According to NASA ADS, which I accept may not capture all geosciences articles, McGuire (W.J.) wrote one refereed paper in 2012, one in 2009, one in 2006, one in 2004, and quite a few before 2000. These are his publications which have to withstand peer-review, not op-ed pieces in the guardian. He was not a co-author with Day and Ward on the paper on Cumbre Vieja, though he comes up on TV programmes on the subject. I would be inclined to believe his assertions if they were made in these few peer-reviewed papers, not in the Guardian and not on TV. These papers are mostly on slope failure of volcanos, his most cited work was done at Mt. Etna in the late 80s and early 90s.