Extreme cloudburst events and glacial lake outburst floods in the arid interior of the Himalayas
Brief overview of study area
Ladakh is a remote region located in the northwest part of India, in the state of Jammu and Kashmir. The regions stretches from 33° to 35° latitude North and 76° to 79° longitude East and shares India’s northern boundary with Pakistan and China. Ladakh is crossed by a system of mountain ranges running roughly parallel to each other from northwest to southeast. From north to south these are Karakoram, Ladakh, Zanskar and the Great Himalaya ranges, and these determine the course of Ladakh’s rivers. The drainage in Ladakh is provided by the Indus River which runs for approximately 450km and receives a series of glacier fed tributaries from the north (for example Shyok, Shigar and Gilgit) and from the south (Hanle, Zanskar and the Suru Shingo). Most of these lie parallel to the mountain ranges and run along fault lines.
Despite its apparent remoteness, Ladakh was a way station for ancient trade routes — notably the famous Silk Road, which connected China, India, Central Asia, Europe and even parts of northern Africa. In more modern times, the high walls of the Himalayan mountain range and the region’s barren, rocky, high-altitude desert plateaus kept modern travellers at bay until quite recently. It wasn’t until the Indian army constructed the Leh-Manali Road that outside visitors were finally able to access the region — less than forty years ago, in 1974.
The climate of Ladakh is typical of a high altitude arid desert and is characterised by large seasonal and diurnal temperature fluctuations, low mean annual precipitation values, low relative humidity during the summer season and fast blowing winds in the afternoon hours. The summer season is short (May-September) whereas the winter season is long (November-April). Vegetation cover is scarce and discontinuous with cropping areas being limited to the low altitude floors of river valleys, where anthropic irrigation is present. Agriculture is the main income generation means for Ladakhis, although due to the above-mentioned environmental characteristics, agriculture is a difficult and risky affair.
In terms of geology, the Ladakh Range of Transhimalaya is a granodioritic, granitic and tonalitic batholith, with minor amounts of mafic rocks such as diorite, grabbro and grabbronorite intruded by leucogranite dykes. The batholith is part of the Cretaceous – Eocene arc batholiths that developed between India and Asia and are currently entrapped into the collisional zone. Topographically, the Ladakh batholith is aligned west-northwest to east-southeast and rises from the Indus valley floor at about 2300 m in the west and 4000 m in the east. The main ridgeline forms a relatively horizontal summit plane with elevations in excess of 6000m in the west and 5800m in the east.
Leh, is the capital and most populous city of Ladakh and is located in a glacial valley adjacent to the Indus River, which flows roughly from southeast to northwest. During the 4-6 August 2010, the area surrounding Leh, experienced a series of flash floods and mud and debris flows that caused serious damage to infrastructure and settlements. Approximately 52 villages with about 1750 houses were destroyed and over 600 people were killed in what was described as the worst storm in living memory. This storm was associated with the intense monsoonal precipitation that caused flooding throughout the lower Indus Valley in Pakistan during July and August 2010.
High Himalaya Mission
We organised a daring trip in the second week of our stay in Ladakh into the High Himalaya range, situated south of the Indus River. The aim was to visit the infamous Kargil, near the border of Pakistan and reproduce a historic photograph of the Drang Drung Glacier, located some 200km southeast of Kargil in the Himalaya. The journey by bus along the Indus valley was a wild adventure, crossing high passes some 4500m high and negotiating numerous roadblocks. The journey from Kargil to Pensi La via the notorious Suru Valley, proved to be a rather difficult endeavour due to the rough character of the road. Thankfully our hired driver proved to be quite skilled in negotiating the numerous obstacles along the road. Fantastic jagged 7000m peaks such as Kun and Nun kept us in high spirits for the duration of this journey. Camping next to the Drang Drung glacier was also a highlight, especially when our attempted stir-fry dish proved to be a complete disaster. A balanced ratio of elements in a dish is crucial for a tasty meal – too much ginger just ruins it!
Chasing Storm Signals
In order to assess the relationship between short – lived, high rainfall, extreme storm events and glacial lake outburst floods (GLOFs) we carried out a series of field analysis including geomorphic mapping, channel surveying, lichenometric relative dating of glacigenic sediments, repeat photographic analysis and remote sensing analysis.
The first valley we explored was Leh, located just near Khardung La – the highest motorable pass in the world (5642m). In this valley we calibrated and tested our long-range lasers, handheld transceivers, altimeters, compass, DLSR cameras and also acclimatised to the high altitude conditions. Unfortunately, while testing our weather station we realised that it was not suitable for the harsh weather conditions of this high altitude environment and we decided to abandon the weather data-gathering mission. We would later use climate data gathered by a nearby weather post installed by the Indians. Nevertheless we did manage to gather some useful geomorphic data and get accustomed to this unique but harsh landscape. Some of the preliminary observations indicated a poor correlation between the debris flow and glacial lake outburst floods in this particular valley.
The second valley we explored was Phyang, which is located west of Leh valley. From this valley came a series of anecdotal reports from villagers of debris flows coming from the uppermost sections of the valley above 5000m. Therefore we were particularly interested to follow these debris flows all the way to their source and assess what was the triggering mechanism. Armed with high altitude camping, cooking and scientific equipment and a burning curiosity, we trekked the long Phyang valley starting at about 4000m and following closely the poorly sorted debris flow. We reached a bizarre bifurcation in the debris flow at about 5000m. One large and relatively fresh debris flow headed left whereas a smaller, better sorted and much older one continued up the valley heading slightly right. We set up camp at this interesting location. Dinner consisted of a large portion of rice with salt and pepper and a spicy noodle soup. We were too tired and hungry to complain about the minimalistic dish – in fact I would say it was rather delicious at that high elevation.
A large yak herd was grazing undisturbed by us, about 400 meters from our tents. The night was cold and for some of us, slightly unpleasant due to headaches caused by the low oxygen concentration. At about 5am we were woken up by the howls of a large pack of wolves. Fortunately they did not dare to attack us. Early next morning, we all went to explore the eastern, secondary valley and its associated debris flow. Three hours later we reached the terminal moraine of the glacier. There was no geomorphic evidence indicative of a debris flow or breach in the moraine. The glacier was calving into a glacial lake that in turn was draining through the base of the terminal moraine through a series of conduits. I carried out my geomorphic measurements and returned to the camp later in the afternoon, quite content with the work I had managed to achieve. The next day, we investigated the western valley characterized by a prominent, fresh and poorly sorted debris flow. Just as expected, the debris flow was coming from a breached terminal moraine. The breach was rather spectacular and consistent with the hypothesis of our study until proven otherwise. There were several indications of a glacial lake outburst flood for example a drained glacial lake, enlarged drainage conduits, blasted dead ice, two large moraine breaches, and poorly sorted angular to sub-angular material. I spent five days mapping both glacial systems, crafting detailed geomorphic graphic descriptions. Additionally quantitative data was gathered from the debris flow, which in turn was used to estimate the volume of material dislodged during the event. Oliver was working further downstream performing similar geomorphic and hydrologic measurements.
Domkhar valley was the most spectacular and loftiest valley we explored. Jagged peaks, a series of cirque and dramatic hanging glaciers, fast flowing glacial streams and a sinister atmosphere, all gave us some “chills”. We asked two Nepali Sherpas to help us carry our heavy loads from village to campsite in the eastern secondary valley. These individuals turned out to be very skilled chefs and they taught us how to properly cook the rice at this altitude. They also taught us how to smoke biddies – some tobacco rolled in eucalyptus leaves – a rather strong delight in this area. Domkhar valley was very complex; there were at least three main glacial systems of which we managed to map only one. The terrain was very rugged and steep and in one area there was geologic evidence of a collapsed glacial system. The lateral and terminal moraine systems were very clear and it was a real pleasure photographing and analyzing the lichen cover on these clean surfaces to determine their relative age. I have found little evidence supportive of a GLOF event in this glaciated catchment. However, I believe there is considerable risk of a GLOF event occurring in one of the three glacial systems in the near future. This is due to a combination of factors including a high lake level, serac and rock avalanches into the lake, dangerously expanding sub-drainage conduits, and a high narrow moraine wall.
This valley was the most sinister and mysterious of all the places we had seen so far. Here I was faced with a fierce Himalayan storm that almost knocked me down while examining the glacier. Besides this scary event, our geomorphic investigation suggested that the storm signal has missed the uppermost section of the valley and was rather concentrated downstream just above the Likkir village. The valley seemed blank with no major catastrophic geomorphologic phenomena. Some peculiar geomorphic features such as a series of closely packed terminal moraines and flat, silty-muddy rich beds with stagnant water, created some considerable confusion when interpreting the train of events that has occurred in this valley. We managed to take some data but insufficient to determine a strong storm signal in this location. Strangely enough, this valley was located in between Phyang and Domkhar – two valleys with a strong geomorphic signal. We returned to Leh, not missing of course the giant golden Buddha statue.
The results of this study indicated that the storm impact is variable across the surveyed valleys (>150km) and the correlation with glacial lake outburst floods is not significant. Geomorphic evidence that accounts for the glacial hazard was found in just one valley, Phyang, with the debris flow concentrated in a 1-3 km band in front of a breached moraine dam. Valley geomorphic, geologic and topographic factors inhibit debris flow evolution downstream by reducing its energy and sediment load until complete cessation. The relative dating of glacigenic landforms using the lichen percentage cover technique is subjective, sensitive to environmental factors and prone to error. However, the photographic technique is effective in producing quantitative data of population sizes. Qualitative analysis of repeat photographs in High Himalaya based on the case of Drang Drung glacier indicated a pronounced melting trend, which has accelerated since 1980.