I always like to have a nice photo to illustrate a post, but this time, viewers of a nervous disposition should look away.
According to Lost Crops of the Incas... " Farmers mound dirt over the base of the plants to encourage stolon formation". But stolons aplenty appear without earthing-up, so maybe a more important reason is to protect tubers from frost once the stems have died back.
Hard or prolonged frost is unusual here in West London, and I consider this year's cold snap a rare event, so do not plan to routinely earth-up Oca crops in the future. Quite apart from the extra work involved, it would be awkward in most bi-crop situations, and it goes against my preference for minimum-tillage cultivation.
Anyhow, plenty of tubers escaped damage...