Floating Rocks!

TempPeck

Hi All,

I know this might not be the best place to post this but I can't find a geology forum and you guys always seem quite knowledgeable about this kind of thing!

Anyway, these "rocks" washed up on Brittas bay shore about 40 years ago.
They are extremely light and filled with air bubbles. They look a bit like metal but its hard to tell. They are so light that they actually float!

The 2nd photo shows the object after it was cut in half (easily by hacksaw)

Any comments / explanations would be gratefully received!

Thanks, TempPeck

Rubecula

It is a kind of pumice stone ejected from a volcano as a pyrotechnic flow or some such. They float because they are filled with bubbles.


EDIT
I did of course mean a pyroclastic not a pyrotechnic .... pyrotechnics is making fireworks Sorry

TempPeck

Thanks Rubecula,

Any idea where it might have come from?
Are they formed under or above water?
What is the material?

Thanks again for your help!

Rubecula

It will have come from a volcano as I said but it will be from above water as you don't get a pyroclastic flow underwater as far as I know. I don't think it is physically possible. as for which volcano. No idea at all, you would need to show it to an expert and even then it is unlikely to be possible to find out without a material analysis, probably not then either.

Basically, the material is the hardened form of the clouds of hot dust and gas that you see on films of fast moving and deadly clouds rolling down the side of volcanoes at tremendous speeds. If mixed with water in the formation it settles like hot mud and sets like concrete. You can buy smoother types of pumice for use as an abrasive on hard skin.

TempPeck

Thanks!

MeteoritesEire

boards needs a geology forum but I think at this point there are too many geology threads scattered all over the place(mostly geography) that to gather them into a proper geology forum would be a lot of work--can't blame the mods for being wary of that task