Louise, you might try carving a large chunk of styrofoam.  You could also cut a cardboard box into a more angular, iceburgy shape and use masking tape to get the shape you want. Good Luck.

what and where do i get styrofoam???

Louise

Styro foam would be way too expensive, in my opinion.  I would just use wads of newspaper and masking tape to get the shape you want.  Them use wide strips (6-10 inches wide) to mache over the form.  And don;t put the paper into the paste.  Wet your hands thouroughly with paste and smeer it and massage it over the paper.  Don't move on to the next layer until the previous layer is completely wet.  By doing it this way you will avoid air-bubbles and chunks of flour which eventually rot and begin to smell bad.  Putting the strips in the paste is usually a bad idea.  Plus it's more fun to get your hands wet!!

I think Sebrink may mean 'until the previous layer is completely dry' (??)

No.  I meant completely WET.  If you wait until each layer dries it will take forever to make your piece.  And by making each layer wet it ensures that no air bubbles will form.  I use this technique when using flour/water paste.  I wouldn't use it for glue pastes because they are so sticky.
When using white glue or wall paper paste I use a paintbrush to apply paste to both the form/mold and the paper.  But I thought the "victim" here was only using flour and water!

My two penneth regards the finish -
paste sheets of toilet tissue onto the iceberg. Brushing them down creates some excellent textures. Paint white. Some pale blue and the odd pale yellow wash followed by drybrushing in white until satisfied should create a pretty realistic effect.