On the southern slopes of the Weiselberg lies a basaltic blockfield, the Steinernes Meer (Rocky Sea). Originally, magma rose from the earth's interior. It gradually solidified under the earth's surface to form mostly pentagonal column formations, which is typical of slowly cooling basalt. Their shape was caused during cooling by shrinkage of the magma, similar to cracks in the drying mud of a puddle. Over a period of millions of years, the surrounding softer rock was eroded. The blockfield visible today was formed during the ice age around 10,000 years ago by solifluction of the weathered rock columns.