Complex sentence: The tarn at Malham has been dammed and then allowed to flood and observers have noted that whilst water surged at Aire Head, it also surged at the bottom of Malham Cove.
Split into simpler sentences: The tarn at Malham has been dammed and then allowed to flood. Observers have noted that whilst water surged at Aire Head, it also surged at the bottom of Malham Cove.