Partial Failure - Dyneema Sling Anchor

UPDATE: It could have been abrasion but rodents likely were a main factor. They ate clean through an old rope I installed as a handline too. 

original post:

We had a tree anchor set up - I had put my new 240cm mammut contact 8mm sling around the tree with a master point, and the sling ran slightly over a rock. We TR'd the route about 3-4 times, stopping often to check out gear placements, and there were a couple falls on TR. 

Here's where the story gets a bit complex: I then manage to forget that sling anchor at the top of the climb. I likely forgot about the anchor via lowering off and pulling the rope through, & forgetting to hike to the top of the crag to retrieve it.

It remained there for 39 days, untouched. The climbing area is new - I'm quite certain no one else goes there. In any case, when we finally found our anchor, it was completely chewed up - all the wear points corresponded with where it would have touched the (now obviously quite sharp) rock, and despite the low angle across the rock (maybe 15° bend), the sling was in near tatters. 

Near the sewn section I was able to break the sling by pulling it apart in my hands - ie, it had been severed by the rock and only some fluffy thread had been holding it together. 

The route below wanders a touch left to right, and the edge was in a diagonal orientation, so it could have scraped side to side.

If we didn't have a redundant anchor, the anchor would have failed. As is, the sling was cut on the other load bearing strand 4/5 of the way through - with one more climber on the system, the anchor would have likely failed as well. A huge wake-up call for us to always check the anchor to make sure it's not on anything at all sharp-looking. I don't have pictures of the exact set-up, but I'll follow up with a re-creation of the anchor best I can when I'm back there.

 I do have pictures of the sling:

Some other thoughts: The anchor was up there for a good while (39 days) by itself but I don't believe where it was would have been exposed to extreme winds/weather. The rock is granodiorite (granite). It's possible though unlikely that a tree somehow fell on the anchor and sailed off the cliff or some other very unlikely scenario but it's pretty flat up top so those explanations I think are exceedingly unlikely. The sling was new (bought this season). 

Scary to say the least. Never build a TR anchor where it can rub a rock. 

Thanks for posting this.  I think it is a good reminder for folks that climbing gear can and will fail.  If you had pictures of the anchor and tree setup I think it would be even more informative for folks.  

I think another take away should be to choose appropriate material when building top rope anchors.  Using 8mm dyneema for an un-attended top rope anchor that is touching rock isn't really the best practice.  7mm or 8mm cord or even better, an old piece of lead rope makes great anchor material for these situations.  Skinny dyneema is great for multi-pitch climbing where weight is more of a concern but for cragging there are better and cheaper options.

Glad everyone is your party was ok!  

Rodents.

Mikey Schaefer wrote:

  

I think another take away should be to choose appropriate material when building top rope anchors.  Using 8mm dyneema for an un-attended top rope anchor that is touching rock isn't really the best practice.  7mm or 8mm cord or even better, an old piece of lead rope makes great anchor material for these situations.  Skinny dyneema is great for multi-pitch climbing where weight is more of a concern but for cragging there are better and cheaper options.

X2

Thanks for sharing a great reminder.

It could be rodents or birds (seen birds "collecting" dyneema once), but if it ran over an edge, that seems likely. I seem to recall someone sawing through a 10 or 11mm static in one day of route development before.

I'm partial to some semi static polyester 8mm cord for unattended TR-over-an-edge anchors. I've seen dynamic ropes wear quickly when loaded/unloaded on an edge.

A few places sell 10 and 11mm static by the foot which could be handy for someone doing a lot of this stuff.

Terry E wrote:

Rodents.

That was one of my first thoughts as well - it could have been and I'd love to believe that that was the case - but the wear points lined up well with where the sling was on the rock. Could be coincidence though.

I was just inspecting the sling closely where it was cut through - the cut fibres have that burnt/heat affected feel. It's scratchy in that melted plastic way. Don't think it really shows in the picture but it feels like there's burrs on it from heat:

 The other sections that are worn don't have this burnt feel. I think that kinda rules out rodents - I  guess the friction generated enough heat to singe the sling while we were on TR. I'm not sure when I'll be able to get photos of the exact spot and how we set up the anchor but likely the next week or so. 

Buy another sling and recreate the scenario as best a possible.

with the burnt feel to it, could be landsharks with laser beams

Buff Johnson wrote:

with the burnt feel to it, could be landsharks with laser beams

I agree with this guy

Mikey Schaefer wrote:

Thanks for posting this.  I think it is a good reminder for folks that climbing gear can and will fail.  If you had pictures of the anchor and tree setup I think it would be even more informative for folks.  

I think another take away should be to choose appropriate material when building top rope anchors.  Using 8mm dyneema for an un-attended top rope anchor that is touching rock isn't really the best practice.  7mm or 8mm cord or even better, an old piece of lead rope makes great anchor material for these situations.  Skinny dyneema is great for multi-pitch climbing where weight is more of a concern but for cragging there are better and cheaper options.

Glad everyone is your party was ok!  

A better solution is not to put things over edges unprotected. A few years ago I set up this top rope anchor on a very easy ice climb that was about 10 m high. I used a thick static rope (10.5 mm if I remenber correctly) with two legs, one going to a bolt, the other around a block. One of the legs was obviously going over an edge, but I did not care since it was an easy 10 m climb and the top rope anchor had two legs. I think we climbed the ice six times, no one fell and we lowered the climbers. Then I retrived the static rope it was almost cut. Fixing ropes over edges is vary scary.

Wind can whip slings back and forth and saw across edges. When static lines have to be up for a while, people are very careful place directionals and if they can tension them a bit so that the rope isn't free to blow around.

Rodents also seem likely, the thread used for the bartacks can be lubricated, perhaps some animal found it tasty, or it was salty from sweat.

These things happen. 39 days is a long time for a material to be sawing against rock.

The first photo could possibly be rodents but the 2nd two photos are cut/abrasion for sure. I've never been fond of the skinny 8mm or 6mm slings but this is a great reminder for me as to why. Sorry that this happened to your brand new sling, though, it's quite a bummer

So I just was up at the crag and an old rope that I installed last week as a hand line also got chewed up; the rope fully cut. Rodents is right. Probably the reason why the anchor looked the way it did too. 

I'll never know if it was entirely rodents for the anchor or if the anchor partly cut while we were on it and then rodents finished the damage, but I can rest a bit easier knowing rodents almost certainly played a part in why the sling looked so particularly beat up. 

^ my poor hand line (at least it was only 20m of dead rope) 

mouse attack — I think the color scheme gave a retro sixties vibe, making all of the other mice jealous.

Imagine the rodents chewed through the sling while you were TRing!!!