There is evidence that hydraulic fracturing caused the massive mud volcano in Indonesia that has since wiped out villages and farmland, displacing 30,000 people: “The eruption demonstrates that mud volcanoes can be initiated by fracture propagation through significant thicknesses of overburden and shows that the mud and fluid need not have previously coexisted, but can be “mixed” within unlithified sedimentary strata.”
(First published in The Geological Society of America’s news magazine, GSA Today, in February 2007)
