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Conglomerate: how does it usually break?

ldshield

29-Mar-2016
10:45:39 AM

Over Easter I visited Peterson's Lookout, a crag of conglomerate (that rock that looks like lots of stones or pebbles held together with cement) in the Tyers area of Gippsland.

There's nowhere to place trad gear, but it looked as though it might make for an entertaining day of top-roping, with protruding river pebbles offering numerous smooth rounded holds. While it all *seemed* very solid, a quick search of the forum suggests that in other places conglomerate is often crumbly, as you'd expect from a rock that is basically made up of many smaller rocks compacted together.

I realise it's difficult to say, but when conglomerate breaks is it the odd individual stone that falls out, or does it tend to frequently break off in large, hazardous chunks that make climbing unreasonably dangerous?
Any thoughts would be appreciated- thanks!

IdratherbeclimbingM9

29-Mar-2016
12:09:53 PM

On 29/03/2016 ldshield wrote:
>Over Easter I visited Peterson's Lookout, a crag of conglomerate (that
>rock that looks like lots of stones or pebbles held together with cement)
>in the Tyers area of Gippsland.
>
>There's nowhere to place trad gear, but it looked as though it might make
>for an entertaining day of top-roping, with protruding river pebbles offering
>numerous smooth rounded holds. While it all *seemed* very solid, a quick
>search of the forum suggests that in other places conglomerate is often
>crumbly, as you'd expect from a rock that is basically made up of many
>smaller rocks compacted together.
>
> I realise it's difficult to say, but when conglomerate breaks is it the
>odd individual stone that falls out, or does it tend to frequently break
>off in large, hazardous chunks that make climbing unreasonably dangerous?
>
>Any thoughts would be appreciated- thanks!

There are many types of conglomerate.
Most is friable but some is ok for climbing on...
The stuff I've climbed on mostly lets the holds in use separate from the cliff, but size and hardness of pebble/etc isn't a good indicator of how well they will stay stuck, as often what you might expect to let go doesn't, and sometimes interestingly, and entertainingly, I've had pebbles snap leaving the stuck bit still 'cemented in'!

Go and do your planned top-roping and you will soon find out which type you are on.
Oh, and if belaying from the bottom, make sure belayer wears a helmet and is out of the line of fire, along with any excess rope, etc, at the base...

dalai

29-Mar-2016
3:56:58 PM

It can be strong enough to climb on.

Most famous crags I can think of would be Maple Canyon in the USA

and Riglos in Spain

JamesMc

29-Mar-2016
8:28:13 PM

My observation has been pebbles falling out. Not all: just some.

martym

29-Mar-2016
11:08:28 PM

The guidebook for Montserrat lists all the different pebble types by colour; which ones are solid, slippery, likely to fall off in your hands...

pmonks

30-Mar-2016
1:45:25 AM

Generally it'll be the cobbles that pull out, and depending on their size and the height of the cliff, that could be anywhere from an annoyance to a major danger to the belayer. I'd suggest abseiling over (with a helmet and eye protection, and ideally with your rope tucked up in a bag) and kicking (or better yet whacking with a hammer) any protruding cobbles as you go down, to try to get a sense of how solidly they're embedded. Or, if there are smaller boulders near the base of the cliff, test those before you get out the rope.

Whether cobbles ripping out is likely or not depends almost entirely on the strength of the cement that holds the cobbles together. I've seen everything from a bomber matrix (Montserrat, Catalonia) to barely compressed dirt (The Pinnacles in California, as well as some cliffs I checked out near Murrurundi one time). With enough traffic the softer areas can become quite good for climbing (The Pinnacles is pretty popular, despite being freakishly chossy) - it's partly a question of whether what's left after all the prominent cobbles rip off is climbable.

ldshield

31-Mar-2016
10:12:01 AM

Cool, thanks for the advice. I'll abseil it first to have a look, and take it from there.

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