PUB POSER: WHY DO SUMMITS HAVE BOULDERFIELDS?

We take the fragmented, round-stoned expanses of our highest peaks for granted – but have you ever wondered what caused them?

Scafell Pike's summit boulders. But why are they there? Photo: Tom Bailey / Trail Magazine

Scafell Pike's summit boulders. But why are they there? Photo: Tom Bailey / Trail Magazine

The UK’s mountains used to be taller, some of them much, much taller. But over millions of years they have been eroded down to their current size, a process which continues. Rain, wind and ice constantly attack summits, creating cracks, crevices and hollows. Moisture gets in to these weak points and, when it freezes and expands, exerts pressure on the rock. Regular freeze-thaw cycles can eventually split stone apart. Repeat this process over millennia and you end up with carpets of shattered rock, such as those seen on the summits of Scafell Pike, Tryfan and the Glyders, and Ben Nevis. These in turn are exposed to the perpetual battering by the elements, sculpting the stone into irregular shapes – all of them the result of the weather’s war of attrition with our peaks.