The Last Permafrost in Hawai'i

From Office of Mauna Kea Management, October 18, 2017

Hawai'i is known not only for its balmy weather and lush beaches, but also for its large variety of climate zones. In the coldest climate, on the tallest summits of Hawai'i, temperatures fall below freezing during winter nights. In 1969 an ingenious scientist, Alfred Woodcock (1905-2005), discovered areas inside cinder cones on Maunakea that are permanently frozen. At one place the ice was about 32 feet thick and 27 yard long, buried beneath about one foot of boulders.

This was the only permanent ice known in all of the Hawaiian Islands, and nearly half a century has passed since. Is it still there? Recently, a group of scientists and their students investigated the state and health of this unique permafrost, in a way that involves minimal disturbance to the environment. Because these ice-rich bodies lie buried beneath the surface, they are not easy to locate. After extensive temperature measurements and targeted geophysical surveys sponsored by the Office of Maunakea Management, the permafrost has been re-documented.

Some of the ice found by Woodcock inside Pu'uwēkiu Crater is still there, but most of it has disappeared. Its north-south extent, once 27 yards, is now 12 yards; its thickness, once 32 feet, is now 12 feet. The ice has retreated all around. If the trend between 1973 and 2015 is extrapolated, the remainder may disappear within a few years.

Three people stand inside Pu'uwēkiu Crater, marking the bottom and top end of a buried ice body documented in 1974. The shaded areas illustrate the extent then and now.

A much bigger body of ice was identified in a neighboring cinder cone crater, Pu'uhaukea, based on ground penetrating radar surveys and temperature sensors. This ice body is currently at least 50 yards wide and about 32 feet thick. No prior documentation is available to judge how much it has shrunk, but due to its larger volume, it will outlast the permafrost in Pu'uwēkiu.

The surprise is not that the ice is melting, but that it was ever there to begin with. It is found only in two well-shaded locations, but many other equally shaded locations on Maunakea have no permafrost. The age of the ice is also unknown. It could date back to the last ice age, many thousands of years ago, or merely a few centuries.

Either way, the old ice of Maunakea will be a victim of climate warming. We are witnessing the disappearance of the last permafrost in Hawaii.

The results of the permafrost survey were recently published in the journal Permafrost and Periglacial Processes, http://onlinelibrary.wiley.com/doi/10.1002/ppp.1954/abstract

Forthcoming publications will address the climate processes that likely maintain this permafrost as part of this OMKM sponsored research.