Heat Wave Causes Major Melting Event in 2017 at 3 Glaciers Along the Lower Iskut River, British Columbia, Canada

The Coast Mountains of northwestern British Columbia, Canada, host several ice fields, ice caps and outlet glaciers with sparse field measurements. In August 2017 we visited two outlet glaciers and one small ice cap at Hoodoo Mountain, a Late Pleistocene-Holocene glacierized volcano (56.77°N, 131.28°W) on the north bank of the lower Iskut River, in order to conduct a survey of glacier conditions. We used a differential GPS to measure elevation change and velocity at Hoodoo and Twin Glaciers. On Hoodoo ice cap, we collected a GPS transect that intersected a GPS/GPR campaign conducted in 1997 to compare the ice cap elevation from 1997 to 2017. On Twin and Hoodoo glaciers we found a maximum melt rate of 98.6 ± 14.6 m yr-1 and a maximum velocity of 55.6 ± 17.5 m yr-1 from 3 to 10 August 2018. To compare these temporally constrained measurements to annual averages we use remotely sensed data from the Landsat 8 and Worldview 2 satellites in 2013 through 2016. We used Landsat 8 imagery to create ice velocity maps for Hoodoo and Twin glaciers and found that they flow between 30 and 40 m yr-1 in proximity to our field measurements. From 2012 to 2013 we find that most of the glacier area lost between 0 to 10 m of elevation, with losses in some areas as high as 50 m. This suggests that in 2017 we observed a period of extremely high melt rates and higher than average velocities from August 3 to 10. Because there are no local weather stations, we used the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua Satellite as a proxy for temperature. We extracted a daily temperature record from 31 August 2002 to 9 April 2018 around Hoodoo Mountain. Temperature has only exceeded 20°C, as measured by AIRS, in this area 35 times over the course of 16 years. During our study period we observed 5 days over 20°C, suggesting that a heat wave may have caused the observed excessive melting and elevated ice velocity. This shows that heat waves on a week time scale play a substantial role in mass balance as we measured as much as 1.89 ± 0.28 m of elevation loss in just 7 days. However, we find that the Hoodoo Icecap (1100 m higher than Twin Glacier and 1300 m higher than Hoodoo Glacier), which has lost as much as 6.8 m of ice and gained as much as 5.0 m from 1997 to 2017, has been less impacted by warming than the lower elevation ice bodies of Hoodoo and Twin Glaciers.