Glastonbury felt a sudden thud on Saturday February 17 in 2018, like a pile-driver at work next door or a big lorry going over a kerb, or a sonic boom.

  The radio news reported that it was a small earthquake, magnitude 4.2, at 14:31 GMT, centred about five miles underground near Swansea. People noticed it as far away as Blackpool, London and Cornwall. No damage worse than rattling crockery was mentioned.

  Four centuries ago, however, a tsunami — as we would call it now — a 15-foot wall of water moving at 30 miles an hour — crashed into Somerset and killed thousands of people. More of that story was told in Newsletter 134. The floodwater came up as far as the chancel of St Benedict’s church in Glastonbury.

Richter elucidated

  The Richter scale for measuring earthquakes is logarithmic, which means, for example, that magnitude 5 is ten times stronger than magnitude 4. Thus Japan’s 2011 quake of magnitude 9, one of the worst ever recorded, was 100,000 times stronger than the Swansea thud of magnitude 4 on February 17.