• Question: Could carbon dioxide erode away rocks underneath the earth and if it did would the ground collapse from us and we would then die?

    Asked by musicallyhappy4968 to Gemma on 27 Jun 2012.
    • Photo: Gemma Purser

      Gemma Purser answered on 27 Jun 2012:

      Hi musicallyhappy4968,

      I think i tried to answer this question on the live chat i think but I didn’t type fast enough so Im so glad it got through to here!! 🙂

      Right, well…… Carbon dioxide as a gas has less effect but when it is dissolved in water it can actually errode away rocks underground. Carbon dioxide reacts with water to form carbonic acid. Its a weak acid that can breakdown rocks like limestone, chalk and gypsum . Limestone and chalk are made mainly of a compound called calcium carbonate. This dissolves easily in acid. You could try this at home using egg shell (calcium cabonate) and vinegar (acid). you see bubbles form as the carbon dioxide is given off by the calcium carbonate breaking down. Underground the acidic water very slowly errodes away channels and caves in the rock. Sometimes the roofs of these caves are very thin but look normal from the surface. If enough of the rock has been erroded away then the roofs can collapse and form holes in the ground, called sink holes.
      Heres a few interesting links with some good pictures:
      http://www.bgs.ac.uk/foundation-web/PoolesCavern.html

      http://www.bgs.ac.uk/science/landUseAndDevelopment/shallow_geohazards/dissolution.html

      If you mean what would happen to the rocks if we inject carbon dioxide underground then thats different. The type of rock that carbon dioxide is injected into is mainly sandstone deep underground. This rock is really slow to react with dissolved carbon dioxide. There is a carbon dioxide storage site called Sleipner. Here the carbon dioxide has been underground since 1996. It has moved slightly but it is still trapped underground, between the grains of sand that make the sandstone and is very unlikely to collapse the ground.
      If you were stood over any area that suddenly collapsed I guess you would have a chance of dying but if the area was part of a CCS storage site then you wouldnt be able to get as close to it. There are certain monitoring techniques too such as sesmics, remote sensing and tilt meters that can help us to detect any slight changes in the surface of the ground above a storage site so that we can put in place a plan of action if the unlikely did occur.

      Hope that helps and wasn’t too much to read! 🙂

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