Slowly the immense glacier, 410 m thick at its maximum, moved down the valley, scouring everything in its path, turning the valley into a barren, U-shaped trough Then, 15,000 years ago, climatic conditions changed, and a slight Warming trend began to develop.
(a slight Warming trend; to develop; ) (climatic conditions; changed; T:15,000 years ago) (a slight Warming trend; began; )
a slight Warming trend climatic conditions a slight Warming trend
to develop changed began
T:15,000 years ago