Nature at Work: Liquefaction, Boils, Carbuncles, Aquifers and Silt Volcanoes

In previous posts at about the Canterbury earthquake, I have been trying to compare what we have been seeing on the flats at the western base of Banks Peninsula, where the ancient volcanic peninsula  butts up against the shingle plains, with what has been written elsewhere on these phenomena.  I now know that the silt volcanoes are sometimes termed earthquake ‘boils’. Where they run together they are sometimes called ‘carbuncles’.  What delightful terminology!

I also now know that there are similarities between liquefaction and quicksand, where, for different reasons, the sand particles go into suspension and lose all supportive strength. There is also an association in the literature between  silt (and sand ) volcanoes and the presence of natural artesian water. However, whereas in some parts of Christchurch, such as Bexley, there has been massive liquefaction and fundamental associated structural failure, that does not seem to have been  the case with the silt and clay soils in Halswell, where there has been much less house damage, but lots of silt volcanoes, and uplifted water.    

Clearly what we are observing is caused by complex factors. Soil types, the presence of aquifers, and the role of Banks Peninsula would all seem to be mediating factors.  In the meantime, the aftershocks continue, with this morning’s shake from beneath the Peninsula itself being the biggest aftershock we have received at our house.

About Keith Woodford

Keith Woodford is an independent consultant, based in New Zealand, who works internationally on agri-food systems and rural development projects. He holds honorary positions as Professor of Agri-Food Systems at Lincoln University, New Zealand, and as Senior Research Fellow at the Contemporary China Research Centre at Victoria University, Wellington.
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