How does Kevin Henkes use imagery in Olive's Ocean?

Imagery:

"Martha couldn't shake Olive Barstow from her thoughts. She felt a stab of loneliness, the source of which she couldn't name."

"Everything took on a gloomy significance: the Last Lunch, the Last Dinner, the Last Sunset. The sadness was the familiar going-home-lump-in-the-throat feeling."

"She watched intently - the concrete turned dark and then light again as the water evaporated. Olive's name was there one moment, then gone the next, like a flicker in the great scheme of things."