China is home to many mountain ranges that host thousands of glaciers, which are important sources of water and energy for millions of people downstream.
Recent research, published in Geology, has revealed that China's mountain glaciers are not only shrinking in size, but also becoming more asymmetric in altitude, meaning that they have different heights on different slopes of the same mountain.
This asymmetry has profound implications for the landscape evolution and the hydrological cycle of the region.
Asymmetry in mountain glaciers
Asymmetry in mountain glaciers refers to the difference in glacier altitude between opposite slopes of a mountain range, such as north and south or east and west, as per Phys.org.
This difference is mainly driven by the spatial variation in solar radiation and precipitation, which affect the glacier mass balance, or the balance between accumulation and ablation of ice and snow.
Solar radiation is stronger on south-facing slopes than on north-facing slopes in the Northern Hemisphere, due to the tilt of the Earth's axis.
This effect is more pronounced in mid-latitudes and sunny climates, where solar radiation is more intense and variable.
Precipitation is also unevenly distributed across mountain ranges, depending on the direction and strength of the prevailing winds and the orographic effect, or the enhancement of precipitation by mountain barriers.
The monsoon winds are stronger on the northern and eastern slopes of the mountain ranges, where they encounter higher terrain and are forced to rise and cool, producing more rain or snow.
The combined effects of solar radiation and precipitation create a complex pattern of asymmetry in China's mountain glaciers, which varies from region to region and from season to season.
In the Qilian Shan range in northwestern China, the glaciers are more asymmetric in altitude between north and south than between east and west, due to the dominant role of solar radiation over precipitation.
In contrast, in the Hengduan Shan range in southwestern China, the glaciers are more asymmetric in altitude between east and west than between north and south, due to the dominant role of precipitation over solar radiation.
Also Read: Alaska Glaciers Leading to Global Sea Level Rise
Asymmetry affects landscape evolution?
Asymmetry in mountain glaciers has significant impacts on landscape evolution, as it influences the rates and patterns of erosion and sediment transport by glaciers and rivers, as per Cambridge Core.
Glaciers erode the bedrock by plucking, abrasion, and frost cracking, creating U-shaped valleys, cirques, moraines, and other glacial landforms.
Rivers erode the bedrock by incision, abrasion, and plucking, creating V-shaped valleys, gorges, alluvial fans, and other fluvial landforms.
Asymmetry in mountain glaciers creates different erosion rates on different slopes of a mountain range, as higher glaciers tend to erode more than lower glaciers due to their greater ice thickness, length, and flow velocity.
This differential erosion can cause the drainage divide, or the boundary between adjacent drainage basins that flow in different directions, to migrate towards the lower-altitude slope over time.
This migration can also affect the river network downstream by changing its slope gradient, discharge volume, and sediment load.
It also increased the steepness of river channels on north-facing slopes by about 20%, compared to south-facing slopes.
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