I’ve just received another fascinating email from ‘Chris in Finland’:
I took this photo a few days ago on Lake Näsijärvi, Tampere, Pirkanmaa, Finland.
This is the first time I have seen this ice wall feature. I thought you would enjoy seeing it.
The conditions for the creation of this feature apparently only occur about once a decade in Southern Finland. You need the rare combination of thick ice, 61 cm at the time, plus a large variation in the day and night temperatures.
The temperature on the lake can fluctuate by as much as twenty degrees within 24 hours. The huge ice sheet expands and contracts with the changing temperature. As the ice melts, it creates a chasm, but when it freezes again and expands, it forces the edge of the chasm upwards, creating the ‘wall’ effect.
It makes sense that this ice wall appeared around the time of the equinox . When temperatures are plus degrees during the day and nights are still sub zero.
The aspect is north-south and when I observed smaller versions of this feature on the lake they too were in the same orientation. I assume that’s because of the sunny aspect?
And this is one of the small cracks I observed. This was on the Näsijärvi ice skating, cycling walking trail which runs East- West
The prime reason I am sending this is that it’s nice to share my excitement at seeing this and working out why it is there.
Thanks for another very interesting email.
When any natural features have a N-S alignment, it’s fair to suspect a solar cause. I can’t claim that as the definite the cause here, as it’s not a feature I know well; which makes it all the more fun to receive your email and photos.
(If anyone else has come across these patterns or can add anything please do get in touch and I’ll update this post.)
Thanks again, Tristan.