High winter snowline mount everest glaciers – From a Glaciers Perspective

Mount Everest region snowline identified on Dec. 11, 2019 Landsat image (yellow dots). Green dots indicate the terminus and pink arrows flow direction of specific glaciers: T=Trakarding, DN=Drogpa Nagtsang, M=Melung, BK=Bhote Koshi, S=Shalong, Y=Yanong, G=Gyabarg, YN=Yanong North, GY=Gyachung, J=Jiuda, R=Rongbuk, ER=East Rongbuk, I=Imja, L=Lhotse, M=Marala, K=Khumbu, N=Ngozumpa.

The winter monsoon for the Himalaya is a dry cold period with limited new snow accumulation. The Landsat image of Dec. 11, 2019 highlights the snowline at 5500-6200 m on glaciers around Mount Everest. This high of an elevation indicates the accumulation area of the glaciers is too small to sustain the current ablation areas. This is explored in detail below. King et al (2019) found during the 2000-2015 period Himalaya mass balance losses of debris-covered and clean-ice glaciers to be substantially the same, with mass balance loss for lake-terminating glaciers being significantly higher. The overall mean was −0.39 m/year. Maurer et al (2019) found a doubling of the average rate of loss across the Himalaya during 2000–2016 relative to the 1975–2000 interval. King et al (2017) observed the mass balance of 32 glaciers in the Mount Everest area from 2000-2015 finding a mean mass balance of all glaciers was −0.52 m/year, increasing to -0.7 m/year for lake terminating glaciers. Brun et al (2017) identify a mean balance of -0.33 m/year for 2000-2016 in Eastern Nepal, similar to King et al (2019) and not the highest loss rate in the region. Dehecq et al (2018) examined velocity changes across High Mountain Asia from the 2000-2017 period identifying a widespread slow down in the region. The key take away is warming temperatures lead to mass balance losses, which leads to a velocity slow down, and both will generate ongoing retreat.

For an alpine glacier to be in equilibrium requires at least 50% of its area to be in the accumulation zone, this is the accumulation area ratio (AAR). On Dec. 11, 2019 the snowline indicates where the accumulation zone begins. The elevation ranges from 5500 m on Melung Glacier to 6200 m East Rongbuk Jiuda and Gyabarg Glacier. The area above the snowline, AAR, is less than 30% of the total glacier on: Trakarding, Drogpa Nagtsang, Melung, Bhote Koshi, Shalong, Yanong, Gyabarg, Jiuda, Rongbuk, East Rongbuk, Imja, Lhotse, Marala Glacier. Gyachung and North Yanong Glacier have an AAR between 30 and 40%. Khumbu and Ngozumpa Glacier have a high mean elevation and an AAR of close to 50%.

In 2015 and again in 2018 high winter snowlines indicated the same process in the Mount Everest region. See below the rise from Nov. 2017 to Feb. 2018 to similar elevation as seen in Dec. 2019. The high snowlines indicate an accumulation area that is too small to maintain these glaciers, which drives continued retreat, such as reported at Drogpa Nagtsang and Yanong Glaciers.

Dec. 11, 2019 snowline:

6200 m =East Rongbuk, Jiuda, and Gyabarg

6100 m = Gyachung,

5900 m= Rongbuk, Imja, Lhotse

5800 m=Trakarding, Melung, Yanong North

5700 m= Ngozumpa, Drogpa N., Yanong, Shalong, Bhute Khosi

5600 m= Marala, Khumbu

5500 m= Melung

Landsat images from Nov. 17 2017 and Feb. 10 2018 indicate a rise in the snowline, purple dots, on glaciers east of Mount Everest, indicating ablation even in winter from the terminus to the snowline. Rongbuk Glacier=R, East Rongbuk Glacier=ER Far East Rongbuk Glacier=F, Kada Glacier=K, Barun Glacier=B, Imja Glacier=I and Kangshung Glacier=KX.

The Mount Everest region glaciers are summer accumulation type glaciers with 70% of the annual precipitation occurring during the summer monsoon. This coincides with the highest melt rates low on the glacier. October has been considered the end of the melt season in the region. There is little precipitation early in the winter season (November-January). The limited snowpack with warmer winter temperatures have led to high snowlines during the first few months of the winter season in recent years. There is an expanded ablation season that extends beyond October into January or February. The melt rates do to solar radiation or sublimation are not rapid, but are significant on many glaciers. This has occurred with increasing air temperatures since the 1980’s. Mean annual air temperatures have increased by 0.62 °C per decade over the last 49 years; the greatest warming trend is observed in winter, the smallest in summer (Yang et al., 2011). The winter season of 2017-18 has been warm in the region as indicated by global temperature anomalies from, NCDC/NOAA (at right). Here we examine Landsat images from Oct. 21 2017, Nov. 17 2018 and Feb. 10 2018 on the east side of Mount Everest to observe changes in the snowline during the winter period. We observed the same phenomenon of high snowlines and winter ablation at Nup La on the west side of Mount Everest in January of 2016, On Chutenjima Glacier, China in 2016 and Gangotri Glacier, India in 2016 (see below).

At the end of the typical melt season on 10-21-2017, the snowline is at 5850 m on Rongbuk Glacier, 6250 m on East Rongbuk Glacier, 6300 m on Far East Rongbuk Glacier, 5900 m on Kada Glacier, 6050 m on Barun Glacier and ~6100 m on Imja Glacier.

A month later on 11-17-2017 the snowline has decreased to 5700 m on Rongbuk Glacier, 6200 m on East Rongbuk Glacier, 6200 m on Far East Rongbuk Glacier, 5820 m on Kada Glacier, 5950 m on Barun Glacier and still at ~6100 m on Imja Glacier.

Three months later on 2-10-2018 the snowline has risen indicating ablation from the terminus area up to the snowline. The snowline is at 5900 m on Rongbuk Glacier, 6400 m on East Rongbuk Glacier, 6400 m on Far East Rongbuk Glacier, 5950 m on Kada Glacier, 6200 m on Barun Glacier and 6600 m on Imja Glacier. Notice on Far East Rongbuk Glacier the snowline reaches the glacier divide in February. The mean rise in snowline from November 2017-February 2018 on the east side of Mount Everest is 200 m.

The ablation rates necessary to raise the snowline are not large on a daily basis, but cumulatively are significant as noted on Lirung Glacier by Chand et al (2015)

Kundu et al (2015) noted that from Sept. 2012 to January 2013 the snowline elevation on Gangotri Glacier varied little, with the highest elevation being 5174 m and the lowest 5080 m. Bolch et al (2011) observed strong thinning in the accumulation zone on Khumbu Glacier, though much less than the ablation zone. This can only happen with reduced retained snowpack particularly in winter.

Landsat image from Oct. 21 2017 indicate a rise in the snowline, purple dots, on glaciers east of Mount Everest, indicating ablation even in winter from the terminus to the snowline. Rongbuk Glacier=R, East Rongbuk Glacier=ER Far East Rongbuk Glacier=F, Kada Glacier=K, Barun Glacier=B, Imja Glacier=I and Kangshung Glacier=KX.

Purple dots indicate the transient snowline on Gangotri Glacier in the fall and early winter of 2016. Red arrow indicates the terminus of the glacier. Landsat 12-9-16

Landsat image from January 4, 2016 indicating the actual Nup La (N), west side of Mount Everest. Purples dots is the snowline. Green arrows are expanding bedrock exposures and pink arrow a specific rock know amidst the glacier.