Shimshal Lake: Some New Revelations from Past and Present
By Gomal Amin
Glacial Lake Outburst Flood (GLOF) is a natural phenomenon which occurs upon failure of dams containing glacier’s melt water. The formation of a glacier dam is mainly due to glacier retreat. As glaciers retreat, glacial lakes are formed behind the debris. A sudden breach in dam walls may lead to discharge huge amount of water and debris. The failure of glacial lakes in recent past has caused loss of human lives and destruction to infrastructure in the mountainous areas.
The northern Pakistan is a mountainous area, where numerous glaciers and glacial lakes are found in the high mountain ranges of Hindu Kush, Himalayas and Karakorum Range (HKH).
ICIMOD published a very brief inventory of glaciers and glacier lakes of Pakistan in 2005. According to ICIMOD’s inventory, a total of 2,420 glacial lakes have been identified in ten river basins of HKH region of Pakistan. Overall, there are 52 potentially dangerous lakes identified in Pakistani HKH mountain ranges, majority of which are located in Gilgit-Baltistan.
Hindu Kush, Himalayas and Karakorum regions are concentrated with large volume of glacier mass after the Polar Regions. The reasons behind the formation of new lakes, expansion of existing glacial lakes and GLOF events are glacier thinning and retreat due to topographical features and regional meteorological factors.
According to a study conducted by UNDP (2007), during the past 200 years almost 35 destructive GLOF events have occurred in Gilgit-Baltistan. According to the available records, the frequency and intensity of GLOF events has increased during the recent years. It should be noted that five GLOF events have occurred during the single year (2008-2009) in Gojal valley of Hunza District.
One of the remote valley prone to GLOF events is the Shimshal valley (Hunza sub-basin). Shimshal valley is located in Central Karakorum Range of Pakistan, known for its massive floods originating from notorious Shimshal Lake. The valley houses five major glaciers. The North-faced tributary glaciers are Khurdopin/Yukshin Gardan (47/17 km), Yazghil (31 km) and Malungutti (23 km) which advance into the Shimshal valley and form potential glacier dams over a horizontal distance of merely 25 km river basin. Viržrav glacier (misspelled as Virjerab ~ Editor) is main source of Shimshal River and it is the largest among these glaciers (47 km).
The first ever detailed field observation on lake formation in the upper Shimshal valley was conducted by a Dutch couple, Visser-Hooft (1926) and Visser (1928, 1938), who investigated the Viržrav (misspelled as Virjerab ~ Editor) lake basin and recognized settlement losses due to glacier lake outbursts. Famous geoscientists and travelers Todd (1930) and Charles (1985) have reported GLOF event in Shimshal valley back in the year 1884, which originated from the advancement of Khurdopin glacier. Both research groups reported a considerable damage to lands at Altit and Ganish villages in central Hunza. During the year 1906, a major GLOF event occurred which was reported by Singh, Mason and Todd in year 1917, 1929 and 1930 respectively. During 1906 flood it was said in the literature that, bridges at Askurdas (Nagar), Tashot (Nagar) and Chamogarh (Gilgit) were destroyed by flood. Rise of river level in Chilas upto 36 ft and in Chalt (Nagar) upto 55 ft was also documented. Researchers also noted the damages to agricultural fields (35), houses (3) and watermills (3) at Passu, Hussani, Gulmit and Ganish.
The recent GLOF activity (1 August, 2017) was originated from the surging activity of Khurdopin glacier which blocked the Virjerab River and formed temporary glacier dam. Which upon some triggering factors busted and caused large damages. It has damaged the only accessible road connecting central Hunza and Shimshal valley. Pamir Times reported damages to the hanging bridges and agricultural lands during the outburst. The damages caused by GLOFs are many which cannot be listed here.
With the help of satellite images of Sentinel-2 (2018) and LANDSAT-7, the approximate area, volume and peak discharge is calculated. The preliminary study using GIS techniques has revealed that approximately 403% change in the Glacier Lake’s area has occurred during the last 3 months (24 Oct, 2017 to 18 Jan, 2018).
Using equations derived by Huggel et al., maximum discharge (Qmax), assuming the worst case scenario when a GLOF event will cause bursting out of all water in the lake (PE), is calculated.
The graph shows the lake area and lake volume for the 24 Oct, 2017 and 18 Jan, 2018.
Potential energy and Maximum probable flow are given in below table:
| 2017 | 2018 | |
| Lake Area (Sq.m) | 33804 | 170067 |
| Volume (m3) | 108473.096 | 1075642.154 |
| PE (potential energy)
|
– | 7.0×1011 |
| Qmax (m3/s)
|
– | 1672.34 |
(Note: All the measurements and calculations are conducted in ArcGIS and ENVI by Gomal Amin).
GLOFs are very powerful natural phenomena and very few mitigation options are available to stay safe from them. To encounter the risk of GLOF, government should involve local communities and researchers to gather the meteorological and glacier related data for a brief scientific study as the mitigation plans will be based on these technical studies.
Another approach which can be used for mitigation of GLOFs risk is the dealing of Glacier Lake at their location. Many lakes in Nepal, Bhutan and other parts of the world have been successfully drained either completely or their level was lowered to a safe position. It can be done either by dredging artificial channels in the natural dam or by conducting controlled blasting. It should be noted that above mentioned approaches require professional skills and financial resources.
A very little has been done to study the glacier lakes and their outburst potential. It is suggested and recommended to use remote sensing data to monitor and analyze the potential risks associated to GLOFs in Gilgit-Baltistan. Using of flood modeling techniques and developing risk maps can be done in future to make community more resilient and prepare.
The contributor is a graduate student of Remote Sensing and GIS at COMSATS Institute of Information Technology, Islamabad. He can be reached at gomalhunzai@gmail.com. He writes a blog at http://www.gripenvironment.blogspot.com and tweets as @gomalhunzai.
