Morgan J. Gibson

Changes in glacier surface cover on Baltoro glacier, Karakoram, north Pakistan, 2001–2012

ABSTRACT The presence of supraglacial debris on glaciers in the Himalaya-Karakoram affects the ablation rate of these glaciers and their response to climatic change. To understand how supraglacial debris distribution and associated surface features vary spatially and temporally, geomorphological mapping was undertaken on Baltoro Glacier, Karakoram, for three time-separated images between 2001–2012. Debris is supplied to the glacier system through frequent but small landslides at the glacier margin that form lateral and medial moraines and less frequent but higher volume rockfall events which are more lobate and often discontinuous in form. Debris on the glacier surface is identified as a series of distinct lithological units which merge downglacier of the convergence area between the Godwin-Austen and Baltoro South tributary glaciers. Debris distribution varies as a result of complex interaction between tributary glaciers and the main glacier tongue, complicated further by surge events on some tributary glaciers. Glacier flow dynamics mainly controls the evolution of a supraglacial debris layer. Identifying such spatial variability in debris rock type and temporal variability in debris distribution has implications for glacier ablation rate, affecting glacier surface energy balance. Accordingly, spatial and temporal variation in supraglacial debris should be considered when determining mass balance for these glaciers through time.

The sky is the limit : Reconstructing physical geography from an aerial perspective

Abstract In an era of rapid geographical data acquisition, interpretations of remote sensing products are an integral part of many undergraduate geography degree schemes but there are fewer opportunities for collection and processing of primary remote sensing data. Unmanned Aerial Vehicles (UAVs) provide a relatively inexpensive opportunity to introduce the principles and practice of airborne remote sensing into field courses, enabling students to learn about image acquisition, data processing and interpretation of derived products. Two case studies illustrate how a low-cost “DJI Phantom Vision+” UAV can be used by students to acquire images that can be processed using Structure-from-Motion photogrammetry software. Results from a student questionnaire and analysis of assessed student reports showed that using UAVs enhanced student engagement and equipped them with data processing skills. The derivation of bespoke orthophotos and Digital Elevation Models has the potential to provide students with opportunities to gain insight into various remote sensing data quality issues, although additional training is required to maximize this potential. Recognition of the successes and limitations of this teaching intervention provides scope for improving future UAV exercises. UAVs are enabling both a reconstruction of how we measure the Earth’s surface and a reconstruction of how students do fieldwork.

Supraglacial Ponds Regulate Runoff From Himalayan Debris‐Covered Glaciers

Meltwater and runoff from glaciers in High Mountain Asia is a vital freshwater resource for one fifth of the Earths population. Between 13% and 36% of the regions glacierized areas exhibit surface debris cover and associated supraglacial ponds whose hydrological buffering roles remain unconstrained. We present a high-resolution meltwater hydrograph from the extensively debris-covered Khumbu Glacier, Nepal, spanning a seven-month period in 2014. Supraglacial ponds and accompanying debris cover modulate proglacial discharge by acting as transient and evolving reservoirs. Diurnally, the supraglacial pond system may store >23% of observed mean daily discharge, with mean recession constants ranging from 31 to 108 hours. Given projections of increased debris-cover and supraglacial pond extent across High Mountain Asia, we conclude that runoff regimes may become progressively buffered by the presence of supraglacial reservoirs. Incorporation of these processes is critical to improve predictions of the regions freshwater resource availability and cascading environmental effects downstream.

Variations in near-surface debris temperature through the summer monsoon on Khumbu Glacier, Nepal Himalaya: Near surface debris temperature variability on Khumbu Glacier, Nepal

Debris surface temperature is a function of debris characteristics and energy fluxes at the debris surface. However, spatial and temporal variability in debris surface temperature, and the debris properties that control it, are poorly constrained. Here, near‐surface debris temperature (Ts) is reported for 16 sites across the lower elevations of Khumbu Glacier, Nepal Himalaya, for the 2014 monsoon season. The debris layer at all sites was ≥1 m thick. We confirm the occurrence of temporal and spatial variability in Ts over a 67‐day period and investigate its controls. Ts was found to exhibit marked temporal fluctuations on diurnal, short‐term (1–8 days) and seasonal timescales. Over the study period, two distinct diurnal patterns in Ts were identified that varied in timing, daily amplitude and maximum temperature; days in the latter half of the study period (after Day of Year 176) exhibited a lower diurnal amplitude (mean = 23°C) and reduced maximum temperatures. Days with lower amplitude and minimum Ts were concurrent with periods of increased seasonal variability in on‐glacier air temperature and incoming shortwave radiation, with the increased frequency of these periods attributed to increasing cloud cover as the monsoon progressed. Spatial variability in Ts was manifested in variability of diurnal amplitude and maximum Ts of 7°C to 47°C between sites. Local slope, debris clast size and lithology were identified as the most important drivers of spatial variability in Ts, with inclusion of these three variables in the stepwise general linear models resulting in R2 ≥0.89 for six out of the seven sites. The complexity of surface energy fluxes and their influence on Ts highlight that assuming a simplified relationship between air temperature and debris surface temperature in glacier melt models, and a direct relationship between debris surface temperature and debris thickness for calculating supraglacial debris thickness, should be undertaken with caution.