We spotted these paragliders whilst climbing Scafell. The highest of them must have reached over 1000m above sea level. The sun was hot and the infra-red radiation is absorbed by the ground. This heats the air that is in contact with the ground. This air expands and becomes less dense. Being less dense, it floats upwards. It is this upward current of warm, less dense air that is called a thermal. The paraglider spirals to stay in that column of air and is taken up and up. I'm not sure how wide the column would be. However, the force must be enough to lift the person and the parachute.
