Extreme storms present a major risk to coasts. Increasing populations worldwide, together with sea level rise, exacerbate concerns for coastal settlements, but the low frequency of extreme storms makes an assessment of risk difficult. In southeast Australia, the severest beach retreat on record relates to a series of extratropical cyclones in the 1970s, but the relatively short observational record hinders assessment of how frequent these events are. At Moruya in New South Wales, four decades of beach monitoring has provided new insights into response of beaches to extreme storms. We augment this recorded history with morphostratigraphic analysis of beach ridge evolution by using ground-penetrating radar and optically stimulated luminescence dating. We find an episode of extreme retreat over 550 years, proving that the 1970s extreme event is a recurrent phenomenon. Our high-precision morphostratigraphic analysis provides evidence with which to better plan coastal adaptation.