Complex sentence: The rock is approximately 1 metre in height, 13 metres in diameter, with an area of approximately 300 sq. metres, and as such is covered at high tide and in heavy seas, often only visible, as in the photograph below, as breaking waves.
Split into simpler sentences: The rock is approximately 1 metre above low water, 13 metres in diameter, with an area of approximately 300 sq. metres. It is covered at high tide and in heavy seas, often only visible, as in the photograph below, as breaking waves.