La Palma is the steepest inhabited island in the wold, so it’s in a losing battle with gravity. Sometimes rocks fall on the road, particularly after heavy rain, a freeze or a thaw. (Of course the last two only happen at high altitude.) Normally the roads get cleared pretty quickly, but the road to the observatory takes a little longer, maybe a day and a half. Then you get to slalom around the rocks.
Public spirited locals will sometimes shift the rocks off the road. Feel free to join in.