Which two factors most contribute to glacial movement that results in a "U" shaped valley?

Producers (autotrophs) are in the bottom (first) trophic level, primary consumers are in the second trophic level, secondary consumers are in the third trophic level and tertiary consumers are in the top trophic level. energy moves through the trophic levels when one living organism is being consumed by another. moreover, energy level becomes lower as it moves up the energy pyramid because of it being released as heat. food chain is when there is a single pathway of energy transfer whereas a food web is when there are multiple pathways of energy transfer.