Using the thinking map for skilful causal explanation (see the start of this section) to guide you, write a brief evaluative response to the following passage: An underwater survey of the Witch...

Using the thinking map for skilful causal explanation (see the start of this section) to guide you, write a brief evaluative response to the following passage: An underwater survey of the Witch Ground, in the North Sea off Aberdeen [Scotland], has discovered a trawler which was probably sunk by a sudden burst of methane gas escaping from a vent in the sea fl oor – known as the Witch’s Hole. When methane – or natural gas – bubbles through the sea in big enough volumes, it lowers the density of the water around it to a point at which objects, including ships, will no longer fl oat. ‘Any ship caught above [such a blow-out] would sink as if it were in a lift shaft,’ said Alan Judd, a marine geologist from the University of Sunderland who led the Witch Ground survey expedition. In this case the trawler had sunk ‘fl at’ with its hull sitting horizontally on the sea bed exactly over the Witch’s Hole vent. This was consistent with the vessel being sunk by a methane blow-out; if she had been holed she would have sunk with the holed end lowest. Even sailors who jumped overboard wearing lifejackets would sink like stones. The Witch Ground, and the Witch’s Hole in particular, have long been known among fi shermen as treacherous waters. Methane blow-outs are thought to have destroyed about 40 oil platforms around the world; the Witch Ground is just 22 miles from the Forties oil fi eld. (Adapted from an article in The Times, 30 November 2000, by their science correspondent Mark Henderson)