years, researchers and enthusiasts have suggested for these formations, from , to . The key question is, why do the 鈥渞idges鈥� get preserved while the hollows they surround get eroded? In recent years researchers have homed in on water and salt as crucial factors.
Bruthans and his colleagues focused on an area just below the rock鈥檚 surface called the 鈥渆vaporation front鈥�. Here, water in the rock can escape into the air, leaving behind any salt it was carrying. This salt can form crystals. These expand when heated, causing cracks in the rock and causing it to 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.
Bruthans says uneven surfaces of only a few millimeters between hollows and protrusions is enough to spur honeycombs to develop.
Geomorphology
