We completed our post-drainage site visit on 24 July, roughly one week after completion of the lake drainage. We surveyed the basin with the drone, measured ice melt at the melt wires, and also installed a new melt wire up on Suicide Glacier. This new melt wire at 950 m above sea level complements the temperature sensor deployed next to Suicide Glacier and allows for a melt model calibration across the entire Suicide Basin watershed.
The water level in the basin was at 383 m above sea level, which is 3 m lower than the water level measured during last year’s post-drainage visit. Last year, we visited the basin four days after drainage completion (on 23 July 2018), as opposed to seven days this year. Over these seven days, the water level kept dropping slowly.
Digital elevation model (DEM) differencing of the pre-drainage and post-drainage DEM suggests a volume loss of 0.034 km3, which is slightly more than last year (0.032 km3). The pre-drainage DEM was taken on 8 July 2019 (early into overflow), so the above volume estimate includes the water volume lost through overflow. It also includes the water lost after the main drainage event. Overall, these numbers suggest that the water loss during this year’s combined event (overflow and subglacial drainage) must have been similar to last year’s event.
The new ice cliff (where the ice tongue broke off the main glacier earlier this year) lies about 100 m further towards Mendenhall Glacier than the cliff last year, indicating that the basin has grown laterally. This lateral growth has partly counteracted the volume reduction caused by the thinning ice dam.
The pre-drainage overflow left an incised spillway along the glacier boundary, up to about 4 m deep. The ice-cored moraine next to the spillway is actively adjusting to the new topography, with lots of moving debris.