Mount Tambora experienced several centuries of dormancy before 1815, caused by the gradual cooling of hydrous magma in its closed magma chamber. Inside the chamber at depths between , the exsolution of a high-pressure fluid magma formed during cooling and crystallisation of the magma. An over-pressurization of the chamber of about was generated, with the temperature ranging from . In 1812, the volcano began to rumble and generated a dark cloud.