Wet Sandstone

May 2015 Tim Kuss

In the climbing guide, I talk about staying off of our sandstone when when it's wet. With all the wet weather that we've had in May, there has been some discussion about when to climb or not to climb, and there seems to be some angst about it all. I went climbing at X-rock yesterday. The rock was dry on the surface but it still hadn't recovered from being wet. The grains were still weakly bonded and you could feel the weakness in the rock. I climbed anyway because I was confident (I've been climbing on this rock for like 38 years) that I wouldn't, and I didn't, break any holds. I think the anchors I might have used were still safe. It might be worth a little amature geology, though, a little scientific process. People can to be as blocky and insensitive to this as others might be clueless about the state of politics and their own environment.

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Recently I even read one opinion that even granite is weaker when it's wet. Perhaps, to a tiny extent, but we can observe: When a well driller is drilling for water, he can only find it in strata called aquifers. Typically, sandstones are aquifers, meaning water can travel through the rock. It is permeable. Granite, and even some sandstones, such as those found in the Southeast and even the Fountain Formation around Boulder, which are compressed and seem to be closer to quartzite, may not be. Years ago, I was drilling (rapel), the bolts on The Kong Route, it has been raining for several days beforehand. The surface of the rock seemed dry, but as the drill bit got deeper, maybe two inches, the fines coming out of the hole were a little muddy. It was water perking through the rock but not close enough to the surface to evaporate as fast.

There is all kinds of talk about not climbing at Indian Creek after it rains, and people going on about "how irresponsible" people are and preserving the rock for future generations. There's even a Facebook page. Obviously, ya don't want to climb when it's wet, it's probably even more slippery than when it's dry. You know that cams rip right out of that (barely) rock, even in drought conditions, right? Seems like all you need is a few millimeters of dry surface and you're good to go. There are no holds to break off and sure, there are some strong climbers out there but I don't think your handjams are going to blow the side of the crack off, right?

Go climbing! If it's wet, don't. Just don't break off the holds. Pick routes that are free of lichen and oxidized rock. You can look at the cliff and see where it gets wet. The pink areas of rock at East A obviously stay more dry than drainage zones. If there is a blackish water streak, that's from water. Lichen grows in the pores that hold its nutrient, water. Xrock is prone to being wet because of the lower angle and lack of overhangs. On the same hand, most of the weaker rock has largely broken off. Certainly there is some potential for further erosion. The Dakota Sandstone bouldering seems to be of a more quartzite content and slightly harder, but is broken by softer areas of rock or larger grained portions.

Here's an interesting post that I copied from Mountain Project:
Greg Twombly wrote:
As a climber it seems some sandstones are weaker after rain. As a geologist I dont know why. Sandstones come in many varieties depending on the sand it's made of. Sand from ground up rocks like volcanics, granites, metamorphics, even limestone and is called lithic arenite. Sandstone composed of well rounded quartz would be quartz arenite, and can be aeolian (from wind, like the Navajo), fluvial (from a river), or marine or mixed (like the Dakota). Quartzite is a pure quartz sandstone with a silica cement (originally the term meant metamorphic). Sandstones are held together with cements, which can be clay, calcite, iron, or silica. Lyons sndstone in the Garden of the Gods is an aeolian/beach sand with clay and iron cements. The Fountain Formation in Eldorado and the Flatirons is arkosic conglomerate with silica and clay cements. Silica cements are very hard, not easily water soluble, and shouldnt weaken after a rain. Sandstones that are much weaker after a rain, like the Dakota or Lyons, seem to have more clay cements so I speculate that the clays (which can take up water in their crystal lattices) are the part that weakens when wet.

Another poster Rigggs 24 said:

Im a geologist so stuff like this is interesting to me. I think the type of cement has a role but it might be more due to permeability, which the cement is definitely related to but factors such as grain sorting, grain shape, if the rock has been metamorphosed, etc...also play a role.                                                  

 My thought is that sandstone that is highly permeable will become weaker with the presence of water in it pores. Whereas, highly impermeable sandstone(or any impermeable rock) will see little effect from water in regards to climbing on it after rain since the water is really just on the surface and not within the pores. Im sure there are all types of in between as well. Why I think this is for a couple reasons. Although both are more of just hypotheses. 1) When you apply a stress (stepping or pulling on holds) to a water saturated rock, I would think that you actually instantaneously increase the pore pressure within a very localized portion of the rock. When pore pressure is increased, a rock becomes easier to break. (this is my understanding of why earthquakes have been occurring near areas with a lot of water injection) 2) the friction between sand grains at the pore level is decreased allowing for it to break/erode more easily.

Here's a link to that discussion