  A historical record of a seismic tsunami is identified in the Irish annals
for October 720 (all dates herein CE). It is contained in the earliest stratum
of the annals, which survives in the form of a handful of iterated scribal
copies of the foundational text of the tradition. This was compiled by the
contemporary observation of noteworthy events for the years c. 563-740 at the
monastery of Iona in the Scottish Hebrides. The 720 event is close outside the
2$\sigma$ radiocarbon terminus ante quem date ranges for tsunami deposits
identified at Dury Voe (530-660) and Basta Voe (430-650) in the Shetland Isles,
and is identified as a candidate progenitor. The possibility of the existence
of associated tsunami deposits in Scotland or on the north coast of Ireland is
highlighted.
