Like a living snake this lavaflow is winding down the valley. It has a velocity of several km/h in the upper part.
The typical "two lane" shape is a result of the fluid mechanics in the flow: The flow moves a lot slower on its sides than in the centre. And at the margin it doesn't move at all. Thus the cold surface material close to the margin is getting twisted and ripped open all the time, whereas the material in the centre remains in a steady flow and has time to cool down at the surface.