mauna kea is home to lake waiau, the highest lake in the pacific basin. at an altitude of , it lies within the puu waiau cinder cone and is the only alpine lake in hawaii. the lake is very small and shallow, with a surface area of and a depth of . radiocarbon dating of samples at the base of the lake indicates that it was clear of ice 12,600 years ago. hawaiian lava types are typically permeable, preventing lake formation due to infiltration. either sulfur-bearing steam altered the volcanic ash to low-permeability clays, or explosive interactions between rising magma and groundwater or surface water during phreatic eruptions formed exceptionally fine ash that reduced the permeability of the lake bed.