I have never been ice climbing, but my friend who has says the following does not work in ice climbing. My friend cannot remember the reason, and I'm puzzled.
Their claim is that, when top-roping a long route using 2 ropes tied together, it is not possible to avoid having the belayer pass a knot.
In rock climbing the knot passing is easy to avoid by having the climber tie into the right spot on the rope. E.g. if top-roping a 40m climb using two 50m ropes tied together, tying in 10 meters from the rope's end avoids the need to pass a knot.
This won't work if the belayer is positioned higher than the start of the climb, but my friend says that is not the problem (the belayer is usually lower in ice climbing).
It also won't work if using e.g. 70+30 for a 50m climb, but if my experience with rock climbers is any indication, people happily buy longer ropes to avoid having to do tricks.
So does anyone know what about ice climbing makes it necessary to pass knots when TRing long routes ?