This is an interesting one, this is caisson lighthouse built between 1957-1958, it was shipped out and installed in 1958.

During the winter of 1969, eleven years later, the lighthouse was shorn off it's foundation by the pressure of the ice around it, this caused it to fall over.

The lighthouse fell over (not very typical), and electric light went out, but the backup gas powered Dalén light turned on and worked!

Here is a diagram of the lighthouse showing the shear point, with helpful text in english:

A new lighthouse was built and installed in 1970.

The picture is as far as I can tell licensed as CC-SA-BY, but I can't find any photographer information, the only ownership information I can find is that it belong to an archive maintained by a person called "G Kjellgren"

What sort of regulations exist to prevent a lighthouse from falling over?

I have actually no idea, but I suspect Sjöfartsverket has a document or two on the subject.

I just read up on how large the pressure from the ice in the Gulf of Bothnia is estimated, and damn, the ice is squeezing hard!

The pressure is estimated at 150-200 tonnes per meter of diameter of the lighthouse.

So if you have a 2 meter wide lighthouse, it has to withstand about 300-400 tonnes of force from just the static pressure of the ice.