comparative weights

[goldenboy]

which is heavier, a cubic foot of snow or a cubic foot of ash ?

[WaldoMcFroog]

It's likely to be ash, but it would depend on how compacted it was.

[goldenboy]

if they both fell from the atmosphere, which then?

[Space]

snow initially has a very low density, but as it naturally melts during the day and freezes back at night, it can become as dense as ice...

[Gef]

Snow and ice are less dense than water. Volcanic ash is basically ground up rock and should be a lot more dense than water but as Waldo says it depends on the amonut of compaction. To put it another way, as Eddie says, you would not be worried by a foot of snow on your roof but a foot of ash is a different matter.

[goldenboy]

i ask because i was watching supervolcano on living tv yesterday and it said that 20 cms of ash causes rooves to collapse. obviously snow wouldnt. i suppose its because snow will melt to some dgree daily but ash will remain. so it appears that ash may be less heavy in its initial stages than snow. i realise that compacted snow and ice can get to very high densities, espicially glacial ice.

[WaldoMcFroog]

Ah, well volcanic ash is different again - it's just rock ground very small, so weighs loads more than ice crystals. Here's a quote from:

http://volcanoes.usgs.gov/Products/Pglossary/ash.html

" Volcanic ash consists of rock, mineral, and volcanic glass fragments smaller than 2 mm (0.1 inch) in diameter, which is slightly larger than the size of a pinhead. Volcanic ash is not the same as the soft fluffy ash that results from burning wood, leaves, or paper. It is hard, does not dissolve in water, and can be extremely small--ash particles less than 0.025 mm (1/1,000th of an inch) in diameter are common."

[Peter Pedant]

It was in Supervolcano - and I heard the same dialogue before er I switched over and watched some other baloney - rise of the nazis i think.

They did a computer simulation - and got up to - 15 cms and then someone said - add some rain and it will collapse the roofs.,

and then a little later 0.1 cm because the ash is so fine can stop machines. and then they showed a nice micrograph of fine ash. (then I switched)

Montserrat - Plymouth has had a few feet or metres of ash and looks pretty wrecked. Ash then