Stability of rock boulders as highline anchors

Just before christmas 2009, the first close to fatal highline accident happened in america. The highliners were very experienced but obviously misestimated the stability of boulders lying on the top of rock when used as highline anchors.

This page tries to give a brief check, if boulders are big enough for anchoring highlines. Nevertheless, this is a theoretical model and it does not guarantee that a boulder declared safe, can't move under any circumstances.

This simple model ignores the influence of angular momentums and is therefore not suitable for judging the stability of rock needles.  Highlining is dangerous and a backup on seperate anchors is always necessary!

Please enter parameters

The size of the block:
length of the block [m]
height of the block [m]
width of the block [m]
type of the rock

Is the block lying on an inclined surface?
inclination [°]

This parameter can introduce some effects of e.g. wet rock (0.5), bulky contact surfaces (1.5), safety factors (<1) etc. Friction goodness

The block has a mass of


On an even surface the block can withstand a
sideward force (applied below the center of gravity) of

0 kN

The Slope angle is bigger than the friction angle. According to the law of physics, the block should not be there or very easy start to slide! Recheck if you entered the slope angle of the contact area between Boulder and Rock.