Ignoramus11448 fired this volley in news:rPidnaFM7Mvp_2XUnZ2dnUVZ snipped-for-privacy@giganews.com:
They're called "snakes". The ash doesn't much resemble lava, unless you stretch the analogy to "cooled lava" .
The "classic" volcano experiment uses ammonium dichromate crystals as the fuel. As it burns, it emits a fluffy greenish ash that cascades down the sides of the model.
Dichromates, in general, are not "friendly" chemicals. Combine virulent oxidizer properties (enough so to burn moist skin) with hexavalent (carcinogenic) chromium, and you have a true witch's brew.
LLoyd