Katie and Evan are back in Kathmandu putting together the final preparations for EverDrill’s autumn field season. The purpose is to revisit the drill sites to collect the monsoon season’s records of temperature, tilt, turbidity, water pressure and electrical conductivity. We are really excited about these data, which are the first of their kind for glaciers in High Mountain Asia, and we’re very curious to see what insights the data provide with regards to glacier thermal regime and hydrology!
Evan will also be resurveying numerous markers with a dGPS system to derive high-resolution surface velocities, and will perform structure-from-motion surveys of the drill sites to assess local changes. The team will perform salt dilutions of Khumbu’s large supraglacial stream and of the glacier’s terminus outlet stream, where they hope to establish a rating curve to convert stage measurements to a record of glacier discharge.
Finally, the two will be carrying out a few favours for colleagues. They will visit an automatic weather station (AWS) on Imja Glacier established by our colleague Dave Rounce (http://davidrounce.weebly.com/ ), a postdoctoral scholar at the University of Alaska in Fairbanks. They will also collect a network of air temperature sensors established throughout the valley and on the glacier by Emily Potter (https://www.geog.cam.ac.uk/people/potter/ ), a PhD student from Cambridge University who was part of the EverDrill fieldwork (and the drilling!) in the premonsoon this year. In addition, the two will visit a permanent GNSS station in Syangboche (SYBC, http://www.unavco.org/instrumentation/networks/status/pbo/data/SYBC ) to collect recent records and troubleshoot, as the data telemetry stopped this past February. These data will be very useful for our dGPS postprocessing, and the excursion is made possible thanks to John Galetzka of UNAVCO, who originally established the station.
With just two scientists and a small Nepali team, the short trip has a lot of ground to cover. We’re all quite nervous about the state of the sensors. Evan has been examining late-monsoon changes to the glacier using Planet 3m-resolution 4-band imagery, and the lower two drill sites have seen a lot of surface change, such as drainage or expansion of supraglacial ponds, and significant backwasting of the ice cliffs. This last topic has been the focus of a recent paper by Scott Watson (https://doi.org/10.1017/jog.2017.47 ), which used M3C2 in CloudCompare (http://www.cloudcompare.org/doc/wiki/index.php?title=M3C2_(plugin) ) to difference structure-from-motion point clouds and indicates that the ponds backwaste at an average rate of 1-5 cm/d over the monsoon.
The resulting surface changes are clearly evident when comparing Planet imagery from May and September 2017, here focusing on the terminus area. In particular, the set of supraglacial ponds has undergone gradual expansion and coalescence in recent years, and may have finally cut off the primary path to Kongma La pass, which is important to us as a fast way to cross the glacier. We will just have to see in a few weeks!
A big thanks to Planet for making their fantastic data available for scientific research!
Planet Team (2017). Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://api.planet.com.