By these considerations I was induced to seek some other Method which would comprise the advantages of the three and be exempt from their defects.
If the cirque is subject to seasonal melting, the floor of the cirque most often forms a tarn (small lake) behind a dam, which marks the downstream limit of the glacial overdeepening.
Tarn (lake) (Wikipedia) A tarn (or corrie loch) is a mountain lake, pond or pool, formed in a cirque excavated by a glacier. A moraine may form a natural dam below a tarn.