The thermal flight
In the middle of the day the ground warms up of course. The warm air, being lighter, tends to rise: it is thus to create an updraft (thermal), able to do the glider climbs at high altitude.
The technique of soaring, which is used by the pilot, is to make the most of warm rising air currents to ascend the spiral flying in all 'inside of the heat itself.
Gliding from one thermal to another, you can travel great distances.
The flight dynamic or slope
When a horizontal air flow (wind) meets orographic obstacle on its path, tends to climb up to jump over the obstacle and then return trajectory. The glider then positioned along the slope by running the "eight" at the bottom to keep the air mass and quadagnare share.
The flight on air
When the wind speed becomes high values (100-150kmh intercepts and other mountain systems (Alps) can reach very well over 10,000 meters.
The world record of altitude is 14938 feet with American Robert Harris in California.