Pretty Easy Erupting Volcano Birthday Cake (Using Dry Ice)

This is a cake I designed and assembled for my older son's 5th birthday.  It's pretty easy, and not that expensive (about $25-$30; $17 was the cake, so if you're a baker, even less).  It requires no specialized scientific knowledge, and is safe (enough for my 5-year-old and his friends; YMMV).  Everyone was duly impressed (if I do say so myself, which, in fact, I do), including the 'Mad Science' guy we hired as the entertainment for the party (you can see him check it out in the video- he's the guy in the lab coat behind the birthday boy).  It's my first Instructable, so constructive criticism and comments are welcome!

Step 1:

For this cake you will need:

A cake (mine was from Costco, $17); I asked them to write on one half and leave the other half blank.  There's no reason that you couldn't bake your own, however.
Candles- traditional in my country (America)

Volcano
Crisp Rice-Type Cereal, chocolate flavor (technically, I cared more about the color than the flavor).
Marshmallows- probably 2 bags, depending on the size of your volcano
(The previous two ingredients are to make the Rice Krispie Treat recipe that will be used to construct the volcano)
1 small plastic cup (mine was from Ikea ; I chose orange to enhance the lavaesque appearance)
Red or orange frosting
Dry Ice; you only need a little bit, but it sublimates quickly, so get more than you need, particularly if you are buying it on a different day than the party.  I got 10 Lbs the day before, and this was probably way too much even with test runs, etc.  5 Lbs should do it.  Google "Dry ice (your zip code)" if you're not sure where to get it.
Tongs/Gloves to handle the dry ice , and a hammer to break off chunks would be handy but not necessary.
Not pictured:
Butter (for Rice Krispie Treat recipe )
A little water
4 Plastic forks, broken to the height of the cake to support the weight of the volcano
Disposable gloves (for volcano molding)
Cooking spray oil
Plastic wrap

Dinosaurs- I bought a couple packs at the dollar store. 
Not pictured:
1 wooden skewer & hot glue gun (for pteranodon support)

Step 2: Plan Your Layout

Plan where you want your dinos and especially your volcano to go.  I used a take-out container with the same diameter I wanted for my volcano base, and laid it on the plastic wrap to mark the position.  In retrospect, this might have been a good step to do before I had them decorate the cake (although it didn't turn out to be a problem).  Give more thought to this if your child has a particularly long name.

Step 3: Make Your Volcano

Make Rice Krispie Treats according to the recipe :
3 T Butter/Margarine
1 10 oz package Marshmallows
6 Cups Crispy Rice-type cereal

Over low heat, melt the butter, add the marshmallows, mix until pretty smooth.  Turn off heat and add the cereal, stirring to coat. 

On a sheet of plastic wrap, while still warm (but don't burn yourself- sorry I had to to say it, but I don't want to hear the comments), mold the mixture into the shape of a volcano using the disposable gloves coated with spray oil.  I found that it was helpful to do this in two or three steps/batches of mixture; the base, the middle, and then after placing the cup on top, the top.  Let the mixture cool (in the refrigerator if you want) before proceeding to the next part so it is structurally sound.

The top is the trickiest part, in that it has to mold to the cup.  You will have to keep re-molding the mixture until it cools sufficiently to stay in place.  Pressing the mixture over the rim helps, and makes it look better.

When it's done, wrap in plastic wrap.

I also made some small , irregular crispy rice "rocks" to use as decorations at this point.

Step 4: Assembly

The following day, I brought all the materiels to the party to assemble.  I realized that the volcano was possibly too heavy to be supported by the cake alone, so I broke off 4 plastic forks to the height of the cake and inserted them inside.  You could use toothpicks or something, but these were sturdy, stable, and easy to find during the eating portion of the festivities (unlike toothpicks might be).

Place volcano on top.

Step 5: Decoration

Decorate your volcano with the frosting to look like lava.

Place the crispy rice "rocks" and the dinosaurs around the cake in aesthetically pleasing and/or dramatic fashion.

Place candles on cake.

Step 6: Serve

Bearing in mind the handling procedures , break off some small chunks of dry ice and place in the cup atop the volcano.
Light the candles.
Pour an ounce or two of water into the volcano.
Sing "Happy Birthday".
Enjoy!

PS Don't forget to eat the volcano as well as the cake!