GLACIER CONTRIBUTION TO TIBETAN PLATEAU LAKE VOLUMUE INCREASE
INFLUENCE OF DEBRIS COVER ON GLACIER MASS BALANCE
– Brun et al. (2019)
HIGH MOUNTAIN ASIA GLACIER MASS BALANCES
High Mountain Asia glaciers occupy approximately 100 000 km2. Very few glaciers have been surveyed in the field for long term mass balance. In the Himalaya, only two glaciers have mass balance records longer than 10 years. This is one of the reason why we decided to measure long term mass balance of these glaciers for the period 2000-2016. To do so, we relied on ASTER imager, which acquired continuously images since 2000. Thanks to the different acquisition angle, it was possible to reconstruct the surface topography at high (30 m) resolution, and thus to track its evolution.
We measured rates of elevation changes for more than 90 % of the total area and found a mean surface mass balance of -0.18 +/- 0.05 m water equivalent per year.
– Kääb A. et al. (2015), Brief Communication: Contending estimates of 2003–2008 glacier mass balance over the Pamir–Karakoram–Himalaya, The cryosphere.
– Brun et al. (2017), A spatially resolved estimate of High Mountain Asia glacier mass balances from 2000 to 2016, Nature Geoscience.
ICE CLIFFS ON DEBRIS-COVERED GLACIERS OF THE NEPALESE HIMALAYAS
Ice cliffs on debris-covered glaciers might play an important role in the energy balance of the glacier and contribute significantly to the total amount of melt (Steiner et al., 2015; Buri et al., 2016). With a team at ETH Zurick, I developed a method to measure the volumetric losses from ice cliffs based on photogrametric surveys (Brun et al., 2016). This method is rather precise, but it can only be applied to single cliffs and require alot of fieldwork. Later, during my PhD, we adapted this method to lower resolution sensors (UAV and Pléides satellite images) to apply it at larger scales. We applied it to the tongue of Changri Nup Glacier in Nepal, and showed that the ice cliffs contributed to approximately 25 % of the net ablation of the tongue, even though they occupy only 7-8 % of the surface (Brun et al., 2018).
– Brun F. et al. (2018), Ice cliff contribution to the tongue-wide ablation of
Changri Nup Glacier, Nepal, central Himalaya, The Cryosphere.
– Brun F. et al. (2016), Quantifying volume loss from ice cliffs on debris-covered glaciers using high-resolution terrestrial and aerial photogrammetry, Journal of Glaciology.
– Buri P. et al. (2016), A grid-based model of backwasting of supraglacial ice cliffs on debris-covered glaciers, Annals of Glaciology.
– Steiner J. et al. (2015), Modelling ice-cliff backwasting on a debris-covered glacier in the Nepalese Himalaya, Journal of Glaciology.
ALBEDO MEASUREMENTS AND LINKS WITH GLACIER MASS BALANCE
Albedo of glacier surfaces is a strong driver of the mass balance as it controls the amount of energy transferred to the glacier. Dumont et al. (2012) showed that the albedo measured from space (by MODIS sensor) could be used as a proxy for mass balance for Saint-Sorlin Glacier (French Alps).
We adapted this method to the Himalayas and showed that it worked well for Chhota Shigri Glacier (in the western part of the range), but didn’t work for Mera Glacier located in the central Himalayas. We attributed these differences to the different climate influences dominating for each glacier.
– Brun, F., M. Dumont, P. Wagnon, E. Berthier, M. F. Azam, J. M. Shea, P. Sirguey, A. Rabatel, and Al. Ramanathan (2015), Seasonal changes in surface albedo of Himalayan glaciers from MODIS data and links with the annual mass balance, The Cryosphere, 9 (1), 341–355, 10.5194/ tc-9-341-2015.
– Dumont, M., Gardelle, J., Sirguey, P., Guillot, A., Six, D., Rabatel, A., and Arnaud, Y.: Linking glacier annual mass balance and glacier albedo retrieved from MODIS data, The Cryosphere, 6, 1527–1539, doi:10.5194/tc-6-1527-2012, 2012.
EXPERIMENTAL GEOMORPHOLOGY – EROSION BY SUSPENDED SEDIMENTS
Erosion by suspended sediment is often assumed to be negligible compared with the bedload erosion in bedrock incision models. Nevertheless, some recent model developments (Lamb et al., 2008) suggested that suspended sediment could account for up to half of the total erosion.
We measured the erosion by suspended sediment in abrasion mills (similar to the one used by Sklar and Dietrich (2001)) and demonstrated their non negligible contribution to total erosion.
– Scheingross, J. S., F. Brun, D. Y. Lo, K. Omerdin, and M. P. Lamb (2014), Experimental evidence for fluvial bedrock incision by suspended and bedload sediment, Geology, 42, 523–526, 10.1130/G35432.1. (pdf)
– Lamb, M. P., W. E. Dietrich, and L. S. Sklar (2008), A model for fluvial bedrock incision by impacting suspended and bed load sediment, Journal of Geophysical Research, 113 (F3), F03,025.
– Sklar, L. S., and W. E. Dietrich (2001), Sediment and rock strength controls on river incision into bedrock, Geology, 29 (12), 10871090.