CPD At The AMI AGM - Snow Anchors

The load cell George brought along. Here it reads 0.67kn of maximum force for the test on the snow anchor.

Last weekend was the AMI AGM. It was a good chance for lots of Mountain Instructors to get together for a good social. Apart from a successful AGM there was a broad range of CPD (continual professional development) day or part day sessions available. On the Saturday I joined the session run by George McEwan on the 'Use and abuse of snow anchors'. We found some snow slopes with fresh snow deposits. We wanted the snow anchors to fail so that we could compare the maximal force required to reach the point of destruction, to get an idea of which anchor type was stronger/weaker. We used a load cell which measured the maximal force (measured in kn). With each anchor we considered the surface area (SA) being utilised and the symmetry of that SA.We did lots of tests (but the amount of data is insufficient to be scientifically analytical) and the reinforced axe was consistently stronger than the single buried axe (perhaps double?). The basic mountaineering axe was not noticeably stronger than the slightly curved mountaineering axe, but was perhaps stronger than the curved tech axe.


A shear fail of a buried axe (1) from Max Hunter on Vimeo.


A shear fail of a reinforced buried axe from Max Hunter on Vimeo.

A bullhorn arrangement for the nomics

We did bullhorn buried axe tests for the Petzl Nomic axes and the DMM Apex axes. We tried various bullhorn configurations - with different levels of overlap - maximal overlap shown in the photo, reduced down to a small overlap (making the bullhorn longer). The reduction of overlap did not seem to increase the strength of the anchor - perhaps it even reduced the strength. The bullhorn has good symmetry, and even though reducing the overlap increases the SA, it did not seem to increase strength. The bullhorn generally failed after a single buried axe but was not reliably stronger than (or as strong as) a reinforced axe.


A shear fail of a Bullhorn arrangement buried axe from Max Hunter on Vimeo.

We tested 2 Deadmen snow anchors, and these proved to be very strong, but were very dependent on the angle of insertion into the snow. They did seem to be repeatedly stronger than a reinforced axe anchor. Deadmen have a very large SA and are perfectly symmetrical down a vertical axis through the cable.

We moved on to build bucket seats. We managed to destroy an obviously weak bucket seat, but could not destroy the second seat.

We moved on to measure the impact force on a climber as they fall past a belayer in a bucket seat. The load cell was attached directly to the falling climber. We used body belaying (with a non dynamic arrest and with a very dynamic arrest), and a belay plate (at least 3 belay plates were tested) with dynamic and non dynamic arrests. With non dynamic arresting the maximal force was over 1kn, but with a hugely dynamic arrest (with body belaying or belay plate) the maximal force was down to 0.4kn. The skill of the belayer seemed crucial here to reduce the maximal impact force.


An impact force test on a falling climber+a belayer in a bucket seat using dynamic belaying from Max Hunter on Vimeo.

We built 2 snow bollards. The first was what we would like to build, for successful abseiling, and the second was of a size that we thought would probably fail. The smaller bollard is in the photo below. Both bollards withstood abseils (without belay plates). Finally we tried to fail the larger bollard, and measure the maximal force we could apply to it. We could not fail the anchor.

Abseiling off the 2 snow bollards

The smaller of the 2 snow bollards

It was an excellent day of CPD. Thank you to AMI, Glenmore Lodge and George McEwan for the day of training. (George I hope I haven't misrepresented any of the tests/results or training).

Trying to destroy the larger of the 2 snow bollards