Volatiles are present in nearly all magma in different concentrations. Examples of volatiles within magma include water, carbon dioxide, and halogen gases. High pressures allow these volatiles to stay relatively stable within solution. However, over time, as the magmatic pressure decreases, volatiles will rise out of solution in the gaseous phase, further decreasing the magmatic pressure. These pressure differences cause drastic differences in the volume of a magma. Pressure difference causes some forms of volcanoes to be highly explosive and others to be effusive.