Complex sentence: The cave systems usually carry away any waters before they reach the fall; however, on 6 December 2015 Malham Cove temporarily became a waterfall following heavy rainfall from Storm Desmond for what is believed to be the first time in centuries.
Split into simpler sentences: The cave systems usually carry away any waters before they reach the fall. However, on 6 December 2015 Malham Cove temporarily became a waterfall following heavy rainfall from Storm Desmond for what is believed to be the first time in centuries.