The basic materials required for this research are satellite images, large-scale topographic maps and the inventory of glacier and glacial lakes. The TM image acquired in the 1990 and the ETM image obtained in 2000 were used to study the activity of glaciers and for the identification of potentially dangerous glacial lakes. The topographic maps as reference used to help interpreting image and obtaining some attribute of glaciers such as elevation, orientation.
 
Remote-sensing data like those from the Land Observation Satellite (Landsat) Thematic Mapper (TM), Indian Remote Sensing satellite series 1D (IRS 1D), Linear Imaging and Self-scanning Sensor (LISS3), and the Système Probatoire d’Observation de la Terre (SPOT) Multispectral (XS) for different dates are also used to study the activity of glaciers and for the identification of potentially dangerous glacial lakes. The combination of digital satellite data and the Digital Elevation Model (DEM) is also used for better and more accurate results for the inventory of glaciers and glacial lakes.

Topographic Maps

The topographic maps used were published in the 1980s (Figure 4.1). There are 148 topographic maps on a scale of 1:50 000 used as reference. Figure 4.1 shows the coverage of topographic maps.



Fig 4.1: index map of topographic maps of the study area

Satellite Images

The satellite data includes TM and ETM images of Landsat, which covered the all research region. Various types of satellite image suitable for the present study are available from different organizations, institutes, and data providers. Due to higher spatial resolutions and relative low costs, the TM and ETM image are acquired as the data source with least cloud cover. The coverage of remote sensing image are shown in figure 4.2. The detailed information about the TM and ETM are explained in Charpter 6.

Fig4.2: Index Map of Landsat ETM images

Inventory of glaciers and glacial lakes

The inventory of glacier published in 2002 and the inventory of glacial lake made in 1987 are used to partly obtain some attribute of digitized glacier and glacial lake in the topographic maps. Because the inventory of glacier was based on the same topographic maps, there is no large difference to cite the data of inventory.

The methodology for the mapping and inventory of the glaciers is based on instructions for compilation and assemblage of data for the World Glacier Inventory (WGI), developed by the Temporary Technical Secretary (TTS) at the Swiss Federal Institute of Technology, Zurich (Muller et al. 1977) and the methodology for the inventory of glacial lakes is based on that developed by the Lanzhou Institute of Glaciology and Geocryology, the Water and Energy Commission Secretariat, and the Nepal Electricity Authority (LIGG/WECS/NEA 1988). The inventory of glaciers and glacial lakes has been systematically carried out for the drainage basins on the basis of topographic maps and aerial photographs. Topographic maps at scale of 1:50000 published during the period from the 1970s to the 1980s are used.

The following sections describe how the compilation of the inventories for both the glaciers and glacial lakes has been carried out.

Inventory of glaciers

The glacier margins

The glacier margins on each topographic map are delineated and compared with aerial photographs, and the exact boundaries between glaciers and seasonal snow cover are determined. The coding system is based on the subordinate relation and direction of river progression according to the World Glacier Inventory (WGI). The descriptions of attributes for the inventory of glaciers are given below.

Numbering of glaciers

The lettering and numbering start from the mouth of the major stream and proceed clockwise round the basin. For convenience, the major river systems are further divided into five levels sub-basins.

For example, "5" indicate Asia, " Z " indicate the inner-land water system of Qingzang plateau (level 1 basin),"2"indicate the selincuo lake basin(level 2 basin). The coding of level 3 and level 4 basin is in Arabic numerals. As for the level 5 basin, the English letter is used. "5Z211F1" indicates Asia, inner-land water system of Qingzang plateau (level 1 basin), Selincuo lake basin (level 2 basin), Chibuzhang lake (level 3 basin), Jinxiwulan lake (level 4 basin), Xianche river (level 5 basin), and the last number indicate the glacial number in the last level basin.

Registration of snow and ice masses

All perennial snow and ice masses are registered in the inventory. Measurements of glacier dimensions are made with respect to the carefully delineated drainage area for each ‘ice stream’. Tributaries are included in main streams when they are not differentiated from one another. If no flow takes place between separate parts of a continuous ice mass, they are treated as separate units.

Delineation of visible ice, firn, and snow from rock and debris surfaces for an individual glacier does affect various inventory measurements. Marginal and terminal moraines are also included if they contain ice. The ‘inactive’ ice apron, which is frequently found above the head of the valley glacier, is regarded as part of the valley glacier. Perennial snow patches of large enough size are also included in the inventory. Rock glaciers are included if there is evidence of large ice content.

Snow line

In the present study, the snow line specially refers to the firn line of a glacier, not the equilibrium line. The elevation of the firn line of most glaciers was not measured directly but estimated by indirect methods. For the regular valley and cirque glaciers from topographical maps, Hoss’s method (i.e. studying changes in the shape of the contour lines from convex in the ablation area to concave in the accumulation area) was used to assess the snow line.

Accuracy rating table

The accuracy rating table proposed by Muller et al. (1977) on the basis of actual measurements is used in the present study. For the snow line an error range of 50-100m in altitude is entered as an accuracy rating of ‘3’.

Table 4.1 Accuracy rating adopted from Muller et al. (1977)

Index

Area/length
(%)

Altitude
(m)

Depth
(%)

1

2

3

4

5

0-5

5-10

10-15

15-25

>25

0-25

25-50

50-100

100-200

>200

0-5

5-10

10-20

20-30

>30

Mean glacier thickness and ice reserves

According to Muller et al. (1977), mean depth can be estimated with the appropriate model developed for each area by local investigators.

For example, the following model was used for the Swiss Alps

 where h is the mean depth (m), F is the total surface area (km2), and a and b are arbitrary parameters that are empirically determined.

There are no measurements of glacial ice thickness for the Himalaya-China regions. Measurements of glacial ice thickness in the Tianshan Mountains, China, show that the glacial thickness increases with the increase of its area (LIGG/WECS/NEA 1988). The relationship between ice thickness (H) and glacial area (F) was obtained there as

H = –11.32 + 53.21 F0.3                            if F>=0.03km2

This formula has been used to estimate the mean ice thickness in the glacier inventory. The same method is also used here to find the ice thickness. The ice reserves are estimated by mean ice thickness multiplied by the glacial area.

Area of the glacier

The area of the glacier is divided into accumulation area and ablation area (the area below the firn line). The area is given in square kilometres. The delineated glacier area is measured by the digital planimeter and checked repeatedly. But in this study, we digitized the glaciers with Arcview software and automatically re-calculated the area and ice reserve.

Length of the glacier

The length of the glacier is divided into three columns: total length, length of ablation and the mean length. The total (maximum) length refers to the longest distance of the glacier along the centerline. The mean value of maximum lengths of glacier tributaries (or firn basins) is the mean length.

Mean width

The mean width is calculated by dividing the total area (km2) by the mean length (km).

Orientation of the glacier

The orientation of accumulation and ablation areas is represented in eight cardinal directions (N, NE, E, SE, S, SW, W, and NW). Some of the glaciers are capping just in the form of an apron on the peak, which is inert and sloping in all directions, is represented as ‘360’. The orientations of both the areas (accumulation and ablation) are the same for most of the glaciers.

Elevation of the glacier

Glacier elevation is divided into highest elevation (the highest elevation of the crown of the glacier), mean elevation (the arithmetic mean value of the highest glacier elevation and the lowest glacier elevation) and lowest elevation.

Morphological classification

The morphological matrix-type classification and description is used in the inventory, which was proposed by Muller et al. (1977) for the TTS to the WGI. Each glacier is coded as a six-digit number, the six digits being the vertical columns of Table 4.2. The individual numbers for each digit (horizontal row numbers) must be read on the left-hand side. This scheme is a simple key for the classification of all types of glaciers all over the world.

Each glacier can be written as a six-digit number following Table 4.2. For example, ‘520110’ represents ‘5’ for a valley glacier in the primary classification, ‘2’ for compound basins in Digit 2, ‘0’ for normal or miscellaneous in frontal characteristics in Digit 3, ‘1’ for even or regular in longitudinal profile in Digit 4, ‘1’ for snow and/or drift snow in the major source of nourishment in Digit 5, and 0 for uncertain tongue activity in Digit 6.

The details for the glacier morphological code values according to TTS are explained below.

Digit 1 Primary classification

0  Miscellaneous: Any not listed.
1  Continental ice sheet: Inundates areas of continental size.
2  Ice field: More or less horizontal ice mass of sheet or blanket type of a thickness not sufficient to obscure the sub-surface topography. It varies in size from features just larger than glacierets to those of continental size.
3  Ice cap: Dome-shaped ice mass with radial flow.
4  Outlet glacier: Drains an ice field or ice cap, usually of valley glacier form; the catchment area may not be clearly delineated (Figure 4.3a).
5  Valley glacier: Flows down a valley; the catchment area is in most cases well defined.
6  Mountain glacier: Any shape, sometimes similar to a valley glacier, but much smaller; frequently located in a cirque or niche.
7  Glacieret and snowfield: A glacieret is a small ice mass of indefinite shape in hollows, river beds, and on protected slopes developed from snow drifting, avalanching and/or especially heavy accumulation in certain years; usually no marked flow pattern is visible, no clear distinction from the snowfield is possible, and it exists for at least two consecutive summers.
8  Ice shelf: A floating ice sheet of considerable thickness attached to a coast, nourished by glacier(s), with snow accumulation on its surface or bottom freezing (Figure 4.3b).
9  Rock glacier: A glacier-shaped mass of angular rock either with interstitial ice, firn, and snow or covering the remnants of a glacier, moving slowly down slope. If in doubt about the ice content, the frequently present surface firn fields should be classified as ‘glacieret and snowfield’.

Digit 2 Form

1 Compound basins: Two or more tributaries of a valley glacier, coalescing (Figure 4.4a).

2 Compound basin: Two or more accumulation basins feeding one glacier (Figure 4.4b).

3 Simple basin: Single accumulation area (Figure 4.4c).

4 Cirque: Occupies a separate, rounded, steep-walled recess on a mountain (Figure 4.4d).

5 Niche: Small glacier formed in initially a V-shaped gully or depression on a mountain slope (Figure 4.4e).

6 Crater: Occurring in and /or on a volcanic crater

7 Ice apron: An irregular, usually thin ice mass plastered along a mountain slope.

8 Group: A number of similar ice masses occurring in close proximity and too small to be assessed individually.

9 Remnant: An inactive, usually small ice mass left by a receding glacier.

Table 4.2: Classification and description of glaciers

 

Digit 1

Digit 2

Digit 3

Digit 4

Digit 5

Digit 6

 

Primary classification

Form

Frontal characteristic

Longitudinal profile

Major source of nourishment

Activity of tongue

0

Uncertain or miscellaneous

Uncertain or miscellaneous

Normal or miscellaneous

Uncertain or miscellaneous

Uncertain or miscellaneous

Uncertain

1

Continental ice sheet

Compound basins

Piedmont

Even: regular

Snow and/or drift snow

Marked retreat

2

Ice field

Compound basin

Expanded foot

Hanging

Avalanche and/or snow

Slight retreat

3

Ice cap

Simple basins

Lobed

Cascading

Superimposed ice

Stationary

4

Outlet glacier

Cirque

Calving

Ice fall

 

Slight advance

5

Valley glacier

Niche

Confluent

Interrupted

 

Marked advance

6

Mountain glacier

Crater

 

 

 

Possible surge

7

Glacieret and snow field

Ice apron

 

 

 

Known surge

8

Ice shelf

Group

 

 

 

Oscillating

9

Rock glacier

Remnant

 

 

 

 

 

Figure 4.3a: Outlet

Figure 4.3b:Ice shelf

Figure 4.4a: Compound basin

Figure 4.4b: Compound basin

Figure 4.4c: Simple basin

Figure 4.4d: Cirque

Figure 4.4e: Niche

Figure 4.5a: Piedmont

Figure 4.5b: Piedmont

Figure 4.5c: Expanded

Figure 4.5d: Lobed

Figure 4.5e: Confluent

 

Digit 3 Frontal characteristics

1  Piedmont: Ice field formed on low land with the lateral expansion of one or the coalescence of several glaciers (Figures 4.5 a and b).
2 Expanded foot: Lobe or fan of ice formed where the lower portion of the glacier leaves the confining wall of a valley and extends on to a less restricted and more level surface. Lateral expansion markedly less than for Piedmont (Figure 4.5c).
3  Lobed: Tongue-like form of an ice field or ice cap (see Figure 4.5d)
4 Calving: Terminus of glacier sufficiently extending into sea or occasionally lake water to produce icebergs.
5 Confluent: Glaciers whose tongues come together and flow in parallel without coalescing (Figure 4.5e).

Digit 4 Longitudinal profile

1

 Even /regular: Includes the regular or slightly irregular and stepped longitudinal profile.

2

 Hanging: Perched on a steep mountain slope, or in some cases issuing from a steep hanging valley.

3

 Cascading: Descending in a series of marked steps with some crevasses and seracs.

4

 Ice fall: A glacier with a considerable drop in the longitudinal profile at one point causing a heavily broken surface.

5

 Interrupted: Glacier that breaks off over a cliff and reconstitutes below.

Digit 5 Major source of nourishment

The sources of nourishment could be uncertain or miscellaneous (0), snow and/or drift snow (1), avalanche and/or snow (2), or superimposed ice (3) as indicated in Table 4.2.

Digit 6 Activity of tongue

A simple-point qualitative statement regarding advance or retreat of the glacier tongue in recent years, if made for all glaciers on Earth, would provide the most useful information. The assessment of an individual glacier (strongly or slightly advancing or retreating etc) should be made in terms of the world picture and not just that of the local area; however, it seems very difficult to establish the quantitative basis for the assessment of the tongue activity. A change of frontal position of up to 20m per year might be classed as ‘slight’ advance or retreat. If the frontal change takes place at a greater rate it would be called ‘marked’. Very strong advances or surges might shift the glacier front by more than 500m per year. Digit 6 expresses qualitatively the annual tongue activity. If observations are not available on an annual basis then an average annual activity is given.

Moraines: Two digits to be given.

Digit 1: moraines in contact with present-day glacier.

Digit 2: moraines further downstream.

0 no moraines

1 terminal moraine

2 lateral and/or medial moraine

3 push moraine

4 combination of 1 and 2

5 combination of 1 and 3

6 combination of 2 and 3

7 combination of 1, 2, and 3

8 debris, uncertain if morainic

9 moraines, type uncertain or not listed.

Remarks: The remarks can, for instance, consist of the following information.

  • Critical comments on any of the parameters listed on the data sheet (e.g. how close is the snow line to the firn line, comparison of year concerned with other years).
  • Special glacier types and glacier characteristics which, because of the nature of the classification scheme, are not described in sufficient detail (e.g. ‘melt structures’, glacier-dammed lakes).
  • Additional parameters of special interest to the basins concerned (e.g. area of altitudinal zones, inclination etc).
  • It is often useful to divide the snow line into several sections (because of different exposition or nourishment). In such cases, the snow line data of each section can be recorded separately.
  • Literature on the glacier concerned.
  • Any other remarks

The inventory database form (see Annex I and II) used for compilation of the inventory of glaciers includes basin numbers, map/satellite codes and year, as well as the glacier parameters described above.

Inventory of glacial lakes

The glacial lakes on each image are delineated by the help of DEM. The descriptions of attributes for the glacial lakes’ inventory based on LIGG, WECS and NEA (1988) are given below.

Numbering of glacial lakes

The numbering of the lakes starts from the outlet of the major stream and proceeds clockwise rounding the basin.

Longitude and latitude

Reference longitude and latitude are designated for the approximate centre of the glacial lake.

Area

The area of the glacial lake is determined from the digital database after digitization of the lake from the topographic maps.

Length

The length is measured along the long axis of the lake, and estimated to one decimal place in km units (0.1 km).

Width

The width is normally calculated by dividing the area by the length of the lake, down to one decimal place in km units (0.1 km).

Depth

The depth is measured along the axis of the cross section of the lake. On the basis of the depth along the cross section the average depth and maximum depth are estimated. The data are collected from the literature.

Orientation

The drainage direction of the glacial lake is specified as one of eight cardinal directions (N, NE, E, SE, S, SW, W, and NW). For a closed glacial lake, the orientation is specified according to the direction of its longer axis.

Altitude

The altitude is registered by the water surface level of the lake in masl.

Classification of lakes

Genetically glacial lakes can be divided into the following.

  • Glacial erosion lakes, including cirque lakes, trough valley lakes, and erosion lakes.
  • Moraine-dammed lakes (also divided into neo end moraine and paleo end moraine lakes), include end moraine lakes and lateral moraine lakes.
  • Blocking lakes formed through glaciers and other factors, including the main glacier blocking the branch valley, the glacier branch blocking the main valley, and the lakes formed through snow avalanche, collapse, and debris flow blockade.
  • Ice surface and sub-glacial lakes.

In the glacial lake inventory, end moraine-dammed lakes, lateral moraine lakes, trough valley lakes, glacial erosion lakes, and cirque lakes are represented by the letters M, L, V, E, and C respectively; B represents blocking lakes.

Activity

According to their stability, the glacial lakes are divided into three types: stable, potential danger, and outburst (when there have been previous bursts). The letters S, D, and O represent these types respectively.

Types of water drainage

Glacial lakes are divided into drainage lakes and closed lakes according to the drainage pattern. The former refers to lakes from which water flows to the river and joins the river system. In the latter, water does not flow into the river. Ds and Cs represent those two kinds of glacial lakes respectively.

Chemical properties

This attribute is represented by the degree of mineralisation of the water, mg l–1.

Other indices

One important index for evaluating the stability of a glacial lake is its contact relation with the glacier. So an item of distance from the upper edge of the lake to the terminus of the glacier has been added and the code of the corresponding glacier registered. Since an end moraine-dammed lake is related to its originating glacier, this index is only referred to end moraine-dammed lakes. As not enough field data exist, the average depth of glacial lakes is difficult to establish in most cases. Based on field data, and as an indication only, the average depth of a glacial lake formed by different causes can be roughly estimated as follows: cirque lake, 10m; lateral moraine lake, 30m; trough valley lake, 25m; blocking lake and glacier erosion lake, 40m; lateral moraine lake, 20m. The water reserves of different types of glacial lakes can be obtained by multiplying their average depth by their area (LIGG/WECS/NEA 1988).

The inventory database form (see Annex II) used for compilation of the inventory of glacial lakes includes basin numbers, map/satellite image codes and year, as well as the lake parameters (attributes) described above.