The dwarf could see them basking in the sun, brown and black hummocks with jagged ridges down the center of their shells.

But the zone is largely treeless, studded with house-size rocky chunks, called hummocks, that broke off the top of the mountain when it exploded.

The researchers measured the retreat of the permafrost border byobserving hummocks known as "palsas, " which form naturally over icecontained in the soil of northern peat bogs.