The Coldest Places in Hawaii: The Ice-Preserving Microclimates of High-Altitude Craters and Caves on Tropical Island Volcanoes

Abstract

AbstractThe coldest places on the Hawaiian island chain are not on the very summits of its tallest volcanoes, Mauna Kea (19.82°N; 4,207 m) and Mauna Loa (19.48°N; 4,169 m), but within craters and caves with perennial ice. Here, we explore unique microclimates in the alpine stone deserts of two tropical island volcanoes, report new temperature extremes for Hawaii, and study the role of microclimates in the preservation of perennial ice bodies. Nocturnal cold-air pools are common in the craters and are responsible for the coldest temperature ever reported from the Hawaiian Islands (–20°C). These cold-air pools are not frequent enough to substantially affect the annual heat budget of the ground, but cold air is frequently trapped between boulders and contributes to freezing conditions in this way. Perennial ice is found beneath even warmer environments in lava tube caves. The lowest annual-mean temperature (–0.7°C) was measured at the distal end of a spectacular ice cave on Mauna Loa, where the outside air temperature averages +8°C. In the current climate, the outside temperature rarely falls below freezing, so the air’s sensible heat cannot contribute to freezing conditions. Considering the effect of recent climate warming and the buoyancy of humid air, cold air that flowed down the lava tubes in winter nights, combined with sublimation cooling, is still a plausible explanation for the perennial ice ponds found there.