The Island That Comes and Goes

Derwentwater in Cumberland has an island that is not always there. A section of the lake's peaty bottom rises to the surface from time to time, floats for a while, and later settles back down.

The explanation the book offers is unglamorous and entirely convincing: the mass is swollen and buoyed up by gas produced as the vegetable matter in it decomposes. Push a boat-hook into the island and carburetted hydrogen comes up out of it in abundance^[1].