“The results are compelling. Prior to 2010, the lake surface area fluctuated between about 5,000 and 7,000 m2 (1.2-1.7 acres), with the variability presumably due to recharge from winter storms balanced by loss due to evaporation. Sometime in early 2010, however, the lake surface area began to shrink and, by late September 2013, had declined to just 115 m2 (0.03 acres) – that is, about 2% of its normal surface area.

Geography professor Donna Delparte, formerly of University of Hawai`i at Hilo and now at Idaho State University, has also been monitoring the recent changes. Her group has made detailed measurements of lake geometry using advanced techniques, such as laser scanning and photogrammetry. Prior to 2010, the maximum depth of the lake was about 3 m (yards), but today the lake is less than 30 cm (1 foot) deep. This means that the current volume of the lake is less than 1% of its normal (pre-2010) value.

Using air photos to extend the time series of lake surface area back to the 1950s, we see no other drops of such scale. Historical photographs taken through the last hundred years, and written reports going back to the early 1800s, give no indication of the lake ever being as small as it is today. This suggests that the current reduction in size is unprecedented in modern times, but we cannot say this with absolute certainty, because there were large time gaps between the recorded observations in the 1800s and early 1900s. Nevertheless, the reduction in lake size that we see today appears to be highly unusual. ”

“An obvious culprit would be the ongoing drought in Hawai`i that began in 2008. The Mauna Kea visitor center weather station shows very little precipitation for several consecutive months in early 2010, which may have been a trigger for the level drop that was sustained by low precipitation over the subsequent few years. The National Drought Mitigation Center shows that the drought across Hawai`i intensified in early 2010, consistent with this local weather data.

Could other factors be contributing to the potentially unprecedented nature of these changes? Lake Waiau is a “perched” water body, in which water is held in a depression by an impermeable substrate. This substrate consists of layers of silty clay, interbedded with ash layers, and it has been proposed that permafrost also underlies the lake.

It has also been proposed that permafrost surrounds the lake and provides a catchment that directs water into the lake. Could changes in the presumed permafrost have altered the water balance in the lake over the past few years? So far, there is no hard evidence to support this possibility, but we cannot yet count it out. We simply don’t know at this point, and more research needs to be done.”

“Given its cultural significance and its uniqueness, the disappearance of Lake Waiau would be a great loss for Hawai`i. The future is far from certain for Lake Waiau, and DLNR, rangers, and scientists will continue to watch this situation closely.”