PERMAFROST AND PERCHED GROUNDWATER ON THE SUMMIT PLATEAU OF MAUNAKEA VOLCANO, HAWAII

Sporadic permafrost in cinder cones near the summit of Maunakea (4,207m, 19.82N) persists near the warm climatic extreme where mountain permafrost has ever been found. Over the period 2012-2016 we have investigated ice and water bodies in cinder cones on the summit plateau using unobtrusive techniques, such as temperature monitoring, shallow geophysical surveys, and previously untapped historical documents. Electrical Resistivity Tomography and Ground Penetrating Radar surveys reveal that two subsurface ice bodies are still present on Maunakea, but one has retreated in volume by an order of magnitude between 1973 and 2015. A second larger ice body is at least 50m wide, but both are expected to continue to degrade due to global climate warming. We have also reconstructed the history of snow cover from historical records, and identified recent time periods when the permafrost may still have been in equilibrium with the climate. No permafrost was found at Lake Waiau, a well-known perennial lake in the summit region (3,970m), nor at a previously undocumented episodic puddle of water at another cinder cone (Puupohaku) at ~4,000m. Both of these bodies of standing water imply the presence of impermeable layers, which are apparently not uncommon in cinder cones, in an otherwise porous volcanic surface. Impermeable layers are also responsible for a newly discovered perched water reservoir east of the lake that can store water volumes larger than the shallow lake itself. A larger survey of the summit area turned up no additional permafrost bodies, so we are likely witnessing the last permafrost in Hawaii.