Brief Description of Glacial Lake Inventory

The inventory of glacial lakes is based on topographic maps and satellite images. There are 148 sheets topographic maps with a scale of 1:50,000 in total, which were published before 1987. The 17 scenes TM images had been used to obtain the changes of glacial lakes, while several decades ASTER images as supplement information when TM images are impacted by snow cover or clouds.

Glacial Lakes—Their Numbering, Type and Characteristics

A glacial lake is defined as a water mass existing in a sufficient amount and extending with a free surface in, under, beside and/or in front of a glacier and originated by glacier activities and/or retreating processes of a glacier.

The numbering of the lakes started from the mouth of the major stream and proceeded clockwise round the basin.

For the inventory of glacial lakes, it is obvious to note that the lakes associated with perennial snow and ice originate from glaciers. But the isolated lakes found in the mountains and valleys far away from the glaciers may not have a glacial origin. Due to the faster rate of ice and snow melting, possibly caused by global warming noticed during the last half of the twentieth century, accumulation of water in these lakes has been increasing rapidly. The isolated lakes above 3,500 masl are considered to be the remnants of the glacial lakes left due to the retreat of the glaciers.

The lakes are classified into erosion lakes, valley trough lakes, cirque lakes, blocked lakes, moraine-dammed lakes (lateral and end moraine-dammed lakes), and supraglacial lakes.

Erosion lakes

Glacial erosion lakes are the water bodies formed in a depression after the glacier has retreated. They may be cirque type and trough valley type lakes and are stable lakes.

Supraglacial lakes

The supraglacial lakes develop within the ice mass away from the moraine with dimensions of from 50 to 100m. These lakes may develop in any position of the glacier but the extension of the lake is less than half the diameter of the valley glacier. Shifting, merging, and draining of the lakes characterise the supraglacial lakes. The merging of lakes results in expansion of the lake area and storage of a huge volume of water with a high potential energy. The tendency of a glacial lake towards merging and expanding indicates the danger level of the GLOF.

Moraine-dammed lakes

A typical example of a moraine-dammed lake is one formed on the tongue of the Cuolangma Glacier in the Pumqu basin (Figure 8.1). In the retreating process of a glacier, glacier ice tends to melt in the lowest part of the glacier surrounded by lateral and end moraines. As a result, many supraglacial ponds are formed on the glacier tongue. These ponds sometimes enlarge to become a large lake by interconnecting with each other and have a tendency to deepen further. A moraine-dammed lake is thus born. The lake is filled with melt water and rainwater from the drainage area behind the lake and starts flowing from the outlet of the lake even in the winter season when the flow is minimum.


Figure 8.1: A typical example of a moraine-dammed lake is one formed on the tongue of the Cuolangma
Glacier in the Pumqu Basin (ASTER satellite image of 13 October 2001)                                               

There are two kinds of moraine: an ice-cored moraine and an ice-free moraine. Before the ice body of the glacier completely melts away, glacier ice exists in the moraine and beneath the lake bottom. The ice bodies cored in the moraine and beneath the lake are sometimes called dead ice or fossil ice. As glacier ice continues to melt, the lake becomes deeper and wider. Finally when ice contained in the moraines and beneath the lake completely melts away, the container of lake water consists of only the bedrock and the moraines.

Blocking lakes

Blocking lakes formed through glacier and other factors, including the main glacier blocking the branch valley, the glacier branch blocking the main valley, and the lakes through snow avalanche, collapse and debris flow blockade.

Ice-dammed lakes

An ice-dammed lake is produced on the side(s) of a glacier, when an advancing glacier happens to intercept a tributary/tributaries pouring into a main glacier valley. The typical ice core-dammed lakes are shown in Figure 8.2. Three lakes are seen on the right bank of the debris covered glacier tongue of the Ngozumpa Glacier in the Dudh Koshi Basin, which is one of the largest glaciers in the Nepal Himalayas and flows from top to bottom in the figure. The lakes were still frozen and covered by snow when the image was captured. Since the glaciers in the Nepal Himalayas produce relatively rich debris, thick lateral moraines are deposited on both sides of the glacier tongue. As such an ice core-dammed lake is usually small in size and does not come into contact with glacier ice. This type of lake is less susceptible to GLOF than a moraine-dammed lake.

A glacial lake is formed and maintained only up to a certain stage of glacier fluctuation. If one follows the lifespan of an individual glacier, it is found that the moraine-dammed glacial lakes build up and disappear with a lapse of time. The moraine-dammed lakes disappear once they are fully destroyed or when debris fills the lakes completely or the mother glacier advances again to lower altitudes beyond the moraine-dam position. Such glacial lakes are essentially ephemeral and are not stable from the point of view of the life of glaciers.


Figure 8.2: The lakes labelled ID, SG, and E represent ice core-dammed, supraglacial, and erosion
lakes respectively around the Ngozumpa Glacier, one of the largest glaciers in the Nepal Himalayas
(LANDSAT TM satellite image of 17 December 1991)                                                                     

In generally, only moraine-dammed lakes pose a threat in the Pumqu Basin. The description hereafter is, thus, mainly concentrated on moraine-dammed lakes and associated outburst floods.

Glacial Lakes of Himalaya-China Region

There are 824 lakes in the Himalayan-China Regions covering an area of around 85.191 sq.km, including erosion lakes, cirque lakes, end moraine dammed lakes, valley trough lakes, and blocking lakes. Among them the largest number and area are associated with end moraine-dammed lakes. This kind of lakes normally develops in the inner side of moraine ridges of the Little Ice Age, not far from their originating glaciers or connects directly to the originating glaciers. Because water level and stability of the dam are directly affected by the glacier variation, and the Little ice Age moraine ridges developed rather recently, the moraine materials have not cemented hard enough to become a rock. The dam is very easy to burst and form an extraordinary serious flood or debris flow (Table 8.1).

Table 8.1: Distribution of lakes in the sub-basins of the Himalaya - China Region

Basin Name

Number of Lakes

Area
(km2)

Mean area per lake
(km2)

Jiazhagangge

14

0.515

0.037

Daoliqu

7

0.377

0.054

Majiacangbu

69

4.734

0.069

Jilongcangbu

72

3.317

0.046

Poiqu

91

15.661

0.172

Pumqu

383

52.008

0.136

Rongxer

183

8.395

0.046

Zangbuqin

5

0.183

0.037

Total

824

85.1914

0.1034

Jiazhagangge basin

The Jiazhagangge basin is the one of westernmost branch of the Himalayan-China basin. There are 10 moraine-dammed lakes in total, and only one lake is dangerous. And the erosion lakes and valley lakes are not potentially dangerous as they are isolated and not associated with the hanging glaciers. (Table 8.2)

Table 8.2: Types of lakes in the Jiazhagangge basin

Type

Number

Number
(%)

Area
(m2)

Area
(%)

Area of largest lake (m2)

Erosion

3

21.43

15854.89

9.24

28598.38

Moraine dammed

10

71.43

43634.61

84.74

68921.52

Valley

1

7.14

31026.18

6.02

31026.18

Daoliqu basin

Though there are only 7 lakes in the Daoliqu basin, all of them are moraine-dammed lakes but one erosion lake. After analysis of these lakes change in two different periods, we found no lakes belong to the potentially danger lakes. (Table 8.3)

Table 8.3: Types of lakes in the Daoliqu basin

Type

Number

Number (%)

Area
(m2)

Area (%)

Area of largest lake (m2)

Erosion

1

14.29

50844.72

13.50

50844.72

Moraine dammed

6

85.71

325659.73

86.50

93291.24

Majiacangbu basin

The Majiacangbu basin is one of the most dangerous basins, and these dangerous lakes locate the eastern of basin. In total, there are 11 danger lakes in this basin (Table 8.4)

Table 8.4: Types of lakes in the Majiacangbu basin

Type

Number

Number (%)

Area (m2)

Area (%)

Area of largest lake (m2)

Cirque

5

7.25

604711.46

12.77

285980.70

Erosion

26

37.68

1363042.92

28.79

624406.40

Moraine dammed

24

34.78

2497764.88

52.77

451944.60

Supraglacial

9

13.04

84393.36

1.78

22738.89

Valley

5

7.25

183824.49

3.88

64860.35

Jilongcangbu basin

In the Jilongcangbu basin, the number of glacial lakes is large, and it is one of dangerous sub-basins. (Table 8.5)

Table 8.5: Types of lakes in the Jilongcangbu basin

Type

Number

Number (%)

Area (m2)

Area (%)

Area of largest lake (m2)

Cirque

4

5.56

101429.15

3.06

50564.51

Erosion

19

26.39

495696.32

14.94

88642.99

Moraine dammed

31

43.06

2111456.10

63.65

424676.27

Supraglacial

6

8.33

69247.21

2.09

19788.16

Valley

12

16.67

539655.68

16.27

162816.11

Poiqu basin

The Poiqu basin also is one of dangerous sub-basins, and there are 91 lakes in total. In final, 9 lakes are identified as potentially danger lakes. (Table 8.6)

Table 8.6: Types of lakes in the Poiqu basin

Type

Number

Number
(%)

Area
(m2)

Area
(%)

Area of largest lake (m2)

Blacking

1

1.10

2295810.38

14.66

2295810.38

Erosion

47

51.65

1618276.07

10.33

312973.43

Moraine dammed

28

30.77

10354219.70

66.11

3373971.19

Supraglacial

3

3.30

87897.50

0.56

37236.95

Valley

12

13.19

1305151.74

8.33

498951.43

Pumqu basin

The Pumqu basin is the largest basin in this research region, and there are 383 lakes distributed in 9 sub-basins. Pumqu basin also is the dangerous basin, 38 lakes are identified as potentially danger lakes. (Table 8.7)

Table 8.7: Distribution of lakes in the sub-basins of the Pumqu basin

Sub-asin Name

Number
of Lakes

Area
(km2)

Mean area per lake
(km2)

Ganmazangbo

56

3.180

0.057

Kadapu

51

6.258

0.123

Zhagarqu

19

1.208

0.064

Zongbuxan

30

7.667

0.256

Moinqu

7

5.290

0.756

Loloqu

56

5.491

0.098

Yarozangbo

43

9.921

0.231

Bailungpu

63

7.374

0.117

Natangqu

58

5.619

0.097

Total

383

52.008

0.136

Ganmazangbo sub-basin

Table 8.8: Types of lakes in the Ganmazangbo sub-basin

Type

Number

Number (%)

Area
(m2)

Area (%)

Area of largest lake (m2)

Erosion

52

92.86

2401414.23

75.50

261329.11

Moraine dammed

1

1.79

323329.85

10.17

323329.85

Valley

3

5.36

455726.82

14.33

391663.40

Kadapu sub-basin

Table 8.9: Types of lakes in the Kadapu sub-basin

Type

Number

Number (%)

Area (m2)

Area (%)

Area of largest lake (m2)

Erosion

21

41.18

1143671.28

18.28

230963.47

Moraine dammed

7

13.73

1276974.35

20.41

607776.41

Valley

23

45.10

3837176.47

61.32

1033599.03

Zhagarqu Sub-basin

Table 8.10: Types of lakes in the Zhagarqu sub-basin

Type

Number

Number (%)

Area
(m2)

Area (%)

Area of largest lake (m2)

Blocking

1

5.26

572276.72

47.38

572276.72

Erosion

6

31.58

216553.90

17.93

109759.78

Moraine dammed

3

15.79

195688.28

16.20

150840.08

Supraglacial

9

47.37

223350.09

18.49

109779.25

Zongbuxan sub-basin

Table 8.11: Types of lakes in the Zongbuxan sub-basin

Type

Number

Number (%)

Area
(m2)

Area (%)

Area of largest lake (m2)

Erosion

9

30.00

446699.29

5.83

269548.80

Moraine dammed

19

63.33

7091489.86

92.50

4135052.36

Supraglacial

2

6.67

128660.57

1.68

107454.62

Moinqu sub-basin

Table 8.12: Types of lakes in the Moinqu sub-basin

Type

Number

Number (%)

Area
(m2)

Area (%)

Area of largest lake (m2)

Moraine dammed

2

28.57

227102.45

4.29

213555.89

Valley

5

71.43

5063375.24

95.71

2783950.82

Loloqu sub-basin

Table 8.13: Types of lakes in the Loloqu sub-basin

Type

Number

Number (%)

Area (m2)

Area (%)

Area of largest lake (m2)

Cirque

3

5.36

767022.59

13.97

543142.21

Erosion

11

19.64

682529.60

12.43

336315.02

Valley

42

75.00

4041626.31

73.60

390059.37

Yarozangbo sub-basin

Table 8.14: Types of lakes in the Yarozangbo sub-basin

Type

Number

Number (%)

Area (m2)

Area (%)

Area of largest lake (m2)

Erosion

7

16.28

301438.26

3.04

146860.56

Moraine dammed

32

74.42

8504304.04

85.72

1112609.70

Valley

4

9.30

1114989.97

11.24

808750.34

Bailungpu sub-basin

Table 8.15: Types of lakes in the Bailungpu sub-basin

Type

Number

Number (%)

Area
(m2)

Area (%)

Area of largest lake (m2)

Blocking

1

1.59

1326268.61

17.98

1326268.61

Erosion

36

57.14

1693892.14

22.97

209914.30

Moraine dammed

19

30.16

3641594.79

49.38

846200.23

Valley

7

11.11

712694.75

9.66

341585.38

Natangqu sub-basin

Table 8.16: Types of lakes in the Natangqu sub-basin

Type

Number

Number (%)

Area
(m2)

Area (%)

Area of largest lake (m2)

Erosion

31

53.45

880510.90

15.67

111650.47

Moraine dammed

20

34.48

2956668.95

52.62

901023.23

Supraglacial

1

1.72

55962.50

1.00

55962.50

Valley

6

10.34

1725403.30

30.71

1458918.72

 

Rongxer basin

The Rongxer basin is also one of dangerous basins, and there are 183 lakes in total. (Table 8.17) In final, 16 lakes are identified as potentially danger lakes.

Table 8.17: Distribution of lakes in the sub-basins of the Rongxer basin

Sub-asin Name

Number of Lakes

Area
(km2)

Mean area per lake
(km2)

Rongxer Qu_A

24

0.2150

0.0090

Rongxer Qu_B

74

2.2973

0.0310

Rongxer Qu_C

85

5.8824

0.0692

Total

183

8.3947

0.0459

Rongxer Qu_A sub-basin

Table 8.18: Types of lakes in the Rongxer Qu_A sub-basin

Type

Number

Number (%)

Area
(m2)

Area (%)

Area of largest lake (m2)

Erosion

20

83.33

180480.17

83.94

25944.61

Moraine dammed

1

4.17

16846.79

7.84

16846.79

Valley

3

12.50

17691.55

8.23

7755.70

Rongxer Qu_B sub-basin

Table 8.19: Types of lakes in the Rongxer Qu_B sub-basin

Type

Number

Number (%)

Area
(m2)

Area (%)

Area of largest lake (m2)

Erosion

35

47.30

746737.47

32.50

76896.94

Moraine dammed

20

27.03

1354046.46

58.94

260082.20

Supraglacial

18

24.32

159066.66

6.92

49558.95

Valley

1

1.35

37462.03

1.63

37462.03

Rongxer Qu_C sub-basin

Table 8.20: Types of lakes in the Rongxer Qu_C sub-basin

Type

Number

Number (%)

Area
(m2)

Area (%)

Area of largest lake (m2)

Blocking

1

1.18

193636.58

3.29

193636.58

Erosion

53

62.35

1448031.64

24.62

175904.69

Moraine dammed

16

18.82

4057936.80

68.98

793293.47

Supraglacial

15

17.65

182774.72

3.11

40657.39

Zangbuqin basin

The Zangbuqin basin is a small basin, and there are only 5 lakes. There are no potentially danger lakes. (Table 8.21)

Table 8.21: Types of lakes in the Zangbuqin basin

Type

Number

Number (%)

Area
(m2)

Area (%)

Area of largest lake (m2)

Erosion

1

20.00

43256.73

23.58

43256.73

Moraine dammed

4

80.00

140155.51

76.42

94743.19