In the large image, the area behind the shoreline is pockmarked by marshes, ponds, and hummocks characteristic of "thermokarst," landscapes created by the melting and refreezing of permafrost.

In 2000 he extracted deep cylinders of ice from Kilimanjaro's glaciers and found that the higher layers were full of elongated bubbles - signs that melting and refreezing had occurred in recent years.

With further melting, refreezing, and increased weight from newer snowfall above, the snow reaches a granular recrystallized stage intermediate between flakes and ice known as firn.