From the Met Office- https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/frost-and-ice/ice-spikes#:~:text=Ice%20spikes%20form%20as%20a,squeezed%20up%20through%20the%20hole.
Ice spikes form as a result of the way water freezes, from the outside in.
As the ‘skin’ of ice...