The first volcanic activity beginning 2 million years ago formed voluminous lava flows from fissure vents. Later the activity focused on deep seated lineaments. Volcanic activity between 1.65 - 1.75 mya occurred beneath ice in the ancient valleys of the Bii Khem river. In the middle-late Pleistocene volcanism occurred in the southeastern parts of the field. Some dates obtained on edifices in the Azas Plateau are 725,000 ± 50,000 - 760,000 ± 50,000 years for Derbi-Taiga, 600,000 - 560,000 years for Kadyr-Sugskii, 600,000 - 290,000 for some volcanoes surrounding Derbi-Taiga, 350,000 - 290,000 for Yurdawa between Derbi-Taiga and Shivit-Taiga, 225,000 ± 50,000 for Ploskii, 150,000 ± 50,000 for Kokhemskii, 130,000 ± 40,000 - 110,000 ± 000 for Shivit-Taiga, 75,000 ± 40,000 for Priozernyi, 60,000 ± 40,000 for Sorug-Chushku-Uzu and 48,000 ± 20,000 for Ulug-Arginskii. Some lava flows in the Bii-Khem valley are even younger than the Ulug-Arginskii volcano. It is possible that when eruptions in the Azas Plateau occurred beneath ice, they caused floods of glacial meltwater called Jokulhlaup; corresponding landforms have been found at Derbi-Taiga and Shivit-Taiga volcanoes.