Comparison of changes in glacier area and thickness on the northern and southern slopes of Mt. Bogda, eastern Tianshan Mountains

Highlights

• Glacier thickness obtained by GPR for two glaciers is presented.

• Glacier thickness variation and volume change are analyzed.

• Glacier changes in the both slopes of Mt. Bogda are compared and its possible reasons are discussed.

Abstract

Rapid shrinkage and dramatic volume loss of the glaciers on Mt. Bogda in the eastern Tianshan Mountains have resulted in water shortages in the surrounding arid regions of China. Understanding ice thickness and its variation is important to the analysis of changes in glacial volume, which are directly related to regional hydrology and water resources. Fan-shaped Diffluence Glacier and Heigou Glacier No. 8 are located on the northern and southern slopes of Mt. Bogda, respectively. In this paper, the spatial distribution of the ice thickness of these two glaciers and the changes in their area and volume are discussed based on a 2009 survey result and comparison to previous investigations. The mean ice thickness of the tongue of Fan-shaped Diffluence Glacier was about 82.3 m and the calculated ice volume was 385.2 × 10⁶ m³ in 2009. It had thinned by 14 ± 8 m (0.30 ± 0.17 m a^− 1) from 1962 to 2009, equivalent to an ice volume loss of 65.5 ± 37.4 × 10⁶ m³. The mean ice thickness of the tongue of Heigou Glacier No. 8 was 58.7 m and the calculated ice volume was 115.1 × 10⁶ m³ in 2009. The tongue of Heigou Glacier No. 8 thinned by 13 ± 6 m (0.57 ± 0.26 m a^− 1) from 1986 to 2009, which corresponds to an ice volume loss of 25.5 ± 11.8 × 10⁶ m³. The greater thinning and retreat of Heigou Glacier No. 8 than those of Fan-shaped Diffluence Glacier is partially due to topographic characteristics. The difference can be attributed mainly to the greater increase in temperature on the southern slope than on the northern slope.

Introduction

The Fifth Assessment Report of the IPCC (IPCC, 2013) demonstrated that global warming has been increasing since the late 1980s. During the past 20 years, ice caps in Antarctica and Greenland, sea ice in the Arctic, and spring snow cover in the northern hemisphere have all been in shrinkage, while glaciers in the world continue to decrease in size. For the eastern Tianshan Mountains, the annual mean temperature and precipitation have experienced an increasing trend at a rate of 0.34 °C (10 a)^− 1 and 11 mm (10 a)^− 1 over the last five decades, respectively. The temperature in the dry seasons (from November to March) has increased significantly at a rate of 0.46 °C (10 a)^− 1 (Wang et al., 2011). Climate warming has left most mountain glaciers, including glaciers in the Tianshan Mountains, in a state of rapid terminus retreat (Li et al., 2006, Aizen et al., 2007, Bolch, 2007, Kutuzov and Shahgedanova, 2009, Narama et al., 2010, Wang et al., 2013, Wang et al., 2014).

Mt. Bogda is the highest peak in the Bogda Mountains, belonging to the eastern Tianshan Mountains, surrounding which are extremely arid regions of China (location shown in Fig. 1). Glacial melt runoff is a very important water source for rivers on both the northern and southern slopes of the mountain. For example, before the 1980s glacial melt water supplied 37.6% of the runoff for the Baiyang River on the northern slope (Kang, 1983) and 49.6% of the runoff for the Heigou River on the southern slope before 1980s (Hu et al., 1990). Due to glacial retreat and excessive exploitation of ground water, the Karez water flow in Turfan basin has decreased in recent decades (Li et al., 2011) (Karez is a ground channel system that is generally used as a water supply for human settlements and irrigation in arid regions; it is also the name of a town in the Turfan basin.). If this continues, the lack of water will result in severe environmental and ecological damage.

Accurate assessment of ice thickness distribution is essential to modeling glacier dynamics (Gudmundsson, 1999). Understanding variation in ice thickness is vital to analyzing changes in glacial volume, since it is directly related to regional hydrology and water resources (Zhang et al., 1985, Sun et al., 2003, Farinotti et al., 2009, Fischer, 2009, Li et al., 2011, Kehrl et al., 2014). Changes in ice thickness can be assessed by comparing the thickness of ice surveyed in different periods or at different parts of the glacial surface DEMs during different periods. Among the glaciers around Mt. Bogda, several were assessed in the 1980s, but the thickness of the ice was measured only at Heigou Glacier No. 8, which is on the southern slope of the mountain. In 2008 and 2009, ice thickness was measured for the Heigou Glacier No. 8 twice and the results were reported by Wu et al. (2013). Nevertheless, the late two measurements were limited to a smaller range than the earlier measurements. For this reason, the glacier was re-assessed and its thickness was surveyed again by the Tianshan Glaciological Station team in 2009 based on GPR. The Fan-shaped Diffluence Glacier on the northern slope was surveyed during this same season. Besides ice thickness, the surface elevation of the Fan-shaped Diffluence Glacier was surveyed using real-time kinematic (RTK)-GPS. The main objectives of this paper are to (1) present new data for glacial thickness obtained in 2009 and thickness data acquired during previous periods for Heigou Glacier No. 8; (2) analyze the variations in ice thickness and the corresponding changes in glacier volume; (3) compare the variations in glacier between the northern and southern slopes of Mt. Bogda; and (4) discuss possible explanations for observed changes.