Grow your own bridge, hill or fortress

From time to time, truly odd ideas emerge, even from such a conservative bunch as geoscientists.  They are often based on quite mundane science.  If you pour sulphuric acid on limestone, of course it fizzes violently because CO2 is a product of the simple reaction.  Less noticeable is that the other product, hydrated calcium sulphate or gypsum, is considerably less dense than the calcite in limestone.  The solid residue swells.  “What if….?”, thought Dutch geochemist Roelof Schuiling (Ravilious, K 2004.  The new stone age.  New Scientist, 20 November 2004, p. 38-41).  His idea was to put the simple phenomenon to practical use; infiltrate sulphuric acid into porous limestone and the swelling will bulge up the surface.  This does happen naturally, where sulphide-sulphate oxidising bacteria generate sulphuric acid, which renders limestone to an easily erodable mess, and in some soils generates gypsum lenses that bulge up the ground into surface blisters.  Schuiling reckons that the huge sulphuric acid surplus, created partly by removing sulphur from vehicle fuels, could be used as a kind of geo-engineering tool on a vast scale.  For instance, the coralline shallows beneath the shallow Palk Straits that separate India and Sri Lanka, could be induced to bulge up and create an island ridge, and so complete what is known as Adam’s Bridge that nearly links the two countries.  Closer to home, the Low Countries might become the “Slightly Higher Countries”.  Worryingly, the technology to make the process viable is simple, if a little expensive on the scales envisaged.  The worry, of course, is yet more CO­2 emission plus the effect on the environment of so much sulphate and a massive fall in pH.

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