Permafrost and seasonal frost thermal dynamics over fifty years on tropical Maunakea volcano, Hawai‘i

Abstract

A unique permafrost thermal state was examined at Maunakea, Hawaiʻi. The presence of the permafrost was determined in 1969. Mean annual ground surface temperature (MAGST) is significantly above zero at permafrost sites, between +2°C and +5°C. This indicates that subsurface thermal processes control and preserve the permafrost state (strong thermal resistance). Year-round high-resolution (1-cm intervals) active layer temperature monitoring reveals the thermal dynamics. Unlike permafrost at higher latitudes, the large thermal offset may be caused by nonconductive heat transfer in the active layer. The permafrost survived many decades because of snow cover, the structure of the ground, and hydraulic permeability. However, over the past fifty years the extent of permafrost has declined. Other periglacial geomorphology has been described in permafrost-free areas mainly above 3,500 m.a.s.l., where freeze–thaw action is ubiquitous. The seasonal frost depth is 40 to 60 cm, and seasonal and diurnal creeping has moved stones about 0.45 to 4.3 cm/year over the last fifty-two years. This research clarified the thermal dynamics of the active layer and the presence of the mountain permafrost at unusually low elevations in the tropics.

Keywords

• Permafrost
• Hawaiʻi
• Maunakea
• thermal offset
• active layer
• tropical mountain permafrost