Complex sentence: Kongsvegen has also been in periods of relative stationery movement as the glacier is currently in, as it is retreating at 3 metres (10 feet) per year and has been doing so since 1990.
Split into simpler sentences: Kongsvegen has also been in periods of relative stationery movement as the glacier is in now. At the moment Kongsvegen is retreating at 3 metres (10 feet) per year and has been doing so since 1990.