What is a cirque and how are they produced?
In short, large masses of ice (glaciers) at high altitude tend to migrate down mountains. As a glacier makes its way down the mountain it can sometimes get stuck or just sit in place for a while.
Whilst it sits the glacier can still be moving but think of it like a stationary conveyor belt, material is being moved under the glacier and then out the other side. Then because of the glaciers weight the material below it begins to be removed. As the material is removed a big pit begins to form and voilà, a cirque!
As an aside, the cirque can then fill with water and thanks to our changing climate, a once cold region may now be warm and the cirque can serve as a fantastic swimming hole!
Image credit: DooFi on Wikipedia.