30 Structural Studies of in the Region

Structural Studies of Glaciers in the Khumbu Region*

Hiroji Fushimi**

Abstract

Glaciers in the Himalaya are different from that in the other regions of the world, because it is composed of immense quantities of rock debris, sands and clays, and its shape and its mode of flow are controlled by unique geological structures which have a great influence on the topography and climate of the Nepal Himalaya. A glacier body is thought to be a compound ice body with different structural units and with certain physical properties of glacier ice and of insoluble materials. Each structural unit has characteristics of textures and structures. There are relationships between textures and structures found in the glacier ice body. In the lower ice body, where the strong shear movements are working, ice are granulated to be fine grains and insoluble materials of clays, sands and rocks (which are brought from the bed rock) form the foliation structure. In the middle ice body, the bubble foliation structures are developed and have two elongated directions with multiple maxima of the fabric pattern. The strongly elongated direction coincides with that of the glacier flow. In the upper ice body, the ice crystals are polygonal and the bubbles are spherical. The ice body shows no preferred orientation of c-axes without the bubble foliation. Though those textural as well as structural elements are formed under conditions of glacier flow, the glacier flow itself is deeply influenced by the textural and structural elements. Glaciers in the Khumbu region are classified according to structural characteristics of the glacier ice body and there is found a sequence of glacier types which is related to the glacier flow, to topography such as ice falls and to climate such as accumulation and conditions.

with superficial to be glaciers. 1. Introduction Most of the glaciers in the Khumbu Himal A glacier in the Nepal Himalaya is a compo- flow down along north-south and east-west dire- und body of glacier ice and rock debris. ction. This inclination is due to the geological In the middle of the 19th century, it was beli- structures which run from east to west, which is eved that there were no glaciers around Mt. called the "main boundary thrust", and recent Kangchenjunga and Mt. Sagarmatha in Nepalese fault systems creating a "block movement" to language (Chomo Lungma in the local language cause a "mountain building" of the Great and Everest in English), though people surveyed run from north to south (2). This the mountain massif by high-power binoculars. fundamental geological setting gives significant Indian surveyors, at that time, considered a gla- differences to the types of glaciers and the modes cier to be a bare ice body and they had never of glacier flow in various regions controlled by thought that many glaciers in the Nepal Himalaya different geological characteristics. were covered with thick superficial moraines (1). There are thick sedimentary rocks, belonging to So, the area down-stream of the glacier looked what are called the "Tibetan Formations" in the like a rock debris flow and this is why they did northern part of the Great Himalayas, which not consider the glacier ice bodies of Nepal gently dip toward the north. Geological structures in this part are rather simple as compared to * Glaciological Expedition of Nepal , Contribution those of fault systems in the Nepal Himalaya, No. 36 which is in the southern part of the Great ** Research Institute , Nagoya University, Himalayas. It can be said that glaciers in the Chikusa-ku, Nagoya, 464. Nepal Himalaya are very much influenced by Seppyo, 1977 H. Fushimi 31 complex geological features such as fault systems and varieties of rock species. These geological characteristics of the Great Himalayas cause geomorphological features to have a fundamental influence upon climate. Glacial phenomena are related to conditions of climate, geomorphology, geology and physical properties of glacier ice. Glaciers in the Nepal Himalaya, which are distributed in a wide range of height, from 4000 to 8000 m, and are affected by the geomorphological complexity of the Great Himalayas, have vast diversities influenced by areal as well as local characteristics of the climate. Fig. 1. One layer of the firn flows over another A glacier is, vertically as well as horizontally, and are formed along he bounda- thought of as a compound ice body. There are ries. Note that the relative flow between vertically different structural units with peculiar layers is large. This picture was taken at the Dzonglha glacier. properties of ice texture and of glacier flow. That is to say, the glacier ice divided into three ice bodies from surface to bottom; the upper ice with the structure of the glacier ice body and the body with well-preserved stratifications, the middle mode of the glacier flow, and the sequence of ice body with bubble foliations and the lower ice glacier types. body with foliation structures of clays, sands and Structural studies were carried out at the rock debris. The upper ice body is formed through Khumbu, , Lobuche, Dzonglha, Gyajo, a process of formation of superimposed ice and Kongma and Kongma Tikpe glacier in the gradually changes into the middle ice body, and Khumbu region. there is always a thrust plane between the middle and the lower ice body. There are also textural 2. Structures and Textures peculiarities such as shapes of crystals and bubbles When the glacier ice reaches a certain thickness, in each ice body. Those structural and textural the ice body begins to flow according to the characteristics are related to a mode of internal gravity, temperature conditions of the ice body movements of glacier ice bodies and the internal and the shape of the glacier basins such as the movements are influenced by shear stress, crystal inclination of bed rock. The mode of the glacier growth and temperature conditions in the ice flow is not uniform and there are differences of bodies (3). the glacier movements caused by changes of It is an aim of structural to find out topography and climate from the accumulation the relations among structural characteristics, to the ablation area. In the ablation area, the history of changes of crystal properties and modes differential movements between layers divided by of glacier flow. The mode of glacier flow creates bedding planes (dirt layers) occur, because there the macro-scale structure of the glacier ice body are melted-water layers along the boundaries and the micro-scale texture. between layers and one layer of the firn flows The term 'structure' refers to large scale features over the another. This is why icicles are formed of glacier ice such as bandings, foliations, crevas- along the boundaries at the ice cliff during the ses, ogives and jointings, etc., and the term warm season (Fig. 1). `texture' to small scale features , which are related The internal movements of the ice body, in to geometrical relationships among crystals and the ablation area, varies from the glacier surface to properties of crystals and bubbles, such as the to the bottom. Thrust fault planes within the grain size, lineations of crystals and bubbles, glacier ice body show that there are differential orientations of c-axes, etc. movements between the upper ice body and the The glacier flow causes erosion, transportation lower. The formation of bubble foliations has a and deposition which form U-shaped valleys, close connection with differential movements and moraines, lake sediments, glaciated plateaus and selective crystal growth. The lower ice body has truncated ridges, etc. This paper mainly deals few bubbles but is marked by thin layers of 32 Structural Studies of Glaciers in the Khumbu Region

Fig. 2. Sequence of glacier types. There is found a continuous sequence of glacier types according to the volume of stagnant and dead ice body and its structural relationship to glacier flow. 1) upper and middle ice body partly covered with superficial mora- ines, 2) lower ice body with foliations of insoluble materials, 3) stagnant or dead ice body, 4) ice fall, 5) lake, 6) , 7) line showing the boundary of superficial moraines, 8) L-I sub-stage , 9) L-V sub-stage moraine. Base Camp, Gorak Shep and Lobuche are indicated as BC, GS and L respectively on the map of the . insoluble materials which result from intense shear 2.1. Structure of Glaciers in the Khumbu Region movements bringing clays, sands and rock 2.1.1. Structures. fragments from the bed rock into the lower ice The Khumbu glacier is a type of a glacier body (3). with compound basins such as the West Cwm, and ogives are formed by the flow the , the - and the movements of the glacier ice body and they have basin to the west of Nuptse (Fig. 2). At the time an order of several tens of meters, but bubble of the previous glacier expansion, the Khumbu foliations are on the order of several centimeters. glacier had other tributaries from the and Thus, it can be said that the mode of the glacier the Changri glaciers which now have no influence flow changes according to the order of the on the movement of the Khumbu glacier. differential movements in the glacier ice body. The down-stream of the Khumbu glacier below The distributions of crystal main axes form 5200 m, at the place where the Changri glacier the texture of the ice body. It has been shown joins, is a stagnant ice body which sometimes that there are relations between the preferred shows backward or irregular movements (5, 6). orientation of c-axes and the mode of the glacier Structures and textures of this ice body resemble flow such as the direction of the glacier flow and those of the lower ice body and there are seen the distribution of stress and strain. Crystal the foliation structures of insoluble materials as textures are also related closely to the mode of well as the weak bubble foliations. There are the glacier flow, the structure of bubble foliations many ponds scattered in this part of the glacier and the macro-structure of the glacier ice body at where the fault systems have no regular (4). relations to the glacier flow. The foliation structure indicates no regular pattern of the glacier flow except the ice body near Lobuche which occupies Seppyo, 1977 H. Fushimi 33

Table 1. 34 Structural Studies of Glaciers in the Khumbu Region

lowest down-stream of the Khumbu glacier (Tab. 1 and Fig. 3). Ablation is noticeably strong at the upper part of this ice body near the junction of the Changri glacier, where the thickness of the superficial moraines is not thick and the height difference from the top of the side moraine to the surface of the glacier is the largest. The mid-stream part is the glacier ice body in in a true sense according to structures and textures of the ice body, and to the mode of the glacier flow. The lower ice body is developed with insoluble materials at and near the junction of the Changri glacier, and there are thrust fault planes between this lower ice body and the stagnant ice body mentioned above (Fig. 3). The mid-stream lies from the Base Camp of Sagarmatha (Chomo Lungma) in the upper part to the junction of the Changri glacier. The glacier ice is partly covered by superficial moraines and huge ice pinnacles

Fig. 4. Structural map near Pumori line in the Khumbu glacier. The ice pinnacles obse- rved at the Pumori survey line preserve the structures of ogives which are parallel to foliation structures. 1) bubble foliation, 2) ice pinnacles, 3) pond, 4) superficial moraine (schistose rocks). P4 is the stake position of the Pumori survey line. Seppyo, 1977 H. Fushimi 35

Fig. 6. Ogives and bubble foliation structures. The ogive structures and bubble foliations are well developed near the Base Camp. Ogives have steeper slopes in the up- stream areas and gentler slopes in the down-stream areas. The structure of bub- ble foliation is clearly seen and it is parallel to that of ogives. This picture was taken at the Base Camp line.

with granitic rocks, and bubble foliations are weakly developed in these ice bodies. The glacier from the West Cwm is divided into three ice bodies, because there are three different systems of ice pinnacles with ogive structures divided by Fig. 5. Structural map of Base Camp line. Ogive streams of melted water on the glacier surface structures are parallel to bubble foliations (Fig. 7). Two systems of ice pinnacles near the and perpendicular to tension cracks. left bank are covered by granitic rocks and the 1) bubble foliation, 2) tension crack, 3) rest near the right bank mainly by schistose rocks. ogive, 4) pond, 5) schistose superficial Judging from the rock species in the superficial moraine, 6) granitic superficial moraine, moraines, the former two ice bodies are originated 7) stake position and its number. from the Nuptse and the basins where granitic rocks predominate and the latter ice are seen. The ice pinnacles observed near the body from the Sagarmatha (Chomo Lunguma) Pumori survey line preserve the structures of the basin where schistose rocks and low-grade meta- ogives seen at the Base Camp (Fig. 4 and 5). The morphic rocks are predominant. The structural as ogive structures and bubble foliations are well well as textural peculiarities of each ice body developed near the Base Camp (Fig. 6), and the disappear as the Khumbu glacier flows down ice body between the Base Camp and Gorak from the Base Camp (Fig. 3), but the distribu- Shep is classified as part of the middle ice body. tions of rock species of the superficial moraine There is also the thrust structure in between this are preserved even in the down-stream part of middle ice body and the lower ice body near the glacier. Gork Shep (Fig. 3). Three glaciers are combined The upper part of the Khumbu glacier above near the Base Camp; glacier ice bodies from the 5600 m and at the lower part of the ice fall West Cwm, the Lho La and the Lingtren-Khu- consists of firns with well preserved stratifications. mbutse basin, and each ice body has its own The firns turn into glacier ice between 5500 and peculiarities of structure and texture, and of 5600 m. This formation of the glacier ice is species of rock in its superficial moraine (Fig. 3 governed by thawing and freezing processes. As and 7). The glaciers from the Lho La and the soon as the superimposed ice is formed, this Lingtren-Khumbutse basin are mainly covered newly formed ice body is influenced by the 36 Structural Studies of Glaciers in the Khumbu Region

Fig. 7. Distribution of supraglacial rock species and topography near the Base Camp line. The glacier ice bodies are horizontally divided by the distribution of rock species which originate from the tributary basin. Numbers 1 to 7 are the stake positions of the Base Camp line. 1) schistose and low-metamorphic rocks from Sagarmatha (Chomo Lungma) basin, 2) granitic rocks from Nuptse and Lhotse basin, 3) granitic rocks from Lho La basin, 4) superficial stream, 5) ogives, 6) ogives estimated, 7) pond.

movements within the ice body. The structure of bubble foliations has an order of 1 to 10 cm (Fig. 8). Ice crystals are granulated to be fine grains in bubble layers where the shear movements dominate, while there are preferable conditions for crystal growth in relatively transparent ice layers where the ice temperature is close to the freezing point and where the influence of shear stresses due to differential movements in the ice body is less (3). Both structures of ogives and bubble foliations have the same inclinations perpendicular to the tension cracks observed at the Base Camp. The ogive structures have an order of several tens of meter and are only formed at the lower part of the ice fall, but these ogive structures are still Fig. 8. Bubble foliations. The structure of bubble foliations is an alternate layer of bubbly preserved in the stretched ice pinnacles which are and transparent ice, and it has an order separated by the central moraines probably of several centimeters. originated from the Geneva Spar (a rock ridge This ice sample was collected near the between Sagarmatha south face and the Lhotse Base Camp. The thin section was cut face) with low-grade metamorphic rocks (Fig. 4), perpendicular to the bubble foliation. There are also transverse superficial moraines on the ice body from the south face of Mt. Sagar- internal movements of the glacier flow and the matha (Chomo Lungma) and this shows that bubble foliation is simultaneously formed by sele- there are intermittent rockslides from the south ctive crystal growth through the process of shear face (Fig. 4 and 7). Seppyo, 1977 H. Fushimi 37

The ice fall gives a strong influence on the glacier ice body indicates general characteristics mode of the glacier flow and on the structure of of the mode of the glacier flow and of the the ice body. There are many ice falls in the physical properties of glacier ice. The volume southern part of the Great Himalayas, while ice ratio of the lower ice body to the total observed falls are not so common in the northern part. at the Gyajo and the Dzonglha glacier is less than This is mainly because there are many fault 10%of the total, a figure which is thought to be systems developed in the south of the Great applicable to many glaciers located below 6000 m Himalayas. There are three falls with a head of in the Khumbu region. But the ratio of the 100 to 300 m in the Gyajo valley near Kunde Khumbu glacier is about 30% of the total, and village and they have a close connection with fault it is thought to have been large when glaciers in systems. The Khumbu ice fall is due to the fault the Khumbu region were advancing in the past. structure running from north to south and most All glaciers once had the stagnant ice body at likely caused by the intrusion of granitic rocks. its down-stream part. The stagnant ice body has The glacier ice body at the ice fall flows down the foliation structures of insoluble materials several to ten times faster than it does in the which is the typical characteristics of the lower rest of the glacier, and this mode of glacier flow ice body. As seen in the Khumbu glacier, the causes the thickness of the ice body to be thinner mid- and the down-stream of the glacier are at the ice fall. The begins from covered with superficial moraines and this shows the lower part of the ice fall in the Khumbu that there are two processes for forming super- region and the ablation factor effectively works ficial moraines at this parts of the glacier : 1) to melt it away if the thickness of the ice body Transportation of insoluble materials from the at the ice fall is not enough to be preserved. bottom and inside of the glacier ice body to This happens at the left bank of the Khumbu the surface by the internal differential movements, ice fall where the area of the bed rock is getting and 2) Deposition of insoluble materials on the larger as compared with that at the time of the surface by the ablation. Since the ice fall controls British Expedition in the 1921, and the same the mode of the glacier flow and the ogive as thing has happened in the Gyajo, the Dzonglha well as the foliation structures having steep dip (No. 10), and the Lobuche glacier, because the are formed, the differential movements having a glacier ice bodies are now separated into two ice close connection to these steep structure cause bodies at the place of the ice fall (Fig. 2). This effective transportations of insoluble materials and phenomenon will possibly be found in other the steep differential movements is also thought regions of the Nepal Himalaya that have similar to cause an upward movements of the glacier characteristics of geological structure and climate. flow at the mid-stream part of the Khumbu The ice fall has an effect on the mode of the glacier (6). The thick superficial moraines are glacier flow and on the shape of the glacier. An preventing the stagnant ice body and the dead ice fall is one of the geomorphological characte- ice body from melting, and consequently, there is ristics and together with climatic conditions is a large stagnant or dead ice body at where the thought to cause the differences in macroscopic materials of the superficial moraine are abundantly features between glaciers in the south and in the supplied by actions of faulting, weathering and north of the Great Himalayas, and even among snowslide. Thus, even the small glaciers such as glaciers in the Nepal Himalaya. the Kyuwo glacier and the Tsuro glacier near This gives a sequence of glacier types in the Lhajung station have the large stagnant ice body Khumbu Himal from the Khumbu type with which continues to the present active glacier ice continuous ice bodies to the Kongma type body. without a stagnant or a dead ice body. There If we consider a triangular diagram with indices are also glaciers of transitional types such as the of the volume ratio of the insoluble materials (A), Lobuche glacier, the Dzonglha glacier and the of the ice mass (B) and of the catchment area Gyajo glacier which are separated into two parts (C). The relations between A and B show the and there are variations in the volume of dead physical properties of the glacier ice. and the ice body (Fig. 2). relations between B and C indicate a glacieriza- The volume ratio of the lower, the middle and tion degree influenced by topographic as well as the upper ice body to the total volume of the climatic changes. Moreover, the relations between 38 Structural Studies of Glaciers in the Khumbu Region

Fig. 9. C-axes distributions. Fig. 9-1 shows a fabric diagram of 100 c-axes of the ice sample taken from the ice fall of the Khumbu glacier and the sample was cut parallel to the bedding structure. Fig. 9-2 shows the preferred orientation of 117 c-axes from the Base Camp; the sample was cut parallel to the bubble foliation structure. The F and T in the diagram indicate the flow direction and the pole of the tension crack respectively.

C and A are thought to be determined by the sitional fabrics without preferred orientations. upheaval rate of the Great Himalayas, the wea- There is a firn line between 5500 and 5600 m thering and the snowslides causing the denudation and the granular firn turns into a glacier in relation to the actions of the glacier flow. ice body in this zone. The firn line coincides 2.1.2. Preferred Orientation of Crystal Main with the lower part of the ice fall. The shape of Axes the crystals is not polygonal and has an interloc- The preferred orientations of c-axes were mea- king texture. The grain size differs according to sured from an ice sample of the Khumbu ice fall the bubble foliation structure, and the grain size at 5800 m and an another ice sample from the is smaller in the bubble layers and coarser in the Base Camp at 5350 m. transparent layers in which the grain There are well-developed hard granular firn size sometimes reaches to 10 cm in diameter. There layers with annual beddings in the middle part is a well preferred orientation of crystal c-axes of the ice fall. The density of this firn ranges which shows three maximum areas around the from 0.45 to 0.50 g/cm3. Especially in the sum- pole of the bubble foliation plane (Fig. 9-2). mer monsoon season, a part of the firn snow in This type of preferred orientation of the c-axes the accumulation area is thawed and the melted has been reported from other glaciers in Alaska water percolates into the firn; this percolating or Antarctica and also experimentally formed water is mainly accumulated along the bedding through the process of stress and temperature planes and there are ice layers developed along annealing (3). these planes. This process gives an important role to the glacier flow in the accumulation area, Acknowledgments as already stated in the previous chapter, because The present author expresses his appreciation to there are differential movements between one Mr. Pemba Tzering and Mr. Lhakpa Gyalbu for layer and another along bedding planes. The grain thier help during the field observations and to size of this firn snow is from 2 to 5 mm. This many Himalayan people who gave us hospitalities. fabric diagram shows no clear preferred orienta- Appreciation is also expressed to Mr. Masayoshi tions (Fig. 9-1), but there is a tendency for crystal Nakawo for his device of the universal stage axes to be parallel to the bedding plane; this which was very valuable for measuring the ori- type of preferred orientation of the c-axes has entation of the crystal c-axes. been observed in Tsurugisawa snow patches and it has been also experimentally formed by the References process of thawing and re-freezing (7). But there 1) Freshfield, D. (1889): Round Kangchenjunga, is also a possibility that this is one of the depo- Translated by Y. Yakushi, Akane Shobo, Tokyo, Seppyo, 1977 H. Fushimi 39

1968. gakukenpi Sogokenkyu (A) Hokokusho, 115-119. 2) Ohta, Y. and others (1973): Geology of the Nepal 5) Muller, F (1968): Medium-term fluctuations of Himalayas, Himalayan Committee of Hokkaido the surface movement of the Khumbu glacier, University, Sapporo, Japan, 286 pp. region, Schweizerische Bauzeitung, 3) Tanaka, H (1972): On preferred orientation of 31, p. 1-4. glacier and experimentally deformed ice, Journal 6) Kodama, H and Mae, S (1976): Flow of glaciers of the Geological Society of Japan, 78, p. 659-675. in the Khumbu region, Seppyo, 38, special issue, 4) Tanaka, H (1974): Kori no kesshososhiki oyobi 31-36. hyotaikozo to fabric pattern no kisokusei ni tsuite 7) Okuhira, F (1969): Tsurugisawa sekkei no kozo (On the regularity of relationships among ice hyogagakuteki kenkyu (Structural glaciology of crystal textures, structures of ice body and its the Tsurugisawa snow patch.), Master thesis, fabric patterns.), Physical and chemical studies on Faculty of Science, Nagoya University, 63 pp. from glaciers and ice sheets, Monbusho Ka-