Erupting volcanoes!

These are some of the volcanoes brought in to school today by the children in the year4 class (8-9 year olds) that I teach on Wednesdays.
I was very impressed by the effort they had all made (only one boy didn't have one - but I have a 'spare' from previous years which he used).
I did hear some funny tales of competitive encouraging dad activities though!

They were given instructions 3 weeks ago (so that they had lots of time to make them) which were roughly:-
1. The base must not be more than 15cm/6ins diameter as we are very short of space to put them all.
2. The crater must have a small, upturned bottle lid in it to facilitate the erupting process.
3. Otherwise feel free to use anything for the construction that you can get your hands on (but ask first!!).
+ one or two other helpful ideas.

One model - not in this shot - was about 40 cm diameter and hollow with a crater about 5cm/2.5ins wide! it couldn't be used. There is always one :-(

We used bicarbonate of soda and lemon juice. Lots of frothing ensued and poured down the volcanoes. (I have used red food dye with older kids too but I dare not risk it with excitable tiddlers!)