"Sue da Nimm" . wrote in message
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"Janet Baraclough.." wrote in
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The message
from "Sue da Nimm" . contains these words:

The pond sides should always slope outwards so that any ice formed
cannot
exert sideways pressure when it melts. (Ice EXPANDS when it melts,
which
is
why it can burst pipes)


Ice expands as it freezes and shrinks as it melts. The expansion of
the frozen ice is what bursts pipes or vessels, not the melting of it.

Janet.

Sorry all - choking on humble pie - you are exactly right )
The overall effect is the same, though, ice can damage ponds if there
isn't
a suitable overflow provided.

(I won't expand on the point any more in case I contract poster's
cramp....)



If I remember my elementary physics correctly (and its a big if, because it
is many years since I had to bother with it) the reason water freezing can
burst pipes is that there is a quick formation of feathery dendritic ice,
which forms a network enclosing the water, restricting the volume so that
when the enclosed water expands on freezing it generates sufficient pressure
to fracture the pipe.

The water in your pond is, I assume, open to the atmosphere, so the pressure
will probably be relieved by vertical (upwards) expansion.