How does John McPhee use imagery in The Control of Nature?

Examples of Imagery:

"Among navigable rivers, the Atchafalaya is widely described as one of the most treacherous in the world, but it just lies there quiet and smooth. It lies there like a big alligator in a low slough, with time on its side, waiting - waiting to outwait the Corps of Engineers - and hunkering down ever lower in its bed and presenting a sort of maw to the Mississippi, into which the river could fall." Atchafalaya, pg. 23

"Like an iceberg that had calved off a glacier, the great bulk of the north side of the volcano remained afloat in a molten sea. It was a mountain in itself, and, moreover, it moved. It was landscape on the loose, an incongruous itinerant alp, its summit high above the lava plain, its heading north by northwest." Cooling the Lava, pg. 138