A snow covered crater on Mauna Kea, Hawaii

A crater on Hawaii’s Mauna Kea, a 4,200-metre-tall volcanic peak that shelters patches of frozen soil on its slopes even in the summer. Credit: Getty

Climate sciences

Why a palm-fringed Pacific island harbours pools of ice

Hawaiian peaks host icy pockets year-round, but the cold spots are at risk from climate change.

The island of Hawaii is renowned for its tropical climate, but the stony deserts on two of its volcanoes support unlikely patches of permanent ice.

Norbert Schörghofer at the University of Hawaii at Manoa in Honolulu and his colleagues gathered weather data from sites near the barren, rocky summits of Mauna Kea and Mauna Loa, Hawaii’s tallest volcanoes. Measurements at a crater high on Mauna Kea yielded the coldest temperature ever reported for the Hawaiian Islands: -20.3°C.

The researchers found that, despite the area’s relatively mild air temperatures, pools of exceptionally cold air sometimes form in the craters during still nights. This cold air is trapped between rocks, helping to preserve patches of ice and frozen soil in the craters.

Similar pooling and trapping of cold night air may also help to maintain ponds of ice found deep inside two caves on Mauna Loa. Evaporation of ice from the ponds’ surfaces removes significant amounts of latent heat. But the ice ponds are showing signs of thawing and will probably vanish as the climate warms.