A small tsunami that struck the south coast of England on 27 June was most likely caused by weather conditions and not a submarine landslide or earthquake, according to the British Geological Survey (BGS).
The tsunami occurred in South West England, between Penzance and Portsmouth, along approximately 200 miles of coastline. It struck the Yealm (see below video) at about 10.30 on 27 June; wave heights were 0.5 - 0.8 metres. Tide data indicates an east to west progression of the wave, confirmed by observations at St Michael's Mount, where the water built up on the east side of the causeway (20 cm higher than on the west) before it was overtopped.
According to the Tidal Gauge Anomaly measure, which records the difference between the forecast tide and actual tide, the wave was higher by 20 cm in Newlyn, 30 cm in Plymouth and 40 cm in Portsmouth. The water levels dropped and withdrew from the coast before the wave came in (Marazion, Cornwall). Video evidence shows the wave as a bore in the Yealm Estuary. At St Michael's Mount there were reports of 'hair standing on end' before the wave struck.