Distribution And Motion Patterns Of The Surge-type Glaciers In High Mountain Asia By Remote Sensing

High Mountain Asia encompasses mountains and plateaus in the western China,also including highlands in the neighboring regions.It is home to the largest number of glaciers outside Earth's polar regions.Glaciers in High Mountain Asia are known as “Asian Water Towers”.The meltwater flowing from High Mountain Asia is the most important water resource for local residence and feeds most cities and oases in the downstream.Fluctuations in mountain glaciers are recognized as a key indicator of climate change.Since the 1990 s,these glaciers have been in a sustained phase of recession,resulting in many regional glacial related hazards.Researches on glacial related hazards have been paid more and more attention by scholars around the world recent years.As one of the glacial related hazards,glacier surges can also induce secondary geological hazards in some cases,such as glacial lake outburst floods,mudslides,avalanches.Due to the suddenness and concealment of glacier surges,the difficulty to detect their processes,and the sparsity of people living in High Mountain Asia,surge-type glaciers in this region have always been a difficult research topic.Glacier surges in High Mountain Asia are also a hot-spot research in the cryosphere nowadays.How do the surge-type glaciers distribute within High Mountain Asia? Is the surge mechanism same with other regions in the world? What are the patterns of motion and mass balance for these surge-type glaciers? Many scientific questions are urgently to be answered.Till nowadays,mankind has collected a huge and global-archive data through space observation,and established many stable observation platforms in outer space.Remote-sensing technologies have provided most of the available data for studying glaciers in High Mountain Asia.In this thesis,I collected thousands of optical satellite images and digital elevation model data,as well as several glacier inventories,and conducted researches on the distribution and motion patterns of surge-type glaciers in High Mountain Asia.Three sets of digital elevation model data are co-registrated and differentiated to obtain glacial surface elevation changes during different study periods.With the help of historical satellite images,these surface elevation changes are used to identify surge-type glaciers.To reduce the impact of climate change to a minimum level and control this research within a manageable scale,this thesis chooses the eastern Pamir as the typical area for studying motion pattern and mass balance pattern,as glaciers in the eastern Pamir are experiencing equilibrium mass changes during recent decade.For the first time,this thesis publishes a new dataset of 492 glaciers including 395surge-type glaciers and 97 likely surge-type glaciers in High Mountain Asia,and gives their distributions.These glaciers in number are 2.48% of those with areas larger than 1 km2 in High Mountain Asia.The area of them is 21.35% of the total glacierized region in High Mountain Asia.They mainly concentrate in the Karakoram and the Pamir regions.The Tianshan Mountains,the Kunlun Shan,and the inner Tibet Plateau also develop dozens of surge-type glaciers.The Himalayas,the Hindu Kush,and the Nyaung Tangula have the least surges during the study period.This thesis proposes a robust remote-sensing standard for surge-type glacier identification.At first step,combining glacial surface elevation changes and glacier inventory data,glaciers with the reservoir zones thinning and the receiving zones thickening,or the reverse happens,are selected.Secondly,the potential surge-type glaciers are further confirmed by their surface feature changes extracting from historical satellite images.Finally,the variations in glacial velocities are judged to make the final confirmation of a surge-type classification,such as a clear surge front in the velocity profiles or an increase of at least 10 times in surface velocities.This thesis proposes the patterns of mass changes and velocity changes of surge-type glaciers.Some surge-type glaciers show short-lived fluctuations in mass balance before,during,and after the surge events.However,there is no statistically significant difference between the mass balances of surge-and non-surge glaciers on a regional scale.The surge periods vary from one decade to several decades,but in general the larger the accumulation area and the narrower the outlet,the shorter the surge period will be.Most glaciers will reach the peak velocities(60-150 m a-1)in the first year of their surges and the termination phases usually last for several years.These characteristics do not completely resemble the well described hydrologically and thermally controlled surges reported in Svalbard and Alaska.This thesis suggests that monitoring intermonth or interannual surface velocity changes of surge-type glaciers,along with hydrological observations,can give a timely prediction for catastrophic surge events.This would be a valuable research reference for glacier surge studies in other regions around High Mountain Asia.