This chemical volcano is a result of the decomposition of Ammonium Dichromate.
A decomposition reaction (aka analysis reaction) follows the general formula below
A--> B + C
A compound breaks down into smaller components.
This is the demonstration of the decomposition of Ammonium Dichromate
(NH4)2Cr2O7 ---> N2 + 4H2O + Cr2O3
Cr2O3 -the green solid
Chromium III and chromium VI, as well at its compounds, including ammonium dichromate, are known carcinogens. Chromium will irritate the mucous membranes. Therefore, take care to perform this demonstration in a well-ventilated area (preferably a ventilation hood) and avoid skin contact or inhalation of the materials. Wear gloves and safety goggles when handling ammonium dichromate.