"Stone-river"

I watched this video and remembered what is happend to me and my friend. I wanted to become an alpinist but nobody wanted accept me on the courses because of my health. So one day one friend that was instructor said me, we can go for a short walk on the mountain. I was so incredibly happy!

The way we choosed was very hard, and because it was after an incredible for that places storm, many trees were broken and every step needed all forces. And then suddenly we were on the bank of the "stone-river". What it is you can see in the video, when the boys throw the stone, it goes down in a little "stone-river".

I did not know anything about this phenomena, but my friend knew, he was an expert instructor.
It is a stripe of stones. They seem to be nothing special, but if something touches one of those stones, all them begin to fall. In our case the river was large and we could not see not the beginning, neither the end of it. My friend told me about and... slid in this "river". Only one foot. But all the river began it's movement. And my friend was inside. I don't know how I could grab him, where I found forces to pull him out... Fortunatelly he went out about 2 meters lower only with great fear. Nothing broken seriously, only livids.

This friend was very contrary to take me with him in the mountains. But after this adventure he allowed me to go with his groups for the easy walks other different times. ;))) ( Moral: if you want, but instructor is contrary, save him the life and he is yourth)