27 February 2011

Geology and rock climbing

Posted by Jessica Ball

As a novice rock climber who’s also a geologist, I’m just as interested in the rock I’m climbing as the route. The type of rock you’re climbing on can have big impacts on the difficulty of the climb, since the way that a rock weathers and erodes determines what kinds of holds are available, whether there are cracks or ledges, vertical faces or overhangs, and what safety concerns you should be aware of. I haven’t had a huge amount of experience with outdoor climbing, but from the scrambling I’ve done on mapping excursions, I certainly know which rocks I prefer to climb on – but what do more experienced climbers prefer?

Most rock climbing guides don’t focus on the rock type as much as the features that make the rocks good for climbing, so I had to do a little research on my own. Out 118 popular US climbing areas listed on Wikipedia, a survey of rock types gives an interesting – but not terribly surprising – distribution. (If I have more time in the future, I’ll try to compile a worldwide list, but this will do for now…)

This is a pretty rough summary, and probably error-prone (and limited by Wikipedia’s list), but it’s possible to make some generalizations. Granite and sandstone are by far the most popular rock types, with basalt in third. This makes sense to me, when I think about it from a climbing perspective; granite, sandstone and basalt can all be pretty tough rocks – which means a hold won’t break off under your hands or feet – and they’re often rough, which provides friction for gripping. Limestone and dolostone are easier to dissolve and may have more “features” to grip, but this can also make them too weak for climbing. The metamorphic rocks are more of a mixed bag; quartzite is tough but also hard on the hands, while gneiss may have planes of weakness that make driving in climbing anchors chancy.

I don’t consider myself a climbing expert by any means, so I checked to see what the authors of my climbing books had to say about different rock types:

“Granite, basalt and sandstone are three types of rock that often have cracks…Sport climbing (bolt-protected face climbs on vertical or overhanging rock) is popular on limestone, sandstone and volcanic rocks” (Woman’s Guide: Climbing)

Climbers at Joshua Tree National Park, CA. © Jarek Tuszynski / Wikimedia Commons / CC-BY-SA-3.0 & GDFL , via Wikimedia Commons

“Granite climbing is characterized by steep slab climbing (often lacking natural protection)…Rhyolite provides some of the very best and most highly featured rocks for climbing…Sandstone grains provide good traction and the rock is often fractured, providing natural protection placements…Water-solution pockets in limestone provide excellent hand- and finger-holds…Conglomerates can have surprising and excellent holds even on overhanging walls, but natural protection is usually unreliable….Quartzite often provides fantastic climbing and reasonable natural protection…Gneiss is a rough rock that can form large cliffs of variable quality…Slate can provide exciting climbing on tiny edges, often devoid of reliable protection. Even drilled bolts are of dubious value.” (The Climbing Handbook)

Weathering and erosion processes can be a mixed blessing when it comes to climbing. Exfoliation in granites, for example, forms cracks and other features which make ascent possible on huge cliff faces like the ones at Yosemite, but it can also create dangerously loose rock that can fall off in huge chunks. Dissolution in carbonates can form pockets that make great hand- and foot-holds, but too much dissolution can weaken the rock too much to support someone’s weight. And persistently wet conditions can basically turn a rock into clayey mush – probably a good reason that many popular rock climbing areas are located in more arid regions.

If there are any climbers out there reading this, what are your favorite climbing locations and rock types? Where do you find the most challenging climbs – or the easiest? Do you ever notice things like grain or crystal size while you’re climbing, and what effect do they have on your climbing?


Long, Steve, 2007. The Climbing Handbook: The complete guide to safe and exciting rock climbing. Firefly Books, Buffalo, NY, 192 pp.

Presson, Shelley, 2000. A Ragged Mountain Press Woman’s Guide: Climbing. Ragged Mountain Press, Camden, ME, 176 pp.