Only in recent geological times, since the tertiary period, did the typical, rounded, spheroidal weathering of granite outcrops and granite boulders of the Brocken take place. Such blockfields are very rare in Central Europe outside the Alps and are subject to conservation measures. They originated mainly under periglacial conditions, i.e. during the course of the ice ages, and their retreat. Today's blockfields of Brocken granite, as well as other rocks in the Harz National Park, particularly in the Oker valley, are therefore at least 10,000 years old. Physical weathering, such as frost shattering, has played a key role in their formation, resulting in giant piles of loosely stacked rocks. In 2006, the granite blockfields of the Brocken, together with 76 other interesting geotopes, were designated as a National Geotope.