The upper picture looks to me like the ice was broken by something like stones, thawed along the edges and then froze again.

The lower shows a structure that is familiar to me but I don't know how it forms.

The ice was higher than the water underneath it (this often happens as water drains into the ground or runs off in a stream). At some point, there was some degree of thaw. The unsupported ice sagged towards the centre of the pond and meltwater collected towards the middle. As the thaw continued, the meltwater found holes in the ice and trickled down them, making the typical patterns of a river system that you can see.

Then Jack Frost came back and froze the whole lot. Voila, as they say in France!

PS Bubbles in the ice was a phenomenon dealt with in this forum a week or two ago.

The ice in the upper

picture seems to be formed from snow, falling onto the

surface of the water at about 0°C. The snow congealed

to snow slush including a lot of air bubbles.

Then temperature fell and this mass froze to an ice

which is rather intransparent due to the tiny bubbles.

The rather rough surface of this ice fits into that.

The dendritic structure arises from some incomplete

melt afterwards, when the water drained to those

sinkholes, as describen above.

Such structures are typical when rather flat areas

are drained.

On can see them around the Gran Canyon and in 

tidal flats   and on Mars.

The lower picture is quite common, air (oxygen) bubbles

rising from ground are always under  ice,

In this case some penetrated into that snow/water-gel

and remained stuck in the middle.

Georg

And marsh gas possibly Georg?

Hello pete,

of course that is possible, in case the ground of the pond is

anaerobic. But that is typical for swamps.

Georg