Dendrites on Ice
Ice crack patterns on Derwent Reservoir, Derbyshire, England.
Saturday 4 March 2006, 11.00am.
A general view of the location is here:
I have called these dendrites on ice, but they are really dedrites in ice, as clear ice fills the pattern. I am sure they should have a formal name, but as of March 2008, I have yet to find any reference to one.
On this occasion there had been about 10 mm of snowfall the previous evening, that probably fell on top of thin ice that had probably formed a few days earlier. The overnight of 2-3rd March had been very cold for early March in this part of England, c -8C. The daytime of Friday the 3rd was mostly sunny, with temperatures rising near to just above freezing. Most of the reservoir was open water, except this small area on the relatively sheltered east side.
The original ice formation on the lake surface may have been encouraged by the earlier snowfall.
The centre of each dendrite may be formed by leaves or other debris encouraging melting of the ice during the day, but what about the rest of the dendritic pattern? Differential ice expansion on the freezing of floating slush is a possible explanation.
At very low temperatures sheet ice contracts, but this forms straight cracks.
Update 20070219. Perhaps these should be called macro negative dendrites in ice, in order to distinguish them from the much smaller water dentrites within ice and snowflake dendrites. For these small dendrites, see the article by Harry Badeshia at
Found on flickr
