A thermal column (or thermal)'s a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and an example of convection. The Sun warms the ground, which in turn warms the air directly above it. The warmer air expands, becoming less dense than the surrounding air mass. The mass of lighter air rises, and as it does, it cools due to its expansion at lower high-altitude pressures. It stops rising… (More on Thermal)